Physiology of the digestive system

Question 1

methods of GIT motility

Answer 1

peristalsis (mouth to anus); retention (digestion and absorption); physical digestion and mixing (segmentation); circulation ( reverse peristalsis).

Question 2

how does the GIT induce movement of content?

Answer 2

smooth - involuntary - muscles; coordinated contractions of longitudinal and circular muscles; contractions are myogenic, initiated by the cells of Cajal. gap junctions (connexons) allows for coordinated contractile waves allowing the walls of the GIT.

Question 3

CNS in the controlling of peristalsis

Answer 3

parasympathetic (acetylcholine) : increases digestion. sympathetic (noradrenaline): reduces digestion.

Question 4

how does the enteric nervous system control the rate of peristalsis?

Answer 4

Myenteric (muscularis externa) plexus and submucosal plexus. afferent sensory neurones. interneurones. efferent secreto-motor neurons; these can work independently of the CNS.

Question 5

what is the Enteric nervous system?

Answer 5

a network of neurones that in the digestive tract that control digestion and other functions

Question 6

How the immune system can effect digestion?

Answer 6

control is mediated via cytokinins; immune response results in faster passage (digestion but not absorption)

Question 7

digestion occuring in the stomach

Answer 7

some carb breakdown by salivary alpha amylase, protein degredation by pepsin, lipid breakdown by lingual and gastric lipase. no absorption of nutrients in the stomach.

Question 8

what is a zymogen (eg: pepsinogen)

Answer 8

secreted in an inactive proenzyme form, preventing autolysis ( eg: chief cells and pepsinogen). Activated by low PH or pepsin.

Question 9

the phases of gastric activity

Answer 9

Cephalic ( the head ) phase; gastric phase ; intestinal phase.

Question 10

processes in the Cephalic phase of gastric activity

Answer 10

increased salivation in buccal cavity (A
Ch) ; preparation of stomach for arrival of food ; increased enzyme synthesis of the pancreas ( ACh).

Question 11

Processes in the intestinal phase of gastric activity

Answer 11

controlled release of chyme; CCK (cholecystokinin) - pancreatic enzyme secretion and bile secretion. GIP ( gastric inhibitory polypeptide) - pancreatic enzyme secretion. Secretin - pancreatic and bile secretions of HCO3-. Gastrin - gastric processes.