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Histology of Urinary system

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					Histology of the Urinary
        System
Histology of Urinary
system
• Urinary system consists of
  – kidneys, ureters, bladder & urethra.
• Kidney
  – Covered by renal capsule composed of
    connective tissue.
• Substance of kidney divided into
  – An outer cortex
  – An inner medulla
• Cortex
  – occupies space b/t medullary
    pyramids & and b/t base of pyramids &
    capsule.
  – Cortical tissue in area b/t sides of
    pyramids is column of Bertini.
• Renal cortex
  – consists of mainly of nephrons & in
    medulla collecting tubules
• A portion of each nephron
  is located in both cortex &
  medulla.
• Medulla
   – composed of 10-18
      medullary pyramids
      whose bases & sides
      are within cortical zone
      & whose apices point
      toward hilum,
      protruding into renal
      calyces.
• Apices of pyramids
  are renal papillae
• The surface of each papilla is
  perforated by 10-25 orifices, which
  are openings of collecting ducts
Medullary rays (of
Ferrein)
• Fr. Base of medullary pyramid, 400-
  500 parall rays of tubules called
  medullary rays penetrate cortex.
• Each medullary ray consists of a
  straight collecting duct surrounded
  by numerous parallel portions of
  nephron.
• Lobe of a kidney
  – Consists of a renal pyramid & cortex over it.
• Lobule of a kidney
  – A single medullary ray & cortical tissue
    surrounding it.
• Each lobule
  – contains a straight collectinfg duct & all filtering
    nephron units that drain into the duct.
• Uriniferous tubule
  – consists of 2 parts

  – 1.nephron or secretory
    part &

  – 2. Collecting tubule or
    excretory part
      Nephron
      functional & structural unit.
It consists of
      1. renal corpuscle or Malphigian corpuscle,
      dilated part (glomerulus+Boman’s capsule)

     2.renal tubule which consists of
           proximal convoluted tubule,
           loop of Henle &
           distal convoluted tubule.
• Renal Corpuscle
   – consists of glomerulus, a
     tuft of capillaries ,
     surrounded by a double-
     layered capsule called
     Bowman’s capsule.
• Internal wall of capsule
   – envelops capillary tuft- a
     visceral layer
   – whereas outer layer forms
     outer limit of renal
     corpuscle- parietal layer.
   – Between the 2 layersof
     Bowman’s capsule is
     capsular space which
     receicves filtered liquid
     filtered thr. Capillary wall &
     visceral layer
•Podocytes
•Cells of visceral layer
•Cell bodies               -give rise to primary processes
•Primary processes         -do not touch the BM
•Secondary processes       - embrace the capillaries
                                   - touch BM
•Filtration slits          - spaces within interdigitation of
                                          secondary process

                      -diaphragm 6 nm thick
•BM –basement membrane
                               P. process


s. process



             Filtration slit
• Renal corpuscle appears
  as dense rounded
  structures, glomeruli,
  surrounded by narrow
  spaces Bowman’s space.

• Cortical tubules seen in
  section mainly consists of
  proximal convoluted
  tubules with small
  number of distal
  convoluted tubules
• Cells of visceral layer
  are called podocytes.
• 2 layers of Bowman’s
  capsule are
  continuous at
  vascular pole.
• Mesangium & mesangial cells
• Near afferent & efferent arteriole there are
  intercapillary spaces where adjacent capillary
  basal laminae are not lined by endothelium.
  Such spaces are occupied by mesangium,
  consisting of mesangial cells.
• They provide support for capillaries & they can
  contract when stimulated by angiotensin with a
  resulting decrease in in bld flow thr. glomerulus.
Development of renal
corpuscle
• Nephrons develop fr. Embryological metanephros
   – as blind-ended tubules consisting of a single layer of cuboidal
     epithelium
   – The end of tubules dilate & become invaginated by a glomerulus.
• The layer of invaginated epithelium flattens &
  differentiates into podocytes which become closely
  applied to the surface of knot of glomerular capillaries.
  The intervening connective tissue disappears so that the
  basement membrane of glomerular endothelial cells &
  podocytes effectively fuse forming glomerular basement
  membrane.
• A small amount of connective tissue remains to
  support capillary loop to support capillary loop &
  differentiate to form mesangium
                 Parietal layer




Visceral invaginated epithelium
• At the vascular pole,
  afferent arteriole
  enters & efferent
  arteriole leaves. They
  form capillary plexus
  within capsule. Both
  layers of capsule are
  lined by simple
  squamous epithelium
Filtration barrier or
glomerular filter
• Term applied to structures that
  separate blood in glomerular
  capillaries from filtrate in capsular
  space of renal corpuscle.
• The barrier comprises
           1.fenestrated endothelium
           2.basal lamina
           3.pedicels of podocytes with
                        filtration slits
• In diseases such as diabetes
  mellitus & glomerulonephritis,

