Urinary system Histology

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Urinary system :

Urinary system

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Function of urinary system The maintenance of water, electrolytes and acid – base homeostasis . Excretion of many toxic metabolic waste product, particular the nitrogenous molecules urea and creatinine . Synthesis of renin Erthryopoietin Vitamin D

Urinary system :

Urinary system Filtration portion Kidney Excretory portion Ureters Bladder Urethra

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Kidney shaped organ Upper retorperitoneal area Concave surface directed medially 10 – 12 cm

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Hilum Cortex Medulla

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Medullary pyramid Renal corpuscles and proximal and distal parts of tubules. Nephrons : Aries in cortex, loop down into medulla and returns to the cortex. Collecting ducts

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10-18 lobes Renal palilla Renal pelvis Calyx Pelvicalyceal system Renal sinus Gerota’s fascia

Renal circulation :

Renal circulation

Microscopic structure :

Microscopic structure Many compactly packed uriniferous tubules embedded in a vascular interstitium. Uriniferous tubule Two part Nephron Collecting tubule

Nephron :

Nephron Structural and functional unit 1- 4 million in each kidney Four part Renal corpuscle Proximal convoluted tubule (PCT) Loop of Henle Distal convoluted tubule ( DCT )

Classes of Nephron:

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Classes of Nephron Figure 23.9a

Renal corpuscle (Malpighian Corpuscle):

Renal corpuscle (Malpighian Corpuscle) Filtration of blood Present in cortex 200 mm in diameter Two component Bowman’s capsule Glomerulus

Bowman’s capsule :

Bowman’s capsule Blind distended end of nephron, which is converted into cup shaped structures by invagination of tuft of capillaries ( Golmerulus ) Two layers Outer parietal Inner visceral layer Bowman’s space

Bowman’s capsule :

Bowman’s capsule Parietal layer : Capsular epithelium (Simple squamous epithelium ) which continuous with cuboidal epithelium of PCT Visceral layer Podocytes Bowman’s/ urinary / Capsule space

Glomerulus :

Glomerulus Bunch of anastomosing network of capillaries supplied by an afferent arteriole and drained by an efferent arteriole.

Glomerulus :

Glomerulus Varying diameters of arterioles a pressure gradient is created which causes active filtration driving many components of blood into Bowman’s space as glomerular filtrate.

Glomerulus :

Glomerulus Lined by fenestrated endothelium Mesangium Mesangial cells Closely invested by podocytes of visceral layer of renal corpuscle.

Podocytes :

Podocytes Cells of visceral layer of renal corpuscle that envelop glomerular capillaries. Primary processes Secondary foot processes or pedicles.

Podocytes :

Podocytes Filtration slits or slit pores Slit membrane or diaphragms An unusually thick and well developed common basement membrane intervenes b/w fenestrated endothelium and processes of podocytes .

Components of glomerular filter:

Components of glomerular filter Three layers Fenestrated endothelium of glomerular capillary Glomerular basement membrane Filtration slits b/w secondary processes of podocytes

Components of glomerular filter:

Components of glomerular filter Chemical composotion similar to blood palsma without plasma proteins. 125 ml of glomerular filtrate per minute. Out of 124 ml reabsorbed by renal tubules and only 1 ml released into renal pelvis as urine. 1500 ml formed

Proximal convoluted tubule :

Proximal convoluted tubule Start at urinary pole of renal corpuscle. Longer and more convoluted than DCT Bulk of cortex Simple cuboidal epithelium whose luminal surface provided with microvilli ,which give a brush border appearance

Proximal convoluted tubule :

Proximal convoluted tubule Basal surface: striation due to infolding of plasma membrane and the longitudinal orientation of mitochondria b/w them. 75% of water and electrolytes are reabsorbed (selective reabsorbtion ) Excretes certain metabolites, dyes and drugs.

Loop of Henle:

Loop of Henle Aries from PCT in cortex. Part : Descending limb: short thick segment , which is straight part of PCT, and a long thin segments Ascending limb: a short thin segments and a long thick segments ,which is the straight part of DCT.

Loop of Henle:

Loop of Henle Structure of Thick segment is similar to PCT & DCT. Thin segments: simple squamous epithelium which permeable to water and sodium

Loop of Henle:

Loop of Henle Thick segment: cuboidal epithelium which impermeable to water. Closely related with capillary loop of vasa recta which play important role in marinating the osmostic gradient of interstitium of medulla.

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27 Desert animals have long nephron Loop  More H 2 O is reabsorbed So, why is the loop of Henle useful? The longer the loop, the more concentrated the filtrate and the medullary IF become Importance : the collecting tubule runs through the hyperosmotic medulla  more ability to reabsorb H 2 O (DESCENDING LIMB)

Loop of Henle:

Loop of Henle Function : to generate a gradual increasing osmotic gradient in the interstitium/tissue fluid of renal medulla by mean of complex countercurrent multiplier system; assisted by countercurrent exchange mechanism operating in the vasa recta. High osmotic pressure in medullary tissue fluid permits the removal of water by osmosis from the fluid

Distal convoluted tubule :

Distal convoluted tubule Short and less convoluted than PCT Found in cortex Simple cuboidal epithelium Actively reabsorbs sodium from tubular fluid. Maintains of acid-base balance in body fluids.

