URINARY SYSTEMURINARY SYSTEM

Dr. Mujahid KhanDr. Mujahid Khan

Urinary SystemUrinary System

It consists of:It consists of:

The kidneys, which excrete urineThe kidneys, which excrete urine

The ureters, which convey urine from the The ureters, which convey urine from the kidneys to the bladderkidneys to the bladder

The urinary bladder, which stores urine The urinary bladder, which stores urine temporarilytemporarily

The urethra, which carries urine from the bladder The urethra, which carries urine from the bladder to the exteriorto the exterior

Development of Kidneys and Development of Kidneys and UretersUreters

Three sets of kidneys develop in human Three sets of kidneys develop in human embryosembryos

The first set is pronephroi, are rudimentaryThe first set is pronephroi, are rudimentary

The second set is mesonephroi, well developed The second set is mesonephroi, well developed but function brieflybut function briefly

The third set is metanephroi, become the The third set is metanephroi, become the permanent kidneyspermanent kidneys

PronephroiPronephroi

These transitory, non functional structures These transitory, non functional structures appear early in the fourth week in the neck appear early in the fourth week in the neck regionregion

The pronephric ducts run caudally and The pronephric ducts run caudally and open into the cloacaopen into the cloaca

They soon degenerate but most of the They soon degenerate but most of the pronephric ducts persist and are utilized pronephric ducts persist and are utilized by the next set of kidneysby the next set of kidneys

MesonephroiMesonephroi

Large, elongated, excretory organ appear Large, elongated, excretory organ appear late in the fourth week, caudal to the late in the fourth week, caudal to the rudimentary pronephroirudimentary pronephroi

Are well developed and function as interim Are well developed and function as interim kidneys for about four weeks, until kidneys for about four weeks, until permanent kidneys developpermanent kidneys develop

They consist of glomeruli and mesonephric They consist of glomeruli and mesonephric tubulestubules

MesonephroiMesonephroi

The tubules open into the mesonephric ductsThe tubules open into the mesonephric ducts

The mesonephric ducts open into the cloacaThe mesonephric ducts open into the cloaca

They degenerate toward the end of the first They degenerate toward the end of the first trimester trimester

Their tubules become the efferent ductules of the Their tubules become the efferent ductules of the testes testes

Mesonephric ducts have several adult derivatives Mesonephric ducts have several adult derivatives in malein male

MetanephroiMetanephroi

These are primordia of permanent kidneysThese are primordia of permanent kidneys

Begin to develop early in the fifth weekBegin to develop early in the fifth week

Start to function about four weeks laterStart to function about four weeks later

Urine formation continues throughout fetal lifeUrine formation continues throughout fetal life

Urine is excreted into the amniotic cavity and Urine is excreted into the amniotic cavity and mixes with amniotic fluidmixes with amniotic fluid

MetanephroiMetanephroi

A mature fetus swallows several hundred ml of A mature fetus swallows several hundred ml of amniotic fluid each day, which is absorbed by amniotic fluid each day, which is absorbed by the intestinethe intestine

The waste products are transferred through the The waste products are transferred through the placental membrane into the maternal blood for placental membrane into the maternal blood for elimination by kidneyselimination by kidneys

They develop from metanephric diverticulum and They develop from metanephric diverticulum and metanephric mass of intermediate mesodermmetanephric mass of intermediate mesoderm

MetanephroiMetanephroi

It is an outgrowth from the mesonephric It is an outgrowth from the mesonephric duct near its entrance into the cloacaduct near its entrance into the cloaca

The metanephric mass of intermediate The metanephric mass of intermediate mesoderm is derived from the caudal part mesoderm is derived from the caudal part of the nephrogenic cordof the nephrogenic cord

Both primordia of the metanephros are of Both primordia of the metanephros are of mesodermal originmesodermal origin

Metanephric DiverticulumMetanephric Diverticulum

It is the primordium of the ureter, renal It is the primordium of the ureter, renal pelvis, calices, and collecting tubulespelvis, calices, and collecting tubules

As it elongates, the metanephric As it elongates, the metanephric diverticulum penetrates the metanephric diverticulum penetrates the metanephric mass of intermediate mesodermmass of intermediate mesoderm

The stalk of the metanephric diverticulum The stalk of the metanephric diverticulum becomes the ureter and its expanded becomes the ureter and its expanded cranial end forms the renal pelviscranial end forms the renal pelvis

Metanephric DiverticulumMetanephric Diverticulum

The straight collecting tubules undergo repeated The straight collecting tubules undergo repeated branching, forming successive generations of branching, forming successive generations of collecting tubulescollecting tubules

First four generations of tubules enlarge to form First four generations of tubules enlarge to form the major calicesthe major calices

Second four generations coalesce to form the Second four generations coalesce to form the minor calicesminor calices

