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HISTOLOGY OF URINARY SYSTEM
Dr.GURUDASAN01.04.13
INTRODUCTION The urinary system
consists of Kidneys Ureters Urinary bladder Urethra
MAIN FUNCTIONS OF URINARY SYSTEM Kidneys filter
ToxinsMetabolic wastesExcess waterExcess ions
Disposes nitrogenous wastes from blood UreaUric acidCreatinine
Regulate the balance of water and electrolytes, acids and bases.
MACROSCOPIC FEATURES
Kidney has two
regions
Cortex: It lies just
beneath the
connective tissue
capsule.
The cortex extends at
the margins between
each pyramid as Renal
columns.
Some of the striated
patterns from the base of
the pyramid may extend
into the cortex, which are
called as Medullary rays.
KIDNEY LOBE:
It is defined as a renal
pyramid with its overlying
cortex and laterally
associated renal columns.
LOBULE OF KIDNEY – IT IS DEFINED AS MEDULLARY RAY WITH ITS LATERALLY ASSOCIATED CORTICAL TISSUE.
GENERAL STRUCTURE OF NEPHRON It is the functional unit of
kidney. Parts: Renal corpuscle Proximal convoluted
tubule Loop of Henle Distal convoluted tubule Collecting duct
Renal corpuscle:- The blind end of each nephron is expanded in the cortical region into a double walled cup called Bowman’s capsule.
- It consists of outer parietal layer (Simple squamous)
- Inner visceral layer(specialised epithelial cells – podocytes)
- Bowman’s space – space between parietal and visceral layer
Glomerulus is the tuft of capillaries fed by afferent arteriole and drained by efferent arteriole (vascular pole).
Afferent arteriole – Large
Efferent arteriole – small Varying diameters of
arterioles facilitate active filtration due to pressure gradient.
Glomerulus has fenestrated endothelium.
Mesangial cells – specialised supporting connective tissue cells in capillary network. These are satellite cells with contractil eand phagocytic property.
Their phagocytic property helps to remove large proteins and filtration residues.
The glomerular capillaries are closely invested by podocytes.
PODOCYTES: These are cells of visceral
layer of renal corpuscles that envelope glomerular capillaries.
They have long cytoplasmic processes called primary processes, which in turn gives rise to short secondary foot processes or pedicles.
The secondary processes interdigitate with adjacent podocytes and form elongated gaps called filtration slits/pores.
JUXTAGLOMERULAR APPARATUS JUXTAGLOMERULAR CELLS:
- Modified smooth muscle cells present in Tunica media of afferent arteriole.
- Sensitive to pressure of blood in the afferent arteriole.
- Secretes renin
MACULA DENSA:
- Specialised region in the wall of DCT which comes in contact with JG cells.
- Cells are taller and their nuclei are denser and close to one another.
- Sensitive to concentration of sodium ions in the fluid present in DCT.
LACIS (NETWORK) CELLS:
Extra glomerular mesangial cells found at the vascular pole of the renal corpuscle.
- May be involved in production of erythropoietin.
COMPONENTS OF GLOMERULAR FILTER During filtration, the glomerular
filtrate passes through three layers.
I) Fenestrated endothelium of glomerular capillary – Acts as coarse filter preventing cellular elemets and allowing only plasma.
II) Glomerular basement membrane – It is a selective macromolecular filter preventing passage of particles greater than 10 nm in diameter.
III) Filtration slitsThis makes glomerular filtrate similar to plasma wihout plasma proteins(macromolecule).
GFR – 125 ml/min. 124 ml is reabsorbed in renal tubules, 1 ml is released as urine
PROXIMAL CONVOLUTED TUBULE Confined to renal cortex Cuboidal epithelial cells
with long microvilli (fuzzy appearance)
Resorption of water, ions and solutes
LOOP OF HENLE Arises from PCT in cortex,
dips down into medulla as descending limb and loops back as ascending limb and continuous with DCT at the cortico-medullary junction.
Thin segment – Simple squamous epithelium (permeable to water and sodium)
Thick ascending limb cuboidal epithelium ( impermeable to water)
DISTAL CONVOLUTED TUBULE Confined to the renal
cortex Simple cuboidal epithelium Selective secretion and
resorption of ions – This is coupled with secretion of Hydrogen and potassium ions ( one hydrogen or potassium ion is secreted for every sodium ion reabsorbed) – this is controlled by aldosterone.
DCT is involved in maintenance of acid-base balance.
DIFFERENCES BETWEEN PCT AND DCT
DIAMETER: It is more (about 45 – 60µm)
Lining cells are pyramidal and broad
Has brush border Lumen of tubule is irregular
and star shaped Cytoplasm is darkly stained
with Eosin and cell outlines are not clear.
Nuclei are large, spherical and basally or centrally placed.
DIAMETER: It is less ( About 25 – 50 µm)
Lining cells are cuboidal
Has no brush border Lumen of tubule is large
and regular Cytoplasm is lightly
stained with Eosin and cell outlines are clear.
Nuclei are small, spherical and located more in apex.
PROXIMAL CONVOLUTED TUBULE DISTAL CONVOLUTED TUBULE
PROXIMAL CONVOLUTED TUBULEDISTAL
CONVOLUTED TUBULE
COLLECTING DUCT It begins in the medullary ray
as the continuation of DCT. As it enters medulla it is
joined by several other collecting tubules to form larger ducts (Ducts of Belini).
These are lined by simple cuboidal epithelium with distinct cell boundaries and clear pale cytoplasm.
Normally not permeable to water, but in the presence of ADH it becomes permeable
THE URETERS Slender tubes about 25
cm (10 “) long leaving each renal pelvis
One for each kidney carrying urine to the bladder
Descend retroperitonealy and cross pelvic brim
Enter posterolateral corners of bladder
Run medially within posterior bladder wall before opening into interior
This oblique entry helps prevent backflow of urine
Three basic layers Mucosa:Transitional
epithelium of mucosa stretches when ureters fill
Muscle layer: Inner longitudinal, outer
circular layers Inferior 3rd with extra
longitudinal layer)Stimulated to contract
when urine in ureter: peristaltic waves to propel urine to bladder
Adventitia (external)
– Loose conn. Tissue with blood vessels, lymphatics and nerves
Collapsible muscular sac Stores and expels urine Lies on pelvic floor
posterior to pubic symphysis Males: anterior to rectum Females: just anterior to
the vagina and uterus
URINARY BLADDER
Bladder wall has three layers (same as ureters)Mucosa with
distensible transitional epithelium and lamnia propria (can stretch)
Thick muscularis called the detrusor muscle 3 layers of highly
intermingled smooth muscle
Squeezes urine outFibrous adventitia
CLINICAL ASPECTS
Glomerulonephritis:In DM, degenerative changes in glomeruli leads to thickening of glomerular basement membrane and damage to the podocytes and alteration of slit pore membrane. As a result glomerular filter becomes more permeable to proteins and subsequent release of proteins in urine (proteinuria)
RENAL CALCULI:- Calcium salts and uric acid
are excreted in glomerular filtrate. These salts are less soluble in water and later crystallize to form stones
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