Embryology - systematic embryology

Question 1

When is the conceptus referred to as a fetus?

Answer 1

After 8 weeks of development

Fetus = recognisable as human

Question 2

What are later stages of pregnancy concerned with?

Answer 2

growth and elaboration of the structures that develop during the first two months.

Question 3

What are the general causes of mal-development?

Answer 3

genetic - 30%
environmental - 15%
multi-factorial - 55%

Question 4

When is embryological development considered to start?

Answer 4

At fertilisation

Question 5

Where are sperm deposited after sexual intercourse?

Answer 5

Near the cervix

Question 6

How does cervical mucus respond to the sperm?

Answer 6

It’s usually hostile forming a physical barrier to the sperm

Question 7

When does cervical mucus change and how does this affect sperm?

Answer 7

Changes mid-cycle and this change permits entry of the sperm into the uterus

Question 8

What is the passage of sperm after it enters uterus?

Answer 8

It passes through the uterus

It passes into the fallopian tube

Question 9

Where does sperm swim to once in the fallopian tube and what’s the pace saying?

Answer 9

Swims to the fallopian tube ampulla
30 um/sec, 2mm/min and 12cm/hour
Survival of the fittest (takes a few days)

Question 10

Where does capacitation take place?

Answer 10

Takes time within the uterus and is essential for preparation of sperm to meet oocyte.

Question 11

What is capacitation?

Answer 11

Second last step of maturation of spertamozoa

Loss of glycoprotein coat, whiplash movements of the tail, change in surface membrane characteristics.

Question 12

What happens after capacitation?

Answer 12

Meeting of sperm with egg and fusion

Question 13

Describe the acrosome reaction that takes place after the fusion

Answer 13

Sperm binds to ZP3 receptor
Ca2+ influx into sperm which is stimulated by progesterone.
Release of hyaluronidase and proteolytic enzymes from acrosome (coating of head of sperm)
This allows penetration of zona pellucida

Question 14

What happens after acrosome?

Answer 14

Meiosis resumption and release of second polar body

Question 15

What happens after the release of second polar body?

Answer 15

Alignment of maternal and paternal chromosomes to generate zygote
Change in zona pellucida to prevent additional sperm binding to zygote.
Initiation of mitotic divisions in embryo, formation of cleavage furrow.

Question 16

How long does it usually take for fertilisation, when is the first mitotic division?

Answer 16

DAY 2

Question 17

When and where does pre-implantation development occur?

Answer 17

Normally occurs within fallopian tube over a period of 6 days characterised by a series of cleavage divisions to produce a ball of undifferentiated cells.

Question 18

What is the ball of undifferentiated cells called?

Answer 18

Morula

Question 19

How does the Morula differentiate?

Answer 19

Inner cells differentiate from outer cells

Question 20

What does the differentiated Morula develop into?

Answer 20

Blastocyst
Outer layer of trophoectoderm
Inner cell mass
Fluid filled cavity

Question 21

What happens at about day 6?

Answer 21

The blastocyst then hatches from the zona pellucida and begins to implant the uterine lining.

Question 22

What has happened to inner cell mass by the time of implantation?

Answer 22

has become a bilayer disk, composed of hypoblast and epiblast cells
Bilayer gives rise to all tissues of the human fetus through a complex series of changes.

Question 23

What is the first of these complex series of changes?

Answer 23

Gastrulation
Conversion of bilayer to trilaminar embryo containing three layer of germ cells (mesoderm, ectoderm, endoderm)
This occurs during 14-18 days post-fertilisation.

Question 24

Which cells of the bilayer form the mesoderm?

Answer 24

Proliferation of epiblasts and then differentiate to form mesoderm cells.
These move into space between epiblast and hypoblast and can generate endoderm which replaces hypoblasts lost by apoptosis.

Question 25

What do each of the 3 layers differentiate into?

Answer 25

Ecto - skin, cns
meso - muscles, blood, skeleton, heart and kidney
endo - gut, lung, liver

Question 26

What is initiated before gastrulation is complete?

Answer 26

Neurulation is the differentiation of the Ectoderm (Epiblast) to generate the central nervous system (Brain and Spinal cord)

Question 27

What controls neurulation?

Answer 27

Notocord of the mesoderm of developing embryo.

Question 28

What happens to neural plate in neurulation?

Answer 28

Neural plate develops two folds, increase in size until they meet over neural groove and fuse to form tube

Question 29

When does the CNS become a sealed tube?

Answer 29

Fusion process continues during week 4 of development as CNS becomes sealed tube

Question 30

Is the structure of the neural folds the same throughout?

Answer 30

More complex at the upper end of the embryo, brain development has started by this stage (week 4)

Question 31

What is happening in parallel with neurulation?

Answer 31

Precursors of other tissues are developing within the embryo and it is being converted from a flattened structure to a 3D embryo..

Question 32

What 2 groups of cells are present outside embryo proper during 3rd week of development?

Answer 32

Primordial germ cells in the yolk sac endoderm at the caudal end of embryo
cardiac and vascular progenitors in primary heart field at the cranial end of embryo.

Question 33

What are the two directions there is folding of the embryo?

Answer 33

Laterally - fuses ventral midline of embryo (chest and abdomen)
Anterio-posterior direction which folds the PGCs into hind gut and developing heart progenitors under head of embryo.

Question 34

What proceeds rapidly during the second month of development?

Answer 34

Urogenital, cardiac, facial and lung development all proceed rapidly

Question 35

When does development stop?

Answer 35

Clearly ceases after 8 weeks of post-fertilisation as conceptus now clearly human.