The Digestive System and Body Metabolism

The Digestive SystemThe Digestive Systemand Body Metabolismand Body Metabolism

Chapter 14Chapter 14

Anatomy of the Digestive Anatomy of the Digestive SystemSystem

The digestive system is broken down The digestive system is broken down into two main groups:into two main groups: Alimentary canalAlimentary canal

Responsible for the actual digestion and Responsible for the actual digestion and absorption of foodsabsorption of foods

Accessory digestive organsAccessory digestive organs Assist in the digestive breakdown processAssist in the digestive breakdown process

Organs of the Alimentary Organs of the Alimentary CanalCanal

Also called the Gastrointestinal Tract (GI)Also called the Gastrointestinal Tract (GI) A continuous coiled, hollow muscular tube that winds through the A continuous coiled, hollow muscular tube that winds through the

ventral body cavity and is open at both ends.ventral body cavity and is open at both ends. Organs consist of the:Organs consist of the:

MouthMouth PharynxPharynx EsophagusEsophagus StomachStomach Small intestineSmall intestine Large intestineLarge intestine AnusAnus

In a cadaver the GI tract is approximately 9 m (30 ft) long but In a cadaver the GI tract is approximately 9 m (30 ft) long but in a healthy living adult is considerably shorter because of its in a healthy living adult is considerably shorter because of its constant muscle tone.constant muscle tone.

Food in this area is considered “outside” the body because it Food in this area is considered “outside” the body because it only has contact with cells that line the GI tract and is open to only has contact with cells that line the GI tract and is open to the external environment on both ends. the external environment on both ends.

Organs of the Alimentary CanalOrgans of the Alimentary CanalGI TractGI Tract

Mouth/Oral cavity:Mouth/Oral cavity: Mucus lined cavity where food enters the Mucus lined cavity where food enters the

digestive tract.digestive tract. Lips (Labia): protect the anterior openingLips (Labia): protect the anterior opening Cheeks: form the lateral wallsCheeks: form the lateral walls Hart palate: forms the anterior roof of Hart palate: forms the anterior roof of

the mouththe mouth Soft Palate: forms the posterior roof of Soft Palate: forms the posterior roof of

the mouththe mouth


Mouth con’t:Mouth con’t: Uvula: fleshy fingerlike projection of the soft palate Uvula: fleshy fingerlike projection of the soft palate

that extends downward.that extends downward. Vestibule: the space between the lips and cheeks Vestibule: the space between the lips and cheeks

externally and between the teeth and gums externally and between the teeth and gums internallyinternally

Oral cavity proper: area where teeth are contained.Oral cavity proper: area where teeth are contained. Tongue: muscle occupying the floor of the mouth. Tongue: muscle occupying the floor of the mouth.

Attaches to the hyoid bone and the styloid process Attaches to the hyoid bone and the styloid process of the skullof the skull

Frenulum: fold of mucous membrane which Frenulum: fold of mucous membrane which secures the tongue to the floor of the mouth and secures the tongue to the floor of the mouth and limits posterior movement.limits posterior movement.

Disorders within the MouthDisorders within the Mouth

““Tongue Tied”: Children born with an Tongue Tied”: Children born with an extremely short frenulum have distorted extremely short frenulum have distorted speech due to restricted tongue movement. speech due to restricted tongue movement. This can be corrected surgicallyThis can be corrected surgically

Tonsillitis: inflammation of the tonsils.Tonsillitis: inflammation of the tonsils. Tonsils are found at the posterior end of the oral Tonsils are found at the posterior end of the oral

cavity and are a mass of lymphatic tissuecavity and are a mass of lymphatic tissue Two pairs of tonsils within the mouth: Palatine Two pairs of tonsils within the mouth: Palatine

tonsils, Lingual tonsilstonsils, Lingual tonsils Are a part of the body’s defense mechanism and Are a part of the body’s defense mechanism and

when they become inflamed will block the when they become inflamed will block the pharynx making swallowing painful and difficult.pharynx making swallowing painful and difficult.


Pharynx:Pharynx: Oropharynx: Oropharynx:

Posterior to the oral cavityPosterior to the oral cavity Laronygopharynx:Laronygopharynx:

Continuation of the oropharynx which turns Continuation of the oropharynx which turns into the esophagus which lies below itinto the esophagus which lies below it

Both are passageways for food, air and Both are passageways for food, air and fluids fluids


Esophagus:Esophagus: Runs from the pharynx through the Runs from the pharynx through the

diaphragm to the stomach and is diaphragm to the stomach and is approx. 10 inches longapprox. 10 inches long

Passageway for food to reach the Passageway for food to reach the stomachstomach

Walls of the Alimentary Canal Walls of the Alimentary Canal OrgansOrgans

The alimentary organ walls consists The alimentary organ walls consists of four basic tissue layers/tunics:of four basic tissue layers/tunics: MucosaMucosa SubmucosaSubmucosa Muscularis ExternaMuscularis Externa SerosaSerosa


Mucosa:Mucosa: Innermost layerInnermost layer Moist membrane lining the cavity of the Moist membrane lining the cavity of the

organorgan Consists mostly of surface epithelium Consists mostly of surface epithelium

and a small amount of connective and and a small amount of connective and smooth muscle tissuesmooth muscle tissue


Submucosa:Submucosa: Found just beneath the mucosaFound just beneath the mucosa Made up of a soft connective tissue Made up of a soft connective tissue

layer which contains blood vessels, layer which contains blood vessels, nerve endings, lymph nodes and nerve endings, lymph nodes and lymphatic vesselslymphatic vessels


Muscularis Externa:Muscularis Externa: Muscle layer made up of an inner Muscle layer made up of an inner

circular layer and an outer longitudinal circular layer and an outer longitudinal layer of smooth muscle cells.layer of smooth muscle cells.


Serosa:Serosa: Outermost layer of the wallOutermost layer of the wall Consists of a single layer of flat serous Consists of a single layer of flat serous

fluid producing cells creating the fluid producing cells creating the Visceral peritoneum which continues into Visceral peritoneum which continues into

thethe Partial peritoneum which lines the Partial peritoneum which lines the

abdominopelvic cavity by a membrane abdominopelvic cavity by a membrane extension called the mesentery.extension called the mesentery.

Nerve Plexuses of theNerve Plexuses of theAlimentary CanalAlimentary Canal

The Alimentary canal contains two The Alimentary canal contains two important nerve plexuses:important nerve plexuses: Submucosal nerve plexusSubmucosal nerve plexus Myenteric nerve plexusMyenteric nerve plexus

These are networks of nerve fibers which These are networks of nerve fibers which are part of the autonomic nervous system are part of the autonomic nervous system and help regulate the mobility and and help regulate the mobility and secretory activity of the GI tract organs.secretory activity of the GI tract organs.

The StomachThe Stomach

The stomach is a c-shaped organ located on The stomach is a c-shaped organ located on the left side of the abdominal cavity almost the left side of the abdominal cavity almost hidden by the liver and diaphragmhidden by the liver and diaphragm

Cardioesophageal Sphincter: located at the Cardioesophageal Sphincter: located at the part of the stomach closest to the heart. Area part of the stomach closest to the heart. Area where food enters the stomach from the where food enters the stomach from the esophagus.esophagus.

Body: Middle portion of the stomachBody: Middle portion of the stomach Pylorus: funnel shaped portion of the stomach Pylorus: funnel shaped portion of the stomach

located on the inferior end of the stomach and located on the inferior end of the stomach and continues as part of the wall of the small continues as part of the wall of the small intestine by the pyloric sphincter intestine by the pyloric sphincter


The stomach is approximately 10 The stomach is approximately 10 inches long but its diameter can inches long but its diameter can change depending on the amount of change depending on the amount of food within it.food within it.

If the stomach is full it can hold If the stomach is full it can hold approximately 1 gallon of food. When approximately 1 gallon of food. When it is empty it collapses in on itself and it is empty it collapses in on itself and becomes a mass of folds called rugae.becomes a mass of folds called rugae.


The lateral surface of the stomach is more convex The lateral surface of the stomach is more convex and referred to as the greater curvature.and referred to as the greater curvature.

The Medial surface is more concave and referred The Medial surface is more concave and referred to as the lesser curvature.to as the lesser curvature.

