Download Urinary bladder

PowerPoint® Lecture Slides
prepared by
Betsy C. Brantley
Valencia College
CHAPTER
18
The Urinary
System
© 2017 Pearson Education, Inc.
Major Functions of the Urinary System (18-1)
1. Excretion of organic wastes, such as urea, from
body fluids
2. Elimination of these wastes into the external
environment
3. Homeostatic regulation of volume and solute
concentration of blood
Organs of the Urinary System (18-1)
• Two kidneys
• Produce urine that flows through urinary tract
• Urinary tract includes:
• Two ureters that transport urine from kidneys to bladder
• Urinary bladder stores urine
• Urethra transports urine from urinary bladder to exterior
of body
• Elimination of urine is process called urination or
micturition
Figure 18-1 The Organs of the Urinary System.
Organs of the
Urinary System
Kidney
Produces urine
Ureter
Transports urine
toward the
urinary bladder
Urinary bladder
Temporarily stores
urine before
urination
Urethra
Conducts urine to
exterior; in males,
it also transports
semen
Anterior view
Homeostatic Functions of the Urinary
System (18-1)
• In addition to removing organic wastes, urinary
system also:
• Regulates blood volume and blood pressure
• Regulates concentration of plasma ions, such as
sodium, potassium, chloride, and calcium
• Helps stabilize blood pH
• Conserves valuable nutrients like glucose and amino
acids
Kidney Location (18-2)
• Located on either side of vertebral column
• Between last thoracic and 3rd lumbar vertebrae
• Right kidney sits slightly lower than left
• Displaced somewhat by the liver
• Situated behind (dorsal to) peritoneum
• Position called retroperitoneal
• Adrenal gland located on superior surface of each
kidney
Figure 18-2a The Position of the Kidneys.
Diaphragm
11th and
12th ribs
Adrenal gland
Left kidney
Lumbar (L1)
vertebra
Ureter
Inferior
vena cava
Right kidney
Renal artery
and vein
Iliac crest
Aorta
Urinary
bladder
Urethra
a This posterior view of the trunk shows the positions of
the kidneys and other organs of the urinary system.
Superficial Anatomy of the Kidneys (18-2)
• Kidneys are bean shaped
• About 10 cm long, 5.5 cm wide, 3 cm thick
• Indentation on one side is the hilum
• Point of entry for renal artery and renal nerves
• Point of exit for renal veins and ureter
• Fibrous capsule
• Covers outer surface
• Lines renal sinus, an internal cavity
Sectional Anatomy of the Kidney (18-2)
• Renal cortex is outer layer
• In contact with fibrous capsule
• Projects into medulla as renal columns
• Renal medulla is inner layer
• Contains 6–18 cone-shaped renal pyramids
• Tip of each pyramid called renal papilla
• Projects into renal sinus
• Kidney lobe
• Contains pyramid, overlying cortex, and renal columns
Sectional Anatomy of the Kidney (cont.) (18-2)
• Urine production begins in nephrons in cortex of
each kidney lobe
• About 1.25 million nephrons in each kidney
• Ducts within renal papilla drain urine into a cup-like
structure called the minor calyx
• 4–5 minor calyces merge to form major calyx
• 2–3 major calyces combine to form large funnelshaped chamber called the renal pelvis
• Renal pelvis connected to the ureter
Figure 18-3a-b The Structure of the Kidney.
Renal
cortex
Renal
medulla
Renal
cortex
Renal
pyramids
Renal
medulla
Renal
sinus
Renal
sinus
Hilum
Major
calyx
Major calyx
Minor calyx
Renal pyramid
Renal
pelvis
Kidney lobe
(dashed lines)
Renal
columns
Renal
papilla
Hilum
Ureter
Renal
columns
Renal
pelvis
Minor
calyx
Renal
papilla
Ureter
Fibrous
capsule
a A diagrammatic view of a frontal
section through the left kidney
Fibrous
capsule
b A frontal section through the left kidney
Figure 18-4a The Blood Supply to the Kidneys.
Medulla
Adrenal
artery
Renal
artery
Cortical radiate
veins
Renal
vein
Cortical radiate
arteries
Interlobar
arteries
Interlobar
veins
Arcuate veins
Arcuate arteries
a This sectional view of a kidney shows the major
arteries and veins.
The Nephron (18-2)
• Basic functional unit of the
Renal corpuscle
kidney
• Consists of two main parts
Proximal convoluted tubule
Distal convoluted tubule
Collecting duct
1. Renal corpuscle
2. Renal tubule
Nephron
loop
Papillary duct
c An enlarged view showing
the location and general
structure of a nephron
Figure 18-3c The Structure of the Kidney.
Renal Corpuscle (18-2)
• Spherical structure consisting of:
• Cup-shaped glomerular (Bowman’s) capsule containing:
• Network of capillaries known as glomerulus
• Blood flows into glomerulus from afferent arteriole
and leaves by efferent arteriole
• Fluid and dissolved solutes forced out of
glomerular capillaries and into surrounding
capsular space
• Process called filtration
• Produces solution called filtrate
Renal Tubule (18-2)
• Filtrate flows into segments of renal tubule in order:
• Proximal convoluted tubule (PCT)
• Nephron loop, or loop of Henle
• Distal convoluted tubule (DCT)
• Filtrate at end called tubular fluid
• Each nephron empties into collecting duct
• Beginning of collecting system
• Collecting ducts drain into papillary ducts and into minor
calyces
• Fluid at this point called urine
Figure 18-5 A Representative Nephron and the Collecting System.
