Download - chapter 20: urinary system
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Hole’s Human Anatomyand Physiology
Twelfth Edition
Shier Butler Lewis
Chapter 20
Urinary System
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20.1: Introduction• A major part of homeostasis is maintaining the composition, pH, and volume of body fluids within normal limits
• The urinary system removes metabolic wastes and substances in excess, including foreign substances like drugs and their metabolites that may be toxic
• It consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra
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Kidney
Hilum
Ureters
Urethra
Renalvein
Renalartery
Inferiorvena cava
Abdominalaorta
Urinarybladder
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© CNRI/SPL/Photo Researchers, Inc.
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20.2: Kidneys
• A kidney is a reddish brown, bean-shaped organ with a smooth surface• In the adult it is about 12 centimeters long, 6 centimeters wide, and 3 centimeters thick• It is enclosed in a tough, fibrous capsule
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Location of the KidneysCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Inferior vena cava
Pancreas
(a)
(b)
Adrenal gland
Kidney
Adipose tissue
Kidney
Spleen
Large intestineSmall intestineAorta
Stomach
Liver
Parietal peritoneum
Renal fasciaRenal fascia
Large intestineHip bone (cut)
Parietalperitoneum
Twelfth rib
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Kidney StructureCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Renal pelvis
Minor calyx
Major calyx
Renal papilla
Renal pyramid
Nephrons
Renal sinus
Renal medulla
Renal capsuleRenal cortex
Ureter
(a)
(b) (c)
Renal corpuscle
Papilla
Minor calyx
Renal column
Fat in renal sinus
Collectingduct
Renalmedulla
Renalcortex
Renaltubule
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Inferior vena cava
Renal cortex
Renal pyramid
Renal medulla
Minor calyx
Renal column
Renal papilla
Renal pelvis
Suprarenal artery
Abdominal aorta
Adrenal gland
Renal capsule
Hilum
Renal vein
Suprarenal vein
Ureter
Renal artery
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Function of the Kidneys
• The main function of the kidneys is to regulate the volume, composition, and pH of body fluids
• The kidneys remove metabolic wastes from the blood and excrete them to the outside of the body, including nitrogenous and sulfur-containing products of protein metabolism
• The kidneys also help control the rate of red blood cell production, regulate blood pressure, and regulate calcium ion absorption
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Renal Blood VesselsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b: © L.V. Bergman/The Bergman Collection
(a)
(b)
Cortex
Medulla
Renal pelvis
Ureter
Afferent arteriole
Cortical radiateartery and vein
Arcuate veinand artery
Interlobarvein and artery
RenalarteryRenalvein
Peritubularcapillary
Efferentarteriole
Proximalconvolutedtubule
Cortical radiateartery and vein
Distal convolutedtubule
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(a) : Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy, by R.G. Kessel and R.H. Kardon. © 1979 W.H. Freeman and Company (b) : Courtesy of R.B. Wilson MD, Eppeley Institute for Research in Cancer, University of Nebraska Medical Center
Glomerulus(a)
Renal tubules
Glomerulus(b)
Peritubularcapillary
Efferentarteriole
Afferentarteriole
Glomerularcapsule
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NephronsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glomerulus
Visceral layer ofglomerular capsule
Proximalconvolutedtubule
Parietal layerof glomerularcapsule
Glomerularcapsule
Bloodflow
Afferentarteriole
Efferentarteriole
Bloodflow
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© David M. Phillips/Visuals Unlimited
Slit pore Pedicel
Slit pore
Pedicel
Primary processof podocyte
Primary processof podocyte
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Glomerulus
Collecting duct
Nephronloop Ascending
limb
Descendinglimb
Peritubularcapillary
Efferentarteriole
Proximalconvolutedtubule
Renalmedulla
Renalcortex
Cortical radiateartery
Cortical radiatevein
Glomerularcapsule
Afferentarteriole
Distalconvolutedtubule
From renalartery
To renalvein
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Collecting ducts
Epithelial cell
Blood vessel
Glomerulus(a)
(b)
Renaltubules
Glomerularcapsule
Renalcorpuscle
a: © Biophoto Associates/Photo Researchers, Inc., b: © Manfred Kage/Peter Arnold
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Juxtaglomerular ApparatusCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glomerulus
Nephron loop
