Digestive System

The Components of the Digestive System

Principle Parts of Alimentary CanalMouth- mechanical breakdown of food; tasting; secretion of salivary glands (salivary amylase)Esophagus- muscular tube that connects the mouth with the stomachStomach- large muscular storage organ; functions in storage, mixing, some secretions (acid and pepsinogen)Small intestine (3 parts)

Duodenum, jejunum, ileumReceives bile, pancreatic amylase, other secretions; absorption of nutrients (most sugars absorbed here)

Large intestine- reabsorption of water; bacteria in colon produce Vit. KAnus- external opening surrounded by sphincter muscle

DIGESTIVE SYSTEM…..Makes up:

1. digestive tractMouth, pharyx, esophagus, stomach, small intestine, large

intestine, rectum, and anus.2. accessory organs of digestion

salivary glands, teeth, liver, gallbladder, and pancreas

Functions: Ingest and mechanically break down food.Digest food: Stomach and small intestine mainly.Absorb nutrients and water.Eliminate waste.

Stages of Food Processing1. Ingestion: The act of eating. Involves placing food in mouth or oral cavity.

2. Digestion: Macromolecules in food (fats, proteins, polysaccharides, etc.) are too large to be absorbed by digestive system.

Must be broken down into small molecules (amino acids, simple sugars, etc.) so they can be absorbed and utilized by the body.

Involves two processes:Mechanical: Chewing, peristalsis, and churning

movement of the stomach and small intestines to mix food with enzymes and digestive juices.

Chemical: Enzymatic breakdown of food.

3. Absorption: Cells lining the digestive cavity take up building blocks (simple sugars, amino acids, etc.), which then enter the bloodstream.

4. Elimination: Undigested food materials are discharged from body.

The Mouth

The digestive tract begins with Mouth(Oral Cavity)

Processes of the Mouth Mastication (chewing) of food Mixing masticated food with saliva Initiation of swallowing by the tongue Allowing for the sense of taste

Structures include:

1. Teeth break down food into small pieces. (Chewing or mastication)2 sets of teeth

a. deciduous teeth (20 milk teeth)b. permanent teeth (32)

Parts of a tooth 1. Crown – covered with hard brittle enamel 2. Neck – connects the crown and neck 3. Root - anchored to the periodontal

membrane by cementum dentin – nerves, blood vessels, and connective tissue called pulp

that supply the tooth with sensation and nutrients

2. Tongue

Muscular organ that occupies the floor of the mouth2 Major Functions a. facilitates chewing and swallowing.

It mixes the chewed food with saliva and then forms the mixture into a mass called a bolus in preparation for

swallowing. b. contains the taste bud and allows us to taste food.

Structures:a. Frenelum – anchors the tongue to the floor of the mouth

(reason you cannot swallow your tongue)“Children born with extremely short frenulum are often referred to as “tongue tied”

b. Extensive capillary network that provides the sublingual area with a rich supply of blood.

3. The Salivary Glands

A number of glands both inside and outside the oral cavity produce and secrete salivaSaliva functions to

Cleanses the mouthDissolves food chemical so that they can be tastedMoistens food and aids in compacting it into a bolusContains enzymes that begin the chemical breakdown of starches Most saliva is produced by three pairs of extrinsic salivary glands

Parotid – largest of the 3 glands- glands infected by mumps virus

Submandibular – located on the floor of the mouthSublingual – under the tongue; smallest

SALIVA – watery fluid that contains mucous and digestive enzyme called salivary amylase or ptyalin

- approximately 1 L of saliva is secreted per day*Sialolithiasis – obstruction of the salivary ducts by a

stone.

