The three germ layers

Question 1

Zona pellucida

Answer 1

Fluid passes from uterine cavity through this structure into blastocystic cavity

Question 2

When is implantation of the blastocyst completed?

Answer 2

2nd week

Question 3

Bilaminar embryonic disc

Answer 3

Epiblast and hypoblast

Question 4

First sign of gastrulation

Answer 4

Formation of primitive streak on surface of epiblast

Question 5

During which week does the primitive streak form?

Answer 5

Beginning of 3rd week

-appears caudally in median plane of dorsal aspect of embryonic disc

Question 6

Primitive node

Answer 6

Formed when cranial end of streak proliferates

-has a primitive pit

Question 7

Primitive groove

Answer 7

Dev in primitive streak, continuous with primitive pit

Question 8

mesoblast

Answer 8

• formed by some mesenchyme
• undiff mesoderm
• forms intraembryonic, embryonic or mesoderm

Question 9

mesenchyme

Answer 9

loosely arranged cells suspended in gelatinous matrix

• phagocytic
• forms supporting tissues of embryo

Question 10

embryonic endoderm

Answer 10

-cells from epiblast and primitive node and displace the hypoblast to form embryonic endoderm

Question 11

embryonic ectoderm

Answer 11

form3ed by remaining cells in epiblast

Question 12

Notochord

Answer 12

Some mesenchymal cells migrate cranially from primitive node and pit to form notochordal process

Question 13

prechordal plate

Answer 13

circular area of columnar endodermal cells where ecto and endo are in contact
-notochordal process grows between ecto and endo until reaching prechordal plate

Question 14

Prechordal mesoderm

Answer 14

• rostral to notochord

- essential in forebrain and eye induction

Question 15

Prechordal plate function

Answer 15

Primordium of orophargyngeal mem, loc at future site of oral cavity , may have role as signalling center for controlling development of cranial structures

Question 16

Notochord function

Answer 16

Primary inductor (signalling center) in early embryo
-induces ectoderm to form neural plate (CNS)

Question 17

Derivates of ectoderm

Answer 17

• epidermis of skin and glands
• epithelial lining of mouth and anus
• cornea and lens of eye
• NS
• sensory receptors in epidermis
• adrenal medulla
• tooth enamel
• epithelium of pineal and pituitary glands

Question 18

Mesoderm

Answer 18

• notochord
• skeletal and muscular system
• muscular layer of stomach and intestine
• excretory system
• circulatory and lymphatic systems
• reproductive system (except germ cells)
• dermis of skin
• lining of body cavity
• adrenal cortex

Question 19

Endoderm

Answer 19

• epithelial lining of digestive tract
• epithelial lining of resp system
• Lining of urethra and bladder, reprod sys
• liver, pancreas, thymus, thyroid and parathyroid glands