Chapter 23— The Urinary
System
23-1
Ch. 23 Study Guide
1. Critically read 23.1 to right before the 23.7
(Urine Storage and Elimination) section (pp.
905-931)
2. Comprehend Terminology (those in bold)
3. Study-- Figure questions, Think About It
questions, and Before You Go On (sectionending) questions
4. Do end-of-chapter questions:
– Testing Your Recall— 2-10, 12-17, 19-20
– True or False– 1-9
– Testing Your Comprehension-- #1-2
2
I. Functions of the Urinary
System
23-3
§ Major Nitrogenous Wastes
Ammonia: very toxic; from
amino group in the a.a.
Urea: less toxic; converted
from ammonia in the
__________
Uric acid:
nucleic acid catabolism
Creatinine
creatine phosphate
catabolism
23-4
§ Major Nitrogenous Wastes
BUN (Blood Urea Nitrogen)
1. Measure the amount of ________ in your blood
2. Why is it done?
3. Disorders:
– Azotemia: an abnormally elevated BUN is
called; may indicate renal insufficiency
– Uremia: toxic effects as wastes (urea)
accumulate in the blood; patients with renal
failure
• Symptoms– vomiting, diarrhea, cardiac arrhythmia
etc.
23-5
• Treatment--Hemodialysis
§ Major kidney functions (1)
1. Eliminate wastes & foreign compounds
– Major nitrogenous wastes?
– Major foreign cpds?
2. Maintain blood volume and electrolyte
(ion) concentration
– For example, water balance during exercise
– Another example, [K+]  and ectopic focus
23-6
§ Major kidney functions (2)
3.Produce hormones— two major ones?
4.Detoxifies free radicals and drugs
5.In times of starvation-gluconeogenesis (makes glucose from
amino acids or fats)
23-7
II. Anatomy of the Kidney
23-8
§ The urinary system
1. Kidneys (a pair)
• Functions--
2. The ureter (a pair)
3. The single urinary bladder
• A muscular sac for _________________
4. The urethra
• Draining urine to the outside
• In females vs. in males (length and
external orifice) + proper toilet habits
Figure 23.1
23-9
Figure 23.1b
23-10
§ Gross Anatomy of Kidney
1. Renal cortex: outer 1 cm; extensions of
the cortex called renal columns
2. Renal medulla: inner zone; renal columns
divide the medulla into 6-10 renal pyramids
(each blunt point called renal papilla)
3. The renal papilla is nestled in a cup called
a minor calyx  major calyx
4. Lobe of kidney: pyramid and it’s overlying
cortex
Fig. 23.4 + a practice figure
23-11
23-12
§ Renal
circulation--
Figure 23.5a
C
A
B
23-13
Path of Blood Through Kidney
• Renal artery: into segmental artery and then
 A--interlobar arteries (up renal columns, between lobes)
 B--arcuate arteries (over pyramids)
 C--interlobular arteries (up into cortex)
 afferent arterioles
 glomerulus (cluster of capillaries)
 efferent arterioles (near medulla  vasa recta)
 peritubular capillaries
 interlobular veins  arcuate veins  interlobar veins
• Renal vein
23-14
A.
B.
23-15
23-16
Two kinds of Nephrons,
depending upon locations
1. Cortical nephrons (85%)
– short nephron loops of Henle
– efferent arterioles branch off into peritubular
capillaries
2. Juxtamedullary nephrons (15%)
– Where?
– very long nephron loops-– Vasa Recta– Efferent arterioles descend into
the medulla and give rise to Vasa Recta instead
of peritubular capillaries.
