human anatomy & physiology ii - classroom websites physiology... · fluid, electrolyte and...

Copyright 2010, John Wiley & Sons, Inc.

Chapter 22

Fluid, Electrolyte and

Acid-Base Balance


End of Chapter 22

Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.


Fluid Compartments Total body water = 55-60% of lean body

mass

Remainder: solid parts of bone, muscles, tendons

Major compartments (3): ICF, IF, plasma

Intracellular fluid (ICF): inside cells= 2/3

Extracellular Fluid (ECF): outside cells = 1/3

Interstitial fluid (IF): 80% of ECF

Includes: lymph; cerebrospinal, synovial, pericardial,

pleural and peritoneal fluids; fluid in eyes and ears

Blood plasma: 20% ECF


Fluid Compartments


Barriers Between Compartments

Plasma membrane: between ECF and ICF

Blood vessel walls: between plasma and

interstitial fluid

Fluid balance correct distribution of water &

solutes

Water redistributes rapidly by osmosis

Thus fluid balance depends on solute

(electrolyte) balance


Fluid Balance Fluid balance requires

Appropriate total volume of body fluid

Appropriate distribution of water and solutes

Fluid balance depends on solute (electrolyte

and nonelectrolyte) balance

Fluids and electrolytes are closely linked

Water redistributes rapidly by osmosis


Fluid Balance Interactions Animations

Water and Fluid Flow

You must be connected to the internet to run this animation.

http://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_fluid_flow/anim_fluid_flow/screen0.swf


Water Gain and Loss Gain: ingestion + metabolic reactions

Ingestion (food and drink): 2300 mL/day

Metabolism: 200 mL/day

Gain should = loss

Daily intake = daily output. Both 2500 mL/day

Loss: skin, lungs, kidneys, GI tract

Kidneys: ~1500 mL/day

Skin: sweat evaporates ~600 mL/day

Lungs: 300 mL/day; more if fever

GI tract: ~100 mL/day; more if diarrhea


Water Balance


Regulation of Gain Thirst center in hypothalamus

~2% dehydration will cause BP Increase in body osmolality dry mouth thirst

Hormonal responses High osmolality hypothalamus releases ADH

water retention by kidneys

BP renin released from kidney angiotensin II aldosterone water retention by kidneys

Sensation of thirst may be decreased, especially in elderly


Regulation of Gain


Regulation of Salt and Water Loss

Urinary NaCl loss mainly determines body fluid volume

Na+ = main solute in ECF determining osmosis

Fluid intake varies so loss must vary also

ANP, angiotensin II and aldosterone regulate

ADH regulates water loss


Regulation of Salt

and Water Loss


Movement of Fluid

ICF and ECF are normally at the same osmolality

Water moves freely

interstitial fluid osmolality cell swelling and vice versa

Most often due to Na+ change

ADH responds rapidly: prevents significant cell change


Electrolytes in Body Fluids

Functions of electrolytes

1. Confined to compartments; control osmosis

2. Help maintain acid-base balance

3. Carry electrical currents

4. Serve as cofactors for enzymes


Electrolyte Distribution Electrolyte content of ICF and ECF differ

significantly

ICF: K+ major cation; protein, HPO42-: anions

ECF: Na+ major cation; Cl- major anion

Na+/K+ pump maintains the cation difference

The two ECF fluids are similar

Electrolytes in plasma similar to those in IF

One difference: plasma contains more protein than interstitial fluid (IF)

Colloid osmotic pressure (due largely to plasma proteins) “holds onto” fluid in capillaries


Electrolyte Distribution


Other Electrolytes

K+ high in ICF, low in ECF

Regulated by aldosterone

Mg2+ and SO42- high in ICF, low in ECF

Ca2+ high in ECF, low in ICF

Regulated in plasma (PTH, calcitriol, and calcitonin)

Bones serve as Ca2+ reservoir


Acid- Base Balance Input: diet, products of metabolism

Such as lactic acid, ketones

Output

Lungs: exhale CO2

Kidney: can eliminate H+ or HCO3-

Regulatory mechanisms

1. Buffers: fastest but incomplete

2. Respiratory responses: fast but incomplete

3. Renal responses: slowest but compete

elimination


1: Buffer Systems

Protein in cells or plasma

Carboxyl and amino groups of amino acids

Hemoglobin (protein) in red blood cells

Carbonic acid-bicarbonate

Especially important in plasma

CO2 + H2O H2CO3 ↔ HCO3- + H+

Phosphate

H2PO4- H+ + HPO4

2-


2: Exhalation of Carbon Dioxide

H+ + HCO3- ↔ H2CO3 ↔ CO2 + H2O

Decrease of CO2 ↔ decrease of H+

Increase of CO2 ↔ increase of H+

Change of rate and depth of ventilation

rapidly alters plasma pH

Negative feedback loop regulates


2: Exhalation of

Carbon Dioxide


3. Renal Responses

Kidney Excretion of H+

Slow but only way to actually eliminate acid or

base

Secrete H+ and replace with HCO3-


Imbalances

Acidosis: arterial blood pH < 7.35

Depresses CNS

Below pH 7.0 can be fatal

Alkalosis: arterial blood pH > 7.45

Overexcitation of CNS

Muscle spasms, convulsions

Compensation

Respiratory or renal mechanisms

Respiratory very rapid; renal slower


Aging

Decrease in control of water and electrolyte

balance can lead to pH problems

Decreases in respiratory and renal

functioning

Decreased capacity to sweat

human anatomy & physiology ii - classroom websites physiology... · fluid, electrolyte and...

Documents