NEPHRON
Proximal Convoluted Tubule
COLLECTING SYSTEM
Distal Convoluted Tubule
Renal Corpuscle
Renal tubule
Efferent arteriole
Collecting Duct
Afferent arteriole
Glomerulus
Loop ends
Loop begins
Nephron Loop
Thick
ascending
limb
Descending limb
Ascending limb
Thin
descending
limb
Papillary Duct
KEY
Flow of tubular fluid
Filtrate
Water reabsorption
Variable water reabsorption
Solute reabsorption
or secretion
Variable solute
reabsorption or secretion
Minor
calyx
Table 18.1
Metabolic Wastes in Urine (18-3)
• Must be excreted to maintain homeostasis
• Eliminated dissolved in urine, which requires water loss
1. Urea
• Most abundant organic waste
• Formed during breakdown of amino acids
2. Creatinine
• Generated in skeletal muscle tissue from breakdown of
creatine phosphate
3. Uric acid
• Formed from breakdown and recycling of RNA
Three Nephron Processes (18-3)
• Kidneys rely on three physiological processes
1. Filtration
• Occurs exclusively in renal corpuscle
• Blood pressure forces water through filtration membrane
• Solute molecules small enough to fit carried through
membrane by water molecules
2. Reabsorption
• Occurs primarily at PCT
• Selective process
• Movement of water and solutes from tubular fluid back into
peritubular fluid (and then into peritubular capillaries)
Three Nephron Processes (cont.) (18-3)
3. Secretion
• Occurs primarily at DCT
• Transport of solutes from peritubular fluid into tubular
fluid
• Allows excretion of substances missed by filtration
• Water, sodium, potassium regulation
• Results from interaction between nephron loop and
collecting system
• Renal processes produce fluid (urine) very different
in composition than plasma
The Ureters (18-5)
• Paired muscular tubes conduct urine from kidneys
to urinary bladder
• Each ureter begins at funnel-shaped renal pelvis
• Ends at posterior, slightly inferior bladder wall
• Slit-like ureteral openings prevent urine backflow
• Ureter wall contains three layers
1. Inner layer of transitional epithelium
2. Middle layer of smooth muscle that moves urine
through tube by peristalsis
3. Outer connective tissue layer (continuous with renal
capsule)
Kidney Stones (18-5)
• Also called calculi
• Solid substances made of calcium deposits,
magnesium salts, or crystals of uric acid
• Can form within kidney, ureter, or urinary bladder
• Results in painful condition called nephrolithiasis
• Obstruct flow of urine
• May reduce or prevent filtration
The Urinary Bladder Location and Size (18-5)
• Hollow muscular organ that stores urine
• Size varies with amount of distention
• When full, can contain up to a liter of urine
• Held in place in pelvic cavity by peritoneal folds
(umbilical ligaments) and connective tissue
• In males:
• Base lies between rectum and pubic symphysis
• In females:
• Sits inferior to the uterus and anterior to the vagina
Internal Anatomy of the Urinary Bladder (18-5)
• Base has triangular area called trigone, formed by:
• Two ureteral openings
• Urethral entrance
• Area surrounding urethral entrance is neck of bladder
• Contains involuntary internal urethral sphincter
• Bladder wall contains:
• Transitional epithelium
• Layers of smooth muscle called detrusor muscle
• Contraction of muscle expels contents into urethra
The Urethra (18-5)
• Extends from neck of urinary bladder to exterior
of body
• Circular band of skeletal muscle surrounds urethra
as passes through muscular floor of pelvic cavity
• External urethral sphincter under voluntary control
• In males:
• Extends 18–20 cm to external opening, or external
urethral orifice, at tip of penis
• In females:
• Very short (2.5–3.0 cm) from bladder to external urethral
orifice near anterior wall of vagina
© 2017 Pearson Education, Inc.
Figure 18-11a Organs for the Conduction and Storage of Urine.
Peritoneum
Left ureter Rectum
Urinary
bladder
Pubic
symphysis
Prostate
gland
External
urethral
sphincter
Urethra
External
urethral
orifice
a Male
Figure 18-11b Organs for the Conduction and Storage of Urine.
Rectum
Right ureter
Peritoneum
Urinary
bladder
Uterus
Pubic
symphysis
Internal
urethral
sphincter
External
urethral
sphincter
Vagina
Urethra
b Female
Figure 18-11c Organs for the Conduction and Storage of Urine.
Ureter
Ligaments
Detrusor
muscle
Ureteral
openings
Center of
trigone
Neck
Internal urethral
sphincter
Prostate gland
External urethral
sphincter
Urethra
c Urinary bladder in male
The Micturition Reflex (18-5)
• Increased urine volume stimulates stretch receptors in
bladder wall
• Afferent sensory fibers carry impulses to sacral spinal cord
• Parasympathetic motor neurons carry information back to
detrusor muscle
• Interneurons relay information to CNS
• Brings conscious awareness of pressure in bladder
• Urge to urinate occurs with about 200 mL of urine in bladder
• Contraction of detrusor muscle increases pressure
• Voluntary relaxation of external sphincter allows relaxation
of internal sphincter as well
• Urination occurs
Figure 18-12 The Micturition Reflex.
Projection fibers
Brain
If convenient, the
C2 from thalamus
deliver sensation
to the cerebral
cortex.
C3 individual voluntarily
relaxes the external
urethral sphincter.
The afferent fibers
stimulate neurons
involved with:
An interneuron
C1 relays sensation
to the thalamus.
L a local pathway,
and
C a central pathway
Parasympathetic
L2 Sensory
fibers in
L3 preganglionic
motor fibers in
pelvic nerves
pelvic
nerves
L1 Distortion
Urinary
bladder
of stretch
receptors
intramural
ganglia stimulate
detrusor muscle
contraction.
Start
C4 Voluntary relaxation of the
external urethral sphincter
causes relaxation of the
internal urethral sphincter.
Urination occurs
© 2017 Pearson Education, Inc.
Postganglionic
L4 neurons in
Control of Urethral Sphincters (18-5)
• Increased urine volume causes increased
stimulation of parasympathetic nerve fibers
• Increases detrusor muscle contraction
• Increases fluid pressure
• Urine volume greater than 500 mL may generate
enough pressure to force open internal sphincter
• External sphincter relaxes as well
• Urination occurs
© 2017 Pearson Education, Inc.
Fluid, Electrolyte, and pH Balance (18-6)
• Restoration of balance is key to effective treatment
of multiple diseases and conditions
• Water balance is essential for cellular function
• Ion concentration balance is essential for various
metabolic reactions
• pH balance is essential to maintain normal chemical
reactions, cell structure, and function
© 2017 Pearson Education, Inc.
Interrelated Factors in Homeostasis (18-6)
1. Fluid balance
• In balance when amount of water gained each day equal to
amount lost
• Balance requires movement into and out of cells
• Water moves by osmosis in response to ion concentration
gradients
2. Electrolyte balance
• Exists when neither net gain nor loss of any ion in body fluids
• Involves balancing rate of absorption across digestive tract
with rate of loss at kidneys
3. Acid-base balance
• In balance when production of H+ equal to loss
• Maintains normal pH in body fluids
© 2017 Pearson Education, Inc.
Basics of Body Fluid Compartments (18-6)
• Water is 50–60 percent of body weight
• Varies with gender
• Females have lower percentage due to larger mass of
adipose tissue (adipose is lower in water content)
• Divided into two fluid compartments
• Intracellular fluid (ICF)
• Extracellular fluid (ECF)
© 2017 Pearson Education, Inc.
Figure 18-13a The Composition of the Human Body.
SOLID COMPONENTS (31.5 kg; 69.3 lb)
WATER (38.5 kg; 84.7 lb)
20
15
Other
Plasma
Liters
Kg
15
10
10
Interstitial
fluid
5
5
0
0
Proteins
Lipids
Minerals
Carbohydrates Miscellaneous
Intracellular fluid
Extracellular fluid
a The body composition (by weight, averaged for both sexes) and major body fluid compartments of a 70-kg (154-lb) person. For technical
reasons, it is extremely difficult to determine the precise size of any of these compartments; estimates of their relative sizes vary widely.
© 2017 Pearson Education, Inc.
Intracellular Fluid (18-6)
• Fluid within cells (also known as cytosol)
• Largest fluid compartment
• 27 percent of total body composition in adult females
• 33 percent of total body composition in adult males
• Contains abundance of K+, Mg2+, HPO42–
• Also contains large numbers of negatively charged
proteins
© 2017 Pearson Education, Inc.
Extracellular Fluid (18-6)
• Contains high levels of Na+, Cl–, HCO3–
• Largest subdivisions include:
• Plasma (water portion of blood)
• 4.5 percent of total body composition in males and females
• Interstitial fluid
• 18 percent of total body composition in females,
21.5 percent in males
• Minor components include:
• Lymph, cerebrospinal fluid, synovial fluid, serous fluid,
aqueous humor, perilymph, endolymph
© 2017 Pearson Education, Inc.
Figure 18-13b The Composition of the Human Body.
