Digestive SystemDigestive System•Digestive Tract Digestive Tract begins with begins with mouth and ends with anusmouth and ends with anus

•Digestion occurs Digestion occurs outside of cells (extracellular)outside of cells (extracellular)

•Enzymes for digestion are found in Enzymes for digestion are found in nearby glands and accessory organsnearby glands and accessory organs

•Enzymes break down proteins (AA’s), Enzymes break down proteins (AA’s), fats (simple lipids), and carbohydrates (sugars). fats (simple lipids), and carbohydrates (sugars).

•These smaller molecules are These smaller molecules are used by the body for energy.used by the body for energy.

The MouthThe Mouth•Mouth is lined with chemical receptors called taste buds, Mouth is lined with chemical receptors called taste buds, which are connected to the brain via cranial nerveswhich are connected to the brain via cranial nerves

•Olfactory receptors in the nose also contribute to our Olfactory receptors in the nose also contribute to our sense of tastesense of taste

•Most humans have 32 teethMost humans have 32 teeth

•Each tooth consists of a crown which is dense with Each tooth consists of a crown which is dense with calcium, and the pulp, which is rich with nerves and blood calcium, and the pulp, which is rich with nerves and blood vesselsvessels

•Dental caries (cavities) are caused by bacteria on the tooth Dental caries (cavities) are caused by bacteria on the tooth that metabolize sugars & give off acids which erode the that metabolize sugars & give off acids which erode the enamel enamel

•Fluoride hardens the enamel and protects it from erosionFluoride hardens the enamel and protects it from erosion

Parts of the MouthParts of the Mouth

Hard palateHard palate bony layer of the top of the mouth. Found bony layer of the top of the mouth. Found toward the anterior of the mouthtoward the anterior of the mouth

Soft palate Soft palate Muscular portion of the roof of the mouth Muscular portion of the roof of the mouth that ends at the uvulathat ends at the uvula

Salivary glands Salivary glands 3 pairs of glands found at the side of 3 pairs of glands found at the side of the mouth (below the ears) and under the tongue (little the mouth (below the ears) and under the tongue (little flaps under the tongue). Saliva contains amylase, an flaps under the tongue). Saliva contains amylase, an enzyme which begins the digestion of starchenzyme which begins the digestion of starch

After physical mastication and some chemical digestion, After physical mastication and some chemical digestion, food in the mouth is mixed into a soft mass called a bolus, food in the mouth is mixed into a soft mass called a bolus, which is then swallowedwhich is then swallowed

Parts of the MouthParts of the Mouth

Parts of the MouthParts of the Mouth

PharynxPharynxThe pharynx is the crossroads between the mouth and the The pharynx is the crossroads between the mouth and the esophagusesophagus

Once food is swallowed, the soft palate moves back to cover Once food is swallowed, the soft palate moves back to cover the nasal cavities; the trachea presses against the epiglottis, the nasal cavities; the trachea presses against the epiglottis, cutting itself off from foodcutting itself off from food

EsophagusEsophagus•The esophagus is a tube that conducts food from the mouth to the The esophagus is a tube that conducts food from the mouth to the stomachstomach•The esophagus is covered by multiple mucous membranes that help The esophagus is covered by multiple mucous membranes that help the food slide toward the stomachthe food slide toward the stomach•Smooth muscles in the esophagus rhythmically contract to push the Smooth muscles in the esophagus rhythmically contract to push the food along, these contractions are called peristalsisfood along, these contractions are called peristalsis•Food passes through to the lower esophagus and enters through the Food passes through to the lower esophagus and enters through the esophageal sphincteresophageal sphincter

EsophagusEsophagus

EsophagusEsophagus•Sphincter muscles are valves that open when relaxedSphincter muscles are valves that open when relaxed•The valve opens and the food enters into the stomachThe valve opens and the food enters into the stomach•If the valve doesn’t close completely, contents of the If the valve doesn’t close completely, contents of the stomach escape into the esophagus, causing heartburnstomach escape into the esophagus, causing heartburn

EsophagusEsophagus

StomachStomach•Stomach is a “J” shaped organ on the left side of Stomach is a “J” shaped organ on the left side of the body below the diaphragmthe body below the diaphragm

•The stomach has many folds, which expand when The stomach has many folds, which expand when food is inside (1L)food is inside (1L)

•Inside the columnar epithelium of the stomach are Inside the columnar epithelium of the stomach are many gastric glands, which secrete the enzyme many gastric glands, which secrete the enzyme pepsin; this enzyme digests proteinspepsin; this enzyme digests proteins

•HCl is present in high levels in the stomach (pH HCl is present in high levels in the stomach (pH =2). It breaks down connective tissue and also =2). It breaks down connective tissue and also kills many bacteria present in food.kills many bacteria present in food.

