Formation Of The Body Plan

Question 1

What makes up a blastocyst?

Answer 1

Trophoblast
ICM
Blastocoel

Question 2

What does the ICM form?

Answer 2

Hypoblast

Epiblast

Question 3

What is Meckels diverticulum?

Answer 3

Remnant of yolk sac- small bulge in intestine

2% population

Question 4

What does ectoderm form?

Answer 4

Epidermis- skin, hair follicles, nails, sweat glands
Nervous system
Some cartilage/bone of head

Question 5

What does mesoderm form?

Answer 5

Notochord
Muscle
Cartilage/bone
Connective tissue
Heart
Kidney
Gonads
Reproductive system
Blood
Vasculature

Question 6

What does endoderm form?

Answer 6

Epithelial lining of:
Digestive tract
Lungs
Liver
Pancreas

Question 7

What is invagination?

Answer 7

Infolding of cell sheet into embryo

Question 8

What is involution?

Answer 8

Turning in of a cell sheet so it spreads of basal surface of an outer layer

Question 9

What is ingression

Answer 9

Migration of individual cells into embryo interior

Question 10

What is epiboly?

Answer 10

Spreading of an epithelial sheet over deeper cells

Question 11

What is formed where the Epiblast and Hypoblast are apposed?

Answer 11

Rostral buccopharyngeal

Caudal cloacal membranes

Question 12

What is the primitive streak and when does it form

Answer 12

• Day 14- start of gastrulation

* Ridge of cells along midline of caudal half of Epiblast layer

Question 13

What is the primitive node and when does it form?

Answer 13

After the primitive streak forms

Mound of cells at anterior end of primitive streak

Question 14

What induces the formation of the primitive node and streak and what’s it made up of?

Answer 14

• Signals from the Hypoblast layer

* Formed on the Epiblast layer

Question 15

How is the mesoderm layer formed?

Answer 15

Epiblast cells ingress through the primitive streak and break away from the Epiblast layer

Question 16

How is endoderm formed?

Answer 16

Cells ingress through primitive streak and displace Hypoblast, becoming endoderm

Question 17

What forms the prechordal mesoderm and notochord?

Answer 17

Cells that ingress through the primitive node

They move in the rostral direction

Question 18

Which part of the vertebral column retains notochord cells?

Answer 18

Nucleus pulposus

Question 19

What are somites formed from and how often?

Answer 19

Paraxial mesoderm

Every 4-5 hours

Question 20

What are the parts of a somite?

Answer 20

Sclerotome
Myotome
Dermatome

Question 21

What does the sclerotome form?

Answer 21

Axial skeleton

Question 22

What does the myotome form?

Answer 22

Skeletal muscles

Question 23

What does the dermatome form?

Answer 23

Connective tissue of dermal layer of dorsal skin

Question 24

What does intermediate mesoderm form?

Answer 24

Blood cells
Kidneys
Bladder
Reproductive organs

Question 25

How is the ectoderm formed?

Answer 25

From non ingressing cells of the Epiblast

Question 26

What is the organiser and why?

Answer 26

Primitive node • Signals mesoderm patterning by releasing Chordin and noggin- inhibitors of BMP (bone mophogenetic protein) • BMP forms a gradient specifying lateral plate, intermediate, paraxial and axial (dorsal) mesoderm —> BMP is a morphogen

Question 27

Outline neurulation

Answer 27

* Neural cells elongate becoming columnar * Lateral edges rise * Neural plate narrows as cells move towards midline * Edges meet and fuse to make neural tube and it’s placed beneath dorsal skin * Closure occurs first at hind brain/spinal cord boundary and zips up

Question 28

When does neural tube closure happen?

Answer 28

Days 18-30

Question 29

What causes anencephaly?

Answer 29

Failure to close anterior neural tube- forebrain in contact with amniotic fluid

Question 30

What causes spina bifida? | How can incidence be reduced?

Answer 30

Failure to close posterior neuropore- severe neurological impairment. Can be closed surgically. Folic avid supplements- reduces by 70%

Question 31

What is the neural crest and what does it form?

Answer 31

Multipotent stem cells Lateral edges of neural tube • Neurones mainly

Question 32

Do invertebrate embryos have neural crest cells?

Answer 32

No

Question 33

What do the pharyngeal arches form?

Answer 33

1st- jaw bones- maxilla and mandible 1st & 2nd- inner ear- stapes, incus, malleus 2nd- squamosal and alisphenoid bones 3rd & 4th- neck cartilage

Question 34

What is the stage at the end of neurulation?

Answer 34

Phylotypic stage