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 Low Na+ and Cl– Major cation: K+ Major anion HPO42– Normal amount of water in the human body Young adult females – 50% Young adult males – 60% Babies – 75% Old age – 45%

Maintaining Water Balance Water intake must equal water output Sources for water intake Ingested foods and fluids Water produced from metabolic processes Sources for water output Vaporization out of the lungs Lost in perspiration Leaves the body in the feces 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 Bicarbonate buffer system Major buffer for the extracellular fluid, also intracellular fluid H2O + CO2 <--> H2CO3 <--> HCO3- + H+ Phosphate buffer system Effective buffer in urine and ICF, where phosphate concentrations are high (H3PO4 <--> H2PO4– + H+ <--> HPO42– + H+), Protein buffer system Mostly active within cells, some effects in plasma Amino groups bind H+ (-NH2 + H+ <--> NH3+) 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

Acidosis and Alkalosis: Why It Matters 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

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 Bladder is small 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