Cardiovascular Physiology Part I

Bio 219Dr. Adam Ross

Napa Valley College

The Cardiovascular System

• The heart, blood vessels, and blood

• Many types of blood vessels• Arteries, arterioles, capillaries, venules, veins

• Veins and venules always carry blood towards heart

• Arteries and arterioles always carry blood away from heart

• Right side of heart pumps DEOXYGENATED blood to pulmonary circulation

• Left side of heart pumps OXYGENATED blood to systemic circulation

Heart Anatomy

Chambers of the Heart

• Artia- receiving chambers• RA is fed by vena cava (deoxygenated)

• LA is fed by pulmonary veins (oxygenated)

• Ventricles- pumping chambers• RV pumps blood into pulmonary artery (deoxygenated)

• LV pumps blood into aorta (oxygenated)

Valves of the Heart

• Atrioventricular valves- prevent backflow from ventricles to atria• Tricuspid (Right side)

• Mitral (Left Side)

• Semilunar Valves- prevent backflow from arteries to ventricles• Pulmonary valve (right ventricle)

• Aortic valve (left ventricle)

Bloodflow in Human Heart

• Deoxygenated blood from venous circulation returns to right atria via vena cava

• Flows through tricuspid valve into Rt Ventricle

• Right ventricle pumps blood through pulmonary valve into pulmonary circulation (pulmonary artery)

• Blood gets oxygenated in lungs and goes to left atria via pulmonary vein

• Left atrium pumps blood through mitral valve into left ventricle

• Left ventricle pumps blood through aortic valve into aorta and into systemic circulation

Heart Anatomy

Cardiac Muscle Cells

• Cardiomyocytes are the contractile cells of the heart• Contraction functions very similarly to skeletal muscle with a few key

differences

• The heart does not require neural input to beat. • It does require ATP (oxygen), and proper ionic balance between cells and ECF/

blood

Initiation of Heartbeat

• Certain parts of the heart have autorhythmic cells• The Sinoatrial (SA) node is the primary pacemaker in the human heart

• These cells become spontaneously depolarized, and spread this depolarization to the rest of the contractile cardiomyocytes.

• There are other pacemaker cells that can take over if SA node is damaged or inhibited.

Pacemaker Potential in Autorhythmic Cells

• Cells spontaneously depolarize due to inward flow of Na+

• Called funny current or If

• This depolarization leads to cell reaching threshold

• AP is fired

• Rapid depolarization due to Ca2+ influx

• At peak of AP calcium channels inactivate and K+ channels open• K+ flows out of cell and repolarizes.

SA Nodal Action Potential

• Phase 0: Depolarization is caused mostly by Ca2+

influx

• No plateau phase

• Phase 3: Repolarization from K+ efflux

• Phase 4: Unstable resting potential due to opening of a non-specific cationchannel (If)

Neural Modulation of the Heart

• Nervous input can affect heart rate and contractility

• Sympathetic input (Epi/β-Adrenergic Receptor) increases heart rate and contractility

• Parasympathetic input (Ach/mAChR) decreases HR and contractility

• Will discuss in more detail in the next two lectures.

Conduction of SA nodal AP

• AP from SA node is spread to the rest of the heart via gap junctions and specialized conduction fibers• AP is delayed at atrioventricular node (border between atria and ventricles)

so that atria contract just before ventricles.

Ventricular Action Potential• Phase 0: Rapid

depolarization due to influx of Na+ and to a lesser extent Ca2+

• Phase 1: Rapid repolarization from inactivation of Na+

channels• Phase 2: Plateau caused

by continued Ca2+ influx• Phase 3: Repolarization

due to K+ efflux and Ca2+

channel inactivation-sets the duration of AP

• Phase 4: Resting membrane potential

Cardiac Muscle Contraction

• Increase in Ca2+ in Phase 2 of AP is important for the increase in Ca2+ needed for contraction

• A further increase in Ca2+ occurs through Ca2+ induced Ca2+ release (CICR)

• Unlike skeletal muscle, L-type Ca2+ channels on the T-tubule are not connected to Ryanodine Receptors (RyR) on the SR

• The influx of extracellular Ca2+ is absolutely necessary for Ca2+

efflux from the SR

• The increase in intracellular Ca2+ will induce contraction in the same manner as in skeletal muscle