Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 16
Urinary System and
Excretion
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Organs of excetion
• EXCRETION: is the process that rids body of
METABOLIC WASTES.
• Excretion is performed by:
KIDNEYS: excrete Nitrogenous Wastes (Ammonia, Urea,
Uric Acid, Creatinine)
LIVER: excrete Bile Pigments
LUNGS: excrete CO2
SKIN: water, urea in sweat
• Excretion is not the same as DEFECATION, which is
the process which rids the body of UNDIGESTED,
UNABSORBED food remains, plus bacteria -- NOT
metabolic end products.
16.1 Urinary System
• Functions of the Urinary System
– Excretion of Metabolic Wastes
• Urea, Creatinine, Uric acid, ammonia
– Maintenance of Water-Salt Balance
• NaCl, K+, HCO3-, Ca2+
– Maintenance of Acid-Base Balance
• Excretion of H+, reabsorption of HCO3-
– Secretion of Hormones
• Renin, Erythropoietin
The Urinary System
Organs of the Urinary System
– Kidneys
• Located in lumbar region
• Produce about 1ml of urine every minute
• Covered by tough capsule of fibrous connective
tissue
• Concave side has a depression called a hilum
– Location of renal artery and vein
Organs of the Urinary System
– Ureters
• Conduct urine from kidney to bladder
• Three-layered wall
– Mucosa, smooth muscle, outer connective tissue
• Conveys urine by peristalsis
16.1 Urinary System
• Organs of the Urinary System
– Urinary Bladder
• Stores urine
• Has three openings
– Two for the ureters, one for the urethra
• The bladder wall is expandable
• Two sphincter muscles control the release of urine into the
urethra (internal and external sphincter)
16.1 Urinary System
• Organs of the Urinary System
– Urethra
• A small tube that leads from the urinary bladder to an
external opening
• It’s function is to remove urine from the body
• The urethra is longer males than females
• The urethra also transports semen in males
16.1 Urinary System
• Urination
– Stretch receptors in
wall of bladder
• Send impulses when
bladder fills to 250 ml
• Motor impulses from
spinal cord
– Bladder contraction
– Micturition occurs
16.2 Anatomy of the Kidney
and Excretion
• There are three regions to a kidney
– The renal cortex
– The renal medulla
– The renal pelvis
• Nephrons are the functional units of the kidney
– Each kidney has over one million nephrons
Gross Anatomy of the Kidney
16.2 Anatomy of the Kidney
• Anatomy of a Nephron
– A nephron is composed of a system of tubules
– Each nephron has its own blood supply
• From renal artery, afferent arteriole leads into the
glomerulus
• Blood leaves the glomerulus via an efferent arteriole
• Efferent arteriole takes blood to peritubular capillaries
– These surround rest of the nephron
– Blood then goes to renal vein
Nephron Anatomy
16.2 Anatomy of the Kidney
• Parts of a Nephron
– Glomerular capsule (Bowman’s capsule)
• Cuplike structure
• Inner layer has podocytes
– Form pores for passage of small molecules
– Proximal convoluted tubule (PCT)
• Cuboidal epithelial cells with microvilli
– Increased surface area for absorption
16.2 Anatomy of the Kidney
• Parts of a Nephron
– Loop of Henle
• U-shaped tube
– Distal Convoluted tubule (DCT)
• Lack microvilli
• Designed for tubular excretion rather than reabsorption
– Collecting Ducts
Processes in Urine Formation
Glomerular Filtration
– Glomerular Filtration
• Blood enters the afferent arteriole and glomerulus
• Blood pressure forces water and small molecules into the
glomerular capsule (filtration)
• Large molecules and formed elements cannot leave the
capillaries
• Remaining processes must reabsorb desirable substances
and allow wastes to pass
Glomerular Filtration
– Glomerular Filtration
Filterable Blood
Components
Nonfilterable Blood
Components
Water
Formed elements
Nitrogenous wastes
Blood cells and
platelets
Nutrients
Plasma proteins
Salts
Tubular Reabsorption
• Tubular Reabsorption(PCT)
• Molecules are reabsorbed both actively and
passively
–Sodium reabsorbed by active transport
–Chloride follows passively
–Water absorbed by osmosis
Tubular Reabsorption
Only molecules recognized by carrier
proteins are actively reabsorbed
–Glucose is an example
–There is a limited number of carrier
proteins
–Excess glucose ends up being excreted
Tubular Reabsorption
• Tubular Reabsorption
Reabsorbed Filtrate Nonreabsorbed
Components
