Cell Transport and Signaling Flashcards

Flashcards based on lecture notes covering cell transport, signaling, and related concepts.

What is the 60-40-20 rule?

60% of TBW is ICF, 40% of TBW is ECF, and 20% of ECF is Plasma

Approximately how much of body weight is TBW for males?

~60%

Approximately how much of body weight is TBW for females?

~50%

How does the intracellular volume change in relation to extracellular osmolality?

Intracellular volume varies with osmolality of the extracellular compartment; it is only altered if extracellular osmolality changes.

What happens to a cell when ECF osmolality increases?

Water moves out of the cell, and the cell shrinks.

What type of fluid loss is associated with diarrhea?

Isotonic loss

What type of fluid gain is associated with infusion of isotonic NaCl?

Isotonic gain

What type of fluid loss occurs when someone is lost in the desert?

Hypotonic loss, leading to a hypertonic state (dehydration/sweating)

What type of fluid gain is associated with excessive NaCl intake?

Hypertonic gain

What type of fluid loss is associated with adrenal insufficiency?

Hypertonic loss, leading to a hypotonic state

What type of fluid gain is associated with SIADH?

Hypotonic gain

What is osmosis?

The net movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration

What determines the concentration of a solution?

The number of particles

What happens to water concentration as the number of particles in a solution increases?

The water concentration decreases

How is water transported across cell membranes?

Passively, through diffusion through the lipid bilayer or facilitated diffusion via aquaporins

What makes water move across a membrane?

A difference in osmolality

What are osmotically active solutes?

Solutes that contribute to the osmolality of a solution, including proteins and other organic molecules, not just ions

What is the difference between osmolarity and osmolality?

Osmolality is the number of osmoles of solute per kilogram of solvent (Osm/Kg), while osmolarity is the number of osmoles of solute per liter of solution (Osm/L).

What is tonicity?

The ability of an extracellular solution to make water move into or out of a cell by osmosis, influenced only by solutes that cannot cross the membrane

What is the normal range for plasma osmolarity?

275–295 mOsm/kg

Which solute is mainly responsible for plasma osmolarity?

Sodium (Na⁺)

What is the relationship between plasma sodium concentration and plasma osmolarity?

If plasma sodium concentration increases, plasma osmolarity increases; if plasma sodium concentration decreases, plasma osmolarity decreases.

What happens to cells when plasma sodium increases?

Water moves out of cells, and the cells shrink.

What happens to cells when plasma sodium decreases?

Water moves into cells, and the cells swell.

Why is the Na+/K+ ATPase pump needed for osmotic equilibrium?

Maintains ion gradients essential for osmotic balance.

What is the mechanism of action of Ouabain?

Inhibits the Na+/K+-ATPase pump

What happens to intracellular sodium and potassium levels when Ouabain is present?

Na⁺ builds up inside the cell, and K⁺ accumulates outside the cell.

What effect does Ouabain have on intracellular fluid distribution?

Water enters the cell, causing the cell to swell.

What is the function of gap junctions?

Rapid signal propagation between adjacent cells, allowing them to communicate directly.

What is the main function of tight junctions?

Form water "tight" seals between adjacent cells, preventing the passage of molecules between cells.

What is the role of cadherins in adhering junctions and desmosomes?

Allows neighboring cells to sense each other and judge their proximity.

What are the four types of Intercellular Signaling?

Endocrine, Paracrine, Autocrine, and Juxtacrine

How does Paracrine Signaling transport signals?

Signal is secreted by a neighbor cell in the vicinity but not touching the target cell.

How does Autocrine Signaling transport signals?

The cell that secretes the signal is the target cell.

How does Juxtacrine Signaling transport signals?

The signaling cell has a MEMBRANE BOUND signal which is received by direct contact with a receptor on an adjacent cell.

List the factors that influence the rate of free diffusion of a molecule across a membrane.

Concentration difference, size of the molecule, area of the diffusion surface, distance of diffusion, and water solubility

What factors increase the rate of diffusion?

Larger concentration gradient, smaller molecule size, nonpolar molecule, higher membrane permeability, larger surface area, shorter distance, and warmer temperature

What is the role of voltage-gated Na⁺ channels during an action potential?

Open, allowing Na⁺ to rush into the cell, causing depolarization.

What is the role of voltage-gated K⁺ channels during an action potential?

Open, allowing K⁺ to rush out of the cell, causing repolarization.

How does the Na⁺/K⁺-ATPase pump contribute to the action potential?

Restores ion gradients after the action potential by pumping 3 Na⁺ out and 2 K⁺ into the cell against their gradients.

What are some examples of passive transport?

Simple diffusion (e.g., O₂ and CO₂), facilitated diffusion (e.g., glucose), ion channels (e.g., Na⁺ and K⁺ channels), and osmosis

Give some examples of primary active transport.

Na⁺/K⁺-ATPase pump, Ca²⁺-ATPase pump, and H⁺-K⁺ ATPase

Give some examples of secondary active transport.

Na⁺/glucose symporter and Na⁺/Ca²⁺ exchanger

What is the primary function of pumps in cell transport?

Move ions or molecules across a membrane against their concentration gradient, using ATP directly for energy.

Describe exchangers.

Move two ions or molecules in opposite directions across the membrane, using the gradient of one molecule (e.g., Na⁺) to drive the movement of the other.

Describe cotransporters.

Move two ions or molecules in the same direction across the membrane, using secondary active transport.

What is the function of the Na⁺/K⁺ ATPase pump

Maintains ion gradients by pumping 3 Na⁺ out and 2 K⁺ in.

During the depolarization phase of an action potential, what happens to the membrane potential?

Becomes more positive (up to +30 or +40 mV).

During the repolarization phase, how does K⁺ channel activity affect membrane potential?

K⁺ exits the cell, making the membrane potential more negative again.

Describe ion channel inactivation.

Na⁺ channels inactivate after opening (like a door that swings shut but isn’t locked). They must reset (go from inactivated → closed) before they can open again.

What is the role of the m gate in a sodium channel?

Activation gate — opens quickly when the membrane depolarizes, allowing Na⁺ to rush in.

What is the role of the h gate in a sodium channel?

Inactivation gate — closes slowly after depolarization, stopping Na⁺ entry even though the membrane is still depolarized.

What is the role of the n gate in a potassium channel?

Activation gate — opens slowly during depolarization, allowing K⁺ to leave the cell (repolarization)

How do potassium channels affect the potassium equilibrium potential (Eₖ)?

Determined by the Nernst equation, which depends on the intracellular vs. extracellular K⁺ concentration.

How does extracellular K⁺, when increased in Hyperkalemia, affect Eₖ

Eₖ becomes less negative → resting membrane potential depolarizes.

What is the overall effect of digitalis on the heart?

Helps the heart beat stronger and pump more blood; controls the heart beat rate.

What is Neostigmine?

Myasthenia gravis drug (short-acting). Also used for the Reversal of neuromuscular blockade after surgery.

What causes muscle weakness in Myasthenia Gravis?

Autoimmune destruction of AChRs (acetylcholine receptors) at the NMJ (neuromuscular junction).

Explain CICR.

Ca2+ Induced Ca2+ Release. Skeletal muscle depends on the calcium that comes from the SR (sarcoplasmic reticulum).

What causes rigor mortis?

Decreased ATP prevents myosin from detaching from actin.