Chapter 25 Fluid, electrolyte, and acid-base homeostasis

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1 Chapter 25 Fluid, electrolyte, ad acid-base homeostasis

2 Body Fluid Compartmets I lea adults, body fluids costitute 55% of female ad 60% of male total body mass Itracellular fluid (ICF) iside cells About 2/3 of body fluid Extracellular fluid (ECF) outside cells Iterstitial fluid betwee cell is 80% of ECF Plasma i blood is 20% of ECF Also icludes lymph, cerebrospial fluid, syovial fluid, aueous humor, vitreous body, edolymph, perilymph, ad pleural, pericardial, ad peritoeal fluids Copyright 2009, Joh Wiley & Sos, Ic.

4 Fluid Balace Body is i fluid balace whe reuired amouts of water ad solutes are preset ad correctly proportioed amog compartmets Water is by far the largest sigle compoet of the body makig up 45-75% of total body mass Process of filtratio, reabsorptio, diffusio, ad osmosis all cotiual exchage of water ad solutes amog compartmets Copyright 2009, Joh Wiley & Sos, Ic.

5 Sources of Body Water Gai ad Loss Fluid balace related to electrolyte balace Itake of water ad electrolytes rarely proportioal Kideys excrete excess water through dilute urie or excess electrolytes through cocetrated urie Body ca gai water by Igestio of liuids ad moist foods (2300mL/day) Metabolic sythesis of water durig cellular respiratio ad dehydratio sythesis (200mL/day) Body loses water through Kideys (1500mL/day) Evaporatio from ski (600mL/day) Exhalatio from lugs (300mL/day) Feces (100mL/day) Copyright 2009, Joh Wiley & Sos, Ic.

7 Regulatio of body water gai Maily by volume of water itake/ how much you drik Dehydratio whe water loss is greater tha gai Decrease i volume, icrease i osmolarity of body fluids Stimulates thirst ceter i hypothalamus Copyright 2009, Joh Wiley & Sos, Ic.

8 Regulatio of water ad solute loss Elimiatio of excess body water through urie Extet of uriary salt (NaCl) loss is the mai factor that determies body fluid volume Mai factor that determies body fluid osmolarity is extet of uriary water loss 3 hormoes regulate real Na + ad Cl - reabsorptio (or ot) Agiotesi II ad aldosteroe promote uriary Na + ad Cl - reabsorptio of (ad water by osmosis) whe dehydrated Atrial atriuretic peptide (ANP) promotes excretio of Na + ad Cl - followed by water excretio to decrease blood volume Copyright 2009, Joh Wiley & Sos, Ic.

10 Major hormoe regulatig water loss is atidiuretic hormoe (ADH) Also kow as vasopressi Produced by hypothalamus, released from posterior pituitary Promotes isertio of auapori-2 ito pricipal cells of collectig duct Permeability to water icreases Produces cocetrated urie Copyright 2009, Joh Wiley & Sos, Ic.

11 Movemet of water betwee compartmets Normally, cells either shrik or swell because itracellular ad iterstitial fluids have the same osmolarity Icreasig osmolarity of iterstitial fluid draws water out of cells ad cells shrik Decreasig osmolarity of iterstitial fluid causes cells to swell Chages i osmolarity most ofte result from chages i Na + cocetratio Water itoxicatio drikig water faster tha the kideys ca excrete it Ca lead to covulsios, coma or death Copyright 2009, Joh Wiley & Sos, Ic.

13 Electrolytes i body fluids Ios form whe electrolytes dissolve ad dissociate 4 geeral fuctios Cotrol osmosis of water betwee body fluid compartmets Help maitai the acid-base balace Carry electrical curret Serve as cofactors Copyright 2009, Joh Wiley & Sos, Ic.

14 Cocetratios i body fluids Cocetratio of ios typically expressed i millieuivalets per liter (me/liter) Na + or Cl - umber of me/liter = mmol/liter Ca 2+ or HPO 4 2- umber of me/liter = 2 x mmol/liter Chief differece betwee 2 ECF compartmets (plasma ad iterstitial fluid) is plasma cotais may more protei aios Largely resposible for blood colloid osmotic pressure Copyright 2009, Joh Wiley & Sos, Ic.

15 ICF differs cosiderably from ECF ECF most abudat catio is Na +, aio is Cl - ICF most abudat catio is K +, aio are proteis ad phosphates (HPO 4 2- ) Na + /K + pumps play major role i keepig K + high iside cells ad Na + high outside cell Copyright 2009, Joh Wiley & Sos, Ic.