ICF
Intracellular
fluid 33%
Interstitial
fluid 21.5%
ECF
ICF
ECF
Intracellular
fluid 27%
Interstitial
fluid 18%
Plasma 4.5%
Solids 40%
(organic and inorganic materials)
Other
body
fluids
(≤1%)
Solids 50%
(organic and inorganic materials)
Adult males
b A comparison of the body compositions of adult males and females, ages 18–40 years.
© 2017 Pearson Education, Inc.
Adult females
Other
body
fluids
(≤1%)
Figure 18-14 Ions in Body Fluids.
200
INTRACELLULAR FLUID
Na+
PLASMA
INTERSTITIAL FLUID
KEY
Cations
HCO3–
Na+
Cl–
K+
Milliequivalents per liter (mEq/L)
150
Ca2+
HCO3–
HCO3–
Mg2+
HPO42–
K+
Anions
100
HCO3–
Na+
Cl–
Na+
SO42–
Cl–
Cl–
HPO42–
50
SO42–
HPO42–
Proteins
Mg2+
0
Cations
© 2017 Pearson Education, Inc.
Anions
Org. acid
K+
Ca2+
Proteins
K+
HPO42–
SO42–
Cations
Anions
Cations
Anions
Organic
acid
Proteins
Fluid Movement (18-7)
• Water moves continuously
• Within ECF compartments
• Across capillary beds throughout body
• Among minor ECF compartments
• Serous membranes, synovial membranes
• Between blood and CSF, eye humors, peri- and
endolymph of inner ear
© 2017 Pearson Education, Inc.
Water Gains and Losses (18-7)
• Water gain
• 40 percent by eating
• 48 percent by drinking
• 12 percent by metabolic generation
• Water losses
• 2500 mL per day lost in urine, feces, and insensible
perspiration
• Loss by sensible perspiration (sweating) varies with
activity level
© 2017 Pearson Education, Inc.
Table 18.4
© 2017 Pearson Education, Inc.
Fluid Shifts (18-7)
• Water movement between ECF and ICF
• Relatively rapid processes
• Occur in response to changes in osmotic
concentration (osmolarity) of ECF
• If ECF osmolarity increases, water leaves cells
• If ECF osmolarity decreases, water moves into cells
• Movement progresses until equilibrium reached
© 2017 Pearson Education, Inc.
Electrolyte Balance (18-7)
• Important because:
• Gain or loss of electrolytes results in gain or loss in
water
• Concentration of individual electrolytes affects cell
functions
• Examples: sodium (Na+) and potassium (K+) play major
roles in osmolarity of ICF and ECF
• Most common electrolyte balance problems caused by
imbalance between sodium gains and losses
• Potassium imbalances are less common but much more
dangerous
© 2017 Pearson Education, Inc.
Sodium Balance (18-7)
• Balance between Na+ absorption from digestive
tract and excretion by kidneys
• Rate of uptake varies with amount in diet
• Losses by excretion in urine and perspiration
• Regulated by aldosterone and ANP
• Aldosterone increases sodium reabsorption
• ANP decreases sodium reabsorption
• Water “follows” salt
• Levels of sodium have direct effect on water levels
• Increase in sodium → increase in blood volume →
increase in blood pressure
© 2017 Pearson Education, Inc.
Potassium Balance (18-7)
• 98 percent of body’s K+ is in ICF
• Low K+ concentration in ECF
• Balance between absorption from digestive tract and
excretion by kidneys
• Rate of loss affected by aldosterone
• Aldosterone increases potassium secretion (or loss)
• Problems with K+ balance less common than
problems with Na+, but much more dangerous
• Disrupts membrane potentials in excitable tissues
© 2017 Pearson Education, Inc.
Acid-Base Balance (18-8)
• Normal pH range of ECF is 7.35–7.45
• Deviation outside that range affects all body systems
• Disrupts stability of cell membranes
• Alters protein structure
• Changes activities of enzymes
• Nervous and cardiovascular systems most sensitive to
change
• Problems with low pH more common
• Normal cellular activities generate acids (e.g., lactic acid,
carbonic acid)
© 2017 Pearson Education, Inc.
Acidosis and Alkalosis (18-8)
• Acidosis
• pH of blood below 7.35
• Severe (pH below 7.0) can be fatal
• CNS function declines leading to coma
• Cardiac contractions weaken leading to heart failure
• Peripheral vasodilation drops blood pressure leading to
circulatory collapse
• Alkalosis
• pH of blood above 7.45
© 2017 Pearson Education, Inc.
Acids in the Body (18-8)
• Carbonic acid (H2CO3) is an important acid in body
fluids
• In lungs, breaks down into carbon dioxide (CO2) and
water
• In peripheral tissues, reverse reaction occurs
• Carbonic acid dissociates into hydrogen and bicarbonate
ions
• These reactions occur more rapidly when enzyme
carbonic anhydrase is present (found in red blood cells)
© 2017 Pearson Education, Inc.
Carbon Dioxide and pH (18-8)
• Partial pressure of CO2 the most important factor
affecting pH of body tissues
• As CO2 levels rise, additional H+ released and pH drops
• PCO2 and pH are inversely proportional
© 2017 Pearson Education, Inc.
Figure 18-15 The Basic Relationship between Carbon Dioxide and Plasma pH.
PCO2
40–45
mm Hg
If PCO2 increases
H2O + CO2
H2CO3
H+ + HCO3–
When carbon dioxide levels increase, more carbonic acid
forms, additional hydrogen ions and bicarbonate ions are
released, and the pH decreases.
© 2017 Pearson Education, Inc.
pH
7.35–7.45
HOMEOSTASIS
If PCO2 decreases
H+ + HCO3–
H2CO3
H2O + CO2
When the PCO2 decreases, the reaction runs in reverse, and
carbonic acid dissociates into carbon dioxide and water. This
removes H+ from solution and increases the pH.
Buffers (18-8)
• Dissolved compounds that can donate or remove
H+ from solution to help stabilize pH
• Weak acids can donate H+
• Weak bases can absorb H+
• Buffer system
• Combination of weak acid and dissociation products (H+
and an anion)
• Three key buffer systems in the body
1. Protein buffer systems
2. Carbonic acid–bicarbonate buffer system
3. Phosphate buffer system
© 2017 Pearson Education, Inc.
Protein Buffer Systems (18-8)
• Regulate pH in ICF and ECF
• Includes proteins and free amino acids
• If pH rises:
• Carboxyl group (–COOH) acts as weak acid
• Dissociates and releases a H+ from amino acid
• If pH drops:
• Amino group (–NH2) acts as weak base
• Picks up a free H+, forming amino ion (–NH3+)
© 2017 Pearson Education, Inc.
Carbonic Acid–Bicarbonate Buffer System
(18-8)
• Primary function is to prevent pH changes caused
by metabolic acids
• Regulates pH in ECF
• Carbonic acid acts as weak acid
• Bicarbonate acts as weak base
• Dissociation of metabolic acids releases H+, lowering pH
• H+ combine with bicarbonate, producing water and CO2
(driving formula to the left)
•
• Abundance of available bicarbonate ions is called the
bicarbonate reserve
• Pco2 rises, respiratory system excretes CO2
© 2017 Pearson Education, Inc.
Phosphate Buffer System (18-8)
• Primary buffer system of ICF
•
© 2017 Pearson Education, Inc.
Maintaining Acid-Base Balance (18-8)
• Buffer systems provide only temporary and limited
solution to pH imbalance
• Can tie up excess H+ but do not affect ion losses or
gains
• Respiratory and renal mechanisms contribute by:
• Secreting or absorbing H+
• Controlling excretion of acids and bases
• Generating additional buffers
• Combination of buffer systems and respiratory and
renal processes maintain body pH within range
© 2017 Pearson Education, Inc.