Filtrate
Components
Most water
Some water
Nutrients
Much nitrogenous
wastes
Required salts (ions)
Excess salts (ions)
Tubular Secretion (DCT)
– Tubular Secretion (DCT)
• Hydrogen ions, potassium, creatinine, many drugs
• Actively transported from the blood
• Tubular secretion occurs here
– Urine Contains
• Filtered substances that have not been reabsorbed
• Substances that have been actively secreted
Reabsorption of Water
• Reabsorption of Water
– Excretion of hypertonic urine depends on
reabsorption of water from the loops of Henle and
the collecting ducts
– Reabsorption of water requires
• Reabsorption of salt
• Establishment of solute gradient
• Reabsorption of water
Reabsorption of Salt
– Reabsorption of Salt
• Regulated by the absorption and excretion of ions
– Na+, K+, HCO3-, Mg2+
• More than 99% of Na+ filtered at the glomerulus is
returned to the blood
– 67% is reabsorbed at the proximal tubule
– 25% is reabsorbed at the ascending limb of the
nephron loop
– The rest is reabsorbed from the distal
convoluted tubule and the collecting duct
Establishment of Solute Gradient in the
renal medulla
– A LOOP OF HENLE has two parts
• Descending limb and ascending limb
– Salt diffuses out of lower part of ascending
limb
– Upper part of ascending limb actively
transports more salt out
– This creates high osmotic pressure (high
solute concentration) within the tissues of the
renal medulla
Establishment of Solute Gradient
– Urea contributes to high solute concentration
in medulla
– Leaks from lower collecting duct
– This results in a concentration gradient
favoring reabsorption of water
Loop of Henle
• Descending limb of loop of Henle
– Water is reabsorbed into the capillary network
due osmosis (hypertonic nature of the tissue
fluid within renal medulla)
• Created by urea leaking from the collecting
duct
Loop of Henle
– Ascending limb of loop of Henle
• Impermeable to water
– As you move up the medulla concentration is decrease
(filtrate is hypertonic to the surrounding)
• At lower region NaCl moves into blood passively
• At upper region NaCl is actively transported into
blood (there is less and less salt available for
transport out as you move up)
Reabsorption of Water
• Reabsorption of Water
– Water leaves distal convoluted tubule because of the
osmotic gradient (responds to aldosterone)
– Water also leaves descending limb of loop of the
nephron
• Countercurrent multiplier
– As filtrate enters collecting duct it is isotonic to cells of
renal cortex so no net movement of water
Collecting duct
• Up to this point blood and filtrate has
similar tonicity
• As the collecting duct moves into the
medulla it is subject to the same [gradient]
as the loop of henle
– Water diffuses out and urine become
hypertonic to blood plasma
Juxtaglomerular Apparatus
Hormonal Regulation at the
DCT
Occurs when blood pressure at the glomerulus is low
»Juxtaglomerular Apparatus
secretes renin
»Renin is an enzyme that changes
angiotensinogen into Angiotensin I
»Angiotensin I is then converted into
Angiotensin II (vasoconstrictor) via
angiotensin-converting enzyme found
in the lungs
Aldosterone release
»Angiotensin II stimulates the adrenal
cortex to release aldosterone
»Aldosterone promotes the excretion
of K+ and the reabsorption of Na+
»The reabsorption of Na+ (in DCT) is
followed by the reabsorption of H2O
»Blood volume and blood pressure
increase
BP regulation by Kidney via
renin
BP regulation by Kidney via
renin
Hormonal Regulation at the
DCT and ANH
Atrial naturietic hormone (ANH)
» Another hormone regulating sodium
» Secreted by right atrium of heart in
response to stretching
» Indicates increased blood volume
» Inhibits renin secretion by juxtaglomerular
apparatus
» Inhibits aldosterone release
» Promotes sodium excretion - natriuresis
Antidiuretic Hormone
• Anti-pee drug
– Permeability of collecting duct is under hormonal
control
• Antidiuretic hormone (ADH) is produced by the
hypothalamus and released by the posterior
pituitary gland
– In the absence of ADH, a dilute urine is
produced
– In the presence of ADH, the collecting duct
become more permeable to water and a
concentrated urine is produced
X= Pituitary Gland
Anterior and Posterior Pituitary
(FSH, LH, MSH, ACTH,
TSH, Prolactin)
ADH and the
hormone oxytocin are
released by the
posterior pituitary.