17 Sodium Na + Most abudat io i ECF 90% of extracellular catios Plays pivotal role i fluid ad electrolyte balace because it accout for almost half of the osmolarity of ECF Level i blood cotrolled by Aldosteroe icreases real reabsorptio ADH if sodium too low, ADH release stops Atrial atriuretic peptide icreases real excretio Copyright 2009, Joh Wiley & Sos, Ic.

18 Chloride Cl - Most prevalet aios i ECF Moves relatively easily betwee ECF ad ICF because most plasma membraes cotai Cl - leakage chaels ad atiporters Ca help balace levels of aios i differet fluids Chloride shift i RBCs Regulated by ADH govers extet of water loss i urie Processes that icrease or decrease real reabsorptio of Na + also affect reabsorptio of Cl - Copyright 2009, Joh Wiley & Sos, Ic.

19 Potassium K + Most abudat catios i ICF Key role i establishig restig membrae potetial i euros ad muscle fibers Also helps maitai ormal ICF fluid volume Helps regulate ph of body fluids whe exchaged for H + Cotrolled by aldosteroe stimulates pricipal cells i real collectig ducts to secrete excess K + Copyright 2009, Joh Wiley & Sos, Ic.

20 Bicarboate HCO 3 - Secod most prevalet extracellular aio Cocetratio icreases i blood passig through systemic capillaries pickig up carbo dioxide Carbo dioxide combies with water to form carboic acid which dissociates Drops i pulmoary capillaries whe carbo dioxide exhaled Chloride shift helps maitai correct balace of aios i ECF ad ICF Kideys are mai regulators of blood HCO 3 - Ca form ad release HCO 3 - whe low or excrete excess Copyright 2009, Joh Wiley & Sos, Ic.

21 Calcium Ca 2+ Most abudat mieral i body 98% of calcium i adults i skeleto ad teeth I body fluids maily a extracellular catio Cotributes to hardess of teeth ad boes Plays importat roles i blood clottig, eurotrasmitter release, muscle toe, ad excitability of ervous ad muscle tissue Regulated by parathyroid hormoe Stimulates osteoclasts to release calcium from boe resorptio Also ehaces reabsorptio from glomerular filtrate Icreases productio of calcitrol to icrease absorptio for GI tract Calcitoi lowers blood calcium levels Copyright 2009, Joh Wiley & Sos, Ic.

22 Phosphate About 85% i adults preset as calcium phosphate salts i boe ad teeth Remaiig 15% ioized H 2 PO 4-, HPO 2-4, ad PO 3-4 are importat itracellular aios HPO 2-4 importat buffer of H + i body fluids ad urie Same hormoes goverig calcium homeostasis also regulate HPO 2-4 i blood Parathyroid hormoe stimulates resorptio of boe by osteoclasts releasig calcium ad phosphate but ihibits reabsorptio of phosphate ios i kideys Calcitrol promotes absorptio of phosphates ad calcium from GI tract Copyright 2009, Joh Wiley & Sos, Ic.

23 Magesium I adults, about 54% of total body magesium is part of boe as magesium salts Remaiig 46% as Mg 2+ i ICF (45%) or ECF (1%) Secod most commo itracellular catio Cofactor for certai ezymes ad sodium-potassium pump Essetial for ormal euromuscular activity, syaptic trasmissio, ad myocardial fuctio Secretio of parathyroid hormoe depeds o Mg 2+ Regulated i blood plasma by varyig rate excreted i urie Copyright 2009, Joh Wiley & Sos, Ic.

24 Acid-base balace Major homeostatic challege is keepig H + cocetratio (ph) of body fluids at appropriate level 3D shape of proteis sesitive to ph Diets with large amouts of proteis produce more acids tha bases which acidifies blood Several mechaisms help maitai ph of arterial blood betwee 7.35 ad 7.45 Buffer systems, exhalatio of CO 2, ad kidey excretio of H + Copyright 2009, Joh Wiley & Sos, Ic.

25 Buffer systems Act to uickly temporarily bid H + Raise ph but do ot remove H + Most cosist of weak acid ad salt of that acid fuctioig as weak base Protei buffer system Most abudat buffer i ICF ad blood plasma Hemoglobi i RBCs Albumi i blood plasma Free carboxyl group acts like a acid by releasig H + Free amio group acts as a base to combie with H + Side chai groups o 7 of 20 amio acids also ca buffer H + Copyright 2009, Joh Wiley & Sos, Ic.

