Reproduction and development

1
Reproduction and development Gametes are formed
by meiosis A zygote is formed by
fertilization Humans have 23 pairs of
chromosomes 22 pairs of autosomal
chrmosomes sex chromosomes female has 2 X
chromosomes male has one X and one Y Y
determines maleness
2
(No Transcript)
3
TDF is the product of the SRY gene on the
Y chromosome Testes develop much more rapidly
than ovaries (7 weeks vs. 15 weeks) TDF
initiates a sequence of events that leads to the
formation of testes and male external genitalia
4
(No Transcript)
5
Disorders of embryonic sexual development Hermaph
roditism- both ovarian and testicular tissue Pse
udohermaphroditism congenital adrenal
hyperplasia testicular feminization
6
(No Transcript)
7
Puberty Gonadotropin secretion stays low until
puberty GnRH secretion increases (by
hypothalamus) sex steroids become less
suppressive Pulsatile secretion of FSH and
LH testosterone in males estradiol in
females Melatonin may inhibit gonadotropin
secretion (inhibited by light)
8
Male reproductive system Testes seminiferous
tubules Sertoli cells stimulated by
FSH spermatogenesis Leydig cells- interstitial
tissue stimulated by LH secrete testosterone
9
(No Transcript)
10
(No Transcript)
11
Functions of androgens in males (and
estradiol?) Sex determination (in
fetus) Spermatogenesis Secondary sexual
development Body growth
12
(No Transcript)
13
(No Transcript)
14
Spermatogenesis begins in embryo arrested at
prophase I testosterone required to complete it
secretion increases at puberty afterward FSH
required for later stages of spermatogenesis Spe
rmatozoa released into the lumen are not motile
must continue to mature in the epididymis
15
(No Transcript)
16
Male fertility Below 20 million sperm per ml is
low Causes can be transient or permanent Male
contraception vasectomy male pill interfere
with hormone secretion or sperm
formation anti-sperm antibodies
17
(No Transcript)
18
Oogenesis begins early in development
all primary oogonia are produced within first 5
months of development Primary oocytes are
arrested at prophase I Number of oocytes
declines from 2 million at birth by 80 at onset
of puberty Only a few hundred will ever ovulate
19
(No Transcript)
20
Menstrual cycle Follicular phase- from first day
until ovulation Luteal phase afterward Endometri
um (uterine lining) menstrual- loss of
lining proliferative- estradiol
stimulates growth of lining, also
progesterone receptors secretory- progesterone
stimulates uterine secretion menstruation
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
Birth control pills Synthetic estrogen and
progesterone prevent gonadotropin
secretion ovulation never occurs