Embryology 1 - Gametogenesis Flashcards
deck complete
a working definition of ‘sex’
blending genetic characteristics of two individuals of the n^th generation to create the (n+1)^th generation
disadvantages of sex
need to find a partner
dilution of a ‘perfect’ set of genes
advantages of sex
each individual has a new mix of genes that give it immunity to pathogens - the red queen syndrome
each individual has a new mix of genes that determine its environmental interactions
female gametes
not many, large gametes - ova
provide nurture - yolk, placenta, milk
male gametes
many small gametes - spermatozoa
provides nurture behaviourally or not at all
general strategy of sexual reproduction
single gametes fuse to form a single cell which then divides many times
germ line
produce gametes
somatic cells
produce everything other than gametes
what does myoid mean
muscle like
spermatogonia
stem cells
some differentiate into spermatocytes which differentiate into sperm cells
sertoli cells
provide metabolic support
spermatogenesis
proliferation of germ line stem cells by mitosis
reduction to haploid state by meiosis
differentiation into mature spermatozoa
mitotic proliferation
begins at puberty
produces about 10,000 sperm per second
typically about 10^8 sperm/ml of semen
where does mitotic proliferation take place
in the basal side of the tubule - the side furthest from the lumen
what does the hypothalamus secrete for mitotic proliferation
gonadotrophin releasing hormone - GnRH
what does the anterior pituitary gland secrete for mitotic proliferation
follicle stimulating hormone (FSH) and luteinising hormone (LH)
what does FSH act on
sertoli cells
what does LH act on
leydig’s cells
what does testosterone act on
sertoli cells
what would an immune response against sperm result in
subfertility
when does sperm production begin
at puberty
what prevents sperm cells reaching immune system
immune cells on luminal side
continuous tight junctions
orch-
prefix for testis
e.g. orchidectomy, cryporchidism
named after orchid
maturation of sperm
sperm are shed and flow to epididymis (by moving passively along tubules) which alters seminal fluid
epididymal secretions (glycoproteins etc) activate sperm and make them capable of swimming
features of the female reproductive system
uterus
vagina
oviduct = fallopian tube
ovary
cervix uteri
when do females have germ line stem cells
as foetuses but not as children or adults
rate of female gamete production
13 per year
rate of male gamete production
150 billion per year
what are primordial follicles
oocytes surrounded by less differentiated squamous granulosa cells and are derived from oocyte nests
what are primary follicles
oocytes surrounded by a single layer of cuboidal granulosa cells that have initiated follicle development
what type of cells are granulosa cells
somatic cells
when does the pituitary gland start producing FSH
puberty
what is stimulated by FSH
some follicles resume development
a surge each month promotes development in around 50 or more follicles
what happens during the primary follicle phase
oocyte grows and synthesises rRNA and mRNA. does not progress further through meiosis
what is a ripening follicle
results in an increase in oestrogen levels, as oestrogen is secreted by follicular cells
what happens during the ripening follicle phase
oocyte synthesises a glycoprotein zona pellucida, and granulosa cells multiply
what are granulosa cells linked by
cytoplasmic bridges
what do granulosa cells secrete
follicular fluid - forms fluid-filled ‘antrum’
what does the developing follicle depend on
receiving a surge of LH from pituitary gland
thecal cells bind LH. cells dies without LH surge
what does the LH surge stimulate
further maturation of the follicle to become a Graafian follicle at the surface of the ovary
what kind of process is follicle death
an active process - will destroy itself
what does atretic mean
dying follicle
from ‘atresia’ - withering
process of preovulatory growth following LH surge
primary oocyte > completion of meiosis 1 > secondary oocyte > arrest in meiosis 2 > connection with granulosa lost
takes about 12 hours
what happens once oocyte is mature
digests way out of edge of ovary and enters fallopian tube
when is meiosis 2 complete
never unless fertilisation occurs
what do the remains of the ruptured follicle become
the corpus luteum - looks yellow
what does the corpus luteum do
produces hormones - progesterone, oestrogen - that prepare the lining of the uterus to receive an embryo
unless woman is pregnant, the CL dies after around a week
what is the early antral stage
a ‘make or break’ time for each follicle
survival depends on adequate stimulation by FSH
what happens if the antral follicle does not receive enough FSH
the follicle matures further to become a Graafian follicle at the surface of the ovary
becomes more sensitive to FSH, makes a signal back to pituitary gland with oestrogen to reduce FSH levels
what do falling FSH levels prevent
recruitment of further follicles in that cycle - dominant follicle has increased sensitivity so still has enough FSH stimulation even with lower serum levels
how many follicles usually mature
one
what do oestrogen detection blocking drugs do
drive higher and longer duration production of endogenous FSH, and more follicles mature
what does FSH ultimately do
prevents atresia at critical stage
what does LH ultimately do
drives ovulation and maintains corpus luteum