Glomerulus
Afferent arteriole
Glomerular capsule
Efferent arteriole
Podocyte
Macula densa
(a)
(b)
Glomerularcapsule
Afferentarteriole
Juxtaglomerularapparatus
Distalconvolutedtubule
Efferentarteriole
Proximalconvolutedtubule
Juxtaglomerularapparatus
Juxtaglomerularcells
Ascending limbof nephron loop
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Cortical and Juxtamedullary Nephrons
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Cortical nephron
Juxtamedullarynephron
Collectingduct
Renalmedulla
Renalcortex
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Blood Supply of a Nephron
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Glomerulus
Nephron loop
Collecting duct
Afferent arteriole
Vasa recta
Peritubularcapillaries
Efferentarteriole
Proximalconvolutedtubule
Glomerularcapsule
Cortical radiateartery and vein
Distalconvolutedtubule
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Renal artery
Cortical radiate artery
Afferent arteriole
Efferent arteriole
Cortical radiate vein
Renal vein
Arcuate artery
Interlobar artery
Glomerular capillaries
Peritubular capillaries
Arcuate vein
Interlobar vein
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20.3: Urine Formation• The main function of the nephrons and collecting ducts is to control the composition of body fluids and remove wastes from the blood, the product being urine
• Urine contains wastes, excess water, and electrolytes
• Urine is the final product of the processes of:
• Glomerular filtration
• Tubular reabsorption
• Tubular secretion
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Urine FormationCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Arteriole Venule
Venule
Renal tubule
Tubular fluid Urine
Net reabsorption
Net filtrationInterstitial fluid
Bloodflow
(a) In most systemic capillaries, filtration predominates at the arteriolar end and osmotic reabsorption predominates at the venular end.
Peritubularcapillaries
Afferentarteriole
Glomerularcapillaries
Efferentarteriole
Bloodflow
Tubularreabsorption
Tubularsecretion
Glomerularfiltration
(b) In the kidneys, the glomerular capillaries are specialized for filtration. The renal tubule isspecialized to control movements of substances back into the blood of the peritubularcapillaries (tubular reabsorption) or from the blood into the renal tubule (tubular secretion).
Filteredfluid
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Glomerular Filtration• Glomerular filtration
• Substances move from the blood to the glomerular capsuleCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fenestrae
(a) (b)
Podocyte
Podocyte
Glomerulus
Glomerularcapsule
Proximalconvolutedtubule
Capillaryendothelium
Glomerularfiltrate
Efferentarteriole
Bloodflow
Afferentarteriole
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Plasma, Glomerular Filtrate, and Urine Components
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Filtrate Pressure
• The main force that moves substances by filtration through the glomerular capillary wall is hydrostatic pressure of the blood inside
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Hydrostaticpressure ofblood
Glomerular hydrostaticpressure
Capsularhydrostaticpressure
Plasma colloidosmotic pressure
Net Outward PressureOutward force, glomerular hydrostatic pressure = +60 mmInward force of plasma colloid osmotic pressure = –32 mmInward force of capsular hydrostatic pressure = –18 mmNet filtration pressure = +10 mm
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Filtrate Rate
Net filtration pressure = force favoring filtration – forces opposing filtration (glomerular capillary (capsular hydrostatic pressure hydrostatic pressure) and glomerular capillary osmotic pressure)
• Glomerular filtration rate (GFR) is directly proportional to the net filtration pressure
• Normally the glomerular net filtration pressure is positive causing filtration• The forces responsible include hydrostatic pressure and osmotic pressure of plasma and the hydrostatic pressure of the fluid in the glomerular capsule
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0
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Lit
ers
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180180 Liters
Glomerular filtrate
(a) (b)
Urine
0.6 – 2.5 Liters
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Control of Filtrate Rate• GFR remains relatively constant through a process called autoregulation• Certain conditions override autoregulation, including when GFR increases• Primarily three mechanisms are responsible for keeping the GFR constant:
• Autoregulation• Increased sympathetic impulses that decrease GFR by causing afferent arterioles to constrict• The hormone-like renin-angiotensin system• There also is the hormone atrial natriuretic peptide (ANP) affects sodium causing an increase in GFR