Lesser Omentum: a double layer of peritoneum Lesser Omentum: a double layer of peritoneum which extends from the lesser curvature to the which extends from the lesser curvature to the liverliver

Greater Omentum: another extension of the Greater Omentum: another extension of the peritoneum which drapes downward and covers peritoneum which drapes downward and covers the abdominal organs and attaches to the the abdominal organs and attaches to the posterior body wall of the stomachposterior body wall of the stomach The greater omentum is covered with fat which helps to The greater omentum is covered with fat which helps to

insulate, cushion and protect the organs and also contains insulate, cushion and protect the organs and also contains lymph nodes and defensive cells of the immune system.lymph nodes and defensive cells of the immune system.

The StomachThe Stomach The stomach is a storage area for food as well as a site for The stomach is a storage area for food as well as a site for

food breakdown.food breakdown. The walls of the muscularis externa help to move food along The walls of the muscularis externa help to move food along

the digestive tract and also to mix and break down the food the digestive tract and also to mix and break down the food into smaller fragments.into smaller fragments.

The chemical breakdown of foods also occurs in the stomach The chemical breakdown of foods also occurs in the stomach by producing excessive amounts of mucus and secreting by producing excessive amounts of mucus and secreting gastric juice from the gastric glands which are found in gastric juice from the gastric glands which are found in hollow pits throughout the stomachhollow pits throughout the stomach

Chief cells produce a protein-digesting enzyme made up of Chief cells produce a protein-digesting enzyme made up of pepsinogenspepsinogens

Parietal cells produce hydrochloric acid which makes Parietal cells produce hydrochloric acid which makes stomach contents acidic and activates the enzymes.stomach contents acidic and activates the enzymes.

Mucus neck cells produce a sticky alkaline mucus that clings Mucus neck cells produce a sticky alkaline mucus that clings to the stomach walls protecting it from the acids and to the stomach walls protecting it from the acids and digestive enzymesdigestive enzymes

Chyme: a heavy cream substance that is created from the Chyme: a heavy cream substance that is created from the processing of foods in the stomach. It also allows it to move processing of foods in the stomach. It also allows it to move through the small intestine.through the small intestine.

Complications of the Complications of the StomachStomach

Peritonitis: Peritonitis: Infection of the peritoneum causing the Infection of the peritoneum causing the

membranes to stick together around the membranes to stick together around the infection site helping to seal off and infection site helping to seal off and localize the infection.localize the infection.

The Small IntestineThe Small Intestine

The body’s major digestive organThe body’s major digestive organ Passageway for foods that are usable to be Passageway for foods that are usable to be

moved into the cells of the bodymoved into the cells of the body The small intestine is a muscular tube The small intestine is a muscular tube

extending from the pyloric sphincter, on extending from the pyloric sphincter, on the bottom of the stomach, to the the bottom of the stomach, to the ileocecal valve (the beginning of the large ileocecal valve (the beginning of the large intestine)intestine)

It is the longest section of the alimentary It is the longest section of the alimentary canal and averages 6 ft in lengthcanal and averages 6 ft in length


The small intestine has three The small intestine has three subdivisions:subdivisions: Duodenum: curves around the head of the Duodenum: curves around the head of the

pancreas and is approximately 10 inches longpancreas and is approximately 10 inches long Jejunum: about 8 feet long and extends from Jejunum: about 8 feet long and extends from

the duodenum to the iliumthe duodenum to the ilium Ilium: about 12 feet long. The terminal Ilium: about 12 feet long. The terminal

portion of the small intestine and joins the portion of the small intestine and joins the large intestine at the ileocecal valve.large intestine at the ileocecal valve.


The small intestine can only process small amounts The small intestine can only process small amounts of food at one time and therefore depends on the of food at one time and therefore depends on the pyloric sphincter to control the movement of food pyloric sphincter to control the movement of food into it from the stomach.into it from the stomach.

Enzymes which are produced by the intestinal cells Enzymes which are produced by the intestinal cells and by the pancreas enter the duodenum through and by the pancreas enter the duodenum through the pancreatic duct to complete the chemical the pancreatic duct to complete the chemical breakdown of foodbreakdown of food

Bile, formed by the liver, also enters the duodenum Bile, formed by the liver, also enters the duodenum through the bile duct.through the bile duct.

The pancreatic and bile ducts join at the duodenum The pancreatic and bile ducts join at the duodenum to form the hepatopancreatic ampulla which allows to form the hepatopancreatic ampulla which allows their juices to be released in the duodenumtheir juices to be released in the duodenum


Almost all of food absorption occurs in the Almost all of food absorption occurs in the small intestine.small intestine.

Its wall has three structures that increase the Its wall has three structures that increase the absorption:absorption: Microvilli: tiny projections of the plasma membrane Microvilli: tiny projections of the plasma membrane

giving the cell surface a fuzzy appearancegiving the cell surface a fuzzy appearance Villi: fingerlike projections of the mucosa that give Villi: fingerlike projections of the mucosa that give

it a velvety appearance and are rich in capillaries it a velvety appearance and are rich in capillaries and modified lymphatic capillaries called lactealand modified lymphatic capillaries called lacteal

Circular folds: also called plicae circulares: deep Circular folds: also called plicae circulares: deep folds of both mucosa and submucosa layers. folds of both mucosa and submucosa layers.

The Large IntestineThe Large Intestine

Larger in diameter than the small intestine but Larger in diameter than the small intestine but shorter in length at only approximately 5 feet.shorter in length at only approximately 5 feet.

It extends from the ileocecal valve to the anusIt extends from the ileocecal valve to the anus Its major function is to dry out indigestible food Its major function is to dry out indigestible food

residue by absorbing water and eliminating residue by absorbing water and eliminating these residues from the body as feces.these residues from the body as feces.

It covers the small intestine on three sides and It covers the small intestine on three sides and is divided into subdivisions:is divided into subdivisions: Cecum, appendix, colon, rectum and anal canalCecum, appendix, colon, rectum and anal canal


Cecum: saclike beginning portion of the Cecum: saclike beginning portion of the large intestinelarge intestine

Appendix: hangs from the cecum and is Appendix: hangs from the cecum and is wormlike in appearance.wormlike in appearance.

Ascending colon: travels up the right side of Ascending colon: travels up the right side of the abdominal cavity and makes a turn, the abdominal cavity and makes a turn, right colic or hepatic flexure, to travel across right colic or hepatic flexure, to travel across the abdominal cavity creating the transverse the abdominal cavity creating the transverse coloncolon

Descending colon: the left side of the colon Descending colon: the left side of the colon which will eventually become the Sigmoid which will eventually become the Sigmoid colon, rectum, then anus.colon, rectum, then anus.


Anal Canal:Anal Canal: External voluntary sphincter: made of skeletal External voluntary sphincter: made of skeletal

musclemuscle Internal involuntary sphincter: formed of smooth Internal involuntary sphincter: formed of smooth

musclemuscle Both sphincters open and close the anal canal and Both sphincters open and close the anal canal and

are mostly closed unless we are getting rid of are mostly closed unless we are getting rid of feces.feces.

The Large intestine is full of goblet cells which The Large intestine is full of goblet cells which produce a mucus to act as a lubricant smoothing produce a mucus to act as a lubricant smoothing the passage of feces until it leaves the digestive the passage of feces until it leaves the digestive tract.tract.

Accessory Digestive OrgansAccessory Digestive Organs Pancreas:Pancreas:

A soft, pink, triangular gland that extends across A soft, pink, triangular gland that extends across the abdomen from the spleen to the duodenum.the abdomen from the spleen to the duodenum.

Most of its “body” lies posterior to the parietal Most of its “body” lies posterior to the parietal peritoneum peritoneum

The pancreas provides enzymes to break down The pancreas provides enzymes to break down digestible foodsdigestible foods

These enzymes are secreted into the duodenum These enzymes are secreted into the duodenum in an alkaline fluid which neutralizes the chyme in an alkaline fluid which neutralizes the chyme coming in from the stomachcoming in from the stomach

The pancreas also produces hormones insulin The pancreas also produces hormones insulin and glucagon to help the functioning of the and glucagon to help the functioning of the endocrine system. endocrine system.

Accessory Digestive OrgansAccessory Digestive Organs Liver:Liver:

Largest gland in the bodyLargest gland in the body Located under the diaphragm to the right side of Located under the diaphragm to the right side of

the body overlying and almost covering the the body overlying and almost covering the stomachstomach

The liver contains four lobes and is suspended The liver contains four lobes and is suspended from the diaphragm and abdominal wall by a thin from the diaphragm and abdominal wall by a thin mesentery cord called the falciform ligamentmesentery cord called the falciform ligament

The function of the liver is to produce bile which The function of the liver is to produce bile which leaves the liver through the common hepatic duct leaves the liver through the common hepatic duct and enters the duodenum through the bile duct. and enters the duodenum through the bile duct.

