Chapter 23
Control of Kidney Function
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Diaphragm
Adrenal
gland
Functions
• Kidneys
filter the blood
T11
T12 Renal
artery
Renal
vein
• Remove watersoluble wastes
• Help control
blood pressure
and
composition
Right
kidney
• Help maintain
red blood cell
levels
Inferior
vena cava
Left
kidney
Aorta
Ureter
Bladder
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Nephrons are Microscopic Tubules That
Form the Urine
Insert fig 23-4
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Three Components of
Urine Formation
• Filtration
• Reabsorption
• Secretion
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Filtration Happens in the Glomerulus
Proximal
tubule
Efferent
arteriole
Bowman’s
space
Afferent
arteriole
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Glomerular Filtration
• Glomerular capillary cells
sit along a basement
membrane
• Bowman’s capsule
epithelium cells sit along
the same basement
membrane
• They stand up away from the
membrane on pseudopods
• Fluid filters across the
basement membrane and
between the pseudopods
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Glomerular Filtration Rate
Glomerular filtration rate = 125 mL/min
Discussion:
• How would it change if you:
– Constricted the efferent arterioles?
– Constricted the afferent arterioles?
– Decreased the blood pressure?
• Which of the following will increase GFR?
– Epinephrine
– Prostaglandins
– NO
– Endothelin
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If 125 mL of Ultrafiltrate Is Formed Each
Minute, How Much Is Formed in a Day?
• Actual urine excretion is 1.5 L a day
• Proximal convoluted tubule reabsorbs about 60%
of nutrients and ions in the urine
– Absorbs at an automatic rate
– The amount of a solute it can reabsorb is the
transport maximum
– Nutrients not reabsorbed pass out in the urine
• Water follows the solutes back into the blood
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Question
Tell whether the following statement is true or false.
If GFR increases, urine output (UO) will decrease.
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Answer
False
Rationale: If GFR increases, it means that fluid is moving
more quickly across the basement membrane/through
the pseudopods. This means that more fluid will become
filtrate and less fluid will be reabsorbed into the blood. If
less fluid is reabsorbed, more fluid is left to be excreted
(increasing UO).
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When Urine Reaches Distal Tubule
Juxtaglomerular
cells
• Juxtaglomerular
cells measure
blood flow in the
afferent arteriole
and urine flow and
composition
• They can release
renin
(Image modified from Bowne, P.S. [2004]. Kidneys tutorial. Used with
author’s permission.)
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Renin Starts the RAA Pathway
• Which turns
on the Na+/K+
ATPase in the
distal tubule
Juxtaglomerular
cells
• Na+ and water
are
reabsorbed
• K+ is secreted
(Image modified from Bowne, P.S. [2004]. Kidneys tutorial. Used with author’s permission.)
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Renin-Angiotensin-Aldosterone System
• Turns on the Na+/K+ ATPase in the distal tubule
• Na+ and water are reabsorbed
– Raises blood volume
– Does not change blood osmolarity
• K+ is secreted
– Lowers blood K+
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Discussion
What changes in these variables would turn
on the RAA system?
• Blood volume
• Blood K+
• Urine volume
• Urine Na+
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Reabsorbing
Water Alone to
Reduce Blood
Osmolality
• This happens
in the inner
layer of the
kidney, the
medulla
• The loop of
Henle contains
ion pumps
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Osmolality
(cont.)
•The NaCl pumped
into the medulla
makes it salty
•It is hypertonic to
the urine in the
collecting duct
• Water moves
from the collecting
duct into the salty
medulla and enters
the blood
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Question
Which renal structure reabsorbs water?
a. Proximal loop
b. Distal loop
c. Collecting duct
d. Glomerulus
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Answer
c. Collecting duct
Rationale: Reabsorption of water occurs in the medulla
(the inner layer of the kidney). Na+Cl- leaves the loop of
Henle, which makes it hypertonic to the urine in the
collecting duct. Water moves from the collecting duct
into the blood (reabsorption).
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Amount of Water
Absorbed
•Depends on
how much can
move out of the
collecting duct
•Antidiuretic
hormone
makes the duct
permeable to
water
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Antidiuretic Hormone (ADH)
• Makes collecting duct more permeable to water
• More water can be reabsorbed from the urine
into the blood
• Blood osmolarity decreases
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Question
Tell whether the following statement is true or false.
Increased ADH decreases urine output (UO).
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Answer
True
Rationale: ADH makes the collecting duct more permeable
to water, so that more water can leave the duct and be
reabsorbed into the blood. More reabsorption means that
there is less fluid to be excreted (↓ UO).
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Scenario
A man was given a drug that stopped the ion pumps in
the loop of Henle.
Question:
• What happened to:
– Medulla osmolarity?
– Na+ levels in the distal convoluted tubule?
– Amount of water reabsorbed from the collecting
duct?
– Renin levels?
– Blood K+?
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Removing NaCl and Water From Your
Blood
• Atrial natriuretic peptide and B-type natriuretic peptide
– ANP is made by overstretched atria
– BNP is made by overworked ventricles
º Both cause the kidneys to stop reabsorbing NaCl
º The NaCl and water are lost in the urine,
reducing blood volume and decreasing the
stretch and workload of the heart
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Discussion
• What will happen to urine if:
– Aldosterone is given?
– ADH levels are high?
– BNP levels are elevated?
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Discussion
A man has severe renal disease.
Question:
• Why does he develop:
– Anemia?
– Weak bones?
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Question
What hormone secreted by the kidneys stimulates RBC
formation in the bone marrow?
a. Renin
b. Erythropoietin
c. Aldosterone
d. Angiotensin
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Answer
b. Erythropoietin
Rationale: Erythropoietin literally means “producing
erythrocytes/RBCs.” Decreased levels of this hormone
lead to anemia; increased levels lead to polycythemia.
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Kidney Functions
• The kidneys clear wastes out of the blood
• Renal clearance is a measurement of how much blood
the kidneys clean in a minute
– If the blood contains 1 mg waste/100 mL blood 
– If the person produces 1 mL urine per minute 
– And if the urine contains 1 mg waste/mL 
Question
• How much blood did the kidney clean in one minute?
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Kidney Functions (cont.)
• If the kidneys fail, waste builds up in the blood
What is the percent of kidney
function when serum creatinine is:
2 mg/dL?
3 mg/dL?
10 mg/dL?
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Kidney Functions (cont.)
• If the kidneys fail, waste builds up in the blood
Kidney function =
Normal serum creatinine
Current serum creatinine
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Discussion
What would each of these test results indicate?
• Severe proteinuria
• Casts with red blood cells in them
• Low specific gravity
• Serum creatinine = 6 mg/dL
• BUN = 35 mg/dL, serum creatinine = 1.2 mg/dL
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