BIO 3342 Study Guide - Fall 2019, Comprehensive Final Exam Notes - Cell Membrane, Skeletal Muscle, Capillary

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30 Nov 2019
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BIO 3342
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Unit 1 Introduction
- Claude Bernard (1813-1878)
o Believed we are shielded form the external environment by an internal environment composed of
the fluid that circulates throughout our body (extracellular fluid)
o Constancy of internal environment is the condition for a free and independent life
- Walter Canon (1871-1945)
o Coined term ‘homeostasis’ that expanded Bernard’s proposals
o Homeostasis : the body’s ability to maintain a relatively stable ‘internal environment’ through a
variety of orchestrated physiologic responses
*nothing is constant consistently
- Purpose of studying physiology is to understand process that maintain homeostasis
- Intracellular fluid : fluid that is within the body’s cells
- Extracellular fluid : fluid that is outside of the body’s cells
o Interstitial fluid : fluid that is between tightly packed cells and surround the cell body
o Plasma : fluid in the blood vessels at the capillary level
Cell Membranes
- The cell membrane is composed of a phospholipid bilayer
- Phospholipid molecules that make up the membrane create a barrier that functions primarily as a lipophilic
structure
o Have a small polar head that is hydrophilic
o Have a long nonpolar tail that is made of carbon chains and is lipophilic
*both of these together creates an amphipathic molecule (having both hydrophilic and hydrophobic
parts)
- Phospholipid bilayer forms because the lipid component (tail) is attracted to
each other and the polar component (water-loving head) is attracted to both
intracellular and extracellular fluid
o Acts as a lipophilic structure because the relative size
of the phospholipid tails is quite long and large in
comparison to the relatively small and thin polar
heads
- Membrane layer is semi-permeable, allowing molecules to
mass into and out of the cell based and dependent on their
chemical makeup
- In addition to the phospholipid molecules, proteins are also present in the molecule
Element
Units
Intracellular
Extracellular
Na+
mEq/L
14
140
K+
mEq/L
120
4
Ca++
mEq/L
0.0001
2.5
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o Integral membrane proteins : integrated into the bilayer membrane
Transmembrane proteins may function as a pathway to allow movement of hydrophilic
substances across the cell membrane
o Peripheral membrane proteins : primarily associates only with the superficial outside layer of the
membrane
Movement of Molecules Across the Membrane
- Molecules move ‘downhill’ when they move down a concentration gradient, they move from an area of
greater concentration to an area of lower concentration
o This is passive process and requires no external energy (diffusion)
o Diffusion : a passive process that is the movement of molecules across a membrane and requires no
external energy
- There are two types of diffusion
(1) Simple diffusion : decreases the movement of molecules downhill, down a concentration gradient,
without the use of any additional facilitators
o This is associated with lipophilic molecules moving through
the membrane layer
o These molecules move by random movement across the
membrane
o Flux : describes the net diffusion across the membrane
Net flux is 0 when the diffusional equilibrium is reached
o The rate of simple diffusion is dependent on 5 factors
1. Concentration gradient
The greater the concentration gradient, the greater the flux
2. Partition coefficient
Describes the solubility of a solute in oil relative to water
A high partition coefficient indicates that the substance is more soluble in oil than in water
and can move across the cell membrane with greater ease
The great the partition coefficient, the easier the substance can pass through the cell
membrane (high polarity = low partition coefficient)
Lipophilic molecules dissolve
well in oil and travel through the membrane more easily than hydrophilic molecules
3. Diffusion coefficient
Related primarily to the size of the solute molecule
The smaller the solute molecule, the greater the diffusion coefficient and the easier it can
pass through the membrane
4. Thickness of membrane
The thicker the membrane, the longer distance a solute must travel
The thicker the membrane, the lower the rate of diffusion
5. Surface area
The area over which diffusion might occur
The greater the surface area, the higher the rate of diffusion
o Lipophilic substances can diffuse directly through the cell membrane
o Hydrophilic substances may not be able to cross the membrane
The exception is water molecules because of their small size and large surface area of the
membrane
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