11.4 - Sexual Reproduction Flashcards
Spermatogenesis
- production of sperm in the testis after puberty in seminiferus tubules
- spermatogonium produce more from mitosis of germinal epithelium cells on the outside layer of seminiferous tubules
- primary spermatocyte derive from the growth of spermatogonium
- 2 secondary spermatocytes derive from the first division of meiosis of primary spermatocyte
- 4 spermatids derive from the second division of meiosis of secondary spermatocytes
- spermatozoa derives from the differenciation of spermatids after association with sertoli nurse cell (tail and acrosome)
oogenesis
- production of eggs in the ovaries starting before birth stopping, then continuing after puberty
- oogonium produced from the mitosis of germ cells and halts at meiosis 1 (prophase) until puberty
- primary oocytes develop from oogonium after puberty
- 1 secondary oocyte and polar body derive from meiosis 1 of primary oocyte
- secondary oocyte starts meiosis 2 in as primary follicle develops into secondary follicle
- egg is released from mature follicle during ovulation
- 1 egg haploid and polar body derived from the completion of meiosis 2 of secondary oocyte after fertilization occurs
- only 1 egg and 2 polar bodies are produced due to unequal distribution of cytoplasm, egg needs enough resources to support fetus
Fertilization and polyspermy
the union of a single sperm and egg cell to form a zygote preventing polyspermy once the first sperm binds to the zona pellucida of the egg
Acrosome reaction:
- acrosome releases enzymes to digest zona pellucida
- the membrane at the tip of the sperm becomes exposed to the egg membrane
Penetration of egg membrane:
- membrane proteins of the sperm bind to the egg membrane fusing together allowing the sperm nucleus enters egg (fertilization)
Cortical reaction:
- Entry of sperm causes the egg to activate cortical granules
- release enzymes by exocytosis
- digest membrane binding proteins (no other sperm can bind)
- harden zona pellucida
internal and external fertilization
External fertilization: gametes are released and fertilizaed outside the body (eg: aquatic animals)
Risks:
- Predation of unprotected developing embryo
- Exposed to environmental variation (temperature, pH fluctuations, pollution)
Internal fertilization: gametes are fertilized inside the body
Benefits:
- Optimal conditions maintained (moisture, pH, temp)
- Prolonged close proximity of sperm and ova
- Developing embryo is protected inside the female
Implantation of blastocyte
ball of embryonic cells move from oviduct to implant into the endometrium of the uterus to receive an external supply of resources from mothers blood to continue development of embryo during pregnancy
HCG (human chronic gonadotropin)
hormone that stimulates corpus lumen to continue to secrete estrogen and progesterone to maintain endometrium wall for the continued development of embryo during pregnancy
Placenta
fetal tissue that develops to facilitate exchange between fetal and maternal blood
- continues secretion of estrogen and progesterone when corpus breaks down
- placental villi circulates fetal blood in capillaries surrounded by maternal blood in intervilli space separated by a selectively permeable plancental barrier
- glucose: mother -> fetus by facilitated diffusion
- waster: mother fetus by osmosis
- antibodies: mother -> fetus by endocytosis
- urea: fetus -> mother
- oxygen: mother -> fetus by diffusion
- CO2: fetus -> mother by diffusion
Amniotic sac
contains amniotic fluid to protect fetus
birth (oxytocin and estrogen)
oxytocin is a hormone secreted by pituitary gland that stimulates the contraction of the myometrium (muscular outer wall of uterus)
at the end of pregnancy:
- progesterone stops secretion, which usually inhibits secretion of oxytocin
- secretion of oxytocin stimulates contraction of myometrium
- stretch receptors detects contractions and signal more secretion of oxytocin
- positive feedback loop
- contractions break amniotic sac and pushes birth of fetus
contraceptive pill
intake of high levels of estrogen to inhibit secretion of FSH to stimulate the maturation of follicles
Altricial and precocial species
altricial species gives birth to underdevelopped offspring
precocial species gives birth to developed offspring
- positive correlation between size of organism and gestation period (more likely to be precocial)
Sperm diagram
head:
- acrosome: releases enzymes to digest zona pellucida
- haploid nucleus: contains genes
- plasma membrane throughout: receptors for directional swimming
- centriole
mid-piece:
- helical mitochondria: energy for swimming
tail:
- protein fibres: strengthen tail
egg diagram
- follicular cells: secrete progesterone and estrogen
- zona pellucida: glycoproteins surrounding to protect egg
- plasma membrane: fuses with sperm for fertilization
- cortical granules: secretes enzymes (cortical reaction)
- cytoplasm: fat droplets
- habploid nucleus
- 2 centrioles