Bile does not actually digest or break down foods Bile does not actually digest or break down foods but provides a greater surface area for fat-but provides a greater surface area for fat-digesting enzymes to work.digesting enzymes to work.

Accessory Digestive OrgansAccessory Digestive Organs

Gallbladder:Gallbladder: Small, thin walled, green sac that is contained in Small, thin walled, green sac that is contained in

a shallow fossa in the inferior surface of the liver.a shallow fossa in the inferior surface of the liver. When digestion is not occurring the bile backs up When digestion is not occurring the bile backs up

into the cystic duct and enters the gallbladder into the cystic duct and enters the gallbladder where it will be stored.where it will be stored.

While it is stored it becomes concentrated by While it is stored it becomes concentrated by having its water removed.having its water removed.

When fatty foods enter the duodenum a When fatty foods enter the duodenum a hormonal stimuli will prompt the gallbladder to hormonal stimuli will prompt the gallbladder to contract and release the stored bile.contract and release the stored bile.

Accessory Digestive OrgansAccessory Digestive Organs Gallbladder Con’t:Gallbladder Con’t:

Gallstones: occur when too much water is Gallstones: occur when too much water is removed from the bile and the cholesterol removed from the bile and the cholesterol contained in it crystallizes.contained in it crystallizes.

If the gallstones become wedged and block the If the gallstones become wedged and block the common hepatic or bile ducts then the bile will common hepatic or bile ducts then the bile will accumulate and back up into the liver. The pressure accumulate and back up into the liver. The pressure on the liver cells causes bleeding to occur which on the liver cells causes bleeding to occur which spreads and causes tissues to become jaundice.spreads and causes tissues to become jaundice.

Hepatitis: Inflammation of the liver (cirrhosis): Hepatitis: Inflammation of the liver (cirrhosis): a chronic inflammatory condition where the a chronic inflammatory condition where the liver is damaged and becomes hard/fibrous.liver is damaged and becomes hard/fibrous.

It is most often due to viral infection or drinking It is most often due to viral infection or drinking contaminated water or transmitted in blood through contaminated water or transmitted in blood through transfusion or use of contaminated needlestransfusion or use of contaminated needles

Accessory Digestive OrgansAccessory Digestive Organs Salivary GlandsSalivary Glands

Three pairs of salivary glands empty their Three pairs of salivary glands empty their secretions into the mouth.secretions into the mouth.

Parotid glands: lie anterior to the ear and if inflamed is Parotid glands: lie anterior to the ear and if inflamed is called mumps.called mumps.

Submandibular glands and sublingual glands: empty Submandibular glands and sublingual glands: empty their secretions into the floor of the mouth through tiny their secretions into the floor of the mouth through tiny ductsducts

Saliva: a mixture of mucus and serous fluid, moistens Saliva: a mixture of mucus and serous fluid, moistens and helps to bind food together into a mass called a and helps to bind food together into a mass called a bolus which makes chewing and swallowing easier.bolus which makes chewing and swallowing easier.

Salivary Amylase: enzyme contained in the clear Salivary Amylase: enzyme contained in the clear serous portion of saliva. Helps with starch digestion in serous portion of saliva. Helps with starch digestion in the mouth and contains substances such as lysozyme the mouth and contains substances such as lysozyme and atibodies to inhibit bacteria.and atibodies to inhibit bacteria.


Teeth:Teeth: Masticate: chewing of food to break it down into small Masticate: chewing of food to break it down into small

fragmentsfragments Deciduous teeth: one of two sets of teeth formed by the Deciduous teeth: one of two sets of teeth formed by the

age of 21. Also called the baby teeth. They erupt around 6 age of 21. Also called the baby teeth. They erupt around 6 months of age and are fully developed by 2 years.months of age and are fully developed by 2 years.

Permanent teeth: the second set of teeth. The deciduous Permanent teeth: the second set of teeth. The deciduous teeth enlarge and develop and the roots are reabsorbed teeth enlarge and develop and the roots are reabsorbed between the ages of 6 and 12 years when they loosen and between the ages of 6 and 12 years when they loosen and fall out.fall out.

By the end of adolescents the permanent teeth are By the end of adolescents the permanent teeth are complete and only the molars (wisdom teeth) are left to complete and only the molars (wisdom teeth) are left to emerge. This occurs between ages 17 and 25. Sometimes emerge. This occurs between ages 17 and 25. Sometimes the wisdom teeth may not erupt or may be absent the wisdom teeth may not erupt or may be absent completelycompletely

As a grown adult we will have 32 permanent teethAs a grown adult we will have 32 permanent teeth


Teeth Con’t:Teeth Con’t: Impacted: teeth that remain embedded Impacted: teeth that remain embedded

in the jawbone.in the jawbone. Teeth are classified according to shape:Teeth are classified according to shape:

Incisors: chisel shaped, meant for cuttingIncisors: chisel shaped, meant for cutting Canines: eye-teeth, meant for tearing or Canines: eye-teeth, meant for tearing or

piercingpiercing Molars: have broad crowns and rounder Molars: have broad crowns and rounder

cusps (tips) and are meant for grinding foods.cusps (tips) and are meant for grinding foods.

Accessory Digestive OrgansAccessory Digestive Organs Teeth con’t again:Teeth con’t again:

A tooth consists of two major regions:A tooth consists of two major regions: Crown: Enamel covered and exposed portion of the tooth Crown: Enamel covered and exposed portion of the tooth

above the gingiva (gums)above the gingiva (gums) Enamel: hardest substance in the body and brittle because it is Enamel: hardest substance in the body and brittle because it is

heavily mineralized with calcium saltsheavily mineralized with calcium salts Root: portion of the tooth embedded in the jawbone.Root: portion of the tooth embedded in the jawbone.

CEmentum: covers the root and attaches the tooth to the CEmentum: covers the root and attaches the tooth to the periodontal membrane which holds the tooth in place to the jawperiodontal membrane which holds the tooth in place to the jaw

Neck: region of the tooth that connects the crown and the Neck: region of the tooth that connects the crown and the rootroot

Dentin: underlies the enamel forms the bulk of the toothDentin: underlies the enamel forms the bulk of the tooth Pulp cavity: surrounded by the dentin, contains a number of Pulp cavity: surrounded by the dentin, contains a number of

structures which are collectively called pulp (blood vessels, structures which are collectively called pulp (blood vessels, nerve fibers and connective tissue)nerve fibers and connective tissue)

Root canal: where the pulp cavity extends into the root. Root canal: where the pulp cavity extends into the root. Provides a route for blood vessels, nerves and other pulp Provides a route for blood vessels, nerves and other pulp structures to enter the pulp cavity of the tooth. structures to enter the pulp cavity of the tooth.

Functions of the digestive Functions of the digestive SystemSystem

The major functions of the digestive tract The major functions of the digestive tract are absorption and digestion but also are absorption and digestion but also require smaller systems which function in:require smaller systems which function in: IngestionIngestion PropulsionPropulsion Food Breakdown – Mechanical DigestionFood Breakdown – Mechanical Digestion Food Breakdown – Chemical DigestionFood Breakdown – Chemical Digestion AbsorptionAbsorption DefecationDefecation


Ingestion:Ingestion: The act of placing food in the mouth to be The act of placing food in the mouth to be

chewed and broken downchewed and broken down Propulsion:Propulsion:

The movement of food through the different The movement of food through the different digestive organs.digestive organs.

Peristalsis: involuntary action involving Peristalsis: involuntary action involving contraction and relaxation of the muscles in contraction and relaxation of the muscles in the organ wall. Squeezes food down the the organ wall. Squeezes food down the digestive tractdigestive tract

Segmentation: helps propel foods through the Segmentation: helps propel foods through the small intestine and moves food back and forth small intestine and moves food back and forth across the internal wall of the organ mixing it across the internal wall of the organ mixing it with the digestive systems.with the digestive systems.


