BIOC 462B: Dr' Tischler

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BIOC 462B Dr. Tischler
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STEROID HORMONES/ VITAMIN D SYNTHESIS
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Objectives   1. Describe the pathway and
regulation of aldosterone synthesis   2. Describe
the pathway and regulation of cortisol
synthesis   3. Describe the pathway and mechanism
of stimulation for androgen biosynthesis in the
testes.   4. Explain the roles for LH and FSH in
the synthesis of estrogen.   5. Outline the
pathway and regulation of vitamin D synthesis
involving the skin, liver and kidney.
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Cholesterol
Pregnenolone
Progesterone
Cortisol glucocorticoid synthesized in adrenal
cortex
Testosterone testes, ovaries
Aldosterone mineralocorticoid synthesized in
adrenal cortex
Estrogen ovaries
Mobilizes fuels by affecting protein, fat and
carbohydrate metabolism anti-inflammatory
anti-allergic
Sex hormones secondary sexual characteristics
female reproductive cycle
Mainly regulates reabsorption of Na in exchange
for K and H
Figure 1. Overview of steroid hormone
biosynthesis.
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ACAT acyl CoAcholesterol acyl transferase
ACTH adrenocorticotropic hormone AT
angiotensin II LH luteinizing hormone
inhibited by AT, ACTH , LH
Pregnenolone ?SER
Figure 2. Initial events common to the
biosyn- thesis of steroid hormones
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Zona glomerulosa cells
Cholesterol
Figure 3. Biosynthesis of aldosterone in the
zona glomerulosa cells
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Zona fasciculata cells
Unique rxn
11-Deoxycortisol
Cortisol primary human glucocorticoid
Figure 4. Biosynthesis of cortisol in the zona
fasciculata cells
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Cholesterol
Leydig cells of the testes
Figure 5. Biosynthesis of testosterone in the
Leydig cells of the testes
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Figure 6. Biosynthesis of estrogens in three
locations.
Aromatase (19-hydroxylase) - SER
17?-Estradiol (E2) most active
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Figure 7. Photobiosynthesis of vitamin D3 and
its metabolism
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1,25(OH)2D3 is classified as the active hormonal
form of vitamin D because it 1) stimulates
calcium absorption more rapidly than any other
vitamin D form, 2) is more active on a molar
basis than any other form, 3) is produced in
kidney in a regulated fashion, according to the
needs for calcium and/or phosphate, 4) has
specific intracellular receptors in intestine,
bone and kidney cells, 5) chemically resembles
the steroid hormones.
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The physiological regulation of vitamin D
production 1. Low dietary calcium increases
secretion of parathyroid hormone that activates
the renal 1-hydroxylase enzyme creating the
active 1,25(OH)2D3 form. 2. Low dietary
phosphate directly enhances the activity of renal
1- hydroxylase. 3. During active growth in
children, growth hormone or insulin-like growth
factor stimulates the renal 1- hydroxylase. 4.
In pregnancy and lactation, estrogens and
prolactin, respectively, increase renal output
of 1,25(OH)2D3.