GIt revision 4

7000ml secreted compared with 1200ml of fluid ingested, 500-800g of food 100-200ml lost in feces

Approximately how much fluid is secreted into the gastrointestinal tract each day compared with the amount of food and drink ingested? How much of this appears in the feces?

By stomach acid

By what mechanism is pepsinogen converted to pepsin in the stomach?

Secretin - simtulates HCO3 release from bile duct epithelial cells CCK - stimulates Gallbladder contraction and Sphincter of Oddi relaxation

Describe the effects of secretin and CCK on the bile ducts and gallbladder.

Distension of the stomach increases the force of contractions and the rate of emptying. Distension of the small intestine and fat, acid, or hypertonic solutions in the intestinal lumen inhibit gastric contractions.

Describe the factors that control gastric emptying.

Functions: Stimulates Stomach acid secretion and motility Stimulates Ileal motility Stimulates mass movement of Large Intestine Stimuli for release: Peptides in Stomach Parasympathetic nerves Stimuli for inhibition: Acid in Stomach Somatostatin

Describe the function of gastrin and the factors controlling it's secretion.

Increased luminal acidity -> intestine secretes Secretin -> stimulates HCO3 secretion Fat and protein digestion products -> intestine secretes Cholecystokinin -> other pancreatic enzymes secreted

Describe the mechanisms controlling pancreatic secretion of HCO3 and enzymes

In epithelium, fatty acids and monoglycerides are recombined to form triglycerides, which are then released as Chylomicrons by exocytosis. These then enter lacteals via the lymphatics

Describe the movement of fat-digestion products from the intestinal lumen to a lacteal.

Ulcerative Colitis Crohn's Disease

Describe the two main types of inflammatory bowel disease.

Secretion of bile Solubilize water-insoluble fats Neutralize HCl entering small intestine from stomach Elimination in feces

Digestive functions of Liver?

Moisten and dissolve food Help neutralize ingested acid Lubrication Polysaccharide-digesting enzyme Help prevent tooth and gum decay

Digestive functions of Salivary glands?

Store, mix, dissolve, and continue digestion of food; regulate emptying of dissolved food into small intestine Solubilization of some food particles Kill microbes Activation of pepsinogen to pepsin Begin the process of protein digestion in the stomach Lubricate and protect epithelial surface

Digestive functions of Stomach?

Trypsin activated by Enterokinase in membrane of small intestine Trypsin then activates other enzymes

How are pancreatic proteolytic enzymes activated in the small intestine?

Fat soluble vitamins are absorbed like fat, via emulsification Water-soluble vitamins are absorbed by diffusion or mediated transport

How does the absorption of fat-soluble vitamins differ from that of water-soluble vitamins?

If the salivary glands fail to secrete amylase, the undigested starch that reaches the small intestine will still be digested by the amylase the pancreas secretes. Thus, starch digestion is not significantly affected by the absence of salivary amylase.

If the salivary glands were unable to secrete amylase,what effect would this have on starch digestion?

Digestion Secretion Absorption Motility

List the four processes that accomplish the functions of the digestive system.

Distension Osmolarity Acidity Digestion products

List the four types of stimuli that initiate most gastrointestinal reflexes.

Bile salts Cholesterol Lecithin HCO3 Bile pigments Trace metals

List the major constituents of bile.

Breakdown of Proteins to peptides by pepsin, trypsin and chymotrypsin Breakdown of Peptides into amino acids by carboxypeptidase and aminopeptidase Active absorption of small peptides into epithelial cells

List three ways in which proteins or their digestion products can be absorbed from the small intestine.

b

Micelles increase the absorption of fat by a. binding the lipase enzyme and holding it on the surface of the lipid emulsion droplet. b. keeping the insoluble products of fat digestion in small aggregates. c. promoting direct absorption across the intestinal epithelium. d. metabolizing triglyceride to monoglyceride. e. facilitating absorption into the lacteals.

Pernicious Anaemia

Specify a condition that may lead to failure to absorb vitamin B12

Failure of bile salts to reach intestine - reduced fat absorption Accumulation of bile pigments in blood - jaundice

What are the consequences of blocking the common bile duct with a gallstone?

Lactose cannot be absorbed, remains in intestine, causing diarrhoea and flatulence when milk products are ingested

What are the consequences of the failure to digest lactose in the small intestine?

Digestion of polysaccharides and proteins increases Osmolarity in lumen

What causes water to move from the blood to the lumen of the duodenum following gastric emptying?

Bile salt concentration in Hepatic Portal Venous blood

What determines the rate of bile secretion by the liver?

Insoluble fatty acids and monoglycerides combine with bile salts to form Micelles, which transport these molecules to the brush border, where they are absorbed by passive diffusion

What is the function of micelles in fat absorption?

Bacterial fermentation of undigested polysaccharides

What produces flatus in the large intestine?

Portal venous system

Where does the venous blood go after leaving the small intestine?

a

Which component/components of bile is/are not primarily secreted by hepatocytes? a. HCO3 b. bile salts c. cholesterol d. lecithin e. bilirubin

c

Which of the following inhibit/inhibits gastric HCl secretion during a meal? a. stimulation of the parasympathetic nerves to the enteric nervous system b. the sight and smell of food c. distension of the duodenum d. presence of peptides in the stomach e. distension of the stomach

a

Which of the following is the primary absorptive process in the large intestine? a. active transport of Na from the lumen to the blood b. absorption of water c. active transport of K1 from the lumen to the blood d. active absorption of HCO32 into the blood e. active secretion of Cl2 from the blood

c

Which of the following is true about pepsin? a. Most pepsin is released directly from chief cells. b. Pepsin is most active at high pH. c. Pepsin is essential for protein digestion. d. Pepsin accelerates protein digestion. e. Pepsin accelerates fat digestion.

e

Which of the following is true about segmentation in the small intestine? a. It is a type of peristalsis. b. It moves chyme only from the duodenum to the ileum. c. Its frequency is the same in each intestinal segment. d. It is unaffected by cephalic phase stimuli. e. It produces a slow migration of chyme to the large intestine.

Secretion of alkaline mucus Tight junctions between epithelial cells Rapid replacement of epithelium

Why is the stomach's wall normally not digested by the acid and digestive enzymes in the lumen?