GI Physiology Flashcards
What gastric factors influence the rate of gastric emptying?
The amount of chyme - stomach distension triggers increased gastric motility through a direct effect of stretching on smooth muscle and ghe involvement of intrinsic and extrinsic nerve plexuses and GI hormones
What duodenal factors can affect the rate kf gastric emptying?
Presence of fat in the duodenum Presence of acid in the duodenum Hypertonicity of the duodenum Distension of the duodenum All of these will reduce the rate of gastric empyting
In what areas of the stomach are oxyntic glands, which mostly contain parietal cells and secrete lots of HCL, mostly present?
Fundus and body
Which cells secrete pepsinogen?
Chief cells
What do D cells in the gastric pits secrete?
Somatostatin
What do eneterochromaffin-like cells in the gastric pits secrete?
Histamime
What do G cells in the gastric pit secrete?
Gastrin
What is the role of hydrochloric acid in the stomach?
Act as an antimicrobial
Activate pepsinogen to pepsin
Denature protein
Explain the process by which parietal cells secrete hydrochloric acid into the stomach lumen.
First water is broken down into hydrogen and hydroxyl ions. The hydrogen ions are actively transported out of the cell using a H+/K+-ATPase. (Potassium passively leaks back out of the cell. Meamwhile the hydroxyl ions are reacted woth carbon dioxide from cellular metabolism to create bicarbknate ions which are actively transported out of the cell and into the plasma in exchange for chloride ions. This builds up a concentration gradient to allow chloride ions to diffuse into the gastric lumen through a protein channel.
What type of signal is the histamine released by ECL cells?
Paracrine
What kind fo signal is the somatostatin released from D cells?
Paracrine
What type of signal is the gastrin secreted from G cells?
Hormone
What is the function of ECL cells?
To release histamine which stimulates parietal cells to produce HCL
What is the function of G cells?
To secrete gastrin which stimulates parietal, chief and ECL cells to increase the secretion of HCl and pepsinogen
What is the function of D cells?
Inhibits parietal, G and ECL cells
How does acetylcholine work to increase HCL secretion?
By stimulating parietal cells, chief cekks, G cells and ECL cells
What is the normal pH of the stomach when not eating?
1.5
Why does the pH of the stomach increase when digesting a meal despite the increased acid secretions?
Because the food (particularly the protein component) is acting as a buffer
Describe the cephalic phase of digestion
When thinking about, smelling, tasting, chewing or swallowing food the vagus nerve sends signals to stimulate increased hydrochloric acid and pepsinogen secretion through the neurotransmitter ACh
Describe the intestinal phase of digestion
The removal of food from the stomach into the duodenum removes protein which js a major stimulus for enhanced gastrin secretion. This removal of food also lowers the pH of the stomach and the acidic environment stimulates D cells to secrete somatostatin. This all leads to decreased gastric secretions
The small intestine secretes a vast amount of water into the lumen. Why does it do this?
In order to help fix pancreatic and gastric secretions with food to aid digestion
What two factors cause the small intestine to secrete water into the lumen?
Luminal osmotic pressure increases as the osmolarity of the foodstuffs imcreases with digestion
Secretion of electrolytes (sodium chloride) into the lumen draws water into the lumen by osmosis
Describe the action of the CFTR channel in The secretion of water into the lumen of the small intestine
Chloride ions enter the enterocyte via cotransport with sodium and potassium ( sodium and potassium are then exported out of the cell again)
This activates adenylyl cyclade to generate cAMP
Elevated intracellular levels of cAMP activates CFTR resulting in the secretion of chloride ions into the lumen of the small intestine
The accumulation of these negatively charged ions in the lumen attracts sodium ions into the lumen
This secretion of sodium chloride into the lumen creates an osmotic gradient which draws water i to the lumen
Explain how cholera infection leads to increased water secretion via CFTR
The cholera toxin binds to crypt cells to cause an elevation in cAMP which results in the abnormal activation of CFTR. This causes hyper-secretion of sodium chloride into the lumen and thus sets up a concentration gradient which leads to the hyper-secretion of eater into the lumen. This can lead to severe and dangerous dehydration
Most proteins are digested before absorption in the small intestine. What protein is an exception to this?
Antibodies in colostral milk
Glucose and galactose are actively absorbed in the small intestine but there is limited absorption of fructose. T/F?
True
Protein is predominantly absorbed in the small intestine as amino acids by active co transport with which ion?
Sodium
In which part of the small intestine is vitamin b12 primarily absorbed?
The terminal ileum
Coeliac disease, whipple’s disease and giardiasis can all result in malabsorption. T/F?
True
What is the name of the glands in the small intestine which secrete bicarbonate ions to neutralise acidic secretions from the stomach?
Brunner’s glands
What is the function of peyers patches in the small intestine?
These are lymphatic areas which protect against ingested pathogens
Bobesin is secreted by the small intestine. What does it do?
Stimulates gastrin release
