Pancreas and small bowel Flashcards
Abdominal accessory organs start out as?
Foregut outgrowths.
How does the pancreas act as an exocrine gland?
Secretes pancreatic juice into the duodenum via main pancreatic duct.
What do acini in the pancreas do?
Secrete pro enzymes into ducts.
What do duct and centroacinar cells secrete into the pancreatic juice?
Bicarbonate ions.
What does bicarbonate in the pancreatic juice do?
Neutralises acid chyme from stomach which prevents damage to duodenal mucosa. Raises pH to optimum range for pancreatic enzymes to work.
What structures also produce bicarbonate instead of bicarbonate present in pancreatic juice?
Bile from liver and alkaline fluid from brunners glands.
How is bicarbonate secrete from pancreatic duct cells?
Carbonic anhydrase catalyses reaction of carbon dioxide with water to produce bicarbonate and H+ ions. Bicarbonate exchanged for chloride ion; bicarbonate enters lumen of duct while chloride enters duct cell. Sodium from blood enters duct cell while H+ enters blood.
How is high sodium in the blood maintained?
Na+/K+ exchange pump driven by ATP. Potassium into duct cell while sodium pumped into blood.
What drives water into lumen of pancreatic duct?
Sodium moves into lumen of duct down gradient from blood via paracellular junctions and water follows.
What channel drives chloride ions return to the lumen of the pancretic duct?
CFTR channel (cystic fibrosis transmembrane conductance regulator).
Why is pancreatic venous blood acidic but gastric venous blood is alkaline?
In pancreas H+ ions are released into blood. In stomach bicarbonate ions are released into blood.
Digestive enzymes in acinar cells are stored in what?
Zymogen granules.
Why are proteases released as inactive pro enzymes?
Protects acini and ducts from auto digestion.
What ensures that enzymes produced in pancreas are only activated once they enter the duodenum?
Trypsin inhibitor and enzymes are secreted as inactive pro enzymes.
Blockage of main pancreatic duct can result in what?
Auto digestion leading to acute pancreatitis.
What is the main enzyme that activates other proteolytic and lipolytic enzymes in the duodenum?
Trypsin.
What protein results in conversion of trypsinogen to trypsin? Where is this protein found?
Enterokinase secreted by duodenal mucosa. Found on the duodenal brush border.
What does lipase require for action?
Colipase and bile salts.
How do pancreatic secretions change based on diet?
Proportion of amylases and proteases changes depending on protein and carbohydrate ingestion.
Production of pancreatic digestion enzymes in response to sight/smell of food is what phase of pancreatic juice secretion?
Cephalic phase.
What is the gastric phase of pancreatic juice secretion?
Pancreatic juice secretion due to food arriving in the stomach.
During cephalic and gastric phase what is mainly secreted in the pancreatic juices?
Enzyme rich juice. Lacks carbonate.
What is the intestinal phase of pancreatic juice secretion? How is it different from the gastric and cephalic phase?
Hormone mediated when gastric chyme enters the duodenum. Both enzymes and carbonate released.
What stimulates enzyme secretion in pancreatic juice?
Acetylcholine from vagus nerve and cholecystokinin from duodenal I cells.
What controls bicarbonate secretion from duct and centroacinar cells?
Secretin.
What cells release cholecystokinin?
Duodenal I cells.
What stimulates release of cholecystokinin?
CCK releasing peptide due to increase in amino acid and fatty acids in lumen of duodenum. Gastrin releasing peptide.
What inhibits release of CCK?
Trypsin.
Acinar fluid composition after leaving acini?
Isotonic.
What stimulates release of acinar fluid?
Cholecystokinin.
What triggers release of secretin from S cells?
Drop in pH in duodenum.
When does CCK affect bicarbonate secretion?
When paired with secretin it can cause a large increase in bicarbonate secretion. On its own has no effect on bicarbonate secretion.
Function of small bowel?
To absorb nutrients, salt and water.
Small bowel parts?
Duodenum, jejunum and ileum.
What is mesentery?
Tissue that suspends the small bowel and large bowel from the posterior abdominal wall.
Function of mesentery?
Anchors small bowel and large bowel while still allowing for some movement. Conduit for blood vessels, nerves and lymphatic vessels.
How is the mucosa layer of the small bowel adapted for maximal absorption?
Contain lots of villi that increase surface area.
Where are villi innervated from?
Nerve plexus from submucosa layer.
What cells cover villi?
Mostly enterocytes. Also have goblet and enteroendocrine cells.
What cells are found at crypts of lieberkuhn?
Stem cells and paneth cells.
How are enterocytes adapted?
Contain microvilli increase surface area even more.
What kind of cells are enterocytes?
Columnar epithelium.
What are the surface of microvilli covered with?
Glycocalyx.
Function of glycocalyx?
Serves as protection from intestinal lumen. Controls rate of absorption from intestinal lumen.
What does mucous do in the bowels?
Facilitates passage of material in bowel by acting as a lubricant.
How does the number of goblet cells change as you go from the duodenum to the small bowel to the large bowel?
Increases.
What do paneth cells do?
Regulate intestinal flora and engulf some bacteria.
What do granules in paneth cells contain?
Lysozyme, glycoproteins and zinc.
What do stem cells in the crypts do?
Migrate to the top of villus and replace older cells that have died by apoptosis.
What distinguishes the duodenum from the jejunum and ileum?
Presence of brunner’s glands.
What distinguishes the jejunum from the ileum?
Ileum has thin wall while jejunum has thick wall.
What is the point of segmentation in regards to small bowel motility?
Mixed contents of lumen.
What is migrating motor complex?
Cycles of smooth muscle contraction sweeping throughout the gut.
Where does pancreatic amylase act and what does it digest?
Digestion of complex carbohydrates in lumen of small bowel.
Where is pancreatic amylase secreted?
Duodenum.
Factors for optimum pancreatic amylase activity?
Chloride ions and neutral pH.
Where does digestion of simple carbohydrates occur at?
Brush border.
Where does digestion of complex carbohydrates occur at?
Lumen.
How are glucose and galactose absorbed?
Secondary active transport by SGLT1 (sodium/glucose cotransporter 1) carrier protein on apical membrane.
How is fructose absorbed?
GLUT5 by facilitated diffusion on apical membrane.
What transporter do simple sugar enter the interstitial space and then the blood?
GLUT2 on basolateral membrane.
Where does protein digestion start? What digests it?
Lumen of stomach by pepsin.
Where does carb digestion occur?
Mouth and small intestine.
What inactivates pepsin?
Alkaline conditions of duodenum.
What transporter on enterocytes absorb small peptides?
PepT1.
What happens to small peptides absorbed by enterocytes?
Digested in the cytoplasm of the enterocytes. Intracellular digestion.
What are the steps of lipid digestion?
Secretion of bile salts and pancreatic lipases. Emulsification of lipids. Lipase activated by co-lipase. Enzymatic hydrolysis of ester linkages. Solubilisation of lipolytic products in bile salt micelles (holds lipolytic products).
What happens when monoglycerides and fatty acids enter the enterocytes?
Reconstructed back into triglycerides by Monoglyceride acylation, Phosphatidic acid pathway. Incorporated in chylomicrons and secreted across basement membrane by exocytosis into lymph vessel.
Function of ileocaecal valve?
Allows passage of material into colon and prevents back flow of bacteria into ileum.
