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Brief overview of mammalian renal physiology

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Title: Brief overview of mammalian renal physiology


1
Brief overview of mammalian renal physiology
  • Jason Williams
  • University of Nevada Las Vegas
  • 2-28-07

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Outline for renal physiology lecture
  • I. Specific functions of the kidney
  • II. Kidney structure
  • III. Nephron the functional unit of the kidney
  • IV. Basic renal process
  • V. Specific renal process
  • VI. How does the kidney create hyperosmotic
    urine?
  • VII. Renal regulation of sodium, water, and
    potassium
  • VIII. Hydrogen ion regulation
  • IX. Diuretics and kidney disease

4
  • What does the kidney do?
  • Kidneys filter plasma to regulate the makeup of
    the interstitial fluid and blood.

5
What is interstitial fluid?
6
Where is Interstitial fluid located?
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  • I. Specific Functions of the Kidney
  • 1. Form urine (95 water, 5 solutes)
  • A. Removal of metabolic waste from plasma
  • i. urea (protein breakdown)
  • ii. uric acid (nucleic acid breakdown)
  • - insoluble in blood
  • - can precipitate out in blood and cause gout
  • iii. creatinine (muscular creatine phosphate
    breakdown)

8
  • B. Removal of foreign compounds
  • - drugs, food additives, pesticides

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  • C. maintain water, inorganic ion concentrations
  • i. important for proper fluid volume

10
2. Other Functions of the kidney
  • A. Acts as endocrine gland
  • i. erythropoietin
  • ii. Renin
  • iii. 1,25 dihydroxyvitamin D3
  • B. Gluconeogenesis during times of fasting
  • i. amino acids ? glucose

11
  • II. Structure of the Kidney
  • 1. Location
  • - retroperitoneal
  • - superior lumbar region
  • - twelfth thoracic to the third
  • lumbar vertebrae

12
  • 2. Part of the urinary system
  • - ureters
  • - bladder
  • - urethra

13
3. External anatomy of the kidney
  • - Bean shaped
  • - vertical cleft called the renal hilus
  • - Ureters, renal blood vessels, lymphatics,
  • and nerves enter and exit at the hilus

14
  • 4. Internal anatomy of a kidney
  • The kidney has three main regions
  • A. Renal Cortex
  • - outer region (granular)
  • B. Renal Medulla
  • - inner region (striated)
  • - consists of a number of
  • triangular structures called
  • renal pyramids
  • C. Renal pelvis
  • - major calyces

15
  • III. Nephron The functional unit of the kidney
  • i. smallest unit capable of forming urine
  • ii. microscopic, each kidney has about 1 million

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  • 1. The nephron consists of two distinct regions
  • A. Renal corpuscle
  • B. Tubule

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A. Anatomy of the renal corpuscle
  • i. Glomerulus
  • - Afferent and efferent arterioles
  • ii. Bowmans capsule
  • - Bowmans space

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B. Anatomy of the tubule
  • i. Very narrow hollow tube of single celled
    epithelial tissue.
  • ii. Contiguous with
  • Bowmans capsule

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C. Tubule consists of
  • 1. Proximal tubule (convoluted and straight)
  • 2. Loop of Henle (descending and ascending)
  • 3. Distal convoluted tubule
  • 4. Connecting tubule
  • 5. Collecting duct

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D. Vascularization of the nephron
  • Two sets of capillaries
  • a. Glomerulus
  • b. Peritubular capillaries
  • Connected by efferent
  • arteriole

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IV. Basic renal process
  • 1. Urine formation
  • A. begins with glomerular filtration ends with
    urine formation.

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  • B. glomerular filtrate has essentially the same
    concentrations of solutes as blood plasma, minus
    proteins

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B. Glomerular filtrate ? Urine
Substance Amount Filtered per day Amount excreted per day
Water, L 180 1.8
Sodium, g 630 3.2
Glucose, g 180 0
Urea, g 54 30
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C. How is glomerular filtrate altered as it moves
through the tubule?
  • -Tubular reabsorption
  • -Tubular secretion
  • Excreted filtered - reabsorbed secreted

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B. Glomerular filtrate ? Urine
Substance Amount Filtered per day Amount excreted per day
Water, L 180 1.8
Urea, g 54 30
Penicillin 3 10
Creatinine, g 20 20
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V. Closer look at renal processes
  • 1. glomerular filtration
  • - glomerular filtrate has essentially the same
    concentrations of solutes as blood plasma,
    minus proteins

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A. Glomerular filtrate passes through three layers
  • i. Single-celled capillary endothelium
  • ?
  • ii. Non-cellular proteinaceous
  • layer of basement membrane.
  • ?
  • iii. Single-celled epithelium
  • lining (podocytes)

28
B. Forces involved in filtration
  • Net glomerular filtration
  • pressure
  • PGC-PBS-pGC
  • 55 - 15 - 30 10mmHG

29
C. Glomerular Filtration Rate (GFR)
  • GFR the volume of fluid/plasma filtered from
    the glomeruli to the Bowmans space per unit
    time.
  • GFR 180 L/day for average adult
  • blood volume filtered 60 times per
    day
  • GFR is under physiological regulation

30
2. Clinical determination of GFR
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  • A. Introduction
  • i. Estimated glomerular filtration rate by
    measuring inulin and creatinine clearance.
  • ii. Why? Abnormal GFR may suggest renal disease
    (the leading cause of death in captive cheetahs)

32
  • B. Brief Materials and Methods
  • i. measure of GFR
  • 1. injected cats with known amount of inulin
  • Inulin
  • - foreign polysaccharide
  • - fully filtered
  • - not reabsorbed

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B. Brief Materials and Methods (Cont.)
  • 2. Determine amount of inulin in serum and urine
    sample
  • 3. Calculate GFR in milliliters
  • (Urine conc. of inulin) X (urine volume)
    (serum conc. of inulin)
  • 4. Report final GFR as ml min-1 kg-1

34
C. Results
Ccr creatinine clearance rate - Creatinine
produced endogenously - typically only
filtered - measured in same fashion as inulin
GFR
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D. Conclusions
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Tubular Reabsorption
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3. Reabsorption
  • A. Occurs in proximal tubule and loop of Henle

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  • B. General process
  • i. Luminal membrane ? basolateral membrane ?
    interstitial fluid ? peritubular capillary

ii. Tight junction ? interstitial fluid ?
peritubular capillary
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  • C. Tubular reabsorption occurs by
  • i. Diffusion
  • water, urea, other lipid soluble substances
  • ii. Mediated transport
  • Move substances uphill against diffusion
    gradient. (glucose, amino acids, etc.)

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D. Efficiency of tubular reabsorption
Substance Amount Filtered per day Amount excreted per day Percent reabsorbed
Water, L 180 1.8 99.0
Sodium, g 630 3.2 99.5
Glucose, g 180 0 100
Urea, g 54 30 44
Rates of reabsorption are under physiological
control
42
Tubular Secretion
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4. Tubular Secretion
  • A. Moves substances from
  • - peritubular capillary ? tubular lumen
  • B. occurs by diffusion or mediated transport
  • C. secreted substances
  • hydrogen ions, potassium, foreign chemicals,
    choline etc.

44
5. Division of Labor in Nephron
  • A. Renal corpuscle filtrate
  • B. Proximal tubule primary reabsorption
  • C. Proximal tubule primary secretion

45
  • D. Renal D. Loop of Henle reabsorption
  • E. Distal segments fine tuning, under
    homeostatic control
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