1st Lecture on the Histology of Urinary System by Dr Roomi

7/31/2019 1st Lecture on the Histology of Urinary System by Dr Roomi

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HISTOLOGY

OF URINARY SYSTEM

By

Dr. Mudassar Ali Roomi (MBBS, M.Phil)


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Urinary system

It comprises ofkidneys, ureters,urinary bladder and

urethra.

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Overview

Large, bean-shaped organwith thin C.T capsule.

Retroperitoneal organ.

The concave, medial borderof the kidney is the hilum,which contains three largestructures.

renal artery

renal vein

funnel-shaped renal pelvis

(expanded upper end of theureter)

Pelvis of kidney is subdividedinto large and small cupsreferred to as major andminor calyces.

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Inspection of Verticalhemisection ofkidney

Darker, granular outer zonecortex

lighter, striated inner zonemedulla

A portion of the cortex alsoextends on each side of therenal pyramids to form therenal columns(of Bertin).

Medullary material continuesinto the cortex as medullaryrays.

Medulla consists of numerous(8-18) cone-shaped renalpyramids.

The round apex of eachpyramid extends downward tothe renal pelvis to form therenal papilla.

Pyramid+ associated cortex= alobe of kidney

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Inspection of Vertical hemisection ofkidney

Each renal papilla issurrounded by a funnel-shaped minor calyx,which collects urine from

the papilla.

The minor calyces join inthe renal sinus to form amajor calyx.

Major calyces, in turn,join to form the largerfunnel-shaped renalpelvis

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Parenchyma of kidneys

Parenchyma of kidneyconsists of uriniferoustubules

Uriniferous tubule=nephron + collecting

tubule. Nephron: 30-40 mm long,

responsible for productionof urine. It is derived frommetanephric blastema

Collecting tubule: about20 mm long, conveys urineto the renal pelvis. Derivedfrom ureteric bud.

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Nephrons

2 Million nephrons are present in eachkidney.

Two types of nephrons:

1. Cortical nephron: their renalcorpuscle is located in the cortex ofkidney.

2. Juxtamedullary nephron: theirrenal corpuscle is situated near the

junction of the cortex and medulla.

Possess longer loops ofHenle

Produce a hypertonic

environment in theinterstitium of the kidneymedulla that results in theproduction of concentrated(hypertonic) urine.

Consists of approx 1/7th oftotal nephron population.

Each nephron, in turn, is subdivided intotwo components, a renal corpuscle andrenal tubules.

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Two types of nephrons9


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Parts of nephron

Bowmans capsule

Renal corpuscle=Bowmans capsule+glomerulus

Proximal tubule =PCT+ PST

Intermediate tubule =thin segment

Distal tubule = DST +DCT

Loop of Henle=PST+DST+Thinsegment


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Renal Corpuscle

Renal corpuscle is the Initial segmentof each nephron

150-205 um in diameter

It has a vascular pole and a urinarypole.

It Consists of a tuft of capillaries,called the glomerulus, surrounded bya double layer of epithelial cells,called the glomerular (Bowmans)capsule.

The inner or visceral layer of thecapsule consists of unique and highlymodified branching epithelial cells,

called podocytes. The podocytes are adjacent to and

completely invest the glomerularcapillaries.

The outer or parietal layer of theglomerular capsule consists of simplesquamous epithelium.

Urinary or capsular space ispresent b/w two layers of theBowmans capsule.

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Podocytes

Star shaped highlymodified epithelial cells

Share a common basallamina with endothelial

cells Primary processes

Secondary processes orfoot processes or footpedicles

filtration slits = 5nm thick.These are elongatedspaces b/w the adjacentpedicles.

Slit diaphragm havingpores (each having an

average diameter of 6nm)


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Renal filtration barrier

Structure:

It is composed offenestrated endothelium ofthe glomerular capillaries,

the basal lamina,

and the filtration slits withthe diaphragm betweenpedicles of the podocytes.

Function: formation ofultrafiltrate of blood plasma

in the Bowmans spacewhich contains water, ionsand small molecules butnot the protein moleculesand other large negativelycharged molecules.


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1st Lecture on the Histology of Urinary System by Dr Roomi

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