The Continuity of Life:

Reproduction

Chapter 46Campbell & 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

– 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”