1. Formation of Urine
Figure 15.5

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

3. 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

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

5. 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

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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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

14. 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

15. Buffering Systems

16. 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)

17. 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

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