Cardiac Function and Membrane Transport Quiz

Questions and Answers

What is the primary focus of pathophysiology?

The study of the structure of organisms and their parts

The examination of chemical messengers between cells

The investigation of the basic units of life

The analysis of disordered physiological processes due to disease or injury (correct)

What component makes up the largest percentage of total body water in humans?

Interstitial Fluid

Plasma Volume

Extracellular Fluid

Intracellular Fluid (correct)

Which of the following correctly describes the function of hormones?

They are broken down and carry signals over long distances

They act as chemical messengers on distant target cells (correct)

They only influence organs and cannot affect tissues

They act on the same cell that produces them

How is Body Mass Index (BMI) calculated?

Weight in kilograms divided by height in meters squared Signup and view all the answers

What type of signaling is characterized by a chemical messenger produced by a cell that acts on itself?

Autocrine signaling Signup and view all the answers

What initiates an action potential?

Depolarization to or above threshold Signup and view all the answers

How does the amplitude of an electronic potential change as it travels along the membrane?

Decreases with distance Signup and view all the answers

What type of process is an action potential?

Active process dependent on ion channel gating Signup and view all the answers

During which period can no action potential be elicited, regardless of stimulus strength?

Refractory period Signup and view all the answers

Which of the following factors affects the conduction velocity of myelinated nerve fibers?

Internodal length and myelin sheath resistance Signup and view all the answers

In relation to axon diameter, where does conduction velocity tend to be faster?

Large diameter axons Signup and view all the answers

What characteristic describes the response of an action potential?

All-or-none response Signup and view all the answers

What does the refractory region ensure during the propagation of action potentials?

Action potentials will move away from each other Signup and view all the answers

What does a reflection coefficient (s) of 1 indicate about a solute's permeability through a membrane?

The solute is completely impermeable. Signup and view all the answers

Which statement correctly describes the role of the Na-K pump in cells?

It helps maintain cell volume under isosmotic conditions. Signup and view all the answers

What is the primary structure of cell membranes that limits the movement of solutes?

A bilayer of phospholipid molecules. Signup and view all the answers

According to Fick’s First Law, which factor influences the movement of solutes across a cell membrane the most?

Concentration gradient of the solute. Signup and view all the answers

In the context of osmosis, what does the term 'net water movement down the osmotic gradient' refer to?

Water moving from an area of lower solute concentration to higher solute concentration. Signup and view all the answers

What effect does digoxin have on intracellular sodium levels?

Increases intracellular sodium levels Signup and view all the answers

Which ion concentration is typically high in intracellular fluids compared to extracellular fluids?

Potassium (K+) Signup and view all the answers

How does the transmembrane potential typically behave in living cells?

It is negative inside relative to the outside Signup and view all the answers

What role do membrane carriers play in cellular function?

They provide passive pathways for solutes to move across membranes Signup and view all the answers

What factor does NOT determine the diffusion potential of an ion across a membrane?

Temperature of the environment Signup and view all the answers

What is the main consequence of digoxin's action on Na+/Ca2+ counter-transport?

Increases intracellular Ca2+ levels Signup and view all the answers

Which of the following statements about channels is true?

Channels are ion selective pores that can open and close transiently Signup and view all the answers

Which ion is typically found at relatively high concentrations in extracellular fluid?

Sodium (Na+) Signup and view all the answers

What characterizes the relative refractory period of a neuron?

It occurs immediately after an action potential. Signup and view all the answers

Which of the following best describes the role of epithelial cells?

They regulate body fluid homeostasis and nutrient absorption. Signup and view all the answers

In which type of epithelia is water permeability extremely low and insensitive to ADH?

Ascending limb of the loop of Henle Signup and view all the answers

What is passive tension in muscle contraction?

Tension developed by stretching the muscle. Signup and view all the answers

Which mechanism regulates sodium transport in epithelial cells?