STIMULUS: Hypothalamus
detects low blood volume (i.e. it
detects concentrated blood)
HYPOTHALAMUS
ADH made here
NEGATIVE
FEEDBACK!
POSTERIOR
PITUITARY
ANTERIOR
PITUITARY
ADH sent here
ADH released into blood
BLOOD VOLUME RISES
(blood becomes more dilute)
ADH travels in blood to kidney.
There, it acts on collecting ducts
and distal tubules, causing them
to reabsorb more water from the
filtrate back into the blood.
STIMULUS: Hypothalamus
detects low blood volume (i.e. it
detects concentrated blood)
HYPOTHALAMUS
ADH made here
NEGATIVE
FEEDBACK!
POSTERIOR
PITUITARY
ANTERIOR
PITUITARY
ADH sent here
ADH released into blood
BLOOD VOLUME RISES
(blood becomes more dilute)
ADH travels in blood to kidney.
There, it acts on collecting ducts
and distal tubules, causing them
to reabsorb more water from the
filtrate back into the blood.
1. blood volume drops if not
enough water is being
consumed
2. this is detected by receptors
in the hypothalamus.
3. This stimulates hypothalamus
to produce ADH and send it to
pituitary gland
4. Pituitary gland releases ADH
into blood
STIMULUS: Hypothalamus
detects low blood volume (i.e. it
detects concentrated blood)
HYPOTHALAMUS
ADH made here
NEGATIVE
FEEDBACK!
POSTERIOR
PITUITARY
ANTERIOR
PITUITARY
ADH sent here
ADH released into blood
BLOOD VOLUME RISES
(blood becomes more dilute)
ADH travels in blood to kidney.
There, it acts on collecting ducts
and distal tubules, causing them
to reabsorb more water from the
filtrate back into the blood.
1.
2.
3.
ADH acts on the collecting duct and distal
convoluted tubule, causing them to reabsorb more
water from the kidney filtrate back into the blood
as there is less water in the filtrate, less urine is
produced.
Blood volume rises. This is detected by the
hypothalamus, which will then shut off the release
of ADH (negative feedback)
16.3 Regulatory Functions
of the Kidneys
• Diuretics
– Increase flow of urine
– Alcohol
• Shuts off ADH
• Dehydration causes hangover
– Caffeine
• Increases glomerular filtration rate
• Decreases tubular reabsorption of sodium
– Diuretic drugs
• Many inhibit active transport of sodium at loop of the nephron or the
distal convoluted tubule
Acid-Base Balance
- Normal pH for most body fluids is 7.4
– Alkalosis: pH is greater than 7.4
– Acidosis: pH is less than 7.4
– Several Mechanisms Maintain a pH of ~ 7.4
• Acid-Base buffer system
• Respiratory Center
• The Kidneys
Acid-Base Balance
– Acid-Base Buffer Systems
• Chemical or combination of chemicals
• Can take up excess H+ or OH• Prevents large changes in pH
• When H+ added to blood the following occurs
H+ + HCO3-  H2CO3
• When OH- added to blood the following occurs
OH- + H2CO3  HCO3- + H2O
Acid-Base Balance
– Respiratory Center
• Increasing breathing rate removes CO2
– Removes hydrogen ions
– Forces reaction to the right
H+ + HCO3-  H2CO3  H2O + CO2
• Respiratory system adjusts proportion of
bicarbonate and carbonic acid
Acid-Base Balance
– The Kidneys
•
•
•
•
•
•
Only kidneys can remove many acids and bases
Slower acting than respiratory system but more powerful
Reabsorbs bicarbonate ions
Excretes hydrogen ions
In urine, ammonia can absorb hydrogen ions
Phosphate provides another means of buffering hydrogen
ions in urine
Acid-Base Balance
Glucose
K+, ions
Amino Acids
HCO3-
Na+
Drugs,
Creatinine
NaCl
Increasing Saltiness
H2O
NH3
H+
H2O
Cortex
H2O
K+, ions
H+
NH3
NaCl
H2O
H2O
H2O
H2O
NaCl
H2O
Outer
Medulla
Urea
Inner Medulla
Active Transport
Passive Transport
16.4 Disorders of the Urinary System
• Disorders of the Kidneys
– Pyelonephritis: Infections of the kidneys
• Kidney infections usually result from bladder infections
• Most are curable with antibiotics if diagnosed in time
• Some infections can cause severe damage
– Kidney Stones
• Hard granules that form in the renal pelvis
• Composed of substances such as calcium, phosphate, uric acid,
and protein
• Excess animal protein in the diet, imbalanced urinary pH, and
urinary tract infections may be contributing factors
• May pass unnoticed in the urine; large stones can be very painful
– The presence of albumin or blood cells in the urine are early
signs of kidney damage
16.4 Disorders of the Urinary System
• Disorders of the Kidneys
– Hemodialysis
• Artificial kidney machine or continuous ambulatory peritoneal
dialysis (CAPD)
• Dialysis
–
–
–
–
–
Diffusion of dissolved molecules through a membrane
Selective permeability
Blood is cleansed
pH is adjusted
Water and salt balance maintained
• In CAPD the peritoneum is the dialysis membrane
An Artificial Kidney Machine
16.4 Disorders of the Urinary System
• Disorders of the Bladder and Urethra
– Bladder Infections
• Urine leaving the bladder is usually bacteria-free
• The urethra is normally colonized with bacteria
• Sometimes bacteria make their way to the bladder
– Usually treatable with antibiotics
– Bladder Stones
• Occur as a result of bladder infections or prostate enlargement
• May actually be kidney stones that were carried to the bladder
• Can be removed surgically or broken apart by lithotripsy
– Bladder Cancer
• Smoking greatly increases the risk
• Some types are very malignant necessitating removal of the
bladder.
