The Heart - Chapter 20

Flashcards about the heart.

Intercalated discs

Where plasma membranes of adjacent cardiac muscle cells intertwine, bound together by desmosomes and gap junctions.

Functional syncytium

Cardiac muscle is called a functional syncytium, meaning a fused mass of cells.

Pericardial sac or fibrous pericardium

Surrounds the heart and is composed of a dense network of collagen fibers that attaches to the central tendon of the diaphragm and sternum which stabilizes the position of the heart.

Pericardial cavity

Area between the parietal pericardium and visceral pericardium, contains 10–15 mL of pericardial fluid secreted by pericardial membranes.

Cardiac tamponade

Condition in which movement of the heart is restricted because fluid accumulates in the pericardial cavity and the heart is unable to expand to fill with blood.

Coronary artery disease (CAD)

Areas of partial or complete blockage of coronary circulation which produces blood flow to area ( coronary ischemia).

Atherosclerosis

The usual cause of coronary artery disease but also may arise from associated blood clot ( thrombus).

Myocardial Infarction or heart attack

Death of a tissue due to lack of oxygen as a result of circulatory blockage, most commonly result from CAD.

Conducting system

Network of specialized cardiac muscle cells, Responsible for initiating and distributing stimulus to contract which can do so on their own (without neural or hormonal stimulation).

Automaticity (or autorhythmicity)

Property of the conducting system which allows the cells to contract on their own

Pacemaker Cells

Part of the conducting system and includes: Sinoatrial (SA) node, Atrioventricular (AV) node.

Conducting Cells

Part of the conducting system and includes: Internodal pathways, AV bundle and bundle branches, Purkinje fibers.

Electrocardiogram (ECG or EKG)

Recording of electrical activities of heart from body surface, used to assess performance of nodal, conducting, and contractile components.

Cardiac arrhythmias

Abnormal patterns of cardiac electrical activity.

Cardiac contractile cell contractions

Three stages of a cardiac action potential: Rapid depolarization, Plateau, Repolarization

Phases of cardiac cycle

Cardiac cycle begins w/ all four chambers relaxed, Ventricles are partially filled w/ blood (due to AV valves being open – passive filling) 70% of ventricle filled this way.

Atrial systole

Contracting atria fill relaxed ventricles w/ blood (active filling last 30% of ventricle filled).

End Diastolic volume (EDV)

When ventricles are 100% filled = End Diastolic volume (EDV).

Ventricular systole—first phase

Contracting ventricles push AV valves closed but there is not enough pressure to open semilunar valves.

Ventricular systole—second phase

Increasing pressure pushes open semilunar valves and blood flows out of ventricles.

End Systolic Volume (ESV)

There is always a small amount of blood left in ventricles after contraction = End Systolic Volume (ESV).

Ventricular diastole—early

Ventricles relax and blood pressure in them drops and blood flowing back against semilunar valve cusps closes the valves

Ventricular diastole—late

All chambers relaxed, AV valves open, Ventricles fill passively to roughly 70%.

S1 (known as “lub”)

Marks start of ventricular contraction and is produced as AV valves close.

S2 (known as “dup”)

Occurs when semilunar valves close.

Cardiac output (CO)

Amount of blood pumped by left ventricle into the aorta each minute.

Stroke volume (SV)

Amount of blood pumped out of ventricle during a single heartbeat.

Cardioacceleratory center

Controls sympathetic neurons.

Cardioinhibitory center

Controls parasympathetic neurons.

Pacemaker potential

Pacemaker cells in SA and AV nodes cannot maintain a stable resting potential and After repolarization, membrane gradually drifts toward threshold.

Bradycardia

Heart rate slower than normal (<60 bpm).

Tachycardia

Heart rate faster than normal (>100 bpm).

Stroke volume analogy

Stroke volume can be compared to pumping water w/ a manual pump, Amount pumped varies w/ pump handle movement

Venous return

Amount of venous blood returned to right atrium.

Filling time

Duration of ventricular diastole, Slowing heart rate (increasing filling time) increases EDV, Increasing heart rate (less filling time) decreases EDV

Preload

Amount of myocardial stretching, Greater EDV = larger preload = greater stroke volume.

Contractility

Amount of force produced during a contraction at a given preload.

Afterload

Tension necessary for ventricular ejection, Greater afterload = decreased stroke volume.

Heart failure

Condition when the heart cannot meet the demands of peripheral tissues.