Esa 3 - Urinary System Session 2

Front 1

Outline the steps in embryological development of the kidneys and the ureter.

Back 1

The development of the kidneys and ureters involves the formation of 3 overlapping systems in sequence in cranial- caudal direction. They originate from intermediate mesoderm. They are the pronephros (rudimentary and non functional) the mesonephros (functions for a short time during fetal development) and the metanephros ( the definitive kidney). The following system will not develop unless the previous system has developed.

Front 2

Describe the pronephros system.

Back 2

The Pronephros appears at the start of week 4 in the cervical region from intermediate mesoderm and comprises of nephrotomes. It regresses by the end of week 4 and never functions as a kidney however the pronephric duct extends from cervical region to the cloaca and drives the mesonephros stage in the urogenital ridge ( region of intermediate mesoderm where gonads and kidneys arise) at the end of the 4th week.

Front 3

Describe the mesonephros system.

Back 3

The mesonephros and mesonephric ducts derive from the intermediate mesoderm from upper thoracic to upper lumbar segments. The nephrotomes form and lengthen to produce S shape loops comprising of the glomerular tuft and bowman’s capsule which form a renal corpuscle. Laterally the corpuscle enters into the mesonephric duct. In the middle of the second month the mesonephros forms a large ovoid organ on either side of the midline from the urogenital sinus. By the end of the second month the cranial tubules degenerate and disappear but in males the caudal tubules and mesonephric duct persist to form the genital system but they disappear in females.

Front 4

Describe the metanephros system.

Back 4

The metanephros, the definitive kidney, appears in 5th week from metanephric intermediate mesoderm (nephrogenic cord). The ureteric bud, an outgrowth from the mesonephric duct, penetrates the metanephric blastema (cap). The bud forms the ureter and dilates proximally to form the renal pelvis which later branches to form the major and minor calyces. From minor calyces, collecting tubules form. A metanephric cap covers each collecting tubule, and the tubules stimulate the cap to form small vesicles which give rise to s-shaped tubules - nephrons. Capillaries grow into one side of the s tubule and differentiate into glomeruli, which are connected to the bowman’s capsule, PCT, loop of henle and distal convoluted tubule. The distal convoluted tubule leads into the collecting tubule. There is an apparent ascent of the kidneys as they move from pelvic region to the abdomen, crossing the arterial fork of the umbilical arteries.

Front 5

What does the metanephric mesoderm and ureteric bud give rise to?

Back 5

The metanephric mesoderm (blastema) gives rise to the parenchyma of the kidney – the nephrons in the cortex and the medulla. The ureteric bud gives rise to the collecting system – the minor and major calices, the renal pelvis and the ureter.

Front 6

When does urine production begin?

Back 6

Urine production begins after the 1st trimester. Urine contributes to amniotic fluid.

Front 7

Define the urogenital ridge.

Back 7

The urogenital ridge is the region of intermediate mesoderm where the embryonic kidneys and gonads arise.

Front 8

Describe a pelvic kidney

Back 8

A pelvic kidney is formed when one kidney fails to ascend through the arterial fork formed by the umbilical arteries. It remains in the pelvis close to the common iliac artery.

Front 9

Describe a horseshoe kidney.

Back 9

Sometimes during ascent of the kidneys, while they are laterally rotating, they become pushed together to such an extent that the lower poles fuse to form a horseshoe shape. The horseshoe kidney is held at the lower lumbar region as its ascent is stopped by the inferior mesenteric artery.

Front 10

Describe accessory renal arteries.

Back 10

Accessory renal arteries are quite common and derive from the persistence of embryonic arteries which form during ascent of the kidneys. As they ascend from the pelvis into the abdomen, they are supplied by new direct branches from the abdominal aorta which usually bypass the renal hilum and enter at the superior and inferior poles.

Front 11

Describe renal agenesis.

Back 11

Renal agenesis is the imperfect development of the kidneys. The ureteric bud fails to interact with the metanephric tissue and so the development of the definitive kidney is not established. Or the nephrons may fail to develop and the uretetic bud fails to branch.
Bilateral renal agenesis results in renal failure and will cause oligohydramnios (decreased amniotic fluid) resulting in the potter sequence.

Front 12

Describe the potter sequence.

Back 12

The potter sequence is the atypical appearance of a child due to anuria (failure of kidneys to produce urine) and thus oligohydramnios ( decreased volume of amniotic fluid). Due to oligohydramnios the maternal uterine cavity is compressed resulting in flattened face, beak like nose and club feet. Other characteristics include hypoplastic lungs, cranial deformities, absence or abnormal vagina and uterus etc.

Front 13

Describe duplication of the ureter.

Back 13

Duplication of the ureter can occur by splitting of the ureteric bud. If partial splitting has occurred then the ureters will join to form one and share the same entry into the bladder. However if complete splitting has occurred, the ureter might empty into an ectopic site such as the vagina, urethra or vestibule. This can cause incontinence because the vagina does not have sphincters.

Front 14

Describe cystic disease of the kidneys.

Back 14

Cystic diseases can result from if the ureteric bud or kidney tissue fails to develop. Some diseases can lead to CRF. Diagnosis is made by finding multiple cysts on ultrasound. A single simple cyst is not an uncommon finding and should be considered normal.

Front 15

Describe cystic renal dysplasia.

Back 15

Cystic renal dysplasia is an area of undifferentiated mesenchyme or cartilage within the parenchyma. It can be unilateral or bilateral and is often associated with obstructive abnormalities in the ureter and lower urinary tract. Presentation is in childhood as an abdominal mass and is treated with surgical incision.

