The Urinary System

    1. urine formation

      excrete waste products, excess water (control ECF volume),
      acid-base balance, electrolyte balance

    2. endocrine function

      Renin -------------- juxtaglomerular cell
      Erythropoietin --- peritubular capillary endothelial cell
      Medullipin -------- medullary interstitial cell



    Kidney ------------ 'solitary organ'
    Urinary Tract ---- 'tubular organ'

      Urinary Bladder


      Capsule, perirenal fat
          Renal Sinus
            Renal pelvis - Major Calyces - Minor Calyces
          Renal artery, vein and nerves


      Cortex ------- dark reddish brown color ---- glomerulus
        medullary ray
      Medulla ----- light color
        renal pyramid
        renal column (column of Bertin)
      cf. Renal Lobe, Renal Lobule
        Renal Lobe ---- renal pyramid and adjacent renal column
          with overlying renal cortex
        -- multilobal (multilobular) human kidney
        Renal Lobule ---- part of cortex, composed of a medullary ray
          and adjacent cortex


    - Uriniferous Tubule

      1. Nephron --- metanephric
        proximal tubule ------- proximal convoluted tubule
          proximal straight tubule (descending thick limb)
        intermediate tubule --- descending thin limb
          ascending thin limb
        distal tubule ---------- distal straight tubule (thick ascending limb)
          distal convoluted tubule
        cf. Henle's loop
          descending thick limb (proximal straight tubule), descending thin limb,
          ascending thin limb, ascending thick limb(distal straight tubule)
      2. Collecting duct (tubule) ---- mesonephric
        connecting tubule
        cortical collecting duct
        outer medullary collecting duct
        inner medullary collecting duct
        papillary duct (duct of Bellini)

    - Vascular System

      Interlobal artery
      Arcuate artery
      Interlobular artery
        afferent arteriole
        glomerular capillary
        efferent arteriole
        peritubular capillary plexus
        vasa recta --- braches of the juxtaglomerular efferent arteriole or
          direct branches of the interlobular artery
      Stellate venule
      Interlobular vein
      Arcuate vein
      Interlobar vein

    Renal Corpuscle

      - vascular pole, urinary pole


        endothelial cell
          fenestrated type (type II) without diaphragm
        mesangial cell
      - Bowman's capsule
        visceral layer --------- podocyte
          primary process, secondary process (foot process, pedicle)
          filtration slit ---- 25-35 nm <39 nm in Krstic>
        parietal layer ---------- simple squamous epithelium
      - Glomerular basement membrane [basal lamina]
          lamina densa, central
          lamina rara, peripheral (l. r. interna et externa) ----- chondoitin sulfate
        * Filtration Barrier
          1. particle over 10 nm in diameter
          2. Mwt > 69,000 (albumin)
          3. anionic (negatively charged) protein

    Renal Tubules

      Proximal Convoluted Tubule
      - Proximal Tubules compared to Distal Tubule
        - wide and more irregular lumen than those of distal tubule
        Cells --- composed of simple cuboidal cells
        - cells are larger than those of distal tubule
        - cell boundaries are less well delinated than distal cells
          - interdigitating lateral processes is abundant in distal tubules
        - microvilli --- brush border is present at proximal tubule
        - apical canaliculi and vesicles are prominent in proximal tubule
        - more abundant mitochondria were found in proximal tubule

      Thick Segment of Loop of Henle
      - Proximal and Distal Straight Tubule

        - basically same cell with proximal and distal convoluted tubules

      Thin Segment of Loop of Henle

        60 → 15 Ռm in diameter, abrupt transition
        Descending Limb ----- permeable to ions and water
          - no interdigitating lateral process
          - prominent basal infolding
        Ascending Limb
          - not permeable to water
          - actively pumps Cl- ions to interstitium, passively Na+ ions follow
          - interdigitating lateral processes
          - scarse basal infolding

      Distal Convoluted Tubule

        - Aldosterone sensitive: Renin-angiotensin system

      Collecting Duct

        - ADH sensitive
        - consists of 4 types of cells
          distal convoluted tubule cell, connecting tubule cell,
          intercalated cell, principal cell

        1. Connecting Tubule Cell
          - electron-lucent cytoplasm
          - small, numerous mitochondria
          - scarse microvilli
        2. Intercalated Cell
          - numerous long microvilli ---- microplicae
          - extraordinary abundance of vesicles in the apical cytoplasm
          - short, plump mitochondria were dispersed throughout the cytoplasm
          - reabsorption of bicarbonate
            controls acid-base balance
            high carbonic anhydrase activity
        3. Principal Cell
          - one short flagella in the center of the cell surface
          - short, stubby microvilli
          - small randomly oriented mitochondria
        4. Distal Convoluted Tubule Cell

    Juxtaglomerular Apparatus

      Macular densa of distal convoluted tubule
        - osmoreceptor
          detect Na concentration
          and transmit it to JG cell to secrete renin
      Juxtaglomerular cells of afferent arteriole
        - modified smooth muscle cell
        - peripheral myofibrils
        - numerous small vesicles
      Extraglomerular Mesangial Cell (Goormightigh cell, Lacis cell)


      Very small amount in cortex
      In the medulla, interstitium increases in volume
      fibroblast, macrophages, mononuclear cell (precursor of macrophage?)
      medullary interstitial cell
        medullipin secretion



      - tubular organ

      1. tunica mucosa

        epithelium ------ transitional epithelium (urothelium)
        lamina propria
      2. tunica muscularis
      3. tunica adventitia


      - 2 muscle layers
        inner longitudinal layer
        outer circular layer

    Urinary Bladder

      - 3 muscle layers
        inner longitudinal
        middle circular
        outer longitudnal


      Female Urethra
        - stratified cuboidal or columnar epithelium
        - stratified squamous epithelium near the orifice
      Male Urethra
        1. Prostatic portion ------------ transitional epithelium
        2. Membranous portion ------ pseudostratified or stratified cuboidal or columnar epithelium
        3. Penile portion --------------- stratified cuboidal or columnar epithelium
          and stratified squamous epithelium near orifice

Lecture Note by Won Taek Lee, M.D., Ph.D.