Embryology

Question 1

What structure forms by week 5 that the kidneys develop from?

What are the 3 overlapping sequences that derive from it?

Answer 1

The urogenital ridge

1. Pronephros
2. mesonephros
3. metanephros

Question 2

When and where does the pronephros develop? What is its purpose?

Answer 2

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

Question 3

How does the pronephric duct induce the mesonephros? What is the blood supply?

Answer 3

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.

Question 4

What are the 2 components of the embryonic kidney?

Answer 4

The mesonephric duct + the mesonephric tubules

Question 5

What does the mesonephric duct give rise to? What unique role does it have in the development of males?

Answer 5

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.

Question 6

What does the ureteric bud form?

Answer 6

After sprouting from the mesonephric duct, it forms the metanephric blastema and the collecting ducts/system

Question 7

What does the blastema do collectively?

Answer 7

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

2. 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

Question 8

Where is the kidney’s original location and where does it end up?

Answer 8

Originally in the pelvis, ends in the posterior abdominal wall

Question 9

Where does the metanephros travel?

What stops the kidneys from continually ascending?

What descends while this is happening?

Answer 9

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

Question 10

How does the metanephros receive blood supply?

Answer 10

In pelvis: supplied by common iliac arteries, renal arteries shorten as the metanephros ascends and the ureters lengthen

Question 11

What happens to the metanephric vesicles?

Answer 11

They form the nephron, which is eventually invaginated by the glomerulus

Question 12

What is one issue that can occur with a polar renal artery?

Answer 12

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.

Question 13

When/how do nephrons develop, how many should be in each kidney and what can happen if you have a low nephron count?

Answer 13

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

Question 14

What determines how the ureteric bud branches?

Answer 14

Species-specific branching

Question 15

What does the cloaca give rise to?

Answer 15

The bladder and urethra

Question 16

What divides the cloaca?

Answer 16

Divided into 2 parts by the urorectal septum which descends down from the allantois and divides the posterior hindgut from the anterior cloaca

Question 17

Name 3 structures that are inevitably formed thanks to the urorectal septum, when should they be complete?

Answer 17

At week 6:

1. The bladder anteriorly with a urogenital membrane
2. Urethra
3. Anorectal canal posteriorly with an anal membrane which has to breakdown before poop can be passed

Question 18

What should the allantois become and what happens if it doesn’t?

Answer 18

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

Question 19

What is the urogenital sinus?

Answer 19

The space anterior to the urorectal septum

Question 20

Name the 3 parts of the urogenital sinus and what they form

Answer 20

1. Vesicle: forms the bladder, continuous with the allantois and receives some mesonephric ducts
2. Pelvic: forms entire urethra, and in reproductive tract…
   Females: some reproductive tract
   Male: prostatic and membranous urethra
3. Phallic: Reproduction
   Female: part of the reproductive tract
   Male: spongy urethra

Question 21

What do the vesicle mesonephric ducts help with?

Answer 21

Forming the muscles and CT of the trigone of the bladder wall

Question 22

What is unilateral renal agenesis? Is it detrimental? How would you check for it?

Answer 22

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

Question 23

What’s a bifid ureter?

Answer 23

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

Question 24

What does oligohydramnios mean? Which disease is most associated with this?

Answer 24

Means not enough amniotic fluid can be due to complete renal agenesis: the ureteric bud fails to develop on both sides

Question 25

What is a pancake kidney?

Answer 25

Fusion of 2 kidneys in the pelvis across the midline

Question 26

What is a supernumerary kidney

Answer 26

A kidney with an extra ureteric bud growing into the mesoderm

Question 27

What happens to the fetus if the pelvic kidney develops but fails to ascend out of the pelvic region?

Answer 27

Usually, nothing since the rest of the UG system developed normally

Question 28

What is a horseshoe kidney? What kinds of signs/symptoms could you experience?

Answer 28

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

Question 29

Why does polycystic kidney disease occur? What are 2 signs that can occur?

Answer 29

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

Question 30

What happens in Wilm’s Tumour?

Answer 30

Stem cells overproduce causing a kidney tumour in children

Question 31

What is an ectopic ureter?

What occurs when you have a crossed ectopia?

Answer 31

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

Question 32

What are the 3 urachal anomalies? Are they a problem?

Answer 32

1. Urachal cyst: A persisting remnant of the epithelial lining of the urachus, forms a sphere and is usually not a problem until inflamed
2. Urachus sinus: the urachus seals close to the bladder but not at the umbilicus (belly button) allowing serous fluid from the umbilicus to discharge
3. Urachal fistula: The urachus doesn’t close at all and urine can leak from the bladder out of the umbilicus (belly button)

Question 33

What happens in exstrophy of the bladder?

Answer 33

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