34 2 Reproductive Processes KEY CONCEPT Human reproductive

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 Meiosis I Completed first polar body Meiosis II Completed only after sperm enters second polar body ovum (egg)

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 uterus 5 to 7 days to uterus follicle egg cell egg released ovary uterine wall corpus luteum

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 Meiosis II 4 sperm cells

34. 2 Reproductive Processes • Sperm cells fully mature in the epididymis. – head contains acrosome – midpiece contains ATP acrosome – tail allows mobility nucleus with 23 chromosomes head mitochondria midpiece tail

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.

34. 2 Reproductive Processes Sexually transmitted diseases affect fertility and overall health. • Sexually transmitted diseases (STDs) are passed from one person to another during sexual contact. – bacterial STDs include chlamydia, syphilis, gonorrhea – viral STDs include hepatitis B, genital herpes, human papillomavirus, and HIV

34. 2 Reproductive Processes • Bacterial STDs can be treated, and in many cases, cured with antibiotics • Viral STDs can be treated, but there is no cure for these diseases. • STDs attack reproductive organs. – can cause infertility – untreated, some can be fatal • STDs can be avoided by A parasite causes trichomoniasis, which can abstinence or by using a affect fertility. condom.