Respiratory Compensation of pH (18-8)
• Accomplished by altering respiratory rate
• Rise in Pco2 (= low pH) stimulates chemoreceptors
• Causes increase in respiratory rate
• Increases loss of CO2 from lungs, decreasing Pco2
• Decreases H+ concentration in the blood
• Increases pH
• Drop in Pco2 (= high pH) inhibits chemoreceptors
• Causes decrease in respiratory rate
• Decreases loss of CO2 from lungs, increases Pco2
• Increases H+ concentration in the blood
• Lowers pH
© 2017 Pearson Education, Inc.
Figure 18-13a The Composition of the Human Body.
SOLID COMPONENTS (31.5 kg; 69.3 lb)
WATER (38.5 kg; 84.7 lb)
20
15
Other
Plasma
Liters
Kg
15
10
10
Interstitial
fluid
5
5
0
0
Proteins
Lipids
Minerals
Carbohydrates Miscellaneous
Intracellular fluid
Extracellular fluid
a The body composition (by weight, averaged for both sexes) and major body fluid compartments of a 70-kg (154-lb) person. For technical
reasons, it is extremely difficult to determine the precise size of any of these compartments; estimates of their relative sizes vary widely.
© 2017 Pearson Education, Inc.
Figure 18-2b The Position of the Kidneys.
Parietal
Renal Renal
Stomach
peritoneum
vein artery Aorta
Hilum of
kidney
Pancreas
Ureter
Spleen
Left kidney
Vertebra
Fibrous capsule
Adipose tissue
Inferior
vena cava
b A superior view of a section at the level indicated in
part (a) shows the kidney’s retroperitoneal position.
Blood Supply to the Kidney (18-2)
• Kidneys receive 20–25 percent of total cardiac output
(about 1200 mL of blood each minute)
• Blood flow starts with renal artery
•
•
•
•
•
•
•
•
•
•
•
→ Interlobar arteries (run between renal pyramids)
→ Arcuate arteries (along cortex-medulla boundary)
→ Cortical radiate arteries (or interlobular arteries)
→ Afferent arterioles (delivering blood to individual nephrons)
→ Glomerular capillaries
→ Efferent arterioles
→ Peritubular capillaries (surrounding nephron)
→ Cortical radiate veins (or interlobular veins)
→ Arcuate veins
→ Interlobar veins
→ Exits kidney by the renal veins
Blood Flow from Peritubular Capillaries (18-2)
• Blood from the peritubular capillaries follows two
possible paths
1. In cortical nephrons (located almost entirely within
renal cortex):
• Blood flows from peritubular capillaries directly into cortical
radiate veins
2. In juxtamedullary nephrons:
• Peritubular capillaries are connected to the vasa recta
• Vasa recta run parallel to long nephron loops deep into the
medulla
• Blood flows from vasa recta into cortical radiate veins
Figure 18-4b The Blood Supply to the Kidneys.
Nephrons
Cortex
Afferent
arterioles
Medulla
b This enlarged view
shows the circulation
in a single kidney lobe.
© 2017 Pearson Education, Inc.
Figure 18-4b-d The Blood Supply to the Kidneys.
Nephrons
Efferent
arteriole
Afferent
arteriole
Cortex
Renal
corpuscle
Afferent
arterioles
Peritubular
capillaries
Medulla
b This enlarged view
shows the circulation
in a single kidney lobe.
Peritubular
capillaries
Collecting
duct
Nephron
loop
c Further enlargement shows the
circulation to a cortical nephron.
Proximal
convoluted
tubule (PCT)
Efferent
arteriole
Glomerulus
Peritubular
capillaries
Distal
convoluted
tubule (DCT)
Afferent
arteriole
Vasa recta
Collecting
duct
Nephron
loop
d Further enlargement shows the
circulation to a juxtamedullary nephron.
© 2017 Pearson Education, Inc.
Functions of the Nephron (18-2)
• Corpuscle
• Produces filtrate by a passive process
• Filtrate includes valuable nutrients, ions, and water
• Tubules
1. Reabsorb useful molecules and ions from filtrate back
into blood
2. Reabsorb >90 percent of water back into blood
3. Secrete any waste products missed by filtration
process
© 2017 Pearson Education, Inc.
The Glomerular Capsule (18-2)
• Forms outer wall of renal corpuscle
• Encloses the glomerular capillaries
• Formed by two layers of cells separated by
capsular space
• Outer layer, or capsular epithelium, forms wall of
corpuscle
• Inner layer, or visceral epithelium, encloses glomerular
capillaries
• Cells in this layer are called podocytes
• Have foot processes called pedicels that wrap around
capillaries
© 2017 Pearson Education, Inc.
Figure 18-6 The Renal Corpuscle.
Glomerular capillary
Glomerular Capsule
Parietal epithelium
Capsular space
Efferent arteriole
Visceral epithelium
(podocyte)
Juxtaglomerular
Complex
Macula densa
Juxtaglomerular
cells
Proximal
convoluted
tubule
Distal convoluted
tubule
Afferent
arteriole
Filtration
Membrane
a This sectional view illustrates
the important structural
features of a renal corpuscle.
Nucleus
Podocyte
Capillary
endothelium
Podocyte
Pedicels
Pores
Basement
membrane
Supporting
cell
Filtration slits
RBC
b This cross section
through a segment
of the glomerulus
shows the
components of the
filtration membrane
of the nephron.
© 2017 Pearson Education, Inc.
Pedicels
A podocyte
SEM × 2300
Capsular space
Capsular
epithelium
c This colorized photomicrograph shows the
glomerular surface, including individual
podocytes and their processes.
Figure 18-6a The Renal Corpuscle.
Glomerular capillary
Glomerular Capsule
Parietal epithelium
Efferent arteriole
Juxtaglomerular
Complex
Capsular space
Visceral epithelium
(podocyte)
Macula densa
Juxtaglomerular
cells
Distal convoluted
tubule
Afferent
arteriole
© 2017 Pearson Education, Inc.
Proximal
convoluted
tubule
a This sectional view illustrates
the important structural
features of a renal corpuscle.
The Filtration Membrane (18-2)
• Filtration process requires solutes to pass through
three levels of structures
1. Pores of endothelial cells of capillaries (called
fenestrations)
2. Fibers of basement membrane
3. Filtration slits between podocyte processes
• These three structures collectively known as
filtration membrane
• Combination of structures prevents passage of
blood cells and most plasma proteins into filtrate
© 2017 Pearson Education, Inc.
Figure 18-6b The Renal Corpuscle.
Filtration
Membrane
Nucleus
Podocyte
Capillary
endothelium
Pores
Basement
membrane
Supporting
cell
Filtration slits
RBC
b This cross section
through a segment
of the glomerulus
shows the
components of the
filtration membrane
of the nephron.
© 2017 Pearson Education, Inc.
Pedicels
Capsular space
Capsular
epithelium
The Proximal Convoluted Tubule (18-2)
• First segment of renal tubule
• Majority of reabsorption occurs here
• Cells lining PCT reabsorb organic nutrients, plasma
proteins, and ions from tubular fluid
• Substances are moved from tubule to interstitial fluid, or
peritubular fluid
• Materials re-enter the blood
• Water follows by osmosis
• Reduces volume of tubular fluid
© 2017 Pearson Education, Inc.