The remaining generations of tubules form the The remaining generations of tubules form the collecting tubulescollecting tubules

Metanephric DiverticulumMetanephric Diverticulum

The end of each arched collecting tubule The end of each arched collecting tubule induces clusters of mesenchymal cells in the induces clusters of mesenchymal cells in the metanephric mass of mesoderm to form small metanephric mass of mesoderm to form small metanephric vesiclesmetanephric vesicles

These vesicles elongate and become These vesicles elongate and become metanephric tubulesmetanephric tubules

As these renal tubules develop, their proximal As these renal tubules develop, their proximal ends are invaginated by glomeruliends are invaginated by glomeruli

Metanephric DiverticulumMetanephric Diverticulum

The renal corpuscle and its proximal convoluted The renal corpuscle and its proximal convoluted tubule, loop of Henle, and distal convoluted tubule, loop of Henle, and distal convoluted tubule constitute a nephrontubule constitute a nephron

Between the tenth and eighteenth weeks of Between the tenth and eighteenth weeks of gestation, the number of glomeruli increases gestation, the number of glomeruli increases graduallygradually

They increase rapidly until the thirty second They increase rapidly until the thirty second

weekweek

Uriniferous TubuleUriniferous Tubule

It consists of two embryologically different It consists of two embryologically different parts:parts:

A nephron derived from the metanephric A nephron derived from the metanephric mass of intermediate mesodermmass of intermediate mesoderm

A collecting tubule derived from the A collecting tubule derived from the metanephric diverticulummetanephric diverticulum

Fetal KidneysFetal Kidneys

They are subdivided into lobesThey are subdivided into lobes

This lobulation diminishes toward the end of the This lobulation diminishes toward the end of the fetal periodfetal period

The lobulation usually disappear during infancy The lobulation usually disappear during infancy as the nephrons increase and growas the nephrons increase and grow

The lobulated character of kidneys is normally The lobulated character of kidneys is normally obscured in adultsobscured in adults

Fetal KidneysFetal Kidneys

At term each kidneys contains 800,000 to At term each kidneys contains 800,000 to 1,000,000 nephrons1,000,000 nephrons

The increase in kidney size after birth The increase in kidney size after birth results mainly from the elongation of the results mainly from the elongation of the proximal convoluted tubules, as well as an proximal convoluted tubules, as well as an increase in interstitial tissueincrease in interstitial tissue

Fetal KidneysFetal Kidneys

Nephron formation is complete at birth, Nephron formation is complete at birth, except in premature infantsexcept in premature infants

Functional maturation of kidneys occurs Functional maturation of kidneys occurs after birthafter birth

Glomerular filtration begins around the Glomerular filtration begins around the ninth week and the rate of filtration ninth week and the rate of filtration increases after birthincreases after birth

Positional Changes of KidneysPositional Changes of Kidneys

Initially the metanephric kidneys lie close Initially the metanephric kidneys lie close to each other in the pelvisto each other in the pelvis

As the abdomen and pelvis grow, the As the abdomen and pelvis grow, the kidneys gradually come to lie in the kidneys gradually come to lie in the abdomen and move apartabdomen and move apart

They attain there adult position by the They attain there adult position by the ninth weekninth week

Positional Changes of KidneysPositional Changes of Kidneys

Initially the hilum of the kidneys lie Initially the hilum of the kidneys lie ventrallyventrally

As the kidney ascends, it rotates medially As the kidney ascends, it rotates medially almost 90 degreesalmost 90 degrees

By the ninth week the hilum is directed By the ninth week the hilum is directed anteromediallyanteromedially

Changes in the Blood Supply of Changes in the Blood Supply of KidneysKidneys

As the kidneys ascend from the pelvis, they As the kidneys ascend from the pelvis, they receive their blood supply from vessels that are receive their blood supply from vessels that are close to themclose to them

Initially the renal arteries are branches of the Initially the renal arteries are branches of the common iliac arteriescommon iliac arteries

As they ascend further, the kidneys receive their As they ascend further, the kidneys receive their blood supply from the distal end of the aortablood supply from the distal end of the aorta

As they reach higher level, they receive new As they reach higher level, they receive new branches from the aortabranches from the aorta

Changes in the Blood Supply of Changes in the Blood Supply of KidneysKidneys

Normally the caudal branches disappearNormally the caudal branches disappear

Their ascent stops when they come in contact Their ascent stops when they come in contact with suprarenal glands in the ninth weekwith suprarenal glands in the ninth week

The kidneys receive their most cranial branches The kidneys receive their most cranial branches from abdominal aorta, which becomes the from abdominal aorta, which becomes the permanent renal arteries permanent renal arteries

The right renal artery is longer and often more The right renal artery is longer and often more superiorsuperior

Urinary BladderUrinary Bladder

The urogenital sinus is divided into three The urogenital sinus is divided into three parts:parts:

A cranial visceral part that forms most of A cranial visceral part that forms most of the bladder, continuous with the allantoisthe bladder, continuous with the allantois

Middle pelvic part becomes the urethraMiddle pelvic part becomes the urethra

A caudal phallic part that grows toward the A caudal phallic part that grows toward the genital tuberclegenital tubercle

Urinary BladderUrinary Bladder

The bladder develops mainly from the vesical The bladder develops mainly from the vesical part of the urogenital sinuspart of the urogenital sinus

Its trigone region is derived from the caudal Its trigone region is derived from the caudal ends of the mesonephric ducts ends of the mesonephric ducts

Its epithelium is derived from the endoderm of Its epithelium is derived from the endoderm of vesical part of urogenital sinusvesical part of urogenital sinus

Other layers of its wall develop from adjacent Other layers of its wall develop from adjacent splanchnic mesenchyme splanchnic mesenchyme

Urinary BladderUrinary Bladder

Initially it is continuous with the allantoisInitially it is continuous with the allantois

The allantois soon constricts and becomes The allantois soon constricts and becomes a thick fibrous cord, called urachusa thick fibrous cord, called urachus

Urachus extends from the apex of the Urachus extends from the apex of the bladder to the umbilicusbladder to the umbilicus

In the adult the urachus is represented by In the adult the urachus is represented by the median umbilical ligament the median umbilical ligament

Urinary BladderUrinary Bladder

As the bladder enlarges, distal parts of the As the bladder enlarges, distal parts of the mesonephric ducts are incorporated into mesonephric ducts are incorporated into its dorsal wallits dorsal wall

Epithelium of the entire bladder is derived Epithelium of the entire bladder is derived from the endoderm of the urogenital sinusfrom the endoderm of the urogenital sinus

As the mesonephric ducts are absorbed, As the mesonephric ducts are absorbed, the ureters come to open separately into the ureters come to open separately into the urinary bladderthe urinary bladder

Urinary BladderUrinary Bladder

The orifices of the mesonephric ducts The orifices of the mesonephric ducts move close together and enter the move close together and enter the prostatic part of the urethra prostatic part of the urethra

Caudal ends of these ducts become the Caudal ends of these ducts become the ejaculatory ductsejaculatory ducts

The distal ends of the mesonephric ducts The distal ends of the mesonephric ducts in females degeneratein females degenerate

Urinary BladderUrinary Bladder

In infants and children, the urinary bladder In infants and children, the urinary bladder is in the abdomenis in the abdomen

It begins to enter the greater pelvis at It begins to enter the greater pelvis at about six years of ageabout six years of age

Does not enter the lesser pelvis and Does not enter the lesser pelvis and become a pelvic organ until after puberty become a pelvic organ until after puberty

UrethraUrethra

The epithelium of most of the male urethra and The epithelium of most of the male urethra and the entire female urethra is derived from the entire female urethra is derived from endoderm of the urogenital sinusendoderm of the urogenital sinus

The epithelium of the terminal part of the urethra The epithelium of the terminal part of the urethra is derived from the surface ectodermis derived from the surface ectoderm

The connective tissue and smooth muscle of the The connective tissue and smooth muscle of the urethra in both sexes are derived from urethra in both sexes are derived from splanchnic mesenchymesplanchnic mesenchyme

Suprarenal Glands Suprarenal Glands

The cortex develops from the mesodermThe cortex develops from the mesoderm

The medulla differentiates from neural crest cellsThe medulla differentiates from neural crest cells

Cortex appears during the sixth week from the Cortex appears during the sixth week from the mesothelium lining the posterior abdomnal wallmesothelium lining the posterior abdomnal wall

The cells that form the medulla are derived from The cells that form the medulla are derived from an adjacent sympathetic ganglion, derived from an adjacent sympathetic ganglion, derived from neural crest cellsneural crest cells

Suprarenal GlandsSuprarenal Glands

Differentiation of the characteristic Differentiation of the characteristic suprarenal cortical zones begins during suprarenal cortical zones begins during the late fetal periodthe late fetal period

The zona glomerulosa and zona The zona glomerulosa and zona fasciculata are present at birthfasciculata are present at birth

The zona reticularis is not recognizable The zona reticularis is not recognizable until the end of the third year until the end of the third year

Suprarenal GlandsSuprarenal Glands

The suprarenal glands of human fetus are 10 to The suprarenal glands of human fetus are 10 to 20 times larger than adult glands relative to body 20 times larger than adult glands relative to body weightweight

This is due to the extensive size of the fetal This is due to the extensive size of the fetal cortex cortex

The glands lose about one-third of their weight The glands lose about one-third of their weight during the first 2 or 3 weeks after birth and do during the first 2 or 3 weeks after birth and do not regain their original weight until the end of not regain their original weight until the end of the second yearthe second year