Food Breakdown: Mechanical Food Breakdown: Mechanical DigestionDigestion Mixing food in the mouth by the tongue Mixing food in the mouth by the tongue

and churning food in the stomach and churning food in the stomach Mechanical digestion prepares food for Mechanical digestion prepares food for

further breakdown by enzymesfurther breakdown by enzymes


Food Breakdown: Chemical DigestionFood Breakdown: Chemical Digestion The sequence of steps when large food The sequence of steps when large food

molecules are broken down into their building molecules are broken down into their building blocks by enzymesblocks by enzymes

Hydrolysis reactions: the water molecule is Hydrolysis reactions: the water molecule is attached to each bond that is to be brokenattached to each bond that is to be broken

Monosaccharides: building blocks of Monosaccharides: building blocks of carbohydratescarbohydrates

Glucose: the body’s sugarGlucose: the body’s sugar Galactose: found in milk or milk productsGalactose: found in milk or milk products Our system is only able to breakdown simple sugars Our system is only able to breakdown simple sugars

such as sucrose, lactose, maltose and starchsuch as sucrose, lactose, maltose and starch


Chemical Digestion Con’t:Chemical Digestion Con’t: Disaccharides: double sugars – sucrose, maltose Disaccharides: double sugars – sucrose, maltose

and lactose – each contains two simple sugars and lactose – each contains two simple sugars linked togetherlinked together

Polysaccharide: formed by hundreds of sugar Polysaccharide: formed by hundreds of sugar units – Starch. Our bodies cannot break them units – Starch. Our bodies cannot break them down and they do not provide us with any down and they do not provide us with any nutrients but do help in moving foods along the nutrients but do help in moving foods along the digestive tract.digestive tract.

Protein is digested to its building blocks the Protein is digested to its building blocks the amino acids.amino acids.


Absorption:Absorption: The transport of digested end products The transport of digested end products

from the GI tract to the blood or lymph from the GI tract to the blood or lymph nodesnodes

Most absorption occurs in the small Most absorption occurs in the small intestine intestine

Defecation:Defecation: The elimination of indigestible substances The elimination of indigestible substances

from the body.from the body.

Digestive Activity ControlsDigestive Activity Controls

Digestive activity is controlled by reflexes via the Digestive activity is controlled by reflexes via the parasympathetic division of the autonomic parasympathetic division of the autonomic nervous system. nervous system.

Sensors involved in these reflexes are located in Sensors involved in these reflexes are located in the walls of the GI tract organs and respond to the walls of the GI tract organs and respond to many stimuli:many stimuli: Stretch of the organ by food in itStretch of the organ by food in it pH contents pH contents Presence of certain breakdown products of digestionPresence of certain breakdown products of digestionThese stimuli then cause:These stimuli then cause:- Glands to secrete digestive juicesGlands to secrete digestive juices- Smooth muscles to mix and propel substances along the Smooth muscles to mix and propel substances along the

digestive tract.digestive tract.

Food Ingestion and Food Ingestion and BreakdownBreakdown

Activities occurring in the mouth, pharynx Activities occurring in the mouth, pharynx and Esophagusand Esophagus Food enters the mouth and mechanical and Food enters the mouth and mechanical and

chemical digestion beginchemical digestion begin Food is physically broken down into smaller Food is physically broken down into smaller

partsparts As food mixes with saliva the digestion of As food mixes with saliva the digestion of

starch begins breaking it down into maltosestarch begins breaking it down into maltose No food absorption occurs in the mouthNo food absorption occurs in the mouth The pharynx and esophagus have NO digestive The pharynx and esophagus have NO digestive

function but to provide a passageway to carry function but to provide a passageway to carry food to the next processing site – the stomachfood to the next processing site – the stomach

Food Propulsion – Food Propulsion – Swallowing and PeristalsisSwallowing and Peristalsis

In order for food to be sent from the mouth to the In order for food to be sent from the mouth to the stomach it must be swallowedstomach it must be swallowed

Deglutition: swallowing: involves the coordinated Deglutition: swallowing: involves the coordinated activity of several structures and has two major activity of several structures and has two major phasesphases Buccal phase: voluntary phase that occurs in the mouth Buccal phase: voluntary phase that occurs in the mouth

and then the tongue pushes it into the pharynx and and then the tongue pushes it into the pharynx and becomes involuntarybecomes involuntary

Pharyngeal-esophageal phase: involuntary phase that Pharyngeal-esophageal phase: involuntary phase that transports food through the pharynx and esophagus. transports food through the pharynx and esophagus. This phase is controlled by the parasympathetic division This phase is controlled by the parasympathetic division of the ANS and depends on the mobility of the digestive of the ANS and depends on the mobility of the digestive organs from this point on. organs from this point on.

All other routes that food might take except those that are All other routes that food might take except those that are distal into the digestive tract are blocked of.distal into the digestive tract are blocked of.

Food is moved through the pharynx and then into the Food is moved through the pharynx and then into the esophagus by peristalsis of the walls of the GI tractesophagus by peristalsis of the walls of the GI tract

Food BreakdownFood Breakdown

Activities of the Stomach:Activities of the Stomach: Gastric Juice: is secreted and controlled by the Gastric Juice: is secreted and controlled by the

nervous system as well as hormonesnervous system as well as hormones The sight, smell and taste of food stimulate the The sight, smell and taste of food stimulate the

nervous system reflexes which increase the nervous system reflexes which increase the secretion of gastric juice by the stomachsecretion of gastric juice by the stomach

Also the presence of food and the falling pH in Also the presence of food and the falling pH in the stomach stimulate the stomach cells to the stomach stimulate the stomach cells to release the hormone gastrinrelease the hormone gastrin

Gastrin: prods the stomach glands to produce Gastrin: prods the stomach glands to produce protein digesting enzymes, mucus and protein digesting enzymes, mucus and hydrochloric acidhydrochloric acid

A healthy human produces approx. 2-3 liters of A healthy human produces approx. 2-3 liters of gastric juice everyday!gastric juice everyday!


Hydrochloric acid: is responsible for Hydrochloric acid: is responsible for making the stomach contents acidic. making the stomach contents acidic. This can sometimes be a problem since This can sometimes be a problem since

the acid and the stomach enzymes the acid and the stomach enzymes could potentially destroy the stomach could potentially destroy the stomach itself and cause ulcers.itself and cause ulcers.

This is prevented by the production of This is prevented by the production of extra mucus to help line the stomach extra mucus to help line the stomach keeping it safe. keeping it safe.


Heartburn:Heartburn: Failure of the cardioesophageal sphincter to Failure of the cardioesophageal sphincter to

close tightly causing gastric juice to back up into close tightly causing gastric juice to back up into the esophagus and if untreated can lead to the esophagus and if untreated can lead to inflammation of the esophagus itself.inflammation of the esophagus itself.

Hiatal Hernia:Hiatal Hernia: Structural abnormality where the superior part of Structural abnormality where the superior part of

the stomach protrudes slightly above the the stomach protrudes slightly above the diaphragm and gastric juices can then flow freely diaphragm and gastric juices can then flow freely into the esophagus.into the esophagus.

Treatment involves restricting food later in the Treatment involves restricting food later in the day – after dinner – taking antacids and sleeping day – after dinner – taking antacids and sleeping with the head slightly elevated.with the head slightly elevated.


Pepsin: the active protein digesting enzyme. Pepsin: the active protein digesting enzyme. Comes from pepsinogen which is activated by the Comes from pepsinogen which is activated by the hydrochloric acid environment in the stomach.hydrochloric acid environment in the stomach.

Rennin: the second protein digesting enzyme Rennin: the second protein digesting enzyme produced by the stomach. In infants rennin is produced by the stomach. In infants rennin is produced in large amounts since that is their produced in large amounts since that is their major intake of food.major intake of food.

When foods enter the stomach it will begin to When foods enter the stomach it will begin to stretch and the layers of the stomachs muscular stretch and the layers of the stomachs muscular wall will become active in compressing and wall will become active in compressing and pushing food to mix with enzymes to form the pushing food to mix with enzymes to form the semi fluid chyme.semi fluid chyme.


Food propulsion: Food propulsion: Once food is mixed in the stomach peristalsis occurs in Once food is mixed in the stomach peristalsis occurs in

the lower half of the stomach and is pushed towards the the lower half of the stomach and is pushed towards the pyloric sphincterpyloric sphincter

With each contraction of the stomach the pyloric With each contraction of the stomach the pyloric sphincter will open just enough to let out 3ml or less of sphincter will open just enough to let out 3ml or less of the chyme into the small intestinethe chyme into the small intestine

Once the duodenum is filled with the chyme its walls Once the duodenum is filled with the chyme its walls with stretch causing a nervous reflex, enterogastric with stretch causing a nervous reflex, enterogastric reflex, to occur and stops the movement of the stomach reflex, to occur and stops the movement of the stomach to allow for the intestinal process to catch up.to allow for the intestinal process to catch up.

The stomach generally takes about 4 hours to empty The stomach generally takes about 4 hours to empty completely and 6 hours or more if the meal is high in fat. completely and 6 hours or more if the meal is high in fat.

