Cleavage and placentation

Question 1

what is cleavage?

Answer 1

rapid mitotic cell division

Question 2

during cleavage are the cells increasing or decreasing in size

Answer 2

decreasing in size, sharing the egg theory

Question 3

what is parthenogenesis?

Answer 3

a process where an unfertilised egg develops to a new individual.

Question 4

When does cleavage occur?

Answer 4

week 1 following fertilisation

Question 5

what is a bilaminar embryonic germ disc

Answer 5

ormed when the inner cell mass forms two layers of cells, separated by an extracellular basement membrane. The external layer is called the epiblast and the internal layer is called the hypoblast. Together, they compose the bilaminar embryonic disc.

Question 6

The formation of the Bilaminar Embryonic Germ Disc establishes and defines the

Answer 6

primitive Dorsal-Ventral Axis of the embryo – epiblast is Dorsal, and hypoblast is Ventral.

Question 7

what is placentation?

Answer 7

This is the formation and growth of the placenta in the uterus. It also includes the type and structural arrangements ofthe Placentas.

Question 8

One of the main reasons for implantation is

Answer 8

to establish a nutritive link between the developing fetus and the mother through a placenta.

Question 9

Some of the key functions of the placenta are:

Answer 9

• to transfer nutrients from the mother to the developing fetus,
• eliminate metabolic wastes from the embryo,
• provide immunity and protect against infections.

Question 10

what are the 3 main types of Placentations in animals based on structural arrangement

Answer 10

Epithelialiochorial placentation

Endotheliochorial placentation

Hemochorial placentation

Question 11

Epitheliochorial placentation

Answer 11

(Ruminants, Horses, Whales and Lower Primates): This is a placenta with the thickest barrier as all the maternal tissue layers separate the maternal blood from the fetal chorion.

Question 12

Endotheliochorial placentation

Answer 12

(Cats and dogs): This is a placenta with a thinner barrier as only the maternal blood vessels endothelial cells separate the maternal blood from the fetal chorion.

Question 13

Hemochorial placentation

Answer 13

(Higher primates, Humans, Mice and Rats): This is a placenta with the thinnest barrier as the maternal blood directly baths the fetal chorion.

Question 14

Hemochorial placentation

Answer 14

(Higher primates, Humans, Mice and Rats): This is a placenta with the thinnest barrier as the maternal blood directly baths the fetal chorion.

Question 15

abnormal placentation can lead to

Answer 15

abortion of the pregnancy

Question 16

Extrauterine or Ectopic Pregnancy results from

Answer 16

a situation when implantation takes place outside the uterus.

Question 17

Hydatiform Mole – Complete or Partial:

Answer 17

Pregnancy developing without a fetus or with a remnant of a fetus

Question 18

dizygotic twins placentation

Answer 18

Implants separately.

Develops separate placentas.

Separate amnion (Diamnionic).

Separate chorionic sac (Dichorionic).

Sometimes placentas are fused – Diamnionic, Dichorionic fused or Monochorionic.

Question 19

dizygotic twins placentation

Answer 19

Implants separately.

Develops separate placentas.

Separate amnion (Diamnionic).

Separate chorionic sac (Dichorionic).

Sometimes placentas are fused – Diamnionic, Dichorionic fused or Monochorionic.

Question 20

monozygotic twins placentation

Answer 20

Two-cell stage split:
Implants separately.

Develops separate placenta.

Separate amnion (Diamnionic).

Separate chorionic sac (Dichorionic).

Question 21

Monozygotic twins:

Early blastocyst stage split:

Answer 21

Have common placenta and chorionic (Monochorionic) cavity.

Separate amniotic (Diamnionic) cavities.

Question 22

Monozygotic twins:

Bilaminar germ disc stage split:

Answer 22

Have common placenta, chorionic (Monochorionic) and amnitic (Monoamnionic) sace.