functions of the kidneys regulation of extracellular fluid volume and blood pressure regulation of...
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Functions of the Kidneys
Regulation of extracellular fluid volume and blood pressure
Regulation of osmolarity--close to 300 mOsm
Maintenance of ion balance: Na+--regulates ECF volume
Homeostatic regulation of pH--kept in a narrow range
Excretion of nitrogenous and other water-soluble wastes Urea & uric acid
Creatinine from muscle metabolism
Urobilinogen (breakdown of hemoglubin)
Production of hormones Renin (sodium balance and blood pressure homeostasis
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Anatomy: The Urinary System
Figure 19-1a
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Figure 19-1b
Anatomy: The Urinary System
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Figure 19-1c
Anatomy: The Urinary System
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Figure 19-1i
Anatomy: The Urinary System
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Figure 19-1g–h
Anatomy: The Urinary System
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Figure 19-1d–e
Anatomy: The Urinary System
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Figure 19-1f
Anatomy: The Urinary System
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Figure 19-1j
Anatomy: The Urinary System
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Renal Summary
Summary of normal renal function: Substance Units Filtered Excreted % Absorbed Water liter 180 1.5 >99 Sodium mEq 25,000 150 >99 Potassium mEq 630 95 85 Chloride mEq 18,000 150 >99 Bicarbonate mEq 4,500 0 100 Glucose grams 180 0 100 Urea grams 58 23 60
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Figure 19-2
Kidney Function
Filtration, reabsorption, secretion, and excretion
Efferentarteriole
Afferentarteriole
Glomerulus
Peritubular capillaries
Proximaltubule
Bowman’scapsule
Collectingduct
To renal vein
F
R
S
E
F
R
S
R R
R
S
R S
E
Loopof
Henle
To bladder andexternal environment
= Filtration: blood to lumen
= Reabsorption: lumen to blood
= Secretion: blood to lumen
= Excretion: lumen to external environment
KEY
Distaltubule
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Figure 19-2 (1 of 4)
Kidney Function: Filtration
Efferentarteriole
Afferentarteriole
Glomerulus
Peritubular capillaries
Proximaltubule
Bowman’scapsule
Collectingduct
To renal vein
F
F
Loopof
Henle = Filtration: blood to lumen
KEY
Distaltubule
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Figure 19-2 (2 of 4)
Kidney Function: Reabsorption
Efferentarteriole
Afferentarteriole
Glomerulus
Peritubular capillaries
Proximaltubule
Bowman’scapsule
Collectingduct
To renal vein
F
R
F
R
R R
R
R
Loopof
Henle = Filtration: blood to lumen
= Reabsorption: lumen to blood
KEY
Distaltubule
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Figure 19-2 (3 of 4)
Kidney Function: Secretion
Efferentarteriole
Afferentarteriole
Glomerulus
Peritubular capillaries
Proximaltubule
Bowman’scapsule
Collectingduct
To renal vein
F
R
S
F
R
S
R R
R
S
R S
Loopof
Henle = Filtration: blood to lumen
= Reabsorption: lumen to blood
= Secretion: blood to lumen
KEY
Distaltubule
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Figure 19-2 (4 of 4)
Kidney Function: Excretion
Efferentarteriole
Afferentarteriole
Glomerulus
Peritubular capillaries
Proximaltubule
Bowman’scapsule
Collectingduct
To renal vein
F
R
S
E
F
R
S
R R
R
S
R S
E
Loopof
Henle
To bladder andexternal environment
= Filtration: blood to lumen
= Reabsorption: lumen to blood
= Secretion: blood to lumen
= Excretion: lumen to external environment
KEY
Distaltubule
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Figure 19-3
Kidney Function
The urinary excretion of substance depends on its filtration, reabsorption, and secretion
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Figure 19-4a
The Renal Corpuscle
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Figure 19-4d
The Renal Corpuscle
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Figure 19-4c
The Renal Corpuscle
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Where does a drink of water go?
Drink watergutfeces
plasmakidneys
everywhere else75-80% ofcardiac output
nephrons
80% of renalplasma flow20% of renalplasma flow
urine
>99% offiltered fluid<1% offilteredfluid
20-25%of cardiacoutput
Where does a drink of water go?
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Figure 19-5
Filtration Fraction
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Kidney Function
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Measuring glomerular filtration rate A. Compare the amount of material filtered at the glomerulus with the amount of material excreted in the urine:
1. You can measure the amount of material excreted per unit of time in the urine by measuring the volume of urine produced over a period of time and measuring the concentration of the material in the urine:
concentration X volume/min = amount/minute
2. It is much harder to measure directly the amount of material that was filtered, but it can be calculated.
3. The most common way to accomplish this calculation is to measure the renal clearance of inulin, which allows you to calculate the glomerular filtration rate (GFR).
a. Inulin (not INSULIN) is a fructopolysaccharide with a molecular weight of approximately 5000. A common source of this molecule is Jerusalem artichokes.
b. It is freely filtered. In other words, the concentration of inulin in the fluid within Bowman's capsule is identical to the concentration of inulin in plasma.
c. It is neither reabsorbed nor secreted in any portion of the nephron. All of the inulin that enters the nephron will be excreted in the urine. Any inulin that is not filtered into the tubule remains in the circulation.
e. Because of these properties, all of the inulin that is filtered into the nephron appears in the urine, and only the inulin that is filtered into the nephron appears in the urine. In other words,
or
where V = volume/time.
f. This measurement is called a "clearance," because it tells you the amount of plasma that was "cleared" of inulin. (You can't measure that volume directly because a lot of it - but you don't know how much - was reabsorbed while the fluid was moving along the nephrons.)
