1. PowerPoint® Lecture Slides prepared by John L. Wilson
Pages
C h a p t e r 26
The Urinary System
PowerPoint® Lecture Slides prepared by John L. Wilson
Copyright © 2009 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings

2. Excretion Defined Elimination of metabolic wastes
Wastes mostly from catabolism of molecules
These molecules excreted by various systems

3. Systems Involved in Excretion
Urinary system
_____
Respiratory system
____________
Digestive system
Integumentary system
Urine
Carbon dioxide
Feces
Sweat

4. Functions of the Urinary System
Excretion of metabolic wastes
Regulates fluid and electrolyte balance
Regulates blood pH
Produces hormones
Calcitriol (vitamin D) helps regulate calcium
Erythropoietin regulates RBC formation
Regulates blood pressure by enzyme renin

5. Nephron
Microscopic filtering units of kidneys composed of renal tubules and a blood supply
Called functional units – make most of urine
About 1.25 million per kidney
Mostly in renal cortex with some tubules extending into renal pyramids of medulla

6. Distal Convoluted Tubule (end of nephron)
Nephron Anatomy
Bowman’s Capsule
Glomerulus
Distal Convoluted Tubule (end of nephron)
Proximal Convoluted Tubule
Descending limb of Henle
Ascending limb of Henle
Collecting Duct
Papillary Duct
Renal Papilla

7. Renal Corpuscle Anatomy
Glomerulus – the capillaries beneath the podocytes
Bowman’s Capsule
Efferent arteriole
DCT
PCT
Capsular space
Afferent arteriole

8. Nephron Blood Supply Efferent arteriole Peritubular capillaries
Afferent arteriole
Vasa Recta

9. Physiology of the Urinary System
Three processes required for urine formation
1. Filtration from the glomerulus to Bowman's capsule
2. Tubular reabsorption from renal tubules to blood of peritubular capillaries
3. Tubular secretion from blood of peritubular capillaries into the renal tubules
Bowman’s capsule
Renal Tubules
Glomerulus
Afferent arteriole
Urine
Efferent arteriole 1 2 3
peritubular capillaries

10. Filtration
Water and many different solutes pass from glomerulus to the Bowman’s capsule
Resulting fluid in capsular space called filtrate
Filtrate contains
Wastes such as urea and uric acid that must be eliminated in the urine
Useful (vital) substances such as water, organic nutrients and electrolytes that must be kept

11. Filtrate Formation
High glomerular blood hydrostatic pressure forces water and solutes through filtration membrane into the capsular space, then into the PCT
Capsular space
PCT
Filtration membrane

12. Filtration Continued
Amount of blood flow through kidneys in one minute = renal blood flow (RBF)
About 1200 mL/minute
Amount of filtrate formed in one minute = glomerular filtration rate (GFR)
Between 105 and 125 mL/minute
So, around 10% of RBF becomes filtrate

13. Tubular Reabsorption
Most of the filtrate is taken back into the blood from the nephron tubules by various methods
Most Water, organic nutrients and electrolytes are kept
Wastes and some water remain in filtrate and become urine
Most reabsorption in proximal convoluted tubule
Blood of peritubular capillaries

14. Tubular Reabsorption Continued
Water reabsorbed by osmosis
Solutes reabsorbed by diffusion, active transport, cotransport, countertransport and pinocytosis

15. Reabsorption Continued
Most actively transported substances have a transport maximum (Tm)
The Tm refers to how much of a substance (in milligrams) the nephron tubules can reabsorb in a minute
When Tm is exceeded, substance shows up in urine

16. Reabsorption Continued
Renal threshold is the maximum blood concentration at which a substance begins to appears in the urine when transport maximum (Tm) is exceeded
Renal threshold for glucose 180 milligrams per 100 mL (deciliter), and above that amount, glucose will appear in the urine
Can you think of what might cause the RT of glucose to be exceeded?

