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Growth hormone secretion(hgh).



Hormone- physiological substance secreted by cells into the environment around them in very small amounts.

This substance reaches its target cell either through the blood stream or acrossthe synapse. That target cell interacts with specific receptors and regulates cellular response.
Functional interaction:
1. One function regulated by many hormones
2. One hormone: multiple functions

In this article:
1. Synthesis + secretion of hormones
2. Transport (when they are in the blood)
3. Metabolism
4. Target sites (how they actually exert an effect on our cells)

Synthesis + secretion of hormones

1.1 Steroids.
a) Presence or absence of enzymes determines which steroids are produced
Example: Steroid synthesis pathway in Adrenal cortex
Adrenal cortex can produce three different classes of hormones.
Always starts with stored Cholesterol converted into the Pregnenolone.
Through the series of intermediates it can be converted into Aldosterone.
Pregnenolone and Progesterone can both be converted into the cortisol
ACTH acts on adrenal cortex receptors to stimulate conversion of cholesterol to pregnenolone.
But gonads can't make mineralocorricoids (aldosterone) or cortisol, but they CAN make sex hormones.
The reason for that is because they LACK 233-Hydroxylase, and ll^-Hydroxylase.
In gonads, LH acts on specific receptors in ovaries, and therefore causes conversion of cholesterol.


b) Store precursor cholesterol not final steroid.
• Steroid secretion has to first involve an increase synthesis of a hormone
c) Release: Lipophilic
Steroid hormones are lipophilicy cell membranes of steroid producing glands are very permeable to lipophilic compounds
1.2 Proteins.
a) Stored in membrane bound secretory granules
Why is storage of proteins important physiologically?
1. Large storage capacity (have proteins ready to release)
2. Aids in hormone release (since proteins are hydrophilic, they need help to be transported out of the cell)
b) Energy is required for release
For the fusion of cell granules with plasma to take place
c) Synthesized as the pre-prohormones or prohormones. In blood hormone contains many more amino acids than are at active site in hormone.
in pre-prohormone, "pre" is a signal peptide, so it gets cleaved inER
Then, in Golgi, prohormone get cleaved into "Pro" and "Hormone" portions, where "pro" portion has no physiological activity.
Both are released the active site of a hormone is a very small portion of a molecule.


1.3 Glycoproteins.
- 4 glycoproteins: FSH, LH, HCG, TSH
a-subunit has to be linked with 3-subunit in order to produce a physiological compound 3-subunit determines unique biological activity


Transport

(Hormones in blood)

1.1 Steroids.
Although almost all steroids are found bound to the transport p rotein in the plasma, some small amount of steroid that is dissolved in the plasma, free, not bound. And it is physiologically active portion of the steroid molecule.
Transport proteins are produced by the liver.
The vast majority of steroids in the plasma is in the bound form Why is binding important?
• Because most are bound in plasma, it allows steroids to be stored in plasma
• INCREASE half-life of hormone in two ways!

1) Decrease the metabolism in the liver 2) Decrease the secretion of hormone by kidney
1.2 Proteins.

1) Metabolized by enzymes in liver (primarily for steroids) and plasma (containspeptidasesfor protein hormones)
2) Broken down at the site of action
Target sites
• Hormones activates specific receptor activation of 6 protein (3 subunits)- 6TP displaces GDP from the a-subunit a-subunit dissociates from 3v-su bun itsa-subunit combines with adenyl cyclase adenyl cyclase catalizes ATP to cAMP
• cAMP - initiates a cascade of reactions
• What slows down adenyl cyclase activity?
1) GTPase in a-subunit slows it down (ADP-^ATP) GTPase converts GTP to GDP
2) Contains phosphodiasterase enzyme(PDE) converts cAMPtoS'AMP (inactive)
3) Hormone-receptor complex is internalized and metabolized
4) Hormone itself is being metabolized by peptidases in plasma
Growth Hormone work for tissue repair, muscle growth, brain function, physical health, bone strength, energy and metabolism. HGH Boosts muscle fiber growth.