This document summarizes key concepts related to body fluid compartments, osmotic pressure, and synaptic transmission in physiology. It discusses that total body water is 60% of body weight, with intracellular fluid making up 40% and extracellular fluid 20%. Extracellular fluid is further divided into interstitial and plasma sub-compartments. Osmotic pressure is determined by effective osmolytes that cannot cross cell membranes. Synaptic transmission can occur electrically through gap junctions or chemically through neurotransmitters acting on ionotropic or metabotropic receptors. Action potentials are generated by the opening and closing of sodium and potassium ion channels in neurons.

1. Semester 1: Physiology Body Fluid Compartments and Introduction to Action Potentials Week 1

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3. Compartments T BW (total body water) = 0.6 BW (body weight) I CF (Intracellular fluid) = 0.4 BW E CF (Extracellular fluid) = 0.2 BW Interstitial: 0.75 ECF Plasma (blood): 0.25 ECF Capillary wall separates Interstitial and Plasma sub-compartments T-I-E = 60-40-20

5. Expansion and Contraction ECF ICF Hct = RBC vol/blood vol Hct ~ ICF/ECF Isoosmotic volume expansion ↑ - ↓ Isoosmotic volume contraction ↓ - ↑ Hyperosmotic volume expansion ↑ ↓ ↓ Hyperosmotic volume contraction ↓ ↓ - Hypoosmotic volume expansion ↑ ↑ - Hypoosmotic volume contraction ↓ ↑ ↑

6. Tonicity

7. Determining Tonicity Need EFFECTIVE OSMOLYTE Effective osmolyte = solute that can't cross the cell membrane; impermeant Sucrose Ineffective osmolyte = permeable solute Urea

8. π = σ(nCRT) π = Osmotic pressure σ = reflection coefficient (0-1) 0 = ineffective osmolyte 1 = impermeant N = dissociable particles C = total [solute] R = gas constant T = Kelvin Determining Tonicity

9. Synaptic Transmission Electrical transmission: Gap junction (for neuron synchronization) 6 connexins = 1 connexon = ½ gap jxn Can be bi-directional Modulated by: pH Neurotransmitters (synthesized in RER, Golgi) Ca2+

10. Synaptic Transmission Chemical Transmission: Pre and post-synapse instead of gap jxn Unidirectional Metabotropic receptors : slow response via intracellular proteins) Ionotropic receptors : fast response via depol/hyperpol ion channels

11. Major Neurotransmitters Acetylcholine (Ach) Excitatory : Glutamate Inhibitory : GABA and Glycine (in vesicles) Amines: Dopamine Norepinephrine/Epinephrine Histamine Seratonin

12. Neuron ion content

13. Depolarization/Action Potential Gates: M-gate = activation gate H-gate = inactivation gate (plug) N-gate = slow-closing K+ channel Temporal/Spatial Summation -> Threshold EPSP depolarization (Na+) IPSP hyperpolarization (Cl-) At resting state: M-gate closed, H and N-gates open Depolarization: All gates open Repolarization: H-gates close After absolute refractory period: All gates closed

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