Gastrointestinal Physiology Flashcards
What are the main functions of the gastrointestinal tract?
digestion - food broken down into absorbable molecules
secretion of juices - hydrolytic enzmes, HCl, HCO3-
motility - propel ingested food from mouth towards rectum
absorption - nutrients, electrolytes, and water are absorbed or transported from lumen of GIT to blood stream
immunity -GIT has largest area of body in potential direct contact with infectious, toxic and immunogenic material. 80% of immunoglobin producing cells are found in small intestine.
What the accessory organs and their function?
exocrine pancreas - acinar cell responsible of zymogen production, duct cell responsible for isotonic bicarbonate production
endocrine pancreas - the btea cell releasing insulin and promotes anabolism, the alpha cell releases glucagon and promotes catabolism, the delta cell releases somatostatin, with wide ranging effects in downregulation
liver - bile production, detoxification, maintainance of blood glucose levels
gall bladder - storage and secretion of bile
What is digestion and what organs are involved?
digestion renders ingested food into absorbable forms, and involves the orchestrated secretion of products that hydrolyze chemical bonds in macromolecules and solubilize fats.
stomach - parietal cells produce HCl, chief cells produce pepsin(ogen)s
accessory organs include the exocrine pancreas which produces zymogens and bicarbonate, the liver which produces bile, and the gall bladder which stores bile and secretes bicarbonate
What are sphincters and their function?
sphincters are specialised circular muscles that reperate the low pressure organs in the GI tract. they function as barriers to flow by maintaining a positive resting pressure, to seperate the two adjacent organs. they regulate antergrade (forward) and retrograde (reverse) movement
What is the purpose of a bolus of chyme in the intestine?
it stretches the wall of the intestine and stimulates contraction of the musculature
What is the minibrain of the GI?
the enteric nervous system is a complete reflex circuit, and can operate totally within the GI tract or in coordination with the CNS. its neurons are primarily clustered in either the submuscosal plexus and the myenteric plexus.
What is the migrating motor complex (MMC)?
rhythmic contractions of the small intestine under control of the parasympathetic nervous system that are observed in the fasting state, ensures that residual products of digestion continue to be propelled down the digestive tract.
What is the functional anatomy of the stomach?
cardia - located distal to the gastroesophagael junction and is devoid of the acid-secreting parietal cells
corpus - largest portion of the stomach, most proximal region is the fundus
antrum - distal portion
surface are of gastric muscoa is increased by presence of gastric glands, which ahs mucous, parietal, chief and endocrine cells.
What occurs in the small intestine?
digestion occurs in the GI lumen by secreted enzymes and on surface of enterocytes by membrane-bound enzymes.
absorption occurs by simple diffusion, facillitated diffusion, active transport, endocytosis, and paracellular transport
How is the surface area of the small intestine increased?
by extensive folding and projection of fingerlike villi covered with microvilli. the brush border membrane contains enzymes and transport proteins to enable nutrient absorption
What is the pattern of nutrient absorption?
related to site of introduction of enzymes and expression of transport proteins in different regions.
Give examples of nutrient absorption patterns
for carbs, proteins and lipids, highest absorption in duodenum, then jejunum then ileum.
for calcium, iron and folate, moderate absorption in duodenum and low calcium absorption in jejunum and ileum.
for bile acids, high absorption in ileum, then jejunum, then duodenum with low absorption in large intestine
for cobalamin, moderate absorption in ileum
Describe digestion and absorption in the small intestine.
glucose - not digested, transported through
proteins - converted to amino acids by luminal hydrolysis of polymer to monomers
sucrose - converted to glucose and fructose by brushborder hydrolysis of oligomer to monomer
peptide - digested by intracellular hydrolysis
triglycerol - coverted to glycerol and fatty acids by luminal hydrolysis followed by intracellular resynthesis
How are carbs digested?
luminal amylase breaks down strach, brush-border enzymes hydrolyse disaccharides into monosaccharides, specific transporters facillitate absorption of monosaccharides
How are proteins digested/amino acids absorbed?
brush-border peptidases fully digest some oligopeptides to amino acids, whereas cytosolic peptidases digest oligopeptides that directly enter the enterocyte.
What is the anatomy and function of the colon?
the proximal (ascending and transverse) colon is responsible for fluid and electrolyte absorption, bacterial fermentation, and short-chain fatty acid absorption
the distal (descending and rectosigmoid) colon provides final desiccation and reservoir function and serves as a storage organ for colonic material before defecation
How is HCl produced by parietal cells?
acid secretion is by parietal cells. when stimulated, H-K pumps extrude H+ into lumen of gastric gland in exchange for K+
What are chief cells?
chief cells secrete pepsinogens that initiate protein digestion