PCT DCT:

PCT DCT 30 Note that the difference is seen on the apical surface; the basal surfaces are identical.

Collecting Tubule & Collecting Duct:

Collecting Tubule & Collecting Duct Begins in medullary ray as the continuation of DCT. Duct of Bellini or Papillary duct

Collecting Tubule & Collecting Duct:

Collecting Tubule & Collecting Duct Collecting tubles Cuboidal epithelium with distinct cell boundaries and clear pale cytoplasm.

Collecting Tubule & Collecting Duct:

Collecting Tubule & Collecting Duct Collecting duct: large,wider and lined by tall columnar cells with pale staining cytoplasm,

Collecting Tubule & Collecting Duct:

Collecting Tubule & Collecting Duct Not permeable to water. In presences of ADH secreted by neurohypophysis ,they become permeable to water To concentrate the urine and conduct it to the calyces.

Juxtaglomerular apparatus (JGA):

Juxtaglomerular apparatus (JGA) Regulation of blood pressure and three components Juxtaglomerular cells Macula densa Lacis (network ) Polkissen cells

Juxtaglomerular apparatus (JGA):

Juxtaglomerular apparatus (JGA) Juxtaglomerular cells Modified smooth muscle cells present in tunica media of afferent arteriole at point of contact with DCT. Internal elastic lamina disappers at the site. EM: Protein secreting cells . Renin Sensitive to pressure of blood in arteriorle

Juxtaglomerular apparatus (JGA):

Juxtaglomerular apparatus (JGA) Macula densa Specialized region of in wall of DCT which come into intimate contact with the JG cells. Lining epithelium convert to macula densa Taller and their nuclei are denser and close to one other. Basement membrane is very thin. Sensitive to concentration of sodium in fluid present in DCT

Juxtaglomerular apparatus (JGA):

Juxtaglomerular apparatus (JGA) Lacis (network ) Polkissen cells Extraglomerular mesangial cells found at vascular pole of renal corpuscle in close relation with macula densa . Function : not understood. Production of erthropoietin

Have break …….:

Have break …….

Ureter:

Ureter

Mucosa :

Mucosa Transitional epithelium Lamina propria rich in elastic fibres . Star shaped lumen in cross section

Muscle coat:

Muscle coat Smooth muscle fibres Two layers Upper two third of ureter inner longitudinal and outer circular Lower one third: outer longitudinal

Adventitia :

Adventitia Outermost layer Loose connective tissue containing blood vessels, lymphatic and nerves.

Urinary bladder:

Urinary bladder

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Muscular bag Urine stored temporarily and is discharged out periodically via urethra during micturition . Empty lie with in pelvis Normal capacity : 200-300 ml Three coat

Mucosa :

Mucosa Transitional epithelium Lamina propria

Mucosa :

Mucosa Empty : Folded and its epithelium is thick consisting of five to six cell layers. Cell often contain two nuclei or even polyploid Osmotic barrier b/w toxic urine and tissue fluid.

Mucosa :

Mucosa Distended with urine: Mucosal fold disappear. Epithelium thin 3 to 4 cell layers Superficial cell become flattened.

Muscle coat:

Muscle coat Three loosely arrange ill-defined layers Inner longitudinal Middle circular Outer longitudinal Internal sphincter

Adventitia :

Adventitia Fibroelastic connective tissue Contain : blood vessels , nerves and lymphatic. Superior surface of bladder : mesothelium making serosa

Urethra :

Urethra

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Epithelium of urethra Transitional epithelium At the proximal end (near the bladder) Stratified and pseudostratified columnar – mid urethra (in males) Stratified squamous epithelium At the distal end (near the urethral opening)

Urethra:

Urethra Internal urethral sphincter Involuntary smooth muscle External urethral sphincter Voluntarily inhibits urination Relaxes when one urinates

Urethra:

Urethra In females Length of 3–4 cm In males – 20 cm in length – three named regions Prostatic urethra Passes through the prostate gland Membranous urethra Through the urogenital diaphragm Spongy (penile) urethra Passes through the length of the penis

The Urinary System Throughout Life:

The Urinary System Throughout Life Kidney and bladder function declines with advancing age Nephrons decrease in size and number Tubules less efficient at secretion and reabsorption Filtration declines Recognition of desire to urinate is delayed Loss of muscle tone in the bladder

Disorders:

Disorders Urinary tract infections More common in females Burning sensation during micturition Diabetic renal disease Renal calculi Kidney stones Bladder cancer 3% of cancers – more common in men Kidney cancer Arises from epithelial cells of uriniferous tubules

Thank you……:

Thank you……

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