Transcript Airgas template - Morgan Community College

Chapter 24
Structure and Function of the
Kidney
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Functions
• Kidneys
filter the blood
• Remove watersoluble wastes
• Help control blood
pressure and
composition
• Help maintain red
blood cell levels
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Three Components of Urine Formation
• Filtration
• Reabsorption
• Secretion
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Filtration Happens in the Glomerulus
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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
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 measure blood flow in the
afferent arteriole and urine flow and composition
• They can release renin, which turns on the Na+/K+
ATPase in the distal tubule
• Na+ and water are reabsorbed
• K+ is secreted
(Image modified from Bowne, P.S. [2004]. Kidneys tutorial. Used with
author’s permission.)
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Renin-Angiotensin-Aldosterone Pathway
• 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 pathway?
• 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
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
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 Henl
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
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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