Food Breakdown & Food Breakdown & AbsorptionAbsorption

Activities of the Small Intestine:Activities of the Small Intestine: Food that reaches the small intestine is Food that reaches the small intestine is

only partially digested.only partially digested. Carbohydrates and proteins have been Carbohydrates and proteins have been

partially digested but no fatspartially digested but no fats By the time that food reaches the end of By the time that food reaches the end of

the small intestine digestion if complete the small intestine digestion if complete and almost all of the food absorption and almost all of the food absorption has occurred. has occurred.

Activities of the Small Activities of the Small IntestineIntestine

Brush border enzymes: break down double sugars Brush border enzymes: break down double sugars into simple sugars completing protein digestion.into simple sugars completing protein digestion.

Pancreatic juice: contain enzymes that complete Pancreatic juice: contain enzymes that complete the digestion of starch with the help of brush the digestion of starch with the help of brush border enzymes and carry about half of protein border enzymes and carry about half of protein digestion and are totally responsible for fat digestion and are totally responsible for fat digestion since the pancreas is the only source of digestion since the pancreas is the only source of lipases (digest fats) and digest nucleic acids.lipases (digest fats) and digest nucleic acids.

Pancreatic juice also contains a rich supply of Pancreatic juice also contains a rich supply of bicarbonate which reaches the small intestine and bicarbonate which reaches the small intestine and neutralizes the acid chyme coming in from the neutralizes the acid chyme coming in from the stomach and provides a good environment for stomach and provides a good environment for activation and activity of intestinal and pancreatic activation and activity of intestinal and pancreatic digestive enzymes. digestive enzymes.


Pancreatitis: rare condition but Pancreatitis: rare condition but extremely serious inflammation of the extremely serious inflammation of the pancreases as a result of over active pancreases as a result of over active pancreatic enzymes in the pancreatic pancreatic enzymes in the pancreatic duct. duct. The pancreatic tissue and duct are The pancreatic tissue and duct are

essentially digested themselves and can essentially digested themselves and can lead to nutritional deficiency since lead to nutritional deficiency since digestion is not accurately occurring.digestion is not accurately occurring.


When chyme enters the small intestine it When chyme enters the small intestine it stimulates mucosa cells to produce several stimulates mucosa cells to produce several hormones:hormones: Secretin: causes the liver to increase bile Secretin: causes the liver to increase bile

productionproduction Cholecystokinin: causes the gallbladder to contract Cholecystokinin: causes the gallbladder to contract

and release stored bile into the bile duct so that the and release stored bile into the bile duct so that the pancreatic juice and bile enter the small intestine pancreatic juice and bile enter the small intestine together. together.

These hormones influence the release of pancreatic These hormones influence the release of pancreatic juice and bilejuice and bile

The hormones then enter the blood and circulate to The hormones then enter the blood and circulate to their target organs – pancreas, liver, and their target organs – pancreas, liver, and gallbladdergallbladder


Food Propulsion:Food Propulsion: Peristalsis is the major mechanism of Peristalsis is the major mechanism of

transport through the small intestinetransport through the small intestine In the small intestine it moves in a more In the small intestine it moves in a more

rythmical pattern and in segmental rythmical pattern and in segmental movements so foodstuffs move movements so foodstuffs move smoothly through with little friction.smoothly through with little friction.

Activities of the Large Activities of the Large IntestineIntestine

Food Breakdown and Absorption:Food Breakdown and Absorption: When food is finally delivered to the large When food is finally delivered to the large

intestine it contains few nutrients but will still intestine it contains few nutrients but will still spend from 12 – 24 hours in the large intestine.spend from 12 – 24 hours in the large intestine.

The nutrients that are still available will be The nutrients that are still available will be broken down by bacteria that “live” within the broken down by bacteria that “live” within the large intestine walls and contribute to the odor of large intestine walls and contribute to the odor of feces.feces.

The bacteria also create some vitamins such as K The bacteria also create some vitamins such as K and some Band some B

Absorption in the large intestine is limited to the Absorption in the large intestine is limited to the production of these vitamins, some ions and production of these vitamins, some ions and water.water.

Feces is then created and delivered to the Feces is then created and delivered to the rectum to be rid ofrectum to be rid of


Propulsion of residue and defecation:Propulsion of residue and defecation: Mass movements: long slow powerful contractile Mass movements: long slow powerful contractile

waves that move over the large areas of the waves that move over the large areas of the colon 3-4 times a day and force the contents into colon 3-4 times a day and force the contents into the rectumthe rectum

Diverticula: mucosa protrudes through the colon Diverticula: mucosa protrudes through the colon walls which will then cause inflammation of the walls which will then cause inflammation of the colon = diverticulosiscolon = diverticulosis

Diverticulitis: condition where the diverticula Diverticulitis: condition where the diverticula themselves become inflamed and can be life themselves become inflamed and can be life threatening if rupturethreatening if rupture

Defacationrelex: spinal reflex that causes the Defacationrelex: spinal reflex that causes the walls of the sigmoid colon and rectum to contract walls of the sigmoid colon and rectum to contract and anal sphincter to relax allowing us to release and anal sphincter to relax allowing us to release the fecesthe feces


Diarrhea: Diarrhea: Watery stools resulting from any condition that Watery stools resulting from any condition that

rushes food residue through the large intestine rushes food residue through the large intestine before that organ has time to absorb the water.before that organ has time to absorb the water.

Because fluids and ions are lost from the body Because fluids and ions are lost from the body prolonged diarrhea may cause dehydration and prolonged diarrhea may cause dehydration and an imbalance of electrolytes in the bodyan imbalance of electrolytes in the body

Constipation:Constipation: Too much water is absorbed because the food Too much water is absorbed because the food

residue has remained in the body for too long.residue has remained in the body for too long. Stools are hard and difficult to passStools are hard and difficult to pass May be the result of lack of fiber in the diet or May be the result of lack of fiber in the diet or

laxative abuselaxative abuse

Nutrition & MetabolismNutrition & Metabolism

Most foods are used as metabolic fuels Most foods are used as metabolic fuels and are oxidized and transformed into :and are oxidized and transformed into : ATP: the chemical energy form needed by ATP: the chemical energy form needed by

body cells to drive their activitiesbody cells to drive their activities Kilocalories: (Kcal) energy value of foods is Kilocalories: (Kcal) energy value of foods is

measured in Kcal.measured in Kcal. Calories: large calories that most people Calories: large calories that most people

watching their dietary intake typically count.watching their dietary intake typically count.

NutritionNutrition Nutrient:Nutrient:

Substance in food that is used by the body to Substance in food that is used by the body to promote normal growth, maintenance and repairpromote normal growth, maintenance and repair

Nutrients are divided into six categories:Nutrients are divided into six categories: Major nutrients are: These nutrients are needed in Major nutrients are: These nutrients are needed in

greater amounts within the body and should make up greater amounts within the body and should make up the bulk of what we eatthe bulk of what we eat

CarbohydratesCarbohydrates LipidsLipids ProteinsProteins Water – makes up 60% of the volume of the food we eat.Water – makes up 60% of the volume of the food we eat.

Nutrients required in only minimal amounts are:Nutrients required in only minimal amounts are: VitaminsVitamins MineralsMinerals

NutritionNutrition

Dietary sources of major nutrients:Dietary sources of major nutrients: Carbohydrates:Carbohydrates:

Sugars and starchesSugars and starches All carbohydrates except for milk sugar All carbohydrates except for milk sugar

(lactose) and glycogen in meats are derived (lactose) and glycogen in meats are derived from plants.from plants.

Sugars come mostly from fruits, sugar cane and Sugars come mostly from fruits, sugar cane and milkmilk

Polysaccharide starch is found in grains, Polysaccharide starch is found in grains, legumes and root vegetables. Cellulose is also legumes and root vegetables. Cellulose is also found in vegetables but cannot be digested by found in vegetables but cannot be digested by humans and provides fiber to increase the bulk humans and provides fiber to increase the bulk of our stool and aid in defecationof our stool and aid in defecation

NutritionNutrition

Dietary sources of major nutrients:Dietary sources of major nutrients: LipidsLipids

Cholesterol & phospholipidsCholesterol & phospholipids Fats or triglyceridesFats or triglycerides Saturated fats are found in animal products – Saturated fats are found in animal products –

meat, dairy, etc.meat, dairy, etc. Unsaturated fats are found in seeds, nuts and Unsaturated fats are found in seeds, nuts and

most vegetable oils.most vegetable oils. Cholesterol also only comes from animal Cholesterol also only comes from animal

products – egg yolk, meats and dairy productsproducts – egg yolk, meats and dairy products

NutritionNutrition Dietary sources of the major nutrients:Dietary sources of the major nutrients:

Proteins:Proteins: Molecules that are amino acid polymersMolecules that are amino acid polymers Animal products contain the highest quality Animal products contain the highest quality

protein – eggs, milk and most meat products are protein – eggs, milk and most meat products are complete proteinscomplete proteins

Complete proteins meet all the body’s amino Complete proteins meet all the body’s amino acid requirements for tissue maintenance and acid requirements for tissue maintenance and growthgrowth

Nuts, cereal and legumes are also rich in protein Nuts, cereal and legumes are also rich in protein but lack one or more of the essential amino acidsbut lack one or more of the essential amino acids

Vegetarians must be sure to make good combinations Vegetarians must be sure to make good combinations of these proteins in order to obtain all the essential of these proteins in order to obtain all the essential amino acids.amino acids.

