Urinary Embryology

Question 1

What are the buccopharyngeal membrane and the cloacal membrane?

Answer 1

Two zones where there is no mesoderm separating the ectoderm and endoderm ,because of the absence of mesoderm it is avascular and so the tissue will eventually die leaving an orifice.

Question 2

What is the urogenital ridge?

Answer 2

Region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad.

Question 3

In general terms how does the kidney develop?

Answer 3

3 kidney system develop sequentially. Once one system has disappeared the next one appears.

Question 4

Where and what is the first appearance of renal tissue?

Answer 4

In the cervical region called the pronephros at the beginning of week 4.

Question 5

What is the pronephros?

Answer 5

This contains a primary duct that drives the next developmental stage. The Pronephros’ main function is to create a duct that extends from the cervical region down into the pelvic region.

Question 6

Does the pronephros ever have any renal function?

Answer 6

No renal function in the pronephros. It’s duct becomes the mesonephric duct.

Question 7

What is the nephrotome?

Answer 7

Nephrotome are the functional unit of the pronephros and are prototype nephrons. It contains a glomerulus, bowman’s capsule, proximal and distal convoluted tubule and a collecting duct. They degenerate in the next stage. During development of the final nephrons the glomerulus pushes into the bowman’s capsule.

Question 8

What is the mesonephros?

Answer 8

The mesonephros appears at the end of week 4 and regresses by week 8. It has limited renal function but no ability to reabsorb water. The mesonephros sprouts tubules that develop caudal to the pronephric region. The mesonephric tubules plus the mesonephric duct = embryonic kidney.

Question 9

What forms the mesonephros?

Answer 9

The mesonephros forms from the duct of the pronephros.

Question 10

What developmental importance does the mesonephric duct have?

Answer 10

The mesonephric duct sprouts the ureteric bud which induces development of the definitive kidney. Mesonephric duct has important roles in development of the reproductive system in the male.

Question 11

What is the metanephros?

Answer 11

The metanephros appears at week 5 and doesn’t regress, it forms the definitive kidneys and has water conserving abilities from the end of the 1st trimester.

Question 12

What does the excretory portion of the definitive kidney form from?

Answer 12

The excretory portion of the definitive kidney forms from the metanephric tissue cap (Cells around the distal end of the metanephric diverticulum that forms the nephrons in the definitive kidneys).

Question 13

What does the collecting system of the definitive kidney form from?

Answer 13

The collecting system develops from the ureteric bud

Question 14

What is the metanephric blastema?

Answer 14

Differentiated intermediate mesoderm

Question 15

How does the ureteric bud and metanephric blastema become one?

Answer 15

The ureteric bud makes contact with the metanephric blastema in the caudal region of the embryo. This bud then expands and branches forming the kidney.

Question 16

What drives the development of the definitive kidneys?

Answer 16

The ureteric bud drives the development of the definitive kidney. The collecting system is derived from the ureteric bud itself and the excretory component is derived from the intermediate mesoderm under the influence of the ureteric bud.

Question 17

Where does the metanephric kidney first appear?

Answer 17

The metanephric kidney first appears in the pelvic region

Question 18

How does it end up in it’s normal position?

Answer 18

It undergoes an apparent caudal to cranial shift, crossing the arterial fork formed by vessels returning blood from the foetus to the placenta (umbilical artery). The kidney moves by sprouting new vessels above its current ones higher up the abdominal aorta, this repeats over and over again pulling the kidney into the lumbar region of the body. (kidney doesn’t actually move trunk just moves downwards).

Question 19

Other than caudal to cranial, what other movements do the kidneys undergo?

Answer 19

There is lateral movement and meeting with the adrenal glands, and a 90degree rotation so that the renal pelvis faces the midline.

Question 20

What is the bladder derived from?

Answer 20

The bladder is a hindgut derivative

Question 21

What is the cloaca?

Answer 21

In early development the gastrointestinal, urinary and reproductive tracts end at a single structure called the cloaca which is separated from the outside by the cloacal membrane.

