1. Maintaining Water-Salt/Acid-Base Balances and The Effects of Hormones
Urinary System

2. Control of Blood Composition
Kidneys filter liters of blood plasma AND only produce liters of urine in 24 hours
Composition depends on 3 factors
Diet
Metabolism
Urine output

3. Blood Composition
Kidneys play an important role in keeping blood composition constant
Excretion of Nitrogen-containing wastes like urea, uric acid, and creatinine
Maintain water and electrolyte balance
Ensure blood pH

4. Maintain water and electrolyte balance
Water accounts for 60% of body weight in females and 50% in males
Water locations in body:
25 Liters in Intracellular Fluid – contained in living cells
15 Liters in Extracellular Fluid – all body fluids outside of cells
12 Liters in Interstitial Fluid: Tissue Fluid, Cerebrospinal Fluid, Serous Fluid, humors of eye, lymph
3 Liters in Blood Plasma

5. Maintain water and electrolyte balance
Intake and Output of body water must be in balance for body to remain hydrated.

6. Maintain water and electrolyte balance
Type and amount of solutes (sodium, potassium, and calcium) in body fluids are vital to overall body homeostasis

7. Reabsorption of water and electrolytes regulated by hormones
Falling blood pressure from blood loss, excess sweat, or low levels of sodium in blood stimulate:

8. KIDNEYS REGULATE THE VOLUME OF BLOOD
This is done by two HORMONES:
 ADH
ALDOSTERONE

9. ADH (ANTIDIURETIC HORMONE)
anti-"increased urine output“
released by pituitary gland 
promotes reabsorption of water from collecting duct and distal convoluted tubule

10. How does ADH work?
Cells in hypothalamus detect low H2O content of blood
ADH released into blood, by the hypothalamus and acts on distal convoluted tubule and collecting duct

11. How does ADH work?
More H2O reabsorbed, thus decreasing the volume of urine (and concentrating it)
So, blood volume increases
As blood becomes more dilute, this is detected by the hypothalamus, ADH secretion stop
a negative feedback loop
In some cases of high blood pressure, DIURETIC DRUGS are prescribed which inhibit ADH secretion 

12. ALCOHOL also inhibits ADH secretion
Drinking alcohol therefore causes increased urination ---> dehydration ---> HANGOVER
Beer and alcohol cannot quench your thirst! You will urinate more liquid than you take in and the body becomes even more dehydrated than before.
The content of water in your body is normally about 50%.

13. ALDOSTERONE This is a hormone released by the ADRENAL GLANDS
Aldosterone acts on the kidney to RETAIN Na+ (& water) and EXCRETE K+.
Remember from last class
[Na+] in the blood is important to the kidneys’ ability to reabsorb H2O

14. ALDOSTERONE
Concentration of sodium in blood, in turn, regulates secretion of aldosterone
another negative feedback loop
If Na+ in blood too low, too little H2O is reabsorbed, results in HYPOTENSION
If Na+ in blood too high, results in HYPERTENSION

15. Fall blood pressure stimulates:
Hypothalamus, which stimulates posterior pituitary to release ADH (antidiuretic hormone)
ADH causes less water loss in urine SO blood volume increases and blood pressure rises

16. Fall blood pressure stimulates:
Adrenal Cortex which releases Aldosterone
Aldosterone stimulates kidney tubules to reabsorb more sodium ions (salt)
WATER FOLLOWS SALT
So if water follows salt, less water will be lost in urine, blood volume increases and blood pressure rises

17. Fall blood pressure stimulates:
Kidney to release Renin
Renin leads to the formation of angiotensin II in the blood
Angiotensin II causes smooth muscle of blood vessels to constrict which increase blood pressure

18. KIDNEYS AND BLOOD pH
Kidneys help maintain blood pH. However, so do the lungs (respiratory system).
You may recall that CO2 is released from the lungs when you exhale.
H+ + HCO3- ↔ H2CO3 ↔ H2O + CO2
Based on the acidity of the blood, chemoreceptors either stimulate or depress breathing.
If, for example, your blood is slightly alkaline, will your depth of breathing rate increase or decrease? ANSWER: IT WILL DECREASE.

19. KIDNEYS AND BLOOD pH
The kidneys, too, rid the body of acidic and basic wastes.
Nephrons vary the amount of H+ and NH3 that they excrete and the amount of HCO3- and Na+ they reabsorb in order to keep the pH levels normal.

20. KIDNEYS AND BLOOD pH
If blood acidic, more H+ and ammonia (NH3) are excreted, and more sodium bicarbonate is reabsorbed.
Sodium bicarbonate neutralizes acid:
Na+HCO3- + HOH --> H2CO3 + NaOH (strong base)

21. KIDNEYS AND BLOOD pH
If blood alkaline, less H+ excreted, less Na+ and HCO3- reabsorbed
Reabsorption and excretion of ions (e.g. K+, Mg++) by kidneys also maintains proper ELECTROLYTE BALANCE of blood.

22. Ensuring proper blood pH
Blood pH must be
Alkalosis: blood pH above 7.45
Acidosis: blood pH below 7.35
Several pH controlling systems

23. pH control system Blood Buffer
First line of defense in resisting pH changes
Chemical buffers that act to prevent dramatic changes in hydrogen ion concentration when a strong acid or strong base is added

24. pH control system Respiratory controls
When CO2 enters blood from tissue cells, it is converted to carbonic acid
Modify blood pH by retaining CO2 (decrease pH) or by eliminating more CO2 from blood (increase blood pH)

25. pH control system Renal Mechanism
Only system that can remove metabolic acids and bases from the body
Kidneys act slowly to change pH (hours to days to regulate)
pH of urine can vary from 4.5 to 8.0

26. KIDNEY PROBLEMS
Kidney functions are vital to homeostasis; problems can be life-threatening
Infections can be detected with URINALYSIS - look for blood cells and proteins in urine.
NORMAL URINE NEVER HAS BLOOD PROTEIN OR BLOOD CELLS IN IT. IT SHOULD ALSO NOT CONTAIN MORE THAN TRACE AMOUNTS OF GLUCOSE

27. KIDNEY PROBLEMS
If water and salts retained, causes fluid accumulation in body tissues, plus ionic imbalances (leads to problems in including loss of consciousness and heart failure). This condition is called EDEMA.