Body Fluids. Physiology of Fluid. Body Fluids, Kidneys & Renal Physiology

Transcription

1 Pc Remember arterioles have more smooth muscle So SNS effects are greater on arterioles than on venules Net effects: SNS P c (vasoconstriction > venoconstriction) SNS P c (vasodilation > venodilation) Body Fluids, Kidneys & Renal Physiology Body Fluids Body Water (TBW) =.6 x body weight (kg) Intracellular =.4 x body weight Extracellular =. x body weight plasma = 1/3 extracellular interstitial = /3 extracellular 75 kg TBW =45 litres intra = 3 litres (⅔ of TBW) extra = 15 litres (⅓ of TBW) plasma = ~5 litres interstitial = ~1 litres Normal Daily Water Loss: 1. Insensible: Skin.4 L Respiratory tract.4 L. Sweat Normal temp.1 L Hot Temp 1.4 L 3. Feces.1 L 4. Urine 1.4 L Normal Water Intake Balances Normal Water Loss Physiology of Fluid Concentration & Osmotic Forces Concentration expressed as molarity Amount relative to molecular weight i.e glucose MW=18g/mol 1 g of glucose in 1 L of water = 1g/L / 18 g/mol =.56mol/L Osmotic Forces determined by the number of solute particles Glucose one solute particle NaCl two solute particles Osmolarity = concentration x # particles/molecule i.e 15 mmol/l solution glucose = 15 mosm 15 mmol/l solution NaCl = 3 mosm Also expressed as osmolality» Number of particles per kg of solvent (mosm/kg H ) 1

2 Plasma Major ionic components are Na +, Cl -, HCO 3 - Plasma osmolality x [Na+] plasma 9 mosm/kg H.9% NaCl solution = Iso-osmotic Any solution < 9 mosm = hypo-osmotic Any solution > 9 mosm = hyper-osmotic Tonicity Tendency of a solution to cause cells to swell or shrink Very important because water moves into and out of cells under osmotic pressure and is not actively transported by pumps Isotonic no effect on cell -.9% NaCl Hypotonic cause cell to swell <.9% NaCl Hypertonic cause cell to shrink >.9% NaCl Under normal circumstances ExtraCellular Fluid (ECF) and IntraCellular Fluid (ICF) are at osmotic equilibrium Changes in osmotic forces lead to a new osmotic equilibrium within ~1 minute Calculating changes in ICF and ECF as fluids are added or removed 1. If iso-osmotic fluid added there is no change in ICF, only an increase in ECF since there is no osmotic effect. If hypo- or hyper-osmotic fluid added then ICF and ECF redistribute to get a new osmotic equilibrium Effect of adding 1 L of water (i.e hypo-osmotic) Body Water Intracellular Extracellular mosm /L Effect of adding L of 4.5% NaCl (i.e hyper-osmotic) Body Water Intracellular Extracellular mosm /L Initial Initial Sol n added 1 1 Sol n added Instant effect Instant effect After osmotic equil After osmotic equil [ ]=116 / 5 = 3 FVxFC=SVxSC Vol FVx3=x9 =754 / FV = = Vol =46 / 3 = 17.5 [ ]=145 / 4 = FVxFC=SVxSC Vol FVx=x9 =754 / FV = = 3.5 Vol FVxFC=SVxSC =46 / FVx=16x435 = 17.5 FV =

3 The Kidney Therefore, 1. hyposmotic solution will be distributed into the intracellular and extracellular space. hypersmotic solution will remove solution from intracellular and bring it to extracellular space 1. Regulation of water & ion balance. Removal of waste from blood & excretion in urine 3. Hormone/enzymes production: a) 1,5 dihydroxyvitamin D b) Renin an enzyme important for Angiotensin II production blood pressure, Na+ regulation The outer layer is the renal cortex; and it contains the sites of filtration and the convoluted tubules. The functional unit in the kidney The inner part of is the renal medulla; this is the location of the longer loops of Henle, and the drainage of the collecting ducts into the renal pelvis and ureter. Proximal tubule Bowman s capsule Bowman s space Blood flow Blood flow The intersection of the macula densa in the distal tubule with the afferent and efferent arterioles forms the juxtaglomerular apparatus, which secretes renin into blood in the afferent arteriole. 3

4 artery Afferent arteriole Glomerular capillary Efferent arteriole Steps in urine formation Bowman s space Peritubular capillary 1. Filtration. Secretion 3. Reabsorption 4. Excretion (urine) 1 3 vein tubule 4 Basic Renal Processing General strategy Everything but cells and protein gets filtered into Bowman s space (called glomerular filtrate) Flitrate has the same substances at same concentrations as plasma Further along tubule, substances are added (secretion) or removed (reabsorption) Amount excreted = amount filtered + amount secreted amount reabsorbed 1. Filtered and secreted; not reabsorbed 3. Filtered and completely reabsorbed For each substance in plasma there is some combination of filtration, reabsorption and secretion For many substances (eg, Na+, Ca++, water) these processes are under physiological control. Filtered, some reabsorbed, some excreted 4

5 Glomerular Filtration Capillary Fenestra allow movement from plasma to Bowman s space Glomerular Filtration A bulk flow process Glomerular Filtration Pressure GFP= ((P GC -P BS )-(π GC - π BS )) P GC P Bs π GC π BS GFP=(6-15)-(9) = 16 mmhg Usually Positive pressure indicates filtration Role of hydrostatic pressure in controlling GFP Glomerular Filtration Rate (GFR) Function of: 1. Filtration pressure. Permeability of substance 7 kg person GFR water = 18 L/day (15 ml/min) 1. P BC primarily a function of the tubules & ureters; movement of fluid through the system keeps P BC low. P GC a function of blood in glomerular capillary Afferent and efferent arterioles may be regulated independently Function of R eff / R aff Constriction of afferent flow into glomerular capillary therefore P GC Constriction of efferent flow out of glomerular capillary therefore P GC Opposites for dilation 5

6 6