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					Urinary System b
    Chapter 26
               Kidney Histology
 Nephron
   Functional unit
   Filters blood
   Separates waste products
    from valuable materials
 Valuable substances
   Organic nutrients, minerals,
    electrolytes, water
 Waste products
   excess electrolytes, minerals,
    metabolic products (urea)
                            Nephron
 Cortical nephron
     Primarily in cortex
     Short loop of Henle
     85% of filtrate
     Most re-absorption
 Juxtamedullary nephrons
   In cortex & medulla
   Long loops of Henle extends
    into renal pyramid
   15% of filtrate
   Produce concentrated urine
 Function
   Blood filtration
   Filtrate re-absorption
              Blood Filtration
 Strainer
 Bulk separation
   Separate blood fluid
    from large blood
    components
   Separates according
    to size
 Cells & large
 substances (protein)
 not filtered
   Remain in blood
Bulk Filtration
                  Filtrate
 Filtered blood fluid & small dissolved
  molecules
 Enter kidney tubule
 Include- electrolytes, minerals, organic
  nutrients, metabolic products (urea),
  water, some proteins
       Filtrate Re-absorption
 Re-absorb valuable filtered components
 Returned to blood
 Re-absorbtion is a selective process
   Cell membranes contain integral membrane
    proteins
 Non-absorbed substances are lost as
 urine (filtrate)
Filtration & Reabsorption
Filtrate Re-absorption
             Nephron Anatomy
 Renal corpuscle
   Blood filtering
    structure
   Site of filtrate
    production
 Renal tubule
   Filtrate modifying
    structure
   Site of re-absorption
           Renal Corpuscle
 In cortex
 Cup shaped chamber
 Receives blood from the afferent arteriole
 2 divisions
   Glomerulus
   Glomerular (Bowman’s) capsule
               Glomerulus
 “ball” of small blood vessels (capillaries)
 Vessels carry blood to nephron
 Blood is filtered through glomerulus
 3 layers of Filter component
   Endothelial cells
   Basal Lamina (aka basement membrane)
   Podocyte layer
Glomerulus
Multiple Layers of Filtration
              Endothelial cells
 Blood vessel epithelial cells (capillary cells)
    Simple squamous
 Fenestrated layer
    Numerous openings allow high degree of filtration
    1st level of filtration
    Blood pressure forces blood fluid & dissolved
     substances through fenestrae
       Becomes filtrate
    Cells & large proteins are not filtered
       Remain in blood
               Basal Lamina
 Thickened
  basement
  membrane
   Lamina Densa
 2nd level of filtration
 Restricts passage of
  larger proteins
 Allows small plasma
  proteins, nutrients
  and ions
                   Podocyte Layer
 Aka Glomerular Epithelium
 Specialized epithelial cells covering glomerular
  capillaries
 Cell foot-like extensions covering capillaries
    Foot-like appearance
    Filtration slits
       Spaces between cells
       Small
    Further filters proteins
    Filtrate
       Small proteins, carbohydrates, nucleic acids, lipids, vitamins,
         minerals, ions, water
    180 L/ filtrate/day
Podocyte Layer
  Glomerular (Bowman’s) Capsule
 Expansion of nephron
   Epithelial “cup” surrounding the glomerulus
 Collects glomerular filtrate & delivers to
  renal tubule
                    Renal Tubule
 Continuation of glomerular
    capsule
   Located primarily within medulla
   Produces striated appearance in
    medulla
   Site of absorption & secretion
   3 divisions
     Proximal convoluted tubule
     Loop of henle
     Distal convoluted tubule
Renal Tubule
       Proximal Convoluted Tubule
 Adjacent to glomerulus
   1st segment of renal tubule
 Cuboidal epithelium w/
  microvilli
 Present within cortex
 Re-absorbs 65% water &
  minerals & ~ 99% organic
  nutrients
                    Loop of Henle
 Continuation of tube into
  medulla & back to cortex
 Thick & thin sections
   Active transport of Na & Cl out of
    tubule
 Re-absorbs ~20% more water
  ions (Na+, Cl-)
   Results in osmosis of water out of
    tubule
 2 regions
   Descending Loop of Henle
   Ascending Loop of Henle
       Distal Convoluted Tubule
 Continuation of tube within cortex
 Secretion of excess ions & minerals
   Selective re-absorption of Na & Cl
   Selective re-absorption of water
 Filtrate at exit from renal tubule
   ~85% h2o, 99% nutrients & minerals have
    been re-absorbed
   Filtrate not re-absorbed= Urine
               Collecting Ducts
 Ducts collecting urine formed in nephrons
 Collect from DCT
 Collecting ducts drain into minor calyx
 Capable of varying the degree of urine
  concentration
 Re-absorb 99.2% water filtered per day (180L)
 Quantity of re-absorption controlled by
  hormones
     Antidiuretic hormone
Collecting Ducts
       Antidiuretic hormone
 Increases kidney re-absorption of water
 Less water excreted- lower urine volume
 Increases blood volume & pressure
               Diuretics
 Decrease water re-absorption
 More water excreted- higher urine volume
 Decreases blood volume & pressure
 Ex. Alcohol, caffeine
          Nephron Blood Supply
 Afferent arterioles
 Glomerulus
 Efferent arteriole
 Peritubular capillary
 Vasa recta
         Afferent Arterioles
 Supply blood directly to the glomerulus
 Branch of interlobular artery
               Glomerulus
 Capillary network
 “tuft” of blood vessels- filtering structures
 Present within glomerular capsule
               Efferent arteriole
 Capillaries collecting
  blood from the
  glomerulus
 Removes filtered blood
  from glomerulus
   Cells & large proteins
         Peritubular capillary
 Extension of efferent arteriole
   In juxatmedullary & cortical nephrons
 Surrounds
   Proximal collecting tubule
   Distal collecting tubule
   Loop of henle
 Collects all re-absorbed molecules (return
  to blood)
                  Vasa Recta
 Region of peritubular
 capillaries
   In juxtamedullary
    nephrons only
 Counter current blood
  flow
 Helps concentrate urine
 Peritubular capillaries
  merge into interlobular
  veins,.. Renal vein back
  to heart
               Kidney Stones
 Deposits of salt crystals in urinary system
 Most common urological disorder
 Can be very painful
 Normally development inhibited chemically by
  urine components
 Crystalization of minerals in normal diet
     Calcium phosphate
     Calcium oxalate
     Some may be caused by infection

				
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posted:9/28/2011
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