It adapts based on the organism's need to excrete or retain salt. Signup and view all the answers

How often can neurons typically fire action potentials under normal conditions?

Rarely exceed 20 Hz Signup and view all the answers

Which type of muscle contraction does not involve motion?

Isometric contraction Signup and view all the answers

Which of the following epithelia always has high water permeability and is not regulated?

Small intestine Signup and view all the answers

What happens to a red blood cell in a hypotonic solution?

The cell swells and may lyse. Signup and view all the answers

What is the primary function of the Na-K pump in maintaining cellular homeostasis?

Creating an osmotic gradient between intra and extracellular fluids. Signup and view all the answers

Which of the following correctly describes an isosmotic solution?

Keeps the red blood cell unchanged in size. Signup and view all the answers

How does active transport differ from passive diffusion?

Active transport requires energy input. Signup and view all the answers

What effect does the activation of the Na-K pump have on cell volume?

It prevents cell swelling by regulating ion balance. Signup and view all the answers

What is the primary energy source for pumps like the Na-K pump in cellular transport?

Adenosine triphosphate (ATP). Signup and view all the answers

Which statement is true regarding hypertonic solutions?

They create a net movement of fluid out of the cell. Signup and view all the answers

What is the role of cardiac glycosides in relation to the Na-K pump?

They inhibit the Na-K pump, strengthening the heartbeat. Signup and view all the answers

What does a reflection coefficient (s) value of 0.5 indicate about a solute's permeability through a membrane?

The membrane is moderately permeable to the solute. Signup and view all the answers

Which statement accurately describes the role of the Na-K pump?

It helps maintain cell volume under isosmotic conditions. Signup and view all the answers

What principle does Fick's First Law describe?

The diffusion of solutes across a cell membrane. Signup and view all the answers

What is a primary function of lipids in cell membranes?

Creating a barrier to water and water-soluble substances. Signup and view all the answers

What outcome is expected when a solute and water are freely permeable across a membrane?

Equilibrium of solute concentration and volume will be achieved. Signup and view all the answers

What is the primary effect of an inward current on membrane potential?

It causes depolarization of the membrane potential. Signup and view all the answers

What change occurs during the repolarizing phase of an action potential?

gNa+ inactivation and gK+ increase. Signup and view all the answers

What determines the amplitude of graded potentials?

The intensity of the stimulus applied. Signup and view all the answers

How does hyperpolarization affect the membrane potential?

It makes the membrane potential more negative. Signup and view all the answers

What mechanism is primarily used by the Na-K ATPase pump?

Metabolic energy to transport ions against their gradient. Signup and view all the answers

Which ion permeability primarily influences the overshoot of an action potential?

Permeability to Na+. Signup and view all the answers

What is a consequence of local graded potentials not reaching threshold?

They decay locally and do not lead to further depolarization. Signup and view all the answers

What happens to membrane potential when gNa+ reaches high levels during an action potential?

The membrane potential approaches ENa. Signup and view all the answers

What is the primary mechanism by which digoxin affects cardiac function?

Inhibits Na/K ATPase activity Signup and view all the answers

Which of the following accurately describes the typical ion concentration gradients in living cells?

High K+ and low Na+ concentrations inside the cell Signup and view all the answers

Which statement correctly reflects the characteristics of membrane potential in excitable cells?

Transmembrane potential can range from -10 mV to -100 mV Signup and view all the answers

What is the consequence of an increased intracellular Na+ level due to digoxin usage?

Increased intracellular Ca2+ concentration Signup and view all the answers

Which factor does NOT influence the diffusion potential of ions across a membrane?

Molecular weight of the ion Signup and view all the answers

In terms of cellular transport, what is a characteristic function of channel proteins?

They selectively allow ions to pass down their gradients Signup and view all the answers

What defines the electrical potential difference known as transmembrane potential?

The potential difference between the inside and outside of the cell Signup and view all the answers

Which condition best describes the effect of digoxin on cardiac muscle contraction?

