Cardiovascular System (Heart Valves) Part 2

Atrioventricular (AV) Valves

To allow blood to flow in only one direction (from atria to ventricles) and prevent backflow.

Between the atria and ventricles

Where are the atrioventricular (AV) valves located?

Tricuspid valve

What is the other name for the RIGHT atrioventricular (AV) valve?

Bicuspid valve (Mitral valve)

What are the other names for the LEFT atrioventricular (AV) valve?

Phase 1: AV Valve Opening (Filling)

Operation of the AV Valves

Blood returns to atria, pressure forces AV valves open.

Phase 2: Ventricular Filling

Operation of the AV Valves

AV valve cusps hang limply into ventricles as they fill.

Phase 3: Atrial Contraction (Systole)

Operation of the AV Valves

Atria contract, pushing additional blood into ventricles. AV valves open (Atrial P > Ventricular P).

Phase 4: Ventricular Contraction (Systole)

Operation of the AV Valves

Ventricles contract, forcing blood against AV valve cusps. AV valves close.

Phase 5: AV Valve Closure Condition

Operation of the AV Valves

AV valves closed; Ventricular P > Atrial P.

Phase 6: Function of Chordae Tendineae

Operation of the AV Valves

Tighten during contraction to prevent valve cusps from everting (flipping backward) into atria.

No. The myocardium (heart muscle) has its own separate circulation system.

Does blood in the heart chambers nourish the myocardium?

Coronary arteries, Cardiac veins, Coronary sinus

What are the components of the heart’s independent nourishing circulatory system

Coronary arteries

Supply oxygenated blood to the heart muscle.

Cardiac veins

Drain deoxygenated blood from the myocardium.

Coronary sinus

Large vein that receives blood from cardiac veins

They branch directly from the aorta.

Where do coronary arteries originate?

Coronary arteries, Aorta

The _____ branch from the _____ to supply the heart muscle with oxygenated blood.

Right Atrium

The coronary sinus is a large vein on the posterior of the heart that receives blood from cardiac veins and empties into the?

Intrinsic conduction system (nodal system)

To generate and distribute electrical impulses that coordinate the contraction of the heart muscle.

Sets the rhythm of the heart and ensures depolarization in one direction only (atria to ventricles)

Spontaneously and independently of nerve impulses (automaticity)

How do cardiac muscles contract in relation to nerve impulses?

The Sinoatrial (SA) node

What is the name of the "pacemaker" of the heart?

This starts each heartbeat.

60–100 beats per minute

Atrial cells beat approximately ___ times per minute independently.

25–55 beats per minute (AV Node/Purkinje fiber rate)

Ventricular cells beat approximately ___ times per minute independently.

Autonomic nervous system (extrinsic) an dIntrinsic conduction system (nodal system)

What are the two main systems that regulate heart activity?

Special nervous tissue (specialized cardiac muscle cells)

The intrinsic conduction system is composed of what type of tissue?

75 beats per minute

What heart rate does the intrinsic conduction system enforce on its own?

Ensures depolarization proceeds in one direction only: Atria to Ventricles.

How does the intrinsic conduction system ensure heart muscle contraction is efficient?

The atria contract (Atrial systole)

What happens immediately after the impulse spreads from the SA node through the atria?

AV node

Where is the electrical impulse briefly delayed.

This delay allows the atria to finish contracting and empty blood into the ventricles before they squeeze.

AV bundle, Bundle branches, Purkinje fibers.

After the AV node delay, what is the path of the impulse to the ventricles?

Tachycardia

A resting heart rate exceeding 100 beats per minute.

Cardiac Cycle

One complete heartbeat, where both atria and ventricles contract (systole) and then relax (diastole).

Systole (Cardiac Cycle)

Contraction phase (heart muscle contracts to pump blood).

Diastole (Cardiac Cycle)

Relaxation phase (heart muscle relaxes to fill with blood).

75 beats per minute

What is the average adult resting heart rate?

0.8 seconds

What is the normal length of one cardiac cycle (at a heart rate of 75 bpm)?

Atrial diastole (ventricular filling)

• Heart is relaxed

• Pressure in heart is low

• Atrioventricular valves are open

• Blood flows passively into the atria and into ventricles

• Semilunar valves are closed

Atrial systole

• Ventricles remain in diastole

• Atria contract

• Blood is forced into the ventricles to complete ventricular filling

Isolovumetric Contraction

• Atrial systole ends; ventricular systole begins

• Intraventricular pressure rises

• AV valves close

• For a moment, the ventricles are completely closed chambers

Ventricular Systole (Ejection Phase)

• Ventricles continue to contract

• Intraventricular pressure now surpasses the pressure in the major arteries leaving the heart

• Semilunar valves open

• Blood is ejected from the ventricles

• Atria are relaxed and filling with blood

Isovolometric Contraction

• Ventricular diastole begins

• Pressure falls below that in the major arteries

• Semilunar valves close

• For another moment, the ventricles are completely closed chambers

• When atrial pressure increases above intraventricular pressure, the AV valves open

Heart Sound: "Lub" (S1)

• Longer, louder heart sound.

• Caused by closing of the AV (Atrioventricular) valves.

• Timing: Start of ventricular systole.

Heart Sound: "Dup" (S2)

• Short, sharp heart sound.

• Caused by closing of the semilunar valves.

• Timing: End of ventricular systole / Beginning of diastole.

Cardiac Output (CO)

The volume of blood pumped by each ventricle (side) of the heart in 1 minute.

Total blood pumped in 1 minute.

Stroke Volume (SV)

The volume of blood pumped by each ventricle in one contraction (per heartbeat).

Blood pumped in 1 heartbeat.

70 ml

What is the average Stroke Volume (SV) per heartbeat in the left ventricle?

Heart Rate (HR) x Stroke Volume (SV)

Formula for Cardiac Output (CO)?

Starling’s Law of the Heart

The law stating that the heart's stroke volume increases in response to an increase in the volume of blood filling the ventricles (preload).

Stretch of the Cardiac Muscle

What is the critical factor controlling Stroke Volume?

Venous return

What is the primary factor influencing the stretch of heart muscle?

Neural (ANS) Controls, Hormones and Ions

What are the two main types of factors that modify the basic heart rate?

Speeds up heart rate

How does the Sympathetic Nervous System affect heart rate?

Slows and steadies heart rate

How does the Parasympathetic Nervous System (specifically the vagus nerve) affect heart rate?

Epinephrine and thyroxine

Which hormones speed up heart rate?

Calcium (Ca2+), Sodium (Na+), and Potassium (K+)

Which ions modify heart activity?

Tunica intima (Inner), Tunica media (Middle), Tunica externa/adventitia (Outer)

What are the three layers (tunics) of blood vessels (excluding capillaries), from inside to outside?

Tunica Intima

It forms a friction-reducing lining (endothelium) for blood flow.

Tunica Media

• Structure: Smooth muscle and elastic tissue.

• Control: Controlled by the sympathetic nervous system (for vasoconstriction/dilation).

Tunica Externa (or Adventitia)

• Function: Forms the protective outermost covering, supporting and anchoring the vessel.

• Composition: Mostly fibrous connective tissue.

Capillaries

Which type of blood vessel consists only of a single tunica intima layer?

Arteries

Have a heavier/stronger tunica media than veins.

Heavier, stronger, stretchier tunica media; high pressure.

Smaller Lumen

Veins

Thinner tunica media; low pressure; possess valves to prevent backflow.

Larger Lumen

Valves

Structural feature of veins that prevents backflow of blood.

Skeletal muscle "milking" (contraction)

What mechanism helps move blood through veins back toward the heart?