Things you didnt know

Question 1

Somatostain

Answer 1

Released by intestinal and gastric D-cells in response to lowered gastric pH, secretin and nutrient absorption. Primary role is to reduce acid secretion back to basal levels in a delayed negative feedback loop. Acts as a neurocrine, endocrine and paracrine regulator to attenuate the action of gastrin mediated acid secretion from parietal cells, does so via binding to SS2 receptors on G-cells (Gi), ECL cells and parietal cells.

Question 2

Cholecystokinin

Answer 2

Released from intestinal I Cells act to decrease gastric motility, stimulate gall bladder contraction and release of the pancreatic juice and maintains the structure of the exocrine pancreas. CCK is released in response too ingestion of food. CCK receptors are Gq coupled and mediate their effects by mitogen activated protein kinase pathway transcription modulation.

Question 3

Secretin

Answer 3

Released from S cells in the duodenum, secretin acts to augment the effects of CCK on the pancreas and gall bladder and stimulates water and bicarbonate secretion in the pancreatic juice.

Question 4

GLP-1

Answer 4

secreted from open type pro-glucagon producing L cells located in the ileum and colon. Acts on Gs coupled G proteins on pancreatic beta cells to stimulate insulin secretion and inhibit gastric motility and secretion.

Question 5

GIP

Answer 5

Secreted from Duodenum intestinal K cells in response to nutrients absorption. Receptors are Gs coupled resulting in decreased gastric motility, and inceased insulin secretion.

Question 6

Intestinal enzymes

Answer 6

Pancreatic enzymes are produced as their inactive form in the pancreas to ensure self-digestion does not occur. Trypsin is responsible for activating the zymogens (procarbocypeptidase, prolipase, prophosphlipase and chymotrypsinogen. Trypsinogen itself is activated by enterokinase enzymes in the brush boarder of the lumen

Question 7

Enteric nervous system

Answer 7

In the enteric nervous system allows autonomous control of the GIT from the CNS. This nervous system is made up of the same neural circuitry as the bodies, with afferent neurons which sense conditions (i.e. chemicals, stretch, osmotic pressure, heat etc) in the lumen and mucosal environments, information is relayed via interneurons to effector neurones which synapse onto smooth muscle in the case of motor neurones or blood vessels or enteroendocrine cells in the case of secretomotor neurones, these neurones also control fluid secretion across the mucosa. The enteric nervous system utilizes a variety of NANC neurotransmitters in its function.

Question 8

Nuclear hormone receptors structure function relationship

Answer 8

Nuclear hormone receptors are monomeric proteins. The n terminus region contains the AF1 domain, this AF1 domain contains sequences which will bind chemical mediators resulting in alterations to the binding and regulatory capacity of the receptor(gene transcription) independently of ligand binding. The core domain is a highly conserved region which contains the DNA binding domain (binds to hormone response elements) and also plays an important regulatory role in receptor dimerization, the structure of this region is informed by the zinc finger motifs. The highly flexible hinge region allows for dimerization with other nuclear receptor complexes and regulates intracellular trafficking (contains the nuclear localization machinery). There is the ligand binding domain, which binds specific ligands and is also important in regulating the binding of coactivator and corepressor proteins and the AF2 region to which molecular chaperones will bind. The binding of molecular chaperones to the AF2 region is dependent on ligand binding, which typically will result in disassociation of the molecular chaperone.