The Nephron Loop (18-2)
• Composed of descending limb and ascending limb
• Fluid in descending limb flows toward renal pelvis
• Epithelium permeable to water, not solutes
• Tubule makes 180-degree turn
• Fluid in ascending limb flows toward renal cortex
• Epithelium not permeable to water
• Actively transports sodium and chloride out of tubule
• Result is unusually high solute concentration in
peritubular fluid of renal medulla
• Water from descending limb moves out by osmosis
© 2017 Pearson Education, Inc.
The Distal Convoluted Tubule (18-2)
• Passes adjacent to afferent and efferent arterioles
• Site for three vital processes
1. Active secretion of ions, acids, drugs, and toxins
2. Selective reabsorption of sodium
3. Selective reabsorption of water
© 2017 Pearson Education, Inc.
The Juxtaglomerular Complex (18-2)
• Combination of closely associated cells in the DCT
and afferent arteriole
• Macula densa
• Region of clustered cells in DCT closest to the glomerulus
• Juxtaglomerular cells
• Unusual smooth muscle fibers in wall of afferent arteriole
• Involved in regulation of blood volume and blood
pressure
• Through secretion of erythropoietin and renin
© 2017 Pearson Education, Inc.
Figure 18-6a The Renal Corpuscle.
Glomerular capillary
Glomerular Capsule
Parietal epithelium
Efferent arteriole
Juxtaglomerular
Complex
Capsular space
Visceral epithelium
(podocyte)
Macula densa
Juxtaglomerular
cells
Distal convoluted
tubule
Afferent
arteriole
© 2017 Pearson Education, Inc.
Proximal
convoluted
tubule
a This sectional view illustrates
the important structural
features of a renal corpuscle.
The Collecting System (18-2)
• Many DCTs empty into one collecting duct
• Several collecting ducts merge to form a papillary duct
• Papillary duct empties into minor calyx
• Functions of the collecting system
• Transports tubular fluid from nephron to renal pelvis
• Adjusts final fluid composition
• Determines final osmotic concentration of urine
• Determines final volume of urine
© 2017 Pearson Education, Inc.
Figure 18-7 Physiological Processes of the Nephron.
Filtration
membrane
Transport
proteins
Transport
proteins
Solute
Blood
pressure
Solute
Solute
Filtrate
Glomerular
capillary
Capsular
space
a In filtration, blood pressure forces water
and solutes across the membranes of the
glomerular capillaries and into the capsular
space. Solute molecules small enough to
pass through the filtration membrane are
carried by the surrounding water molecules.
© 2017 Pearson Education, Inc.
Peritubular
fluid
Tubular
epithelium
Tubular
fluid
b Reabsorption is the removal of water
and solutes from the tubular fluid and
their movement across the tubular
epithelium and into the peritubular fluid.
Peritubular
fluid
Tubular
epithelium
Tubular
fluid
c Secretion is the transport of
solutes from the peritubular fluid,
across the tubular epithelium, and
into the tubular fluid.
Table 18.2
© 2017 Pearson Education, Inc.
Filtration Pressure (18-3)
• Net force promoting filtration
• Combination of outward blood pressure, inward blood
osmotic pressure, and inward fluid pressure from
capsule
• Filtration pressure at glomerulus higher than
capillaries in other parts of the body
• Afferent arteriole has larger diameter
• Efferent arteriole has smaller diameter
• Result is increased blood pressure within glomerular
capillaries
• Serious loss of systemic BP can result in:
• Loss of filtration, fatal reduction in kidney function
© 2017 Pearson Education, Inc.
Glomerular Filtration Rate (18-3)
• GFR
• Amount of filtrate produced in kidneys/minute
• Average is 125 mL/min or 180 L/day
• Over 99 percent of filtrate is reabsorbed in renal tubules
• GFR is dependent on:
• Maintaining adequate blood flow to glomerulus
• Maintaining adequate net filtration pressures
© 2017 Pearson Education, Inc.
Events at the Proximal Convoluted Tubule
(18-3)
• 60–70 percent of filtrate volume is reabsorbed at PCT
• All glucose, amino acids, and other organic
nutrients are reabsorbed
• Actively reabsorbs ions (sodium, potassium,
calcium, magnesium, bicarbonate, phosphate,
sulfate)
• Some of this active reabsorption is hormonally regulated
• Example: parathyroid hormone stimulates calcium
reabsorption
• Some active secretion occurs in PCT as well
• Example: hydrogen ions
© 2017 Pearson Education, Inc.
Events at the Nephron Loop (18-3)
• Filtrate entering loop already has water and many
solutes removed
• Nephron loop removes more than half of remaining
water and about 66 percent of remaining sodium
and chloride ions
• Ascending loop actively pumps sodium and
potassium ions into interstitial fluid
• Impermeable to water
• Creates concentration gradient
• Descending loop permeable to water only
• Results in highly concentrated waste products at
end of loop
© 2017 Pearson Education, Inc.
Events at the Distal Convoluted Tubule (18-3)
• 80 percent of water and 85 percent of solutes have
already been reabsorbed
• Final adjustments made in fluid composition and
concentration by active secretion
• Example: active transport of sodium out of tubular fluid
• Exchanged for potassium or hydrogen ions
• Increased in the presence of aldosterone
© 2017 Pearson Education, Inc.
Water Reabsorption and ADH (18-3)
• In absence of antidiuretic hormone (ADH):
• DCT and collecting duct impermeable to water
• Water stays in tubule and is excreted
• Result is dilute urine
• In the presence of ADH:
• DCT and collecting duct permeable to water
• More water reabsorbed so less excreted
• Serves to concentrate urine as it passes through
collecting duct
© 2017 Pearson Education, Inc.
Figure 18-8 The Effects of ADH on the DCT and Collecting Duct.
Renal cortex
PCT
Compulsory Water
Reabsorption
Glomerulus
Glomerular
capsule
Proximal
convoluted
tubule
Variable Water
Reabsorption
DCT
Glomerulus
Distal convoluted
tubule
Collecting
duct
Solutes
Renal medulla
Collecting
duct
a Tubule permeabilities and
Nephron
loop
the osmotic concentration of
urine without ADH
Urine storage
and elimination
Large volume
of dilute urine
Renal cortex
= Na+/Cl–
transport
= Antidiuretic
hormone
= Water
reabsorption
= Variable water
reabsorption
= Impermeable
to solutes
= Impermeable
to water
= Variable permeability
to water
Renal medulla
b Tubule permeabilities and the osmotic
concentration of urine with ADH
© 2017 Pearson Education, Inc.
Small volume of
concentrated urine
Properties of Normal Urine (18-3)
• Once tubular fluid enters the minor calyx:
• No other secretion or reabsorption can occur
• Fluid is now called urine
• Concentration and composition vary based on metabolic
and hormonal activities
© 2017 Pearson Education, Inc.
Table 18.3
© 2017 Pearson Education, Inc.
Figure 18-9 A Summary of Kidney Function
4
1
The filtrate produced by the
renal corpuscle has the same
osmotic concentration as
plasma—about 300 mOsm/L.
It has the same composition
as blood plasma but does not
contain plasma proteins.
