1. Biology 212 Anatomy & Physiology I Dr. Thompson Fluid Balance

2. Recall: major concept of human physiology = Homeostasis: A state of "dynamic (changing) equilibrium (balance)" in which the body's internal environment is maintained within narrow limits even when 1) the external environment changes significantly and 2) things are introduced into or removed from the body Food Urine Drinks Feces Drugs Sweat Air Bleeding Carbon dioxide

3. Two major components of fluid homeostasis: 1. Keeping the right amounts of water in the right places 2. Keeping the right amounts of electrolytes/ions/minerals in the right places

4. Terms to know: Solvent Solutes Electrolytes or Ions Cations Anions Osmolarity

5. Water Balance: 3 major compartments:

7. That exchange of water and solutes among compartments is possible only because the cells and membranes lining each of those compartments are permeable to them. For example: Fluid from the lumen of the intestine crosses its epithelium to get into the extracellular space, then crosses the epithelium of the blood vessels and lymphatic vessels. Fluid from the plasma of the blood crosses the epithelium of capillaries to enter the extracellular/interstitial compartment, and those fluids can cross the same epithelium to enter the plasma or lymph compartments. Fluid from the extracellular/interstitial compartment crosses the plasma membranes of all cells to enter the intracellular compartment, and that fluid crosses the same membrane to enter the extracellular/interstitial compartment.

8. That equilibrium changes every time - water is added (food, water, etc); or - water is lost through sweat, urine, feces, respiration, etc.

9. We gain water in a number of ways:

10. We also lose water in a number of ways:

11. In order to maintain homeostasis, the body must maintain water balance:

12. Recall that various fluid compartments are all in equilibrium with each other, so any water gain or water loss will be distributed across these.

13. Obviously, the human body must have mechanisms to regulate both water intake and water output: Since most of our water intake comes from liquids we drink, Even a modest amount of dehydration a) b) This stimulates

14. Obviously, the human body must have mechanisms to regulate both water intake and water output: Most of our water loss is urine, Even a modest amount of dehydration Through receptors in

15. Obviously, the regulation of both water intake and water loss have the same objective: Anything that increases water intake Anything that decreases water input Anything that increases water output Anything that decreases water output

16. However, it is not enough to just regulate the total volume of water in the body and in various fluid compartments. We must also regulate Many of these solutes carry electrical charges, so we call them when they are part of any body fluid. While there are dozens of electrolytes, we will focus on five as examples of different ways in which electrolytes can be regulated: Sodium (Na + )Chloride (Cl - ) Potassium (K + )Bicarbonate (HCO 3 - ) Calcium (Ca ++ )

17. Sodium and potassium are regulated together, primarily Either a decrease an increase in the blood stimulates This causes

18. If or If, then This causes

19. Blood Ca ++ level returns to normal Blood Ca ++ level continues to increase Blood Ca ++ level decreases Blood Ca ++ level returns to normal Ca ++ moved from blood to bone Ca ++ moved from bone to blood Calcium is regulated by

20. Chloride so it is normally regulated at the same time as that cation.

21. Bicarbonate is regulated Bicarbonate is formed when carbon dioxide dissolves in water so When you exhale more carbon dioxide you eliminate bicarbonate from the blood. When you exhale less carbon dioxide, you retain bicarbonate in the blood

22. Remember: this regulation maintains homeostasis: Electrolytes are being maintained within narrow limits in body fluids even when additional amounts are being added or removed from the body. For example, in the blood: - Calcium must be between 8.8 and 10.3 mg/100 ml - Chloride must be between 95 and 107 mEq/liter - Potassium must be between 3.5 and 5.2 mEq/liter

23. Unlike water, which can easily cross most membranes to move from one compartment to another, electrolytes (and other solutes such as proteins) can have very different concentrations in different fluid departments: For example: 1.

24. (electrolytes and other solutes can have very different concentrations in different fluid departments): For example: 2.

25. (electrolytes and other solutes can have very different concentrations in different fluid departments): For example: 3.

26. (electrolytes and other solutes can have very different concentrations in different fluid departments): For example: 4.

27. Remember: this regulation maintains homeostasis: Solutes are maintained within narrow limits in body fluids: Even when and Even when