Essentials of Pathophysiology
CHAPTER 24
STRUCTURE AND FUNCTION OF THE
KIDNEY
PRE LECTURE QUIZ
F

T

F

T

T

TRUE/FALSE
Large molecules, such as protein, easily cross
the glomerular wall.
During times of decreased cardiac output, the
glomerular filtration rate is also decreased.
The activation of vitamin A, which is important
for intestinal reabsorption of calcium, occurs in
the kidney.
The kidneys perform excretory and endocrine
functions.
In the adult, the kidneys are perfused with 20%
to 25% of the cardiac output.
PRE LECTURE QUIZ

Bowman’s

Creatinine
erythropoietin 
Henle

nephron

The functional unit of the kidney is the
__________.
Fluid and particles from the blood are filtered
through the capillary membrane into a fluid-filled
space in the __________ capsule.
The loop of __________ plays an important role
in controlling the concentration of the urine, and
is divided into three segments.
The kidney synthesizes __________, which
stimulates bone marrow production of red blood
cells.
Serum __________ reflects the GFR (glomerular
filtration rate) and can be used as an estimate of
renal function.
FUNCTIONS




Kidneys
Diaphragm
filter the blood
Adrenal
Remove watergland
soluble wastes
Help control
blood pressure
and composition
Right
kidney
Help maintain red
blood cell levels
Inferior
vena cava
T11
T12 Renal
artery
Renal
vein
Left
kidney
Aorta
Ureter
Bladder
NEPHRONS ARE MICROSCOPIC TUBULES THAT
FORM THE URINE
Insert fig 23-4
THREE COMPONENTS
OF URINE FORMATION



Filtration
Reabsorption
Secretion
FILTRATION HAPPENS IN THE GLOMERULUS
Proximal
tubule
Efferent
arteriole
Bowman’s
space
Afferent
arteriole
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
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
IF 125 ML OF ULTRAFILTRATE IS FORMED EACH
MINUTE, HOW MUCH IS FORMED IN A DAY?




60 min/hr X 24 hr/day = 1440 min/day X 125 ml/min =
180,000 ml/day =180 L/day of ultrafiltrate
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
QUESTION
Tell whether the following statement is true or
false.
If GFR increases, urine output (UO) will decrease.
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).
WHEN FILTRATE REACHES DISTAL TUBULE

Juxtaglomerular
cells

(Image modified from Bowne, P.S. [2004]. Kidneys tutorial. Used with
author’s permission.)
Juxtaglomerular
cells measure
blood flow in the
afferent arteriole
and urine flow and
composition
They can release
renin
RENIN STARTS THE RAA PATHWAY

Juxtaglomerular
cells


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.)
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+
DISCUSSION
What changes in these variables would turn on the
RAA system?
Blood volume
 Blood K+
 Urine volume
 Urine Na+

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
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
QUESTION
Which renal structure reabsorbs water?
a. Proximal loop
b. Distal loop
c. Collecting duct
d. Glomerulus
ANSWER
Collecting duct
Rationale: Reabsorption of water occurs in the
medulla (the inner layer of the kidney). Na+Clleaves 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).
c.
AMOUNT OF WATER ABSORBED
•Depends on
how much can
move out of
the collecting
duct
•Antidiuretic
hormone
makes the duct
permeable to
water
ANTIDIURETIC HORMONE (ADH)



Makes collecting duct more permeable to water
More water can be reabsorbed from the urine
into the blood
Blood osmolarity decreases
QUESTION
Tell whether the following statement is true or
false.
Increased ADH decreases urine output (UO).
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).
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+?
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
º
Both cause the kidneys to stop reabsorbing NaCl
The NaCl and water are lost in the urine, reducing
blood volume and decreasing the stretch and
workload of the heart
DISCUSSION

What will happen to urine if:
 Aldosterone
is given?
 ADH
levels are high?
 BNP
levels are elevated?
brain natriuretic peptide
made by the ventricles
DISCUSSION
A man has severe renal disease.
Question:
 Why does he develop:
 Anemia?
 Weak bones?
QUESTION
What hormone secreted by the kidneys
stimulates RBC formation in the bone marrow?
a. Renin
b. Erythropoietin
c. Aldosterone
d. Angiotensin
ANSWER
Erythropoietin
Rationale: Erythropoietin literally means
“producing erythrocytes/RBCs.” Decreased
levels of this hormone lead to anemia;
increased levels lead to polycythemia.
b.
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?

RC =

100𝑚𝐿 𝐵𝑙𝑜𝑜𝑑
1𝑚𝑔 𝑊𝑎𝑠𝑡𝑒


RC=
𝟏𝟎𝟎𝒎𝑳 𝑩𝒍𝒐𝒐𝒅
𝒎𝒊𝒏
+
1𝑚𝑔 𝑊𝑎𝑠𝑡𝑒
1𝑚𝐿 𝑈𝑟𝑖𝑛𝑒
+
1𝑚𝐿 𝑈𝑟𝑖𝑛𝑒
1𝑚𝑖𝑛
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?
KIDNEY FUNCTIONS (CONT.)
• If the kidneys fail, waste builds up in the blood
Kidney function =
Normal serum creatinine
Current serum creatinine
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