Renal
corpuscle
Tubular fluid
from cortical
nephrons
H2O
H2O
PCT
DCT
K+
A
H2O
Nutrients
3
In the proximal convoluted
tubule (PCT), the active
removal of ions and organic
nutrients results in a
continuous osmotic flow of
water out of the tubular fluid.
This decreases the volume of
filtrate but keeps the solutions
inside and outside the tubule
isotonic. Between 60 and 70
percent of the filtrate volume
is absorbed here.
Na+Cl–
Na+
RENAL CORTEX
Ions
5
H2O
Na+Cl–
Descending
limb of
nephron loop
Na+
K+
H2O
Na+Cl–
In the PCT and descending
limb of the nephron loop,
water moves into the
surrounding peritubular
fluid. This compulsory
reabsorption of water results
in a small volume of highly
concentrated tubular fluid.
Collecting
duct
A
H2O
Vasa
recta
RENAL MEDULLA
H2O
Increasing osmolarity
2
6
H2O
Na+Cl–
H2O
ADHregulated
permeability
Na+Cl–
H2O
Na+Cl–
Ascending
limb of
nephron loop
= Impermeable
to solutes
= Variable water
reabsorption
= Impermeable
to water
= Na+/Cl–
transport
= Variable permeability
to water
A
= Aldosteroneregulated pump
= Solutes
U
= Urea transporter
7
H2O
H2O
Urea
Vasa
recta
Urea
U
Urine enters
renal pelvis
© 2017 Pearson Education, Inc.
Further adjustments in the
composition of the tubular
fluid occur in the DCT and the
collecting system. The solute
concentration of the tubular
fluid can be adjusted through
active transport (reabsorption
or secretion).
The final adjustments in
the volume and solute
concentration of the tubular
fluid are made by controlling
the water permeabilities of the
distal portions of the DCT and
the collecting system. ADH
levels determine the final urine
volume and concentration.
H2O
KEY
= Water
reabsorption
The thick ascending limb is
impermeable to water and
solutes. The tubule cells
actively transport Na+ and Cl–
out of the tubule, thereby
decreasing the solute
concentration of the tubular
fluid. Because only
Na+ and Cl– are removed, urea
makes up a higher proportion
of the total solute
concentration at the end
of the nephron loop.
Papillary
duct
The vasa recta absorb the
solutes and water reabsorbed
by the nephron loop and the
collecting ducts. By
transporting these solutes and
water into the bloodstream, the
vasa recta maintain the
concentration gradient of
the renal medulla.
GFR and Normal Kidney Function (18-4)
• Normal kidney function depends on adequate
blood flow
• Needed to maintain filtration pressure and stable GFR
• Three levels of control regulate GFR
1. Autoregulation (or local regulation)
2. Hormonal regulation
3. Autonomic regulation
• Through sympathetic division of ANS
© 2017 Pearson Education, Inc.
Local Regulation of Kidney Function (18-4)
• Can compensate for minor variations in blood
pressure
• Involves automatic changes in diameters of
afferent and efferent arterioles
• Example: in response to reduced blood flow and
decreased GFR:
• Afferent arteriole and glomerular capillaries are dilated
• Efferent arteriole is constricted
• Combination increases glomerular blood pressure
• GFR increased back to normal
• Opposite occurs if blood pressure rises
© 2017 Pearson Education, Inc.
Local Regulation with Increased Pressure
(18-4)
• In response to increased blood pressure and flow
(and increased GFR):
• Walls of afferent arteriole are stretched
• Smooth muscle cells respond by contracting
• Reduces afferent arteriolar diameter
• Reduces flow into glomerulus
• Decreases GFR back to normal
© 2017 Pearson Education, Inc.
Hormonal Control of Kidney Function (18-4)
• Results in long-term adjustments of blood pressure
and blood volume
• Stabilizes GFR
• Major hormones involved
• Angiotensin II
• ADH
• Aldosterone
• Atrial natriuretic peptide (ANP)
© 2017 Pearson Education, Inc.
Renin-Angiotensin-Aldosterone System (18-4)
• A drop in blood pressure or blood volume causes:
• Release of renin from juxtaglomerular complex
• Renin converts angiotensinogen into angiotensin I
• Angiotensin-converting enzyme (ACE) converts
angiotensin I into angiotensin II, which causes:
• Peripheral vasoconstriction, increasing blood pressure in
renal arteries
• Constriction of efferent arterioles, increasing GFR
• Adrenal secretion of aldosterone, epinephrine, and
norepinephrine, increasing sodium reabsorption
• Release of ADH from posterior pituitary
• Result is increase in glomerular pressure and GFR
© 2017 Pearson Education, Inc.
Figure 18-10 The Renin-Angiotensin-Aldosterone System and Regulation of GFR.
Renin-Angiotensin-Aldosterone System
Endocrine response
Decreased filtration
pressure; decreased
filtrate and urine
production
Effector
Juxtaglomerular
complex
releases renin into
the bloodstream
Homeostasis
DISTURBED BY
DECREASING
Renin triggers the
formation of angiotensin I.
Angiotensin-converting
enzyme (ACE) in the
capillaries of the lungs
activates angiotensin I to
angiotensin II.
Neural responses triggered by angiotensin II
Angiotensin II
Increases
aldosterone
secretion by the
adrenal glands.
Effector
Angiotensin II
constricts peripheral
arterioles and further
constricts the
efferent arterioles of
nephrons.
blood flow to kidneys
STIMULUS
Nervous system
Aldosterone
increases
Na+ retention.
HOMEOSTASIS
NORMAL GLOMERULAR FILTRATION RATE (GFR)
Increased fluid
consumption
Increased
stimulation of
thirst centers
Increased fluid
retention
Increased ADH
production
RESTORED
Homeostasis
RESTORED BY
INCREASING
Increased
blood pressure
Increased
blood volume
Constriction of
venous reservoirs
blood flow to kidneys
Increased
cardiac output
Together, angiotensin II and
sympathetic activation stimulate
peripheral vasoconstriction.
© 2017 Pearson Education, Inc.
Increased
sympathetic
activation
Antidiuretic Hormone (18-4)
• Release stimulated by:
• Angiotensin II
• Drop in blood pressure
• Increase in plasma solute concentration
• Has two key effects
1. Increased water permeability of DCT and collecting
duct
• Water reabsorbed from tubular fluid
2. Stimulates thirst, leading to intake of water
© 2017 Pearson Education, Inc.
Aldosterone (18-4)
• Release stimulated by:
• Angiotensin II secretion
• Increase in potassium ion concentration of blood
• Key effects along DCT and collecting duct:
• Reabsorption of sodium ions
• Secretion of potassium ions
© 2017 Pearson Education, Inc.
Atrial Natriuretic Peptide (18-4)
• Release by atrial cardiac muscle cells in
response to:
• Rise in blood pressure and blood volume in atria of heart
• Key effect is to lower blood volume and blood
pressure by:
• Opposing renin-angiotensin system
• Inhibits secretion of renin, aldosterone, ADH
• Decreasing rate of sodium reabsorption in DCT
• Dilating glomerular capillaries, increasing GFR
© 2017 Pearson Education, Inc.
Sympathetic Activation in the Kidneys (18-4)
• Direct effects, triggered by sudden crisis
• Constriction of afferent arterioles
• Decreases GFR
• Can override local effects to stabilize GFR
• Indirect effects
• Shunts blood away from kidneys and redirects to tissues
and organs with higher needs
• Example: increased blood flow to skin and muscles during
exercise
• Can create problems for endurance athletes
© 2017 Pearson Education, Inc.
