Physiology of the small intestine and accesory organs Flashcards
What are exocrine cells in the pancreas
- accessory organ to digestion
- secretion of enzyme rich fluid into duodenum
- Break down all categories of digestible food
what are endocrine glands in the pancreas?
- release hormones into bloodstream that affect carbohydrate metabolism
- insulin
-glucagon - somatostatin
What is the structure of the pamcreas?
- similar to salivary glands
acinar cells secrete enzymes and fluid into duct system - the pancreatic duct fuses with the bile duct on entry to duodenum
what is the aqueous component of pancreatic juices ?
- 200-800ml secreted a day
- rich in bicarbonate
- helps to neutralise acid chyme
- secretion stimulated by secretin
what is the proteolytic enzyme component ?
Trypsin, chromotrptins and carboxypeptidases
Secreted in inactive form, activated by the duodenum by enterokinase
what does pancreatic amylase do?
breaks down starch - secreted in active form
what does the lipolytic enzyme in the pancreas do?
Fat digestion
Lipase - secreted in active form
Colipase, cholesterol esterase, phospholipase
Activated by trypsin in the duodenum
what is the control of pancreatic secretions?
- Nervous and hormonal control
- Nervous reflex involves medulla and vagal innervation (cephalic phase)
- gastrin release in response to stomach distension (gastric phase)
- secretin and cck secreted by mucosa in response to presence of chyme in the duodenum (intestinal phase)
what is pancreatitis ?
pancreatic enzymes are activated in the pancreas, causing them to attack the organ itself
- Acute (can resolve) or Chronic (tissue is destroyed and scarring develops)
what are causes of pancreatitis?
gallstones ( pancreatic duct and bile duct fuse so blockage may affect the other)
Alcohol
Idiopathic
what are some function of the liver?
- processing digested food from intestine
- manufacturing of bile
- storage
- metabolism (breaks down stored glycogen, fat or protein to glucose)
what is the structure of the liver?
- hepatic (liver) cells arrange in radial pattern around central vein
- hepatocytes make up functional units called lobules
- lobules form the 2 main lobes of the liver
what does hepatic blood supply do?
- receives double blood supply (oxygenated from hepatic artery, deoxygenated from portal vein)
what does hepatic cells do?
Extract oxygen and most nutrients
Detoxify or story poisons and drugs
Secrete products (except bile) in hepatic vein
what are the two characteristics of bile?
- excretory product of liver metabolism
- a digestive secretion
What does bile salts do?
emulsifies fats into small droplets that enables them to be absorbed and digested more effectively
what are bile pigments called and what do they do?
Bilirubin - yellow/brown give faeces their colour (absorbed by the blood)
Salts, cholesterol and pigments secreted by liver cells (hepatocytes)
what does bicarbonate ions in the bile do?
neutralises acid chyme
it is secreted by epithelial lining bile ducts
what happens to most bile salts and emulsifying?
they are recirculated and reabsorbed
5% is synthesised and lost in faeces
what does the gall bladder do?
stored and concentrates bile by extracting water and ions. Can lead to increased insoluble cholesterol levels
how does bile enter the gallbladder?
by the cystic duct when the SI is empty
when does ejection of bile into the duodenum occur?
when protein or fat-rich chyme enters duodenum
- causes CCK release
- CCK causes gallbladder to contract and sphincter of oddi to relax thus allowing bile to enter the duodenum
what are gallstones?
crystalline deposit that accumulates when there is too much cholesterol and not enough bile salts
how can gallstones be treated?
can be dissolved
if severe gall bladder can be removed (cholecystectomy)
what is jaundice a symptom of gallstones?
Stones can block the common bile duct which causes increased levels of bilirubin in the blood plasma causing discolouration of the skin
what are the three parts of the small intestine?
duodenum
jejunum
ileum
what is the small intestines mucosa consisting of?
epithelium (enterocytes)
lamina propia
muscularis mucosae
What types of muscle causes the small intestine to contract
Smooth muscle (longitudinal and circular )
what are the components of the enteric NS
Myeteric plexus
submucosal plexus
what is the neutransmitter for parasympathetic and sympathetic signals?
para - acetylcholine
symp - noradrenaline
what does the submucosa contain and what does it do?
contains brunner’s glands to secrete alkaline mucous to protect the intestinal wall and neutralise acid chyme
what are lacteals?
components of the lymphatic system for fat digestion
what is the villi’s function?
increase SA for absorption
Microvilli further increases this
what is the components of a villus?
- arteriole and capillary bed (oxygenated blood)
- venule (nutrients from villi)
-lymphatic (fatty end stage products)
what is the combination required for digestion in the SI
pancreatic juice
bile
intestinal juice
how is carbohydrates digested?
- starch converted to disaccharides by pancreatic amylase
- disaccharides converted to monosaccharides by glycosidase
- monosaccharide is absorbed in the epithelium
what are polypeptides arriving from the stomach catabolised by?
trypsin and chymotrypsin
how is glucose and galactose absorbed?
into epithelial cells by co-transport with Na via sodium glucose transporters
-leave epithelial cell and enter blood by facilitated diffusion via glucose transporters
how is peptides absorbed in the SI
uptake into epithelial cell thought to be linked with H+ influx
Broken down to constituent amino acids inside epithelial cell
how are amino acids absorbed in the SI?
uptake into epithelial cells by Na+ dependent co-transport
-leave by facilitated diffusion
when do bile salts remain in the lumen of gut until?
until terminal ileum and then re-cycled into enterohepatic circulation
what are cylomicrons?
when lipids(triglycerides) accumulate in vesicles of smooth ER of epithelial cell and leave by fusion with plasma membrane
how do chylomicrons leave the intestines?
leave in lymph since they are too largs to enter the circulation immediately
what is interstitial spaces ?
spaces between cells/organs
what is lymphatic circulation due to?
muscular movements with slow contractile action of smooth muscle in walls of lymphatics pushing lymph along by peristalsis
