Gametogenesis - Oogenesis and Spermatogenesis Flashcards
where do the oocytes and sperm come from?
derived from a group of specialised cells called primordial germ cells
when can the cells begin to be identified in the embryo?
4 to 6 weeks of gestation so after gastrulation has occurred and its these primordial germ cells that are going tp migrate through the embryo to find their new homes in the developing gonads to create oocytes and sperm
what are primordial germ cells?
-undergo lots of mitotic division within the gonads to populate testes and ovary with cells required to make gametes
-the cells are diploid
-they enter into meiosis to generate haploid gametes capable of fertilisation
when are the gonads present in the embryo?
around week 7 of development
what are the starting cells known as for oogenesis?
oogonia
where are oogonia produced?
by PGC’s dividing by mitosis, they begin meiosis but only get to the point of prophase 1
what happens when oogonia start meiosis?
they enter into the first meiotic prophase and then become arrested. meiosis halts at this stage and they lie dormant.
-they only get to the point of prophase 1 and then become arrested and remain in the developing ovary
what causes the arrest of oocytes in the first meiotic prophase?
-lack of right type of cell cycle proteins at early stages
-cyclic AMP and cyclic GMP have an important role
how long are primary oocytes arrested for?
until puberty but can be arrested for up to 50 years
what makes up the primordial follicle?
supporting cells (follicular cells)
primary oocyte
what are follicular cells?
epithelial cells that surround the developing follicle
when should the primary follicle stage be reached?
about 5 months of fetal development
7 million primary follicles present
how many primordial follicles resume development each month after puberty?
between 5 and 12
what is follicular atresia?
degeneration of these follicular cells
when is it called a secondary oocyte?
when it completes meiosis 1
what happens to the follicular cells in response to hormone stimulation?
they thicken up and divide, help support developing oocyte
when is the oocyte arrested for the second time?
metaphase 2
as only 1/4 daughter cells will develop into a mature oocyte, what are the other cells known as?
polar bodies
what are polar bodies?
much smaller
really only contain nuclear material
oocyte keeps most of it
when does meiosis 2 occur?
if it is fertilised
what happens during the second mitotic division of an oocyte?
will give rise to fertilised egg and another polar body which will degenerate
which types of cells are thought to be partially responsible for some cases of teratoma?
primordial germ cells (PGC’s)
which area of a testes does spermatogenesis take place?
seminiferous epithelium
what are spermatogonia?
the stem cell population of the tesis
immature cells that don’t do much until puberty
divide to populate testis
what is the dominant hormone in the testes at puberty?
testosterone
what does testosterone have a major influence on?
seminiferous epithelial epithelium
what do the spermatogonia divide into?
type A and type B
what do type B spermatogonia produce?
produce the sperm
what are type A spermatogonia?
identical spermatogonia
keep the starting material going by mitotic division
what does mitotic division of type B spermatocyte produce?
a primary spermatocyte
round cell again that is haploid
what type of spermatogonia enters meiosis?
primary spermatocyte
what happens during meiosis 1 in sperm?
primary spermatocyte turn into secondary spermatocyte that are diploid sperm
what happens during meiosis 2 in sperm?
secondary spermatocytes form 4 identical spermatids
spermatids are haploid and go on to form cells
what are the supporting cells of spermatogenesis?
Sertoli cells
leydig cells
pertibular cells
what is spermiogenesis?
differentiation to the final form
change to the structure
what are the stages of spermiogenesis?
formation of acrosome
condense nucelar material into the head of the sperm
flagellum formation
what is an acrosome?
a little hat or cap that forms over the top of the nucleus contains enzyme that helps the sperm penetrate the oocyte at fertilisation
what is the function of the mid piece of sperm?
mainly contain mitochondria to help power the movement of sperm through the reproductive tract
what cells phagocytose the cytoplasm that is removed from the sperm?
sartori cells
how many mature oocytes are produced in life?
around 400
in which stage of meiosis arrested in the primary oocyte?
prophase 1
how many polar bodies are formed in oogenesis?
three
