HA&PII Fluid Balance Weekly Notes
HA&PII Fluid Balance Weekly Notes Biol 2230-001
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This 7 page Class Notes was uploaded by Victoria Hills on Sunday April 24, 2016. The Class Notes belongs to Biol 2230-001 at Clemson University taught by Dr. John Cummings in Fall 2015. Since its upload, it has received 11 views. For similar materials see Human Anatomy & Physiology II in Biology at Clemson University.
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Date Created: 04/24/16
Fluid Balance Slide 1: Introduction • Kidney maintains fluid, electrolyte, and acid-base balance that are all related to blood pressure • 50-60% of the fluid can vary based on many factors -‐ Ex: Increasing age leads to a lower fluid composition • Most of the body is made up of water à Important to maintain homeostatic balance with fluids in order for the body to function properly • Relationship between fluid composition and: a) Body mass: -‐ The more muscle mass, the greater the fluid composition b) Gender: -‐ Testosterone promotes the most development in muscles à Males have a higher fluid composition than females as a result c) Adipose tissue: -‐ As body fat composition increases, the amount of water decreases -‐ Relates to gender difference also à Women have more adipose mass and therefore, less fluid composition Slide 2/3: Fluid Compartments • Intracellular compartment: -‐ Cytoplasm in the cell is a fluid -‐ For substances such as enzymes to be biologically active, that have to be in solution -‐ 2/3 of the fluid in the body is inside cells à Intracellular compartment have the majority of fluid in our bodies • Extracellular compartment: -‐ Fluid outside of cells that makes up 1/3 of the fluid composition of the body -‐ Includes interstitial fluid in the interstitial space and plasma inside blood vessels -‐ Majority of the extracellular fluid is located in the interstitial space • Fluid is able to change and move from one place to another in these 3 total compartments (Intracellular, interstitial, and plasma) • The exchange in fluids starts with fluid leaving the cell à Interstitial space à blood plasma (And can go the opposite way too) Slide 4/5/6: Composition a) Most of the fluid in our bodies is made up of water -‐ Water is a universal solvent that is required for biological activity -‐ Solutes are dissolved inside the water b) Nonelectrolytes -‐ Organic compounds such as glucose and lipids that do NOT dissociate in water -‐ They can still be in water and be transported around c) Electrolytes -‐ Substances that dissociate in water into ions -‐ Includes mostly inorganic substances such as salts, acids, bases, and even proteins -‐ Anything contained within the water can create an osmotic gradient -‐ Selectively permeable membrane: o Surrounds cells o More substances on one side of the selectively permeable membrane draws water to that side o When electrolytes dissociate, the increased number of particles increases the osmotic potential -‐ Electrolytes generally generate the greatest osmotic potential due to their dissociation properties -‐ Ex: Water is drawn back out of the ascending limb of the Loop of Henle due to sodium -‐ Overall: Electrolytes create an osmotic gradient and water follows Slide 7: Composition of Electrolytes • Electrolytes and fluid composition varies from place to place in the intracellular fluid, interstitial fluid, and blood plasma • Selectively permeable membrane surrounds cells so that there is a difference in fluid composition on the inside and outside of cells • For the extracellular fluid compartment, including the interstitial fluid and plasma, the composition is the same in most places of the body for electrolytes -‐ Difference between the plasma and the interstitial fluid is due to proteins that can’t get across the membranes of the capillaries so that they are stuck in circulation and therefore higher in the plasma à Otherwise electrolyte same in the 2 parts of the extracellular • Sodium is higher in the extracellular compartment, while potassium is higher in the intracellular compartment -‐ Relates to regulation of a resting membrane potential -‐ Permeability changes for sodium so that it gets into the cell -‐ Point: Have an unequal distribution of ions and can move them to create an osmotic gradient to cause water to follow • Summary: -‐ Extracellular fluid compartment is the same -‐ Ionic composition varies from one part of the body to another -‐ Exception: Proteins are so large that they have