Cell physiology Flashcards by Rebecca Unknown

What makes up the lips bilayer of cells

Glycerol backbone with hydrophilic heads and 2 fatty acid tails (hydrophobic) that face one another and form a bilayer

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What are some examples of lipid-soluble substances

Oxygen
Carbon dioxide
Steroids

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What are examples of water-soluble substances

Sodium
Chloride
Glucose
Water

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Integral proteins

Anchored to and imbedded in cell membrane through hydrophobic interactions

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Examples of integral proteins

Ion channels
Transport proteins
Receptors
Guanosine 5’-triphosphate (GTP)
Binding proteins (G proteins)

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Zona occludens

Tight junctions- attachments between cells (often epithelial),
True tight junctions are impermeable (ex. renal distal tubule)
Others are leaky (ex. renal proximal tubule, gallbladder)

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Gap junctions

Attachments between cells that permit intercellular communication, permit current flow and electrical coupling between myocardial cells

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Simple diffusion- is a carrier needed

No carrier needed for transport

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Factors that increase permeability

Decrease in size of solute
Increase in oil/water coefficient
Decrease in membrane thickness
Increase of higher concentration of solute
Decrease in lower concentration of solute

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Stereospecificity for carrier-mediated transport

Carries may only allow isomers to be transported

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Saturation of carrier transporters

Transport rate increases as concentration of solute increases until the carriers are saturated (transport max= Tm)

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Facilitated diffusion

Occurs down an electrochemical gradient, similar to simple diffusion. Does not require energy (passive), more rapid than simple diffusion, carrier-mediated

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examples of facilitated diffusion

Glucose transport in muscle and adipose cells
*In diabetes mellitus, glucose uptake is impaired b/c the carriers for facilitated diffusion of glucose require insulin

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Primary active transport

Occurs against an electrochemical gradient (uphill), requires direct input of ATP (active), is carrier mediated

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Na-K ATPase Pump

Primary active transport in cell membranes transporting Na from intracellular to extracellular fluid and K+ from extracellular to intracellular fluid
Maintains low intracellular Na and high intracellular K+

Remember: 3 Na out/2 K in

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Ca++ ATPase

Primary active transport in sarcoplasmic reticulum (SR) or cell membranes transports Ca++ against electrochemical gradient

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H+, K+ ATPase

Primary active transport (aka proton pump)
Gastric parietal cells
Transports H into lumen of stomach against electrochemical gradient

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Secondary active transport

Transport of 2 or more solutes is coupled
One of the substances (usually Na) is traveling “downhill” and provides energy for the transport of other solutes
Metabolic energy is not provided directly, but secondarily through the Na gradient

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Na-glucose transporter

Cotransporter
Carrier for Na-glucose cotransport located on luminal side of intestinal mucosa and renal proximal tubulue
Glucose going “uphill”, sodium going “downhill”

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Where is the Na-K-2Cl co-transporter located

renal thick ascending limb

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Na-Ca countertransporter

-Secondary active transport
-Na-Ca exchanger transports Ca uphill from low IC Ca to high EC Ca
-Ca and Na move in opposite directions
-Energy is derived from the downhill movement of Na
-Gradient is maintained by the Na-K pump

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Osmolarity

Concentration of osmotically active particles in solution

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Isosmotic

2 solutions have same calculated osmolarities

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Osmosis

Flow of water across a semipermeable membrane from a solution with low solute concentration to a solution with high concentration

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Van Hoff's law

-Osmotic pressure depends on the concentration of osmotically active particles

What increases osmotic pressure

When solute concentration increases, more water flows into it (would be a hypertonic solution)

Colloid osmotic pressure or oncotic pressure

Osmotic pressure created by proteins

Reflection coefficient

-Number between 0 and 1 that decreases ease with which a solute permeates a membrane -Coefficient of 1: solute is impermeable -Coefficient of 0: solute is complete permeable

Integral proteins

Span cell membranes, permits passage of ions

Conductance of an ion channel

Depends on probability that channel is open -opening and closing depends on gates, may be voltage-gated or ligand-gated

Diffusion potential

Potential different generated across a membrane because of a concentration difference of an ion