NutrientsNutrients

Vitamins:Vitamins: Organic nutrients of various forms that the Organic nutrients of various forms that the

body requires in small amountsbody requires in small amounts A balanced diet will assure that you are A balanced diet will assure that you are

obtaining your vitamin requirementsobtaining your vitamin requirements Some vitamins have been linked to fighting Some vitamins have been linked to fighting

certain types of cancer but research is still certain types of cancer but research is still inconclusive.inconclusive.

Most vitamins function as coenzymes Most vitamins function as coenzymes They can act with an enzyme to accomplish a They can act with an enzyme to accomplish a

particular catalyst within the bodyparticular catalyst within the body

NutrientsNutrients

Minerals:Minerals: The body requires adequate amounts of seven The body requires adequate amounts of seven

essential minerals:essential minerals: Calcium, phosphorus, potassium, sulfur, sodium Calcium, phosphorus, potassium, sulfur, sodium

chloride and magnesiumchloride and magnesium There are about a dozen others that are also There are about a dozen others that are also

needed but in much less amounts.needed but in much less amounts. Mineral rich foods are: vegetables, legumes, Mineral rich foods are: vegetables, legumes,

milk and some meatsmilk and some meats Fats and sugars = no mineralsFats and sugars = no minerals Cereals and grains = poor sources of mineralsCereals and grains = poor sources of minerals

MetabolismMetabolism

Chemical reactions that are Chemical reactions that are necessary to maintain life. Involves necessary to maintain life. Involves either:either: Catabolism: substances are broken Catabolism: substances are broken

down to simpler substancesdown to simpler substances Energy is released and captured to make Energy is released and captured to make

ATP and used to energize all cell activitiesATP and used to energize all cell activities Anabolism: larger molecules or Anabolism: larger molecules or

structures are built from smaller onesstructures are built from smaller ones


Carbohydrates Carbohydrates Broken down to make ATPBroken down to make ATP

FatsFats Used to build cell membranes, make myelin Used to build cell membranes, make myelin

sheaths and insulate the bodysheaths and insulate the body Also used as the fuel to make ATP when there Also used as the fuel to make ATP when there

are inadequate carbohydrates in the diet.are inadequate carbohydrates in the diet. Proteins:Proteins:

Conserved by the body cells and are used to Conserved by the body cells and are used to build cell structures.build cell structures.


Carbohydrate Metabolism:Carbohydrate Metabolism: The preferred fuel in the body to produce The preferred fuel in the body to produce

cellular energy – ATPcellular energy – ATP Glucose (blood sugar) is the major breakdown Glucose (blood sugar) is the major breakdown

product in carbohydrate digestion and major product in carbohydrate digestion and major fuel used to create ATPfuel used to create ATP

Cellular respiration: Cellular respiration: The breakdown of glucose into ATP and waterThe breakdown of glucose into ATP and water Uses three main metabolic pathways: glycolysis, Uses three main metabolic pathways: glycolysis,

krebs cycle and electron transport chain.krebs cycle and electron transport chain.

Cellular RespirationCellular Respiration

Cellular respirationCellular respiration Glycolysis:Glycolysis:

Energizes the glucose molecule so that it can Energizes the glucose molecule so that it can be split into two pyruvic acid molecules and be split into two pyruvic acid molecules and create a small amount of ATP in the processcreate a small amount of ATP in the process

Krebs Cycle:Krebs Cycle: Produces all the carbon dioxide and water Produces all the carbon dioxide and water

that results during the breakdown of glucose that results during the breakdown of glucose and will also create small amounts of ATPand will also create small amounts of ATP

Cellular RespirationCellular Respiration

Electron Transport Chain:Electron Transport Chain: The action for ATP productionThe action for ATP production Hydrogen atoms are removed during the first Hydrogen atoms are removed during the first

two metabolic phases and loaded with energy. two metabolic phases and loaded with energy. These hydrogens are delivered to the protein These hydrogens are delivered to the protein carriers of the electron transport chain which carriers of the electron transport chain which form part of the mitochondrial membrane.form part of the mitochondrial membrane.

Here the hydrogen atoms are split into hydrogen Here the hydrogen atoms are split into hydrogen and electrons. The electrons give off their energy and electrons. The electrons give off their energy enabling cells to attach phosphate to ADP and enabling cells to attach phosphate to ADP and create ATPcreate ATP

Cellular respirationCellular respiration

Electron transport chain:Electron transport chain: Glucose is the major fuel for making ATP and it Glucose is the major fuel for making ATP and it

is critical that our bodies maintain their is critical that our bodies maintain their homeostasis of blood glucose levels.homeostasis of blood glucose levels.

If levels are excessively high the excess will be If levels are excessively high the excess will be stored in the cells as glycogen. If they maintain stored in the cells as glycogen. If they maintain high the glycogen will be turned into fat. high the glycogen will be turned into fat.

When blood glucose is too low the liver breaks When blood glucose is too low the liver breaks down the stored glycogen and releases glucose down the stored glycogen and releases glucose to the blood for use in the cell.to the blood for use in the cell.

Fat MetabolismFat Metabolism

Our fat metabolism is mostly handled by the body in the liver Our fat metabolism is mostly handled by the body in the liver where some of its cells use the fat to make ATP for their own where some of its cells use the fat to make ATP for their own use. Some will synthesize lipoproteins, thromboplastin and use. Some will synthesize lipoproteins, thromboplastin and cholesterol and then release the rest to the blood in the form of cholesterol and then release the rest to the blood in the form of small fat-breakdown productssmall fat-breakdown products

Body cells then remove the fat products and cholesterol from Body cells then remove the fat products and cholesterol from the blood and build them into their membranes or hormones as the blood and build them into their membranes or hormones as needed.needed.

For fat products to be used for ATP synthesis they must first be For fat products to be used for ATP synthesis they must first be broken into acetic acid which will then be oxidized and corbon broken into acetic acid which will then be oxidized and corbon dioxide, water and ATP will be formed.dioxide, water and ATP will be formed.

When there is not enough glucose to fuel the needs of the cells When there is not enough glucose to fuel the needs of the cells for energy larger amounts of fat will be used to form ATP.for energy larger amounts of fat will be used to form ATP.

This form of energy is not the best because it forms incomplete This form of energy is not the best because it forms incomplete ATP and may have biproducts which are acidic leading to ATP and may have biproducts which are acidic leading to ketosisketosis

Fat MetabolismFat Metabolism

Ketosis:Ketosis: Common consequence of “no carb” Common consequence of “no carb”

diets, uncontrolled diabetes, and diets, uncontrolled diabetes, and starvation where the body is forced to starvation where the body is forced to rely completely on fats to fuel its energy rely completely on fats to fuel its energy needs.needs.

Unlike fats, cholesterol is never used to Unlike fats, cholesterol is never used to form ATP because of its critical role in form ATP because of its critical role in the function of the molecules and the the function of the molecules and the structures they form.structures they form.

Protein MetabolismProtein Metabolism

Proteins make up the bulk of cellular structures Proteins make up the bulk of cellular structures and are conserved in the body cells.and are conserved in the body cells.

When proteins are ingested they are broken down When proteins are ingested they are broken down to amino acids. to amino acids.

Once the liver has finished processing the blood Once the liver has finished processing the blood and has taken al the amino acids it needs the and has taken al the amino acids it needs the remaining amino acids circulate into the body remaining amino acids circulate into the body cells. cells.

The cells then remove the amino acids from the The cells then remove the amino acids from the blood and use them to build proteins for their own blood and use them to build proteins for their own use as well as export.use as well as export.

The cells use the ATP to bring the amino acids into The cells use the ATP to bring the amino acids into their interior and in many cases they contain more their interior and in many cases they contain more amino acids inside than what is flowing outside in amino acids inside than what is flowing outside in the blood. the blood.


