Embryology

Question 1

What does the cephalic limb of primary intestinal loop form?

Answer 1

Duodenum Jejunum Ileum

Question 2

What does the caudal limb of primary intestinal loop form?

Answer 2

Ileum Caecum Appendix Ascending colon Proximal 2/3 transverse colon

Question 3

What happens when the abdomen cannot contain intestines anymore during development?

Answer 3

Physiological umbilical hernia forms, around 6 weeks

Question 4

What happens to the midgut to form the small intestine loops?

Answer 4

270 degree counterclockwise rotation

Question 5

How does the liver and gall bladder form?

Answer 5

End of 3rd week Is outgrowth of distal end of foregut Link narrows to form the bile duct The bile duct then gives rise to the gall bladder

Question 6

How is the pancreas formed?

Answer 6

Forms from pancreatic buds

Question 7

What is atresia?

Answer 7

Complete absence of a lumen

Question 8

What happens to the cloacal membrane during development?

Answer 8

Divides into urogenital membrane and anal membrane

Anal membrane ruptures at week 9

Open anus forms

Question 9

What are the 3 stages of kidney development?

Answer 9

Pronephors

Mesonephros

Metanephros

Question 10

What happens to the mesonephric duct and metanephros during development?

Answer 10

Mesonephric duct = derives kidney around 28 days

Metanephros = persists as funcitoning kidney - forms metanephric blastema

Question 11

What is the role of the ureteric bud during development?

Answer 11

Diltates to form primitive renal pelvis

Forms ureter, renal pelvis, major and minor calyces and millions of collecting tubes

Question 12

What causes the ascent of kidneys during development?

Answer 12

Reduction of body curvature and body growth in lumbar and sacral regions

Question 13

What happens during gonad development?

Answer 13

Germ cells migrate to ridges of gonads along dorsal mesentery

No gonad development if germ cells dont reach them

Question 14

What happens during femal genitalia formation?

Answer 14

• Primitive sex cords disappear at week 6
• Epithelium proliferation in week 7 to form cortical cords
• Cortical cord splitting, forming cell clusters
• Clusters surround germ cells forming primary oocytes
• Surrounded by follicular cells
• Para and mesonephric duct form = anterolateral surface of urogenital ridge
• Paramesonephric duct intially separated by spetum, then fuse forming uterine canal and upper vagina
• Urogenital sinus forms lower part of vagina

Question 15

What happens during male genitalia formation?

Answer 15

• Primitive sex cords continue proliferating into medulla
• Testes cords form
• Become separated from epithelium by tunica albuginea
• Mesonephric duct forms vas deferens
• Degeneration of paramesonephric duct
• Mesonephric duct forms main genital tract
• Urogenital mesentery attaches testes and mesonephros to posterior abdominal wall in 2nd month
• Testes descend through inguinal ring over pubic bone but bloody supply retained

Question 16

What happens during femal external genitalia formation?

Answer 16

• Genital tubercle enlarges and elongates forming clitoris
• Urethral folds form labia minora
• Genital swellings enlarge forming labia majora

Question 17

What happens during male external genitalia formation?

Answer 17

• Androgens cause elongation of genital tubercule tube
• Phallus forms, pulling urethral folds together, close to forms penile urethra
• 4th month forms complete canal and erithral outlet
• Scrotal swellings form

Question 18

Where does the thyroid develop from?

What then forms?

Answer 18

Develops from endodermal downgrowth of floor of pharynx

Develops between anterior two thirds and posterior third of tongue

Grows from foramen caecum to thyroid cartilage

Forms thyroglossal duct

Question 19

What are the origins of the adrenal cortex and medulla?

Answer 19

Cortex = mesoderm

Medulla = neural crest