The Micturition Reflex (18-5)
• Increased urine volume stimulates stretch receptors in
bladder wall
• Afferent sensory fibers carry impulses to sacral spinal cord
• Parasympathetic motor neurons carry information back to
detrusor muscle
• Interneurons relay information to CNS
• Brings conscious awareness of pressure in bladder
• Urge to urinate occurs with about 200 mL of urine in bladder
• Contraction of detrusor muscle increases pressure
• Voluntary relaxation of external sphincter allows relaxation
of internal sphincter as well
• Urination occurs
Figure 18-12 The Micturition Reflex.
Projection fibers
Brain
If convenient, the
C2 from thalamus
deliver sensation
to the cerebral
cortex.
C3 individual voluntarily
relaxes the external
urethral sphincter.
The afferent fibers
stimulate neurons
involved with:
An interneuron
C1 relays sensation
to the thalamus.
L a local pathway,
and
C a central pathway
Parasympathetic
L2 Sensory
fibers in
L3 preganglionic
motor fibers in
pelvic nerves
pelvic
nerves
L1 Distortion
Urinary
bladder
of stretch
receptors
intramural
ganglia stimulate
detrusor muscle
contraction.
Start
C4 Voluntary relaxation of the
external urethral sphincter
causes relaxation of the
internal urethral sphincter.
Urination occurs
© 2017 Pearson Education, Inc.
Postganglionic
L4 neurons in
Control of Urethral Sphincters (18-5)
• Increased urine volume causes increased
stimulation of parasympathetic nerve fibers
• Increases detrusor muscle contraction
• Increases fluid pressure
• Urine volume greater than 500 mL may generate
enough pressure to force open internal sphincter
• External sphincter relaxes as well
• Urination occurs
© 2017 Pearson Education, Inc.
Fluid, Electrolyte, and pH Balance (18-6)
• Restoration of balance is key to effective treatment
of multiple diseases and conditions
• Water balance is essential for cellular function
• Ion concentration balance is essential for various
metabolic reactions
• pH balance is essential to maintain normal chemical
reactions, cell structure, and function
© 2017 Pearson Education, Inc.
Interrelated Factors in Homeostasis (18-6)
1. Fluid balance
• In balance when amount of water gained each day equal to
amount lost
• Balance requires movement into and out of cells
• Water moves by osmosis in response to ion concentration
gradients
2. Electrolyte balance
• Exists when neither net gain nor loss of any ion in body fluids
• Involves balancing rate of absorption across digestive tract
with rate of loss at kidneys
3. Acid-base balance
• In balance when production of H+ equal to loss
• Maintains normal pH in body fluids
© 2017 Pearson Education, Inc.
Basics of Body Fluid Compartments (18-6)
• Water is 50–60 percent of body weight
• Varies with gender
• Females have lower percentage due to larger mass of
adipose tissue (adipose is lower in water content)
• Divided into two fluid compartments
• Intracellular fluid (ICF)
• Extracellular fluid (ECF)
© 2017 Pearson Education, Inc.
Intracellular Fluid (18-6)
• Fluid within cells (also known as cytosol)
• Largest fluid compartment
• 27 percent of total body composition in adult females
• 33 percent of total body composition in adult males
• Contains abundance of K+, Mg2+, HPO42–
• Also contains large numbers of negatively charged
proteins
© 2017 Pearson Education, Inc.
Extracellular Fluid (18-6)
• Contains high levels of Na+, Cl–, HCO3–
• Largest subdivisions include:
• Plasma (water portion of blood)
• 4.5 percent of total body composition in males and females
• Interstitial fluid
• 18 percent of total body composition in females,
21.5 percent in males
• Minor components include:
• Lymph, cerebrospinal fluid, synovial fluid, serous fluid,
aqueous humor, perilymph, endolymph
© 2017 Pearson Education, Inc.
Figure 18-13b The Composition of the Human Body.
ICF
Intracellular
fluid 33%
Interstitial
fluid 21.5%
ECF
ICF
ECF
Intracellular
fluid 27%
Interstitial
fluid 18%
Plasma 4.5%
Solids 40%
(organic and inorganic materials)
Other
body
fluids
(≤1%)
Solids 50%
(organic and inorganic materials)
Adult males
b A comparison of the body compositions of adult males and females, ages 18–40 years.
© 2017 Pearson Education, Inc.
Adult females
Other
body
fluids
(≤1%)
Figure 18-14 Ions in Body Fluids.
200
INTRACELLULAR FLUID
Na+
PLASMA
INTERSTITIAL FLUID
KEY
Cations
HCO3–
Na+
Cl–
K+
Milliequivalents per liter (mEq/L)
150
Ca2+
HCO3–
HCO3–
Mg2+
HPO42–
K+
Anions
100
HCO3–
Na+
Cl–
Na+
SO42–
Cl–
Cl–
HPO42–
50
SO42–
HPO42–
Proteins
Mg2+
0
Cations
© 2017 Pearson Education, Inc.
Anions
Org. acid
K+
Ca2+
Proteins
K+
HPO42–
SO42–
Cations
Anions
Cations
Anions
Organic
acid
Proteins
Fluid Movement (18-7)
• Water moves continuously
• Within ECF compartments
• Across capillary beds throughout body
• Among minor ECF compartments
• Serous membranes, synovial membranes
• Between blood and CSF, eye humors, peri- and
endolymph of inner ear
© 2017 Pearson Education, Inc.
Water Gains and Losses (18-7)
• Water gain
• 40 percent by eating
• 48 percent by drinking
• 12 percent by metabolic generation
• Water losses
• 2500 mL per day lost in urine, feces, and insensible
perspiration
• Loss by sensible perspiration (sweating) varies with
activity level
© 2017 Pearson Education, Inc.
Table 18.4
© 2017 Pearson Education, Inc.
Fluid Shifts (18-7)
• Water movement between ECF and ICF
• Relatively rapid processes
• Occur in response to changes in osmotic
concentration (osmolarity) of ECF
• If ECF osmolarity increases, water leaves cells
• If ECF osmolarity decreases, water moves into cells
• Movement progresses until equilibrium reached
© 2017 Pearson Education, Inc.
Electrolyte Balance (18-7)
• Important because:
• Gain or loss of electrolytes results in gain or loss in
water
• Concentration of individual electrolytes affects cell
functions
• Examples: sodium (Na+) and potassium (K+) play major
roles in osmolarity of ICF and ECF
• Most common electrolyte balance problems caused by
imbalance between sodium gains and losses
• Potassium imbalances are less common but much more
dangerous
© 2017 Pearson Education, Inc.
Sodium Balance (18-7)
• Balance between Na+ absorption from digestive
tract and excretion by kidneys
• Rate of uptake varies with amount in diet
• Losses by excretion in urine and perspiration
• Regulated by aldosterone and ANP
• Aldosterone increases sodium reabsorption
• ANP decreases sodium reabsorption
• Water “follows” salt
• Levels of sodium have direct effect on water levels
• Increase in sodium → increase in blood volume →
increase in blood pressure
© 2017 Pearson Education, Inc.
Potassium Balance (18-7)
• 98 percent of body’s K+ is in ICF
• Low K+ concentration in ECF
• Balance between absorption from digestive tract and
excretion by kidneys
• Rate of loss affected by aldosterone
• Aldosterone increases potassium secretion (or loss)
• Problems with K+ balance less common than
problems with Na+, but much more dangerous
• Disrupts membrane potentials in excitable tissues
© 2017 Pearson Education, Inc.
