Physiology Exam I
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- What do phospholipids form in membrane
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bilayer, outside heads are highly polar, form hydrophilic interface with water
inside tails are hydrophobic aliphatic chains - What are glycolipids
- phospholipids with carbohydrate chains
- Describe integral proteins
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Lie within lipid bilayer
Functions - transport, receptors, enzymes, signaling
Hydrophobic regions attach proteins to membranes - Describe peripheral proteins
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Adjacent to membrane
Provide anchoring sites for cytoskeleton
attach by charge interaction (H bonding) - Name 3 types of transport mechanisms
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VESICULAR - membrane mediated - endocytosis and exocytosis
MOLECULAR - protein mediated - channels and carriers
SIMPLE DIFFUSION - lipid soluble solutes and water - Name 3 types of endocytosis
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RECEPTOR MEDIATED - activated by receptors - LDL receptors, clathrin coated, occurs at coated pits
PINOCYTOSIS- responsive to changes in pH
PHAGOCYTOSIS-immune response, destroys foreign bodies, debris - What is an exocytosis
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Movement out of the cell
example - secretory enzyme release, NT release - Describe voltage gated channels
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2 types - VOLTAGE GATED and LIGAND GATED
-change configuration only to open and close
Movement through channels determined by ELECTRICAL and CHEMICAL gradients
Functions - extracellular signaling (AP), intracellular signallng (controling intracellular Ca) - Describe carriers
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3 types - COTRANSPORT, ANTIPORT, FACILITATIVE DIFFUSION
Active - uses ATP directly
Passive - doesnt use ATP
Secondary active - indirect need for ATP
-FIXED stoichiometry
-change conformation with every transport cycle - Describe ligand gated channels
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Opened by ligands - any chemical that binds to channel (hormone, NT)
Functions - neural decision making (EPSP, IPSP), intracellular signaling (control of intracellular pH, Ca) - Describe cotransport
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-Moves more then one solute
-All solutes move in SAME direction - Describe Antiport
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-Moves more then one solute
-At least one solute moves in OPPOSITE direction - Facilitated Diffusion
- Only ONE solute, makes membrane more permeable
- Describe saturation of carriers
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Can only transport so many molecules. Maximum is called Tm or Transport maximum, simple diffusion doesnt have transport maximum
Glucose appears in urine of diabetics because proximal tubule transport maximum is exceeded - Simple diffusion
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Cell membrane is permeable for lipid soluble substances (hydrophobic)
Cell membrane also has aquaporins - water channels - What is the name for movement between cells
- Paracellular route
- What is the name for movement thorugh cells
- Transcellular route
- Give an example of epithelial transport
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Oral rehydration therapy
Transcellular movement of Na makes lumen more negative (negative transepithelial potential) which causes paracellular movement of Cl.
Transepithelial movement of solutes NaCl and glucose causes H2O to follow by osmosis - Describe electrical equivalent voltage
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Ion movements determine cell membrane potential Vm
Electrical (Vm) and chemical (concentration gradient) forces cause ion movements
Electrical equivalent voltage - Ei is chemical force acting on ion stated in electrical terms - How do you determine net force acting on ion
- By combining Vm and Ei
- What is the direction of net movement of ions
- From higher to lower concentration
- What is the prefered direction for Na
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From outside to inside
Outside - 140 Mm, inside 8Mm - What is the preferred direction for K
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From inside to outsidde
Outside - 4mM, inside - 155 mM - What is the direction for Cl
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From outside to inside
Outside - 100 mM, inside - 4 mM - Is Ca higher inside or outside
- Outside, very very low inside (0.0001 mM)
- Nernst eqution for K
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Ek= RT/zF ln [Kin]/[Kout]
Ek= 60 mV log [Kin]/[Kout]
If switch in and out, sign will change - What is the Vm for most neurons
- from -70 to -85
- What is Vm for muscle
- -95 mV
- What is the Vm for epithelial cells
- Apical and basolateral membranes of epithelial cells have different Vm due to transepithelial potential
- WHat is Ek
- -90 to -95 mV, always more NEGATIVE then Vm
- WHat is E Na
- +70-+80, always more POSITIVE then Vm
- Is Ecl more positive or negative then Vm
- More positive in neurons so it want to enter the neuron, but in small epithelial cells wants to exit
- How do you determine net electrochemical driving force
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Sum of chemical and electrical driving forces
Force = Ei - Vm
Ei - chemical driving force
Vm- resting membrane potential
In case of Na - Ei and Vm act together
In case of K and Cl, they oppose each other, so driving force determines movement - When does equilibrium exist in cell
- When Ei=Vm
- Why is Vm of neurons normally around -90?
- Many K channels are open and few Na channels are open.
- Conductance equals to
- 1/resistance
- What are local potentials
- Changes in neurons Vm in response to NT's released from other neurons
- How do NT s generate local potentials
- by opening ligan gated Na, K and Cl channels
- Why does Vm returns to resting potential after AP
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1. Na channels closed
2.K channels slowly open - What is the name for transition of open Na voltage gated channels to closed state?
- Repolarization phase
- Slow transition of voltage gated K channels from resting to open state causes
- After hyperpolarization
- Overshoot
- There are many more open Na than K channels, membrane potential becomes positive since E Na is positive
- What is responsible for repolarization phase
- close Na channels, open K channels
- Absolute refractory period
- Na channels in open state automatically start to move to closed state, many of channels must return to RESTING STATE before new AP can be generated. 5 msec
- Relative refractory period
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Until there are as many Na channels in resting state as there were before AP, greater depolarization is needed to generate second AP. 20 msec
Help prevent repetitive firing, retrograde transmission and cardiac arrhythmias. - What are two gates voltage gated channels have
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m gate - activation gate
h gate - inactivation gate - How AP's originate
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-in the HILLOCK
-in skeletal and smooth muscle originate at MOTOR END PLATE
-cardiac muscle originate at PACEMAKER CELLS - Which cells conduct faster - at depolarization or hyperpolarization
- At depolarization fewer channels are in resting state, so fewer available for AP
- Depolarizing factors
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HIGH K - drugs, kidney failure, severe trauma, burns
INHIBITION OF Na, K ATPase - digitalis and similar drugs
CELL DAMAGE or HYPOXIA - ischemia, MI - How does myelin increase speed
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1. Myelin axon interaction concentrates Na channels at nodes, increasing current and power
2. Myelin reduces impedance by decreasing membrane capacitance, allowing voltage to change more quickly
3. Myelin reduces membrane ion leaks by increasing resistance, increases current flow