DEVELOPMENT OF KIDNEYS AND URETERS
Learning Objectives:
At the end of the lecture, the student should be able to:
• Describe the development of excretory organs in human
embryo.
• Describe the term Interim Kidneys.
• Give the week in which the permanent kidneys start to
develop.
• Describe the post natal changes of the kidneys.
• Describe the changes in the blood supply of the kidneys.
DEVELOPMENT OF KIDNEYS AND URETERS:
• Three sets of excretory organs develops in human embryos;
–Pronephros
–Mesonephros
–Metanephros
*The First set of kidneys are rudimentary and nonFunctional, They are analogous to the kidneys in primitive
fishes.
*The Second set is well developed and function briefly, they are
analogous to the kidneys of amphibians.
*The Third set of kidneys become the permanent kidneys.
PRONEPHROI:
• These transitory, non-functional structures appear in human
embryo in 4th week and are represented by few cell clusters
and tortuous tubular structures in the neck region.
They runs caudally and open into the cloaca,They become
degenerate, however, most of the ducts persists and are
utilized by the next set of kidneys.
MESONEPHROI:
• These large, elongated, excretory organs appear late in the 4th
week caudal to the rudimentary pronephroi.
• They are well developed and function as INTERIM KIDNEYS
Until the permanent kidneys
develops.
• This set consists of glomeruli and mesonephric tubules, which
opens into the mesonephric duct, which was originally the
pronephric duct.
• The mesonephric duct opens into the cloaca.
The mesonephroi degenerate toward the end of 1st
trimester.However,Their tubules become the efferent ductules
of the testes and mesonephric ducts have several adult
derivatives in the male.
METANEPHROI:
• These are permanent kidneys begin to develop early in the 5th week
and start to function about four weeks later, urine formation
continues through out fetal life.
• Metanephroi develop from two sources;
*The metanephric diverticulum or ureteric bud,
*The metanephric mass of intermediate mesoderm (nephrogenic
blastema).
*The ureteric bud is the primordium of the ureter,renal
pelvis,callices and collecting tubules.
 These tubules undergo repeated branching forming
successive generation of collecting tubules.
 The first four enlarge and become confluent to form major
calices and second four generations coalesce to form the
minor calices. The remaining generations form the
collecting tubules.
The end of each arched collecting tubule induces clusters
of mesenchymal cells in the metanephric mass of mesoderm to
form METANEPHRIC VESICLES, they elongate and become
metanephric tubules.
URINIFEROUS TUBULES:
• It consists of two embryo- logically different parts;
–Nephron from metanephric mass of mesoderm
–A collecting tubule derived from metanephric diverticulum.
FETAL KIDNEYS:
• Lobulated that are visible externally. This lobulation
diminishes toward the end of the fetal period, but the lobes
are still indicated in the kidneys of newborn infant. At term
each kidney contains 8,00,000 to 10,00,000 nephrons.
Glomerular filteration begin around the 9th fetal week.
POSTNATAL CHANGES OF THE KIDNEYS:
• Initially the permanent kidneys lie close to each other in the
pelvis, ventral to sacrum.
• As the abdomen and pelvis grow, the kidneys gradually come
to lie in the abdomen and move farther apart.
• They attain their adult position by the 9th week.
This migration (relative ascent) results mainly from growth of
the embryos body caudal to the kidneys. initially the hilum of
the kidney faces ventrally, however, As they ascend it rotates
medially almost 90 degrees. By the 9th week the hilum is
directed anteromedially.
CHANGES IN THE BLOOD SUPPLY OF THE KIDNEYS:
• As they ascend from pelvis they receive blood from vessels
that are close to them. Initially the renal arteries are branches
of the common iliac arteries,
Then from the distal end of the aorta. when they reach a higher
level they receive new branches from aorta. Normally the
caudal branches undergo involution and disappear.
They receive their most cranial arterial branches from the
abdominal aorta, which become the permanent renal arteries.
The right is longer and often more superior.
CONGENITAL ANOMALIES OF KIDNEYS AND URETERS:
• Accessory renal arteries
• Renal agenesis;
–Unilateral
–Bilateral
• Malrotation of the kidney
*Ectopic ureter
*Multicystic dysplastic kidney
*Ectopic kidneys e.g. pelvic kidney.
*Horse shoe kidney.
*Duplications of urinary tracts.