• glomerular filter is altered & become
  much more permeable to protein,
  with release of protein into urine
  (proteinuria)
Renal tubule
• Begins at urinary pole of renal
  corpuscle as continuation of parielal
  layer.
Renal tubule
     1.consists of proximal convoluted
                tubule
     2.loop of Henle, &
     3.distal convoluted tubule.
Proximal convcoluted
tubule(p.c.t)
• Initial tortuous segment
• Cell type-simple striated
  cuboidal epithelium.
• Strongly acidophilic
  cytoplasm.
• 3-4 cells on cross section
• Cell margin indistinct
• Has prominent brush
  border of microvilli
Loop of Henle
• Consits of 3 parts-thin segment,
  apex of loop,& thick segment.
• A.continuation of PCT,lumen wide,
  wall consists of simple squamous
  cells whose nuclei protrude into
  lumen; resemble a capillary.
• Distal Convoluted Tubule( DCT)
• Cell type – simple cuboidal
  epithelium, cells flatter & smaller
  than that of PCT.
• Cells less acidophilic
• On cross section 5-8 nuclei
• Lumen wider
• Functions of renal tubules

• Reabsorption of some substances fr
  glomerular filtrate
• Active secretion of some some
  substances into urine
Justa-glomerular
apparatus
• 3 components- i.juxta-glomerular
  cells,ii.Macular densa, iii.Lacis cells
  – Tunica media cells of afferent arteriole
    which is in contact with macula densa
    of DCT becomes modified as epitheloid
    cells called juxta-glomerular cells.
  – These cell together with macula denda
    cells they form juxta-glomerular
    apparatus.
• These cells produce renin.
Macula Densa
• DCT comes into contact with renal
  corpuscle of its own nephron, close
  to afferent & efferent arterioles.
• At this point of close contact, cells of
  DCT becomes columnar & their
  nuclei are closely packed together.
• This modified segment of DCT is
  called macula densa
     Polar Cushion
• lacis cells
• In the space b/t tubule & angle of V formed
  by afferent & efferent arterioles, lies a
  small mass of lightly stained cells called
  polar cushion (extraglomerular mesengial
  cells, lacis cells or polkissen)
They are extra-glomerular mesangial cells &
produce hormone erythropoietin
Collecting Tubule
• Urine passes fr.DCT into collecting
  tubule, which join together forming
  larger straight ducts, papillary ducts
  of Billini which widen gradually as
  they approach papillae. Smaller
  collecting tubules are lined with
  cuboidal epithelium. As they
  approach papilla their cells become
  taller until they are columnar cells
    Histology of Ureter & Bladder


Calyces, pelvis, ureter and bladder have the
 same basic structure.

Composed of 3 layers
       1.Mucosa
       2.Muscular layer
       3.Adventia
• Urinary epithelium, also called transitional
  epithelium is a specific feature of pelvis,
  ureter and bladder.
• Ureter is a small tube with stellate lumen.
• Bladder is a large organ, and only sections
  from sample blocks are seen.
• Pelvis & calyces have squeezing or
  Milking function aiding passage of urine
  from papillary ducts to calyces.Ureter
  shows peristaltic movements, downward.
• Urinary bladder
• Epithelium : transitional (5 layer
  when empty & 3 layers when
  distended.)
• Numerous mucosal fold ( except at
  trigone region, which is smooth).
• Smooth muscles form an internal
  sphincter.
• Detrusor muscle (multidirectional
  muscle fibres.
• Urethra
• Male
  – 20 cm long
  – Prostatic urethra : trasitional epithelium
  – Membranous urethra: stratified or pseudostratified
    columnar epithelium
    Penile urethra : pseudostratified columnar
              epithelium
              :stratified squamous
    epithelium ( at very distal end)
  – Bulbourethral & Litttre’s glands present
    Urethra -
    female


•3-5 cm long .

•Proximal region : trasitional epithelium.

•Mid portion :stratified or pseudostratifed columnar epithelium
•
• Distal region        : Stratified squamous epithelium

• Paraurethral & perurethral glands
• From the loop of Henle, the filtrate enters the
  distal convoluted tubule with it’s peritubular
  capillaries surrounding this section of the
  nephron.
• The early distal convoluted tubule (DCT) actually
  comes back around near the PCT and the
  afferent arteriole.
• The early DCT and the afferent arteriole form
  the endocrine structure known as the
  juxtaglomerular apparatus (JGA).
• The hormones secreted from this region are:
•                  Erythropoietin
  (EPO)            signal the red bone marrow to
  make RBCs
• Calcitrol                        formed
  from Vitamin D, signals the DCT
• Renin                       signal the
       DCT and collecting ducts to
•
Reclaim sodium by the renin-angiotensin