Glucocorticoids Figs(7 pages)
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- Lecture number:
- Lecture Note
- University of Southern California
- Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 17 Current Lecture Anatomy of the Adrenal Gland Adrenal cortex – adrenal gland is on top of the kidney. It has two parts – an outer cortex and inner medulla (which synthesizes catecholamines like epinephrine). For now we will focus on the cortex. (coid = steroid, corti = from the adrenal cortex) The cortex has 3 layers: 1. Zona glomerulosa, the outer layer which secretes mineralocorticoids. These are involved with ion and mineral balance in the body. The main one in humans is aldosterone and it has two targets: distal part of kidney tubules where it stimulates sodium reabsorption from tubular fluid back into blood, and potassium secretion from blood into tubular fluid. It does the same thing in the large intestine. 2. Zona fasciculate, the middle part, where glucocorticoids come from. Gluco means they have to do with levels of glucose. It will be the main subject of today’s lecture. 3. Zona reticularis, innermost layer: secretes androgens. It is not important in men, because we have much higher levels of testosterone, so much that they overshadow the androgens being secreted by the zona reticularis. But in women, after menopause, ovarian follicles stop cycling and the only source of estrogenic hormones in the body is the adrenal cortex. It becomes important in maintaining libido, bone strength, muscle strength, etc. Steroid Hormone Synthesis Don’t need to memorize this. It is a simplified view of the pathway for synthesis of steroid hormones. There are lots of details left out. Some of the intermediates in the boxes aren’t labeled. The main take away is that all these steroid hormones are synthesized from cholesterol and are related structurally. Many of the important ones (in the colored boxes) are related to the others as products or precursors. After a couple of steps, cholesterol is converted to progesterone, which is the precursor for synthesis of corticosterone and cortisol. These two hormones are the main glucocorticoids we are focusing on. In humans, cortisol is more abundant than corticosterone, which is the precursor to aldosterone. Progesterone and other intermediates are precursors to androstenedione and so is DHEA. Androstenedione is important because it is the precursor to testosterone. Progesterone, estrone, and estradiol are the main female hormones. Estrone and estradiol are the estrogens, which is a term that covers functionally steroid hormones in humans. Androgen is a collective term for the steroid hormones in males. Main ones being testosterone and dihydrotestosterone. Also, in about half of the places in the male body where testosterone acts to promote maleness, it is aromatized to estradiol and it binds estrogen receptors. So it doesn’t necessarily activate testosterone receptors. All of these steroid hormones are water soluble and lipid insoluble – so they cannot be synthesized in advanced and stored in vesicles because they would diffuse right out. Synthesized on demand mostly by oxidases in mitochondria. And once synthesized and released, they just take off. Not very soluble so they diffuse and travel bound to carrier proteins. For ...
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