Case 3- embryology

Question 1

The three stages of kidney development

Answer 1

Pronephros -> mesonephros -> metanephros. Develops from the dorsal band of the intermediate mesoderm from the 4th week of development in a cranial to caudal sequence

Question 2

First stage of kidney development

Answer 2

Pronephros- consists of a few vestigial remnant’s in the cervical region. They are transient and non-functioning (week 4-5), associated with pronephric duct

Question 3

Second stage of kidney development

Answer 3

Mesonephros= appears in the upper thoracic to upper lumbar segments (weeks 4-12). By the sixth week it forms a large oval structure on either side of the midline with the gonads in the centre. Excretory tubules form which are the Mesonephric (Wolffian) ducts which lies laterally, extending from the cranial limits of the Mesonephric to the Cloaca. The mesonephros is a derivative of the intermediate mesoderm.

Question 4

Third stage of kidney development

Answer 4

Metanephros- starts to form in the 5th week and coexists with the mesonephros till it disintegrates. The ureteric bud grows from the caudal end of the mesonephric duct and penetrates the Metanephric blastema. This bud forms all the collecting systems in the kidney and the filtration system, as a result of growing and branching. The first branch forms the major calyx, then the minor calyx. The metanephros (ureteric bud and metanephric mass) detaches from the mesonephric duct. As the kidneys develop the bladder is formed from the cloaca, a chamber derived from endoderm. From the 5th to 7th week the cloaca divides to form the urogenital sinus anteriorly and the anal canal posteriorly. Formed from the downgrowth of the uro-rectal septum. Growth of the urogenital sinus form the metanephric ductus. Growth continues till the ureters are incorporated causing the metanephric ducts to enter the urethra. The ureters enter into the bladder. Metanephric duct forms a triangular region of the bladder called the trigone.

Question 5

What happens to the mesonephric duct after the metanephros detaches?

Answer 5

In a male the Mesonephric duct forms the ejaculatory duct, seminal vesicles and ductus deferens. In females it degenerates.

Question 6

Third stage of kidney development- migration and rotation

Answer 6

The metanephros develops in the caudal area but migrates to the lumbar region, in the posterior abdominal wall. In the 8th week kidneys migrate cranially. The renal hilum now points medially as the kidney has rotated, before it was ventral. The renal hilum supplies blood to the kidneys from the 6th week (transient). The kidneys then migrate more cranially, so that they connect with the super renal glands. The transient vessels break down. This is the final position

Question 7

Third stage of kidney development- structures within the kidney

Answer 7

Lobules which form the renal tubule develop. Capillaries grow at one end of the tubule to form the Glomerulu. At the proximal end each renal tubule forms a Bowman’s capsule, at its distal end the tubule lengthens to form the loop of Henle, this attaches to a collecting duct. In the kidneys Metanephric mesoderm make up the excretory units, the ureteric bud forms the collecting system. Urine production begins in the 12th week from amniotic fluid but development begins in the 5th week.

Question 8

Autosomal dominant polycystic kidney disease (APKD)

Answer 8

Inherited condition causing cysts to develop in the kidneys. Kidney function will gradually deteriorate till kidney failure occurs.

Question 9

Horseshoe kidney

Answer 9

Most common fusion defect of the kidneys. Abnormalities in position, rotation and vascular supply to the kidneys. Kidneys fuse together.

Question 10

Supernumerary kidney

Answer 10

Development of another kidney with a ureteric bud and metanephros, non-functional. Completely separated from the other kidney or lies closely separated by thin layer of fibrous tissue.

Question 11

Calyceal diverticula

Answer 11

Outpourings or cavities from the renal calyx or pelvis into the renal cortex

Question 12

Agenesis/ hypoplasia

Answer 12

Kidneys fail to grow/develop respect respectively. Can be unilateral or bilateral, bilateral is fatal

Question 13

Supernumerary renal vessels

Answer 13

Failure of regression of transient renal vessels. Ureter can be trapped by vessels which leads to Hydronephrosis (build up of urine).

Question 14

Renal ectopia

Answer 14

Incomplete migration of kidneys, so they remain in the pelvis

Question 15

Crossed ectopia

Answer 15

Two kidneys remaining on the same side