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What are the functions of the digestive system?
To obtain nutrients, water, vitamins and electrolytes needed for energy production, growth & repair.
What structures are in the alimentary canal?
mouth, pharynx, esophagus, stomach, small intestine, large intestine.
What structures are in the accessory structures?
teeth, tongue, gallbladder, salivary glands, liver, pancreas
What are the 6 digestive processes?
ingestion, propulsion, mechanical digestion, chemical digestion, absorption, defecation.
What is propulsion?
Begins with deglutition (swallowing) which initially is voluntary then peristalsis takes over.
What is mechanical digestion?
Physically breaking down the foodstuff. Chewing, stomach churning and segmentation in the small intestine.
What is absorption?
Moving nutrients from the gut to the bloodstream (water soluble) or lymphatic system (fat soluble).
What are the 4 layers of the gut wall. Specifically in the small intestines.
Mucosa, submucosa, muscularis externa, serosa
What does the mucosa protect and function as?
The mucosa lines the gut and functions in secretion and absorption.
What is the epithelium of the mucosa consist of?
simple columnar epithelium with goblet cells (produce mucus) and enteroendocrine cells (produce hormones).
What is the lamina propria contain?
Made of loose c.t. containing the ends of nerves, capillaries, and lymphatic vessels.
What does the submucosa consist of and it's function?
Layer of dense c.t. containing blood vessels, lymph vessels, nerves, and epith glands. Has extensive vascular system to transport absorbed materials.
What does the muscularis exererna consist of and it's function?
Responsible for motility for peristalsis. Made of skeletal muscle at both ends of gut, smooth muscle in between.
What does the serosa consist of and it's function?
Layer of loos (areolar) c.t. covered by simple squamous epith.
Forms part of the peritoneum, layer of tissue lining the ab cavity
Above diaphragm the lining is fibrous c.t. - adventitia
What does the enteric nervous system regulate?
motility, secretions, and blood flow of the digestive system.
The enteric nervous system are composed of what 2 networks that are pare of the parasympathetic n.s.?
Submucosal nerve plexus.
Myenteric nerve plexus.
What does the submucosal nerve plexus regulate?
It is sensory and motor.
Regulates the glands & smooth muscles in the mucosa.
What does the greater omentum cover?
Layer of fat. Hangs down from the stomach that covers the intestines.
What does the omenta contain?
Lymphatic vessels with a large number of lymph nodes and help prevent infection in the peritoneal cavity.
What are the functions of the salivary glands?
Cleans the mouth
Contains lysozyme - digestive
Contains IgA - lines digestive tract
Contains salivary amylast - b/d starch
Contains lingual lipase - b/d lipids
What are the inner lining of the stomach that have creases called?
Rugae - stretch out as the stomach fills.
What are the 4 regions of the stomach?
Cardiac - esophagus goes into stomach
Fundic - dome-shaped upper portion
Body - bulk of stomach
Pyloric - narrow pouch at the end
The simple columnar epithelium in the stomach are made of what?
mucous cells that produce alkaline mucus
What are the 4 secretory cells of the gastric glands?
mucous neck cells
What does the mucous neck cells produce?
Acidic mucus that lines the stomach in the neck region of the glands.
What does the enteroendocrine cells produce?
hormones that regulate digestion such as
gastrin, serotonin, cholecystokinin
Which segment of the small intestine comes directly off the stomach?
Duodenum - with ducts coming from liver & pancreas.
What are the adaptations of the small intestines to increase surface area?
Circular folds - plicae
Villi - fingerlike projections
Microvilli - projections off of the apical membrane (called brush border)
What are the major brush border enzymes?
maltase, sucrase, lactase - digest CHOs
aminopeptidase & dipeptidase - digest proteins
What are the 3 major structures of the large intestine?
cecum-contains vermiform appendix
colon-contains ascending, transverse, descending & sigmoid colon
rectum-Muscular for defecation & last inch is vascular anal canal.
What are the functions of the liver?
Produce bile, makes & stores glycogen, makes NE amino acids, turns ammonia to urea, makes plasma proteins, builds up & breaks down triglycerides, phospholipids, and cholesterol, detoxifies poisons, stores fat soluble vitamins (A,E,K,D) and recycles hemoglobin
What is the function of the bile?
Stores and concentrates bile from the liver
Contains bile salts - emulsify fats
What are the 2 main components in pancreatic juices?
NaHCO3 - buffers chyme & balances the gastric juices from the stomach.
What are the main digestive enzymes?
All of these are secreted in inactive form and contain -gen at the end of the word.
What is secretin?
From enteroendocrine cells of duodenum
Release stimulated by acid in the duodenum.
Stimulates pancrease to release bicarbonate-rich pancreatic juice
Stimulate liver to release bile salts.
What is cholecystokinin?
Stimulated by protein and fat ingestion from duodenum.
Stimulates release of enzyme-rich pancreatic juice
Stimulates contraction of gallbladder forcing out bile
What is gastrin?
From the G cells in pyloric glands
Stimulates release of HCl & intrinsic factor from parietal cells.
Enzymes are specific to what?
Reactions they catalyze due to binding to a specific substrate forming an enzyme-substrate complex
What is the job of pancreatic amylase?
Quickly breaks the short glucose chains to the disaccharide maltose.
What are the 2 brush border enzymes that breakdown sucrose and lactose to monosaccharides?
How are glucose and galactose absorbed?
They are cotransported with sodium across the apical membrane.
Facilitated diffusion is used to get them across the basal membrane.
What does HCl do to protein in the stomach?
Breaks down the c.t. around the muscle to allow enzyme access.
How is protein digestion finished
Using 3 brush border enzymes: Carboxypeptidase, Aminopeptidase, Dipeptidase
How are amino acids absorbed?
Being cotransported with Na+ using active transport across the apical membrane
Then facilitated diffusion across the basal membrane and enters the blood.
Bile Salts and lecithin break up what?
Break up fat globules into fatty droplets and this increases surface area allowing lipase to do job quickly.
What does the lipase do?
Removes 1st & 3rd fatty acid producing 2 free fatty acids and a monoglyceride.
What are the 2 F.A.s and monoglycerides coated with?
Coated with bile salts forming micelles which include cholesterol and fat-soluble vitamines (A,E,D,K)
What do the micelles do?
Difuse to gut wall and release their lipids which diffuse across epith cells of villi. Bile salts are then recycled in gut.
Inside the cell, the Free FA and monoglycerides enter what? What happens to them there?
They enter smooth ER where they are put back together as triglyceride.
What does the Golgi do with the triglyceride?
Coated with phospholipids and proteins to form chylomicrons. Packaged into secretory vesicles, migrate to basal membrane. release their contents, enter lacteals.
DNA is broken down into what?
Deoxyribonuclease breaks down DNA into:
Deoxyribose + Bases + Phosphate
What is the function of the large intestines?
Absorbe right amount of water, absorb sodium and chloride ions, defecation.
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