Transcript NVCC Bio 212

Marieb’s Human
Anatomy and Physiology
Ninth Edition
Marieb w Hoehn
Chapter 26
Fluid, Electrolytes, and Acid-Base Balance
Lecture 17
Part 1a: Overview, Compartments,
Osmolarity, and Equivalents
Overview
• Our survival depends upon maintaining a
normal volume and composition of
– Extracellular fluid (ECF)
– Intracellular fluid (ICF)
• Ionic concentrations and pH are critical
• Three interrelated processes
– Fluid balance (How does water move from one place to the other? )
– Electrolyte balance (What is an electrolyte?)
– Acid-base balance (What is normal pH?)
2
Water Content of the Human Body
Of the 40 liters of water in
the body of an average adult
male:
- one-third (15L) is
extracellular
- two-thirds (25L) is
intracellular
Figure from: Hole’s Human A&P, 12th edition, 2010
3
Fluid Compartments
Figure from: Hole’s Human A&P, 12th edition, 2010
‘Compartments’ commonly behave as distinct entities in
terms of ion distribution, but ICF and ECF osmotic
concentrations are identical (about 290-300 mOsm/L). Why?
4
Osmolarity
Amount of solute
Osmolarity =
Volume of H2O
A weekend ‘snacker’ consumes a bag of salty chips
containing 900 mOsm of salt.
How much water must she drink to restore her
body fluids to their normal 300 mOsm/L?
5
Osmolarity
• Recall that osmolarity expresses total solute concentration of a
solution
– Osmolarity (effect on H2O) of body solutions is determined by the total
number of dissolved particles (regardless of where they came from)
– The term ‘osmole’ reflects the number of particles yielded by a particular
solute (milliosmole, mOsm, = osmole/1000)
• 1 mole of glucose (180g/mol) -> 1 osmole of particles
• 1 mole of NaCl (58g/mol) -> 2 osmoles of particles
• Osmolarity = #moles/L X # particles yielded in solution
6
Milliequivalents (mEq)
• An equivalent is the positive or negative charge equal
to the amount of charge in one mole of H+
– The SIGN of the charge is irrelevant when calculating the
number of equivalents/milliequivalents
– A milliequivalent (mEq) is one-thousandth of an Eq
– Number of Eq = #moles X valence
7
Review
• There are two major fluid compartments of
the body
– Intracellular
• About 2/3 of body’s fluid
• Includes the fluid within cells
• Major ions: K+, Mg2+, PO43-, Proteins
– Extracellular
• About 1/3 of body’s fluid
• Includes interstitial fluid, plasma, lymph, and
transcellular fluid
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