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Bloodstream
Angiotensin I
LiverKidney
Lung capillaries
Angiotensin II
• Increased thirst
Angiotensinogen
Renin
Stimulation
Angiotensin-convertingenzyme
Release intobloodstream
• Vasoconstriction• Increased aldosterone secretion• Increased ADH secretion
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Tubular Reabsorption
• Tubular reabsorption• Substances move from the renal tubules into the interstitial fluid where they then diffuse into the peritubular capillaries• The proximal convoluted tubule reabsorbs (70%):
• Glucose, water, urea, proteins, and creatine• Amino, lactic, citric, and uric acids• Phosphate, sulfate, calcium, potassium, and sodium ions
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Glomerulus
(a) (b)Blood flowBlood flow
Glomerulus
Bloodflow
Afferentarteriole
Glomerularcapsule
Glomerularfiltrate
Efferentarteriole
Peritubularcapillary
Tubularreabsorption
Renaltubule
Renaltubule
Tubularsecretion
Peritubularcapillary
Efferentarteriole
Afferentarteriole
Bloodflow
Glomerularcapsule
Glomerularfiltrate
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Peritubular capillary
Glomerulus
+
+
–
––
–
++–+–
+–
+–+–
–+
+++––+––++––
1
2
3
4
Bloodflow
Glomerularcapsule
BloodflowGlomerular
filtrate
Proximalconvolutedtubule Sodium ions
are reabsorbed byactive transport
Negatively charged ionsare attracted to positivelycharged ions
As concentration of ions(solute) increases in plasma,osmotic pressure increases
Water moves from proximaltubule to capillary byosmosis
Bloodflow
Isotonictubular fluid
Na+
Na+
PO4–3
N+
Cl–
HCO3–
Cl–
Na+
H2O
H2O
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Tubular Secretion• Tubular secretion
• Substances move from the plasma of the peritubular capillaries into the fluid of the renal tubules• Active transport mechanisms function here• Secretion of substances such as drugs and ions
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Blood flowPeritubular capillary
Distal convoluted tubule
Na+
Na+
Na+
Na+
Na+
K+ K+
K+
K+
H+
H+
Collecting duct
K+ or H+
Na+
Na+
Tubular reabsorption Tubular secretion
Tubular fluid
Ascending limbof nephron loop
Na+
Na+
Na+
Na+
Na+
Na+
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Regulation of Urine Concentration and Volume
• Hormones such as aldosterone and ANP affect the solute concentration of urine, particularly sodium• The ability of the kidneys to maintain the internal environment rests in a large part on their ability to concentrate urine by reabsorbing large volumes of water• The distal convoluted tubule and the collecting duct are impermeable to water, so water may be excreted as dilute urine• If ADH is present, these segments become permeable, and water is reabsorbed by osmosis into the extremely hypertonic medullary interstitial fluid• A countercurrent mechanism in the nephron loops (the descending and the ascending limbs) ensures that the medullary interstitial fluid becomes hypertonic• This mechanism is known as the countercurrent multiplier• The vasa recta also contributes as a countercurrent mechanism
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Collecting duct
Dilute urine Concentrated urine
Collecting duct
H2O
H2O
(a) (b)
Medullaryinterstitial fluid
Distal convolutedtubule
Hypertonicinterstitialfluid
Hypertonicinterstitialfluid
high ADH levelslow ADH levels
H2O
H2O H2O
H2OH2O
H2O
Medullaryinterstitial fluid
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Isotonic fluid
Hypotonic fluidNa+
Cl–
(a) (b)
Na+
Cl–
Salty
H2O1
2
3
Descendinglimb(permeableto water)
IncreasingNaClconcentration
Thick ascendinglimb (impermeableto water)
Hypertonicfluid
Medullaryinterstitialfluid
Moresalty
Evenmoresalty
Na+
Cl–H2O
Na+
Cl–H2O
H2O
H2O
H2O
Na+
Cl–
Na+
Cl–
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NaCl
NaCl
NaClNaCl NaCl
NaCl
NaCl
NaCl
Bloodflow
IncreasingNaClconcentration
Bloodflow
Medullaryinterstitialfluid
Vasarecta
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Urea and Uric Acid Excretion• Urea:
• A by-product of amino acid catabolism• The plasma concentration reflects the amount or protein in diet• It enters the renal tubules through glomerular filtration• It contributes to the reabsorption of water from the collecting duct• About 80% is recycled
• Uric acid:• Is a product of nucleic acid metabolism• It enters the renal tubules through glomerular filtration• Most reabsorption occurs by active transport• About 10% is secreted and excreted