Acid-Base Balance (18-8)
• Normal pH range of ECF is 7.35–7.45
• Deviation outside that range affects all body systems
• Disrupts stability of cell membranes
• Alters protein structure
• Changes activities of enzymes
• Nervous and cardiovascular systems most sensitive to
change
• Problems with low pH more common
• Normal cellular activities generate acids (e.g., lactic acid,
carbonic acid)
© 2017 Pearson Education, Inc.
Acidosis and Alkalosis (18-8)
• Acidosis
• pH of blood below 7.35
• Severe (pH below 7.0) can be fatal
• CNS function declines leading to coma
• Cardiac contractions weaken leading to heart failure
• Peripheral vasodilation drops blood pressure leading to
circulatory collapse
• Alkalosis
• pH of blood above 7.45
© 2017 Pearson Education, Inc.
Acids in the Body (18-8)
• Carbonic acid (H2CO3) is an important acid in body
fluids
• In lungs, breaks down into carbon dioxide (CO2) and
water
• In peripheral tissues, reverse reaction occurs
• Carbonic acid dissociates into hydrogen and bicarbonate
ions
• These reactions occur more rapidly when enzyme
carbonic anhydrase is present (found in red blood cells)
© 2017 Pearson Education, Inc.
Carbon Dioxide and pH (18-8)
• Partial pressure of CO2 the most important factor
affecting pH of body tissues
• As CO2 levels rise, additional H+ released and pH drops
• PCO2 and pH are inversely proportional
© 2017 Pearson Education, Inc.
Figure 18-15 The Basic Relationship between Carbon Dioxide and Plasma pH.
PCO2
40–45
mm Hg
If PCO2 increases
H2O + CO2
H2CO3
H+ + HCO3–
When carbon dioxide levels increase, more carbonic acid
forms, additional hydrogen ions and bicarbonate ions are
released, and the pH decreases.
© 2017 Pearson Education, Inc.
pH
7.35–7.45
HOMEOSTASIS
If PCO2 decreases
H+ + HCO3–
H2CO3
H2O + CO2
When the PCO2 decreases, the reaction runs in reverse, and
carbonic acid dissociates into carbon dioxide and water. This
removes H+ from solution and increases the pH.
Buffers (18-8)
• Dissolved compounds that can donate or remove
H+ from solution to help stabilize pH
• Weak acids can donate H+
• Weak bases can absorb H+
• Buffer system
• Combination of weak acid and dissociation products (H+
and an anion)
• Three key buffer systems in the body
1. Protein buffer systems
2. Carbonic acid–bicarbonate buffer system
3. Phosphate buffer system
© 2017 Pearson Education, Inc.
Protein Buffer Systems (18-8)
• Regulate pH in ICF and ECF
• Includes proteins and free amino acids
• If pH rises:
• Carboxyl group (–COOH) acts as weak acid
• Dissociates and releases a H+ from amino acid
• If pH drops:
• Amino group (–NH2) acts as weak base
• Picks up a free H+, forming amino ion (–NH3+)
© 2017 Pearson Education, Inc.
Carbonic Acid–Bicarbonate Buffer System
(18-8)
• Primary function is to prevent pH changes caused
by metabolic acids
• Regulates pH in ECF
• Carbonic acid acts as weak acid
• Bicarbonate acts as weak base
• Dissociation of metabolic acids releases H+, lowering pH
• H+ combine with bicarbonate, producing water and CO2
(driving formula to the left)
•
• Abundance of available bicarbonate ions is called the
bicarbonate reserve
• Pco2 rises, respiratory system excretes CO2
© 2017 Pearson Education, Inc.
Phosphate Buffer System (18-8)
• Primary buffer system of ICF
•
© 2017 Pearson Education, Inc.
Maintaining Acid-Base Balance (18-8)
• Buffer systems provide only temporary and limited
solution to pH imbalance
• Can tie up excess H+ but do not affect ion losses or
gains
• Respiratory and renal mechanisms contribute by:
• Secreting or absorbing H+
• Controlling excretion of acids and bases
• Generating additional buffers
• Combination of buffer systems and respiratory and
renal processes maintain body pH within range
© 2017 Pearson Education, Inc.
Respiratory Compensation of pH (18-8)
• Accomplished by altering respiratory rate
• Rise in Pco2 (= low pH) stimulates chemoreceptors
• Causes increase in respiratory rate
• Increases loss of CO2 from lungs, decreasing Pco2
• Decreases H+ concentration in the blood
• Increases pH
• Drop in Pco2 (= high pH) inhibits chemoreceptors
• Causes decrease in respiratory rate
• Decreases loss of CO2 from lungs, increases Pco2
• Increases H+ concentration in the blood
• Lowers pH
© 2017 Pearson Education, Inc.
Renal Compensation of pH (18-8)
• Change in the rates of hydrogen ion and
bicarbonate ion secretion or reabsorption by
kidneys
• Only way to truly eliminate H+
• Kidney tubules can:
• Reabsorb H+ and excrete HCO3– when pH is high
• Excrete H+ and reabsorb HCO3– when pH is low
© 2017 Pearson Education, Inc.
Acid-Base Disorders (18-8)
• Respiratory acid-base disorders
• Abnormal respiratory function
• Causes extreme changes in CO2 in ECF
• Metabolic acid-base disorders
• Caused by overproduction of acids
• Can also be caused by conditions altering HCO3–
concentrations
© 2017 Pearson Education, Inc.
Table 18.5
© 2017 Pearson Education, Inc.
Age-Related Changes in the Urinary System
(18-9)
1. Decrease in number of functional nephrons
• Drops 30–40 percent between ages 25 to 85
2. Reduction in GFR
• Result of fewer glomeruli, cumulative damage to filtration
structures, and reduced renal blood flow
3. Reduced sensitivity to ADH and aldosterone
• More water is lost in urine
4. Problems with micturition reflex
• Sphincters weaken
• CNS loss of control over sphincters
• Prostate enlargement in males restricts urine flow,
causing urinary retention
© 2017 Pearson Education, Inc.
Age-Related Changes in the Urinary System
(cont.) (18-9)
5. Gradual decrease in total body water content
• Less dilution of waste products, toxins, medications
6. Net loss of body mineral content
• Occurs over age 60 as muscle mass and skeletal mass
decrease
• May be limited with exercise and increased mineral
intake
7. Increased incidence of disorders affecting major
systems
• Impacts fluid, electrolyte, and pH balance
© 2017 Pearson Education, Inc.
Coordinated Excretion of Wastes (18-10)
• Urinary system excretes wastes produced by other
organ systems
• Yet, not the only system involved in excretion
• Combination of multiple systems regarded as
excretory system
• Integumentary system
• Excretion through perspiration
• Respiratory system
• Removes CO2
• Digestive system
• Excretes metabolic waste products in bile
© 2017 Pearson Education, Inc.
Kidney Positioning (18-2)
• Kidneys held in place by:
• Overlying peritoneum
• Contact with adjacent organs
• Supportive connective tissue
• Fibrous capsule covers each kidney
• Capsule surrounded by adipose tissue
• Outer fibrous layer anchors to surrounding structures
• Damage to suspensory fibers of outer layer may result in
displaced or floating kidney