Embryology

Question 1

the kidney is derived form which germ layer?

Answer 1

intermediate mesoderm

Question 2

describe the intermediate structures in the development of the kidney

Answer 2

development of pronephros which are segmented at the cranial end
these regress completely and mesonephros develop below where the pronephros was

Question 3

describe the mesonephros

Answer 3

unsegmented

associated with an adjacent long tube-like structure called the mesonephric duct

Question 4

how does the mesonephros change during development?

Answer 4

begins to segment from the top downwards

segments connect to the mesonephric duct (forming mesonephric tubules) which connects to the cloaca (primitive bladder)

Question 5

what happens to the mesonephric tubules during development?

Answer 5

40 pairs are produced craniocaudally

more cranial pairs regress by week 5 leaving 20 remaining pairs at level of L1-L3

Question 6

what happens to the mesonephric duct during development?

Answer 6

differentiates into excretory units which function between 6-10 then

• completely regress in females
• becomes genital duct in males

Question 7

what is the metanephros?

Answer 7

final intermediate stage of kidney development

becomes the permanent kidney

Question 8

what forms the metanephros?

Answer 8

ureteric bud (forms at caudal end of mesonephric duct) and metanephric blastema

Question 9

what is the metanephric blastema?

Answer 9

sacral 1/3rd of nephrogenic cord (mesenchymal tissue surrounding mesonephric duct comes away and encircles the ureteric bud)

Question 10

what triggers the formation of the ureteric bud and when does this occur?

Answer 10

connecion of metonephros (mesonephric duct) with the cloaca

occurs around day 28

Question 11

what happens to the metanephros during development?

Answer 11

around day 32 the ureteric bud begins to branch out and penetrate into the metanephric blastemal forming the major and minor calyxes, ureter, renal pelvis and collecting ducts

Question 12

what can cause agenesis of the kidney?

Answer 12

if uteric bud not present or not long enough to enter metanephric blastema

Question 13

describe the shape of the kidney in early life and why

Answer 13

very lobular

as the ureteric bud branches into the metanephric blastema it divides the kidney to an extent into lobules

Question 14

how do the major and minor calyxes develop?

Answer 14

ureteric bud branches for 4 generations, these early branches then coalesce/merge back together forming the major calyxes
this then happens again as the ureteric bud branches further a few times and then merges again to form the minor calyxes

Question 15

what is a nephron and what is it derived from?

Answer 15

functional unit of the kidney for the filtration of blood and production of urine
derived from metanephric blastema

Question 16

what are the 4 parts of the nephron?

Answer 16

bowmans capsule
proximal convoluted tubule
loop of henle
distal convoluted tubule

Question 17

what is bowmans capsule?

Answer 17

expansion around group of capillaries (glomerulus)

Question 18

what are the steps in formation of nephrons?

Answer 18

collecting tubule branches with each tip being in contact with metanephric tissue which communicate with each other
this triggers mesonephric tissue cells to reorganise and form renal vesicles
these renal vesicles then elongate to form an S shaped structure which grows towards the vasculature forming the bowmans capsule and towards the collecting tubule at the other end
wall between the collecting duct and growing vesicle (developing nephron) breaks down allowing communication between both structures - forming the nephron

Question 19

describe the ascent of the kindeys

Answer 19

ascend from pelvis to level of L1/L2 during weeks 6-9
blood supply is initiallt the common iliacs however new vessels form to supply the kidneys at each level of ascent
these usually regress however accessory renal arteries are often seen in adulthood

Question 20

name 2 common developmental anomalies in the kidneys

Answer 20

pelvic kidney - one kidney fails to ascend - harmless

horseshoe kidney - kidneys fuse in pelvis before ascent - can become trapped behind inferior mesenteric artery

Question 21

which germ layer is the bladder developed from?

Answer 21

hindgut endoderm

Question 22

how does the bladder develop?

Answer 22

hindgut endoderm forms the cloaca
cloaca is divided into anterior and posterior by wedge of mesoderm (urorectal septum)
anterior becomes primitive urogenital sinus which develops into
- bladder
- pelvic urethra
- definitive urogenital sinus

Question 23

what does the posterior cloaca become?

Answer 23

rectum/anal canal

Question 24

pelvic urethra develops into what?

Answer 24

urethra in females

prostatic urethra in males

Question 25

what part of the ureteric bud becomes the ureter and how does this come into contact with the bladder?

Answer 25

proximal part
ureteric bud branches off of mesonephric duct before it enters the cloaca
the mesonephric duct frays out into the cloaca until the ureteric bud is in direct contact with the cloaca

Question 26

name 2 bladder defects which can occur due to urachal fistula

Answer 26

urachal fistula usually closes and becomes a ligament

• can have a bit left open in the middle forming a urachal cyst
• can close proximally causing while open distally forming a urachal sinus