Lecture 1: Body Fluids and Diffusion

Question 1

Internal environment

Answer 1

The solution of dissolved substances present within and around all cells/blood vessels. Developed by Bernard.

Question 2

Intracellular fluid

Answer 2

Fluid within all cells; comprises about 2/3rds of the body’s water or 40% body weight

Question 3

Plasma

Answer 3

The fluid portion of the blood which suspends all blood cells. Comprises about 20% of the ECF.

Question 4

Interstitial fluid

Answer 4

Fluid around and between cells in the interstitum. Comprises about 80% of the ECF.

Question 5

Extracellular fluid

Answer 5

All body fluid outside of the cells; includes interstitial fluid and plasma. Comprises 1/3rd of the body’s water or 20% body weight

Question 6

60/40/20 rule

Answer 6

Total body water is 60% body weight, ICF is 40%, and ECF is 20%. Interstitial is 80% ECF and plasma is 20% ECF.

Question 7

Homeostasis

Answer 7

A state of dynamic constancy where variables may vary short term but are stable/predictable when averaged long-term. Must be described differently for each variable.

Question 8

Homeostatic control systems

Answer 8

Systems that perform compensatory mechanisms to correct changes in the internal environment. Systems are regulated and integrated with each other

Question 9

Steady state

Answer 9

System in which a variable is constant but requires continual energy input to maintain homeostasis

Question 10

Equilibrium

Answer 10

System in which a variable stays constant without energy input

Question 11

Set point

Answer 11

The physiological value around which normal range fluctuates. Control systems operate around set points.

Question 12

Negative/positive feedback

Answer 12

System where change in the regulated variable induces a compensatory/accelerating response. Positive feedback is much rarer (e.g. clotting)

Question 13

Feedforward regulation

Answer 13

When changes in variables are anticipated and prepared for ahead of time, e.g. sensing the outside temperature before internal temperature actually decreases.

Question 14

Simple diffusion

Answer 14

Random heat energy movement of molecules to disperse evenly throughout a medium; results in “downhill” motion without energy input.

Question 15

(Net) flux

Answer 15

Amount of material crossing a surface per unit time. Net flux is the difference between 2 one-way fluxes

Question 16

Factors affecting net flux

Answer 16

Molecule speed (temperature, mass); surface area; medium (# of collisions)

Question 17

Limitations of diffusion

Answer 17

Diffusion time increases proportional to the square of distance. Simple diffusion is only effective within a few cm for physiological nourishment.

Question 18

Fick’s 1st law of diffusion for biological membranes

Answer 18

J = PA delta C where J = rate of diffusion, P = permeability constant, A = surface area, C = concentration

Question 19

Relative permeability of lipid bilayer

Answer 19

Nonpolar and small polar molecules can cross lipid bilayers. Ions and large molecules are essentially impermeable.

Question 20

Ion channel

Answer 20

Type of integral membrane protein that allows ions to diffuse across the membrane very quickly. Exhibits selectivity and can be gated or constitutive.

Question 21

Selectivity factors

Answer 21

Channel diameter, charge/polarity, # of H2O molecules associated with a given ion

Question 22

Electrochemical gradient

Answer 22

The gradient of electrical potential and solute concentration difference across a membrane. Both parts influence the movement of ions across membranes

Question 23

Types of channel gating

Answer 23

1. Ligand-gated (e.g. synapses)
2. Voltage-gated (e.g. Na+ channels in neurons)
3. Mechanically-gated (e.g. channels in ear attached to stereocilia and stretch receptors)

Question 24

Blood volume

Answer 24

Equal to plasma volume plus erythrocyte volume. The buffy coat (leukocyte) volume is negligible (<1%)

Question 25

Hematocrit

Answer 25

Percent volume of erythrocytes out of total blood volume. Normal adult range is 35-50%.

Question 26

Molarity/molality

Answer 26

moles of solute per liter of solution or per kg of solution. E.g. MW of CaCl2 -> moles

Question 27

Osmolarity/osmolality

Answer 27

Osmoles of solute (solute particles) per liter of solution or per kg of solution. E.g. each mole of CaCl2 = 3 osmoles

Question 28

Normality

Answer 28

Equivalents of solute (valence, aka # of e- transferred upon ionization) per liter of solution. E.g. each mole of CaCl2 = 2 equivalents

Question 29

Ion concentrations for ECF vs ICF

Answer 29

Na+: 140 out, 12 in
K+: 4 out, 150 in
Cl-: 110 out, 10 in
HCO3-: 24 out, 10 in
Protein-: 16 out (plasma), 60 in

Question 30

Ion composition of fluid compartments

Answer 30

Interstitial fluid has no proteins; endothelium is impermeable to proteins. Ionic concentration between interstitial and plasma is very similar.

The ECF and ICF are macroscopically electroneutral. Membrane potential involves a tiny amount of particles relative to the entire compartment.

Question 31

Osmolality of body fluids

Answer 31

Approximated as 300 mOsm/L for all body fluids; however, ICF has a higher normality (valence)