– The capillaries of the vasa recta lead into
venules that empty into the interlobular and
arcuate veins
23-17
§ The Nephron (1)
23-18
§ The Nephron (2)
1. How many nephrons in each kidney?
Answer: ___________
2. The nephron are blood-processing
units and each one of them is a
functional unit of the kidneys
3. Vascular and tubular parts of the
nephron
• Vascular parts first--Figure 23.6, 23.7
23-19
4. Efferent arteriole
3. Glomerulus
2. Afferent arteriole
1. Interlobular
Artery
6. Interlobular vein
23-20
5. Peritubular capillaries
To renal pelvis
Glomerular capsule &
glomerulus together:
Renal Corpuscle
23-21
§ Vascular part of the Nephron (3)
1. The renal artery (. . . interlobular
artery)–
2. Afferent arteriole –
• supplies each nephron and delivers blood
to the glomerulus
3. The glomerulus– cluster of capillaries
(1st set of capillary in each nephron);
function?
23-22
§ Vascular part of the Nephron (4)
4.The efferent arteriole—
• Where the glomerular capillaries rejoin
5.The peritubular (2nd set of) capillaries-• Impt in exchanges between blood and
______________
6.The renal veins-• The major blood vessels leave the kidney
---------------------------------------------------------------
• Tubular parts of the nephron– @Fig. 23.8
23-23
1. Bowman’s capsule
4. Distal
tubule
2. Proximal tubule
Glomerulus
Artery
Vein
5.
Collecting
duct
Cortex
Medulla
3. Loop of Henle
(nephron loop)
To renal pelvis
23-24
§ Tubular part of the Nephron (5)
• A hollow tube formed by a single layer
of epithelial cells; They are, in order:
1.Bowman’s (Glomerular) capsule–
• Cup-shaped; double-wall invagination
• Surround each __________
2.Proximal tubule– closest to
Bowman’s capsule
• Lies entirely within the cortex
23-25
§ Tubular part of the Nephron (6)
3.The loop of Henle (nephron loop)–
• Forms a U-shaped loop
4.The distal tubule–
• most distant from the capsule; lies entirely within
the ____________
5.Collecting tubule/duct—
• drains fluid from up to 8 nephrons
Figure 23.8
23-26
1.
Figure 23.8b
2.
ID parts (1-5) of
the nephron.
3.
4.
5.
23-27
Questions?
Muddiest points?
23-28
III. Urine Formation
23-29
§ Three urine forming processes
1.-- Glomerular filtration
• From the glomerulus into Bowman’s
(glomerular) capsule
2A.--Tubular reabsorption
• From the tubular lumen into ___________
2B.--Tubular secretion
• From the peritubular capillaries into the
__________________
3.-- Water conservation
Figure 23.9
23-30
Different names (fluid in renal
tubules) in different areas:
1. Glomerular
filtrate (in the
capsular space)
2. Tubular fluid
(proximal tubule
to distal tubule)
3. Urine
(collecting duct
and beyond)
23-31
III. Urine Formation;
1. GLOMERULAR FILTRATION
23-32
§ 1. Glomerular filtration
A. Def.– filtering blood by forcing small
molecules into the Bowman’s capsule
B. What in the filtrate?
• Small molecules can pass—
• Large molecules cannot—
C. Mechanism? ATP?
• What is the major force? Glomerular blood
hydrostatic pressure (BHP)
23-33
§ 1. Glomerular filtration (cont.)
D. Layers of the glomerular filtration mem.
i.
1-Fenestrated endothelium of capillaries
• Large pores (100x more permeable)
• Molecules can pass–
ii. 2-(Acellular) basement mem.
• Collagen & glycoproteins
• Function--
iii. 3a-Filtration slits; present in inner layer of
the Bowman’s capsule-- podocytes (3b)
bear many foot processes (pedicles)
Figure 23.10 (a-d)
23-34
Afferent arteriole
Efferent arteriole
Glomerulus
Bowman’s
capsule
Lumen of
Bowman’s
capsule
Outer layer of
Bowman’s capsule
Inner layer
of Bowman’s capsule
(podocytes)
Proximal convoluted tubule
Lumen of
glomerular
capillary
Endothelial
cell
Basement
membrane(see
Podocyte
foot process
next
slide)
23-35
3b. Podocyte
& foot process
3a.Filtration
slits
2. Basement
membrane
1. Capillary
pore
23-36
1a. Capillary
pore
1b. Endothelial
cell
Lumen of glomerular
capillary
2. Basement
membrane
3a.Filtration
slit
3b. Podocyte
foot process
Lumen of
Bowman’s capsule
(capsular space)
23-37
A.