•HCl stays in the middle of the stomach. Mucus HCl stays in the middle of the stomach. Mucus lines the outer edges of the stomach, which lines the outer edges of the stomach, which protects the wall of the stomach from ulcersprotects the wall of the stomach from ulcers

StomachStomach

•Although food is broken down in the Although food is broken down in the stomach, no food is absorbed into the body stomach, no food is absorbed into the body from the stomach.from the stomach.

•Food leaves the stomach (after 2-6 hours) in Food leaves the stomach (after 2-6 hours) in a pasty form called chyme. Chyme leaves the a pasty form called chyme. Chyme leaves the stomach and enters the small intestine via thestomach and enters the small intestine via the

pyloric sphincter.pyloric sphincter.

Small IntestineSmall IntestineDiameter: 2.5 cmDiameter: 2.5 cm

Length: 18 feetLength: 18 feet

Receives bile from the gall bladderReceives bile from the gall bladder

Receives secretions from the pancreasReceives secretions from the pancreas

Absorbs nutrients and sends undigestedAbsorbs nutrients and sends undigested

food to large intestinefood to large intestine

1st 25 cm of the SI is called the duodenum1st 25 cm of the SI is called the duodenum

Pancreatic juice is released into the duodenum and Pancreatic juice is released into the duodenum and contains (NaHCO3)contains (NaHCO3)

Bicarbonate neutralizes the chymeBicarbonate neutralizes the chyme

SI contains small finger-like projections called SI contains small finger-like projections called microvillimicrovilli

Small IntestineSmall IntestineThese projections break down chyme into These projections break down chyme into small, absorbable molecules that are small, absorbable molecules that are absorbed into epithelial cells in the SI, which absorbed into epithelial cells in the SI, which are then transported throughout the bodyare then transported throughout the body

Active Transport takes sugars and AA’s and Active Transport takes sugars and AA’s and passes them into the blood stream; fats are passes them into the blood stream; fats are passed into the ducts of the lymphatic systempassed into the ducts of the lymphatic system

Large IntestineLarge Intestine•Diameter: 6.5 cmDiameter: 6.5 cm

Length: 4.5 feetLength: 4.5 feet

What does it do?What does it do?•Absorbs water, salts, and vitaminsAbsorbs water, salts, and vitamins

Parts of the LIParts of the LI•Cecum: blind (dead) end of the LI on the Cecum: blind (dead) end of the LI on the

right side of the bodyright side of the body•Appendix: at the end of the Appendix: at the end of the

cecum (may play a role in immunity)cecum (may play a role in immunity)

The ColonThe Colon•Ascending ColonAscending Colon travels up to the travels up to the right side of the body to the liverright side of the body to the liver•Transverse Colon Transverse Colon crosses over crosses over from right to leftfrom right to left•Descending Colon Descending Colon travels down the travels down the left side of the bodyleft side of the body•Last 20cm of the LI is called the Last 20cm of the LI is called the rectumrectum•Opening at the end of the rectum is Opening at the end of the rectum is called the anuscalled the anus•Defecation occurs out the anusDefecation occurs out the anus

What is in my Feces?What is in my Feces?•Non-digestible parts of foodNon-digestible parts of food

•Bile pigments (color)Bile pigments (color)

•Lots of anaerobic bacteria (bacteria) Lots of anaerobic bacteria (bacteria) that die in the presence of oxygen; that die in the presence of oxygen; they also provide us with some they also provide us with some vitaminsvitamins

DiarrheaDiarrhea•Caused by infection of the lower LI Caused by infection of the lower LI and/or nervous system stimulationand/or nervous system stimulation

•In the case of infection, peristalsis In the case of infection, peristalsis increases, water is not absorbed, all increases, water is not absorbed, all “bad stuff” is released at once“bad stuff” is released at once

