Homeostasis: Regulation Of Body Water & Electrolyte Balance (PDF)

Homeostasis: REGULATION OF BODY WATER & ELECTROLYTE BALANCE Mohamad Razif bin Othman PRH 1016  Previously on Homeostasis Pt 1 + Introduction + Negative feedback + Body temperature regulation + Blood glucose regulation  Importance of body water + Average percentage 60%, can vary roughly from 45...

Homeostasis: REGULATION OF BODY WATER & ELECTROLYTE BALANCE Mohamad Razif bin Othman PRH 1016  Previously on Homeostasis Pt 1 + Introduction + Negative feedback + Body temperature regulation + Blood glucose regulation  Importance of body water + Average percentage 60%, can vary roughly from 45 – 75 % Functions as: + Protecting the spinal cord and other sensitive tissues + Removing waste by urination, sweating, and bowel movements + Regulating body temperature + Lubricating and cushioning joints + Provides an optimum medium for cells to function + Provides a medium for chemical reaction + Breaks down food particles in the digestive system Body fluid compartments Body fluid compartments  Fluid Balance + 2 barriers separate Intra Cellular Fluid (ICF) and Extracellular fluid (EF), which contains interstitial fluid (IF) and plasma. Barrier between ICF and EF: plasma membrane Barries between IF and plasma: capillary membrane + Body is in fluid balance when required amounts of water and solutes are present and correctly proportioned among compartments + Continuous exchange of water (solvents) and solutes among compartments through process of filtration, reabsorption, diffusion, and osmosis Daily water gain and loss Regulation of body water gain + Mainly by volume of water intake + Dehydration – when water loss is greater than gain + Decrease in volume, increase in osmolarity of body fluids + Stimulates thirst center in hypothalamus  Kidneys + Main organ involved: 2 kidneys (left & right) Involved in body water regulation (urine formation) Also involved in electrolyte balance  Nephron Nephron is the functional unit of the kidney: Has a number of functionally distinct parts Each human kidney has about one million nephrons Urine is manufactured by the nephrons  Nephron: Parts & Function + Glomerulus: acts as filter of blood + Proximal convoluted tubules: reabsorption of glucose, salts and amino acids + Loop of Henle: reabsorption of water and salts + Distal convoluted tubules: reabsorption of salts + Collecting duct: reabsorption water and salts + Large volume of filtrate produced (180 litre/day). + How much is secreted out? + The higher than normal filtration at the glomerular capillaries in the glomerulus is known as ultrafiltration  Hormone Regulating Water Balance + Main hormone: Antidiuretic hormone (ADH) + Produced by hypothalamus, released from posterior pituitary + Increases tubules permeability to water + Acting mainly on distal tubules & collecting duct of a nephron + More ADH released, less urine (concentrated urine) Factors That Maintain/Regulate Body Water balance Regulation Of Water Output Obligatory water losses + Insensible water loss: from lungs and skin + Faeces + Minimum daily sensible water loss of 500 ml in urine to excrete wastes Body water and Na+ content are regulated in tandem by mechanisms that maintain cardiovascular function and blood pressure  REGULATION OF WATER OUTPUT: INFLUENCE OF ADH + Water reabsorption in collecting ducts is proportional to ADH release + Low ADH resulted in diluted urine and low volume of body fluids, high ADH makes concentrated urine + Hypothalamic osmoreceptors trigger or inhibit ADH release + Other factors may trigger ADH release via large changes in blood volume or pressure, e.g., fever, sweating, vomiting, or diarrhea; blood loss; and traumatic burns DISORDERS OF WATER BALANCE: DEHYDRATION + Dehydration Due to extra cellular fluid (ECF) water loss Causes by: haemorrhage, severe burns, prolonged vomiting or diarrhea, water deprivation, diuretic abuse, excessive perspiration + Signs and symptoms: thirst, dry flushed skin, oliguria May lead to weight loss, fever, mental confusion, hypovolemic shock, and loss of electrolytes  If water is lost, but electrolytes retained: ECF osmotic concentration (osmolarity) rises Water moves from (intra cellular) ICF to (extra cellular) ECF in a fluid shift Both ECF and ICF will be slightly more concentrated than before but they will be osmotically balanced Net change in ECF is small Homeostatic responses (Triggers increase in ADH release) will occur to replace lost water If water is gained, but electrolytes are not: ECF is at lower osmotic concentration, higher volume Homeostatic responses: Triggers decrease in ADH release, fluid is lost (via urine) and ICF will lose some water back to ECF, restoring both volume and concentration balance  ELECTROLYTES IN BODY FLUIDS Ions form when electrolytes dissolve and dissociate 4 general functions: I. Control osmosis of water between body fluid compartments II. Help maintain the acid-base balance III. Carry electrical current IV. Serve as co-factors MOVEMENT OF WATER BETWEEN COMPARTMENTS + Normally, cells neither shrink or swell because intracellular and interstitial fluids have the same osmolarity Increasing osmolarity of interstitial fluid draws water out of cells and cells shrink Decreasing osmolarity of interstitial fluid causes cells to swell Changes in osmolarity most often result from changes in Na+ concentration ICF DIFFERS CONSIDERABLY FROM ECF + ECF most abundant cation is Na+, anion is Cl- + ICF most abundant cation is K+, anion are proteins and phosphates (HPO42-) + Na+ /K+ ion pumps play major role in keeping K+ high inside cells and Na+ high outside cell  Most abundant ion in ECF 90% of extracellular cations SODIUM, NA+ Plays important role in fluid and electrolyte balance because it account for almost half of the osmolarity of ECF Level of Na+ in blood is controlled by: Aldosterone – increases in renal reabsorption ADH – if sodium too low, ADH release stops Atrial natriuretic peptide (ANP) – increases renal Na+ excretion  + Most prevalent anions in ECF + Can help balance levels of anions in CHLORIDE, CL- different fluids + Regulated by ADH – governs extent of water loss in urine Processes that increase or decrease renal reabsorption of Na+ also affect reabsorption of Cl-  + Most abundant cations in ICF POTASSIUM, K+- + Key role in establishing resting membrane potential in neurons and muscle fibers + Also helps maintain normal ICF fluid volume, regulation of pH + Controlled by aldosterone – stimulates principal cells in renal collecting ducts to secrete excess K+  DANGERS OF TOO MUCH WATER + How much is too much? + When you drink more water than your kidneys can get rid off via urine. + This water can dilute the electrolytes in your blood, especially sodium. When sodium levels fall below 135 mmol/L, it is called hyponatremia. Your kidneys can eliminate about 20-28 liters of water a day, but they can't get rid of more than 0.8-1.0 liters per hour SERIES OF EVENTS IN WATER INTOXICATION DIALYSIS END OF HOMEOSTASIS.