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The Urinary SystemThe Urinary System

KidneyKidney

Introduction Introduction Components of Urinary systemComponents of Urinary system

a. kidneysa. kidneysb. uretersb. uretersc. urinary bladderc. urinary bladderd. urethrad. urethra

Urine formationUrine formation Body fluid is collected via filtration thru Body fluid is collected via filtration thru

selective permeable membrane via selective permeable membrane via Hydrostatic pressure forcing water and small Hydrostatic pressure forcing water and small solutes thru it, large molecules are retained= solutes thru it, large molecules are retained= filtratefiltrate

Selective reabsorption and secretion of Selective reabsorption and secretion of solutes. Active transport reabsorb solutes as solutes. Active transport reabsorb solutes as glucose, salts and amino acids.Large glucose, salts and amino acids.Large molecules are actively secreted into the molecules are actively secreted into the filtrate.filtrate.

Active and passive concentration of filtrate Active and passive concentration of filtrate expells an ultrafiltrate fluid = urine. expells an ultrafiltrate fluid = urine.

Functions of Urinary systemFunctions of Urinary system Removes metabolic waste ( nitrogenous from Removes metabolic waste ( nitrogenous from

protein and nucleic acid breakdown)protein and nucleic acid breakdown) Regulates the body water and solute (electrolyte) Regulates the body water and solute (electrolyte)

composition including osmoregulation of pH.composition including osmoregulation of pH. Endocrine function:Endocrine function:

Erythropoietin to regulate erythropoietic cells in Erythropoietin to regulate erythropoietic cells in blood marrow.blood marrow.Renin (RAA system) to control blood pressure and Renin (RAA system) to control blood pressure and volumevolume

* Vitamin D synthetic pathway occurs in the kidney.* Vitamin D synthetic pathway occurs in the kidney.

DevelopmentDevelopment          The urinary and genital systems The urinary and genital systems

are closely tied through development are closely tied through development which explains their use of common which explains their use of common ducts.  Both systems originate from ducts.  Both systems originate from intermediate mesoderm which gives intermediate mesoderm which gives rise to the urogenital ridge from rise to the urogenital ridge from which the two organ systems which the two organ systems emerge.emerge.

Kidneys (Gross Structure)Kidneys (Gross Structure) The kidney is an encapsulated bean-shaped organ.  The kidney is an encapsulated bean-shaped organ. 

The The hilumhilum is a depression on the medial surface that is a depression on the medial surface that serves as portal for the renal vessels, nerves and serves as portal for the renal vessels, nerves and ureter. The renal sinus is the cavity deep to hilum ureter. The renal sinus is the cavity deep to hilum that is occupied by the that is occupied by the renal pelvisrenal pelvis and vessels.  The and vessels.  The renal pelvis (L, basin) is simply an expansion of the renal pelvis (L, basin) is simply an expansion of the ureter which receives urine from the major ureter which receives urine from the major calycescalyces.  . 

The capsule of the kidney in humans is bi-laminar, The capsule of the kidney in humans is bi-laminar, consisting of an consisting of an outerouter layer of dense connective layer of dense connective tissue and an tissue and an innerinner layer composed of myfibroblasts.  layer composed of myfibroblasts.  The function of the inner layer is debated.The function of the inner layer is debated.

CortexCortexThe cortex (outer region) is grossly The cortex (outer region) is grossly

divisible into alternating divisible into alternating medullary medullary raysrays (which appear striated to the eye) (which appear striated to the eye) and and cortical labyrinthscortical labyrinths.  The medullary .  The medullary rays are rich in rays are rich in straight tubulesstraight tubules and and collecting ductscollecting ducts; the cortical labyrinths ; the cortical labyrinths are rich in are rich in renal corpusclesrenal corpuscles, , convoluted convoluted tubulestubules and and collecting collecting tubulestubules.                                   .                                  

