Lecture 11 - Embryology II

Question 0

What are the pharyngeal arches?

Answer 0

They are a vestige of gills

In humans, they develop into the pharynx, larynx, jaw etc

Question 1

When are the pharyngeal arches visible?

Answer 1

Only in the embryo

Question 2

When do limbs start to form?

Answer 2

Fourth to eighth week

Question 3

Describe limb formation

Answer 3

A bud starts to form out (pulls dermatome with it)

HOX genes set up the various regions of the limb

Question 4

Describe how HOX genes form the regions of the limb

Answer 4

Hand: HOXd genes 9-13
Wrist: HOX 9-12
Arm: HOX 9-10
Scapula: 9

Question 5

Which germ layers are involved in limb development?

Answer 5

Initiated by mesoderm, controlled by ectoderm

Question 6

Describe formation of hands and feet

Answer 6

Start off as flat, symmetrical disks

Apoptosis sculpts the fingers and toes

Question 7

All derivates of the endoderm are…

Answer 7

Epithelial tissue

Question 8

Describe how the yolk sac separates from the lumen of the gut

Answer 8

Pinches off like a draw string

However, it remains attached for a long time at the midgut region

Question 9

How does the trilaminar disk become a hollow tube?

Answer 9

A coelom forms from the split in the lateral mesoderm

The splanchnic mesoderm extends down and meets to form the GIT
The somatic mesoderm extends down and meets, enclosing the GIT and coelom

Question 10

When do the mouth and anus form?

Answer 10

After three weeks of development

Question 11

Describe formation of the mouth

Answer 11

Stomadeum separated from forget by the oral plate

The oral plate breaks down to form a continuous tube

Question 12

Describe formation of the anus

Answer 12

The proctodeum is initially sealed by the cloacal membrane

The urorectal septum extends down, separating the rectum and the allantois

Question 13

What is in between the allantois and the rectum?

Answer 13

Urorectal septum

Question 14

What does the allantois give rise to?

Answer 14

Urethra and bladder

Question 15

From what does the heart develop?

Answer 15

Splanchnic mesoderm

Question 16

Describe the formation of the heart

Answer 16

Initially as two tubes from the splanchnic mesoderm which fuse to form the myocardium

After fusion, the heart folds

Symmetrically aortic arches develop, and are then remodelled

Question 17

What is interesting about the time scale of the developing heart?

Answer 17

Organogenesis continues while the heart beats from day 22 onwards

Question 18

Describe the flow of blood in the developing heart

Answer 18

Unidirectional during development: flow of blood through the fossa ovalis

At birth, the whole needs to close up immediately

This is a very common birth defect

Question 19

Describe the arterial supply of the regions of the gut

Answer 19

Foregut: coeliac artery
Midgut: superior mesenteric artery
Hindgut: inferior mesenteric artery

Question 20

Describe growth of the GIT

Answer 20

Quickly starts to lengthening –> herniation out of the body wall

Rotation gives rise to the large intestine

Gut retracts back between week 6-9

Question 21

What is omphalocoele?

Answer 21

Failure of the gut to retract

Question 22

What is an umbilical hernia?

Answer 22

Retraction, but failure of the body wall to seal up

Question 23

Describe formation of viscera

Answer 23

Endodermal outpocketings interacting with mesoderm

Question 24

Does the genital or urinary system form first?

Answer 24

Urinary

Question 25

Describe the development of the urinary system

Answer 25

Pronephos
- pronephric duct
Mesonephros
- mesonephric duct
Metanephros

Question 26

What becomes of the neohrostomes?

Answer 26

Degenerate

Question 27

What becomes of the mesonephric duct?

Answer 27

Vas deferens in males

Degenerates in females

Question 28

What becomes of the metanephros?

Answer 28

Becomes the kidneys and ureters

Question 30

What becomes of the Müllerian duct?

Answer 30

Fallopian tube, uterus, distal vagina

Question 31

What does the somatic mesoderm go on to form?

What about the splanchnic mesoderm?

Answer 31

Somatic:
• body wall

Splanchnic:
• viscera

NB ectoderm and endoderm are involved

Question 32

Which structure will become the coelom?

Answer 32

The gap in the lateral mesoderm between somatic and splanchnic mesoderm

Question 33

What does the metanephros consist of?

Answer 33

Kidney and ureters

Question 34

What does the neural tube go on to form?

Answer 34

The brain and spinal cord

Question 35

What does the notocord go on to form?

Answer 35

Nucleus pulposus