1. REGULATION OF WATER & ELECTROLYTES BALANCE
by:
Husnil Kadri
Biochemistry Departement
Medical Faculty Of Andalas University
Padang

2. Maintenance of Blood Pressure Homeostasis

3. Angiotensin Pathway

4. Regulation of Water The hypothalamic thirst center is stimulated:
By a decline in plasma volume of 10%–15%
By increases in plasma osmolality of 1–2%
Via baroreceptor input, angiotensin II, and other stimuli

5. Osmoregulation Osmoreceptors:
Increase in plasma osm--> hypothalamus stimulated to release ADH (hypothalamic set point ≈ 285 mOsm/L solution)
Respond to < 2% change in plasma osmolarity

6. Regulation of Water
Thirst is quenched as soon as we begin to drink water
Feedback signals that inhibit the thirst centers include:
Moistening of the mucosa of the mouth and throat
Activation of stomach and intestinal stretch receptors

8. Regulation of Water Loss
Obligatory water losses include:
Insensible water losses from lungs and skin
Water that accompanies undigested food residues in feces
Obligatory water loss reflects the fact that:
Kidneys excrete mOsm of solutes to maintain blood homeostasis
Urine solutes must be flushed out of the body in water

9. Regulation of ADH
Factors that specifically trigger ADH release include:
prolonged fever; excessive sweating,
vomiting, or diarrhea; severe blood loss;
and traumatic burns.

10. Regulation of ADH

12. Disorders of Water Balance: Dehydration
Causes include: hemorrhage, severe burns, prolonged vomiting or diarrhea, profuse sweating, water deprivation, and diuretic abuse
Signs and symptoms: cottonmouth, thirst, dry flushed skin, and oliguria
Other consequences include hypovolemic shock and loss of electrolytes

13. Disorders of Water Balance: Edema
Atypical accumulation of fluid in the interstitial space, leading to tissue swelling
Caused by anything that increases flow of fluids out of the bloodstream or hinders their return

14. Edema
Hindered fluid return usually reflects an imbalance in colloid osmotic pressures
Hypoproteinemia – low levels of plasma proteins
Forces fluids out of capillary beds at the arterial ends
Fluids fail to return at the venous ends
Results from protein malnutrition, liver disease, or glomerulonephritis

15. Edema Blocked (or surgically removed) lymph vessels:
Cause leaked proteins to accumulate in interstitial fluid
Exert increasing colloid osmotic pressure, which draws fluid from the blood
Interstitial fluid accumulation results in low blood pressure and severely impaired circulation

16. Electrolyte Balance
Electrolytes are salts, acids, and bases, but electrolyte balance usually refers only to salt balance
Salts enter the body by ingestion and are lost via perspiration, feces, and urine

17. Sodium in Fluid and Electrolyte Balance
Sodium salts:
Account for 90-95% of all solutes in the ECF
Contribute 280 mOsm of the total 300 mOsm ECF solute concentration
Sodium is the single most abundant cation in the ECF
Sodium is the only cation exerting significant osmotic pressure

18. Sodium Reabsorption: Primary Active Transport
Sodium reabsorption is almost always by active transport
Na+ enters the tubule cells at the luminal membrane
Is actively transported out of the tubules by a Na+-K+ ATPase pump

19. Sodium Reabsorption: Primary Active Transport
From there it moves to peritubular capillaries due to:
Low hydrostatic pressure
High osmotic pressure of the blood
Na+ reabsorption provides the energy and the means for reabsorbing most other solutes

20. Regulation of Sodium Balance: Aldosterone
Sodium reabsorption
65% of sodium in filtrate is reabsorbed in the proximal tubules
25% is reclaimed in the loops of Henle
When aldosterone levels are high, all remaining Na+ is actively reabsorbed

21. Regulation of Sodium Balance: Aldosterone
Adrenal cortical cells are directly stimulated to release aldosterone by elevated K+ levels in the ECF
Aldosterone brings about its effects (diminished urine output and increased blood volume) slowly

25. Atrial Natriuretic Peptide (ANP)
Reduces blood pressure and blood volume by inhibiting:
Events that promote vasoconstriction
Na+ and water retention
Is released in the heart atria as a response to stretch (elevated blood pressure)
Has potent diuretic and natriuretic effects
Promotes excretion of sodium and water
Inhibits angiotensin II production

26. Mechanisms and Consequences of ANP Release

27. Regulatory Site Of Potassium: Cortical Collecting Ducts
Less than 15% of filtered K+ is lost to urine regardless of need
K+ balance is controlled in the cortical collecting ducts by changing the amount of potassium secreted into filtrate
When K+ levels are low, the amount of secretion and excretion is kept to a minimum

28. Influence of Aldosterone
Aldosterone stimulates potassium ion secretion by principal cells
In cortical collecting ducts, for each Na+ reabsorbed, a K+ is secreted
Increased K+ in the ECF around the adrenal cortex causes:
Release of aldosterone
Potassium secretion

29. Potassium Balance

30. Renal Potassium Handling

31. Regulation of Calcium and Phosphate
PTH promotes increase in calcium levels by targeting:
Bones – PTH activates osteoclasts to break down bone matrix
Small intestine – PTH enhances intestinal absorption of calcium
Kidneys – PTH enhances calcium reabsorption and decreases phosphate reabsorption
Calcium reabsorption and phosphate excretion go hand in hand

32. Regulation of Calcium and Phosphate
Filtered phosphate is actively reabsorbed in the proximal tubules
In the absence of PTH, phosphate reabsorption is regulated by its transport maximum and excesses are excreted in urine
High or normal ECF calcium levels inhibit PTH secretion
Release of calcium from bone is inhibited
Larger amounts of calcium are lost in feces and urine
More phosphate is retained

33. Influence of Calcitonin
Released in response to rising blood calcium levels
Calcitonin is a PTH antagonist, but its contribution to calcium and phosphate homeostasis is minor to negligible

34. Regulation of Anions
Chloride is the major anion accompanying sodium in the ECF
99% of chloride is reabsorbed under normal pH conditions
When acidosis occurs, fewer chloride ions are reabsorbed
Other anions have transport maximums and excesses are excreted in urine

35. Calcium, phosphate, and magnesium metabolism

37. Hereditary disorders of tubular transport

38. Disorders of s odium and w ater m etabolism

39. Hyponatremia and h ypernatremia

41. Reference Ivkovic, A and Dave, R. Renal review. ppt. 2008
Marieb, EN. Fluid, electrolyte, and acid-base balance. ppt. Pearson Education, Inc. 2004
Marieb, EN. The urinary system part B. ppt
Silverthorn, DU. Integrative Physiology II: Fluid and Electrolyte Balance. Chapter 20, part B. ppt. Pearson Education, Inc. 2004