MedullaMedulla The medulla (inner region) is divisible into The medulla (inner region) is divisible into

alternating alternating pyramidspyramids and and renal columnsrenal columns.  Renal .  Renal columns are simply extensions of cortex into the columns are simply extensions of cortex into the medullary region and their composition is the medullary region and their composition is the same as the cortex.  The renal pyramids are same as the cortex.  The renal pyramids are variable in number and contain variable in number and contain straight tubulesstraight tubules ((thick and thinthick and thin),  ),  collecting ductscollecting ducts and  and  vasa rectavasa recta.  .  The apex of each pyramid terminates in a papilla The apex of each pyramid terminates in a papilla The papilla is perforated by numerous openings The papilla is perforated by numerous openings of the terminal collecting ducts and its surface is of the terminal collecting ducts and its surface is described as the described as the area cribosaarea cribosa

                

Medullary pyramid Medullary pyramid     The tubular composition of a medullary The tubular composition of a medullary

pyramid varies between its inner and outer pyramid varies between its inner and outer portions . In the outer portion (adjacent to the portions . In the outer portion (adjacent to the cortex) thick tubules predominate; conversely, cortex) thick tubules predominate; conversely, in the inner portion thin tubules are more in the inner portion thin tubules are more commonly found.commonly found.

  Each pyramid drains at its papillae into a Each pyramid drains at its papillae into a minor calyx; several minor calyxes unite to minor calyx; several minor calyxes unite to form a major calyx.  In turn,  major calyxes form a major calyx.  In turn,  major calyxes unite to form the unite to form the renal pelvisrenal pelvis which is drained which is drained by by ureterureter.  . 

NephronNephron Types of NephronsTypes of Nephrons Renal CorpusclesRenal Corpuscles Renal tubuleRenal tubule Proximal convoluted tubuleProximal convoluted tubule Proximal Straight tubuleProximal Straight tubule Descending thin tubuleDescending thin tubule Ascending thin tubuleAscending thin tubule Distal straight tubuleDistal straight tubule Distal convoluted tubuleDistal convoluted tubule

The KidneyThe Kidney     The tubular composition of The tubular composition of

a medullary pyramid varies a medullary pyramid varies between its inner and outer between its inner and outer portions . In the outer portions . In the outer portion (adjacent to the portion (adjacent to the cortex) thick tubules cortex) thick tubules predominate; conversely, in predominate; conversely, in the inner portion thin tubules the inner portion thin tubules are more commonly found.are more commonly found.

         Each pyramid drains at its Each pyramid drains at its

papillae into a minor calyx; papillae into a minor calyx; several minor calyxes unite several minor calyxes unite to form a major calyx.  In to form a major calyx.  In turn,  major calyxes unite to turn,  major calyxes unite to form the form the renal pelvisrenal pelvis which is which is drained by drained by ureterureter.  . 

  

The NephronThe Nephron The The nephronnephron is the functional is the functional

unit of the kidney.  It consists unit of the kidney.  It consists of (1) a renal corpuscle of (1) a renal corpuscle (filtration) and (2) renal (filtration) and (2) renal tubule (selective resorption tubule (selective resorption and secretion).  The tubule and secretion).  The tubule can be subdivided into can be subdivided into several portions (starting several portions (starting from the renal corpuscle): from the renal corpuscle): proximal convoluted tubule, proximal convoluted tubule, proximal straight tubule proximal straight tubule (descending thick limb; thin (descending thick limb; thin descending limb; thin descending limb; thin ascending limb, distal ascending limb, distal straight tubule (thick straight tubule (thick ascending limb; and distal ascending limb; and distal convoluted tubule.  convoluted tubule. 

Types of NephronTypes of Nephron (1) (1) Cortical Cortical (sub-capsular) nephrons are the most (sub-capsular) nephrons are the most

common type of nephron.  Their renal corpuscles are common type of nephron.  Their renal corpuscles are found in the outer cortex and their short loops are found in the outer cortex and their short loops are formed by distal straight tubules in the outer medulla.formed by distal straight tubules in the outer medulla.

(2) (2) JuxtamedullaryJuxtamedullary nephrons account for nephrons account for approximately 20% of all nephrons; their corpuscles approximately 20% of all nephrons; their corpuscles are  found adjacent to the medulla.  They are long are  found adjacent to the medulla.  They are long looped nephrons whose loop is formed by thin limbs.  looped nephrons whose loop is formed by thin limbs.  These nephrons are These nephrons are responsible for producing the responsible for producing the urine-concentrating mechanismurine-concentrating mechanism of the kidney.  of the kidney. 