to stay in the plasma portion Slide 8: Fluid Movement • The movement of fluid is regulated by 2 forces: a) Hydrostatic pressure: -‐ Blood pressure) b) Colloid osmotic pressure: -‐ Concentration gradient that draws water across a membrane • Osmotic gradients cause substances to move so that water moves from a hypotonic (Are of less solute concentration) to a hypertonic (Area of higher solute concentration) • Hydrostatic pressure pushes water across the filtration membrane in the kidney • Hydrostatic and colloid osmotic pressure work together • Between the plasma and into the interstitial fluid (Coming out of the blood stream): -‐ Hydrostatic pressure is the most important force in making this happen -‐ Proteins will NOT pass out of the capillary as blood is flowing -‐ Most of the fluid that passes out of the capillary into the interstitial space makes its way back into the capillary on the other side of the capillary bed • Between the plasma and into the intracellular space: -‐ Colloid osmotic pressure is the most important force in making this happen -‐ Hydrostatic pressure plays a minor role • As fluid starts moving from one compartment to another, it’s important to regulate and maintain fluid balance Slide 9: Water Balance • Generally, water in = water out and we lose • Water intake: -‐ Sources of fluid/water come from liquids and food + water is a result of metabolic activity -‐ As glucose is broken down to liberate energy through cellular respiration à Carbon dioxide and water are by products • Water output: -‐ Vaporization: Water vapor that is in our breath as we exhale -‐ Perspiration: Secrete water onto the body surface so that it evaporates off -‐ Feces contains a certain amount of water that is lost when defecation occurs (Elimination) -‐ Lose water through urination Slide 10: Regulation Mechanisms • Body operates to maintain homeostatic water balance • An increase in plasma osmolarity à Blood is more concentrated with more solute in it -‐ One way to get more solutes in the blood is to decrease the amount of water (Decreased blood volume) -‐ Low blood volume and high osmolarity is detected by the brain via a signal that activates the thirst center à Drink water as a response • Decrease in extracellular fluid osmolarity: -‐ Loop of Henle: o Fluid is located outside before it moves back into the vasa recta -‐ Decreased ADH production: o Creates a more dilute urine so that more water stays in the distal convoluted tubule and and isn’t reabsorbed back into the body • Large decrease in blood pressure à ADH production increases so the aquaporins open à Increases water reabsorption to increase blood volume • Summary for water regulation: Thirst is stimulated to bring more water into the body or reabsorption of water is regulated in the kidneys Slide 11: Electrolyte Balance • Electrolyte intake: -‐ Dietary sources -‐ Metabolic production o Ex: Breakdown nucleic acids and other components à Electrolytes • Electrolyte output: -‐ Perspiration -‐ Elimination -‐ Urination -‐ Vomiting à Extreme case that forces loss of electrolytes -‐ *Don’t lose electrolytes via vaporization when breathing occurs Slide 12: Sodium • Sodium is at its highest concentration in the extracellular compartment • Plays large role in creating osmotic gradients Slide 13: Sodium Regulation • Sodium plays a role in blood pressure regulation due to playing a role in blood volume regulation • Most critical of all electrolytes in creating and maintain osmotic gradients à As a result, this means that there are NO chemoreceptors specific to sodium • Monitoring blood pressure activates sodium regulation • Changes in blood pressure à changes what happens to sodium • 99% of sodium is reabsorbed back into the blood • 90% of sodium reabsorption occurs naturally in the proximal convoluted tubule • Remaining 9% of sodium reabsorption depends on the body’s needs and the variability is controlled by hormones + other factors: a) Aldosterone: -‐ Increases sodium reabsorption -‐ Most important mechanism for sodium -‐ Aldosterone synthesis is stimulated by renin angiotensin mechanism o Production of renin is regulated by the juxtaglomeruluar cells that detect blood pressure levels in the afferent arteriole o Ex: If blood pressure is low in the afferent arteriole à Secretion of renin occurs à Increase in aldosterone production that stimulates the reabsorption of sodium à Increased water reabsorption à Increase in blood volume à Blood pressure increased -‐ Aldosterone can be fined tuned by ADH production