WSU BIOLOGY 251 - Fluid & Ion Balance (5 pages)

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Fluid & Ion Balance

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Fluid & Ion Balance


Topic 22-Fluid & Ion Balance

Lecture number:
Lecture Note
Washington State University
Biology 251 - Introductory Human Physiology
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BIO 251 1st Edition Lecture 22 Outline of Last Lecture I Tubular reabsorption a Process b Reabsorption of Ba in proximal tubule c Reabsorption of Na in distal tubule d Reabsorption of substances via Na dependent secondary active transport e Reabsorption of substances via Na dependent passive processes f II Reabsorption of phosphate Tubular secretion a H b K c Waste ions III Urine concentration a Countercurrent multiplication b Controlling urine concentration Outline of Current Lecture I Input output of fluids ions a Balance concept b Types of input output These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II Fluid ion distribution in body a Fluid compartment within body b Ion distribution c Mvmt of water ions w I ECF d Regulation of fluid ion distrb III Regulation of ECF volume a Na balance b Mechanisms regulating Na in kidney c Control of Na reabsorption IV Regulation of ECF osmolarity a Purpose b How ECF effects ICF c Mechanisms of water reg Current Lecture I Input and Output of Fluids and Ions A Balance concept Fig 19 2 1 If the amount of fluids ions are to remain stable in body input must equal output 2 Not all input and output pathways are regulated a most input pathways are poorly regulated 1 people will eat drink what they want even if they don t need it 2 H ions are uncontrollably produced internally b some output poorly regulated 1 Salt water and H are lost uncontrollably through vomiting and sweating c Humans regulate water salt and H balances primarily through kidney function B Types of input and output Fig 19 1 19 3 1 Input a From Environment 1 ingestion inhalation absorption b Metabolically produced 1 products e g amino acids and by products e g H and water of metabolic processes 2 Output a Excretion to environment 1 through kidneys digestive tract lungs body surface e g urine feces sweat water vapor in breath sloughed off skin b Metabolically consumed II Fluid and Ion Distribution in Body review from Topic 1 A Fluid Compartments within Body Fig 1 5 1 Intracellular Fluid ICF a within cells 2 Extracellular Fluid ECF a outside cells b further compartmentalized into 1 Plasma 2 Interstitial fluid 3 Boundry is capillary walls 3 Boundry between ECF and ICF are cell membranes B Ion Distribution among compartments 1 Table 4 1 C Movement of water and ions within the ECF 1 Water moves freely by osmosis between plasma and interstitial fluid 2 Most solutes EXCEPT plasma proteins move freely by passive means between plasma and interstitial fluid D Movement of water and ions between ECF and ICF 1 Water moves freely between ECF and ICF a This movement is determined by osmotic effects alone 2 Ions do not move easily between ECF and ICF a Solute movement restricted across cellular membranes b Cellular proteins in the ICF usually can t leave cells and generally are not found in the ECF c Na and K and their associated anions are unequally distributed between ECF and ICF this is maintained in large part by the Na K ATPase pump E Regulation of fluid and ion distribution 1 The ECF is intermediate between the ICF and the external environment a All exchanges of water and solutes between the ICF and the external environment must go through the ECF 2 Plasma is the only fluid that has its volume and composition regulated However if plasma volume or composition changes a the interstital fluid also changes b the ICF changes to the extent allowed by cell membrane permeability 3 Why you must regulate fluid and ion levels a ECF volume must be regulated to maintain blood pressure Maintenance of salt balance is the primary way that ECF volume is regulated over the long term b ECF osmolarity mg solutes ml fluid must be regulated to prevent shrinking or swelling of cells because ECF osmolarity affects ICF osmolarity Maintenance of water balance is the primary way this is accomplished c ECF volume and ECF osmolarity are intimately related to each other III Regulation of ECF Volume Controlling the Amount of Na A Purpose Long term regulation of blood pressure by regulating plasma volume which is accomplished by regulating the total quantity of Na 1 Baroreceptor reflex and fluid shifts between the plasma and interstitial fluid are important short term mechanisms of regulating blood pressure 2 If plasma volume is too far from normal short term mechanisms are ineffective so amount of Na must be regulated 3 Increases in Na lead to increases in ECF volume because of osmotic forces if you hold on to Na you automatically hold onto water too and hence increase blood pressure decreases in Na lead to decreases in ECF volume and hence decreases in blood pressure B Na Balance 1 Input eating salt not well controlled most Americans eat way more salt than is needed 2 Output Loss of salt in sweat feces and urine only excretion in urine is regulated C Mechanisms regulating Na excretion in kidney 1 Control of filtration rate in kidney a increasing filtration rate causes an increase in Na filtration and hence Na excretion water is excreted along with the Na so ECF volume decreases b decrease in filtration rate leads to decrease in Na filtration and excretion Na and associated water conserved which leads to an increase in ECF volume 2 Control of Na reabsorbed in kidneys Fig 18 3 19 15 19 16 19 17 19 18 a In proximal tubule and loop of Henle a constant percentage of filtered Na is reabsorbed regardless of the absolute amount present b In the distal tubule Na reabsorption is regulated c Primary positive regulation system is the renin angiotensin aldosterone system you can upregulate or downregulate this system to alter Na and hence bp 1 If Na levels fall which causes a decline in ECF volume and blood pressure the juxtaglomerular apparatus secretes the hormone renin into the blood 2 Renin activates angiotensinogen by converting it to angiotensin I which is then converted to 3 angiotensin II by angiotensin converting enzyme found mostly in lungs 4 Angiotensin II then stimulates the adrenal cortex to secrete 5 aldosterone which increases Na reabsorption in the distal and collecting tubules by adding more Na K ATPase pumps to the basolateral membranes 6 This promotes Na retention and so increases ECF volume and arterial blood pressure 7 Angiotensin II also is vasoconstrictor stimulates thirst and stimulates vasopressin which induces water retention by the kidneys all of which also result in an increase in ECF volume and arterial

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