Physio1: Week 1

Semester 1: Physiology

Body Fluid Compartmentsand

Introduction to Action Potentials

Week 1

Contact us:

Julie: julieyumi@gmail.com

Jenesha: jnarayanan@rossmed.edu.dm

Compartments TBW (total body water) = 0.6BW (body

weight) ICF (Intracellular fluid) = 0.4BW ECF (Extracellular fluid) = 0.2BW

Interstitial: 0.75ECF Plasma (blood): 0.25ECF

Capillary wall separates Interstitial and Plasma sub-compartments

T-I-E = 60-40-20

Expansion and ContractionECF 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

↓ ↑ ↑

Tonicity

Determining Tonicity Need EFFECTIVE OSMOLYTE Effective osmolyte = solute that can't

cross the cell membrane; impermeant Sucrose

Ineffective osmolyte = permeable solute Urea

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

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+

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

Major Neurotransmitters Acetylcholine (Ach) Excitatory: Glutamate Inhibitory: GABA and Glycine (in vesicles) Amines:

Dopamine Norepinephrine/Epinephrine Histamine Seratonin

Neuron ion content

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

Love,Julie and Jenesha