(3) (3) IntermediateIntermediate nephrons have their renal nephrons have their renal corpuscles in the mid-region of the cortex and their corpuscles in the mid-region of the cortex and their loops are intermediate in length. loops are intermediate in length. 

Renal Corpuscle – site of Renal Corpuscle – site of filtration = filtration = GlomerulusGlomerulus

200 um dm. with 200 um dm. with tufts of capillaries tufts of capillaries within an epithelial within an epithelial capsule, Glomerular capsule, Glomerular capsule capsule

The capillaries of the The capillaries of the glomerulus are fed by glomerulus are fed by an an afferent arterioleafferent arteriole and drained by an and drained by an efferent arterioleefferent arteriole at at the the vascular polevascular pole

Bowmans capsuleBowmans capsuleBi-laminar consisting of a Bi-laminar consisting of a visceral visceral

layerlayer which covers the glomerulus and which covers the glomerulus and a a parietal layer parietal layer of simple of simple squamous squamous epitheliumepithelium which defines the which defines the perimeter of the corpuscle.  Between perimeter of the corpuscle.  Between the parietal and visceral layers is the the parietal and visceral layers is the urinary spaceurinary space (Bowman’s space) (Bowman’s space) which opens to a proximal convoluted which opens to a proximal convoluted tubules at the tubules at the urinary poleurinary pole..

Glomerular capsule…..Glomerular capsule….. The glomerulus forms the filter apparatus of the The glomerulus forms the filter apparatus of the

nephron and is comprised of 3 components:  nephron and is comprised of 3 components:  (1) The (1) The endotheliumendothelium of the glomerular of the glomerular

capillaries is highly fenestrated without capillaries is highly fenestrated without diaphragmsdiaphragms

(2) the glomerular (2) the glomerular basement membranebasement membrane is a is a thick basal lamina produced by both the thick basal lamina produced by both the endothelial cells and podocytesendothelial cells and podocytes

(3)  the visceral layer of Bowman’s capsule (3)  the visceral layer of Bowman’s capsule comprised of podocytes and comprised of podocytes and mesangialmesangial cells.  cells. 

Visceral layer of Bowman’s capsuleVisceral layer of Bowman’s capsule The podocytes possess processes called The podocytes possess processes called

pediclespedicles that wrap around the capillaries and that wrap around the capillaries and interdigitate to form filtration slits interdigitate to form filtration slits approximately 25nm wide.  approximately 25nm wide. 

The mesangial cells serve a phagocytic The mesangial cells serve a phagocytic function and keep the basement membrane function and keep the basement membrane clear of debris.  All 3 components combine clear of debris.  All 3 components combine to retains cells and macromolecules to retains cells and macromolecules (proteins > 70 kd) but permit the passage of (proteins > 70 kd) but permit the passage of water and small solutes (salts, glucose, water and small solutes (salts, glucose, amino acids, nitrogenous wastes) into the amino acids, nitrogenous wastes) into the urinary space as filtrate.urinary space as filtrate.

Renal tubule – site of selective Renal tubule – site of selective re-absorption / secretion of re-absorption / secretion of

solutessolutesThe renal tubule serves to recover The renal tubule serves to recover

water and other desirable solutes water and other desirable solutes (sugar, ions, small proteins) from the (sugar, ions, small proteins) from the filtrate.  filtrate. 

The The proximal convoluted tubuleproximal convoluted tubule receives filtrate from the urinary receives filtrate from the urinary space and is the site of the selective space and is the site of the selective re-absorption of most solutes re-absorption of most solutes including all the glucose and amino including all the glucose and amino acids and most of the water and salts.  acids and most of the water and salts. 

Renal tubuleRenal tubule

Proteins are absorbed by pinocytosis, Proteins are absorbed by pinocytosis, broken down by lysosomal broken down by lysosomal degradation and released as amino degradation and released as amino acids to the peritubular capillary acids to the peritubular capillary network.  This is also the site of pH network.  This is also the site of pH balancing and elimination (active balancing and elimination (active transport) of creatine.  transport) of creatine. 

Histology of tubulesHistology of tubules Structurally the proximal convoluted tubule is Structurally the proximal convoluted tubule is

formed by a formed by a simple cuboidal to low columnar simple cuboidal to low columnar epitheliumepithelium.  . 

The apical surface is covered with microvilli The apical surface is covered with microvilli creating a light microscopic creating a light microscopic brush borderbrush border that that increases the surface area for ion absorption.  increases the surface area for ion absorption. 

The cells are tightly bound to one another to seal The cells are tightly bound to one another to seal off the intercellular spaces from the lumen using off the intercellular spaces from the lumen using junctional processes apically and interdigitating junctional processes apically and interdigitating plicae (folds) laterally.  plicae (folds) laterally. 

Basally, interdigitating processes contain numerous Basally, interdigitating processes contain numerous mitochondria which create light microscopic basal mitochondria which create light microscopic basal striations that are associated with ion transport.striations that are associated with ion transport.

Histology…Histology… Proximal convoluted tubules are the most abundant Proximal convoluted tubules are the most abundant

tubule in the cortex.  tubule in the cortex.  They have a eosinophilic cytoplasm with a basal They have a eosinophilic cytoplasm with a basal

nucleus.  nucleus.  The brush border is rarely preserved and the The brush border is rarely preserved and the

indistinct cells margins are due to basal and lateral indistinct cells margins are due to basal and lateral border interdigitations.border interdigitations.

The The proximal straight tubulesproximal straight tubules are located within or are located within or near the medulla, depending upon the type of near the medulla, depending upon the type of nephron.  nephron. 

They are formed by lower cuboidal epithelium and They are formed by lower cuboidal epithelium and their microvilli and basal and lateral interdigitations their microvilli and basal and lateral interdigitations are less well developed.  Histologically they are are less well developed.  Histologically they are similar to proximal convoluted tubulessimilar to proximal convoluted tubules

Histology….Histology…. Descending thin tubulesDescending thin tubules are located within the are located within the

medulla and are formed by low cuboidal to squamous medulla and are formed by low cuboidal to squamous epithelium.epithelium.

The microvilli are poorly developed as are the basal The microvilli are poorly developed as are the basal and lateral interdigitations creating a very leak cell and lateral interdigitations creating a very leak cell that serves as the site of passive transport of ions that serves as the site of passive transport of ions (inward) and water (outward) between the lumen (inward) and water (outward) between the lumen and interstitium.and interstitium.

The The ascending thin tubulesascending thin tubules are also located within are also located within the medulla and are similar in appearance to the medulla and are similar in appearance to descending thin tubules.  descending thin tubules. 

However, these tubes are impermeable to water and However, these tubes are impermeable to water and permit passive transport of NaCl into the interstitium.permit passive transport of NaCl into the interstitium.

  

Histology….Histology…. Distal straight tubulesDistal straight tubules are located within both are located within both

the medulla and cortex .  the medulla and cortex .  Histologically these appear as a simple cuboidal Histologically these appear as a simple cuboidal

epithelium with sparse microvilli and lacking epithelium with sparse microvilli and lacking lateral interdigitations.  lateral interdigitations. 

The nucleus is apical and basal interdigitations The nucleus is apical and basal interdigitations with abundant mitochondria are present.  with abundant mitochondria are present. 

These tubes are impermeable to water and are These tubes are impermeable to water and are the site of ion transport from the lumen to the the site of ion transport from the lumen to the interstitium that establishes the ion gradient of interstitium that establishes the ion gradient of medullary interstitium.  medullary interstitium. 

  

Histology….Histology….Distal convoluted tubules are located Distal convoluted tubules are located

within the cortex.  They are within the cortex.  They are approximately 1/3rd as long as their approximately 1/3rd as long as their proximal counterparts.  They contact the proximal counterparts.  They contact the renal corpuscle forming a renal corpuscle forming a macula densamacula densa which is part of the which is part of the juxtaglomerular juxtaglomerular apparatusapparatus (see below).  Histologically (see below).  Histologically they are similar to the distal straight they are similar to the distal straight tubules and also function in ion tubules and also function in ion exchange.exchange.

Collecting tubules….Collecting tubules…. The collecting system starts in the cortex as a The collecting system starts in the cortex as a

continuation of the distal convoluted tubules and continuation of the distal convoluted tubules and descend through the medulla.  descend through the medulla. 

As the ducts coalesce and increase in size, the cells of As the ducts coalesce and increase in size, the cells of the tubes change from somewhat squamous to cuboidal the tubes change from somewhat squamous to cuboidal to columnar and similarly become increasing stratified.  to columnar and similarly become increasing stratified. 

They terminate at the tip of the renal pyramid as the They terminate at the tip of the renal pyramid as the papillary ductspapillary ducts .  . 

Histologically they appear as tubes with distinguishable Histologically they appear as tubes with distinguishable cells margins, central nuclei and poorly staining cells margins, central nuclei and poorly staining cytoplasm.  cytoplasm. 

At the EM level many posses a single cilium and sparse At the EM level many posses a single cilium and sparse microvilli.  microvilli. 

The collecting system functions to concentrate urine The collecting system functions to concentrate urine through ADH-regulated and ADH-independent water through ADH-regulated and ADH-independent water channels channels

Juxtaglomerular apparatusJuxtaglomerular apparatus The The juxtaglomerular apparatusjuxtaglomerular apparatus is the site of blood is the site of blood

pressure regulation via the renin-angioensin-pressure regulation via the renin-angioensin-aldosterone system.  They are located at the vascular aldosterone system.  They are located at the vascular pole of Bowman’s capsule and are formed by the pole of Bowman’s capsule and are formed by the conjunction of cells of (1) the conjunction of cells of (1) the macula densamacula densa (distal (distal straight tubule),straight tubule),

(2) (2) juxtaglomerular cellsjuxtaglomerular cells of the afferent arteriole, of the afferent arteriole, (3) (3) extraglomerular mesangialextraglomerular mesangial cells. cells. The The macula densamacula densa is a portion of terminal distal is a portion of terminal distal

straight tubule adjacent to the renal corpuscle.  These straight tubule adjacent to the renal corpuscle.  These cells monitor the NaCl levels in the afferent arteriole cells monitor the NaCl levels in the afferent arteriole and regulate the juxtaglomerular cells within that and regulate the juxtaglomerular cells within that vessel.  The vessel.  The juxtaglomerular cellsjuxtaglomerular cells are specialized are specialized smooth muscle cells of the afferent arteriole which smooth muscle cells of the afferent arteriole which synthesize and secrete renin.  The extraglomerular synthesize and secrete renin.  The extraglomerular mesangial cells are of unknown function.mesangial cells are of unknown function.

How does the Juxtaglomerular How does the Juxtaglomerular apparatus workapparatus work

The macula densa cells monitor NaCl levels in the The macula densa cells monitor NaCl levels in the fluid of the afferent arteriole.  fluid of the afferent arteriole. 

Renin secretion of the juxtaglomerular cells is Renin secretion of the juxtaglomerular cells is stimulated by paracrine activity from the macula stimulated by paracrine activity from the macula densa.  Renin is a protease that cleaves plasma densa.  Renin is a protease that cleaves plasma angiotensinogen into angiotensin I.  angiotensinogen into angiotensin I. 

Angiotensin I is converted to angiotensin II in the Angiotensin I is converted to angiotensin II in the lung (by an enzyme in the capillaries).  lung (by an enzyme in the capillaries). 

Angiotensin II promotes vascular smooth muscle Angiotensin II promotes vascular smooth muscle contraction and release of aldosterone from the contraction and release of aldosterone from the suprarenal cortex.  suprarenal cortex. 

Aldosterone stimulates absorption of NaCl and water Aldosterone stimulates absorption of NaCl and water in the distal convoluted tubule thus increasing blood in the distal convoluted tubule thus increasing blood volume resulting in an increase in blood pressure volume resulting in an increase in blood pressure

Interstitium…..Interstitium…..The interstitium is the connective tissue The interstitium is the connective tissue

matrix of the kidney. [Yes. it is the matrix of the kidney. [Yes. it is the stroma of the kidney, but remember not stroma of the kidney, but remember not all stromas are connective tissue.]  It is all stromas are connective tissue.]  It is sparse in the cortex and most abundant sparse in the cortex and most abundant the deep medulla.  The extracellular the deep medulla.  The extracellular matrix consists of collagen fibers and matrix consists of collagen fibers and glycosamionglycans (GAGs) and the glycosamionglycans (GAGs) and the cells are fibroblasts and macrophages.cells are fibroblasts and macrophages.

Blood supply…Blood supply… Arterial:  renal artery > inter-lobar arteries > Arterial:  renal artery > inter-lobar arteries >

arcuate arteries > inter-lobular arteries > arcuate arteries > inter-lobular arteries > afferent arterioles > renal corpuscle afferent arterioles > renal corpuscle (capillaries!) > efferent arteriole > (capillaries!) > efferent arteriole > peritubular capillary network (for cortical peritubular capillary network (for cortical nephrons) --or-- > vasa recta (for nephrons) --or-- > vasa recta (for juxtamedullary nephrons).juxtamedullary nephrons).

Venous::  Peritubular capillary network > Venous::  Peritubular capillary network > interlobular veins > arcuate veins > interlobular veins > arcuate veins > interlobar veins > renal vein.interlobar veins > renal vein.

The vasa recta (L. straight vessels) are The vasa recta (L. straight vessels) are comprised of arteriolae rectae and venulae comprised of arteriolae rectae and venulae rectae and their associated capillaries.  rectae and their associated capillaries. 

Nerve SupplyNerve SupplyThe smooth muscle of the glomerular The smooth muscle of the glomerular

arterioles receives sympathetic innervation. arterioles receives sympathetic innervation.   

Vasoconstriction of afferent arteriole Vasoconstriction of afferent arteriole decreases filtration rate (lowers pressure) decreases filtration rate (lowers pressure) whereas vasoconstriction of the efferent whereas vasoconstriction of the efferent arterioles increases filtration rate.  arterioles increases filtration rate. 

Neither innervation is neither for normal Neither innervation is neither for normal function.function.

  

The nephronic loop (of The nephronic loop (of Henle) of the juxtamedullary Henle) of the juxtamedullary nephrons creates an osmotic nephrons creates an osmotic gradient in interstitium of gradient in interstitium of medulla.  The most import medulla.  The most import component of the loop is the component of the loop is the thick ascending limb where thick ascending limb where active transport of solutes active transport of solutes occurs.  The vasa recta occurs.  The vasa recta maintains the osmotic maintains the osmotic gradient by its counter-gradient by its counter-current flow thru medulla.  current flow thru medulla.  The collecting duct is the The collecting duct is the site of osmotic site of osmotic concentration; modulated by concentration; modulated by ADH secreted by the ADH secreted by the hypophysis:  ADH increases hypophysis:  ADH increases the water permeability of the water permeability of collecting duct cells allowing collecting duct cells allowing water into the interstitium water into the interstitium and back into blood via vasa and back into blood via vasa recta resulting in a more recta resulting in a more concentrate urine. concentrate urine. 

  

The histological structure of the The histological structure of the calyces, renal pelvis, ureter and calyces, renal pelvis, ureter and

urinary bladderurinary bladder is broadly similar and consists of 3 layers.  is broadly similar and consists of 3 layers.  (1) The (1) The mucosamucosa is lined by transitional is lined by transitional

epithelium over a lamina propria of dense epithelium over a lamina propria of dense irregular connective tissue.  The transitional irregular connective tissue.  The transitional epithelium is impermeable to water and epithelium is impermeable to water and salts.  salts. 

(2) The (2) The muscularismuscularis is a bilaminar smooth is a bilaminar smooth muscle layer with inner longitudinal and muscle layer with inner longitudinal and outer circular bundles.  It produces peristalsis outer circular bundles.  It produces peristalsis to move the urine. to move the urine.

(3) The (3) The adventitiaadventitia is the outer connective is the outer connective tissue coat.  If it is covered with peritoneum tissue coat.  If it is covered with peritoneum (mesothelium) it is referred to as (mesothelium) it is referred to as serosaserosa..

Ureter and Urinary bladderUreter and Urinary bladderThe ureters are muscular tubes The ureters are muscular tubes

connecting the renal pelvis to the connecting the renal pelvis to the urinary bladder.urinary bladder.

The urinary bladder [vesica] is a The urinary bladder [vesica] is a distensible reservoir.  distensible reservoir. 

It receives the bilateral ureters and It receives the bilateral ureters and empties via the  midline empties via the  midline urethraurethra.  . 

The muscularis layer forms a detrussor The muscularis layer forms a detrussor muscle which is thickened distally to muscle which is thickened distally to form the form the internal urethral sphincterinternal urethral sphincter

UrethraUrethra The urethra is a fibromuscular tube The urethra is a fibromuscular tube

connecting the bladder to the external connecting the bladder to the external urethral orifice.  It is sexually dimorphic.  In urethral orifice.  It is sexually dimorphic.  In the males it is the terminal duct for both the the males it is the terminal duct for both the urinary and genital systems.  In the female it urinary and genital systems.  In the female it empties only the bladder.  In the sexes the empties only the bladder.  In the sexes the lining grades from a transitional epithelium lining grades from a transitional epithelium adjacent to the bladder to a stratified adjacent to the bladder to a stratified squamous epithelium at the orifice.  Males squamous epithelium at the orifice.  Males often have a stratified columnar or often have a stratified columnar or pseudostratified columnar epithelium in the pseudostratified columnar epithelium in the middle portion.middle portion.

Urine flowUrine flow urinary space of Bowman's urinary space of Bowman's

capsule ---capsule --- > convoluted proximal > convoluted proximal

tubule ---tubule --- > descending, thick, > descending, thick,

straight, proximal tubule ---straight, proximal tubule ---

> descending, thin, straight, > descending, thin, straight, proximal tubule --proximal tubule --

> ascending, thin, straight > ascending, thin, straight proximal tubule ---proximal tubule ---

> ascending, thick, straight, > ascending, thick, straight, distal tubule ----distal tubule ----

> convoluted, distal tubule > convoluted, distal tubule ------

> collecting tubule ----> collecting tubule ---- > collecting ducts ----> collecting ducts ---- > papillary ducts of Bellini > papillary ducts of Bellini

---------- > minor calyx ------> minor calyx ------ > major calyx ----> major calyx ---- > renal pelvis -----> renal pelvis ----- > ureter -----> ureter ----- > bladder -----> bladder ----- > urethra -----> urethra ----- > outside > outside

NephrolithiasisNephrolithiasis Concretions of calcium Concretions of calcium

and uric acid that can and uric acid that can form in the renal form in the renal pelvis when the pelvis when the concentration is high.concentration is high.

Can be removed by Can be removed by sound waves or sound waves or lithotripsylithotripsy

by surgery, by surgery,

Urinary bladderUrinary bladder Three layers of Three layers of

smooth muscles smooth muscles and the outer and the outer serosa / adventitia.serosa / adventitia.

The outer layer The outer layer may contain may contain Pacinian Pacinian corpuscles.corpuscles.

URETHRAURETHRA Lined by stratified Lined by stratified

squamous epithelium.squamous epithelium.

urinary space of Bowman's capsule urinary space of Bowman's capsule (neonatal or just born urine) ---(neonatal or just born urine) ---

> convoluted proximal tubule > convoluted proximal tubule (infantile urine) ---(infantile urine) ---

> descending, thick, straight, proximal > descending, thick, straight, proximal tubule (toddlerish urine) ---tubule (toddlerish urine) ---

> descending, thin, straight, proximal > descending, thin, straight, proximal tubule (childish urine) --tubule (childish urine) --

> ascending, thin, straight proximal > ascending, thin, straight proximal tubule (pre-pubescentish urine) ---tubule (pre-pubescentish urine) ---

> ascending, thick, straight, distal > ascending, thick, straight, distal tubule (pubescentish urine) ----tubule (pubescentish urine) ----

> convoluted, distal tubule (post-> convoluted, distal tubule (post-pubescentish urine) ---pubescentish urine) ---

> collecting tubule (Gen Xish urine) ----> collecting tubule (Gen Xish urine) ----

> collecting ducts (midlife urine) ----> collecting ducts (midlife urine) ---- > papillary ducts of Bellini (old fart > papillary ducts of Bellini (old fart

urine) -----urine) ----- > minor calyx ------> minor calyx ------ > major calyx ----> major calyx ---- > renal pelvis -----> renal pelvis ----- > ureter -----> ureter ----- > bladder -----> bladder ----- > urethra -----> urethra ----- > outside (in the grave urine)> outside (in the grave urine)

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