b) Cardiovascular baroreceptors: -‐ Detect pressure -‐ High blood pressure activates the cardiovascular baroreceptors à Causes increase in systemic blood pressure à Response of decreased sympathetic stimulation to the kidneys so that epinephrine (Vasoconstrictor) shuts off à Dilation of the afferent arteriole à Increased filtration rate à More sodium and water is moved out of the blood (More filtrate produced) à More urine produced -‐ *Cardiovascular baroreceptors increase filtration rate and NOT cause changes in reabsorption -‐ When blood pressure starts dropping due to loss of blood volume, the cardiovascular baroreceptors shut off and sympathetic nervous stimulation will start again à Contraction of arteriole (Self regulating pathway) c) Atrial natriuretic peptide: -‐ Produced by the heart when the heart muscle itself is stretched due to high blood pressure -‐ ANP is a vasodilator à Filtration increases à Urine output increases -‐ ANP suppresses ADH and renin à Suppression of sodium reabsorption -‐ Overall: Decrease in blood pressure as a result d) Estrogen: - Promotes sodium reabsorption à Water follows à Water retention produced as a result e) Glucocortiocoids: - Produced in the adrenal cortex to fight stress à Promotes sodium reabsorption à High blood pressure Slide 14: Acid- Base Balance • There are many factors that regulate acid-base balance • Each enzyme in the body as an optimal pH under which it will perform and it’s important to maintain this pH or enzymatic activity will be lost • Blood pH: 7.35-7.4 (Slightly basic) • pH of intracellular compartment: ~7 à Neutral but the inside of cells are more acidic than the plasma • pH between blood and cells • Oxidation of glucose results in the production of carbon dioxide that accumulates in a cell and acts as an acid to lower the pH • Certain metabolites produced in a cell can reduce the pH • Most of the substances ingested in the body are on the acidic side • Blood pH is maintained on the basic side despite ingestion of acids à There are mechanisms to maintain this so that everything functions how it’s supposed to Slide 15: Sources of H+ • Most of the metabolic pathways are involved in REDOX reactions which has to do with the transfer of H+ • Relates to abnormalities of pH Slide 16: Abnormalities • Acidosis: -‐ Decrease in blood pH -‐ 2 forms: a) Respiratory acidosis: o Caused by accumulation of carbon dioxide that acts as an acid o Slow breathing b) Metabolic acidosis: o Accumulation of acids • Alkalosis: -‐ Increase in blood pH -‐ 2 forms: a) Respiratory alkalosis: o When more carbon dioxide is rid of more than normal o Hyperventilation b) Metabolic alkalosis: o Accumulation of bases Slide 17: Regulation • Chemical buffer systems à Where compounds that act as proton acceptors or donors temporarily bind to acids or bases to remove them (Temporarily takes them out of solution) -‐ Types: a) Bicarbonate buffer system: o Can accept or donate H+ for temporary binding o Functions mostly in the extracellular compartment b) Phosphate buffer system: o Action occurs inside the cells o Phosphate accepts or donates H+ to regulate pH c) Protein buffer system: o Better than bicarbonate and phosphate buffer systems (Most important) o Temporarily bind and do NOT eliminate o Amphoteric molecules: § Function as an acid or base § Proteins à Long chains of amino acids that have different compositions + part of the protein can be acidic or basic § Ex: Hemoglobin • Physiological buffer systems: -‐ Eliminates excess acid -‐ Functions via respiratory exchange breathing -‐ Takes care of carbon dioxide + other acids -‐ Slower to act than chemical buffer systems, but it is more efficient since they eliminate excess acid and not just temporarily remove it -‐ Types: a) Respiratory mechanisms: o Body responds to changes in pH o Blood pH increases à Breathing rate decreases to accumulate carbon dioxide in blood that can act as an acid à Decrease blood pH o Blood pH decreases à Breathing rate increases à Increase blood pH • Renal mechanisms: -‐ Permanently eliminates all acids other than carbon dioxide -‐ Types: a) Reabsorbing bicarbonate: o Comes out of the filtrate and into the tubule à Can reabsorb bicarbonate to get it back into solution b) Bicarbonate synthesis: o In addition to reabsorbing bicarbonate when more is needed, the kidney is able to make bicarbonate c) Bicarbonate excretion: o Can permanently eliminate bicarbonate when there is too much bicarbonate in the blood
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