Fertilisation and embryo development

Question 1

What is induced ovulation?

Answer 1

Ovulation that is stimulated by mating

Cats, mink, rabbits, camels

Question 2

Outline the events in ovulation?

Answer 2

— folicular wall bursts
— oocyte & granulosa cells released from
Granulosa cell anchor point
— oocyte carried with follicular fluid into the
peritoneal cavity
— captured by fimbria of the infundibulum on
the oviduct.

Question 3

What is the fertile period?

Answer 3

. The fertilisation period is the time when oocytes
are available to be fertilised by sperm — in most
species this is immediately after ovulation for up
to hours (but days in the bitch!)
. The fertile period is the time when mating could
result in pregnancy

Question 4

What acts as a receptor on the oocyte for sperm?

Answer 4

ZP3

Question 5

What is the acrosome reaction?

Answer 5

— Loss of acrosome contents, enzymes digest
zona pellucida, exposed sperm surface
proteins bind to ZP2 at this point sperm and
egg begin to fuse together.

Question 6

What is sperm capacitation?

Answer 6

— Removal of glycoprotein coat and alteration of

sperm mitochondria

Question 7

What sequence of events does sperm membrane fusion start?

Answer 7

— Causes depolarisaton of egg membrane
— Causes cortical reaction (underneath ZP and egg membrane are cortical granules and these are released on outside major important in blocking polyspermy these granules induce a lot of calcium to come into egg from extracellular space)
- Oocyte activation: completion of meiosis II (extrusion of second polar
body)

Question 8

What is the pronucleus?

Answer 8

the nucleus of a sperm and egg cell during the process of fertilization, after the sperm enters the ovum, but before they fuse. When both pro nuclei are visible the egg is called an ootid.

Question 9

Following fusion of the two pro nuclei what is the egg called?

Answer 9

Zygote

Question 10

Each individual cell within a zygote is called what?

Answer 10

Blastomere. The blastomeres have the ability to form all cells necessary for normal development.

Question 11

At 16 cells what is the embryo called?

Answer 11

Morula

Question 12

What cells are totipotent and what does this mean?

Answer 12

Blastomere cell number can be decreased or increased without adverse effect to the embryo. The cells at this stage are called ‘Totipotent’

Totipotency is not demonstrated beyond the 16-cell stage (morula)

Question 13

What does a blastocyst look like?

Answer 13

Has a distinct cavity with inner cell mass and trophoblast.

Question 14

What happens when the blastocyst hatches?

Answer 14

The blastocyst continues to undergo mitosis and
fluid continues to be produced (increase of pressure)
— Proteolytic enzymes are produced by trophoblast in
order to break through ZP
— Zona pellucida weakens
— Zona pellucida splits and the blastocyst emerges
—The blastocyst becomes a free floating embryo
after hatching
—Secretions derived from endometrial glands
provide nutritional support before the placenta is
established
— The secretions contain carbohydrate, proteins and lipids and are described as uterine milk or histiotroph

Question 15

What forms the amniotic ectoderm?

Answer 15

Epiblast. ICM gives rise to the epiblast.

Question 16

The extraembryonic mesoderm continues to grow

and forms what?

Answer 16

A sac that surrounds the yolk sac. It also folds dorsally to form the amniotic folds.

Question 17

What forms from an out-pouching of the hind gut?

.

Answer 17

A third fluid filled sac forms from an out-pouching of the
hind gut the allantois.
The allantois makes contact with the chorion and
eventually fuses to form the chorioallantoic
membrane