Heart Valves and Circulation of Blood

Atrioventricular (AV) Valves

One-way gates with rounded cusps that sit between the atrium and ventricles

AV Valves: Relaxation

When the ventricles relax, the papillary muscles and chordae tendineae also relax, allowing blood to flow from the higher-pressure atria into the lower-pressure ventricles through the open AV valves.

AV Valves: Contraction

When the ventricles contract, the papillary muscles and chordae tendineae also contract, increasing ventricular pressure as they close the AV cusps from opening into the atria.

Semilunar (SL) Valves

One-way gates with three crescent-shaped cusps that sit between the ventricles and arteries (e.g., aortic and pulmonary valves).

SL Valves: Relaxation

When the ventricles relax, blood flows back toward the heart, contracting the SL valves and closing the opening between the ventricle and artery.

SL Valves: Contraction

When the ventricles contract, ventricular pressure rises rapidly until it exceeds arterial pressure, opening the SL valves and ejecting blood into the pulmonary trunk and aorta.

Missing Valves

The points where the venae cavae and pulmonary veins enter the heart lack physical valves, allowing a small amount of blood to flow backward from the atria into these vessels when the atria contract.

Pulmonary Circulation

The pathway through which the heart pumps deoxygenated blood to the lungs for oxygenation and returns oxygenated blood to the heart.

Pulmonary Circulation: Step 1

Deoxygenated blood from the systemic circulation enters the right atrium via the superior and inferior vena cava.

Pulmonary Circulation: Step 2

The right atrium pumps blood into the right ventricle through the tricuspid valve.

Pulmonary Circulation: Step 3

The right ventricle pumps blood into the pulmonary trunk through the pulmonary valve.

Pulmonary Circulation: Step 4

The pulmonary trunk divides into the right and left pulmonary arteries to oxygenate the blood in the right and left lungs.

Pulmonary Circulation: Step 5

In the pulmonary capillaries surrounding the alveoli, blood releases CO₂ to be exhaled and absorbs O₂ from inhaled air.

Pulmonary Circulation: Step 6

Freshly oxygenated blood returns to the left atrium through the pulmonary veins.

Systemic Circulation

The pathway through which a network of blood vessels carries oxygenated blood from the heart to tissues and cells throughout the body, and returns deoxygenated blood to the heart.

Systemic Circulation: Step 1

The left atrium receives freshly oxygenated blood from the lungs and pumps it into the left ventricle through the mitral valve.

Systemic Circulation: Step 2

The left ventricle pumps blood into the aorta through the aortic valve

Systemic Circulation: Step 3

Blood travels through progressively smaller arteries from the aorta to reach the body's organs— except the pulmonary alveoli, which are supplied by pulmonary circulation, not systemic circulation.

Systemic Circulation: Step 4

Arteries then branch into smaller arterioles, which lead to large networks of systemic capillaries where nutrient and gas exchange occurs.

Systemic Circulation: Step 5

Blood enters systemic capillaries, where oxygen and nutrients move into body cells while carbon dioxide and waste products move into the blood through the thin capillary walls.

Systemic Circulation: Step 6

Freshly deoxygenated blood leaves the capillaries and enters systemic venules that eventually merge into larger systemic veins.

Systemic Circulation: Step 7

Deoxygenated blood eventually returns to the right atrium, which then repeats the cycle for both pulmonary and systemic circulations.

Coronary Circulation

The pathway through which blood is pumped to the heart itself through coronary arteries at high pressure.

Coronary Circulation: Coronary Arteries

Blood vessels that supply oxygen-rich blood and nutrients directly to the heart muscle

Coronary Circulation: Contraction

When the heart contracts, little blood flows in the coronary arteries because they are squeezed shut.

Coronary Circulation: Relaxation

When the heart relaxes, high blood pressure in the aorta propels blood through the coronary arteries into capillaries, then into coronary veins, supplying the heart with oxygen.

Left Coronary Artery

A major blood vessel that passes oxygenated blood to the left auricle that divides into the anterior interventricular and circumflex arteries.

Left Coronary Artery: Anterior Interventricular Artery

The left anterior descending (LAD) artery supplies oxygenated blood to the walls of both ventricles from the anterior interventricular sulcus.

Left Coronary Artery: Circumflex Artery

The circumflex artery distributes oxygenated blood to the walls of the left ventricle and left atrium from the coronary sulcus

Right Coronary Artery

A major blood vessel that supplies oxygenated blood to the right atrium through atrial branches, then passes to the right auricle and divides into the inferior interventricular and marginal branches.

Right Coronary Artery: Inferior (Posterior) Interventricular Artery

The inferior interventricular artery runs along the inferior interventricular sulcus and supplies the walls of the two ventricles with oxygenated blood

Right Coronary Artery: Marginal Branch

The marginal branch runs along the right margin of the heart toward the apex and transports oxygenated blood to the wall of the right ventricle.

Anastomoses

A network of arteries supplies the same region and provides collateral circulation for blood to reach a particular organ or tissue.

Anastomoses: Collateral Circulation

A backup network of blood vessels that provides an alternate route for blood flow when a main artery or vein is blocked or damaged; the myocardium has many collateral vessels to maintain its oxygen supply.

Coronary Veins and Drainage: Step 1

Blood enters capillaries from the coronary arteries, where oxygen and nutrients move into body cells while carbon dioxide and waste products move into the blood through the thin capillary walls.

Coronary Veins and Drainage: Step 2

Freshly deoxygenated blood leaves the capillaries and enters coronary veins and then the coronary sinus.

Coronary Veins and Drainage: Coronary Sinus (Step 3)

Largest vein of the heart, acting as the main channel that collects used, deoxygenated blood from the body and delivers it back into the right atrium

Coronary Veins and Drainage: For Major Veins

The principal tributaries carrying deoxygenated blood into the coronary sinus are the great cardiac vein, middle cardiac vein, small cardiac vein, and anterior cardiac veins

Coronary Veins and Drainage: Great Cardiac Vein

The great cardiac vein, located in the anterior interventricular sulcus, drains areas supplied by the left coronary artery (left and right ventricles and left atrium)

Coronary Veins and Drainage: Middle Cardiac Vein

The middle cardiac vein, located in the posterior interventricular sulcus, drains areas supplied by the inferior interventricular artery of the right coronary artery (left and right ventricles)

Coronary Veins and Drainage: Small Cardiac Vein

The small cardiac vein, located in the coronary sulcus, drains the right atrium and right ventricle

Coronary Veins and Drainage: Anterior Cardiac Vein

The anterior cardiac vein, located in the right ventricle, drains directly into the right atrium.

Reperfusion

The return of blood and oxygen to tissues after a period of low or zero blood flow

Reperfusion Injury

Reperfusion restores oxygen, but the sudden return of oxygen can sometimes cause additional damage through free radicals that cause chain reactions that lead to cellular damage and death.

Reperfusion Injury: Counter

Enzymes such as superoxide dismutase and catalase convert free radicals into less reactive substances, while nutrients such as vitamins E and C, beta-carotene, zinc, and selenium remove oxygen free radicals from the blood.