ConstipationConstipation•Feces are dry and hardFeces are dry and hard•Usually caused by ignoring the urge Usually caused by ignoring the urge to defecate; body habituates to holding to defecate; body habituates to holding in wastein waste•Laxatives usually make a bulk of Laxatives usually make a bulk of cellulose in the LIcellulose in the LI•Milk of Magnesia prevents water from Milk of Magnesia prevents water from being absorbed in LIbeing absorbed in LI

Accessory Organs of the Accessory Organs of the Digestive SystemDigestive System

•PancreasPancreas lies deep in the abdominal lies deep in the abdominal cavity; on posterior abdominal wall; cavity; on posterior abdominal wall; flattened organflattened organ

•Produces pancreatic juice, which Produces pancreatic juice, which contains enzymes that digest contains enzymes that digest carbohydrates, proteins, and fatscarbohydrates, proteins, and fats

•Pancreatic fluid flows through ducts Pancreatic fluid flows through ducts (little hallways) into the duodenum of (little hallways) into the duodenum of

the SIthe SI

Accessory Organs of the Accessory Organs of the Digestive SystemDigestive System

The LiverThe Liver

Largest gland in the bodyLargest gland in the body

Located in the upper right section of Located in the upper right section of the abdominal cavitythe abdominal cavity

Liver produces almost 2 liters of Liver produces almost 2 liters of bile/daybile/day

Bile is sent to the gall bladder (under Bile is sent to the gall bladder (under the liver) for storagethe liver) for storage

Bile salts (made from cholesterol) Bile salts (made from cholesterol) emulsify (break down) fat molecules emulsify (break down) fat molecules that are broken down my pancreatic that are broken down my pancreatic juicejuice

Accessory Organs of the Accessory Organs of the Digestive SystemDigestive System

Liver & Blood FiltrationLiver & Blood Filtration

Once nutrients are have been Once nutrients are have been absorbed by the small intestine, they absorbed by the small intestine, they are sent to the liver, through the blood, are sent to the liver, through the blood, by the hepatic portal veinby the hepatic portal vein

Liver filters the blood, removing toxins Liver filters the blood, removing toxins and excess materials; then sends the and excess materials; then sends the blood to the lungs for oxygenblood to the lungs for oxygen

Accessory Organs of the Accessory Organs of the Digestive SystemDigestive System

ExampleExample

Liver removes excess glucose from the Liver removes excess glucose from the blood, and stores it as glycogenblood, and stores it as glycogen

Liver, in times of need, can convert Liver, in times of need, can convert amino acids to glucose (deamination)amino acids to glucose (deamination)

Liver detoxifies ethanol (toxic) into Liver detoxifies ethanol (toxic) into acetate (non-toxic)acetate (non-toxic)

CirrhosisCirrhosis

Liver tissue turns to inactivated scar Liver tissue turns to inactivated scar tissue; no longer detoxifiestissue; no longer detoxifies

Caused by excessive detoxification of Caused by excessive detoxification of ethanolethanol

Accessory Organs of the Accessory Organs of the Digestive SystemDigestive System

Digestive EnzymesDigestive Enzymes

Amylase: Found in mouth; breaks down starchAmylase: Found in mouth; breaks down starch

Pepsin: found in stomach; breaks down proteinsPepsin: found in stomach; breaks down proteins

Pancreatic Amylase: found in pancreas; breaks down starchPancreatic Amylase: found in pancreas; breaks down starch

Trypsin: made by pancreas; breaks down proteinsTrypsin: made by pancreas; breaks down proteins

Lipase: made by pancreas; breaks down fatLipase: made by pancreas; breaks down fat

Peptidase & Maltase; secreted by small intestine; breaks Peptidase & Maltase; secreted by small intestine; breaks down proteins & carbsdown proteins & carbs

Accessory Organs of the Accessory Organs of the Digestive SystemDigestive System

Hormones of the Digestive SystemHormones of the Digestive System

Gastrin: found in stomach; stimulates production of Gastrin: found in stomach; stimulates production of pancreatic juicespancreatic juices

Secretin: found in SI; stimulates pancreas to secrete Secretin: found in SI; stimulates pancreas to secrete sodium bicarbonatesodium bicarbonate

Cholescystokinin (CCK); found in SI; stimulates gall Cholescystokinin (CCK); found in SI; stimulates gall bladder to release bilebladder to release bile