Digestive System - Pancreas and Bile Flashcards
What are the pancreatic digestive enzymes ?
Proteins - proteases and peptidases, they’re secreted from the pancreas as inactive precursors and are only activated by enzymatic degradation in the small intestine by enterokinase
Carbohydrate - pancreatic amylase digests carbohydrates under alkaline conditions, releasing oligosaccharides
Fats - bile salts, lipase and cholesterol esterase
How do enterogastric reflexes inhibit gastric emptying ?
Powerful duodenal reflexes which inhibits stomach emptying
Signals sent to stomach of volume of chyme in duodenum is excessive via enteric nervous system in gut wall, vagus nerve and pre-vertebral sympathetic side chain
Inhibits pyloric pump and increases sphincter tone
What are inhibitory entergogastric reflexes influenced by ?
Inhibitory enterogastric reflexes influenced by;
Distension in duodenum
Irritation of duodenal mucosa
Acidity of duodenal chyme
Osmolarity of chyme
Describe the structure and function of the pancreas .
Pancreas lies parallel to and beneath the stomach
Large compound gland that has pancreatic acini which secrete digestive enzymes
Join the common bile duct and enter the duodenum at sphincter of Oddi
Pancreatic juice is alkaline and neutralises the gastric acid entering the duodenum
Pancreatic secretion can be divided into an aqueous, alkaline or bicarbonate component and an enzymatic component
Aqueous component neutralises duodenal components preventing damage to duodenal mucosa
Enzymatic component contains multiple enzymes for digesting all major food types
Secretes around 1 litre of fluid a day that is isotonic with ECF
What is the structure and function of the pyloric sphincter?
Pyloric sphincter - thickened region of circular muscle in pylorus, open enough for water and other fluids to leave the stomach for the duodenum
Contraction of the sphincter prevents food passing from stomach to duodenum until it has a fluid-like consistency
The degree of constriction of sphincter is influenced by both nervous and hormonal reflexes from both the stomach and duodenum
This ensures that chyme cannot enter the duodenum at a rate greater than the rate at which it can be digested and absorbed by the small intestine
Describe the process of gastric emptying.
- Motility of the stomach is organised to achieve orderly emptying of stomach contents to duodenum
- Stomach emptying is promoted by intense peristaltic contractions in the stomach antrum and at the same time opposed by varying degrees of resistance to passage of chyme at the pylorus
- Emptying requires the mixing of food with gastric secretions
- Strong contractions begin in mid stomach and spread to caudad region, as stomach empties these contractions move up pinching off the food
- Each strong wave forces chyme into duodenum when pyloric tone is normal
How is pancreatic secretion controlled ?
Pancreatic secretion occurs in 3 phases similar to gastric secretion
Cephalic phase - mediated by acetylcholine and causes moderate amounts of enzymes to be secreted into pancreatic acini
Gastric phase - nerve stimulation of enzyme secretion continues, but again only small amounts of pancreatic juice reach the duodenum because of a lack of significant fluid secretion
Intestinal phase - the release of secretin (aqueous component) and CCK (enzymatic component) as chyme enters the small intestine causes copious amounts of pancreatic secretion into the duodenum
What is the function and components of bile?
- Produced by hepatocytes in the liver
- Secreted into the bile canaliculi and stored and concentrated in the gallbladder
- Following a meal the gallbladder contracts (stimulated by the presence of CCK released by the duodenum) and the bile travels to the duodenum via the bile duct
- Bile salts aid emulsification of fats by breaking down into smaller particles
- Also serves as a means for excretion of several important endogenous waste products from the blood
- Bile is an aqueous complex mixture of organic and inorganic components.
- It contains NaHCO3 (sodium bicarbonate), bile salts, bile pigments (bilirubin), lecithin, cholesterol and electrolytes of plasma
What are bile salts and their 2 functions ?
Bile salts have a steroid nucleus which is usually conjugated with an amino acid making them part water soluble and part fat soluble (amphipathic)
2 important functions in gastrointestinal tract;
Emulsification - bile salts decrease the surface tension of the particles and allow agitation of the intestinal tract to break the fat goblets into minute particles
Absorption - stabilise lipid products by forming smaller complexes known as micelles
Describe bile secretion.
Initial stage, bile is secreted by hepatocytes into bile canaliculi
Bile then flows through bile ducts before reaching hepatic and common bile duct
Then it enters directly into the duodenum or directed into gallbladder
How is bile secretion regulated?
Substances that increase the secretion of bile are known as choleretics e.g bile acids
Cholecystokinin stimulates gall bladder contraction pushing bile into the duodenum
Secretin increases bile secretion
Describe bile pigments.
Bile pigments, produced by the liver as a byproduct of hemoglobin breakdown, are primarily bilirubin, which gives bile and stool their yellow-brown color.
There are two forms: unconjugated and conjugated bilirubin.
Unconjugated bilirubin is insoluble in water and is transported to the liver.
It is conjugated with glucuronic acid to form conjugated bilirubin, which is water-soluble and excreted into bile.
It then travels to the intestines, where it is metabolized by bacteria to form urobilinogen, which gives stool its brown color.
Abnormal levels of bilirubin can lead to jaundice, a condition characterized by yellowing skin and eyes.
