Body fluid homeostasis

Body fluid volume regulation according to course curriculum of medical biochemistry for MBBS

1. BODY FLUID Dr. Farhana Atia Associate Professor Department of Biochemistry Nilphamari Medical College Nilphamari

2. Distribution of total body water TBW ECF/ICF ratio Male 60% of total body mass ECF: ICF= 1:2 Female 50% (more body fat) Newborn/ Infant 75-80% ECF= ICF ECF> ICF (intrauterine life) 42 L in 70 kg adult

3. Distribution of total body water

4. Transcellular fluid Fluid produced by the secretory activity of the lining epithelium of potential spaces of the body and is separated from plasma by a bilayer membrane consisting of a capillary endothelium & lining epithelium TCF includes CSF Synovial fluid (150 ml) Fluid of potential spaces Pleural Peritoneal Pericardial Fluid of eye

5. Water Intake Output Chart Intake Output Drinking 1400 ml Urine (Obligatory- 500 ml) 1500 ml In food & beverage 700 ml Sweat 100 ml Metabolic water 400 ml Feces 100 ml Insensible loss -Through skin (perspiration: 400 ml) -Expiration (Transpiration: 400 ml) 800 ml Total 2500 ml Total 2500 ml

6. Daily water requirement Daily water requirement in ml/kg body weight for Adult: 40-50, Children: 100, Infant: 140 Requirement is more in infant due to More basal heat production (↑ physical activity  ↑ heat evaporation  ↑ water loss) The ratio of body surface area & body weight is more  ↑ water loss through skin Renal concentrating power is less than adult Low ADH activity Short length of loop of Henle Resulting high urine output in infant

7. WATER TURNOVER It is the percentage of ECF volume that is lost and gain everyday in a normal condition. Water turnover = In adult: (2500/ 14000 X 100) 16-18% In children: 45-50% (1/2 of ECF, so easily dehydrated in diarrhea) Important during fluid & electrolyte loosing condition. Water input/output X 100 ECF volume

8. Regulation OF WATER BALANCE Both intake and loss of water are controlled by the osmotic gradient across the cell membrane in hypothalamic center Water balance is regulated by- Thirst centre ADH (Antidiuretic hormone) Other hormone Aldosterone: ↑ Na reabsorption ANP (atrial natriuretic peptide): ↑Na excretion

9. Neither water nor solute lost from body separately ADH mechanism is more sensitive than thirst mechanism ECF osmolarity is absolute predictor of routine control of water balance Hyperosmolarity of ECF is more sensitive than hypovolemia If ECF volume is decreased >10% then osmolarity is totally ignored CONTROL OF WATER BALANCE

10. Water depletion ↓ Blood volume ↑ Osmolarity Thirst centre stimulated & ↑ ADH secretion ↑ Water reabsorption in CD ↑ Water intake ↓ Water excretion ↓ Osmolarity Correction of water volume

11. Water overload ↑ Blood volume ↓ Osmolarity ↓ ADH secretion Thirst centre depressed ↓ Water reabsorption ↑ Water excretion ↓ Water intake Water overload corrected

12. VOLUME DISORDER

13. Effect of tonicity on cell volume Hypotonic Isotonic Hypertonic

14. Isotonic volume contraction Causes- Loss of isotonic fluid Massive bleeding Small intestinal content loss Small intestinal fistula Pancreatic/ biliary fistula Colostomy Ileostomy Small intestinal obstruction & paralytic ileus

15. Hypotonic volume contraction Electrolyte loss is more than fluid loss. Extra-renal cause Vomiting Excessive sweating Diarrhea Extensive dermatitis Ascites Peritonitis Acute pancreatitis Intestinal obstruction Burn

16. Hypotonic volume contraction Electrolyte loss is more than fluid loss 2. Renal cause Osmotic diuresis -DM - Mannitol Adrenocortical insufficiency Diuretics Metabolic acidosis Salt loosing nephritis Chronic renal insufficiency

17. Hypertonic volume contraction More fluid loss than electrolytes Increase loss from skin Fever Hyperthyroidism Hot environment Reduce intake Water unavailable Voluntary Coma Inability to swallow Nausea

18. Hypertonic volume contraction Increase loss from respiratory tract Hyperventilation High altitude Fever Increase loss in urine Diabetes insipidus Diabetes mellitus Chronic nephritis Drugs: Lithium Congenital

19. Isotonic volume expansion Iatrogenic: Excessive infusion of normal saline Hypertonic volume expansion Iatrogenic: Excessive infusion of Hypertonic saline

20. Hypotonic volume expansion Congestive cardiac failure Chronic liver disease Nephrotic syndrome Advance renal failure Kwashiorkor Protein loosing enteropathy

21. Basic Mechanism CCF ↓ ↓ CO ↓ ↓ ECV ↑ Renal vasoconstriction ↑ Renin secretion ↓ GFR ↓ ↑ Tubular Na, water reabsorption ↓ ↑ ADH ↓ ↑ Aldosterone ↓ Water reserve ↑ Fluid ↓ ↑ Water reabsorption ↓ ↑ Na reabsorption ↓ edema ↑ Water volume ↑ Renal retention of water

22. Nephrotic syndrome ↓ Cirrhosis ↓ ↓ Kwashiorkor ↓ ↑ protein loss ↓ ↓ protein synthesis in liver ↓ ↓ Plasma oncotic pressure ↓ plasma oncotic pressure ↓ Blood volume ↓ ↓CO ↓↓ Basic Mechanism

23. Water Intoxication Water intoxication is a potentially fatal disturbance in  brain  functions that results when the normal balance of  electrolytes  in the body is pushed outside safe limits by excessive  water  intake M ostly occurs when water is being consumed in a high quantity without adequate electrolyte intake

24. Causes of Water Intoxication Excessive intake of salt free fluid Renal failure SIADH Psychogenic polydipsia Iatrogenic – Excessive infusion of parental fluid

25. Pathophysiology of water intoxication

26. Thank You