4. Cheeks- forms its lateral wall1) Hard palate forms its anterior roof.2) Soft palate- forms its posterior roof.

5. Uvula – V- shaped piece of soft tissue that hangs down at the upper back region of the mouth.

-prevents food from entering the nose

6. PHARYNX

Upon swallowing bolus enters the oropharynxPushed downward into the laryngopharynxEpiglottis closes and bolus enters the Esophagus

Oesophagus “food tube”

The Oesophagus. “food tube”

Passes food down to your stomach.Food moves through the esophagus by Peristalsis

[wave of contractions that pushes foods]Contains 2 sphincters

a. pharyngoesophageal sphincter- located at the top of esophagus

b. gastroesophageal or lower esophageal sphincter (LES) – at the base of the esophagus

Gastroesophageal Reflux Disease – poorly functioning LES- allows reflux of stomach into the stomach

Paralytic ileus- Intestinal obstruction involves a partial or complete blockage of the

bowel that results in the failure of the intestinal contents to pass through.

Gastroesohageal Reflux Disease-A result of stomach acid backwash into the esophagus, commonly

known as heartburn-The lower esophageal sphincter is normally tightly closed, however,

fatty foods, cigarettes, alcohol, chocolate, caffeine, and certain meds can relax the sphincter.

Deglutition (Swallowing)Three phases

Voluntary• Bolus of food moved by tongue from oral cavity to

pharynxPharyngeal

Reflex: Upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, food pushed into esophagus

Esophageal• Reflex: Epiglottis is tipped posteriorly, larynx elevated

to prevent food from passing into larynx

The Stomach

STOMACHPouch like organ that lies in the upper

part of the abdominal cavity under the diaphragm.

5 digestive functions 1. Secretion of gastric juice

Hydrochloric acid (HCl) Mucus (protective)

Pepsinogen (inactive form of a protein-digesting enzyme)2. Secretion of gastric hormones and intrinsic factor (Gastrin Hormone)3. Regulation of the rate at which the partially digested food is delivered to the small intestine.4. Digestion of food.5. Absorption of small quantities of water and disolved substances.

absorbs alcohol efficiently.

Regions of the Stomach

Fundus - is the expanded part of the stomach lateral to the cardiac region.Body- is the mid portion.Pylorus- funnel shaped terminal part of the stomach.

-The pylorus is continuous with the small intestine through pyloric sphincter or valve.

Rugae – accordion like folds that allows the stomach to expand.

The StomachFood digestion starts in stomach with pepsin.Food is churned in stomach with gastric juice (HCl) to form chyme.

Food remains in stomach from 2 to 6 hours, after which it is released into the small intestine

Small Intestine

Small IntestineAround 6m in an adultFood takes 1-6 h to pass through2 main tasks = digestion, absorption

3 partsDuodenum JejenumIleum

Plays important roles in digestion and absorptionPARTS:1. Duodenum – Most digestion and absorption occur in the doudenum

2. Jejunum – Have folds and villi (finger like projections)- Villi have microvilli - Surface area for absorption increases

3. Ileum - Contains fewer folds and villi- Less absorption occurs and passes undigested food to large

intestineIleocecal Valve – prevents reflux of contents from the cecum (part

of the large intestine) back into the ileum.

Pancreas and liver empty digestive enzymes and bile into the small intestine.

• Pancreatic amylase: Breaks down starch• Trypsin and Chymotrypsin: Break down proteins• Lipases: Break down fats

• Peptidases: Break down proteins• Nucleases: Break down DNA and RNA• Bile: Helps fat digestion by emulsifying fats.

Very large surface area for absorption due to:• Large circular folds (villi)• Tiny cell surface projections (microvilli).

Capillaries drain nutrients from small intestine and then sends them to first to liver and then rest of body.

Large Intestine

Mainly fibre, dead cell, bacteria and water reach here!As it moves along here most of the water is absorbed into the blood.Faeces are stored in the rectum.Eventually egested out of the anus, roughly 24 –48 hours after eating.

Structures:1. Cecum - sac like; the first part of the large intestine.

