gastrulation and germ layers

Question 1

what is gastrulation

Answer 1

process of epiblastic cells movement (ingression or invagination) that leads to the transformation of the Bilaminar Germ Disc into a Trilaminar Germ Disc… with the establishment of all the three primary germ layers – Ectoderm, Mesoderm and Endoderm.

Question 2

Gastrulation commences with the formation of a

Answer 2

morphogenic inductive centre” called the Primitive Streak on about the 15th Day

Question 3

morphogenic inductive centre- primitive streak

Answer 3

-through which the epiblastic cells ingress or invaginate to form the mesoderm and endoderm, while the remaining epiblastic cells become the ectoderm.

Question 4

The formation of the Primitive Streak and gastrulation establish

Answer 4

all the major body axes: cranio-caudal axis, medio-lateral axis, dorso-ventral axis and left-right axis.

Question 5

One of the congenital malformations resulting from errors in Gastrulation is

Answer 5

Caudal Dysplasia, also called Caudal Regression Syndrome, Caudal or Sacral Agenesis (e.g. Sirenomelia).

Question 6

derivatives of the germ layers

Answer 6

very complex cross overs

Question 7

the Ectodermal Germ Layer gives rise to

Answer 7

organs and structures that maintain contact with the outside world.

Question 8

what is induced to for the neuroectoderm?

Answer 8

ectodermal layer

Question 9

neuroectoderm leads to the formation of

Answer 9

the neural tube (via Neurulation) from where the nervous system (Central and Peripheral) is derived.
Also gives rise to the Neural Crest cells and pituitary gland.

Question 10

other ectoderm formed structures

Answer 10

• sensory epithelium of the ear, nose and eye.
• epidermis of the skin and other integumentary structures – hair, nails, sweat glands, mammary glands, etc.
• enamel of the teeth.
• oral and proctodeal (anal canal) epithelium

Question 11

what 3 layers make up the mesoderm?

Answer 11

Paraxial mesoderm

Intermediate mesoderm

Lateral plate mesoderm

Question 12

Paraxial mesoderm form

Answer 12

segmental blocks called somitomeres which in the head region is called neuromeres in assoaciation with the neural plate.

Question 13

Paraxial mesoderm form

Answer 13

segmental blocks called somitomeres which in the head region is called neuromeres in assoaciation with the neural plate.

Question 14

The neuromeres contribute to

Answer 14

the mesenchyme (connective tissue) in the head

Question 15

Somites

Answer 15

From the neck (occipital) region downwards, the somitomeres form segmemented pair of blocks of mesoderm, on either side of the developing neural tube

Question 16

the first pair of somite arise

Answer 16

in the occipital region of the embryo at about the 20th day of development.

Question 17

New somites appear craniocaudally at the rate of about

Answer 17

3 pairs per day

Question 18

at the end of the 5th week how many pairs of somites have formed

Answer 18

about 42 to 44 pairs of somites would have been formed.

Question 19

number and distribution of somites

Answer 19

There are 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 8-10 coccygeal pairs of somites.

Question 20

how many commits would a 23 day old embryo have

Answer 20

12 somites

Question 21

how can the age of an embryo be accurately determined

Answer 21

by counting somites numbers during this period of development because somites are formed with a specific periodicity.

Question 22

The Intermediate mesoderm:

Answer 22

Contribute in the formation of the structures of the urogenital system including the primordial germ cells, gametes and gonads.

Question 23

The Lateral Plate mesoderm:

Answer 23

splits into parietal (somatic) and visceral (splanchnic) layers.

The parietal layer lines the body (intraembryonic) cavity walls.

Mesoderm of the visceral layer together with the endoderm form the wall of the gut tube

Question 24

Mesoderm from the parietal layer together with the overlying ectoderm, forms

Answer 24

the lateral body wall

Question 25

what does the parietal layer of lateral plate mesoderm also form?

Answer 25

the dermis of the skin in the body wall and limbs, bones and connective tissue of the limbs and sternum.

the costal cartilage, limb muscles and most of the body wall muscles.

the mesothelial or serous membranes (parietal layer) that line the peritoneal, pleural and pericardial cavities and secret serous fluid.

Question 26

what does the visceral layer of lateral plate mesoderm also form

Answer 26

the serous membrane (visceral layer) that surrounds organs.

the blood cells and blood vessels.

Question 27

The main derivative of the endodermal germ layer is the

Answer 27

Gastrointestinal Tract including the pharynx.

Question 28

The main derivative of the endodermal germ layer is the

Answer 28

Gastrointestinal Tract including the pharynx.

Question 29

what does the endodermal germ layer also form

Answer 29

the epithelial lining of the respiratory tract, the urinary bladder and urethra, and the tympanic cavity and auditory tube.

the parenchyma of the thyroid, parathyroids, liver, and pancreas.

Question 30

that walls of the GIT – smooth muscles and other connective tissues are derived from

Answer 30

the mesoderm - because muscles