Embryology

Question 1

What are the 3 periods of development? What weeks are these

Answer 1

Pre-embryonic: Weeks 1,2
Embryonic: Weeks 3-8
Foetal: Weeks 9-38

Question 2

Compare Embryonic and Gestational Age

Answer 2

Embryonic: Time since fertilisation

Gestational: Time since last menstruation

Question 3

Where is the Oocyte fertilised by Sperm cell

Answer 3

Ampulla of Fallopian tubes

Question 4

What 5 processes occur in Week 1

Answer 4

Cleavage
Morula Formation
Compaction
Hatching 
Implantation

Question 5

What is cleavage? What happens in this process

Answer 5

First mitotic division, produces 2 blastomeres, Zona Pellucida formed

Question 6

What is the Zona Pellucida

Answer 6

A glycoprotein shell that keeps sperm from penetrating the blastomeres

Question 7

What is a blastomere

Answer 7

Every embryonic cell formed after cleavage, until a blastocyst is produced

Question 8

What is a Morula?

Answer 8

A ball of 16 blastomeres that are totipotent

Question 9

What is Compaction

Describe the cell potency

Answer 9

Formation of the first cavity, and the Blastocyst

Pluripotent- Can become many types. (Not all types- totipotent)

Question 10

What is a blastocyst

Answer 10

A hollow sphere of cells formed from the morula through compaction

Question 11

Wha happens in the hatching stage

What is the blastocyst now able to do?

Answer 11

Blastocyst hatches from the Zona Pellucida

Blastocyst can now enlarge and implant on the uterine surface

Question 12

What happens as implantation begins?

Answer 12

There’s now 100 cells

8 make the embryo
92 help development of fetal membranes

Question 13

What 3 things happen on Day 8

Answer 13

• Embryoblast differentiates into Epiblast and Hypoblast
• Trophoblast differentiates into Synctio-/ Cytotrophoblsst
• Amniotic cavity formed

Question 14

What 2 things happen on days 9-10

Answer 14

• Synctiotrophoblast develops rapidly

- Primitive yolk sac formed

Question 15

What happens on Day 11

Answer 15

Primitive yolk sac membrane pushed away from Cytotrophoblast by extraembryonic reticulum

Extraembryonic mesoderm formed from extraembryonic reticulum

Question 16

What 2 things happen on day 12

Answer 16

• Maternal sinusoids invaded by lacunae of Synctiotrophoblast
• Uterine stroma (layer of connective tissue) prepares to support embryo

Question 17

What happens on Days 13-14

Answer 17

13: Secondary Yolk Sac Forms by pinching off Primitive Sac

14: Spaces in Extraembryonic Mesoderm join-> Chorionic Cavity
Embryo and it’s cavities are suspended by Connecting Stalk

Question 18

Define;

1. Gastrulation
2. Germ layer
3. Primitive Streak

Answer 18

1. The differentiation of Bilaminar into Trilaminar Disc
2. Group of embryonic cells that interact with each other and contribute to the formation of all organs and tissues
3. Thickened region of Epiblast at Caudal end of bilaminar disk. Site from which Gastrulation begins

Question 19

What are the 5 stages of Early Development

Answer 19

1. Fertilisation and Implantation
2. Gastrulation
3. Neurulation
4. Segmentation
5. Folding

Question 20

Describe the derivatives of the Ectoderm layer

Give 2 examples

Answer 20

Structures that maintain contact with outside world

Epidermis
Nervous system

Question 21

Describe the derivatives of the Mesoderm layer

Give 4 examples

Answer 21

Supporting tissues

Muscle
Bones
Cartilage
Vascular System

Question 22

Describe the derivatives of the Endoderm layer

Give 3 examples

Answer 22

Internal structures

Epithelial lining of GI tract and Respiratory Tract
Parenchyma of glands

Question 23

What process is Migration and Invagination part of?

Describe the process

Answer 23

Gastrulation

Epiblast cells migrate to Primitive Streak and move through tight junctions, displacing the Hypoblast layer

Question 24

What is responsible for establishing left-right asymmetry

How does this happen?

Answer 24

Primitive node
Actions of ciliated cells result in left-ward flow of signalling molecules, leading to a cascade of side-specific signals

Question 25

What is situs invertus? How does it occur

Answer 25

Is when internal organs are reversed/ mirror image Occurs due to immotile cilia at Primitive Node

Question 26

What is the notochord | What is it’s role

Answer 26

Solid rod of cells running in the midline, with an important signalling role

Question 27

What does the Notochord convert What do notochord signals cause?

Answer 27

- Ectoderm to Neuroectoderm | - Cause Ectoderm to thicken, forming NEURAL PLATE, whose edges curl up to form Neural Tube

Question 28

What is Teratogenesis What is the Intraembryonic Coelom

Answer 28

Major congenital malformation A cavity( between Somatic and Splanchnic Mesoderm) into which organs can grow

Question 29

What 5 things does the Mesoderm differentiate into?

Answer 29

1. Parasail Mesoderm 2. Intermediate Mesoderm 3. Somatic Mesoderm 4. Splanchnic Mesoderm 5. Intraembryonic Coelom

Question 30

What make up the Lateral Mesoderm (Differentiated from mesoderm)

Answer 30

Splanchnic and Somatic Mesoderm leaves

Question 31

What happens to the Notochord in adult life?

Answer 31

Has no function | Forms Nucleus Pulposus of intervertebral disc

Question 32

What do the Splanchnic and Somatic Mesoderm differentiate into?

Answer 32

Splanchnic- Viscera | Somatic- Connective Tissue of body

Question 33

What structures are formed from the Paraxial Mesoderm, and how many?

Answer 33

Somites 44-44 made, but ONLY 31 remain

Question 34

Describe how somites undergo ORGANISED DEGENERATION to form Sclerotome, Dermatome, Myotome. What do these 3 end up as?

Answer 34

1. Ventral walls of somites break down—> Sclerotome->Bones 2. Further organisation of dorsal potion->Dermomyotome 3. Myotome proliferates and migrates, Dermatome disperses Myotome- Muscles Dermatome- Dermis

Question 35

What are the 2 folding types the trilaminar disc undergoes

Answer 35

- Cephalocaudal | - Lateral

Question 36

What are the results of folding?

Answer 36

- Connecting stalk pulled ventrally - Ventral body wall created - Amniotic membrane pulled around disc - Draws together the margins of the Trilaminar disc

Question 37

What has happened by the end of week 4?

Answer 37

- Nervous system has started to form - Segments have appeared, assigning specific cells to specific tasks - Embryo has folded

Question 38

Bleeding on Day ______ can be mistaken for menstrual bleeding

Answer 38

Day 14 (Chorionic cavity and connecting stalk form)