a) Label the parts indicated
above and give one
function for structures Y
and Z
b) Which of the following is
not a function of the
organ shown?
A. to produce urea B. to
excrete metabolic wastes
C. to regulate the acidity
of the blood D. to
maintain a constant blood
volume
a) Identify the parts of the
nephron in the following
diagram.
b) Compare and contrast the
composition of blood in V with
Z
c) In a healthy person, the
sequence of structures through
which most glucose molecules
pass is
a) U, X, Y b) U, W, Z c) W, Z, X
d) W, X, Y
1. The process that occurs at
W is A. tubular
excretion. B. pressure
filtration. C. reabsorption
of water. D. selective
reabsorption.
2. The permeability of which
structure is altered by
secretions from the adrenal
cortex?
A. W B. X C. Y D. Z
• Demonstrate your understanding of
negative feedback by describing how the
kidneys and the hypothalamus work
together to regulate blood volume. (5
marks)
1. Describe the process by which each of
the following affects the composition of
filtrate in the nephron. (4 marks: 2 marks
each)
a) Proximal Tubule
b) Loop of Henle
a) Name the parts X
and Y in the diagram
b) List three ways that
the blood in vessel Y
differs from the blood
in vessel X
COMPONENT
glucose
amino acids
proteins
inorganic salts
urea
uric acid
1.
PLASMA
0.10
1.05
8.00
0.72
0.03
0.004
FILTRATE
0.10
1.05
0.01
0.72
0.03
0.004
URINE
nil
nil
0.01
1.50
2.00
0.05
The table shows the amounts of substances present in human
blood plasma, glomerula filtrate and urine. All are measured in
grams per 100 cm3 of fluid.
a) Account for the differences in the levels of proteins in the plasma
and filtrate. ( 1 mark)
b) The concentration of inorganic salts in urine is approximately double
that present in the filtrate. Explain this difference. (3 marks)
1. Alcohol appears to inhibit the secretion of
anti-diuretic hormone (ADH). Predict the
results of alcohol intake on the following.
Include in your answer a description of
the mechanism responsible for the
resulting concentration.
a) solute concentration of the blood plasma
(3 marks)
b) urine production (2 marks)
1. Assume that a bacterial infection results in large
perforations in the glomerulus and the Bowman’s
capsule of a patient.
a) How will the glomerular filtrate in the diseased person
compare to the glomerular filtrate of a healthy person?
(2 marks)
b) What effect will this have on the level of antidiuretic
hormone (ADH) circulating in the bloodstream? (1 mark)
c) A person with this disease would experience swelling of
the body tissues. Using your knowledge of kidney
function and the blood tonicity, explain the mechanism
that accounts for this swelling. (3 marks)
SUBSTANCE
a. Glucose
b. Protein
c. Ammonia
CONCENTRATION
IN PLASMA g/100 mL
0.100
8.00
0.004
CONCENTRATION
IN FILTRATE g/100 mL
0.100
0.000
0.004
CONCENTRATION
IN URINE g/100 mL
0.000
0.000
0.07
a) Account for the filtrate and urine
concentrations in each of the above
substances by stating the part of the
nephron and the process or processes
responsible for producing each of the
concentration values. (9 marks)
b) Explain what could cause high levels of
glucose in the urine. (2 marks)