Enhanced contractility due to increased intracellular Na+ and Ca2+ levels Signup and view all the answers

What is the difference between electronic potential and action potential in terms of response type?

Action potential exhibits a graded response. Signup and view all the answers

How does myelination affect the conduction velocity of nerve fibers?

Myelinated fibers enhance conduction speed due to insulation. Signup and view all the answers

What characterizes the absolute refractory period in action potential propagation?

No action potential can be elicited regardless of stimulus strength. Signup and view all the answers

In what way does the diameter of a nerve fiber relate to its conduction velocity?

Larger diameter fibers conduct impulses faster. Signup and view all the answers

What is a consequence of local circuit current flow during action potentials?

It contributes to the continued spread of depolarization to adjacent membrane regions. Signup and view all the answers

How does the excitability of large diameter axons compare to small diameter axons?

Large diameter axons have high excitability. Signup and view all the answers

What happens to the amplitude of action potentials as they travel along the membrane?

Amplitude decreases with distance along the membrane. Signup and view all the answers

What role does the refractory period play in the propagation of action potentials?

It prevents action potentials from moving in both directions. Signup and view all the answers

Study Notes

Digoxin and Cardiac Function

Digoxin inhibits Na+/K+ ATPase, leading to increased intracellular sodium (Na+) and decreased sodium gradient.
This results in a decreased Na+/Ca2+ counter-transport, ultimately increasing intracellular calcium (Ca2+).
It has been a foundational treatment for heart failure and is currently the only oral inotropic agent in clinical use.

Cell Membrane Transport

Carriers are enzyme-like proteins that create passive pathways for solutes to cross membranes along concentration gradients.
Channels are ion-selective pores that open and close transiently, facilitating ionic movement based on electrical and chemical gradients.
Signals in excitable cells are produced through channel activity that alters membrane potential.

Excitable Cells and Membrane Potential

The transmembrane potential (Em) is the voltage difference across the cell membrane, typically negative inside relative to the outside.
Em ranges from -10 mV to -100 mV in living cells, indicating high intracellular potassium (K+) and anionic protein levels, while sodium (Na+) and chloride (Cl-) are relatively low.
Diffusion potential depends on ion charge, membrane permeability, and ion concentration differences.

Excitable Cells: Action Potential

Action potentials are initiated by depolarization reaching a threshold, following a passive process dependent on membrane properties.
The local circuit current maintains depolarization spread, increasing Na+ permeability as the threshold is met.
Refractory regions help ensure action potentials propagate away from each other.

Nerve Fibers and Action Potential Propagation

The speed of action potential conduction in nerve fibers is influenced by axon diameter and myelination.
Larger diameter unmyelinated fibers conduct signals faster than smaller ones, while myelination significantly increases conduction velocity.
Absolute refractory period prevents subsequent action potentials regardless of stimulus strength.

Cellular Physiology and Organization

The human body is formed from ~100 trillion differentiated cells organized into tissues, organs, and organ systems.
Hormones are chemical messengers acting on distant cells, while paracrine and autocrine signals target nearby and self cells, respectively.

Body Fluid Composition

Body water content is approximately 57%, with variations (65-70% in infants).
Total body water distribution: intracellular fluid (ICF) at ~63%, extracellular fluid (ECF) at ~37%, with interstitial fluid and plasma volumes noted.

Body Mass Index (BMI)

BMI is calculated as weight (kg) divided by height (m²) and serves as a key metric for assessing obesity.
Categories include underweight, normal weight, overweight, and obesity.

Cell Membrane Functions and Solute Movement

Cell membranes regulate solute movement, with Fick’s First Law detailing solute diffusion across membranes.
Lipid bilayers serve as barriers to water and water-soluble substances, while specific channels facilitate transport.
Reflection coefficient indicates solute permeability through membranes, ranging from impermeable (s = 1) to highly permeable (s = 0).