Endothelial
cell
Lumen of glomerular
capillary
B.
Filtration
slit
Lumen of
Bowman’s capsule
C.
23-38
§ 1. Glomerular filtration (cont.)
Disorders:
1.Albuminuria– also called proteinuria;
presence of ________ in the urine
• Criteria: >250 mg/day: pathological
2.Hematuria– presence of ______ in the
urine
23-39
III. Urine Formation;
2A. TUBULAR REABSORPTION
23-40
§ 2. Tubular reabsorption
1. Def. reclamation process to move
molecules back into the blood
2. Goal: to move molecules from tubular
lumen to the peritubular capillaries (or
vasa recta)
Table x & Figure y
23-41
§ 2. Tubular reabsorption (cont.)
Table x
Substances in
filtrate
% of filtered
substances
reabsorbed
% of filtered
substances
excreted
99
1
Sodium
99.5
0.5
Glucose
100
0
Urea
50
50
0
100
Water
Phenol
42
§ 2.Tubular reabsorption (cont.)
1. What are reabsorbed?
• All the glucose, vitamins, and . . .
2. How efficient?
• Glucose— no glucose escapes
• Water— 180 L filtrate to 1-2 L of urine/day
• Analogy— Clean out a cluttered drawer
23-43
III. Urine Formation;
2A. TUBULAR REABSORPTION–
in the proximal convoluted T.
23-44
§ 2. Tubular reabsorption (cont.)
Two examples—Na+, water in proximal
convoluted tubules and beyond
3.--1st example– sodium reabsorption
• Where are sodium ions been
reabsorbed? Most of the tubule
Exception is the descending limb of the
loop of Henle
• Routes taken: both transcellular and
paracellular routes
23-45
§ 2. Tubular reabsorption (cont.)
• Mechanisms of sodium reabsorption—
– A--symport proteins (channels)—
– B--Na+-H+ antiport—
– C--Na+-K+ pumps– basal and lateral
membrane
– D– Paracellular route-Figures 23.16
23-46




23-47
§ 2 Tubular reabsorption (cont.)
4. --2nd example– water reabsorption
Locations? All the renal tubule;
however, 2/3 occurs in PCT
• Mechanisms—
 Via water channels (aquaporins)
 Between cells
 Water moves into blood plasma
Figures 23.16
23-48



23-49
§ Reabsorption Limit
1. Def.-- A limit to the amount of solute the
renal tubule can reabsorb
2. Why? Limited no. of transport proteins
3. Tm = Transport maximum; example-– Glucose’s Tm is 320 mg/min
– Glucose normally enters the renal tubule
at 125 mg/min; will all of it be reabsorbed?
– Threshold of glucose in the plasma– 220
mg/dL (= 220mg/100mL); begin to see
glucose in the urine called glycosuria
– Untreated diabetes mellitus patients– 400
mg/dL (plasma glucose)
23-50
23-50
III. Urine Formation;
2A. TUBULAR REABSORPTION–
in the nephron loop
23-51
§ The nephron loop (loop of
Henle)
• Primary function— to generate a
salinity gradient that enables the
collecting duct to concentrate the urine
and conserve water
• Mechanism—
– Thick segment (ascending limb) of
the loop: Impermeable to water
– Tubular fluid becomes very dilute by the
time it reaches the DCT
Fig. 23.19
23-52
23-52
Cortex
Low
Increasing
Osmolarity
High
Nephron loop
Medulla
23-53
III. Urine Formation;
2A. TUBULAR REABSORPTION–
in the distal convoluted tubule
and collecting duct
23-54
§ DCT and collecting duct (CD)
• Reabsorption regulation– by several
hormones including aldosterone etc.
