30 - Steroid Hormones Flashcards
Steroid hormones
o Steroids are a class of lipid derived from cholesterol
o Cholesterol is converted into steroid hormones in sterogenic endocrine cells (adrenal and gonads)
What do steroid hormones include?
o Cortisol and aldosterone, made in the adrenal cortex
o Testosterone, made by the testis
o Progesterone and oestradiol, made in the ovary
What do steroid hormones affect?
o Carbohydrate metabolism
o Salt and water balance reproductive function
What does synthesis of steroid hormones require?
Synthesis of steroid hormones from cholesterol requires modifications that occur to the basic ring structure
Structure of steroids that is altered
The ring structure itself isn’t altered, rather the side chains can be altered
o In the case of progesterone, glucocorticoids, and mineralocorticoids, the side chain is split giving a 21-carbon compound
o In the case of androgens, it is split to give a 19-carbon compound
o In oestrogen it gives a C18 compound
Where does the synthesis of steroid hormones take place?
The synthesis of steroid hormones takes place in the adrenal gland and we have 2 adrenal glands, each located above one kidney
Adrenal gland divided into how many zones?
Adrenal hormones, epinephrine and norepinephrine, are synthesised in the adrenal medulla, whereas the adrenal steroid hormones are synthesised in the adrenal cortex
Adrenal cortex zones
The adrenal cortex is further subdivided into three zones:
o The inner zone (zona reticularis) which is next to the adrenal medulla
o The zona fasciculata
o The outer zone (zona glomerulosa)
Surrounding all of these zones is connective tissue to protect the organ
What are in each of the individual zones?
In each of the individual zones there are enzymes that synthesise particular classes of steroids
What is the first conversion of the synthesis of a steroid hormone?
Whenever we are synthesising a steroid hormone, the first conversion is always cholesterol to pregnenolone, and this takes place in the mitochondria
Zona glomerulosa
o The enzymes which can covert cholesterol to aldosterone
- Aldosterone acts on the glomeruli of the kidney
o Aldosterone is the principal mineralocorticoid
Zona fasciculate and zona reticularis
o Have the enzymes to synthesise a group of corticoids and small amounts of androgens
o Androgens are produced massively in the testes of males, but both male and females produce small numbers of androgens
Zona fasciculata
- Cholesterol is converted to glucocorticoids of which the principal one Is cortisol
- There is also corticosterone which is an anti-inflammatory drug
- The enzymes are present for the conversions
Zona reticularis
The initial conversion of cholesterol to pregnenolone doesn’t take place in the zona reticularis
o Intermediatory metabolisms, including 17 hydroxyprogesterone and 17 hydroxy pregnenolone is transported into the zona reticularis for further conversion to the androgens