105 - Development 2

Question 1

What does thalidomide do to embryos?

Answer 1

Causes amelia and meromelia (lacking entire limb, or part of a limb)

Question 2

When is thalidomide prescribed?

Answer 2

Complications of leprosy. Multiple myeloma.

Question 3

When is thalidomide able to affect development?

Answer 3

Between 20-36 days post-conception

Question 4

How does endoderm line organs in development?

Answer 4

Forms organ along with mesodermal tissue

Question 5

Coelom

Answer 5

Hollow space around viscera

Question 6

How does coelom form? 1 2 3 4 5 6 7

Answer 6

1) Lateral mesoderm splits. 2) Upper part become somatic mesoderm, joins to ectoderm 3) Lower part becomes splanchnic mesoderm, joins to endoderm. 4) Becomes continuous with extra-embryonic space 5) Edges of embryo fold in laterally to form coelom. 6) Most medial layer of splanchnic mesoderm/endoderm forms wall of the gut, dorsal and ventral mesentaries. 7) Somatic mesoderm joins to seal off coelom

Question 7

*Coelom formation

Answer 7

Question 8

Relationship between developing coelom and yolk sack

Answer 8

For a while the developing midgut is continuous with the yolk sack.

Question 9

Stomadeum

Answer 9

A pit where the mouth will form

Question 10

Proctadeum

Answer 10

A pit where the anus will form

Question 11

How is the stomadeum opened?

Answer 11

At ~3 weeks of age, oral plate that separates foregut from stomadeum breaks, oral cavity forms. Ectoderm and endoderm meet here

Question 12

How are anal and urogenital openings formed?

Answer 12

1) Anus is sealed by cloacal membrane (ectoderm and endoderm) 2) Allantois forms as branch of the hind gut 3) Between allantois and hindgut is urorectal septum (mesoderm) 4) Urorectal septum extends to divide rectum from the urogenital tract

Question 13

Allantois 1 2

Answer 13

1) Lies within the body stalk 2) Stores nitrogenous waste in some species, vestigial in humans (but very important in human development)

Question 14

What does the allantois give rise to in humans?

Answer 14

Bladder

Question 15

Pharyngeal arches 1 2 3

Answer 15

1) Prominent arches near head. 2) Resemble some of the structures of gills (but aren’t gills) 3) Modified for other purposes (EG: jaw, blood vessels, muscles of face, middle ear, Eustachian tube, hyoid, larynx and pharynx, parathyroid gland)

Question 16

Pharyngeal pouches

Answer 16

Structure between pharyngeal arches. Endodermal lining of pharyngeal pouches forms distinct structures.

Question 17

Germ layer derivation of heart

Answer 17

Splanchnic mesoderm (lateral mesoderm)

Question 18

Initial formation of heart

Answer 18

Forms tubes bilaterally

Question 19

Stage in cardiac development, after the formation of the two endocardial tubes

Answer 19

Fusion of endocardial tubes.

Question 20

*Arrangement of heart once fusion of endocardial tubes has taken place

Answer 20

Question 21

Stages of heart development 1 2 3

Answer 21

1) Splanchnic mesoderm forms endocardial tubes 2) Fusion of endocardial tubes 3) Folding of heart 4)

Question 22

Features of congenital heart defects 1 2

Answer 22

1) Often of no consequence to the foetus. 2) An issue immediately after birth

Question 23

Most common cardiac developmental defect

Answer 23

Ventricular septal defect (~25%)

Question 24

Ventricular septal defect aetiology 1 2 3

Answer 24

1) Initial single ventricle is divided partly by ventricular septum. 2) Leaves intraventricular foramen 3) Filled by membranous part of intraventricular septum

Question 25

Atrial septal defects 1 2 3

Answer 25

1) Patent hole in atrial septum to allow bypass of pulmonary circulation (formen ovalae) 2) Valve on formen should shut once baby begins breathing (increases left atrial pressure) 3) If valve is defective, won’t close on first breath

Question 26

Aspect of heart contributed to by neural crest

Answer 26

Outflow tract of the heart. If malformed, results in an issue with atrial outflow of heart

Question 27

GIT at one month

Answer 27

At around one month, GIT consists of foregut and hindgut and a midgut still connected to the yolk sac by yolk stalk

Question 28

*Folding of GIT in a foetus

Answer 28

Question 29

Folding of GIT in a foetus 1 2 3 4 5 6

Answer 29

• Initially GIT only as long as the foetus • Quickly lengthens • Begins to buckle in midgut around yolk stalk • Rotates around axis of yolk stalk and superior mesenteric a. • Folds large intestine across small intestine • Further elongation of large intestine gives characteristic folding

Question 30

Developmental herniation of GIT 1 2 3

Answer 30

1) Week 6-7 - Growing gut is too big for body cavity. 2) Pushes into body stalk. 3) Week 9 - Body cavity is larger, but retracts back.

Question 31

Name for failure to retract gut back into body cavity

Answer 31

Omphalocoele

Question 32

Name for retraction of gut but failure to seal abdominal wall

Answer 32

Umbilical hernia

Question 33

Development of viscera 1 2

Answer 33

• Trachea, lungs, liver and pancreas initially appear as endodermal out-pocketings • Endoderm in out-pocketings is interacting with mesoderm

Question 34

Name for when organs are in mirror image to normal

Answer 34

Situs invertus

Question 35

Situs invertus prevalence

Answer 35

1:10000

Question 36

How is anterior-posterior axis determined?

Answer 36

By first division of zygote.

Question 37

How is dorsal-ventral axis set?

Answer 37

Blastocyst

Question 38

What sets left-right asymmetry?

Answer 38

Primitive groove. Patch of cilia, which normally beat counter-clockwise. Leads to concentrations of factor on the left

Question 39

How does situs invertus come about?

Answer 39

Cilia in primitive groove beat in clockwise direction, or don’t beat at all

Question 40

Three stages of kidney development

Answer 40

Pronephros, mesonephros, metanephros

Question 41

Development of the definitive kidney 1 2 3 4

Answer 41

• Kidney is from mesoderm not endoderm • Mesonephros induces metanephros • Mesonephros degenerates (leaving mesonephric duct) • Mesonephros connects to developing testes in male, degenerates completely in females. Separate mesodermally-derived duct (Mullerian) survives in females, becomes fallopian tubes

Question 42

Migration of kidneys in development

Answer 42

Develop quite low in body cavity, ascend.

Question 43

Development of external genitalia 1 2 3 4

Answer 43

1) Initial development is identical between sexes 2) When cloaca is present, genital tubercle overlies urogenital folds and cloacal membrane 3) Once anus splits from urogenital tract, males and females become different. 4) Shaft of penis forms from urogenital folds fusing (urethral groove can fail to fuse)

Question 44

Name for failure of fusion of male urethral groove

Answer 44

Hypospadiasis (1:300)