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

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

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

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 (Voiding) Both sphincters must open internal relaxes after bladder stretches Activation - impulse to spinal cord and back via pelvic splanchnic nerves external voluntarily relaxes

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