Physiology

• Study of the logic of life
• No longer just FUNCTION - understand how/why life works

• Using purpose as a means of explanation
• Ie, we breathe to oxygenate our bodies

• Using cause and effect as a means of explanation
• Ie, concentration gradients are created in capillary beds and drive exchange

• Quantity = Concentration x Volume
• Volume can be exchanged for Flow

• Flow = Force x Conductance
• Flow = Force / Resistance

• The property of an open system (organism) to regulate its internal environment to maintain a stable, constant condition
• Accomplished by adjusting multiple dynamic equilibriums which are controlled by interrelated control mechanisms

• Positive > Negative
• Na⁺ > Cl^- >> K⁺

• Positive > Negative
• Na⁺ > Cl^- >> K⁺

• Negative > Positive
• K+ > Cl- > Na+
• Note: there are many negatively charged proteins

3L

12L

• Kidneys
• Skin
• Lungs
• GI Tract

25L

• Urine
• Insensible water
• Feces

• Drink
• Water content in food
• Oxidative metabolism

2.5L

• Osmolarity acts as a regulator of homeostasis
• The increased amount of fluid into the system dropped osmolarity of the blood
• This triggered increased renal filtration to re-establish proper levels

• A lipid bilayer (hydrophobic in, hydrophilic out)
• Proteins

• Describes the motility/fluidity of the membrane
• Proteins and lipids are free to diffuse around
• Membrane can buckle and expand

It is semipermeable based on molecule: size, polarity, and solubility

• Barrier
• Cell Adhesion
• Bearer of self-identity markers/transport proteins

• Extrinsic (perepheral)
• Intrinsic (integral)

• Carrier - must change shape to permit passage
• Channel - always open

• Diffusion
• Osmosis

• Carrier-mediated transport
• Active transport
• Vesicle transport

• Spreading of molecules based solely on their thermal energy
• Move from high => low concentration

• Diffusion only occurs down a concentration gradient (until uniformly dispersed)
• BM describes the actual motion - when gradient is abolished, movement still occurs

• Concentration gradient
• Lipid solubility of molecule
• Membrane surface area
• Molecular weight of molecule
• Membrane thickness

Residues within the "ion filter" portion selectively filter the correct ion

• Carrier-mediated requires conformational change of protein
• Carrier-mediated may require energy input
• Carrier-mediated reaches a saturation point (speed of which protein can change shape maxed)

• Specificity
• Saturation
• Competition

• Primary - require direct use of ATP
• Secondary - driven by ion concentration gradient established by a primary pump

No

• Endocytosis
• Pinocytosis
• Receptor-mediated
• Phagocytosis
• Exocytosis

ALL cells

Differences in charge are sequestered to opposite sides of the PM

• The separation of charge across the PM in all cells
• Nerves maintain this when they are not firing an action potential

Ion channels

Pores' existance was postulated long before they were discovered (due to size)

• The membrane potential is determined by the intracellular K+
• Julius Bernstein
• Used squid axon

• Membrane potential in nerves is based both on intracellular K+ and extracellular Na+
• Hodgkin & Huxley
• Had better instruments - could see action potential better

• Stated an AP was generated to due breakdown of membrane potential
• Did not account for Na+

• Em = ~(60/z) log10 [K+]outside / [K+]inside (mV)
• For 1 ion
• z = charge

• At equilibrium, the force exerted by ion concentration is balanced by force exerted by charge
• Chemical vs Electrical

• It accounts for numerous ions permeating the PM
• Can simplify to Nernst when permeability of one ion >> other

• At rest, K >> Na
• At peak AP, NA >> K

Allows researcher to analyze (hopefully) a single ion channel in a membrane

The abolishment of a membrane potential

The re-establishment of a membrane potential

The further reduce (more negative) the membrane potential

To increase (make less negative) the membrane potential

• As a weak base, they can cross membrane in uncharged state
• Inside cell, the charged form can bind to voltage gated Na+ channels
• Prevent generation of an AP

• Leaky K+
• Voltage gated Na+
• Voltage gated K+

The wrinkling of a cell (ie, RBC) due to a high salt solution

• By osmosis across bilipid layer (slow)
• Thru aquaporins (fast)

• 6 transmembrane segments that associate into an hourglass shape
• 

• Orthodox - extremely selective to water
• Cocktail set - homologs; will let similar molecules pass

• The net diffusion of water down its concentration gradient
• Thru a selectively permeable membrane impermeable to the SOLUTE
• Moves from low => high SOLUTE CONCENTRATION

When osmotic pressure = hydrostatic pressure

• Measure of a solution's total solute concentration
• Expressed in Osmoles/L
• A colligative property

• One that depends solely on the number of particles, not the nature of them
• Ie, Osmolarity

290-300 mOsm

• π = RTΦic
• Calculates osmotic pressure
• "i" is the number of moeities the molecule dissolves into
• "c" (molarity) can also be substituted for "m" (molality)
• Φ is the osmotic coefficient
• Closer to ideal the more dilute a solution is

• Ideal = 1
• Monovalent = 0.9-0.95
• Multivalent < 0.9
• Mono-/disaccharides ~ 1 (a little over)

• J_v(net) = K_f (deltaP –σdeltaπ)
• σ is the reflection coefficient
• K_f is the filtration coefficient

• σ = 1 - P(solute)/P(water)
• Describes the permeability of the solute
• σ = 1, impermeable
• σ = 0, permeable

• Related to the size of the membrane
• Related to relative conductivity of water thru the membrane

The concentration of nonpenetrating solutes in the ECF is carefully regulated to match the osmolarity of the ISF

The effect nonpenetrating solutes in a solution have on cell volume

• Osmolarity has units to describe concentration in each compartment
• Tonicity is merely the relative concentration between two compartments

Equal solute concentrations between compartments

[Solutes in ECF] > [Solutes in cell]

[Solutes in ECF] < [Solutes in cell]

• 0.9% NaCl
• 154mM
• 308mOsm

NO

• Net blood pressure entering causes solutes to cross into tissues
• Net osmotic pressure exiting causes the reverse

• Maximized surface area
• Velocity of blood flow is relatively slow

• Water soluble molecules can diffuse thru water-filled gaps
• Lipid soluble can diffuse across endothelial PM
• Proteins CANNOT diffuse across

• Proteins
• Since all other solutes have a σ~0, and proteins are σ~1, only the proteins affect osmotic pressure

• 
• Describes how net pressure on either end of the capillary beds drives molecule transport