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
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What does the kidney do?
Kidneys filter plasma to regulate the makeup of the
interstitial fluid and blood.
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What is interstitial fluid?
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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)
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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
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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
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II. Structure of the Kidney:
1. Location:
- retroperitoneal
- superior lumbar region
- twelfth thoracic to the third
lumbar vertebrae
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2. Part of the urinary system
- ureters
- bladder
- urethra
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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
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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
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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. Bowman’s capsule
- Bowman’s space
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B. Anatomy of the tubule:
i. Very narrow hollow tube of single celled epithelial
tissue.
ii. Contiguous with
Bowman’s 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)
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B. Forces involved in filtration
Net glomerular filtration
pressure=
PGC-PBS-πGC
55 - 15 - 30 = 10mmHG
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C. Glomerular Filtration Rate (GFR)
GFR = the volume of fluid/plasma filtered from the
glomeruli to the Bowman’s space per unit time.
GFR = 180 L/day for average adult
blood volume filtered ~60 times per day
GFR is under physiological regulation
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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)
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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
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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 Amount
Percent
Filtered excreted reabsorbed
per day per day
Water, L
180
1.8
99.0
Sodium, g
630
3.2
99.5
Glucose, g
180
0
100
Urea, g
54
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Rates of reabsorption are under physiological control
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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.
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5. Division of Labor in Nephron:
A. Renal corpuscle = filtrate
B. Proximal tubule = primary reabsorption
C. Proximal tubule = primary secretion
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D. Renal D. Loop of Henle = reabsorption
E. Distal segments = fine tuning, under homeostatic
control
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