Basic Embryology

Question 1

What are the 3 stages of development? What happens in each?

Answer 1

Cleavage - mitotic divisions of the zyote
Embryonic period - germ layers, main body systems and placenta, up to 2 months
Foetal period - further organ development and locomotor system becomes functional

Question 2

Cleavage is the mitotic division of the zygote (fertilised ovum) into what structure?

Answer 2

Morula - sphere of cells

Question 3

What stimulates morula cell division? What does this form?

Answer 3

Uterine secretion

Blastocyst

Question 4

Cells are reorganised around the blastocyst cavity. The inner cell mass eventually becomes what? Which pole is this at?

Answer 4

Foetus - at animal pole

Opposite the vegetal pole

Question 5

What is the trophoblast? What does it eventually become?

Answer 5

Outer superficial layer that develops through rearrangement of blastocyst cells
Foetal part of the placenta

Question 6

What is implantation? Which way does the inner cell mass face?

Answer 6

Blastocyst loosely attaches to endometrium

Towards endometrium

Question 7

The trophoblast develops into 2 layers, which go on to form what?

Answer 7

Foetal part of placenta

Chorion. (one of the membranes)

Question 8

One of the trophoblast layers produces enzymes, what do these enzymes do?

Answer 8

Break down the endometrial cells, so the blastocysts can penetrate the uterus wall further

Question 9

The inner cell mass eventually becomes the foetus. However, it differentiates first into the bilaminar disc, which is made up of what layers? What do these layers eventually become?

Answer 9

Hypoblast - goes on to form endoderm

Epiblast - goes on to form ectoderm

Question 10

A cavity in the epiblast forms what? What do the epiblast cells become?

Answer 10

The amniotic cavity

Amnion - thin, protective foetal membrane

Question 11

What happens to the amnion? What does it fill with? WHat is this?

Answer 11

Surrounds the embryo

Amniotic fluid - filtrate of mothers blood, contains foetal urine excretions

Question 12

Hypoblast cells cover the inner surface of the blastocyst. These cells become what to form the exocoelomic membrane? What does the exocoelomic membrane and hypoblast form?

Answer 12

Squamous

Yolk sac

Question 13

What is gastrolation? What does this establish?

Answer 13

the rearrangement and migration of the epiblast cells in the bilaminar disc
Body plan of the embryo

Question 14

The bilaminar disc is transformed into the trilaminar disc. What are the epiblast cells now referred to as? What are the hypoblast cells referred to as? What becomes the mesoderm?

Answer 14

Ectoderm
Endoderma
Mesenchyme - loosely organise connective tissue

Question 15

During gastrulation, which essential part of the body is formed?

Answer 15

CNS

Question 16

Which tissues originated from ectoderm?

Answer 16

Nervous tissue
Epidermis
Lens/cornea
Inner and outer ear
Epi lining of oral and nasal cavities
Renal medulla

Question 17

What tissues originate from mesoderm?

Answer 17

All skeletal and cardiac muscle, most smooth muscle
Cartilage, bone and connective tissue
Epi linings of the visceral cavities
Dermis
Eyeball layers
Adrenal cortex

Question 18

Which tissues originate from endoderm?

Answer 18

Epi linings of the GI, urinary, genital and respiratory tract
Epi lining of the thyroid gland, pancreas and thymus

Question 19

What is organogenesis? WHat are the parts to the gut?

Answer 19

Development of organ systems

Foregut, midgut, hindgut

Question 20

What are pharyngeal clefts?

Answer 20

Grooves which seperate pharyngeal arches

Question 21

What do the pharyngeal pouches develop with? What is the difference?

Answer 21

Pharyngeal arches and clefts

Pouches develop outside of the embryo

Question 22

What is the allantois? What does it do for the embryo?

Answer 22

Sac with clear fluid and blood vessels

Nutrition and excretion for embryo

Question 23

What are the 4 extraembryonic membranes?

Answer 23

Chorion
Allantois
Yolk sac
Amnion