Blood & Body Fluid Volumes PDF

# Blood & Body Fluid Volumes ## **Blood Volume** * Constitutes small fraction of total body fluid * 2/3 of body H₂O is inside cells (intracellular compartment) * 1/3 total body H₂O is in extracellular compartment * 80% of * Intracellular 27-30 L * Extra...

# Blood & Body Fluid Volumes ## **Blood Volume** * Constitutes small fraction of total body fluid * 2/3 of body H₂O is inside cells (intracellular compartment) * 1/3 total body H₂O is in extracellular compartment * 80% of * Intracellular 27-30 L * Extracellular 14-16.5 L * Water excretion per 24 hrs * *Fig 14.8* - Shows the distribution of water between the intracellular and extracellular compartments ## **Exchange of Fluid between Capillaries & Tissues** * Distribution of ECF between blood & interstitial compartments is in state of dynamic equilibrium * Movement out of capillaries is driven by hydrostatic pressure exerted against capillary wall * Promotes formation of tissue fluid * **Net filtration pressure** = hydrostatic pressure in capillary (17-37 mmHg) - hydrostatic pressure of ECF (1 mmHg). ## **Exchange of Fluid between Capillaries & Tissues** * Movement also affected by colloid osmotic pressure * osmotic pressure exerted by proteins in fluid * Difference between osmotic pressures in & outside of capillaries (oncotic pressure) affects fluid movement * Plasma osmotic pressure = 25 mmHg; interstitial osmotic pressure = 0 mmHg ## **Overall Fluid Movement** * is determined by net filtration pressure & forces opposing it (Starling forces) * - P_c + Π_i(fluid out) - P_i + Π_p (fluid in) * P_c = Hydrostatic pressure in capillary * Π_i = Colloid osmotic pressure of interstitial fluid * P_i = Hydrostatic pressure in interstitial fluid * Π_p = Colloid osmotic pressure of blood plasma * *Fig 14.9* - A diagram showing fluid moving out of the arterial end of a capillary and into the venous end. * Arterial end of capillary (P_c + Π_i) − (P_i + Π_p) (Fluid out) (37 + 0) – (1 + 25) = 11 mmHg Net filtration * Venous end of capillary (P_c + Π_i) − (P_i + Π_p) (Fluid in) (17 + 0) – (1 + 25) = -9 mmHg Net absorption ## **Edema** * Normally filtration, osmotic reuptake, & lymphatic drainage maintain proper ECF levels * Edema is excessive accumulation of ECF resulting from: * High blood pressure * Venous obstruction * Leakage of plasma proteins into ECF * Myxedema (excess production of glycoproteins in extracellular matrix) from hypothyroidism * Low plasma protein levels resulting from liver disease * Obstruction of lymphatic drainage ## **Regulation of Blood Volume by Kidney** * Urine formation begins with filtration of plasma in glomerulus * Filtrate passes through & is modified by nephron * Volume of urine excreted can be varied by changes in reabsorption of filtrate * Adjusted according to needs of body by action of hormones ## **ADH (vasopressin)** * ADH released by Post Pit when osmoreceptors detect high osmolality * From excess salt intake or dehydration * Causes thirst * Stimulates H₂O reabsorption from urine * ADH release inhibited by low osmolality ## **Aldosterone** * Is steroid hormone secreted by adrenal cortex * Helps maintain blood volume & pressure through reabsorption & retention of salt & water * Release stimulated by salt deprivation, low blood volume, & pressure ## **Renin-Angiotensin-Aldosterone System** * When there is a salt deficit, low blood volume, or pressure, angiotensin II is produced * Angio II causes a number of effects all aimed at increasing blood pressure: * Vasoconstriction, aldosterone secretion, thirst ## **Angiotensin II** * Fig 14.12 shows when & how Angio II is produced, & its effects * *Fig 14.12* - A flow chart diagram showing how angiotensin II is produced and the effects it has on the human body ## **Atrial Natriuretic Peptide (ANP)** * Expanded blood volume is detected by stretch receptors in left atrium & causes release of ANP * Inhibits aldosterone, promoting salt & water excretion to lower blood volume * Promotes vasodilation