The Urinary System

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The Urinary System

• Chapter 26
• (or 25)

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Functions of the Urinary System

• Removal of metabolic wastes (especially
  nitrogenous wastes e.g. urea uric acid).
• Water balance (and therefore blood pressure).
• Control of electrolyte balance.
• Control of pH.
• Removal of toxins.

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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)

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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?)

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The Kidneylocation
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Kidneys in transverse section
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Kidneycloser look
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Blood flow
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A slice of kidney
Cortex
Medulla
Glomeruli
Capsule
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The Nephron functional unit of the kidney
Interlobular artery
Afferent Arteriole
Glomeruli
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Functional histology of a nephron
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Renal Corpuscle
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Filtrate Urine flow
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Nephrons
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The renal corpuscle and the Juxtaglomerular
apparatus
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The renal filtration membranePodocytes and
fenestrated capillaries
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Filtration slits
Pedicles
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The filtration membrane
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Three stages of urine formation

• Filtration 2. Reabsorption 3. Secretion

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Blood pressure drops due to peripheral resistance
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Filtration pressures NFP must be positive for U2P
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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.

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Renal autoregulation
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Compensatory Mechanisms to maintain GFR
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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?

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Reabsorptionof sodium
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Reabsorption of glucose
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Reabsorption of electrolytes and water
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Reabsorption of ions in the Loop of Henle
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Formation of dilute urine
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In the collecting duct
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Reabsorption in the Distal Convoluted Tubule
Collecting Duct
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Summary of tubular reabsorption/excretion
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After the Kidneysthe bladder urethra
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The HumanBladderIt can hold a maximum of 800
1000 ml!
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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.

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Composition of Urine

• Normal
• Urea
• Uric acid
• Creatinine
• Na
• K
• Phosphates
• Sulfates
• Bicarbonate
• Ca
• Mg

• Abnormal
• Glucose glycosuria
• Proteins proteinuria or
• albuminuria
• Ketones ketonuria
• Hemoglobin hemoglobinuria
• Erythrocytes hematuria
• Bile pigments bilirubinura
• Leukocytes pyruia

Abnormally low output oliguria No output
anuria Abnormally high output polyuria Diuresis
increased urine output Diuretic substance
that leads to diuresis
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The micturition reflex
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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 lt 15

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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).
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Kidney stones
Renal Calculi
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Well Mr. Osborne, I dont think that its kidney
stone after all