The cells must have an abundance of The cells must have an abundance of amino acids because in order to build amino acids because in order to build their proteins they must have all 20 their proteins they must have all 20 amino acids present.amino acids present.

Eight of these amino acids cannot be Eight of these amino acids cannot be created by the cells so they must be created by the cells so they must be obtained by the diet and are therefore obtained by the diet and are therefore named “essential amino acids”named “essential amino acids”


Amino acids will only be used to make ATP when Amino acids will only be used to make ATP when proteins are overabundant or when proteins are overabundant or when carbohydrates and fats are not availablecarbohydrates and fats are not available

When amino acids are oxidized to become ATP When amino acids are oxidized to become ATP their amine groups are removed as ammonia and their amine groups are removed as ammonia and the rest of the molecule enters the krebs cycle.the rest of the molecule enters the krebs cycle.

The ammonia that is released is toxic to the body The ammonia that is released is toxic to the body cells, especially nerve cells. cells, especially nerve cells.

The liver will then help out by combining the The liver will then help out by combining the ammonia with carbon dioxide to form urea which ammonia with carbon dioxide to form urea which is not harmful to body cells and will be excreted is not harmful to body cells and will be excreted from the body as urinefrom the body as urine

The role of the Liver in The role of the Liver in metabolismmetabolism

Without our liver we would die within 24 Without our liver we would die within 24 hours. hours.

Liver cells detoxify drugs and alcohol, Liver cells detoxify drugs and alcohol, degrade hormones, make substances vital to degrade hormones, make substances vital to the body, and play a role in metabolism as the body, and play a role in metabolism as they process nearly every class of nutrient.they process nearly every class of nutrient.

Because of its importance our body has an Because of its importance our body has an excess of liver tissue and when damaged is excess of liver tissue and when damaged is one of the only organs that can regenerate one of the only organs that can regenerate rapidly and easily.rapidly and easily.


Hepatic circulationHepatic circulation Circulation in the liverCirculation in the liver Brings nutrient rich blood from the digestive viscera Brings nutrient rich blood from the digestive viscera

directly to the liverdirectly to the liver Since the liver is the body’s major metabolic organ it Since the liver is the body’s major metabolic organ it

takes the nutrients it needs to function from the takes the nutrients it needs to function from the blood firstblood first

As the blood moves through the liver, liver cells As the blood moves through the liver, liver cells remove amino acids, fatty acids and glucose from remove amino acids, fatty acids and glucose from the bloodthe blood

These nutrients are then stored for later use or processedThese nutrients are then stored for later use or processed At the same time the phagocytic cells in the liver At the same time the phagocytic cells in the liver

remove and destroy bacteria that have gotten into remove and destroy bacteria that have gotten into the digestive tract and into the bloodthe digestive tract and into the blood


General metabolic functions:General metabolic functions: Liver helps to maintain blood glucose levels within Liver helps to maintain blood glucose levels within

a normal range – approx. 100 mg glucose/100 ml a normal range – approx. 100 mg glucose/100 ml bloodblood

Glycogen is formed from glucose molecules that Glycogen is formed from glucose molecules that are removed from the blood and combined to form are removed from the blood and combined to form this large polysaccharide moleculethis large polysaccharide molecule

Glycogenisis: the formation of glycogen and its Glycogenisis: the formation of glycogen and its storage in the liverstorage in the liver

As the body cells remove glucose from the blood to As the body cells remove glucose from the blood to meet their needs the blood glucose levels drop and meet their needs the blood glucose levels drop and the liver cells break down their stored glycogen to the liver cells break down their stored glycogen to release small amounts of glucose into the blood.release small amounts of glucose into the blood.

Glycogenisis: the breakdown of glycogen to Glycogenisis: the breakdown of glycogen to produce glucoseproduce glucose


Most of the time this glycogenisis is Most of the time this glycogenisis is accomplished by using carbohydrates as its accomplished by using carbohydrates as its food source, but if necessary the liver can food source, but if necessary the liver can also make glucose from fats and proteins.also make glucose from fats and proteins. Gluconeogenesis: the formation of “new sugar” Gluconeogenesis: the formation of “new sugar”

from a non-carbohydrate formfrom a non-carbohydrate form Fats and fatty acids picked up by the liver cells Fats and fatty acids picked up by the liver cells

are oxidized for energy for use by the liver cells are oxidized for energy for use by the liver cells themselves – the rest are broken down to themselves – the rest are broken down to simpler substances such as acetic acid and simpler substances such as acetic acid and acetoacetic acid and released into the blood or acetoacetic acid and released into the blood or stored as fat reserves in the liver.stored as fat reserves in the liver.


Blood proteins made in the liver are built from the Blood proteins made in the liver are built from the amino acids that it picks up from the blood.amino acids that it picks up from the blood.

Completed proteins are then released back into Completed proteins are then released back into the blood to travel throughout circulation.the blood to travel throughout circulation.

Albumin:Albumin: Most abundant protein in bloodMost abundant protein in blood Holds fluid in the bloodstreamHolds fluid in the bloodstream When its levels are insufficient fluid laves the When its levels are insufficient fluid laves the

bloodstream and accumulates in the tissues causing bloodstream and accumulates in the tissues causing edemaedema

Nutrients not needed by the liver cells are released Nutrients not needed by the liver cells are released into the blood and drain from the liver in the into the blood and drain from the liver in the hepatic vein to enter the systemic circulation hepatic vein to enter the systemic circulation where they are now available to other body cells.where they are now available to other body cells.

Cholesterol Metabolism Cholesterol Metabolism and Transportand Transport

Cholesterol is a very important lipid in the Cholesterol is a very important lipid in the diet but is NOT used as an energy fueldiet but is NOT used as an energy fuel

Cholesterol is used as the structural basis of Cholesterol is used as the structural basis of steroid hormones and vitamin D and is the steroid hormones and vitamin D and is the major building block of plasma membranes.major building block of plasma membranes.

Only 15% of blood cholesterol comes from Only 15% of blood cholesterol comes from the diet itself, 85% is made in the liverthe diet itself, 85% is made in the liver It is lost from the body when it is broken down It is lost from the body when it is broken down

and secreted in bile salts, which leave the body and secreted in bile salts, which leave the body as fecesas feces


Lipoproteins: a class of proteins made by the Lipoproteins: a class of proteins made by the liver and known as HDL’s and LDL’s play an liver and known as HDL’s and LDL’s play an important role in fat and cholesterol transport.important role in fat and cholesterol transport. Fatty acids, fats and cholesterol are insoluble in Fatty acids, fats and cholesterol are insoluble in

water and cannot circulate in the bloodstream freely water and cannot circulate in the bloodstream freely and must be transported by binding to a lipoproteinand must be transported by binding to a lipoprotein

Low density lipoproteins (LDL’s): transport Low density lipoproteins (LDL’s): transport cholesterol and other lipids TO body cells.cholesterol and other lipids TO body cells.

If large amounts of LDL’s are circulating there is a high If large amounts of LDL’s are circulating there is a high chance of the fatty substances being deposited into the chance of the fatty substances being deposited into the arterial walls and causing artherosclerosisarterial walls and causing artherosclerosis

Because of this possiblity LDLs are usually called “bad Because of this possiblity LDLs are usually called “bad lipoproteins”lipoproteins”


High Density Lipoproteins (HDL’s): High Density Lipoproteins (HDL’s): Transport cholesterol from the tissue cells to the Transport cholesterol from the tissue cells to the

liver for disposal.liver for disposal. High HDL levels are considered good because the High HDL levels are considered good because the

cholesterol is going to be broken down and cholesterol is going to be broken down and eliminated from the body.eliminated from the body.

Both HDL’s and LDL’s are “good and necesssary” it Both HDL’s and LDL’s are “good and necesssary” it is their ratio in the blood stream that deterines is their ratio in the blood stream that deterines whether or not potentially lethal cholesterol whether or not potentially lethal cholesterol deposits are likely to be laid down in the artery deposits are likely to be laid down in the artery walls.walls.

Generally a diet low in saturated fats and Generally a diet low in saturated fats and cholesterol, exercise and not smoking and drinking cholesterol, exercise and not smoking and drinking coffee will create a desirable HDL/LDL level.coffee will create a desirable HDL/LDL level.

Body Energy BalanceBody Energy Balance

When any fuel is burned it consumes When any fuel is burned it consumes oxygen and creates heat.oxygen and creates heat.

““Burning” of food fuels by body cells Burning” of food fuels by body cells also do this same thing.also do this same thing. Energy cannot be created or destroyed it Energy cannot be created or destroyed it

can only be converted from one form to can only be converted from one form to another.another.

