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 glandslubricants
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”