Embryo bullshit

Question 1

What must occur before sperm is able to fertilise egg

Answer 1

Capacitation

Question 2

What does capacitation entail

Answer 2

Loss of inhibitory molecules (cholesterol, proteins, glycoproteins) from acrosome, enabling chemo/thermotaxis.

Question 3

What is division of zygote called

Answer 3

Cleavage

Question 4

What does cleavage form

Answer 4

Blastomeres

Question 5

How does the morula transform into the blastocyst

Answer 5

Uterine milk enters the morula, reconfiguring the cells to form a blastocyst cavity

Question 6

Two cell populations of the blastocyst

Answer 6

Embryoblast (inner cell mass) - forms embryo

Trophoblast - forms chorionic sac

Question 7

Why does the blastocyst shed the zona pellucida

Answer 7

So that implantation can occur (it prevents implantation in uterine tubes)

Question 8

What does the trophoblast develop into

Answer 8

Synctiotrophoblast - deeper into uterus

Cytotrophoblasts - closer to embryo

Question 9

Function of synctiotrophoblasts and cytotrophoblasts

Answer 9

Secrete enzyme to burrow deeper into uterine lining

Release horomes e.g human chorionic godatropin which stops corpus luteum degenration and prevents menstruation

Question 10

How does the bilaminar disc form

Answer 10

Embryoblast splits into
Hypoblast - primitive endoderm
Epiblast - primitive ectoderm
Cavity forms in epiblast, forming amniotic cavity

Question 11

How does amnion form

Answer 11

Amnion (simple squamous cells) forms over epiblast, forming roof to amniotic cavity.
As embryonic disc increases in size, amnion eventually surrounds entire embryo

Question 12

How does yolk sac form

Answer 12

During implantation, hypoblast proliferates and migrates around inside of blastocyst, forming the exocoelomic membrane.

Question 13

Function of yolk sac

Answer 13

Nutrients for embryo for first 2-3 weeks
Source of RBC
Gives rise to primordial germ cells which become gametes
Forms part of gut

Question 14

How do sinusoids form

Answer 14

Synctiotrophoblasts expand, creating lacunae.
Lacunae fuse to form lacunae network
Network joins up with maternal sinusoids and endometrial glands

Question 15

What is the extraembryonic mesoderm

Answer 15

Mesoderm cells derived from yolk sac, forming a mesenchyme layer around the amnion and yolk sac
Extraembryonic coelom eventually forms in it

Question 16

What does chorion consist of

Answer 16

Extraembryonic mesoderm
Cyto + synctiotrophoblasts
These surround the embryo

Question 17

Function of chorion

Answer 17

Principal embryonic part of placenta
Suppresses immune response
-Secretes antibody production suppressing proteins
-Suppresses immune response
Produces human chorionic gonadotropin

Question 18

How does the chorion develop

Answer 18

Fuses with amnion

Extraembryonic coelom now called chorionic cavity

Question 19

What is the connecting stalk

Answer 19

Band of extraembryonic mesoderm connecting the bilaminar disc and trophoblast

Question 20

What is gastrulation

Answer 20

Process that transforms bilaminar into trilaminar embryonic disc of three germ layers
Involves rearrangement and migration of cells from epiblast

Question 21

What are the primary germ layers and what do they become

Answer 21

Ectoderm
Mesoderm
Endoderm

Question 22

What is the first evidence of gastrulation

Answer 22

Formation of the primitive streak - a faint groove on the epiblast that elongates from the posterior to the anterior part of the embryo.
At the head is the primitive node

Question 23

What occurs after formation of primitive streak

Answer 23

Epiblast cells detach and move inword below primitive streak via invagination

Question 24

What are the effects of invagination

Answer 24

Epiblast cells displace hypoblast forming the endoderm
Cells between endoderm and epiblast become the mesoderm
Epiblast becomes ectoderm

Question 25

What does the ectoderm become

Answer 25

All nervous tissue
Epidermis
Skeletal and connective components of head
Epithelium of oral and nasal cavities, paranasul sinuses, salivary glands, anal canal, pineal and pituitary gland, adrenal medullae

Question 26

What does endoderm become

Answer 26

Epithelium of gastrointestinal tract and its glands
Epithelium of urinary bladder, gall bladder, liver
Epithelium of thyorid and parathyroid glands, pancreas and thymus
Gametes

Question 27

What does mesoderm become

Answer 27

All skeletal and cardiac muscle
Most smooth muscle
Cartilage and bone
Blood, red marrow, lymphatic tissue
Kidneys and ureters 
Gonads

Question 28

Formation of notochord

Answer 28

Mesodermal cells from primitive node migrate towards head end
This leaves a hollow tube of cells called the notochordal process
This eventually becomes a solid cylinder of cells called the notochord

Question 29

Function of the notochord

Answer 29

Induction
This is the stimulation of nearby unspecialised tissue to develop into specialised tissue
e.g mesodermal tissue to form vertebral bodies

Question 30

Formation of the neural plate

Answer 30

Ectodermal cells above notochord are induced to form the neural plate

Question 31

Process of neuralation

Answer 31

Lateral edges of neural plate become elevated, forming the neural fold
Depressed mid region called neural groove
Folds approach and fuse to form neural tube
This occurs in the middle of the embryo and extends towards the head and tail ends

Question 32

What does the neural tube become

Answer 32

Brain and spinal cord

Question 33

Formation and function of neural crest

Answer 33

Formed during neuralation as ectodermal cells from tube migrate and form several layers of vells
These give rise to the PNS

Question 34

Somite formation

Answer 34

Notochord instructs the lateral mesoderm (on either side of the neural tube) to form cuboidal structures called somites which form in parallel pairs

Question 35

Function of somites

Answer 35

These give rise to the vertebrae and muscles in the back.
There are three regions of somites (counting from the ectodermal side): dermatome connective tissue), myotome (muscles in the back/neck) and sclerotome (vertebrae and ribs).