(see following slides)
• Cells here in DCT and CD—
A. PRINCIPAL CELLS–
– more abundant; they have receptors for
these hormones
– Functions– involved in salt and water
balance
B. INTERCALATED CELLS–
– fewer; functions– in acid-base balance
23-55
23-55
§ Aldosterone (1)
• Chemistry – peptide, steroid, or
monoamine? (which one)
• Secreted by – the adrenal cortex
• Function-- to promote sodium retention
and increase blood pressure
• Triggered by –
– low blood sodium concentration
– a drop in blood pressure (via renin)
Fig. 23.15
23-56
ReninAngiotensinAldosterone
mechanism



23-57
§ Aldosterone (2)
• Acts on– three areas in the kidneys
– the thick segment of the ascending limb
of the nephron loop
– The DCT
– The cortical portion of the collecting duct
• Physiology Effects—
– Retain NaCl and water
– Maintain blood volume
23-58
§ Atrial Natriuretic Peptide (1)
• Chemistry –
• Secreted by – atrial myocardium of the
heart
• Triggered by – high blood pressure
23-59
§ Atrial Natriuretic Peptide (2)
• Physiology Effects–
– Promoting sodium and water loss
– Reducing blood volume and pressure
• Actions— on Kidney
– Dilates the afferent arteriole and
constricts the efferent arteriole
– Inhibits renin and aldosterone secretion
– Inhibits ADH secretion and the action of
ADH on the kidney
– Inhibits NaCl reabsorption by the
collecting duct
23-60
III. Urine Formation;
2B. TUBULAR SECRETION
23-61
§ Tubular secretion
1. Process— transfer of selective molecules
from the capillary blood and secrete them
into the ___________
2. Locations– PCT, nephron loop, DCT
3. Purposes—
– Waste removal—
• For example—
– Acid-base balance– hydrogen and
bicarbonate ions
Fig. x
23-62
Blood
pathway
Fig.-- the nephron &
molecule movements (demo)
Glomerular
capillaries
Efferent
arteriole
Glomerular
filtration
Bowman’s
capsule
Peritubular
capillaries
Tubular
reabsorption
Filtrate
pathway
Venous
blood
Tubular
secretion
Tubule (from proximal
tubule to collecting duct)
Urine
23-63
III. Urine Formation;
3. WATER CONSERVATION
The principal function left to the
collecting duct is to conserve water.
23-64
§ The Collecting Duct (CD)
1. Location –
– Begins in the cortex and passes through
the medulla
2. Mission – it reabsorbs water and
concentrates the urine
3. Mechanisms—
– Osmolarity of the ECF is ______ times as
high in the lower medulla as it is in the
cortex
– Medullary portion of the CD is more
permeable to _______ than to NaCl
Fig. 23.19
23-65
Figure 23.17
Cortex
Medulla
Which portion
of the renal
tubule?
23-66
§ Control of water loss
How concentrated the urine becomes
depends on the state of hydration
1. Dehydration– your urine becomes little &
more concentrated:
– High blood osmolarity  release ADH
(more/less; circle one)
–  renal tubule synthesize aquaporins
–  install them in the plasma mem.
–  CD reabsorbs more water
2. Well hydrated– opposite to the above
23-67
23-67
§ Countercurrent Multiplier (1)
1. The ability of the collecting duct to
concentrate urine depends on the salinity
gradient of the renal medulla.
– Mechanism behind this: The nephron loop
acts as a countercurrent multiplier
– Result: the nephron continues to return salts
to the deep medullary tissue
– Hence it is called multiplier b/c it multiplies
the salinity deep in the __________
– Countercurrent? Fluid flows in opposite
directions. Where? Descending limb and
ascending limb of the nephron loop
Fig. 23.20
23-68
23-68
1
2
PCT
DCT
Cortex
5
Medulla
3
4
Nephron loop
23-69
§ Countercurrent Multiplier (2)
2. How countercurrent multiplier works?
A. Medulla-- An environment of
increasing salinity toward deeper part
of medulla
B. Descending limb (nephron loop)– very
permeable to _______ but not to NaCl
C. Ascending limb– impermeable to
_____, but has pumps to transport ions
– Keeps the osmolarity high in medulla
– Tubular fluid: more and more diluted
toward the distal tubule
23-70
§ Countercurrent Multiplier (3)
3. In the lower end of collecting duct (CD)–
urea helps to maintain (40%) the
osmotic gradient in medulla
How?
