KP222/HN220 Human Physiology: Cardiovascular System - The Heart

These vocabulary flashcards cover the electrical conduction system, action potentials of cardiac cells, the phases of the cardiac cycle, and the regulation of cardiac output as presented in the Human Physiology lecture notes.

Contractile cells

Cardiocytes that account for $99\%$ of cardiac muscle cells and are responsible for generating the force of the heart.

Autorhythmic cells

Cardiac cells that can generate and spread action potentials spontaneously, including pacemaker cells that establish heart rhythm and conduction fibers that transmit the potentials.

Sinoatrial (SA) node

The pacemaker of the heart where the heartbeat starts, setting the pace of depolarization for all other myocytes.

Atrioventricular (AV) node

A component of the conduction system that delays the electrical impulse from the atria to the ventricles to allow for coordinated contraction.

Intercalated disks

Junctions between adjacent myocardial cells containing desmosomes to resist mechanical stress and gap junctions for electrical coupling/depolarization spread.

P wave

An ECG deflection representing the movement of depolarization through the atria and the initiation of atrial contraction.

QRS complex

An ECG deflection representing ventricular depolarization and contraction; atrial repolarization is obscured within this complex.

T wave

An ECG deflection representing the repolarization of the ventricles.

Funny channels

Unusual channels in pacemaker cells that spontaneously open to let potassium ($K^+$) out and sodium ($Na^+$) in, initiating the pacemaker potential.

T-type calcium channels

Transient channels that contribute to the slow depolarization of pacemaker cells as the membrane potential approaches threshold.

L-type calcium channels

Long-lasting channels responsible for rapid depolarization in pacemaker cells and the plateau phase in contractile cells.

Phase 0 (Contractile Cell)

The phase of rapid depolarization in cardiac contractile cells caused by increased permeability to sodium ($Na^+$).

Phase 2 (Contractile Cell)

The plateau phase of the cardiac action potential where permeability to calcium ($Ca^{2+}$) increases and permeability to potassium ($K^+$) decreases.

Systole

The period of the cardiac cycle characterized by ventricular contraction.

Diastole

The period of the cardiac cycle characterized by ventricular relaxation.

Cardiac Output (CO)

The volume of blood pumped by each ventricle per minute, calculated as $CO = HR \times SV$. Average resting value is approximately $5\,L/min$.

Stroke Volume (SV)

The volume of blood ejected from a ventricle during each cardiac cycle, calculated as $SV = EDV - ESV$.

End-diastolic volume (EDV)

The volume of blood present in the ventricle at the end of the relaxation period (diastole).

End-systolic volume (ESV)

The volume of blood remaining in the ventricle at the end of the contraction period (systole).

Ejection Fraction (EF)

The fraction of end-diastolic volume ejected during a heartbeat, calculated as $EF = \frac{SV}{EDV}$. At rest, this is typically about $54\%$.

Isovolumetric contraction

Phase 2 of the cardiac cycle where the ventricles begin to contract and AV valves close, but semilunar valves remain shut, so no blood leaves the heart.

Isovolumetric relaxation

Phase 4 of the cardiac cycle where the ventricles relax and all valves are closed, occurring after the semilunar valves close.

Muscarinic cholinergic receptors

Receptors on SA nodal cells that bind Acetylcholine ($ACh$) from the parasympathetic nervous system to slow the heart rate.

$\beta_1$ receptors

Receptors in the SA node that bind norepinephrine or epinephrine from the sympathetic nervous system to increase the rate of spontaneous depolarization and heart rate.