The Continuity of Life: Reproduction  Chapter 46 Campbell & Reece

Sexual reproduction Involves 2 events: Meiosis + Fertilization Meiosis produces Haploid (1/2 Chromosomes) Gametes, specialized for: 1) Motility (sperm) 2) Nutrient storage (eggs) Fertilization unites haploid gametes from two individuals Restores diploid in offspring New combinations of genes in offspring = unique

The Male Reproductive System Testes: sperm and testosterone production Epididymus: sperm maturation (~18 hrs.); motility Vas Deferens: storage, Leads sperm from scrotum into abdominal cavity, thru glands, and around bladder Glands: add seminal fluids Cowper's Gland Prostate- add fructose (carbohydrate) Seminal vesicles- add alkaline fluids (semen) Urethra Penis bulbourethral glands-lubricants

In the Testes: Spermatogenesis each testis is divided into about 250 compartments, each packed with coiled seminiferous tubules which produce the sperm cells. Interstitial cells (between the tubules secrete testosterone) Semeniferous tubules contain 2 types of cells: 1) Spermatogenic (sperm-producing) cells: 2) Sertoli cells (nourish & support developing cells)

1st stage: "spermatogonia" (diploid): proliferate continuously by mitosis--> some differentiate into --> 2nd stage: "Primary Spermatocytes" => 1st meiotic division (Now Haploid) 3rd stage: "secondary spermatocytes" => 2nd meiotic division 4th stage: "spermatids“, mature into"spermatozoa" (sperm cell)

Sperm diagram Tail Neck Head axial filament Mitochondria (in sheath) Nucleus Acrosome (contains enzymes to penetrate egge membrane) Axial filament contains 9+2 array of microtubules (typical of cilia and flagella)

Ejaculation a. Erection of the Penis b. Ejaculation erectile tissues: 2 Corpus Cavernosa 1 Corpus Spongiosum fill with blood b. Ejaculation Mechanoreceptor stimulation causes reflexive nerve arc to smooth muscles which propels semen thru tract, up vas deferens, into urethra. 3-4 ml per ejaculation; only 10% is actually sperm cells (300-400 billion)

The Role of Hormones in the Male Androgens-produced in testes and adrenal cortex Testosterone- sperm production secondary sex characteristics aggression Under control of Secretion from Pituitary: LH -> testosterone FSH -> acts on Sertoli cells

The Female Reproductive System 2 ovaries (3 cm each) Outer layers form oocytes (immature egg cells) 2 oviducts (Fallopian tubes) Uterus Cervix Vagina outer stuctures: labia, clitoris

primary oocytes already forming in fetal female; reach prophase of 1st meiotic division secondary oocytes continue meiosis at sexual maturity + polar body ("extra" cytoplasm-not fertile) grow, mature ovulation (released from ovary) produces 2nd meiotic division (occurs after fertilization) = OVUM and one additional polar body

Ovulation Oocytes develop near surface of ovary and are surrounded by special cells Called "ovarian follicle“, comprised of oocyte, follicular cells During ovulation, the follicle ruptures and releases the 2nd degree oocyte Follicle secretes Estrogens (grows Endometrium) The follicle then enlarges and forms the Corpus Luteum "yellow body" which increases levels of progesterone to maintain pregnancy.

Fertilization Secondary oocyte (egg) is "swept" into fallopian tubes by cilia. Then, egg is propelled by waves of muscle contractions down the oviducts. Oocyte breaks down after 72 hours. Fertilization takes place in oviducts The fertilized egg will reach uterus in 3 days.

Female Hormonal Controls Controlled by Hypothalamus GnRH, which triggers pituitary… Pituitary Gland—releases-->LH, FSH which triggers… Ovaries----> Estrogens + Progesterone Under "feedback control system”