Reproduction

Why Sexual Reproduction? Combines traits from two genetically distinct parents = unique genetic mix Variation in species is booted through independent assortment and crossing over during meiosis

Strategies External fertilization: More gametes produced, higher probability for fertilization Amphibians = male discharges sperm directly onto the eggs Watery environments necessary

Internal fertilization: Local aquatic environment can be maintained Selective advantage – improves odds of gametes meeting Hence, typically less gametes produced

Human reproduction Both sexes produce gametes Male = spermatozoa (sperm) Female = Ova (eggs) Female also responsible for providing environment in which zygote can develop fully Reproduction regulated by hormones

Males External: Penis Scrotum – temperature within is several degrees cooler than rest of body; necessary for the formation of sperm If testes do not descend during fetal development – sterility will occur due to high temperatures

Males - Inside Urethra – shares two jobs: Conveys sperm during periods of sexual excitement and/or ejaculation Excretion of urine

Formation of Sperm Testis composed of entirely tubular elements – seminiferous tubules (length 7x length of football field) Within occurs the formation of the sperm Between are endocrine cells responsible for production of testoterone

Sperm formation Spermatids (immature sperm cells) must make it to the epididymis (tubule, 20 feet long) coiled within the testes to mature After several weeks, move onto the vas deferens – tubule that transports the male gametes to the urethra

Male Accessory Glands Before release from the penis, sperm are mixed with secretions to form semen from: Cowper’s glands, prostate gland, seminal vesicles Secretion is rich in fructose, prostaglandins Provides food for mitochondria of sperm to produce ATP, protection in an acidic environment, liquid medium for mobility Sperm make up a small percentage of volume – 5 billion sperm into a space size of aspirin tablet

Females Oogenesis occurs in the Ovaries External Genitalia Collectively known as vulva Labia majora, labia minora and clitoris Clitoris sole function is to receive sexual stimulation Vagina: channel that receives sperm and forms the birth canal – leads to internal organs of reproductive system

Female -- Internally Vagina is separated from the uterus by the cervix – contains opening thru which sperm must travel to fertilize Uterus (womb) – pear shaped, thick walled chamber that houses embryo and fetus during pregnancy Oviducts (fallopian tubules) serve as sites where sperm and egg become united during fertilization

Formation of eggs Oocytes (germ cells for eggs) housed within the follicles which are scattered throughout the tissue of the ovary Oocytes remain in suspended meiotic division until needed (released) Human pair of ovaries contain approx. 400,000 “primordial” oocytes Only a few will undergo oogenesis during the ovarian cycle

Ovulation When the wall of the follicle suddenly ruptures, the egg is released and swept into the broad, funnel shaped opening of the oviduct

Hormones – In due time Infant and childhood Males = testes must descend Puberty: Males = testosterone stimulates the maturing development of the reproductive tract and penis Secondary sex characteristics = facial and chest hair, enlargment of the larynx, increased muscle mass Into adulthood = testosterone plays a role in development and maintenance of libido (desire)

Hormones – in due time Females: increased estrogen levels during puberty: Maturation of external genitals Secondary sex characteristics: Enlargment of breasts Growth of body hair Maturation of uterine tissue Ovary begins to produce mature ova on a cyclic basis

Menopause:cessation of female reproductive cycle Typically occurs in late forties Due to a drop in GnRH hormone

On Your Own Red books – List the various methods of contraceptives p 677 – 681 STD’s – Chapter 36 – we’ve already covered this – p