Epithelial Transport Mechanics

Epithelia act as barriers between internal and external environments, regulating fluid balance, nutrient absorption, and waste excretion.
Na+ transport in epithelial cells can be intrinsic or extrinsic, adjusting to maintain electrolyte homeostasis.
Epithelial water transport can vary significantly between regions, displaying high, low, or regulated permeability depending on specific needs.

Excitable Cells: Muscle Types

Skeletal muscle exhibits isometric contractions without motion, characterized by passive and total tension measurements at various lengths.
Active tension stems from cross-bridge cycling, while passive tension accumulates from muscle stretching.

Cell Volume Regulation and Na-K Pump

Cells swell and burst without the Na-K pump, which transports 3 Na+ out for every 2 K+ in.
Proteins and organic compounds inside cells are anionic, leading to cation accumulation and water influx.
The Na-K pump is activated by a 15% increase in cell size.

Body Fluid Distribution: Tonicity

Isotonic: No net fluid movement in or out of red blood cells.
Hypotonic: Causes net fluid influx into red blood cells, leading to swelling or lysis.
Hypertonic: Causes net fluid outflow, resulting in cell shrinkage.
Isosmotic: Equal concentration of osmotically active particles across a semipermeable membrane.

Osmolarity vs Tonicity

Osmolarity indicates concentration of solutes and varies with solute type (NaCl, Urea, CaCl2).
NaCl concentrations and their corresponding osmolarity impact tonicity classifications (isotonic, hypertonic, hypotonic).

Cell Membrane Transport

Diffusion: Passive transport, movement down a concentration gradient without energy.
Active Transport: Involves energy and a "carrier" to move solutes against a concentration gradient.

Pumps and Membrane Carriers

Pumps, like ATP-dependent Na-K pump, establish ion gradients and utilize energy (ATP).
Cardiac glycosides inhibit Na-K ATPase, leading to increased intracellular Na+ and Ca2+ for heart function.

Reflection Coefficient

Measures permeability of solute through membranes (ranges from 0 to 1), where 1 indicates complete impermeability.

Membrane Structure and Solute Movement

Cell membranes limit solute movement, maintaining concentration gradients.
Fick’s First Law describes solute movement across membranes, emphasizing permeability and concentration differences.

Ion Concentration Gradients in Excitable Cells

High intracellular potassium (K+) and anionic proteins (Pr-); low sodium (Na+) and chloride (Cl-).
Extracellular fluid is rich in Na+ and Cl-, almost devoid of K+.

Membrane Potential in Excitable Cells

Transmembrane potential (Em) is negative inside relative to outside, typically between -10 mV to -100 mV.
Changes in permeability to ions regulate Em; Na-K ATPase maintains homeostasis.

Graded and Action Potentials

Graded Potential: Local depolarization that may not reach threshold; proportional to stimulus intensity.
Action Potential: A rapid and all-or-nothing signal.
Depolarizing phase caused by increased Na+ permeability; repolarizing phase by K+ efflux.

Excitable Cell Functionality

Types include neurons, skeletal, cardiac, and smooth muscle.
Action potentials are crucial for signaling and muscle contraction.

Membrane Potential Dynamics

Depolarization increases Na+ permeability; hyperpolarization decreases it.
Overshoot occurs when Em surpasses 0 mV, returning to repolarization.

Refractory Periods

Absolute Refractory Period: No new action potential can be generated regardless of stimulus strength.

Factors Influencing Nerve Conduction

Conduction velocity in nerve fibers is influenced by axon diameter and myelination.
Myelinated fibers offer faster conduction due to insulated segments (internodal lengths).

Overall Functional Properties of Axons

Large diameter axons enable fast conduction and high excitability, while smaller diameters result in slower conduction.

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Description

Test your knowledge on digoxin's effects on cardiac function as well as the principles of cell membrane transport. Explore how ion channels and carriers facilitate solute movement and understand the significance of membrane potential in excitable cells. This quiz covers essential concepts in cardiovascular physiology and cellular biology.