Question 22

How is the Urogenital tract is separated from the GI tract.

Answer 22

Urogenital sinus is created from hindgut by urorectal septum – a wedge of mesoderm growing downwards towards to cloacal membrane driving a wedge of tissue separating the cloaca into 2 tracts, the urogenital and GI separately.

Question 23

What is a diverticulum?

Answer 23

A blind ended tube comign from a cavity of passage?

Question 24

What is the allantois?

Answer 24

The allantois is a diverticulum of the hindgut that extends into the umbilical cord and helps the embryo with the exchange of gases and liquids. It is involved in the formation of the bladder and eventually the lumen is obliterated to form the urachus which in adults forms the median umbilical ligament.

Question 25

How is the urogenital sinus divided up?

Answer 25

Urogenital sinus is divided into 3 parts. The upper part is the largest and is the future bladder, pelvis and phallic are parts of the future urethra.

Question 26

How does the bladder develop in males?

Answer 26

• Mesonephric ducts reach the urogenital sinus and drains embryonic urine into the cloaca
• Ureteric Bud sprouts from the mesonephric duct, the ureteric bud will become ureter opening into the bladder
• Smooth musculature begins to appear this will become the trigone of the bladder
• Urogenital sinus begins to expand
• Ureteric buds and mesonephric buds make independent openings in urogenital sinus
• Prostate and prostatic urethra formed. Mesonephric duct is maintained in the male, forming the prostate and ductus deferens of the male reproductive system.

Question 27

How does the bladder form in females?

Answer 27

The female bladder develops in much the same way, but without male hormones the Mesonephric duct regresses. Therefore, females do not form prostates or the tubes of the male reproductive system.

Question 28

How are the urethra’s formed in males and females?

Answer 28

Female urethra is formed by the pelvic part of the urogenital sinus. The male urethra is divided into 4 parts: pre-prostatic, prostatic, membranous (all three from the pelvic part of the urogenital sinus) and spongy (phallic part). These first 3 parts are the same as in females.

Question 29

What is renal agenesis

Answer 29

Ureteric bud fails to interact with the intermediate mesoderm, this can affect one or both kidneys. If bilateral will result in low amounts of amniotic fluid as urine is the major contributor to the amniotic fluid.

Question 30

Describe a pelvic kidney

Answer 30

A kidney could fail to ascend properly if it gets caught on the arterial fork – known as a pelvic kidney.

Question 31

What causes a horse shoe shaped kidney to form?

Answer 31

As the kidneys lie so close to each other they can fuse to form a horse shoe shaped kidney as it then ascends it gets caught on the first midline unpaired branch off the aorta called the inferior mesenteric artery and so is located at the pelvic brim.

Question 32

What duplication defects can arise?

Answer 32

If the ureteric bud splits you can end up with two ureters coming from a kidney and one of them may open ectopically i.e. into the vagina or urethra bypassing the bladder and leading to incontinence.

Question 33

What is cystic kidney disease?

Answer 33

Polycystic kidney disease is recessive and present early so has a poor prognosis. Multiple cysts appear on the kidney.

Question 34

What is a fistulae?

Answer 34

This is an abnormal or surgically made passage between a hollow or tubular organ and the body surface, or between two hollow or tubular organs.

Question 35

What is exstrophy of the bladder?

Answer 35

This is where the bladder opens into the abdominal wall due to a mal development of part of the abdominal wall so the bladder communicates with the amniotic fluid. This usually happens due to a urachal fistula

Question 36

What are Supernumery Arteries

Answer 36

As the kidneys ascend it requires new arteries to be grown, usually the old one ascends but sometimes it may not and as a result it will continues supplying the kidney in question. These arteries are end artereis so if they become damaged then ths part of the kidney will become infarcted.

Question 37

What is Hypospadias

Answer 37

Defect in fusion of the urethral folds, urethra opens onto the ventral surface of the penis rather than at the end of the glans and the incidence of this is increasing.