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Digestive System
Digestive System Functions
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1. Ingestion-of food through
the mouth
2. Mechanical processingtearing, chewing, mixing,
churning
3. Digestion-chemical
breakdown. Makes small
particles that can be absorbed
by the digestive epitelium
Digestive System Functions
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4. Secretion-acids, enzymes, buffers from
digestive lining or accessory organs
5. Absorption- nutrients and water go into
interstitial fluids of digestive tract.
6. Compaction- undigested matter loses
water and, therefore, takes up less space
7. Defecation- excretion
Digestive System
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Digestive System = Digestive Tract
 Also GI (gastrointestinal) Tract, Alimentary canal
Digestive Tract
 Basically a tube from mouth to anus
 Lined with mucus membrane (protects against digestive
acids and enzymes)
 Peritoneum—membrane lining abdomino-pelvic cavity
 Peristalsis-wave like smooth muscle contraction that move
things along( liquid and solid) through the digestive tract
 Segmentation movements- churn and mix digestive contents
(as in the stomach)
Salivary
Glands
Oral Cavity
Sublingual
Submandibular
Parotid Gland
Tongue
Pharynx
Epiglottis
Esophagus
Spleen
Liver
Duodenum
Gallbladder
Pancreas
Stomach
Transverse Colon
Descending Colon
Ascending
Colon
Jejunum
Appendix
Sigmoid Colon
ileum
Rectum
Anus
Oral Cavity
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Functions:
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Analyzes ingested matter
Mechanical processing
Lubricates ingested matter
Begins digestion of carbohydrates
Oral cavity = buccal cavity
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1.
2.
3.
4.
Cheeks are the lateral walls
Labia = lips
Gingiva = gums
Lingual frenulum attaches
tongue to epithelium
Oral Cavity (cont.)
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Uvula
 Small, soft structure hanging from the soft palate
Tongue
 Functions
 Mechanical processing
 Manipulation
 Sensory analysis
Teeth
 Deciduous teeth-primary teeth/baby teeth- 20
 Permanent teeth-secondary- 32 including wisdom teeth
Mastication = chewing
Bolus-food is chopped and ground and mixed with saliva.
Bolus is swallowed
Pharynx and Esophagus
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Pharynx = throat
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Esophagus
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Muscular action moves
bolus down through
pharynx to..
About 1 foot long and
¾ in. diameter
Deglutition =
swallowing
Stomach
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Functions
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1. storage of ingested matter
2. mechanical breakdown
3. chemical breakdown with
acids and enzymes
Chyme
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mixture of bolus with gastric
juices (acids and enzymes)
Stomach (cont.)
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Pyloric Sphincter- at bottom of the stomach, regulates
passage of chyme from stomach to small intestines
Gastric juice- made of parietal cells and chief cells in
stomach
 Parietal cells secrete:
 Intrinsic factor (helps with vit. B12 absorption)
 Hydrochloric acid (decreases pH, kills organisms,
breaks down cell walls and connective tissues in food
and activates chief cells
 Chief cells- secretion result in the production of pepsin
which breaks down proteins
Gastric Functioning
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Cephalic phase- vagus nerve stimulated by thought
or sight of food leads to increased production of
gastric juices
Gastric phase- begins when food gets to stomach.
Increased production of gastric juices and gastric
contractions (segmentation movements)
Intestinal phase- food enters small intestine. Gastric
activity slows down so small intestine can absorb
nutrients effectively
Stomach Diseases and Disorders
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Gastritis- inflammation of gastric mucosa
 Can be caused by alcohol, aspirin, severe emotional or
physical stress, bacterial infection of gastric wall or
ingestion of strong acid or alkaline chemical
Peptic Ulcer- sore in the stomach linked to too much acid
or not enough alkaline mucus.
 Often caused by bacteria
 Causes sharp pain, sometime bleeding
 Treatment: antacids or prescription meds to decrease
acid secretions
Small Intestine
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Subdivisions
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Duodenum- 1 ft., closest to the stomach. Adds
buffers to increase pH of chyme entering from the
stomach
Jejunum- 8 ft., middle part , absorption
Ileum- part that joins to large intestines. Absorption
is completed. Contains lymphatic nodules
Small Intestine (cont.)
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Vomiting reflex- happens in response to irritation of
digestive lining. Soft palate and pharynx are especially
easily stimulated by unpleasant stimuli. Vomiting can
also be caused by irritation of esophagus, stomach or
upper parts of small intestine. Medulla oblongata
contains vomiting center
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emesis = vomiting
Gasroenteritis- inflammation of stomach and intestines.
Combination of vomiting and diarrhea
Large Intestine
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2 parts—colon and rectum
Also known as the bowel (About 5 feet long)
Functions
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1. Reabsorb water and compact feces
2. Absorb vitamins freed by bacterial action
3. Store feces before defecation
Chyme (food and gastric juices enters the Cecum
then to -> Ascending colon
then to -> Transverse colon
Then to -> Descending colon
then to ->Sigmoid colon
Large Intestine
(continued)
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Diverticulosis
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Diverticulitis
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Pockets of mucosa of colon
Inflammation of divericula causing pain and
occasionally bleeding
Colitis- general term for inflammation of colon
Irritable Bowel Syndrome- diarrhea,
constipation or alternation between the two
Large Intestine (cont.)
