11.4 Flashcards
compare spermatogenesis with oogenesis
seminiferous tubules structure and function
interstitial cells: located b/w seminiferous tubules and secrete testosterone
germinal epithelium cells: divide by mitosis to produce spermatogonia (diploid 2n)
sertoli cells: nourish supernatural during their development
spermatozoa: formed by meiosis located near lumen of seminiferous tubule
spermatogenesis
- germinal epithelial cells divide by mitosis to produce spermatogonia (2n)
- spermatogonia grow to develop into primary spermatocytes (2n)
- primary spermatocytes divide by meiosis to produce secondary spermatocytes (n)
- secondary spermatocytes divide by meiosis 2 to produce spermatids (n)
- spermatids differentiates into spermatozoa (n)
diagram of mature sperm cell
oogenesis
- germinal epithelium cells divide by mitosis to form oogonia which grow to form oocytes (2n)
- each oocyte is surrounded by follicle cells to form a primary oocyte
- once a month b/w puberty and menopause the primary follicle enlarges and the oocyte undergoes meiosis 2 to form a secondary oocyte & polar body
- the second meiosis division stops during prophase and the follicle bursts open = oocyte is released (ovulation)
- the empty follicle degenerates into a corpus luteum which secrets progesterone and oestrogen if fertilisation does not occur
fertilisation in humans
- is internal and is the fusion of male and female gametes to form a zygote
acrosome reaction:
- spermatids cells break through the layers of follicle cells of the egg and fuse with the zone pellucida underneath which triggers the acrosome reaction
- enzymes released by the acrosome digest a path through the zona pellucida to reach the plasma membrane
penetration of egg cell membrane:
- the first sperm cell that gets through the zona pellucida binds to the plasma membrane and the speed and egg cell membrane fuse together
- the sperm nucleus enters the eggs cell (fertilisation moment)
cortical reaction:
- penetration of sperm into the egg cell triggers cortical reaction
- small vesicles called cortical granules move towards the plasma membrane and fuse with it releasing their contents by exocytosis
- enzymes released by cortical granules cause cross linking of glycoproteins in the zona pellucida which hardens it and prevent polyspermy
internal vs external fertilisation
structure of a blastocyst
- outer layer called trophoblast which develops into the placenta
- inner cell mass which develops into the embryo
- fluid filled cavity called blastocoele
why is implantation of blastocyst vital for continuation of pregnancy
- implantation protects and nourishes developing embryo
- the blastocyst grows finger like projections into the endometrium which develops into feral part of placenta
- causes secretion of hcG (human chorionic gonadotropin) which stimulates the ovary to secrete progesterone to prevent degeneration of corpus luteum AND progesterone maintains endometrium
how is the structure of the placenta adapted for its function
- maternal blood pools via open ended arterioles into intervillous spaces called lacunae
- blood from fetus is transported to chorionic villi via umbilical artery
- chorionic villus extend into pools of maternal blood in lacunae and are lined with microvilli to increase SA for exchange
- fetal capillaries lie close to the surface to minimise diffusion distance
- materials exchanged are transported to fetus via fetal vein in umbilical cord which also maintains conc grad for diffusion
exchange of materials across placenta
birth
- is a positive feedback loop
contractions of uterus wall pushes baby’s head into the cervix
cervix is stretched by baby’s head
stretch receptors are stimulates and sends signal to the brain
causes pituitary gland to release oxytocin
oxytocin stimulates muscle contraction of uterus wall
birth breaks feedback loop