17. Tubular Secretion
Some solutes move from the blood of the nephron capillaries into the filtrate
Potassium, ammonium, hydrogen and bicarbonate ions are secreted into filtrate
Helps regulate acid-base balance and electrolyte concentrations
Blood of peritubular capillaries

18. Water Reabsorption Each day we lose about as much water as we gain
If loss exceeds gain, become dehydrated
If gain exceeds loss, become over-hydrated
Controlled by reabsorption of varying amounts of water

19. Water Reabsorption Continued
Each day, between L of filtrate
Each day, 1-2 L of urine
What does this tell you?

20. Types of Water Reabsorption
Obligatory water reabsorption
In PCT and descending LOH
More constant
Facultative water reabsorption
In DCT and CD
Variable, depending on degree of hydration
This reabsorption controlled by hormones, particularly the antidiuretic hormone (ADH)

21. Amounts of H2O Reabsorbed
65% in proximal convoluted tubules
15% in descending limbs of Henle
None in ascending limb of Henle
10-15% in distal convoluted tubules
Remainder in collecting ducts
Next slide illustrates these amounts

22. Water Reabsorption Drawing
H2O-65%
Obligatory Reabsorption –
about 80 percent of H2O
reabsorbed at a more
constant rate in PCT and descending LOH
Facultative
Reabsorption-
remainder of
H2O reabsorption
is from the DCT
and CD; variable,
depending on
water balance –
mostly controlled
by hormone ADH.
Less salt and urea
H2O-15% from descending LOH
No water reabsorbed
by thick ascending LOH,
it reabsorbs only salt
(NaCl)
ISF and Blood
ISF and Blood
More salt
and urea

23. Concentration and Dilution of Urine
When water loss exceeds water gain, our kidneys can increase facultative water reabsorption
Results in a smaller volume of a darker urine
Our kidneys are thus concentrating our urine
When water gain exceeds water loss, our kidneys can decrease facultative water reabsorption
Results in a larger volume of a lighter-colored urine
Our kidneys are thus diluting our urine

24. Steps in Concentration of Urine
1. As water loss exceeds gain, hypothalamus stimulates secretion of antidiuretic hormone (ADH) from the posterior pituitary
2. ADH makes the cells of the DCT and CD more permeable to water – adds water pores
3. More water leaves the DCT and CD and enters concentrated interstitial fluid and blood of the pyramid

25. Steps in Concentration of Urine
4. Concentrated interstitial fluid and blood take more water out of the filtrate and concentrate the urine
5. Result is less of a darker, concentrated urine
Also, aldosterone from adrenal cortex increases salt reabsorption from tubules and thus helps to concentrate urine
How does this work?

26. Concentration of Urine-ADH Present
DCT and CD more permeable to water thus more water reabsorbed and urine is concentrated
ADH

27. Steps in Dilution of Urine
1. As water gain exceeds loss, hypothalamus stops secreting ADH
DCT and CD become less permeable to water – water pores decrease
Less water is reabsorbed
More water stays in filtrate and urine

28. Steps in Dilution of Urine
5. Results in more of a dilute urine
6. Adrenal cortex decreases aldosterone
secretion, thus less salt is reabsorbed
from tubules and this helps to dilute
urine

29. Dilution of Urine–ADH Absent
No ADH, so DCT and CD less permeable to water, thus less water reabsorbed and urine is diluted

30. Urine composition 95% H2O 5% solutes (solids) Electrolytes
Nitrogenous wastes such as urea, creatinine and uric acid
Urea from __________________
Creatinine from ________________
Uric acid from ____________________
protein metabolism
muscle metabolism
nucleic acid metabolism

31. Characteristics of Urine
Color
Turbidity
Specific gravity pH

32. Clinical Terms Glomerulonephritis – page 1030
Acute and Chronic Renal failure – page 1030
Hemodialysis (kidney dialysis) –page 1022
Renal Calculi – page 1030

33. Polycystic Disease – page 1030&1031
Incurable, kidney disease in which cysts form in kidney, and destroy it. Cysts can be clearly seen in kidney below; it weighed 17 pounds.
Cyst