Biomedical Engineering Reference
In-Depth Information
•
promoting sperm cell synthesis;
•
promoting development and maintenance of male secondary sexual characteristics at/after
puberty;
•
general growth-promoting effects;
•
behavioural effects (e.g. male aggressiveness, etc.);
•
regulation of serum gonadotrophin levels.
The follicular granulosa cells are the major site of synthesis of female steroid sex hormones:
the oestrogens.
-Oestradiol represents the principal female follicular oestrogen. Oestriol is
produced by the placenta of pregnant females. Oestriol and oestrone are also produced in small
quantities as products of
β
-oestradiol metabolism.
Testosterone represents the immediate precursor of the oestrogens, the conversion being
catalysed by the aromatase complex, i.e. a microsomal enzyme system. The biological actions
of oestrogens may be summarized as:
β
•
growth and maturation of the female reproductive system;
•
maintenance of reproductive capacity;
•
development and maintenance of female secondary sexual characteristics;
•
female behavioural effects;
•
complex effects upon lipid metabolism and distribution of body fat;
•
regulation of bone metabolism (oestrogen defi ciency promotes bone decalcifi cation, as seen
in postmenopausal osteoporosis).
family of proteins. The inhibins are heterodimers consisting of
α
- and
β
-polypeptide subunits. Ac-
tivins are
ββ
dimers. The mature form of the
α
-subunit is termed
α
c
, and it consists of 134 amino
acid residues. Two closely related (but structurally distinct)
β
-subunit forms have been character-
β
B
. These exhibit in excess of 70 per cent amino acid homology and differ in size by
only a single amino acid. The naming and polypeptide composition of the inhibin/activin family
may be summarized as follows:
ized:
β
A
and
•
inhibin A
α
c
β
A
•
inhibin B
α
c
β
B
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