Module 3: Embryology

Question 1

Define the embryological period

Answer 1

Stage of development from fertilization (sperm meeting egg @ around week 3) until around the 8th week of pregnancy

Question 2

Outline the process of gastrulation

Answer 2

Gastrulation is the formation of a trilaminar disc from the bilaminar embryonic disc. The three cell layers that make up the trilaminar disc are called the primary germ layers and will give rise to all structures of the tinana.

Question 3

What are the two layers of the bilaminar embryonic disc?

Answer 3

Epiblast: upper layer. Hypoblast: lower layer.

Question 4

The bilaminar disc is a two-layered structure derived from what?

Answer 4

The inner cell mass, which is part of the blastocyst.

Question 5

What are the layers of the trilaminar disc?

Answer 5

Ectoderm, Mesoderm & Endoderm

Question 6

What is the Endoderm?

Answer 6

The first cells to invade the hypoblast and replace it with the definitive endoderm. This is the inner most germ layer which forms the digestive tract, and much of the respiratory system: respiratory glands, & mucosal lining of tracts.

Question 7

What is the Mesoderm?

Answer 7

middle germ layer; develops into muscles, gonads, dermis of skin, skeleton (except cranial bones), heart + blood vessels, kidneys, serous membranes

Question 8

What is the Ectoderm?

Answer 8

Outermost germ layer which is formed from the remaining epiblast cells; produces cranial bones, brain and spinal cord, epidermis + glands of skin

Question 9

What is a teratogen?

Answer 9

Any agent such as a food, drug or chemical that causes malformation/abnormality by damaging fetal growth.

Question 10

What are the effects of smoking on the embryo?

Answer 10

can cause irreparable damage and congenital malformations during the embryological period (cleft lip, congenital heart defects) and can induce fetal hypoxia and growth retardation

Question 11

What is the overall critical period for a pepi is the embryological period which is:

Answer 11

3-8 embryological weeks

Question 12

What is the critical period for embryo - CNS

Answer 12

3 - 32 weeks

Question 13

What is the critical period for embryo - Heart

Answer 13

3 - 6 weeks

Question 14

What is the critical period for embryo - upper limbs + lower limbs

Answer 14

4 - 6 weeks

Question 15

What is the critical period for embryo - Upper lip

Answer 15

5 - 7 weeks

Question 16

What is the critical period for embryo - Ears + Eyes

Answer 16

4 - 9 ish weeks

Question 17

What is the critical period for embryo - Teeth + Palate

Answer 17

6 - 9 weeks

Question 18

What is the critical period for embryo - External genitalia

Answer 18

7 - 10 weeks

Question 19

What are the effects of alcohol on the embryo?

Answer 19

alcohol can cross the placental barrier and can lead to different Fetal Alcohol Spectrum Disorders. Fetal Alcohol Syndrome (FAS): causes structural deformities + neurological impacts

Question 20

What are the effects of chemicals on the embryo?

Answer 20

radiation (mental retardation, childhood leukemia), Lead (premature/low birth weight), Cadmium (effects kidneys/lungs), Mercury (disrupts nervous system/slows growth/cerebral palsy)

Question 21

Outline the embryonic development of: NS

Answer 21

First organ system to begin developing after gastrulation and it begins with neurulation. At the end of neurulation we have the formation of the brain and spinal cord (CNS+PNS)

Question 22

Outline the embryonic development of: Head + Neck

Answer 22

Involves all three primary germ layers. By the 4th embryological week

Question 23

Outline the embryonic development of: Cardiovascular system

Question 24

Outline the embryonic development of: Respiratory system

Question 25

Outline the embryonic development of: GI system

Question 26

Outline the embryonic development of: Renal system

Question 27

Outline the embryonic development of: Reproductive system

Question 28

Outline the embryonic development of: Musculoskeletal system

Question 29

Outline the embryonic development of: Integumentary system

Question 30

What is the primitive streak?

Answer 30

Before gastrulation, in the amnion where the epiblast & hypoblast come together (bilaminar disc) the epiblast cells migrate to the primitive streak; which forms around day 15 at the CAUDAL end of the bilaminar disc. This defines the major body axes - cranial, caudal, L/R.

Question 31

What is neurulation?

Answer 31

Formation of the neutral tube & involves the growth, movement and differentiation of cells the ectoderm.

Question 32

What is the first event of neurulation?

Answer 32

Formation of the neural plate: which forms at the cranial end of the embryo & grows in a cranial to caudal direction. Cranial end becomes brain and caudal end becomes spinal cord.

Question 33

What is the second event of neurulation after the formation of the neural plate (end of week 3)?

Answer 33

Lateral edges of the neural plate become elevated and move together to form the neural folds.

Question 34

What is the third event of neurulation after the formation of the neural folds?

Answer 34

Neural folds fuse together and the neural plate then transforms to form the neural tube: which is the precursor to the central nervous system (CNS). The neural tube begins forming in the middle + moves outwards to ends. Once closed forms brain + spinal cord.

Question 35

What are the neural crests and when are they formed?

Answer 35

Neural crests are formed and neural tube closed by the end of the third embryological week (~day 21).

The neural crests will develop into the nerves of the peripheral nervous system (PNS) as well as the bones and blood vessels of the head

Question 36

By the end of the fifth embryological week, the brain will have formed three distinct regions:

Answer 36

forebrain (cerebrum + diencephalon)
midbrain (midbrain of brainstem)
hindbrain: pons and medulla of brainstem and cerebellum