case 6 - PBL and somatostatin Flashcards
what are the three parts of the hypothalamus that regulate food intake
ventromedial nuclei
Lateral hypothalamic area - known as the hunger centre
Arcuate nucleus
what is the satiety centre
the ventromedial centre
how is thirst detected
the osmoreceptors in the hypothalamus detect sodium concentration in the blood
in response to this high sodium level, the hypothalamus activates the thirst mechanism and concurrently stimulates the release of antidiuretic hormone
what are the thirst areas in the brain
lateral hypothalamic area
Hypothalamic paraventricular nucleus
Periaqueductal gray
what is the result of glucose transport in beta cells in T2DM being reduced
shifting the control point for insulin secretion from glucokinase to the glucose transport system. This defect is improved by the Sulfonylureas
what is somatostatin also referred to as
growth hormone inhibiting hormone
what is the structure of somatostatin
is a polypeptide hormone capable of inhibiting the actions of various pancreatic and gastrointestinal hormones
what does somatostatin have high binding affinity to
five different SS receptors in the G protein coupled receptor superfamily
These receptors are coupled to inhibitory G proteins and are involved in motility, mucous and hormone secretion and inflammatory responses.
what is somatostatin produced by
D cells in the stomach and duodenum and the delta cells in the islet of Langerhans in the pancreas
what is SS secretion stimulated by
the presence of glucose, amino acids, and glucagon-like peptide-1
what is somatostatins primary role in gastric physiology
Its primary role in gastric physiology is to inhibit both gastrin release and parietal cell acid secretion.
what is somatostatins effect on gastric acid secretion
inhibits gastric acid secretion via an indirect and direct pathway
why does it matter what the source of the somatostatin is
can act in a paracrine or an endocrine fashion
where are D cells found in the stomach
found near the base of the oxyntic glands, the predominant gland type within the body and the fundus of ths tomach
what happens once somatostatin is released into the stomach
Somatostatin binds to the a alpha-1 G protein coupled receptor on the basolateral membrane of the parietal cell
what does this binding lead to
leads to the inhibition of adenylyl cylcase, antagonising the stimulatory effects of histamine, and thus inhibiting gastric acid secretion by parietal cells
what is the indirect pathway
somatostatin can activate tow indirect paracrine pathways on G and D cells of the stomach
what are examples of secretagogues and what are they
histamine and gastrin are both examples of secretagogues which are substances that cause another substance to be secreted and due to this function, Somatostatin can inhibit gastric acid secretion
what happens in the corpus of the stomach
D cells release the hormone to inhibit the release of histamine from the ECL cells
what happens in the antrum of the stomach
the release of somatostatin from the D cells inhibits the release of gastrin from the G cells.
this is an example of redundant regulatory pathways that control acid secretion
what happens in the pancreas
somatostatin is secreted by delta cells
what happens once somatostatin is released
it acts as a powerful inhibitor of glucagon and insulin secretion from the alpha and beta cells respectively
what does glucose stimulate somatostatin via
G proteins
what happens when blood glucose concentrations are high
activation of cellular receptors causes the closure of ATP-sensitive K+ channels, initiating membrane depolarisation and increasing somatostatin release from delta cells.
how does somatostatin also suppress pancreatic exocrine secretions
through the inhibition of cholecystokinin-stimulated enzyme secretion and secretin-stimulated bicarbonate secretion
give a summary list of gastrointestinal effects of somatostatin
Decrease gastrin release leading to reduced gastric acid
Increase fluid absorption
Increase smooth muscle contraction
Paracrine inhibition of insulin and glucagon secretion from α and β-cells of the Islets of
Langerhans
Decrease bile flow
Decrease blood glucose concentration
what is somatostatin produced by aswell as the GI tract
the brain
what is a key producer of this neuropeptide
hypothalamus, which predominantly synthesises the 14 amino acid form of the hormone in the periventricular region
where is SS-14 released
into the hypophyseal portal blood stream
what is SS
a potent growth hormone inhibitor
what is control if GH regulated through
both positive and negative control
give a summary of somatostatin neurological effects
Inhibits secretion of growth hormone from the anterior pituitary
Inhibits secretion of thyroid-stimulating hormone from the anterior pituitary
