34.2 Reproductive Processes KEY CONCEPT Human reproductive processes depend on cycles of hormones.

34.2 Reproductive Processes Eggs mature and are released according to hormonal cycles. Follicle-stimulating hormone (FSH) and lutenizing hormone (LH) regulate egg production. –meiosis produces eggs and polar bodies –each egg has 23 chromosomes –meiosis is completed at fertilization potential egg first polar body second polar body ovum (egg) Meiosis I Completed Meiosis II Completed only after sperm enters

34.2 Reproductive Processes FSH, LH, and estrogen stimulate the release of eggs. –follicle ruptures at ovulation –egg travels into fallopian tube –ruptured follicle becomes corpus luteum fallopian tube egg cell egg released corpus luteum uterine wall ovary follicle uterus 5 to 7 days to uterus

34.2 Reproductive Processes Eggs mature and are released according to hormonal cycles. The menstrual cycle has three phases. –flow phase: endometrium sheds –follicular phase: ovulation occurs –luteal phase: corpus luteum forms

34.2 Reproductive Processes The menstrual cycle stops at menopause. –cycle continues until a woman’s mid-40’s or 50’s –decline in hormone levels make cycles irregular –eventually, cycle stops altogether

34.2 Reproductive Processes Sperm production in the testes is controlled by hormones. Testosterone, FSH, and LH stimulate sperm production. –one sex cell divides into four sperm –each sperm has 23 chromosomes potential sperm 4 sperm cells Meiosis I Meiosis II

34.2 Reproductive Processes acrosome head midpiece tail mitochondria nucleus with 23 chromosomes Sperm cells fully mature in the epididymis. –head contains acrosome –midpiece contains ATP –tail allows mobility

34.2 Reproductive Processes Fertilization occurs when a sperm cell joins an egg cell. Sperm penetrates an egg. –membrane keeps out other sperm –nucleus of sperm joins with egg –zygote formed

34.2 Reproductive Processes Multiple zygotes can result from fertilization. –identical twins from the same egg –fraternal twins from two separate eggs Infertility makes reproduction difficult or impossible.