[ i n u l i n ]p l a s m a
× Vf i l t e r e d
= [ i n u l i n ]u r i n e
× Vu r i n e
Vf i l t e r e d
= G F R =
[ i n u l i n ]u r i n e
[ i n u l i n ]p l a s m a
× Vu r i n e
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Measuring renal plasma flow It is difficult to measure total renal blood flow, but it can be calculated by measuring the renal clearance of
PAH, or any other substance that is entirely removed from the blood in the renal vasculature in a single pass through the kidney.
1. All molecules of PAH that enter the afferent arterioles are either filtered or secreted into the tubular fluid, so all PAH has been transferred into the tubular fluid before the blood leaves the kidney.
2. I.e.,
and
C. The ratio of the inulin clearance to the PAH clearance, then, tells you the fraction of the plasma entering the kidney that got filtered into the nephrons; this value is called the filtration fraction.
D. Normal values for humans are (from Guyton and Hall's Textbook of Medical Physiology):
1. Renal blood flow = 1200 ml/minute.
2. The normal hematocrit is about 45%, so renal plasma flow = 650 ml/minute. REMEMBER TO CORRECT FOR HEMATOCRIT if a question asks for plasma flow, rather than blood flow!
3. Normal GFR = 125 ml/minute. This value remains remarkably constant even when the renal blood flow varies.
[ P A H ]p l a s m a
× Vr e n a l p l a s m a
= [ P A H ]u r i n e
× Vu r i n e
R P F =
[ P A H ]u r i n e
[ P A H ]p l a s m a
× Vu r i n e
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Forces that Influence Filtration
Hydrostatic pressure (blood pressure)
Colloid osmotic pressure
Fluid pressure created by fluid in Bowman’s capsule
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Figure 19-6
Filtration
Filtration pressure in the renal corpuscle depends on hydrostatic pressure, colloid osmotic pressure, and fluid pressure
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Figure 19-7
Filtration
Autoregulation of glomerular filtration rate takes place over a wide range of blood pressure
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Figure 19-8a
Filtration
Resistance changes in renal arterioles after GFR and renal blood flow
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Figure 19-8b
Filtration
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Figure 19-8c
Filtration
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GFR Regulation
Myogenic response Similar to autoregulation in other systemic arterioles
Tubuloglomerular feedback
Hormones and autonomic neurons By changing resistance in arterioles
By altering the filtration coefficient
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Figure 19-9
Juxtaglomerular Apparatus
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Figure 19-10, step 1
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
1
1
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Figure 19-10, steps 1–2
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
Flow through tubule increases.
2
1
1
2
2
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Figure 19-10, steps 1–3
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
Flow through tubule increases.
Flow past macula densaincreases.
2
1
1
2
3
23
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Figure 19-10, steps 1–4
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
Flow through tubule increases.
Flow past macula densaincreases.
Paracrine diffuses from macula densa to afferent arteriole.
2
1
1
2
3
42
3
4
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Figure 19-10, steps 1–5 (1 of 4)
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
Flow through tubule increases.
Flow past macula densaincreases.
Paracrine diffuses from macula densa to afferent arteriole.
Afferent arteriole constricts.
2
1
1
2
3
4
5
23
4
5
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Figure 19-10, steps 1–5 (2 of 4)
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
Flow through tubule increases.
Flow past macula densaincreases.
Paracrine diffuses from macula densa to afferent arteriole.
Afferent arteriole constricts.
Resistance in afferent arteriole increases.
2
1
1
2
3
4
5
23
4
5
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Figure 19-10, steps 1–5 (3 of 4)
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
Flow through tubule increases.
Flow past macula densaincreases.
Paracrine diffuses from macula densa to afferent arteriole.
Afferent arteriole constricts.
Resistance in afferent arteriole increases.
Hydrostatic pressurein glomerulus decreases.
2
1
1
2
3
4
5
23
4
5
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Figure 19-10, steps 1–5 (4 of 4)
Tubuloglomerular Feedback
Afferentarteriole
Maculadensa
Efferent arteriole Bowman’s capsule GlomerulusDistal tubuleProximal
tubule
Collectingduct
Loopof
Henle
Granularcells
GFR increases.
Flow through tubule increases.
Flow past macula densaincreases.
Paracrine diffuses from macula densa to afferent arteriole.
Afferent arteriole constricts.
Resistance in afferent arteriole increases.
Hydrostatic pressurein glomerulus decreases.
GFR decreases.
2
1
1
2
3
4
5
23
4
5