26 Buffer Systems Carboic acid- bicarboate buffer system Based o bicarboate io (HCO 3- ) actig as weak base ad carboic acid (H 2 CO 3 ) actig as weak acid HCO 3 - is a sigificat aio i both ICF ad ECF Because CO 2 ad H 2 O combie to form this buffer system caot protect agaist ph chages due to respiratory problems i which there is a excess or shortage of CO 2 Phosphate buffer system Dihydroge phosphate (H 2 PO 4- ) ad moohydroge phosphate (HPO 4 2- ) Phosphates are major aios i ICF ad mior oes i ECF Importat regulator of ph i cytosol Copyright 2009, Joh Wiley & Sos, Ic.

27 Exhalatio of carbo dioxide Icrease i carbo dioxide i body fluids lowers ph of body fluids Because H 2 CO 3 ca be elimiated by exhalig CO 2 it is called a volatile acid Chages i the rate ad depth of breathig ca alter ph of body fluids withi miutes Negative feedback loop Copyright 2009, Joh Wiley & Sos, Ic.

Regulatio of blood ph by the respiratory

29 Kidey excretio of H + Metabolic reactios produce ovolatile acids Oe way to elimiate this huge load is to excrete H + i urie I the proximal covoluted tubule, Na + /H + atiporters secrete H + as they reabsorb Na + Itercalated cells of collectig duct iclude proto pumps that secrete H + ito tubule fluid Urie ca be up to 1000 times more acidic tha blood 2 other buffers ca combie with H + i collectig duct HPO 4 2- ad NH 3 Copyright 2009, Joh Wiley & Sos, Ic.

30 Acid-base imbalaces Normal ph rage of arterial blood Acidosis blood ph below 7.35 Alkalosis blood ph above 7.45 Major physiological effect of Acidosis depressio of syaptic trasmissio i CNS Alkalosis overexcitability of CNS ad peripheral erves Copyright 2009, Joh Wiley & Sos, Ic.

31 Physiological resposes to ormalize arterial blood ph Chages i blood ph may be coutered by compesatio Complete brought withi ormal rage Partial still too low or high Respiratory hypervetilatio or hypovetilatio Real secretio of H + ad reabsorptio of HCO 3 - Copyright 2009, Joh Wiley & Sos, Ic.

32 Respiratory acidosis/ alkalosis results from chages i partial pressure of CO 2 i systemic arterial blood Respiratory acidosis abormally high P CO2 i systemic arterial blood Iadeuate exhalatio of CO 2 Ay coditio that decreases movemet of CO 2 out emphysema, pulmoary edema, airway obstructio Kideys ca help raise blood ph Goal to icrease exhalatio of CO 2 vetilatio therapy Copyright 2009, Joh Wiley & Sos, Ic.

33 Respiratory alkalosis Abormally low P CO2 i systemic arterial blood Cause is hypervetilatio due to oxyge deficiecy from high altitude or pulmoary disease, stroke or severe axiety Real compesatio ca help Oe simple treatmet to breather ito paper bag for short time Copyright 2009, Joh Wiley & Sos, Ic.

34 Metabolic acidosis/alkalosis Results from chages i HCO 3 - cocetratio Metabolic acidosis abormally low HCO 3 - i systemic arterial blood Loss of HCO 3 - from severe diarrhea or real dysfuctio Accumulatio of a acid other tha carboic acid ketosis Failure of kideys to excrete H + from metabolism of dietary proteis Hypervetilatio ca help Admiister IV sodium bicarboate ad correct cause of acidosis Copyright 2009, Joh Wiley & Sos, Ic.

35 Metabolic alkalosis Abormally high HCO 3 - i systemic arterial blood Norespiratory loss of acid - vomitig of acidic stomach cotets, gastric suctioig Excessive itake of alkalie drugs (atacids) Use of certai diuretics Severe dehydratio Hypovetilatio ca help Give fluid solutios to correct Cl -, K + ad other electrolyte deficiecies ad correct cause of alkalosis Copyright 2009, Joh Wiley & Sos, Ic.

Principles of Anatomy and Physiology

Principles of Anatomy and Physiology 14 th Edition CHAPTER 27 Fluid, Electrolyte, and Acid Base Fluid Compartments and Fluid In adults, body fluids make up between 55% and 65% of total body mass. Body