The Urinary System


Kidney

Excretory passages

    ureter
    urinary bladder
    urethra

Function:

    1) Eliminate toxic byproducts of metabolism
    2) Regulation of electrolyte balance & acid-base balance
    3) Regulation of blood pressure
    4) Renin, Erythropoietin, prostaglandin secretion

Extremely rich blood supply


KIDNEY

retroperitoneal organ (11 x 5 x 3 cm) 150 gm

    hilum-blood vessel, lymph vessel, ureter

Vertical hemisection

1) Medulla
6-12 pyramid-pale, striated
cortical column of Bertin
2) Cortex
dark brown, granular (renal corpuscles)
medullary rays
3) Pelvis
2-3 major calyx
8-12 minor calyx
papilla (10-25 ducts of Bellini, collecting ducts)

Lobe: pyramid with overlying cortex
Lobule: medullary ray with asociated cortical tissue


URINIFEROUS TUBULE
Functional and structural unit of the kidney

Nephron: metanephric blastema 30-40 mm
Collecting duct: ureteric bud 20 mm

Nephron

Renal corpuscles
Proximal convoluted tubule
Henle's loop (thick & thin segment)
Distal convoluted tubule

1. RENAL CORPUSCLE (Malpighian corpuscle)

      150-250 um
      juxtamedullary nephron 1/7
    Glomerulus

    Bowman's capsule

      outer parietal layer: simple squamous epithelium
      inner visceral layer: 'podocyte'
        (pedicle-slit like space 20-40 nm
          slit membrane 5 nm thickness )

      * Filtration barrier

        1) Capillary endothelium - attenuated & perforated 70-80 nm
        2) Continuous basal lamina 150-300 nm
          lamina densa & rara
        3) Podocyte - interpedicular space (slit membrane)
          * functional pore size of filtration barrier
            plasma albumin 70,000
          * 170-200 L / day filtration
            99 % reabsorption

    Mesangial cell
      mesodermal origin, pericyte like cell

    Juxtaglomerular apparatus
    1. Juxtaglomerular cell
      smooth muscle cell in afferent arteriole
      epithelioid cell ( large pale staining, conspicuous granules)
      renin secretion (angiotensinogen - angiotensin I)
    2. Macula densa
      specialized region in distal tubule
      very thin lamina
      regulation of blood flow to glomerulus by detecting sodium change
      morphological characteristics:
        a) widely distribued small, ovoid mitochondria
        b) subsurface vacuolization
        c) irregular shallow folds of basal plasmalemma
        d) infranuclear Golgi
        e) taller than surrounding cells
    3. Lacis cell (extraglomerular mesangial cell)
      erythropoietin production

2. PROXIMAL CONVOLUTED TUBULE

    nephron 30-40 mm (proximal tubule 14mm, 50-60 um diameter)
    tortuous course
    6-12 truncated pyramidal cell (eosinophilic)
      basal striation (mitochondria)
      brush border (microvilli)
      complex intercellular interdigitation
    85% < water and NaCl reabsorption

3. LOOP OF HENLE

    thick limb: less mitochondria, interdigitation, lysosome
    thin limb: 12-15 um abrupt change
      juxtamedullary nephron - long (type I & II)
      subcapsular nephron - short (type I)
    thick distal limb : macula densa

4. DISTAL CONVOLUTED TUBULE

    shorter than proximal tubule
    6-8 cuboidal cell, central spherical nucleus
    less intense eosinophilia, less diameter, no brush border
    abundant mitochondria

Collecting Tubule

Developmentally different origin to nephron
low cuboidal - tall columnar cells
pale staining with few organelles
Intercalated dark cell: mitochondria, small apical vesicle, microplicae
Principal light cell: glycogen

RENAL INTERSTITIUM

Cortex:
sparse connective tissue
fibroblast-like cell (lipid droplets)
mononuclear cells (phagocytic)
Medulla:
fibroblast-like cells (prostaglandin)
pericyte associated with the vasa recta
mononuclear cells

Renal Circulation

    Renal a. - 3 branches - interlobar a. - arcuate a. - interlobular a. - afferent arteriole -
    glomerulus - efferent arteriole - (cortex)peritubular capillary plexus -
    stellate vein - interlobular v.- arcuate v. - interlobar v. - renal v. (medulla)
    arteriolae rectae spuriae (vasa recta) - arcuate v.

EXCRETORY PASSAGES

Calyces

Ureter

transitional epithelium, no submucosa
inner longitudinal outer circular M.

Urinary bladder

transitional epithelium : plaques, interplaque region
lamina propria: no glands except urethral orifice region
inner longitudinal, middle circular, outer longitudinal M.

Urethra

Female: 4-5 Cm
transitional ep.
stratified squamous ep.
Male: 15-20 Cm
prostatic urethra - transitional epithelium
membranous urethra - str. columnar epithelium
penile urethra - str. columnar (patches of pseudostr. columnar, str. squamous ep)



Lecture Note by Kyung Ah Park, M.D., D. med.