Front 16

Describe Adult polycystic kidney disease.

Back 16

Adult disease is caused by an autosomal dominant genetic mutation that causes 10% of chronic renal failures ( uraemia = symptoms). The mutations alter tubular epithelium growth and differentiation. Presentation is at 30-40years old with complications of hypertension, acute loin pain and/or haematuria or bilateral large palpable kidneys. End stage renal failure can occur in 50-60s leading to dialysis or kidney transplant. It is diagnosed early nowadays as relatives of affected individuals are screened with abdominal ultrasound.
Cysts develop anywhere in the kidney when dilated tubules or bowmans capsules compress the surrounding parenchyma and impair renal function. The kidneys are large with clear yellow fluid filled cysts, lined by cuboidal epithelium. Haemorrhage into cysts can occur. Cysts may also be found in liver, pancreas, lungs, ovaries, spleen and other organs.

Front 17

Describe children’s polycystic kidney disease.

Back 17

Children’s disease is caused by an autosomal recessive genetic mutation. It is a rare condition and presents with enlarged kidneys or stillbirth. Both sexes are affected equally. Both kidneys are enlarged by multiple dilated collecting ducts which form the cysts. These replace the medulla and cortex and extend into the capsule. The liver is almost always affected with cysts, bile duct cell proliferation, fibrosis and eventual portal hypertension.
The prognosis is poor and death usually occurs due to renal or respiratory failure within the first few weeks of life, unless renal replacement therapy is given.

Front 18

Describe wilm’s tumour.

Back 18

Wilms tumour is a kidney tumour which affects children by 5 years old but may occur in the foetus.

Front 19

Describe the formation of the urogenital sinus

Back 19

The hindgut, the caudal region of the primitive gut tube, has a single opening to the outside world via the cloaca. The cloca, becomes divided by the urogenital septum into the urogenital sinus comprising of the future bladder and urethra and the anal canal.
The urogenital sinus contains 3 parts: the largest upper part which forms the bladder and the lower pelvic and phallic parts which together form the urethra.

Front 20

Describe the relationship of the allantois, uracus, median umbilical ligament with the bladder.

Back 20

Initially the bladder is continuous with the allantois, but when the lumen of the allantois is destroyed, a thick fibrous cord remains called the urachus which connects the apex of the bladder with the umbilicus. In the adult, it forms the median umbilical ligament

Front 21

Describe the formation of bladder, vas deferens and urethra in males.

Back 21

In males the mesonephric ducts don’t regress and they extend to the urogenital sinus, entering at the upper bladder. The ureteric buds sprout from the mesonephric ducts. The urogenital sinus develops smooth muscle and the mesodermal lining is replaced by endoderm. It begins to expand so that the mesonephric ducts and ureteric buds have different openings in the UGS. The ureteric buds open into the trigone of the bladder and the mesonephric ducts enter into the prostate at the level of the prostatic urethra. The mesonephric ducts become the vas deferens.
The urethra is divided into pre-prostatic, prostatic, membranous which is the pelvic part of the UGS and the spongy urethra which is the phallic part.
.

Front 22

Describe the formation of the bladder and urethra in females

Back 22

The mesonephric ducts reach the urogenital sinus, entering at the upper bladder. The ureteric buds develop from the ducts. The urogenital sinus begins to expand and the mesonephric ducts start to degenerate. The ureteric buds open into the trigone of the bladder. The urethra is formed by the pelvic part of the urogenital sinus.

Front 23

Describe the formation of external genitalia.

Back 23

The components involve genital tubercle, genital folds and genital swellings.
In males the genital tubercle elongates and the genital folds fuse whereas in the female there is no fusion and the urethra opens onto the vestibule, anterior to the vagina.

Front 24

Describe urachal fistula, urachal cysts and urachal sinus.

Back 24

If the lumen of the allantois persists, this may cause urine to drain from the umbilicus forming a urachal fistula. If the lumen only remains in the middle of the median umbilical ligament, a urachal cyst may form. When the lumen in the upper part persists, a urachal sinus is formed which may or may not be continuous with the urinary bladder.

Front 25

Describe exstrophy of the bladder.

Back 25

The bladder opens onto the abdominal wall and ectopic urethral orifices are formed - epispadias is constant ( urethra opens onto upper dorsum of penis). It is probably due to failure of the lateral body wall folds to close in the midline of the pelvic region. The pelvic bones will not be joined either.

Front 26

Describe exstrophy of the cloaca.

Back 26

This is the most severe birth defect in the exstrophy-epispadias complex. A child with this condition will have the bladder and a portion of the intestines, exposed outside the abdomen, with the bony pelvis open like a book. In males the penis is either flat and short or sometimes split. In females the clitoris is split and there may be two vaginal openings. Also, frequently the intestine is short and the anus is not open. There is a high association with other birth defects, especially spina bifida , which occurs in up to 75 percent of cases. Omphalocele, a defect of the abdominal wall in the region of the umbilicus, is also common as are kidney abnormalities.

Front 27

Decribe hypospadias

Back 27

Hypospadias is a defect in the fusion of folds of the urethra so that the urethra opens on to ventral openings rather than end of glans.

Front 28

What foetal abnormality might you suspect if you examined a pregnant patient and discovered that
there was an abnormally low amniotic fluid volume?

Back 28

Bilateral renal agenesis - oligohydramnios.