Ureters
 Slender tubes attaching the
kidney to the bladder
• Continuous with the renal
pelvis
• Enter the posterior aspect
of the bladder
 Runs behind the peritoneum
 Peristalsis aids gravity in urine
transport
Urinary Bladder
 Function
• Smooth, collapsible, muscular sac
• Temporarily stores urine
 Trigone Structure
 Bladder Wall
• Three layers of smooth muscle
(detrusor muscle)
• Mucosa made of transitional
epithelium
• Walls are thick and folded in an
empty bladder
• Bladder can expand significantly
without increasing internal pressure
• Internal and external sphincters
Figure 15.6
Urethra
 Thin-walled tube that carries urine from the bladder to
the outside of the body by peristalsis
 Release of urine is controlled by two sphincters
•
Internal urethral sphincter (involuntary)
•
External urethral sphincter (voluntary)
 Length and Location
•
Females – 3–4 cm (1 inch), along wall of the
vagina
•
Males – 20 cm (8 inches) through the prostate and
penis
 Function
•
Females – only carries urine
•
Males – carries urine and is a passageway
Micturition (Voiding)
 Both sphincter muscles must open to allow
voiding
• The internal urethral sphincter is relaxed
after stretching of the bladder
• Activation is from an impulse sent to the
spinal cord and then back via the pelvic
splanchnic nerves
• The external urethral sphincter must be
voluntarily relaxed
Urinary System I: Kidneys and Urine Formation
 Functions of the Urinary System
 Organs of the Urinary System
 The Kidney
• Coverings and Regions
• Blood Flow
• Nephrons: Glomeruli and Renal Tubules
• Urine Formation
 Urinalysis
 Ureters, Bladder, and Urethra
Characteristics of Urine Used for Medical Diagnosis
 Colored somewhat yellow due to the pigment
urochrome (from the destruction of hemoglobin)
and solutes; darker if patient dehydrated, lighter
if over hydrated.
 Sterile
 Slightly aromatic
 Normal pH of around 6
 Specific gravity of 1.001 to 1.035; higher if
concentrated, lower if dilute.
 Checking for
•
Glycosuria (excessive sugary food intake or diabetes)
•
Proteinuria (intense exercise, pregnancy, hypertension)
•
Pyuria (pus from urinary tract infections)
•
Hemoglobinuria (from transfusion reactions or
hemolytic anemia)
•
Bilirubinuria (hepatitis)
•
Pyelonephritis (high specific gravity)
Urinary System II: Fluid, Electrolyte, and Acid/Base Balance
 Distribution of Body Fluid
 Maintaining Water Balance
 Hormornal Regulation of Water and
Salt
 Acid-Base Balance
• Blood Buffers
• Regulation by Lung Respiration
• Regulation by Kidney on
Bicarbonate
 Developmental Aspects of the Urinary
System
Most Body Fluid is Within Cells
 Intracellular fluid (inside
cells)
 Extracellular fluid
(outside cells)
• Interstitial fluid
• Blood plasma
 Normal amount of water in the human
body
• Young adult females – 50%
• Young adult males – 60%
• Babies – 75%
• Old age – 45%
•Low Na+ and Cl–
•Major cation: K+
•Major anion HPO42–
Maintaining Water Balance
 Water intake must equal water output
• Sources for water intake
o Ingested foods and fluids
o Water produced from metabolic processes
• Sources for water output
o Vaporization out of the lungs
o Lost in perspiration
o Leaves the body in the feces
o Urine production
 Urine Output
• Dilute urine is produced if water intake is excessive
• Less urine (concentrated) is produced if large amounts of water are lost
• Proper concentrations of various electrolytes must be present
Maintaining Water and Electrolyte Balance
Maintaining Acid-Base Balance in Blood
 Blood pH must remain between 7.35 and 7.45 to maintain
homeostasis
• Alkalosis – pH above 7.45
• Acidosis – pH below 7.35
 Most ions originate as byproducts of cellular metabolism
 Acid-base control
• Blood buffers (immediate, first line regulator of pH)
• Respiration rate (reacts in 1-3 minutes)
• Renal/Kidney mechanisms exert strongest effect but
slow (hours-days)
Chemical Buffer Systems of the Body
 Buffers react to prevent dramatic changes in hydrogen ion (H+) concentrations
• Bind to H+ when pH drops
• Release H+ (or bind OH-) when pH rises
1. Bicarbonate buffer system
o
Major buffer for the extracellular fluid, also intracellular fluid
o
H2O + CO2 <--> H2CO3 <--> HCO3- + H+
2.
Phosphate buffer system
o
Effective buffer in urine and ICF, where phosphate concentrations
are high
o
(H3PO4 <--> H2PO4– + H+ <--> HPO42– + H+),
3.
Protein buffer system
o
Mostly active within cells, some effects in plasma
o
Amino groups bind H+ (-NH2 + H+ <--> NH3+)
o
Carboxyl groups remove OH- (-COOH + OH- <--> -COO- + H2O
The Bicarbonate Buffer System
Renal Mechanisms of Acid-Base Balance
 Excrete bicarbonate ions if needed
 Conserve or generate new bicarbonate ions if needed
• Bicarbonate conservation or production causes rise in blood pH
• Bicarbonate excretion causes fall in blood pH
• H+ excretion in the urine
 Urine pH varies from 4.5 to 8.0
CO2 + H2 O

H2 CO3

-
H+ + HCO3
Acidosis and Alkalosis: Why It Matters
 Acidosis
• Blood pH below 7  depression of CNS 
coma  death
• Enzymes denature
 Alkalosis
• Blood pH above 7.8  excitation of nervous
system  muscle tetany, extreme nervousness,
convulsions, respiratory arrest
• Enzymes denature
Metabolic Acidosis and Alkalosis
 Any pH imbalance not caused by abnormal blood CO2 levels;
indicated by abnormal HCO3– levels
 Metabolic Acidosis
• Caused by ingestion of too much alcohol ( acetic acid),
excessive loss of HCO3– (e.g., persistent diarrhea)
• Causes by accumulation of lactic acid, shock, ketosis in
diabetic crisis, starvation, and kidney failure
 Metabolic Alkalosis (much less common than metabolic
acidosis)
• Indicated by rising blood pH and HCO3–
• Caused by vomiting of the acid contents of the stomach
or by intake of excess base (e.g., antacids)
Developmental Aspects of the Urinary System
 Fetal Development and Newborns
•
Functional kidneys are developed by the third
month
•
Urinary system of a newborn
o
Bladder is small
o
Urine cannot be concentrated
•
Control of the voluntary urethral sphincter does not
start until age 18 months
•
Urinary infections are the only common problems
before old age
 Effects of Aging on Urinary System
•
There is a progressive decline in urinary function
•
The bladder shrinks with aging
•
Urinary retention is common in males
 Congenital Abnormalities of the Urinary System
•
Polycystic kidney
•
Hypospadias
Hypospadias
Urinary System II: Fluid, Electrolyte, and Acid/Base Balance
 Distribution of Body Fluid
 Maintaining Water Balance
 Hormornal Regulation of Water and
Salt
 Acid-Base Balance
• Blood Buffers
• Regulation by Lung Respiration
• Regulation by Kidney on
Bicarbonate
 Developmental Aspects of the Urinary
System