In the body this means that Energy intake In the body this means that Energy intake = Energy output= Energy output

Body Energy BalanceBody Energy Balance

Energy Intake:Energy Intake: Energy created during food oxidization = Energy created during food oxidization =

reaction of glycolysis, the krebs cycle and the reaction of glycolysis, the krebs cycle and the electron transport chain.electron transport chain.

Energy Output:Energy Output: Energy we lose as heat – about 60% of our Energy we lose as heat – about 60% of our

total energy. total energy. Plus energy used to do work and energy stored Plus energy used to do work and energy stored

in the form of fat or glycogenin the form of fat or glycogen Energy storage is important during periods of Energy storage is important during periods of

growth growth

Regulation of food intakeRegulation of food intake

When energy intake and energy outflow are When energy intake and energy outflow are balanced body weight remains consistent.balanced body weight remains consistent.

When they are not in balance either weight When they are not in balance either weight gain or weight loss occurs.gain or weight loss occurs.

How do we control food intake?How do we control food intake? Researchers have found that several factors Researchers have found that several factors

contribute to eating behaviors:contribute to eating behaviors: Rising or falling blood levels of nutrients, hormones, Rising or falling blood levels of nutrients, hormones,

body temperature and psychological factorsbody temperature and psychological factors

Regulation of food intakeRegulation of food intake

Psychological factors are said to be Psychological factors are said to be the cause of obesity the cause of obesity Even when psychological factors are the Even when psychological factors are the

underlying cause of obesity these underlying cause of obesity these individuals will not continue to gain individuals will not continue to gain weight endleselyweight endlesely

With obesity even though their body’s With obesity even though their body’s feeding controls are still operating they feeding controls are still operating they maintain a body energy content at a maintain a body energy content at a higher than normal rate.higher than normal rate.

Metabolic rate and Metabolic rate and Body heat productionBody heat production

Basal Metabolic Rate:Basal Metabolic Rate: When nutrients are broken down to produce When nutrients are broken down to produce

ATP they yeild different amounts of energy.ATP they yeild different amounts of energy. The energy of food values is measured in units The energy of food values is measured in units

called Kilocalories (Kcal)called Kilocalories (Kcal) Carbohydrates and proteins yeild about 4 Carbohydrates and proteins yeild about 4

Kcal/gram and fats yeild 9 Kcals/gram when Kcal/gram and fats yeild 9 Kcals/gram when they are broken down for energythey are broken down for energy

To determine the total calorie value of a meal To determine the total calorie value of a meal you must know how many grams of each of you must know how many grams of each of these nutrients the food contains.these nutrients the food contains.


Basal metabolic rate (BMR)Basal metabolic rate (BMR) Amount of heat produced by the body per unit of Amount of heat produced by the body per unit of

time when it is at rest.time when it is at rest. This reflects the energy supply a person needs This reflects the energy supply a person needs

just to perform essential life activities such as just to perform essential life activities such as breathing, heartrate, and kidney function.breathing, heartrate, and kidney function.

Factors that influence BMR are:Factors that influence BMR are: Surface area and genderSurface area and gender A small thin male will have a higher BMR than a large A small thin male will have a higher BMR than a large

obese femalobese femal Children and adolscents require large amounts of energy Children and adolscents require large amounts of energy

for growth and will therfore have higher BMR’sfor growth and will therfore have higher BMR’s In old age BMR will decrease as the muscles begin to In old age BMR will decrease as the muscles begin to

atrophyatrophy


Thyroxine:Thyroxine: Produced by the thyroid gland is one of the Produced by the thyroid gland is one of the

most important factors in determining BMRmost important factors in determining BMR The more thyroxine you produce the higher The more thyroxine you produce the higher

the oxygen consumption and TP use and the oxygen consumption and TP use and the higher the metabolic rate will be. the higher the metabolic rate will be.

Thyroxin levels can easily be assesed by Thyroxin levels can easily be assesed by blood tests which give a good idea of how blood tests which give a good idea of how well the thyroid is working.well the thyroid is working.


Hyperthyroidism:Hyperthyroidism: Excessive metabolic rateExcessive metabolic rate Body increases its use of stored fats and tissue Body increases its use of stored fats and tissue

proteins and despite the increased hunger and proteins and despite the increased hunger and food intake this person will usually lose weightfood intake this person will usually lose weight

Bones will weaken and body muscles, including Bones will weaken and body muscles, including the heart, will atrophythe heart, will atrophy

Hypothyroidism:Hypothyroidism: Decreased metabolic rateDecreased metabolic rate Results in obesity and diminished thought Results in obesity and diminished thought

processprocess


Total Metabolic RateTotal Metabolic Rate When we are active more glucose must be oxidized When we are active more glucose must be oxidized

to provide energy for these extra activitiesto provide energy for these extra activities Food digestion and physical actvitiy increase the Food digestion and physical actvitiy increase the

body’s caloric requirementsbody’s caloric requirements Total metabolic rate (TMR) refers to the total amount Total metabolic rate (TMR) refers to the total amount

of Kcals the body must consume to fuel all actvitiies. of Kcals the body must consume to fuel all actvitiies. Muscular work is the major body activity that Muscular work is the major body activity that

increases the TMRincreases the TMR When a well trained athlete exercises vigorously for When a well trained athlete exercises vigorously for

several minutes the TMR may increase to 15-20 several minutes the TMR may increase to 15-20 times normal and will remain elevated for hours times normal and will remain elevated for hours afterafter


When TMR is equal to the total amount of When TMR is equal to the total amount of calories being consumed homeostasis is calories being consumed homeostasis is maintained and our weight remains maintained and our weight remains consistent.consistent.

If we eat more than we need to sustain TMR If we eat more than we need to sustain TMR excess calories will appear in the form of fat excess calories will appear in the form of fat depositsdeposits

And if we do not eat enough to sustain TMR And if we do not eat enough to sustain TMR then our bodies will break down fat reserves then our bodies will break down fat reserves and tissue proteins to maintain homeostasisand tissue proteins to maintain homeostasis


Body Temperature RegulationBody Temperature Regulation Most of the energy released as food is oxidized escapes as Most of the energy released as food is oxidized escapes as

heatheat Less than 40% of available food energy is actually used to Less than 40% of available food energy is actually used to

form ATPform ATP The heat released warms the tissue and the blood which The heat released warms the tissue and the blood which

circulates to all the body tissues keeping them at circulates to all the body tissues keeping them at homeostatic temperatures allowing metabolism to occur homeostatic temperatures allowing metabolism to occur efficiently.efficiently.

Body temperature is the balance between heat production Body temperature is the balance between heat production and heat lossand heat loss

The thermostat of the body is the hypothalamus of the The thermostat of the body is the hypothalamus of the brain and through the ANS pathways continually regulates brain and through the ANS pathways continually regulates body temperature around 96-100body temperature around 96-100˚F by initiating heat loss ˚F by initiating heat loss or heat producing mechanisms.or heat producing mechanisms.


Heat promoting mechanisms:Heat promoting mechanisms: When temperature is cold body heat must be When temperature is cold body heat must be

conserved. conserved. The short term method of doing this is The short term method of doing this is

vasoconstriction of the blood vessels and vasoconstriction of the blood vessels and shiveringshivering

When vessels constrict the skin is temporarily When vessels constrict the skin is temporarily bypassed by the blood and blood is routed to bypassed by the blood and blood is routed to the deeper, more vital, tissues.the deeper, more vital, tissues.

When this occurs temperature of the exposed When this occurs temperature of the exposed skin drops below environmental temperature.skin drops below environmental temperature.


Homeostatic imbalance:Homeostatic imbalance: Restriction of blood deliver to the skin is not a Restriction of blood deliver to the skin is not a

problem for brief periods of time but if problem for brief periods of time but if extended the skin cells will be deprived of extended the skin cells will be deprived of oxygen and nutrients and will die.oxygen and nutrients and will die.

When core body temperature drops to the When core body temperature drops to the point beyond simple constriction of skin point beyond simple constriction of skin capillaries shivering begins. capillaries shivering begins.

Shivering is very effective in producing heat Shivering is very effective in producing heat because of the energy produced by muscles because of the energy produced by muscles that produces large amounts of heat. that produces large amounts of heat.


Homeostatic Imbalance:Homeostatic Imbalance: Extremely low temperatures resulting Extremely low temperatures resulting

from prolonged exposure to cold is from prolonged exposure to cold is hypothermia.hypothermia.

Documents

The Digestive System and Body Metabolism