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Inflammatory bowel disease = ulcerative colitis
 Chronic infection of the digestive tract ( inflamed and
ulcerated mucosa)
Colectomy – part of the colon removed
Colostomy- new opening created for evacuation of feces
(also known as ileostomy)
1500 ml chyme enter large intestine each day. 200 ml
feces are defecated
Feces—75% water, 5% bacteria,
20% undigested
matter
Rectum
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Last 6 inches of digestive
system
2 sphincters- internal and
external
Anus-external opening
Hemorroids= distended veins of
rectum and anus (similar to
varicose veins)
Rectum (cont)
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Colo-rectal cancer- high mortality rate
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Test for diagnosis- check feces for blood
Lower GI series (barium enema with x-rays) will
show masses
Colonoscopy- scope that visualizes and collects
tissue samples and can remove polyps
Defecation
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Distention of rectum triggers defecation reflex
Diarrhea- lots of watery feces. Feces move through the
colon too fast.
 Cause can be bacterial, viral or protozoal infection or
anything irritating to the intestines.
 Diarrhea removes the irritant, put prolonged diarrhea can
lead to dehydration and electrolyte loss
 Cholera- diarrheal disease caused by bacterial toxin.
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Can cause loss of 1 liter of fluid per 1 hour
Caused by poor santitation
Vaccine not effective and short lasting, treat with IV and
oral fluids
Defecation (cont)
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Constipation- fecal material moves through
the colon too slowly, so too much water is
absorbed.
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Feces become dry, hard, abrasive and difficult to
move
Cause: too little fluid, too little fiber in diet, too
little exercise
Treatments: stool softener, laxatives, enemas
Accessory Organs
Salivary Glands
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Parotid
Sublingual
Submandibular
Makes 1-1 ½ liters of fluid daily which is >99%
water
Saliva functions:
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Lubricates,
Dissolves chemicals
Stimulates taste buds
Salivary Glands Diseases
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Mumps- virus targets parotid glands
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First exposure usually give permanent immunity
Vaccine
In males after adolescene, virus can infect testes
and lead to sterility
Mumps virus in pancreas can lead to diabetes
(temporary or permanent)
Liver
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Hepar, hepat = liver
3 functions
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1. metabolic regulation
2. hematologic regulation
3. bile production
Liver Diseases and Disorders
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Hepatitis- there are several types of Hepatitis
(A,B,C,D, and E). Caused by a virus. Virus
attacks liver cells.
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Hepatitis A- “infectious hepatitis” from eating
contaminated food, water, milk, shellfish
Hep B- “serum hepatitis” spread by intimate contact
with blood, body fluids. Vaccine
Hep C- “chronic hepatitis” spread through blood
Liver Diseases and Disorders
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Hepatitis continued
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Virus attacks liver cells.
The person can get a fever.
The liver can become inflamed and tender.
Blood contents of liver are affected as well as
liver function.
Can lead to jaundice.
Victims usually recover.
Some have no signs or symptoms
Liver Diseases and Disorders
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Cirrhosis- liver cells are destroyed by
exposure to alcohol or other drugs, viral or
bacterial infection, nutritional
deficiency(lack of proteins) or blockage of
hepatic ducts.
Extensive areas of scar tissue form in liver.
Symptoms include jaundice, ascites (too
much peritoneal fluid)
Gallbladder
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Stores bile
Cholelithiasis –(condition of having gall stones)caused by bile being too concentrated, causing
crystals and salts to appear (gallstones)
Cholecystitis – inflammation of the gallbladder.
Gallstones enter and jam the bile duct or cystic
duct. Painful- surgery removes large gallstones.
Cholecystectomy – surgical removal of
gallbladder
Pancreas
2 functions
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1. Endocrine
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Pancreatic islets secrete insulin and glucagon
2. Exocrine
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Secrete water, ions and digestive enzymes
Most of the Pancreatic Enzyme’s work of digestion is
in the small intestine.
Digestion and Absorption
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Carbohydrate digestion
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Begins in mouth
Completed in duodenum
Flatus (intestinal gas) caused
by indigestible carbohydrates)
Lactose intolerance- no
lactase production. Ones can’t
digest milk products. Causes
gas, cramps, diarrhea. Has
genetic basis. About 15% of
Caucasian, 80-90% of AfricanAmericans and Asians
Digestion and Absorption
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Lipid digestion and absorption
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Begins in the duodenum with the release of bile
salts, then moves into lymphatics and blood
stream
Protein digestion and absorption
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Mechanical processing begins in the mouth.
Actual digestion starts in the stomach with acids
and pepsin. Pancreatic enzymes finish digestion,
then proteins move into interstitial fluids, then
blood stream
Digestion and Absorption
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Water and electrolytes
 Normal daily fluid intake 2000ml in food and drink
 Most absorbed in intestines
Water soluble vitamins (except B12)
 Absorbed easily by digestive epithelium. B12 needs
intrinsic factor from parietal cells in stomach in order to
be absorbed
Fat soluble vitamins
 Contained in fat droplets absorbed with emulsification
via duodenum. Vitamin K manufactured by bacterial
action and absorbed in colon
Aging and the Digestive System
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Most elders have normal digestion and
absorption
Common difficulties:
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Decreased peristalsis which leads to increased
constipation
Decreased sense of taste
Increased likelihood of indigestion
Increased likelihood of digestive system cancers
Digestive epithelium becomes more fragileincreases likelihood of ulcers
 In
general, the bad habits of a lifetime
create these problems- cumulative
damage can lead to tooth loss,
cirrhosis, diverticulitis…