Appendix - Hanging from cecum Function unknown – in herbivores they contain bacteria that help digest cellulose

2. Colon - Reabsorbs water – so waste is converted to semi-solid = faeces

a. Ascending colon - on right, between cecum and right colic flexure

b. Transverse colon - horizontal portionc. Descending colon - left side,

between left colic flexured. Sigmoid colon - S bend near terminal end

3. Rectum – short, terminal segment of the digestivetube, continuous with the anal canal

4. Anus - external body opening

Food Breakdown and Absorption in the Large Intestine No digestive enzymes are produced Resident bacteria digest remaining nutrients

Produce some vitamin K and B Release gases

Water and vitamins K and B are absorbed Remaining materials are eliminated via feces

Defecation occurs with relaxation of the voluntary (external) anal sphincter and iinvoluntary sphincter (internal)

Associated Structures

of Digestive System

3 important organs – the liver, gallbladder, and the pancreas – empty their secretions into the duodenum. These secretions are necessary for the digestion of food.

A. LIVER - Composed of 2 lobes made up of about 100,000 lobules

FunctionsRemoves bilirubin, a hemoglobin breakdown waste product, from the blood and incorporates it into bile.Produces bile which is stored in gallbladder. Bile is released into the small intestine after a meal. Bile contains no enzymes, but helps solubilize fat particles.Detoxifies blood by removing and metabolizing poisonous substancesStores iron and fat-soluable vitamins A, D, E, K, and B12Produces urea after breaking down amino acids

B. Gallbladder

Liver produces about 1,000 ml of bile a day with excess being stored in the gallbladder.Gallbladder reabsorbs water making bile thick and mucus like. Gallstones may form due to precipitation of cholesterol.

C. GallstonesMost commonly caused by too much cholesterol in bile, these stones are

typically green or yellow. People with gallstones suffer from “attacks”, in which extreme pain is

experienced in the upper abdominal region and steadily increases for approx. 30-60 min.

D. PancreasExocrine gland between stomach and small intestine.Produces several digestive enzymes:

trypsin: digests proteins pancreatic amylase: digests starches lipase: digests fats

Processes of the Digestive System

Ingestion – getting food into the mouth Propulsion – moving foods from one region of the digestive system to

anotherperistalsis - a series of involuntary muscle contractions that

moves food through the digestive tract. (alternating waves of contraction

Absorption - End products of digestion are absorbed in the blood or lymph- Food must enter mucosal cells and then into blood or

lymph capillaries Defecation - Elimination of indigestible substances as feces

Propulsion in the StomachThe pylorus meters out chyme into the small intestine (30 ml at a time)The stomach empties in four to six hours

NUTRITIONThe science that studies the relationship of food to the functioning of the body.

Food provides us with fuel to live, energy to work and play, and the raw materials to build new cells. All the different varieties of food we eat are broken down by our digestive system and transported to every part of our body by our circulatory system.

We eat about 500kg of food A Year!

Nutrient – substance used by the body for growth, maintenance, and repair

Categories of nutrients Carbohydrates: simple sugars, starches, fiber Lipids: triglycerides, phospholipids, fatty acids Proteins: amino acids Vitamins Mineral Water

CarbohydratesThese include simple sugars such as glucose and sucrose and polysaccharides such as starch and celluloseThey are important as structural compounds and as a source of energy that can be used as ATP

Starch is a complex polysaccharide made in plants cells for the storage of energy

Foods such as potatoes and pumpkins are rich in starch and can be good sources of energy

Cellulose is one of the most common carbohydrates and can be found in the cell walls of plants

Human digestive system is unable to break down cellulose and is the largest component of dietary fiber

Vitamins and MineralsSmall organic molecules that serve as coenzymes in metabolic reactions or have highly specific functions.Must be obtained from the diet because the body does not produce them, or does so in insufficient amounts.Certain vitamins function as antioxidants.2 classes of vitamins:

Fat-solubleWater-soluble

GROUP NUTRTION:SOLIMEN, KatelynTERNOLA, Shari AnneVALLES, Leo KarloWAKAT, Wennie ClareWALSI-EN, Marianne