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Cholesterol and the steroid hormones part 1: structure and functions
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Endocrinology Mind Map on Cholesterol and the steroid hormones part 1: structure and functions, created by maisie_oj on 13/04/2013.
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endocrinology
endocrinology
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Resource summary
Cholesterol and the steroid hormones part 1: structure and functions
Basic steroid structure
All steroid hormones based on the same 4 ring structure
Cyclopentanoperhydrophenanthrene (C17)
Fully saturated (no double bonds) C17 molecule
Three six carbon rings (A, B, C) and one five carbon ring (D)
Most natural steroids have 2 methyl (CH3) groups = C19 structure
Numbering (CH3 groups: on C13 = "C18" and C10 = "C19")
1 (A)
2 (A)
3 (A)
4 (A)
5 (A/B)
6 (B)
7 (B)
8 (B/C)
9 (B/C)
10 (A/B)
11 (C)
12 (C)
13 (C/D)
14 (C/D)
15 (D)
16 (D)
17 (D)
This C19 steroid nucleus = androstane (all steroids are modified versions of this)
Derived from cholesterol (from the diet, stores or de novo synthesis)
Steroid hormones (and vitamin D3)
Vitamin D3
Steroid derivative
Formed by action of sunlight on skin
UV radiation causes the B-ring of 7-dehydrocholesterol to open
= cholecalciferol
Undergoes first hydroxylation in the liver at C25
Second hydroxylation in the kidney at C1 = 1, 25 dihydroxycholecalciferol
(Active vitamin D3)
Acts on the vitamin D receptor (intracellular)
Receptor forms transcription complex and plays a major role in calcium metabolism
Progestogens (C21)
e.g. progesterone
feature characteristic D-ring
Has a ketone group [C(=O)CH3] attached at C17
Receptor: Progesterone receptor (PR)
Function: During the menstrual cycle and the maintenance of pregnancy
Produced by: developing follicle and corpus luteum (ovary)
Glucocorticoids (C21)
e.g. cortisol (humans); corticosterone (rodents) - parallel synthesis and difference of x1 OH group at C17
Receptor: glucocorticoid receptor (GR)
Function: Stress adaption
Secreted by: adrenal cortex (zona fasciculata)
Mineralocorticoids (C21)
e.g. main one = aldosterone
Receptor: mineralocorticoid receptor (MR)
Function: promote Na+ reabsorption in distal convuluted tubule (DCT) in the kidneys
increases blood volume and pressure
Secreted by: adrenal cortex (zona glomerulosa) and in a small quantity by cadiac myocytes
Androgens (C19)
e.g. ...
Testosterone - main male sex hormone
Adrostenedione - features two ketone groups at C3 and C17
Dihydroepiandrosterone (DHEA) - most produced steroid hormone
Male sex hormones
Lack side chains at C17
Receptor: androgen receptor (AR)
Function: male sex hormones - sexual differntiation (in utero), development of sex characteristics at puberty, libido, increased muscle and bone mass
Secreted by: leydig cells (testes) - primary source; and adrenal cortex (zona reticularis) - weak androgens, e.g. DHEA
Oestrogens (C18)
Characterised by an aromatic, phenolic A ring (alternating double, single C-bonds - with an -OH group at C3)
e.g. ...
Oestradiol - two -OH groups (C3 and C17)
Oestrone - features a ketone group at C17
Oestriol - three -OH groups (C3, C16 and C17)
Receptor: Oestrogen receptor (ER)
Function: Menstrual cycle (uterine development) and development of female secondary sex characteristics
Secreted by: ovaries and adipose tissue
Principle female sex hormones
Oestrogen-like (oestrogenic) compounds
ellicit response at ER, but not necessarily ture oestrogens
Can be used as alternative therapies (e.g. phyto-oestrogens) in menopause
Medical use:
DES (diethylstilbestrol) - in advanced prostate cancer and breast cancer (in postmenopausal women)
SERMS (selective ER modulators) - tissue selective (e.g. tamoxifen (Br ca), raloxifene (OP, Br ca) and femarelle (menopause))
Used in: osteoporosis, breast cancer, menopause
Problems: Can contaminate the environment and result in adverse effects in nature
e.g. oestrogenic compounds from industrial compounds (dicofol or DDT -> DDE when metabolised)
DDE is oestrogenic
e.g. alligators in lake Apopka (reduced fertility, fewer hatching eggs, small peninses and dysfunctional reproductive organs in the young
In humans?
Some evidence of increased incidence of problems with male fertility and in utero development....
Falling sperm count
Increased numbers of; hypospadias (underdeveloped penis - urethra opening along the length of the penis) and cryptorchidism (undescended testes)
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