Water, Electrolyte, and Acid-Base Balance

1. Water, Electrolyte, and Acid-Base Balance

2. Function of Water: Most of cellular activities are performed in water solutions.

3. 4% TBW 40%TBW Body Fluid - makes up ~60% of total body weight (TBW) - distributed in three fluid compartments. 16% TBW

4. 4% TBW 40%TBW Fluid is continually exchanged between the three compartments. 16% TBW

5. 4% TBW 40%TBW Exchange between Blood & Tissue Fluid • - determined by four factors: • capillary blood pressure • plasma colloid osmotic pressure • interstitium Hydrostatic Pressure • Interstitium colloid osmotic pressure 16% TBW

6. 4% TBW 40%TBW Exchange between Blood & Tissue Fluid - not affected by electrolyte concentrations - Edema = water accumulation in tissue fluid 16% TBW

7. 4% TBW 40%TBW Exchange between Tissue Fluid & Intracellular Fluid • - determined by two: • 1) intracellular osmotic pressure • electrolytes • 2) interstitial osmotic pressure • electrolytes 16% TBW

8. Water Gain Water is gained from three sources. 1) food (~700 ml/day) 2) drink – voluntarily controlled 3) metabolic water (200 ml/day) --- produced as a byproduct of aerobic respiration

9. Routes of water loss 1) Urine – obligatory (unavoidable) and physiologically regulated, minimum 400 ml/day 2) Feces -- obligatory water loss, ~200 ml/day 3) Breath – obligatory water loss, ~300 ml/day 4) Cutaneous evaporation -- obligatory water loss, ~400 ml/day 5) Sweat – for releasing heat, varies significantly

10. Regulation of Water Intake - governed by thirst. blood volume and osmolarity  peripheral volume sensors central osmoreceptors  hypothalamus  thirst felt

11. Regulation of Water Output - The only physiological control is through variations in urine volume. - urine volume regulated by hormones

12. 1) ADH dehydration  blood volume and/or osmolarity  hypothalamic receptors / peripheral volume sensors  posterior pituitary to release ADH   H2O reabsorption  Water retention

13. 2) Atrial Natriuretic Factor  blood volume  atrial volume sensors  atria to release ANF  inhibits Na+ and H2O reabsorption   water output

14. Dehydration • - decrease in body fluid • Causes • the lack of drinking water • 2) excessive loss of body fluid due to: • overheat • diabetes • overuse of diuretics • diarrhea

15. Edema • - the accumulation of fluid in the interstitial spaces • caused by: • increased capillary filtration, • or • 2) reduced capillary reabsorption, or • 3) obstructed lymphatic drainage

16. ELECTROLYTE BALANCE

17. Electrolytes = smallions that carry charges

18. Major cations • Na+ • K+ • Ca++ • H+ • Major anions • Cl- • HCO3- • PO4---

19. Distribution of Electrolytes Na+ K+ Ca++ Cell PO4--- Cl- Extracellular space

20. Na+ K+ Ca++ Cell PO4--- Cl- • SodiumNa+ • Functions • - involved in generating action membrane potential of cells • make a major contribution to extracellular osmolarity.

21. Regulation of plasma Na+ • Aldosterone Na+ • plasma Na+ •   aldosterone •  • renal Na + excretion   plasma Na + plasma

22. Renin-angiotensin-II renin •  • angiotensin-II •   aldosterone •   renal Na+ excretion   plasma Na+ Na+ plasma

23. 3) ADH increases water reabsorption in kidneys  water retention  dilute plasma Na+ H2O Na+ plasma

24. Atrial Natriuretic Factor • inhibits renal reabsorption of Na+ and H2O and the excretion of renin and ADH •  • eliminate more sodium and water •   plasma Na + Na+ plasma Na+

25. Sodium imbalance • hypernatremia • plasma sodium > 145 mEq/L, • hyponatremia • plasma sodium < 130 mEq/L

26. Na+ K+ Ca++ Cell PO4--- Cl- Potassium Functions - the greatest contributor to intracellular osmosis and cell volume - determines the resting membrane potentials - an essential cofactor for protein synthesis and some other metabolic processes. K+

27. Regulation of Potassium • by aldosterone • Aldosterone •  • stimulates K+ • secretion by the kidneys •  •  Plasma K+ K+ plasma K+

28. Potassium Imbalance • hyperkalemia (> 5.5 mEq/L) • hypokalemia (< 3.5 mEq/L)

29. Na+ K+ Ca++ Cell PO4--- Cl- Chloride - makes a major contribution to extracellular osmolarity - required for the formation of stomach acid (HCl)

30. Regulation of Cl– • No direct regulation • indirectly regulated as an effect of Na+ homeostasis. As sodium is retained or excreted, Cl– passively follows. • Chloride Imbalance • hyperchloremia (> 105 mEq/L) • hypochloremia (< 95 mEq/L).

31. Na+ K+ Ca++ Cell PO4--- Cl- Calcium

32. Functions of Ca++ • - lends strength to the skeleton

33. Functions of Ca++ • - lends strength to the skeleton • - activates muscle contraction [ Ca++ ]i Contraction Excitation (Action Potentials) (shortening)

34. Functions of Ca++ • - lends strength to the skeleton • - activates muscle contraction • - serves as a second messenger for some hormones and neurotransmitters

35. Functions of Ca++ • - lends strength to the skeleton • - activates muscle contraction • - serves as a second messenger for some hormones and neurotransmitters • - activates exocytosis • of neurotransmitters and • other cellular secretions

36. Functions of Ca++ • - lends strength to the skeleton • - activates muscle contraction • - serves as a second messenger for some hormones and neurotransmitters • - activates exocytosis of neurotransmitters and other cellular secretions • - essential factor • in blood clotting.

37. Functions of Ca++ • - lends strength to the skeleton • - activates muscle contraction • - serves as a second messenger for some hormones and neurotransmitters • - activates exocytosis of neurotransmitters and other cellular secretions • - essential factor in blood clotting. • - activates many cellular • enzymes

38. Dynamics of Calcium Ca++ Ca++ Ca++ plasma Ca++

39. Regulation of calcium • 1) parathyroid hormone (PTH):

40. Regulation of calcium • 1) parathyroid hormone (PTH): • - dissolving Ca++ in bones • - reducing renal excretion of Ca++ Ca++ Ca++ plasma

41. 2) calcitonin (secreted by C cells in thyroid gland):

42. 2) calcitonin (secreted by C cells in thyroid gland): depositing Ca++ in bones Ca++ Ca++ plasma

43. 3) calcitrol (derivative of vitamin D): - enhancing intestinal absorption of Ca++ from food Ca++ Ca++ plasma Ca++

44. Calcium imbalances • hypocalcemia (< 4.5 mEq/L) • hypercalcemia (> 5.8 mEq/L).

45. Phosphates • needed for the synthesis of: • ATP, GTP • DNA, RNA • phospholipids

46. Regulation of Phosphate • by parathyroid hormone • PTH •  • increases renal excretion of phosphate •  • decrease plasma phosphate • - no real phosphate imbalances PO4--- plasma PO4---

47. ACID-BASE BALANCE

48. Acid An acid is any chemical that releases H+ in solution. Base A base is any chemical that accepts H+.

49. pH is the negative logarithm of H+ concentration, and an indicator of acidity.   pH = - log [H+ ] Example: [H+ ] = 0.1 M = 10 –7 M

50. pH is the negative logarithm of H+ concentration, and an indicator of acidity.   pH = - log [10 –7] = 7 log 10 = 7 Example: [H+ ] = 0.1 M = 10 –7 M