Embryology Flashcards
the kidney is derived form which germ layer?
intermediate mesoderm
describe the intermediate structures in the development of the kidney
development of pronephros which are segmented at the cranial end
these regress completely and mesonephros develop below where the pronephros was
describe the mesonephros
unsegmented
associated with an adjacent long tube-like structure called the mesonephric duct
how does the mesonephros change during development?
begins to segment from the top downwards
segments connect to the mesonephric duct (forming mesonephric tubules) which connects to the cloaca (primitive bladder)
what happens to the mesonephric tubules during development?
40 pairs are produced craniocaudally
more cranial pairs regress by week 5 leaving 20 remaining pairs at level of L1-L3
what happens to the mesonephric duct during development?
differentiates into excretory units which function between 6-10 then
- completely regress in females
- becomes genital duct in males
what is the metanephros?
final intermediate stage of kidney development
becomes the permanent kidney
what forms the metanephros?
ureteric bud (forms at caudal end of mesonephric duct) and metanephric blastema
what is the metanephric blastema?
sacral 1/3rd of nephrogenic cord (mesenchymal tissue surrounding mesonephric duct comes away and encircles the ureteric bud)
what triggers the formation of the ureteric bud and when does this occur?
connecion of metonephros (mesonephric duct) with the cloaca
occurs around day 28
what happens to the metanephros during development?
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
what can cause agenesis of the kidney?
if uteric bud not present or not long enough to enter metanephric blastema
describe the shape of the kidney in early life and why
very lobular
as the ureteric bud branches into the metanephric blastema it divides the kidney to an extent into lobules
how do the major and minor calyxes develop?
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
what is a nephron and what is it derived from?
functional unit of the kidney for the filtration of blood and production of urine
derived from metanephric blastema
what are the 4 parts of the nephron?
bowmans capsule
proximal convoluted tubule
loop of henle
distal convoluted tubule
what is bowmans capsule?
expansion around group of capillaries (glomerulus)
what are the steps in formation of nephrons?
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
describe the ascent of the kindeys
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
name 2 common developmental anomalies in the kidneys
pelvic kidney - one kidney fails to ascend - harmless
horseshoe kidney - kidneys fuse in pelvis before ascent - can become trapped behind inferior mesenteric artery
which germ layer is the bladder developed from?
hindgut endoderm
how does the bladder develop?
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
what does the posterior cloaca become?
rectum/anal canal
pelvic urethra develops into what?
urethra in females
prostatic urethra in males
what part of the ureteric bud becomes the ureter and how does this come into contact with the bladder?
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
name 2 bladder defects which can occur due to urachal fistula
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
