Cardiac Muscle and Circulatory Physiology Flashcards

Vocabulary flashcards based on lecture notes covering cardiac muscle function, cardiac cycle, and circulatory physiology.

Atrial muscle

Responsible for the contraction of the atria.

Ventricular muscle

Responsible for the contraction of the ventricles.

Specialized excitatory and conductive muscle fibers

Includes structures like the SA and AV nodes.

Phase 0 (Depolarization)

Fast Na⁺ channels open, resulting in rapid depolarization.

Phase 1 (Initial repolarization)

Na⁺ channels close; transient K⁺ efflux.

Phase 2 (Plateau)

Ca²⁺ influx via slow channels; K⁺ efflux decreases.

Phase 3 (Repolarization)

Ca²⁺ channels close; K⁺ efflux resumes.

Phase 4 (Resting potential)

Maintained at approximately -90 mV.

Diastole

Relaxation, filling phase of the cardiac cycle.

Systole

Contraction phase of the cardiac cycle.

P wave

Represents atrial depolarization on an ECG.

QRS complex

Represents ventricular depolarization on an ECG.

T wave

Represents ventricular repolarization on an ECG.

Rapid ventricular filling

First third of diastole, characterized by rapid ventricular filling.

Diastasis

Middle third of diastole.

Atrial systole

Last third of diastole, contributes 20% of ventricular filling.

Isovolumic contraction

Phase with no volume change, pressure increases.

Ejection phase

Phase when left ventricular pressure rises slightly above 80 mm Hg.

Ejection phase

Phase when right ventricular pressure rises slightly above 8 mm Hg.

Fast ejection

First third of ejection, ejects 70% of blood.

Slow ejection

Last 2/3 of ejection, ejects 30% of blood.

Isovolumic relaxation

Phase where intraventricular pressures decrease rapidly.

T-tubules

Conducts action potential, leading to Ca²⁺ release and contraction.

Refractory Period

Period when muscle is unresponsive to new stimulus.

0.25–0.30 sec

Ventricular refractory period duration.

Heart Rate and Cardiac Cycle Relationship

Increased heart rate leads to decreased duration of both systole and diastole.

Preload

Initial muscle stretch before contraction (EDV).

Afterload

Resistance the heart must pump against (e.g., BP).

Frank-Starling Mechanism

Greater stretch leads to stronger contraction and more blood ejected.

Effect of High Potassium (K⁺)

High K⁺ levels lead to a flaccid heart, bradycardia, and risk of arrest.

Effect of High Calcium (Ca²⁺)

High Ca²⁺ levels leads to spastic contraction and cardiac weakness.

Effect of Fever (↑Temp)

Fever leads to increased heart rate.

S1 Heart Sound

Closure of AV valves (loudest heart sound).

S2 Heart Sound

Closure of semilunar valves.

S3 Heart Sound

Ventricular gallop (pathologic heart sound).

S4 Heart Sound

Atrial gallop (pathologic heart sound).

Sinoatrial (SA) Node

Located at RA near SVC; pacemaker of the heart.

SA Node Automaticity

Automaticity due to slow Na⁺ and Ca²⁺ influx → rhythmic firing.

Atrioventricular (AV) Node

Located in posterior RA behind tricuspid valve.

AV Node Function

Delays impulse to allow atrial emptying before ventricles contract.

Purkinje Fibers

Very fast conduction for synchronized ventricular contraction.

Parasympathetic Regulation

ACh → ↓ HR, ↓ conduction. Controlled by the Vagus Nerve.

Sympathetic Regulation

NE/Epinephrine → ↑ HR, ↑ force, ↑ excitability.

Systemic Circulation

High pressure, supplies tissues.

Pulmonary Circulation

Low pressure, oxygenates blood.

Arteries

High pressure, fast flow vessels.

Arterioles

Resistance vessels, regulate flow.

Capillaries

Exchange of gases and nutrients.

Venules

Begin venous return.

Veins

Low pressure, blood reservoir.

84%

Distribution of blood volume in the systemic circulation.

64%

Distribution of blood volume in the veins.

13%

Distribution of blood volume in the arteries.

7%

Distribution of blood volume in the capillaries/arterioles.

7%

Distribution of blood volume in the heart.

9%

Distribution of blood volume in the pulmonary circulation.

Basic Circulatory Principle 1

Local blood flow matches tissue needs.

Cardiac Output

Cardiac output equals the sum of local tissue flows.

Blood Pressure Regulation

Arterial pressure regulated independently from local flow.

Nervous Reflex Function 1

Increases heart rate and contractility.

Nervous Reflex Function 2

Venoconstriction leads to increased preload.

Nervous Reflex Function 3

Arteriolar constriction leads to increased BP.

Lymphatic System

Drains interstitial fluid, returns proteins, filters through lymph nodes.

Blood Flow Function 1

O₂ and nutrient delivery.

Blood Flow Function 2

CO₂ and waste removal.

Blood Flow Function 3

pH and electrolyte regulation.

Blood Flow Function 4

Hormone distribution.

Acute Control of Local Blood Flow

Rapid vasodilation/constriction (secs–mins).

Long-term Control of Local Blood Flow

Vessel remodeling (days–weeks).

Vasomotor Center

Located in medulla and lower third of pons.

Cardiac Cycle

One full heartbeat that includes diastole and systole.

Cause of rapid depolarization in Phase 0

The opening of fast sodium channels.

Cause of initial repolarization in Phase 1

The closing of sodium channels.

Cause of prolonged Plateau phase in Phase 2

The release of calcium from the Sarcoplasmic Reticulum.

Cause of Repolarization in Phase 3

The closure of Calcium channels, with Potassium efflux resuming.

Characterization of Phase 4

The maintenance of resting potential at approximately -90 mV.

S1

Closure of AV Valves.

Atrial Systole

The period when the atria are contracting to fill the Ventricles.

What happens in Isovolumic contraction

Increase in pressure.

What happens in Isovolumic relaxation

Relaxation.

Location of the SA Node

Located in the right atrium near the opening of the Superior Vena Cava.

Location of the AV Node

Located in the posterior wall of the right atrium immediately behind the Tricuspid valve

Where do the Purkinje fibers send the electrical impulse?

From the AV Node to the Ventricles.

The nerve responsible for parasympathetic output

The Vagus Nerve.

What compounds does the Sympathetic nervous system release to act on the heart?

Epinephrine and Norepinephrine.

What effects do sympathetic nerves have on the heart?

Increased heart rate, increased contractility, and increased excitability.

Where is the largest percentage of blood in the body located?

Veins.

Which circulation has a high pressure?

Systemic.

Which circulation has a low pressure?

Pulmonary.

Which vessels act at the 'resistance' vessels?

Arterioles.

Where does exchange of gasses and nutrients primarily occur?

Capillaries.

What vessels start the venous return pathway?

Venules.

In what vessels is the majority of blood volume stored?

Veins.

Circulatory System Primary Principle

Matching local blood flow with local tissue needs.

What is the purpose of the Lymphatic System

To drain interstitial fluid and return proteins to the blood.

What changes occur during acute maintenance of local blood flow?

Rapid changes in vasodilation and constriction.

What changes occur during long term maintenace of local blood flow?

Structural remodeling of vessels.

Where is atrial muscle located?

The cardiac muscle in the atria.

Where is ventricular muscle located?

The cardiac muscle in the ventricles.

Give an example where specialized excitatory and conductive muscle fibers are found

SA, AV Node.