Chapter 21
Body Fluids
Memmler’s
The Human Body in Health and Disease
11th edition
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
The Importance of Water
• Body wt. is 50-70% water – in infants 75% (why
diarrhea is so crucial)
Body fluid maintenance (based on electrolytes – cations +
and anions -)
• Thirst mechanism maintains volume
• Kidney activity regulates volume and composition
• Hormones regulate fluid volume and electrolytes
• Buffers, respiration, and kidney function regulate pH
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Fluid Compartments
• Intracellular fluid (ICF)
– Two-thirds to three-fourths of all body fluids
• Extracellular fluid (ECF)
– Interstitial fluid
– Blood plasma
– Lymph
– Fluid in special compartments
** remember : fluids not static; there is a constant
exchange
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Main fluid
compartments
showing relative
percentage by
weight of body fluid.
Fluid percentages
vary but total about
60% of body
weight. Fluids are
constantly
exchanged among
compartments, and
each day fluids are
lost and replaced.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Water Balance
* The amt of water gained and lost every day are approx. equal
• Water gain from
– Beverages
– Food
– Cellular respiration
• Water loss from
– Kidneys
– Skin
– Lungs
– Intestinal tract
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What changes fluid balance?
• Burns
• Sweating-fever / Diaphoresis
• Draining wound
• High glucose levels
• Dehydration
• Hemorrhage
• Too much fluid
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Sense of Thirst
Control center for thirst
• Located in hypothalamus
• Regulates total fluid volume
• Excessive thirst – polydipsia (seen in diabetes)
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Electrolytes and Their Functions
Conduct electrical current in solution (separate in water)
• Positive ions (cations)
–
Sodium (osmotic pressure, body fluid volume, brain, muscle,
kidneys)
–
Potassium (nerve impulses, kidney, digestion, heart)
–
Calcium (Vit.D, bone formation, muscle, nerve, heart and
clotting)
–
Magnesium (enzyme reactions, heart)
• Negative ions (anions)
–
Phosphate (bone, acid-base balance, plasma membranes, ATP)
–
Chloride (HCL, fluid balance, pH, digestion)
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Electrolyte Balance
• Kidneys do majority of balancing
• Hormones involved
– Aldosterone (adrenal cortex)
– Antidiuretic hormone (ADH) (pituitary)
– Parathyroid hormone (parathyroid & thyroid glands)
– Calcitonin hormone (thyroid)
– Atrial natriuretic peptide (ANP) (from the heart)
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Acid–Base Balance
• pH scale measures hydrogen ion (H+) concentration
• Body fluids have normal pH of 7.35 to 7.45
• Three-tenths of a point shift in either direction is
fatal!
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Regulation of pH
• Buffer systems accept or release ions as needed
– Bicarbonate
– Phosphate
– Proteins
• Respiration provides short-term regulation
• Kidney function provides long-term regulation (main
balancer by excretion)
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Abnormal pH
• Acidosis
–
pH less than 7.35
–
Causes: depressed nervous system, respiratory obstruction, lung
disease preventing CO2 release, kidney failure, diarrhea,
starvation, diabetic ketoacidosis
• Alkalosis
–
pH greater than 7.45
–
Causes: excited nervous system, hyperventilation, high doses of
antacids, vomiting
• Origins
–
Respiratory—change in blood CO2
–
Metabolic—change in other acids
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Acidosis and Alkalosis
Respiratory
Metabolic
• Acidosis
• Acidosis
• Alkalosis
pH - < 7.35
pH - < 7.35
PaCO2 - > 45
PaCO2 – Normal
HCO3 - > 26
HCO3 - <22
pH - > 7.45
• Alkalosis
pH - > 7.45
PaCO2 - < 35
PaCO2 – Normal
HCO3 - Normal
HCO3 - >26
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Disorders of Body Fluids
• Edema – accumulation of excess fluid in intercellular
spaces
- causes: abnormal fluid return to heart (ex. Pulmonary edema), lack
of protein in blood (albumin), kidney failure, increased loss of fluid
through capillaries (allergic rxn, infection)
• Water intoxication – dilution of body fluids in ICF & ECF
• Effusion – escape of fluid into a cavity or space
• Ascites – effusion with accumulation of fluid within the
abdominal cavity
• Dehydration – severe deficit of body fluids
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Fluid Therapy
Fluids administered intravenously
• Normal (.9%) saline
• 5% dextrose in .45% saline
• 5% dextrose in water
• Ringer lactate solution
• Serum albumin 25%
• Nutritional solutions
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IV Fluids
• Isotonic – same concentration as cellular fluids (will not
cause net gain or loss of water)
• Hypertonic – more concentrated than cellular fluid (will
draw water out of cells)
• Hypotonic – less concentrated than cellular fluids (will
take water in)
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End of Presentation
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins