Transcript Sex determination in humans

Male Reproductive Biology
The Testes
• Gamete Development (sperm)
• Hormonal Production (testosterone)
The Sperm’s Journey
• Spermatids released
into lumen of
seminiferous tubules
• Move through tubules
• Stored in Epididymis
The SPERM
genetic material
Head
Enzymes dissolve
egg membrane
Middle piece
microtubules (cilia and flagella) Tail
Seminal vesicles & Prostate gland: Provide seminal fluid
Cowper’s gland: Provide pre-ejaculatory fluid (lubricant)
Erection
• Facilitates penetration
• Occurs when sexually aroused (mostly)
• Mechanism: artery dilation  filling of corpora
VIAGRA:
• Not an aphrodisiac
• Sildenafil increases levels of cGMP which causes
vasodilation of the corpora
• Without sexual arousal, it can not cause an erection
Male Hormonal
Functioning
Male hormonal function
HYPOTHALAMUS
GnRH
PITUITARY
LH
FSH
FSH -> + spermatogenesis
LH -> + testosterone
TESTES
TESTOSTERONE
testosterone -> - GnRH.
Testosterone
• Sperm maturation
• development of penis and testes
• Male secondary sexual characteristics
– Axillary hair,
– larynx,
– oil and sweat gland secretion
• Threshold for sexual activity and libido
• muscle anabolism
• Risk of prostate cancer
Testosterone and Aggression
• Differences in testosterone don’t tell us
about individual differences in levels of
aggression
Individuals with more T not more
aggressive
Effect of Social cues on hormonal
and sexual behavior
The sexually dominant male (bottom) has vivid coloration and special markings.
Female reproductive biology
HYPOTHALAMUS
Menstrual Cycle
Follicular phase
(first half of cycle)
GnRH
ANTERIOR PITUITARY
FSH
LH
OVARY
Follicle
Estrogens
Estrogen effects
• increases progesterone receptor density in
breasts
• Initiates proliferative phase in uterus
• Causes changes in cervical mucous
tangled fibers to line up,
allowing sperm to get
through
cervix closes soon after
ovulation
Copyright © Allyn & Bacon 2004
HYPOTHALAMUS
GnRH
ANTERIOR PITUITARY
FSH
LH
OVARY
Follicle
Corpus Luteum
Progesterone
Estrogens
UTERUS
Endometrium, Cervix, Vagina
Progesterone Effects
• P is secreted by the Corpus Luteum after ovulation
• Increased concentration in breast in luteal phase
– increases tenderness
– increases nipple sensitivity
• Initiates secretory phase of endometrium
– Heavy vascularization
– Secretion of nutrient rich medium for embryonic growth
• Signals the pituitary to stop producing LH
Secretory Phase of Uterus
• No fertilization
– Corpus Luteum regresses after about 12
days
– Progesterone products drops off sharply
– Endometrium sloughs off (menstruation)
• Fertilization
– Corpus luteum remains active
– Progesterone levels remain high  uterine
lining remains strong
– Implantation occurs
– hCG from fetus takes over
• In rabbits, the act of coitus stimulates the pituitary gland
to release gonadotropin which induces ovulation &
increases the probability of pregnancy.
– Organizational effect:
• The effect of a hormone on tissue differentiation and
development.
– Activational effect:
• The effect of a hormone that occurs in the fully developed
organism; may depend on the organism’s prior exposure
to the organizational effects of hormones.
defeminization
masculinization
Pheromone:
A chemical released by one animal that affects the
behavior or physiology of another animal; usually
smelled or tasted.
Vomeronasal organ (VNO):
, mediates the effects of some
pheromones
Lesion to VNO:
female rat fails to recognize male as
such
Behaves as male
This suggests bipotentiality of adult
female brain (male/female)
Copyright © Allyn & Bacon 2004
– Effects of Pheromones
• female animals housed together -> stop estrous cycle
• synchronization of estrous cycle by pheromone in a
male’s urine.
• female animals housed with males -> early onset of
puberty
• Termination of pregnancy when new male other than the
one that impregnated the female.