– Lower end of CD is permeable to urea; urea
diffuses into the ECF
– Urea enters the descending thin segment; but
the thick segment of the loop and DCT is NOT
permeable to urea
– Therefore, continual recycling of urea from
the CD to the medulla and back
Fig. 23.21
23-71
Next
slide
23-72
§ Countercurrent Exchange System
1. Vasa recta that supply the medulla
recycle the salt and urea; How?
– Blood flows in opposite directions in adjacent
parallel capillaries called countercurrent
exchange system
– It flows downward– exchanges water for salt
– It flows back toward the cortex– exchange salt
for water
– Thus, vasa recta gives the salt back and DO
NOT subtract from the osmolarity of the
medulla
23-73
IV. Urine and Renal Function
Tests
23-74
§ Urine Volume (1)
1. Normally, 1-2 liters of urine per day
2. Polyuria (or diuresis)– output in excess of
2 L/day (detail next slide)
– Causes– fluid intake, some drugs, diabetes
3. Oliguria– output of less than 500 mL/day
4. Anuria– output of 0-100 mL/day
– Causes– kidney disease, dehydration, etc.
– Result-- Azotemia
23-75
§ Urine Volume (2)
5. Polyuria (details)—
A. Results from all four forms of diabetes—
• Diabetes mellitus type I, type II, gestational
diabetes (all three above are due to
hyperglycemia), and diabetes insipidus
(due to ADH hyposecretion)
B. Diabetes mellitus and gestational diabetes
are glycosuria but NOT in diabetes insipidus
patients
23-76
§ Urine Volume (3)
6. Diuretics— def. chemicals that increase
urine volume
– Mechanisms–
A. increasing glomerular filtration rate (GFR) or
B. reducing tubular reabsorption
– Example 1: Caffeine, dilates the afferent
arteriole and increases GFR (due to A or B
above; circle one)
– Example 2: Alcohol inhibits ADH secretion
(due to A or B above; circle one)
23-77
§ Renal Clearance
1. Def.– the volume of blood plasma from
which a particular waste is completely
removed in 1 minute; Example:
A.
B.
C.
–
Urea concentration in urine = 6.0 mg/mL
Rate of urine output = 2 mL/min
Urea concentration in plasma = 0.2 mg/mL
Renal clearance = AB/C = (6.0 mg/mL x 2
mL/min)/0.2 mg/mL = 60 mL/min
– This means the equivalent of 60 mL of blood
plasma is completely cleared of urea per
minute
• Renal clearance of glucose? (healthy adults) 23-78
§ Glomerular filtration rate (GFR)-(1)
1. Def.– the rate at which glomerular filtrate is
formed; volume of filtrate formed each
minute by all glomeruli; Example: Inulin (no
tubular reabsorption, nor tubular secretion)
A.
B.
C.
D.
Urine concentration of inulin = 30 mg/mL
Urine output is = 2 mL/min
Plasma concentration of inulin = 0.5 mg/mL
GFR = AB/C = (30 x 2)/0.5 = 120 mL/min = Renal
clearance of inulin (why?) (next slide)
79
§ Glomerular filtration rate (GFR)-(2)
For inulin, GFR (120 mL/min) is equal to the
renal clearance. Why?
1. All inulin filtered by the glomerulus
remains in the renal tubule and appears in
the urine.
2. A solute that is reabsorbed by the renal tubules
will have renal clearance less than the GFR;
renal clearance of urea @ 60 mL/min
3. A solute that is secreted by the renal tubules will
have a renal clearance greater than the GFR;
renal clearance of creatinine @ 140 mL/min
80