Cardiovascular System Overview

Study Notes

Systemic Circulation carries oxygenated blood from the left ventricle to the body organs through arteries, arterioles, capillaries, venules, veins, and ultimately to the right atrium.
Pulmonary Circulation carries deoxygenated blood from the right ventricle to the lungs through pulmonary arteries, arterioles, capillaries, and ultimately returns oxygenated blood to the left atrium through pulmonary veins

Two atrioventricular (AV) valves (tricuspid and mitral) prevent backflow from the ventricles to the atria during diastole
Papillary muscles are attached to the AV valves by chordae tendineae, which prevents the valves from inverting
Two semilunar valves (aortic and pulmonary) prevent backflow from the aorta and pulmonary artery to the ventricles during systole.

Cardiac muscle is composed of contractile tissue (98-99%) and excitatory-conductive system (1-2%)
Contractile tissue contains contractile muscle proteins (actin, myosin, tropomyosin, and troponin)
Excitatory-conductive system initiates and propagates electrical impulses throughout the heart, contains few contractile proteins, and is composed of the sinoatrial node (SAN), atrioventricular node (AVN), AV bundle (bundle of Hiss), right and left bundle branches, and Purkinje fibers.
Titin is a large, elastic protein that binds myosin to the Z line, acts as a bidirectional spring, and provides structural support for the sarcomere.
Dystrophin connects actin to the extracellular matrix (ECM), providing structural support to the myocyte, and defects in dystrophin can cause cardiac muscle weakness.

Cardiac muscle is striated in morphology (similar to skeletal muscle) but is involuntary like smooth muscle.
Two functional syncytia: the two atria act as one syncytium, and the two ventricles act as another syncytium.
Intercalated discs provide mechanical strength and electrical continuity between myocytes.
Desmosomes provide intracellular connections between the cytoskeletons of adjacent cells.
Gap junctions allow the spread of action potentials from one fiber to another, enabling cardiac muscle to function as a syncytium.

Excitability: the ability to respond to an adequate stimulus by generating a propagating action potential followed by contraction.
Automaticity (Rhythmicity): the ability to initiate its own electrical impulse without external stimulation, allows for the regulated beating of the heart.
Conductivity: the ability to propagate electrical impulses throughout the heart, ensures coordinated contraction of the heart chambers.
Contractility: the ability to contract, enables the heart to pump blood throughout the body.

Resting Membrane Potential (RMP): the electrical potential difference between the inside and outside membrane surfaces during rest, typically -90 mV.
Ionic basis of RMP: the unequal distribution of charged ions across the membrane, with more cations on the outside than the inside.