Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
16.1 Urinary System
• Functions of the Urinary System
– Excretion of Metabolic Wastes
• Urea, Creatinine, Uric acid
– 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
16.1 Urinary System
• Organs of the Urinary System
– Kidneys
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•
•
•
Located in lumbar region
Behind peritoneum
Covered by tough capsule of fibrous connective tissue
Concave side has a depression called a hilum
– Location of renal artery and vein
– 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
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
and Excretion
• 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
and Excretion
• 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
and Excretion
• Parts of a Nephron
– Loop of Henle
• U-shaped tube
• Simple squamous epithelium
– Distal Convoluted tubule (DCT)
• Lack microvilli
• Designed for tubular excretion rather than reabsorption
– Collecting Ducts
Processes in Urine Formation
16.2 Anatomy of the Kidney
and Excretion
• Urine Formation
– 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
16.2 Anatomy of the Kidney
and Excretion
• Urine Formation
– Glomerular Filtration
Filterable Blood
Components
Nonfilterable Blood
Components
Water
Blood cells and
platelets
Nitrogenous wastes
Plasma proteins
Nutrients
Salts
16.2 Anatomy of the Kidney
and Excretion
• Urine Formation
– Tubular Reabsorption
• Molecules are reabsorbed both actively and passively
– Sodium reabsorbed by active transport
– Chloride follows passively
– Water absorbed by osmosis
• 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
16.2 Anatomy of the Kidney
and Excretion
• Urine Formation
– Tubular Reabsorption
Reabsorbed Filtrate Nonreabsorbed
Components
Filtrate
Components
Most water
Some water
Nutrients
Much nitrogenous
wastes
Required salts (ions)
Excess salts (ions)
16.2 Anatomy of the Kidney
and Excretion
• Urine Formation
– Tubular Secretion
• Hydrogen ions, potassium, creatinine, many drugs
• Actively transported from the blood
– Urine Contains
• Filtered substances that have not been reabsorbed
• Substances that have been actively secreted
16.3 Regulatory Functions
of the Kidneys
• Reabsorption of Water
– Excretion of hypertonic urine depends on
reabsorption of water from the loops of the nephrons
and the collecting ducts
– Reabsorption of water requires
• Reabsorption of salt
• Establishment of solute gradient
• Reabsorption of water
16.3 Regulatory Functions
of the Kidneys
• Reabsorption of Water
– 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
16.3 Regulatory Functions
of the Kidneys
• Reabsorption of Water
– Reabsorption of Salt
• Hormonal Regulation at the Distal Convoluted Tubule
– 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
» Angiotensin II stimulates the adrenal cortex to release aldosterone
» Aldosterone promotes the excretion of K+ and the reabsorption of
Na+
» The reabsorption of Na+ is followed by the reabsorption of H2O
» Blood volume and blood pressure increase
16.3 Regulatory Functions
of the Kidneys
• Reabsorption of Water
– Reabsorption of Salt
• Hormonal Regulation at the Distal Convoluted Tubule
– 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
Juxtaglomerular Apparatus
16.3 Regulatory Functions
of the Kidneys
• Establishment of Solute Gradient
– A long loop of nephron 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
– Urea contributes to high solute concentration in medulla
– Leaks from lower collecting duct
– This results in a concentration gradient favoring reabsorption of
water
Reabsorption of Water
16.3 Regulatory Functions
of the Kidneys
• Reabsorption of Water
– Water leaves distal convoluted tubule because of the
osmotic gradient
– Water also leaves descending limb of loop of the
nephron
• Countercurrent multiplier
– As filtrate enters collecting duct it is hypotonic to cells
of renal cortex
– Permeability of collecting duct under hormonal control
16.3 Regulatory Functions
of the Kidneys
• Reabsorption of Water
– Permeability of collecting duct is under hormonal
control
• Antidiuretic hormone (ADH) is produced 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
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
16.3 Regulatory Functions
of the Kidneys
• 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
16.3 Regulatory Functions
of 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
16.3 Regulatory Functions
of the Kidneys
• 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
16.3 Regulatory Functions
of the Kidneys
• Acid-Base Balance
– The Kidneys
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•
•
•
•
•
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
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
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–
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–
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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.