Reproduction Flashcards
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 (at your age) about 10,000 sperm per
second!
• Typically about 108 sperm / ml of semen.
Mitotic proliferation takes place in the basal side of
the tubule (the side furthest from the lumen).
hormonal inputs of spermatogenisis
hypothalmus secreted GnRH acting on anterior pituitary which secretes FSH and LH. FSH acts on sertoli cells that stimulate spermatogenisis and inhibit further GnRH secretion. LH acts on leydig cells which secrete testosterone that acts on sertoli cells and reproductive tract organs as well as inhibiting further GnRH release
Maturation of sperm
Sperm are shed and flow to the epididymis The epididymis alters the seminal fluid Epididymal secretions (glycoproteins etc) activate sperm and make them capable of swimming
UNLIKE men, adult women have no germ line stem cells
Mitosis to bulk up numbers • Entrance into meiosis • Pause (for 12-50 years) • Completion of meiosis Rate of female gamete production – 13/yr
At puberty, the pituitary produces
Follicle Stimulating Hormone (FSH)
In response to this, some follicles resume development (each month, a surge in FSH causes about 50 more to do so, throughout the woman’s reproductive life).
Primary follicle
During this phase (about 85 days), oocyte grows and
synthesises rRNA and mRNA. It does not progress further
through meiosis
Ripening follicle
During this phase (10 days), the oocyte synthesises a
glycoprotein zona pellucida, and granulosa cells multiply. Next, granlulosa cells
secrete follicular fluid
that form the fluid-filled
“antrum
At a critical stage of the cycle, the developing follicle
depends on receiving a surge of LH from the pituitary
gland; (Thecal cells bind it)
If it does not receive this, it dies.
If it does receive it, it matures further to become a Graafian
follicle at the surface of the ovary
Maturing Follicle
“antral stage”
following LH surge
primary oocyte completes meiosis 1 and forms a polar body and secondary oocyte that is arrested in meiosis 2
Meiosis II is never completed unless
fertilization happens
The remains of the ruptured follicle
become the corpus luteum
The Corpus luteum produces hormones (progesterone, oestrogen) that prepares the lining of the uterus to receive an embryo Unless the woman is pregnant, the CL dies after a week or so.
fertility drugs
Exogenous FSH, or drugs that block oestrogen detection and thus drive higher production of endogenous FSH, can stimulate oogenesis
Capacitation
Glycoprotein and sterol coat acquired in epididymis is
removed by proteases in the uterine/ cervical fluid.
• This causes the cell membrane to become more
permeable to calcium ions
• These (indirectly, via cAMP) activate strong tail
lashing and make the acrosome reaction possible
later.
When sperm meet the Zona Pellucida of the egg,
they undergo an Acrosome Reaction
Acrosome membrane and plasma membrane fuse at many points Acrosomal contents spill out and can digest the zona pellucida Fusion causes a wave of calcium entry, which keeps repeating. Calcium waves have two effects; 1 – cortical granules are released; these alter the ZP and make it impenetrable by sperm (and also block fusion) 2 - Meiosis of the oocyte resumes
Assisted fertilizatio
Blocked/ absent oviducts (pelvic inflammatory disease – Chlamydia or
Gonorrhoea often damage oviducts; also congenital absence,
endometriosis of earlier elective tubal ligation).
Blocked vasa deferentia/ eferentia; impotence; low male fertility
Female age
ICSI
Intra-Cytoplasmic Sperm Injection
“Cleavage”
mitosis with no growth
At the 4 cell stage
mRNA synthesis from embryo’s own DNA
begins
maternal mRNA is destroyed at an
increasing rate.
2 cell stage, 4 cell stage, morula
morula cell mass trophectoderm Cells on the inside have contact all round. Cells on the outside have a free surface. This is the first difference, and the embryo uses it.
throphoblast
becomes placenta
balstocyst
hatches through zona pellucida
Implantation
the trophoblast
of the hatched blastocyst
invades the uterine epithelium
All of the cells that make your body
now came from your Inner Cell Mass
Monozygotic Twinning (1)
cells separate inside Z.P.
Monozygotic Twinning (2)
Two Inner Cell Masses form - Danger of foetal
transfusion syndrome
(‘twin-to-twin transfusion
syndrome)
epiblast at top then hypoblast beneath
cels at the centre make hex, hex expressing cells move out to tim and congregate at one point. the hex cells release a protein that inhibits progress in epiblast, the cells in epiblast far enough away from hex begin making the tail end of the primitive streak, primitive streak then extends along epipblast and forms a node.
Monozygotic Twinning (3)
Two Primitive Streaks form
partial axis duplications
conjoined twins
Gastrulation
the node on epiblast has formed. epiblast invaginates to form endoderm some cells touch hypoblast and then rise to form notochord
the cns tube
derives from the ectoderm CNS formation begins when the
ectoderm along the dorsal surface
folds inwards, driven by local cell
shape changes along three stripes;
neural tube forms above notochord
Much later, cells in the neural tube send out processes to each other and to other structures in the body. Bundles of such processes are nerves, and together the processes and the cells make the nervous system
he sealing up of the edges of the tube, and its separation from the
ectoderm, sometimes fails:
Anencephaly (the inside of the brain is open to
the back of the head: this stops brain growth so
the upper-back head is effectively missing.
Incompatible with post-natal life).
Spina bifida (a very serious case)
Orofacial cleft
It is treatable surgically
Hypospadias
urethra not at end of penis
h gigantism
Pituitary tumours are associated with gigantism
Growth hormone
e itself affects post-natal
muscle growth directly, but other
tissues only indirectly.
Limb growth is therefore uniquely vulnerable to anything that
impairs vascular growth
Limb growth has a peculiar vulnerability: it takes place very
rapidly, and makes high demands for oxygen.
It therefore needs the vascular system to grow very quickly into
the elongating limbs
Phocomelia
It is now known that thalidomide slows
blood vessel growth (it kills developing
blood vessels).
This makes it a valuable anti-cancer drug,
but one
That can only be used safely where there is
no risk of pregnancy.
Achondroplasia
activating mutation in FGFR3
FGF signalling via FGFR3 usually inhibits
both proliferation and differentiation of
chondrocytes
Activating mutations in FGFR3 cause
growth plates full of chondrocytes, and
premature closure of the growth plates.
Your gonads developed in the
trunk of your body, about half
way between shoulder and
pelvis (whatever sex you are).
The germ line comes from epiblast cells that were
removed from the body around the time of gastrulation.
It therefore ends up outside the body, in the yolk sac.
The yolk sac has a connection to the gut (endoderm)
The primordial germ cells use this connection, and the gut and its
mesentery, as a way to invade the body;
SRY)
A gene on the Y chromosome (SRY)
determines sex;
Primitive gonads consist of somatic cells and germ
line cells
• Somatic cells express SRY (if it is present)
• SRY forces somatic cells to develop into testis
cells (otherwise they form ovary cells).
Complete
Androgen
insensitivity
this person is
XY
guevedoces’
XY children with deficient 5α-reductase
(‘guevedoces’) therefore make female bodies:
Testosterone itself is a relatively weak
androgen
• Testes secrete testosterone. This stimulates
androgen receptors only weakly
• Tissues - 5α-reductase converts it to 5αdihydrotestosterone
5α-dihydrotestosterone stimulates androgen receptors
strongly
Testosterone rises at puberty
Foetus infant adolescent
This is high enough to act as
an androgen even in the
absence of 5α-reductase