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Urine Composition• Urine composition reflects the volumes of water and solutes that the kidneys must eliminate from the body or retain in the internal environment to maintain homeostasis• It varies from time to time due to dietary intake and physical activity, but is:
• About 95% water• Usually contains urea, uric acid, and creatinine• May contain trace amounts of amino acids and varying amounts of electrolytes• Volume varies with fluid intake and environmental factors
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Renal Clearance• This is the rate at which a chemical is removed from the plasma• It indicates kidney efficiency• Tests of renal clearance:
• Inulin clearance test• Creatinine clearance test• Para-aminohippuric acid (PAH) test
• These tests of renal clearance are used to calculate the GFR (glomerular filtration rate)
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20.4: Elimination of Urine• After forming along the nephrons, urine:
• Passes the collecting ducts to:• Openings of the renal papillae:
• Enters the minor and major calyces:• Passes through the renal pelvis:• Enters into the ureters:• Enters into the urinary bladder:•The urethra carries the urine out of the body
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Ureters• The ureters:
• Each is about 25 centimeters long• Extends downward posterior to the parietal peritoneum• Runs parallel to vertebral column• Join the urinary bladder in the pelvic cavity• The wall of ureter has three layers:
• The inner mucous coat• The middle muscular coat• The outer fibrous coat
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Mucous coat
LumenMuscular coat
Fibrous coat
Adipose tissue
© Per H. Kjeldsen
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Urinary Bladder• The urinary bladder is a hollow, distensible, muscular organ located within the pelvic cavity, posterior to the symphysis pubis and inferior to the parietal peritoneum
• It contacts the anterior walls of the uterus and vagina in the female, and lies posteriorly against the rectum in the male
• The openings for the ureters is the area of trigone
• It has four layers: inner mucous coat, a submucous coat, a muscular coat, and an outer serous coat
• Smooth muscle fibers comprise the detrusor muscle which is the muscle of the bladder wall
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Symphysis pubis
Prostate gland
Urinary bladder
Urethra
Ureter
Rectum
Parietal peritoneum
Abdominal wall
Rectum
(a) (b)
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(a) (b)
Mucous coat
Trigone
Internal urethral sphincter
Neck
Prostate gland
Urethra
Serous coatUrinary bladder
Ureter
Ureter
Prostate gland
UrethraRegion of externalurethral sphincter
Seminalvesicle
Ductus (vas)deferens
Detrusormuscle
Submucouscoat
Openings ofthe ureters
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Muscular coat Mucous coat
Lumen
Submucouscoat
© John D. Cunningham/Visuals Unlimited
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Trigone
Ureter
Penis
(b)
Urethra
Ureter
(a)
Urinarybladder
Externalurethral orifice
Urinarybladder
Prostategland
Bulbourethralgland
Membranousurethra
Prostaticurethra
Penileurethra
Externalurethral orifice
Trigone
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Urethra• The urethra is a tube that conveys urine from the urinary bladder to the outside of the body• Its wall is lined with a mucous membrane and it has a thick layer of longitudinal smooth muscle fibers• In a female:
• It is about 4 centimeters long• It runs obliquely
• In a male:• It is about 17.5 centimeters long• It has a dual function for both urination and reproduction• It has three sections:
• Prostatic urethra• Membranous urethra• Penile urethra
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Urethral glands
Muscle layer
Lumen of urethra
Mucous membrane
© Ed Reschke
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Micturition
• Urine leaves the urinary bladder by micturition or urination reflex
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Micturition
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20.5: Lifespan Changes• The urinary system is sufficiently redundant, in both structure and function, to mask age-related changes• The kidneys become slower to remove nitrogenous wastes and toxins and to compensate for changes that maintain homeostasis• Changes include:
• The kidneys appear scarred and grainy • Kidney cells die• By age 80 the kidneys have lost a third of their mass• Kidney shrinkage is due to loss of glomeruli• Proteinuria may develop• The renal tubules thicken• It is harder for the kidneys to clear certain substances• The bladder, ureters, and urethra lose elasticity• The bladder holds less urine