Reproduction

Question 1

Spermatogenesis

Answer 1

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).

Question 2

hormonal inputs of spermatogenisis

Answer 2

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

Question 3

Maturation of sperm

Answer 3

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

Question 4

UNLIKE men, adult women have no germ line stem cells

Answer 4

Mitosis to bulk up numbers
• Entrance into meiosis
• Pause (for 12-50 years)
• Completion of meiosis
Rate of female gamete production – 13/yr

Question 5

At puberty, the pituitary produces

Follicle Stimulating Hormone (FSH)

Answer 5

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).

Question 6

Primary follicle

Answer 6

During this phase (about 85 days), oocyte grows and
synthesises rRNA and mRNA. It does not progress further
through meiosis

Question 7

Ripening follicle

Answer 7

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

Question 8

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)

Answer 8

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

Question 9

Maturing Follicle

Answer 9

“antral stage”

Question 10

following LH surge

Answer 10

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

Question 11

The remains of the ruptured follicle

become the corpus luteum

Answer 11

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.

Question 12

fertility drugs

Answer 12

Exogenous FSH, or
drugs that block
oestrogen detection
and thus drive
higher production of
endogenous FSH,
can stimulate
oogenesis

Question 13

Capacitation

Answer 13

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.

Question 14

When sperm meet the Zona Pellucida of the egg,

they undergo an Acrosome Reaction

Answer 14

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

Question 15

Assisted fertilizatio

Answer 15

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

Question 16

ICSI

Answer 16

Intra-Cytoplasmic Sperm Injection

Question 17

“Cleavage”

Answer 17

mitosis with no growth

Question 18

At the 4 cell stage

Answer 18

mRNA synthesis from embryo’s own DNA
begins
maternal mRNA is destroyed at an
increasing rate.

Question 19

2 cell stage, 4 cell stage, morula

Answer 19

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.

Question 20

throphoblast

Answer 20

becomes placenta

Question 21

balstocyst

Answer 21

hatches through zona pellucida

Question 22

Implantation

Answer 22

the trophoblast
of the hatched blastocyst
invades the uterine epithelium

Question 23

All of the cells that make your body

Answer 23

now came from your Inner Cell Mass

Question 24

Monozygotic Twinning (1)

Answer 24

cells separate inside Z.P.

Question 25

Monozygotic Twinning (2)

Answer 25

Two Inner Cell Masses form - Danger of foetal
transfusion syndrome
(‘twin-to-twin transfusion
syndrome)

Question 26

epiblast at top then hypoblast beneath

Answer 26

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.

Question 27

Monozygotic Twinning (3)

Answer 27

Two Primitive Streaks form

Question 28

partial axis duplications

Answer 28

conjoined twins

Question 29

Gastrulation

Answer 29

the node on epiblast has formed. epiblast invaginates to form endoderm some cells touch hypoblast and then rise to form notochord

Question 30

the cns tube

Answer 30

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;

Question 31

neural tube forms above notochord

Answer 31

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

Question 32

he sealing up of the edges of the tube, and its separation from the
ectoderm, sometimes fails:

Answer 32

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)

Question 33

Orofacial cleft

Answer 33

It is treatable surgically

Question 34

Hypospadias

Answer 34

urethra not at end of penis

Question 35

h gigantism

Answer 35

Pituitary tumours are associated with gigantism

Question 36

Growth hormone

Answer 36

e itself affects post-natal
muscle growth directly, but other
tissues only indirectly.

Question 37

Limb growth is therefore uniquely vulnerable to anything that
impairs vascular growth

Answer 37

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

Question 38

Phocomelia

Answer 38

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.

Question 39

Achondroplasia

Answer 39

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.

Question 40

Your gonads developed in the
trunk of your body, about half
way between shoulder and
pelvis (whatever sex you are).

Answer 40

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;

Question 41

SRY)

Answer 41

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).

Question 42

Complete
Androgen
insensitivity

Answer 42

this person is

XY

Question 43

guevedoces’

Answer 43

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