Lecture 1: Body Fluids and Diffusion Flashcards
Internal environment
The solution of dissolved substances present within and around all cells/blood vessels. Developed by Bernard.
Intracellular fluid
Fluid within all cells; comprises about 2/3rds of the body’s water or 40% body weight
Plasma
The fluid portion of the blood which suspends all blood cells. Comprises about 20% of the ECF.
Interstitial fluid
Fluid around and between cells in the interstitum. Comprises about 80% of the ECF.
Extracellular fluid
All body fluid outside of the cells; includes interstitial fluid and plasma. Comprises 1/3rd of the body’s water or 20% body weight
60/40/20 rule
Total body water is 60% body weight, ICF is 40%, and ECF is 20%. Interstitial is 80% ECF and plasma is 20% ECF.
Homeostasis
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.
Homeostatic control systems
Systems that perform compensatory mechanisms to correct changes in the internal environment. Systems are regulated and integrated with each other
Steady state
System in which a variable is constant but requires continual energy input to maintain homeostasis
Equilibrium
System in which a variable stays constant without energy input
Set point
The physiological value around which normal range fluctuates. Control systems operate around set points.
Negative/positive feedback
System where change in the regulated variable induces a compensatory/accelerating response. Positive feedback is much rarer (e.g. clotting)
Feedforward regulation
When changes in variables are anticipated and prepared for ahead of time, e.g. sensing the outside temperature before internal temperature actually decreases.
Simple diffusion
Random heat energy movement of molecules to disperse evenly throughout a medium; results in “downhill” motion without energy input.
(Net) flux
Amount of material crossing a surface per unit time. Net flux is the difference between 2 one-way fluxes
Factors affecting net flux
Molecule speed (temperature, mass); surface area; medium (# of collisions)
Limitations of diffusion
Diffusion time increases proportional to the square of distance. Simple diffusion is only effective within a few cm for physiological nourishment.
Fick’s 1st law of diffusion for biological membranes
J = PA delta C where J = rate of diffusion, P = permeability constant, A = surface area, C = concentration
Relative permeability of lipid bilayer
Nonpolar and small polar molecules can cross lipid bilayers. Ions and large molecules are essentially impermeable.
Ion channel
Type of integral membrane protein that allows ions to diffuse across the membrane very quickly. Exhibits selectivity and can be gated or constitutive.
Selectivity factors
Channel diameter, charge/polarity, # of H2O molecules associated with a given ion
Electrochemical gradient
The gradient of electrical potential and solute concentration difference across a membrane. Both parts influence the movement of ions across membranes
Types of channel gating
- Ligand-gated (e.g. synapses)
- Voltage-gated (e.g. Na+ channels in neurons)
- Mechanically-gated (e.g. channels in ear attached to stereocilia and stretch receptors)
Blood volume
Equal to plasma volume plus erythrocyte volume. The buffy coat (leukocyte) volume is negligible (<1%)
