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REGULATION OF WATER & ELECTROLYTES BALANCE

REGULATION OF WATER & ELECTROLYTES BALANCE. by: Husnil Kadri Biochemistry Departement Medical Faculty Of Andalas University Padang. Maintenance of Blood Pressure Homeostasis. Angiotensin Pathway. Regulation of Water. The hypothalamic thirst center is stimulated:

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REGULATION OF WATER & ELECTROLYTES BALANCE

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  1. REGULATION OF WATER &ELECTROLYTES BALANCE by: HusnilKadri 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

  7. 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 900-1200 mOsm of solutes to maintain blood homeostasis • Urine solutes must be flushed out of the body in water

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

  9. Regulation of ADH

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. Mechanisms and Consequences of ANP Release

  22. 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

  23. 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

  24. Potassium Balance

  25. Renal Potassium Handling

  26. 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

  27. 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

  28. 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

  29. 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

  30. Calcium, phosphate, andmagnesium metabolism

  31. Hereditary disorders of tubular transport

  32. Disorders of s odium and w ater m etabolism

  33. Hyponatremia and h ypernatremia

  34. 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. 2004. • Silverthorn, DU. Integrative Physiology II: Fluid and Electrolyte Balance. Chapter 20, part B. ppt. Pearson Education, Inc. 2004

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