Formation of Urine Figure 15.5

Characteristics of Urine Yellow due to pigment urochrome (from break-down of hemoglobin) & solutes Sterile Slightly aromatic Normal pH of ~ 6 Specific gravity of 1.001 to 1.035 ~1500 ml daily

Chemical Composition of Urine 95% water and 5% solutes Nitrogenous wastes: urea, uric acid, and creatinine Other normal solutes Na+, K+, PO43–, and SO42–, Ca2+, Mg2+ and HCO3– Abnormally high concentrations of any constituent may indicate pathology

Ureters Slender tubes from kidney to bladder - Continuous with renal pelvis - Enter the posterior aspect of the bladder Runs behind the peritoneum Peristalsis aids gravity in urine transport

Ureters As bladder pressure increases, distal ends of the ureters close, preventing backflow of urine

Lumen Adventitia Circular layer Longitudinal layer Transitional epithelium Lamina propria Figure 25.20

Renal Calculi Kidney stones form in renal pelvis Crystallized calcium, magnesium, or uric acid salts Larger stones block ureter, cause pressure and pain in kidneys May be due to chronic bacterial infection, urine retention, Ca2+ in blood, pH of urine Lithotripsy

Urinary Bladder Smooth, collapsible, muscular sac Temporarily stores urine Trigone – 3 openings - Two from ureters - One to urethrea

Urinary Bladder Retroperitoneal, on pelvic floor posterior to pubic symphysis Males—prostate gland surrounds the neck inferiorly Females—anterior to the vagina and uterus

Urinary Bladder Wall Detrusor muscle – pushes down 3 layers of smooth muscle Walls - thick & folded in empty bladder Transitional epithelium - expands without increasing internal pressure

Urethra Thin-walled tube Carries urine from bladder by peristalsis Release controlled by 2 sphincters Internal urethral sphincter (involuntary) External urethral sphincter (voluntary)

Urethra Gender Differences Length - Females – 3–4 cm (1 inch) - Males – 20 cm (8 inches) Location - Females – along wall of the vagina - Males – through the prostate and penis Function - Females – only urine - Males –urine and sperm

Micturition Urination or voiding Three simultaneous events Contraction of detrusor muscle by ANS Opening of internal urethral sphincter by ANS Opening of external urethral sphincter by somatic nervous system

Maintaining Water Balance Normal amount of water in humans (~1/2) - Adult females – 50% - Adult males – 60% - Babies – 75% - Old age – 45% Water is necessary for many functions and levels must be maintained Water intake = water output Sources for water intake - foods and fluids - metabolic processes Sources for water output - Vaporization from lungs - perspiration - feces - Urine

Distribution of Body Fluid Intracellular fluid (inside cells) Extracellular fluid (outside cells) - Interstitial fluid - Blood plasma

Link Between Water and Salt Changes in electrolyte balance causes water to move from one compartment to another. Water follows salt! - Alters blood volume & blood pressure - Can impair the activity of cells

Regulation of Reabsorption Hormones - Antidiuretic hormone (ADH) prevents excessive water loss in urine Aldosterone regulates sodium Triggered by the renin-angiotensin mechanism Monitored by kidneys and hypothalamus

Maintaining Blood pH Normal Blood pH - Alkalosis – pH above 7.45 - Acidosis – pH below 7.35 Most ions are metabolic byproducts Most pH balance is maintained by kidneys Other acid-base controlling systems - Blood buffers - Respiration

Blood Buffers Molecules to prevent dramatic changes in [H+] - Bind to H+ when pH drops - Release H+ when pH rises Three major chemical buffers Bicarbonates Phosphates Proteins

Buffering Systems

Fetal/Newborn Developmental Aging Functional kidneys by 3rd month Bladder is small in newborn Urine cannot be concentrated Developmental Control of voluntary sphincter ~ 18 mos Urinary infections - common problems Aging Bladder shrinks Decline in function Retention if prostate enlarges (males)

Conditions UTI (urinary tract infection) - caused E.coli. Frequent urgency to urinate, cloudy urine, dysuria (trouble / painful urination) Prostate Enlargement (Hypertrophy) – causes dysuria due to pressure on urethra Incontinence – normal for children, heavy sleepers, during pregnancy or infection, old age

Renal Calculus – kidney stones; urine too concentrated and substances crystalize; causes oliguria (decreased urine) Addison’s Disease (hypoaldosteronism) – causes polyuria