2. The Urinary System
Chapter 26
(or 25)

3. Functions of the Urinary System
Removal of metabolic wastes (especially nitrogenous wastes e.g. urea & uric acid).
Water balance (and therefore blood pressure).
Control of electrolyte balance.
Control of pH.
Removal of toxins.

4. Anatomy of the Urinary System
The Kidneys: the functional heart of the urinary system.
The Ureters: pipeline from the kidneys to the bladder.
The Urinary Bladder: holding tank of urine.
The Urethra: avenue of relief
(word of the day “micturition” = voiding the bladder)

5. The Kidneys
Location: retroperitoneal against the dorsal wall of the abdominal cavity. The right kidney is slightly lower than the left.
Size & weight: approximately 150 grams (about 5 ounces) each and 12 cm x 10 cm x 4 cm.
Shaped like a bean (or are beans shaped like kidneys?)

6. The Kidney: location

7. Kidney: up close & personal

8. A slice of kidney
Cortex
Medulla
Glomeruli
Capsule

9. The Nephron: functional unit of the kidney
Interlobular artery
Afferent Arteriole
Glomeruli

10. Functional histology of a nephron

11. Kidney tissue
Glomerular (Bowman’s) capsule
Glomerulus

12. Nephrons

13. Blood pressure drops due to peripheral resistance

14. The renal corpuscle and the Juxtaglomerular apparatus

15. The renal filtration membrane: Podocytes and fenestrated capillaries

16. Filtration slits
Pedicles

17. Three stages of urine formation
Filtration
Reabsorption
Secretion

18. Filtration pressures: NFP must be positive for U2P

19. GFR GFR is “Glomerular Filtration Rate”.
It is directly proportional to NFP.
It is a measurement of FLOW in milliliters per minute (ml/min).
If NFP drops more than 15% below 10 mmHg, GFR goes to 0.
If NFP goes up less than 30% above normal, the kidneys can handle it without major compensatory mechanisms kicking in.

20. Compensatory Mechanisms to maintain GFR

21. Tubular reabsorption
Reabsorption of filtered solutes occurs in the Proximal Convoluted Tubules.
Most solutes are reabsorbed by secondary active transport with Na+. Does this look familiar?

22. Solute reabsorption

23. Reabsorption of NaCl & water in the Loop of Henle

24. Reabsorption in the Distal Convoluted Tubule & Collecting Duct

25. Summary of tubular reabsorption/excretion

26. After the Kidneys: the bladder & urethra

27. The Human Bladder: It can hold a maximum of 800 – 1000 ml!

28. Physical characteristics of Urine
Color - Clear to deep yellow, almost rusty, depending on concentration.
Odor - Fresh urine is slightly aromatic, stale urine smells like downtown Tacoma on a Sunday morning.
pH – range of 4.5 – 8 depending on diet. High protein leads to low pH (acid ash diet), vegetarian (alkaline ash) diet leads to high pH. Heavy vomiting and bacterial infection can also lead to alkaline urine.
Specific gravity – Normal range is – Distilled water has a s.g. of Anything solutes cause the specific gravity of a liquid to go up. Concentrated urine has a higher s.g. than dilute urine.

29. Composition of Urine Normal Urea Uric acid Creatinine Na K Phosphates
Sulfates
Bicarbonate Ca Mg
Abnormal
Glucose “glycosuria”
Proteins “proteinuria” or
“albuminuria”
Ketones “ketonuria”
Hemoglobin “hemoglobinuria”
Erythrocytes “hematuria”
Bile pigments “bilirubinura”
Leukocytes “pyruia”
Abnormally low output = oliguria
No output = anuria
Abnormally high output = polyuria
Diuresis = increased urine output
Diuretic = substance that leads to diuresis

30. The micturition reflex

31. Stages of Renal Disease
Stage 1: signs of kidney damage w/ GFR ≥ 90.
Stage 2: signs of kidney damage w/ GFR 60 – 89.
Stage 3: GFR 30 – 59.
Stage 4: GFR 15 – 29.
Stage 5: < 15

32. Renal Clearance RC = UV/P
The volume of plasma that is cleared of a particular substance in a given time (usually one minute).
RC = UV/P
U = concentration of the substance in urine (mg/ml)
V = flow rate of formation (ml/min)
P = concentration of the substance in the plasma (mg/ml)
High renal clearance values means that the substance is being effectively cleared, low values means that more is being reabsorbed. For some solutes low is good (glucose should be 0). For others, high RC would be expected (creatinine should be complete, urea should be about 80%).

33. Kidney stones
Renal Calculi

34. “Well Mr. Osborne, I don’t think that it’s kidney stone after all”