Nernst equation

Used to calculated equilibrium potential at a given concentration difference of a permeable ion across a cell membrane -tells us what potential would exactly balance tendency for diffusion down the concentration gradient

Resting membrane potential

Expressed as the measured potential difference across the cell membrane in millivolts -conventially expressed as the intracellular potential relative to extracellular potential

which ion is most permeable to a nerve membrane at rest

potassium -RMP of K is -85mV -RMP of nerve is -70mV

Action potential

Property of excitable cells that consists of a rapid depolarization followed by depolarization of the membrane potential

Upstroke of action potential

Depolarization causes rapid opening of activation gates of Na channels

How does lidocaine block sensation

-Blocks voltage-gated sensitive Na channels -Abolishes action potentials

Which ion is more permeable during depolarization of an action potential

potassium

what effect does hyperkalemia have on skeletal muscle

causes slight depolarization of the AP by bringing the RMP closer to threshold -muscle weakness results from lack of AP due to closure of Na inactivation gates

conduction velocity of action potentials is increased by

increased nerve fiber size and myelination

where are action potentials generated in myelinated nerve fibers

nodes of ranvier

which ion causes release of neurotransmitters after depolarization at the presynaptic membrane

Calcium enters the presynaptic terminal after depolariation

What effect does botulinum toxin have on neuromuscular transmission

Blocks release of Ach from presynaptic terminals causing total neuromuscular blockage (muscle weakness)

what effect does curare have on neuromuscular transmission

competes with Ach for receptors on motor end plate (decreases size of end plate potential) -max doses will produce paralysis of respiratory muscles and death

what effect does neostigmine have on neuromuscular transmission

inhibits acetylcholinesterase -prolongs and enhances action of Ach at muscle end plate

Which receptor does the neurotransmitter Ach bind to

Nicotinic receptors on post synaptic membranes

Which channels open when presynaptic terminal is depolarized

Ca channels

Describe the events that take place at the neuromuscular junction

1. choline acetyltransferase catalyzes the formation of Ach from acetyl coenzyme A and choline in the presynaptic terminal. Ach is stored in synaptic vesicles 2. action potentials conducted down the motor neuron, depolarization at presynaptic terminal opens Ca channels 3. Ca uptake causes release of Ach into synaptic cleft 4. diffusion of the Ach to the postsynaptic membrane (muscle end plate) and binding to Ach to nicotinic receptors 5. binding of Ach to alpha subunits of receptor causes a conformation change that increases conductance to Na and K

Example of a substance that has a reflection coefficient of 1

Serum albumin -impermeable, creates osmotic pressure

Example of a substance that has a reflection coefficient of 0

Urea -solute is completely permeable, does not exert osmotic effect

Ligand-gated channels

Opened or closed by hormones, second messengers, or neurotransmitters (ex. nicotinic receptor)

What determines resting membrane potential

Potassium -K is actively pumped into the cell by the Na/K ATPase

How does myasthenia gravis cause muscle weakness

Presence of antibody to Ach receptor- reduced number of Ach receptors

Treatment for myasthenia gravis

Neostigmine -AchEsterase inhibitor to increase the Ach available for binding at motor endplate

What are examples of excitatory neurotransmitters

Ach, norepinephrine, epinephrine, dopamine, glutamate, serotonin, histamine

What is the action of an excitatory neurotransmitter

Depolarizes postsynaptic cell (brings it closer to the threshold)

What are examples of inhibitory neurotransmitters

GABA, glycine, nitric oxide (NO)

How do inhibitory neurotransmitters hyper polarize the postsynaptic cell

Open chloride channels

How do excitatory neurotransmitters depolarize the postsynaptic cells

Open Na and K chanels

How is norepinephrine removed from the presynaptic terminal

Reuptake or metabolized by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT)

How is epinephrine synthesized

Phenylethanolamine-N-methyltransferase in the adrenal medulla

Where is dopamine released from

Hypothalamus -inhibits prolactin secretion

What metabolized dopamine

MAO and COMT

What is N-methyl-D-aspartate a receptor for

Glutamate -an excitatory neurotransmitter

How do benzodiazepines lead to relaxation

Potentiation of GABA-a receptors

Cell physiology Flashcards

(65 cards)