Embryology Flashcards
What structure forms by week 5 that the kidneys develop from?
What are the 3 overlapping sequences that derive from it?
The urogenital ridge
- Pronephros
- mesonephros
- metanephros
When and where does the pronephros develop? What is its purpose?
The 4th week in the cervical region.
The pronephric duct is formed by divisions of the intermediate mesoderm known as “nephrotomes” extends from the cervical region to the cloaca and drives the development of the next stage
How does the pronephric duct induce the mesonephros? What is the blood supply?
The pronephric duct continues as the mesonephric duct.
The pronephric duct also induces nearby intermediate mesoderm in the thoracolumbar region to form mesonephric tubules, supplied by the dorsal aorta.
What are the 2 components of the embryonic kidney?
The mesonephric duct + the mesonephric tubules
What does the mesonephric duct give rise to? What unique role does it have in the development of males?
Sprouts the ureteric bud which induces the development of the definite kidney.
The mesonephric duct disintegrates in women and gives rise to testicles in men.
What does the ureteric bud form?
After sprouting from the mesonephric duct, it forms the metanephric blastema and the collecting ducts/system
What does the blastema do collectively?
Forms the metanephric system:
1. Collecting ducts derived from the ureteric bud: dilate to create the ureter, renal pelvis, calyces, CTs and terminates at the DCT
- Excretory system derived from the metanephric blastema: Each CT covered by metanephric tissue and gives rise to the proximal nephron (LOH, PCT and DCT) and bowman’s capsule
Where is the kidney’s original location and where does it end up?
Originally in the pelvis, ends in the posterior abdominal wall
Where does the metanephros travel?
What stops the kidneys from continually ascending?
What descends while this is happening?
Ascends from the pelvic region and medially rotates 90 degrees. (Hilum goes from facing forwards - medial)
The suprarenal glands stop the kidneys from continuously ascending
The gonads descend:
Male scrotum and female internal pelvic cavity
How does the metanephros receive blood supply?
In pelvis: supplied by common iliac arteries, renal arteries shorten as the metanephros ascends and the ureters lengthen
What happens to the metanephric vesicles?
They form the nephron, which is eventually invaginated by the glomerulus
What is one issue that can occur with a polar renal artery?
A polar renal artery is a persisting older vessel (branched off the aorta) that supplied the kidney when it was lower in the fetus.
If it fails to degenerate and lays across the ureter it can obstruct the flow: resulting in an enlarged ureter and renal pelvis, kidney damage and the calyces may flatten rather than cup due to increased pressure.
When/how do nephrons develop, how many should be in each kidney and what can happen if you have a low nephron count?
They develop before birth through nephrogenesis from the metanephric mass
Before birth, 0.8-1mill nephrons, a low count can mean an increased risk of hypertension and renal insufficiency
What determines how the ureteric bud branches?
Species-specific branching
What does the cloaca give rise to?
The bladder and urethra
What divides the cloaca?
Divided into 2 parts by the urorectal septum which descends down from the allantois and divides the posterior hindgut from the anterior cloaca
Name 3 structures that are inevitably formed thanks to the urorectal septum, when should they be complete?
At week 6:
- The bladder anteriorly with a urogenital membrane
- Urethra
- Anorectal canal posteriorly with an anal membrane which has to breakdown before poop can be passed
What should the allantois become and what happens if it doesn’t?
Forms the urachus which becomes the umbilical cord (channel from the bladder). After birth, it should degenerate into the median umbilical ligament
If it fails to degenerate a urachal abnormality can occur
What is the urogenital sinus?
The space anterior to the urorectal septum
Name the 3 parts of the urogenital sinus and what they form
- Vesicle: forms the bladder, continuous with the allantois and receives some mesonephric ducts
- Pelvic: forms entire urethra, and in reproductive tract…
Females: some reproductive tract
Male: prostatic and membranous urethra - Phallic: Reproduction
Female: part of the reproductive tract
Male: spongy urethra
What do the vesicle mesonephric ducts help with?
Forming the muscles and CT of the trigone of the bladder wall
What is unilateral renal agenesis? Is it detrimental? How would you check for it?
Failure of the ureteric bud to develop from the mesonephric duct on one side: results in one fetal kidney failing to develop.
Not usually a problem as they still have one healthy kidney. Can detect this in infants by checking the umbilical cord for one umbilical artery
What’s a bifid ureter?
The complete division of the ureteric bud means a divided kidney or 2 kidneys are formed, which drain into separate ureters that unite before the bladder
What does oligohydramnios mean? Which disease is most associated with this?
Means not enough amniotic fluid can be due to complete renal agenesis: the ureteric bud fails to develop on both sides
What is a pancake kidney?
Fusion of 2 kidneys in the pelvis across the midline
What is a supernumerary kidney
A kidney with an extra ureteric bud growing into the mesoderm
What happens to the fetus if the pelvic kidney develops but fails to ascend out of the pelvic region?
Usually, nothing since the rest of the UG system developed normally
What is a horseshoe kidney? What kinds of signs/symptoms could you experience?
Horseshoe kidney is when kidneys join at their lower poles, so the lower calyces are closer to the spine than upper ones
Usually asymptomatic, but can cause hematuria, kidney stones and recurrent UTIs
Why does polycystic kidney disease occur? What are 2 signs that can occur?
Inherited: autosomal dominant diagnosed in adulthood, and autosomal recessive occurs in babies as they’re born leads to abnormal nephron dilation which forms fluid-filled cysts in the kidney.
Raised BP and renal failure
What happens in Wilm’s Tumour?
Stem cells overproduce causing a kidney tumour in children
What is an ectopic ureter?
What occurs when you have a crossed ectopia?
A ureter that doesn’t terminate in the bladder, instead terminating in the urethra for males and urethra or vagina in females
In a crossed ectopia one kidney can migrate to the other side
What are the 3 urachal anomalies? Are they a problem?
- Urachal cyst: A persisting remnant of the epithelial lining of the urachus, forms a sphere and is usually not a problem until inflamed
- Urachus sinus: the urachus seals close to the bladder but not at the umbilicus (belly button) allowing serous fluid from the umbilicus to discharge
- Urachal fistula: The urachus doesn’t close at all and urine can leak from the bladder out of the umbilicus (belly button)
What happens in exstrophy of the bladder?
Anterior abdominal wall failed to fuse, bladder opens onto the ventral wall of the embryo and is exposed to the outside, urine can trickle out of the openings
