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Questions and Answers
What is the primary function of secretin in the gastrointestinal system?
What is the effect of CCK and secretin on the parietal cells and chief cells?
What is the primary stimulus for the production of gastrin?
What is the role of bicarbonates in the absorption of vitamins and minerals?
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What is the function of the intrinsic factor in the absorption of vitamins and minerals?
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What is the effect of CCK on the gallbladder?
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What is the role of potassium in the gastrointestinal system?
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What is the function of leptin in the regulation of food intake?
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What is the effect of beneficial bacteria on colon motility?
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What is the primary function of the vomiting center in the medulla?
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What is the main function of the parietal cells in the stomach?
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What is the primary enzyme responsible for breaking down triglycerides into monoglycerides and fatty acids?
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What is the process by which bile salts are reabsorbed in the ileum and returned to the liver via the hepatic portal vein?
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What is the role of bile in the digestion and absorption of fats?
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What is the result of lipase acting on emulsified fats in the small intestine?
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What is the mechanism by which fats are absorbed in the small intestine?
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What is the role of the gallbladder in fat digestion and absorption?
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Which hormone stimulates the release of gastric juices and pepsinogen in the stomach?
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What is the result of the action of enterokinase on trypsinogen?
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What is the primary site of fat absorption in the gastrointestinal tract?
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Study Notes
Gastrointestinal Hormones
- CCK (Cholecystokinin) stimulates enzyme secretions, amplifies Secretin's effects, and suppresses parietal and chief cells' secretions.
- Secretin stimulates bicarbonate secretion, amplifies CCK's effects, and suppresses parietal and chief cells' secretions.
- Gastrin stimulates gastric secretions and motility, relaxes the ileocecal sphincter, and stimulates mass movement of the colon.
- CCK and Secretin inhibit gastric secretion and motility.
- GIP (Glucose-dependent Insulinotropic Peptide) inhibits gastric secretion and motility and stimulates insulin secretion.
Absorption of Vitamins and Minerals
- Vitamins A, D, E, and K are absorbed with lipids.
- Water-soluble vitamins are absorbed by transport proteins.
- Vitamin B12 absorption requires intrinsic factor.
- Na+ and Cl- are absorbed passively in the duodenum and jejunum, but can be absorbed actively in the ileum and colon.
- K+ is absorbed passively in the small intestine.
- Bicarbonates are absorbed passively.
- Ca2+ binds to calcium-binding proteins on the brush border and is then taken into the cell.
- Iron binds to receptors and causes receptor-mediated endocytosis.
Regulation of Food Intake
- Leptin is the "satiety hormone".
- Ghrelin is the "hunger hormone", secreted by the stomach.
Daily Fluid Flow in the Gastrointestinal System
- Large intestine: 1-3 mass movements/day, largest immune organ in the body, and beneficial bacteria enhance colon motility, produce vitamin K, and aid in calcium and magnesium absorption.
GI Motility and Its Regulation
- Circular muscle layer of the GI tract generates spontaneous, graded action potentials called "slow waves".
Swallowing Reflex (Deglutition)
- Vomiting is caused by illness, strong emotional state, severe pain, severe distention of the stomach or small intestine, motion sickness, or ingestion of harmful substances.
Defecation
- Defecation reflex is triggered by distention of the rectum.
- Stretch receptors trigger several events, including the contraction of the rectal wall, relaxation of the internal anal sphincter, and contraction of the external anal sphincter.
Digestive System
- Functions: digestion, secretion, absorption, and motility (peristalsis).
Layers of GI Wall
- The GI wall has four major layers: mucosa, submucosa, muscularis, and serosa.
Stomach
- Functions: stores food until ready to empty into the small intestine, secretes gastric juices, and mixes/churns the bolus into chyme.
- Gastric secretory products: mucus, pepsinogen, H+ and intrinsic factor, and gastrin.
Small Intestine
- Parts: duodenum, jejunum, and ileum.
- Site of digestion and absorption.
- Has digestive enzymes on the brush border membrane.
Saliva
- Mostly water (99.5%).
- Contains bicarbonates, mucus, electrolytes, enzymes, lysozyme, and minerals.
- Saliva moistens the mouth and facilitates swallowing and chemical breakdown.
Pancreas
- Releases proteolytic enzymes, pancreatic amylase, and pancreatic lipase.
Liver
- Most important metabolic organ.
- Functions: processes lipids, proteins, and carbohydrates, detoxifies drugs, hormones, and wastes, makes plasma proteins, stores fats, glycogen, ions, and vitamins, and activates vitamin D.
Carbohydrate Digestion
- Most carbohydrates in our diet are disaccharide or polysaccharide (starches, cellulose, and glycogen).
- Disaccharides are 2 monosaccharides bonded together.
Starch Digestion
- Starch is broken down into maltose and limit dextrins, then into glucose monomers.
Absorption of Monosaccharides
- Glucose and galactose are absorbed at the apical membrane via sodium-linked secondary active transport and at the basolateral membrane via facilitated diffusion.
- Fructose is absorbed by facilitated diffusion across both membranes.
Protein Digestion
- In the stomach: pepsinogen is converted to pepsin, which breaks down proteins into peptide fragments.
- In the small intestine: brush border enzymes and pancreatic secretions break down peptides into amino acids.
Amino Acid Absorption
- Amino acids cross the apical membrane via sodium-linked secondary active transport or facilitated diffusion.
- Dipeptides and tripeptides cross the apical membrane via active transport and the basolateral membrane via facilitated diffusion.
Regulation of Acid and Pepsinogen Secretion
- Smell, taste, and thought of food stimulate parietal cells and chief cells to secrete acid and pepsinogen.
- Gastrin also stimulates parietal cells and chief cells.
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Description
This quiz covers the functions and effects of gastrointestinal hormones, including CCK and Secretin, on enzyme secretions, bicarbonate secretion, and bile secretion.
