Homeostasis and Transport Flashcards
Circulation
Moves fluids and gases
Diffusion
of fluid to interstitial space, into and out of a cell; of gas from extracellular fluid into or out of a cell; of ions/molecules from high to low concentration gradient
Transport
Movement of ions/molecules through channels or transporters into and out of cells; pumping of ions/molecules against concentration gradient
Homeostasis
Regulation of blood gases, ion concentration/water, blood pressure, and hormones
Positive feedback
causes a self-amplifying cycle, where change leads to even greater change in same direction (Na channel activation activates more channels)
Negative feedback
process in which the body senses change and activates mechanisms to reverse that change (K channels inhibiting Calcium channel)
Na+ Concentration
Extracellular: 142 mEq/L
Intracellular: 10 mEq/L
K+ Concentration
Extracellular: 4 mEq/L
Intracellular: 140 mEq/L
Ca++ Concentration
Extracellular: 2.4 mEq/L
Intracellular: 0.0001 mEq/L
Cl- Concentration
Extracellular: 103 mEq/L
Intracellular: 4 mEq/L
HCO3- Concentration
Extracellular: 28 mEq/L
Intracellular: 10 mEq/L
Glucose
Extracellular: 90 mg/dl
Intracellular: 0-20 mg/dl
Proteins
Extracellular: 2 g/dl (5mEq/L)
Intracellular: 16 g/dl (40mEq/L)
Sodium Reference Range
135-146 mmol/L
Potassium Reference Range
3.5-5.3 mmol/L
Chloride Reference Range
98-110 mmol/L
Passive Transport
does not require energy and may require channel protein or carrier protein. Down concentration gradient
Factors that alter passive transport
Membrane permeability, concentration difference, electrical potential, and pressure
Simple diffusion
does not require energy and moves from high to low concentration
Factors effecting simple diffusion
Concentration difference, electrical difference, and permeability (channels being open)
Two types of ion channels
Voltage-gated ion channel
Ligand-gated ion channel
Voltage-gated ion channels
open or closes in response to membrane potentials; only allow one type of ion through
Ligand-gated ion channel
open or closes in response to binding of small molecule; less selective allows two or more types of ions through
Voltage-gated sodium channels
Have two gates (activation and inactivation gate) when resting activation gate is closed, when active both are open and during inactivation the inactivation gate closes. Very fast (1-2ms)
Voltage-gated potassium channels
Has only one gate. Is slower activating/opening compared to Na+ channels (50ms)
Ligand-gated channel examples
ACh binding nicotinic receptors causes influx of Na+; G-Protein Coupled ion channels
Facilitated diffusion
Goes down the concentration gradient; needs a carrier protein (Ex. GLUT4 is a glucose carrier protein across the cell membrane
Facilitated diffusion is determined by
Concentration of carrier molecules (Vmax) and the rate of movement of carrier molecules across the channel
Active transport
Movement of molecules against their concentration gradient, requires energy, and a carrier protein (exhibit Vmax)
Examples of active transport
Na+/K+ Pump; Ca2+ Pump, and H+ Pump
Secondary active transport
using energy from one solute moving with their gradient to move another substance against their gradient
Secondary active transport: Cotransport (symport)
both ions in the same direction (Sodium glucose co-transporter)
Secondary Active Transport: Exchangers (counter-transport or antiport)
Ions move in separate directions (Chloride shift; bicarb leaving against and chloride in with gradient or vice versa)
Osmotic pressure
Pressure required to maintain an equilibrium with no net movement of solvent
Semi-permeable
Water can move but ions cannot; movement determined by molar concentration of solute
Osmolarity
osmoles of solute (can dissociate within solution) per liter of solution; 1 mole of NaCl yields 2 osmoles of solute particles in water
Osmolarity of normal body fluid
280-310 mOsm/L
What is the osmolarity of 50mM CaCl2 and 5mM NaHCO3?
160 mOsm/L (HCO3 = 1)
Hypertonic solution
Water rushes out of the cell; the solution (outside of cell) has a greater solute concentration compared to the inside of the cell (hyperosmotic)
Hypotonic solution
Water rushes into the cell; solution has lesser solute concentration compared to inside the cell (hypoosmotic)
Isotonic solution
Has the same concentration inside compared to the outside
Resting membrane potential
the difference in electrical potential between the interior and exterior of a biological cell at rest
Graded potential
changes in membrane potential that vary in size, as opposed to being all-or-none. They include diverse potentials such as synaptic potentials, end plate potentials, receptor potentials, pacemaker potentials, and slow-wave potentials, which scale with magnitude of stimulus
Action potential
occurs when the membrane potential rapidly rises and falls in excitable cells, which include neurons, muscle cells, cardiac cells, and endocrine cells
Resting membrane potential is set by:
opening of leak K+ channels
Nernst equation simplified
Eion = (61/Z) x Log(IONoutside/IONinside) Z = charge of the ion
Goldman equation
equilibrium potential for multiple ions; P = permeability in the equation
EPSP
excitatory postsynaptic potential
ISPS
inhibitory postsynaptic potential
Axon hillock
Spike-initiation zone; Action potential generation point
Beginning of action potential until threshold is reached
RMP: K+ leak channel maintains this
AP begins with ligand-gated channels which leads to depolarization
Depolarization
the opening of voltage gated Na+ channels increases AP (Na+ in»_space; K+ out) until it reaches a balanced peak
Repolarization
reaches balance point and repolarization begins with the close of voltage gated Na+ channels and and K+ opening (K+ out»_space; Na+ in)
Hyperpolarization
Voltage gated K+ channels remain open after potential reaches resting level; causes a little overshoot
AP Stages: All or none
Resting stage: K+ leak channels
Threshold: EPSPs (Na+ in) > (K+ out)
Depolarization: VG Na+ channels > VG K+ Channels
Repolarization: VG K+ channels > Na+ channels
Hyperpolarization: VG K+ channels
Graded potential (synaptic potentials)
Generated on dendrites and cell bodies; have to reach a threshold potential at axon hillock to stimulate AP; can decay over distance; neurotransmitters open ion channels on dendrites and cell bodies and create graded potentials summed at axon hillock (ESPS and ISPS)
spatial summation
eliciting an action potential in a neuron with input from multiple presynaptic cells
temporal summation
effects of impulses received at the same place can add up if the impulses are received in close succession
Conduction of an AP down axon
Depolarization of the axon at one point causes voltage-gated Na+ channels to open ahead of this point which migrates the AP down the axon
Myelinated nerve fibers
Schwann cells (PNS) or oligodendrocytes (CNS) 100m/s myelinated - 0.25 m/s unmyelinated
Absolute refractory period
Inactivation gate of Na+ channel closed
Relative refractory period
Need a stronger stimulus to initiate a response (during hyperpolarization)
Graded Potential vs Action Potential
Graded: does not reach threshold, causes local membrane change (-70 to -60), dies down over short distance, can be summated, does not obey all or none law
Action: reaches threshold which causes AP, causes depolarization to threshold level, is propagated, can be summated, obeys all or none law
What does the Na+/K+ pump do?
Establish ion gradients, helps set membrane potential, creates negative potential, helps determine excitability of nerve/muscle (fatigue), control cell volume
