The Urinary System - PowerPoint 3

							The Urinary System

     Chapter 26
       (or 25)
    Functions of the Urinary System
1. Removal of metabolic wastes (especially
   nitrogenous wastes e.g. urea & uric acid).
2. Water balance (and therefore blood pressure).
3. Control of electrolyte balance.
4. Control of pH.
5. Removal of toxins.
      Anatomy of the Urinary System
• The Kidneys: the functional heart of the urinary
  system.
• The Ureters: pipeline from the kidneys to the
  bladder.
• The Urinary Bladder: holding tank of urine.
• The Urethra: avenue of relief

(word of the day “micturition” = voiding the bladder)
                 The Kidneys

• Location: retroperitoneal against the dorsal wall
  of the abdominal cavity. The right kidney is
  slightly lower than the left.
• Size & weight: approximately 150 grams (about
  5 ounces) each and 12 cm x 10 cm x 4 cm.
• Shaped like a bean (or are beans shaped like
  kidneys?)
  The
Kidney:
location
Kidney:
up close
   &
personal
          A slice of kidney

Cortex

           Glomeruli          Medulla


Capsule
The Nephron: functional unit of the kidney




                                     Interlobular artery


                           Afferent Arteriole



     Glomeruli
Functional histology of a nephron
        Kidney tissue
              Glomerular (Bowman’s) capsule




Glomerulus
Nephrons
Blood pressure drops due to peripheral resistance
The renal corpuscle and the Juxtaglomerular
                apparatus
   The renal filtration membrane:
Podocytes and fenestrated capillaries
Filtration
             Pedicles
   slits
Three stages
  of urine
 formation
 1. Filtration
 2. Reabsorption
 3. Secretion
Filtration pressures: NFP must be positive for U2P
                   GFR
GFR is “Glomerular Filtration Rate”.
• It is directly proportional to NFP.
• It is a measurement of FLOW in milliliters
  per minute (ml/min).
• If NFP drops more than 15% below 10
  mmHg, GFR goes to 0.
• If NFP goes up less than 30% above
  normal, the kidneys can handle it without
  major compensatory mechanisms kicking
  in.
Compensatory
 Mechanisms
 to maintain
    GFR
      Tubular reabsorption

•Reabsorption of filtered solutes occurs in
the Proximal Convoluted Tubules.
•Most solutes are reabsorbed by
secondary active transport with Na+. Does
this look familiar?
Solute reabsorption
Reabsorption of NaCl & water in
      the Loop of Henle
Reabsorption
 in the Distal
 Convoluted
   Tubule &
  Collecting
     Duct
Summary of tubular reabsorption/excretion
After the
Kidneys:
   the
bladder
    &
urethra
  The
Human
Bladder:
 It can hold
a maximum
   of 800 –
 1000 ml!
   Physical characteristics of Urine
• Color - Clear to deep yellow, almost rusty, depending on
  concentration.
• Odor - Fresh urine is slightly aromatic, stale urine smells
  like downtown Tacoma on a Sunday morning.
• pH – range of 4.5 – 8 depending on diet. High protein
  leads to low pH (acid ash diet), vegetarian (alkaline ash)
  diet leads to high pH. Heavy vomiting and bacterial
  infection can also lead to alkaline urine.
• Specific gravity – Normal range is 1.001 – 1.030.
  Distilled water has a s.g. of 1.000. Anything solutes
  cause the specific gravity of a liquid to go up.
  Concentrated urine has a higher s.g. than dilute urine.
            Composition of Urine
Normal                       Abnormal
Urea                         Glucose       “glycosuria”
Uric acid                    Proteins      “proteinuria” or
Creatinine                                 “albuminuria”
Na                           Ketones       “ketonuria”
K                            Hemoglobin “hemoglobinuria”
Phosphates                   Erythrocytes “hematuria”
Sulfates                     Bile pigments “bilirubinura”
Bicarbonate                  Leukocytes “pyruia”
Ca
            Abnormally low output = oliguria
Mg
            No output = anuria
            Abnormally high output = polyuria
            Diuresis = increased urine output
            Diuretic = substance that leads to diuresis
The micturition reflex
        Stages of Renal Disease
• Stage 1: signs of kidney damage w/ GFR ≥ 90.
• Stage 2: signs of kidney damage w/ GFR 60 –
  89.
• Stage 3: GFR 30 – 59.
• Stage 4: GFR 15 – 29.
• Stage 5: < 15
                 Renal Clearance
The volume of plasma that is cleared of a particular
substance in a given time (usually one minute).
                         RC = UV/P
U = concentration of the substance in urine (mg/ml)
V = flow rate of formation (ml/min)
P = concentration of the substance in the plasma
(mg/ml)
High renal clearance values means that the substance is being
effectively cleared, low values means that more is being
reabsorbed. For some solutes low is good (glucose should be 0).
For others, high RC would be expected (creatinine should be
complete, urea should be about 80%).
Kidney stones
   Renal Calculi
   “Well Mr.
  Osborne, I
  don’t think
that it’s kidney
stone after all”