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Somatostatin

October 11, 2019


Somatostatin or somatotropin release-inhibiting
factor) or somatotropin release-inhibiting hormone is a peptide hormone that regulates
the endocrine system and affects neurotransmission and cell proliferation via interaction with
G protein-coupled somatostatin receptors and inhibition of the release of numerous secondary
hormones. Somatostatin regulates insulin and glucagon. Somatostatin has two active forms produced
by alternative cleavage of a single preproprotein: one of 14 amino acids, the other of 28 amino
acids. In all vertebrates, there exist six different
somatostatin genes that have been named SS1, SS2, SS3, SS4, SS5, and SS6. The six different genes along with the five
different somatostatin receptors allows somatostatin to possess a large range of functions. Humans have only one somatostatin gene, SST. Production
Digestive system Somatostatin is secreted in several locations
in the digestive system: stomach
intestine delta cells of the pancreas
Somatostatin will travel through the portal blood system, to the heart, and then to systemic
circulation, where it will exert its digestive system effects. In the stomach, somatostatin acts on the acid-producing
parietal cells via G-coupled receptor to reduce secretion. Somatostatin also indirectly decreases stomach
acid production by preventing the release of other hormones, including gastrin, secretin
and histamine which effectively slows down the digestive process. Brain
Somatostatin is produced by neuroendocrine neurons of the ventro medial nucleus of the
hypothalamus. These neurons project to the median eminence,
where somatostatin is released from neurosecretory nerve endings into the hypothalamo-hypophysial
system through neuron axons. Somatostatin is then carried to the anterior
pituitary gland, where it inhibits the secretion of growth hormone from somatotrope cells. The somatostatin neurons in the periventricular
nucleus mediate negative feedback effects of growth hormone on its own release; the
somatostatin neurons respond to high circulating concentrations of growth hormone and somatomedins
by increasing the release of somatostatin, so reducing the rate of secretion of growth
hormone. Somatostatin is also produced by several other
populations that project centrally, i.e., to other areas of the brain, and somatostatin
receptors are expressed at many different sites in the brain. In particular, there are populations of somatostatin
neurons in the arcuate nucleus, the hippocampus, and the brainstem nucleus of the solitary
tract. Actions Somatostatin is classified as an inhibitory
hormone, whose actions are spread to different parts of the body:
Anterior pituitary In the anterior pituitary gland, the effects
of somatostatin are: Inhibit the release of growth hormone)
Inhibit the release of thyroid-stimulating hormone
It is induced by low pH. Inhibit adenylyl cyclase in parietal cells. Inhibits the release of prolactin
their funcion is always paracrine No,OR negligible amount is present in blood. It is present only in the vicinity of cells. Gastrointestinal system
Somatostatin is homologous with cortistatin and suppresses the release of gastrointestinal
hormones Gastrin
Cholecystokinin Secretin
Motilin Vasoactive intestinal peptide
Gastric inhibitory polypeptide Enteroglucagon Decrease rate of gastric emptying, and reduces
smooth muscle contractions and blood flow within the intestine
Suppresses the release of pancreatic hormones Inhibits insulin release when somatostatin
is released from delta cells of pancreas Inhibits the release of glucagon Suppresses the exocrine secretory action of
pancreas. ,l
Synthetic substitutes Octreotide is an octapeptide that mimics natural
somatostatin pharmacologically, though is a more potent inhibitor of growth hormone,
glucagon, and insulin than the natural hormone and has a much longer half-life. Since it is absorbed poorly from the gut,
it is administered parenterally. It is indicated for symptomatic treatment
of carcinoid syndrome and acromegaly. It is also finding increased use in polycystic
diseases of the liver and kidney. Lanreotide is a medication used in the management
of acromegaly and symptoms caused by neuroendocrine tumors, most notably carcinoid syndrome. It is a long-acting analogue of somatostatin,
like octreotide. Lanreotide is manufactured by Ipsen and marketed
under the trade name Somatuline. It is available in several countries, including
the United Kingdom, Australia, and Canada, and was approved for sale in the United States
by the Food and Drug Administration on August 30, 2007. Evolutionary history
There are six somatostatin genes that have been discovered in vertebrates. The current proposed history as to how these
six genes arose is based on the three whole-genome duplication events that took place in vertebrate
evolution along with local duplications in teleost fish. An ancestral somatostatin gene was duplicated
during the first whole-genome duplication event to create SS1 and SS2. These two genes were duplicated during the
second whole-genome duplication event to create four new somatostatin genes: SS1, SS2, SS3,
and one gene that was lost during the evolution of vertebrates. Tetrapods retained SS1 and SS2 after the split
in the sarcopterygii and actinopterygii lineage split. In teleost fish, SS1, SS2, and SS3 were duplicated
during the third whole-genome duplication event to create SS1, SS2, SS4, SS5, and two
genes that were lost during the evolution of teleost fish. SS1 and SS2 went through local duplications
to give rise to SS6 and SS3. References Further reading

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2 Comments

  • Reply Safy O December 12, 2015 at 3:44 am

    I can't watch these videos with a fake computer voice. If it was a person I would probably watch it. the content may be fine I just find the voice very off putting.

  • Reply Cramerica66 September 25, 2018 at 9:19 pm

    It’s not 2004 anymore. No need for Microsoft Sam voice overs.

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