Genitourinary System

Part 2

Spermatogenesis• The production of spermatozoa

• Produced in the testis:

Seminiferous Tubules Micrograph

Stages of Spermatogenesis

Oogenesis – the production of an ovum

Ovary cross sectional micrograph

Stages of Oogenesis

Gametes• Human Sperm – structure

Hormonal Control of Spermatogenesis

Semen Production

• 3 main structures play a role

• Epididymis – storage/holding area where sperm mature and become fully motile

• Seminal vesicle and prostate gland – produce, store and expel fluid during ejaculation– Fluid mixes with sperm to increase volume of

ejaculate; s.v. fluid contains nutrients (including fructose) and mucus (protection);

– Fluid from p.g. contains mineral ions, and is alkaline (protection)

Human Egg – structure: (n) nucleus; corona radiata; cortical granules;

diameter 100um (1/10th mm)

Spermatogenesis vs. oogenesis

• Guys• Millions daily• Released during

ejaculation• Starts during puberty• Production continues

throughout adult life• Four functional gametes

per meiosis

• Girls• 1/28 days• Released via ovulation

• Starts prenatally• Stops at menopause

• 1 functional gamete per meiosis

Fertilization

Stages of Fertilization

Stages of Early embryological Development

Development of the Fetus

Development of Fetus cont’d• By 8 weeks of development, bone and tissue

start to develop, embryo now referred to as a fetus.

• Placenta and umbilical cord develop

Development of Fetus: Placenta cont’d

• Site of nutrient and gas exchange

• No mixing of maternal and fetal blood

Amniotic Sac and Fluid• Support and protection

• Basis for amniocentesis

Hormonal Control of Pregnancy

• Estrogen and progesterone – needed to stimulate the development of uterine lining throughout pregnancy.

• Secreted by corpus luteum (c.l.) for first week following fertilization

• Following implantation embryo secretes HCG = prevents degeneration of c.l. = continued secretion of est. and progest.

• C.l. degenerates middle of term, placental cells now produce est. and progest. Until end of pregnancy

Childbirth

Childbirth cont’d

• End of pregnancy signalled by fall in progesterone level

• Oxytocin begins being secreted = stimulates smooth muscle (uterus) contraction

• Positive feedback loop