Heart Anatomy and Function

The heart has a middle layer containing cardiac muscle.
The human heart has four chambers, four great blood vessels, four smaller blood vessels, and four heart valves.
Heart development begins at the end of the fourth week and the beginning of the fifth week of gestation.

The two superior chambers are called atria (plural).
Right and left atria.
Interatrial septum: A divider between the two atria, located behind the large vessels.
Foramen Ovale:
- An oval-shaped hole in the interatrial septum during fetal development.
- After birth, it closes to become the fossa ovalis, a generalized depression.
Ventricles: right and left ventricles separated by the interventricular septum.

Three great vessels carry oxygen-poor blood, while the aorta carries oxygen-rich blood.
Four pulmonary veins carry oxygen rich blood.
The superior vena cava drains blood from the brain into the right atrium.
The inferior vena cava drains blood from structures inferior to the heart into the right atrium.
The coronary sinus drains blood from the coronary circuit into the right atrium.
Four pulmonary veins (two from each lung) empty into the left atrium.
Pulmonary trunk: Carries oxygen-poor blood and divides into two branches to send blood to the right and left lungs.
Aorta: The fourth great vessel that carries oxygen-rich blood from the left ventricle to the body.
Exceptions:
- Pulmonary trunk, superior vena cava, inferior vena cava: carry oxygen-poor blood.
- Aorta, pulmonary veins: carry oxygen-rich blood.

Right atrium: Three openings from the superior vena cava, inferior vena cava, and coronary sinus.
Left atrium: Four openings from the pulmonary veins.

Valves located in between the atria and the ventricles are called atrioventricular (AV) valves.
- Located between the atrium and ventricle.

Right AV valve (tricuspid valve): Formed by three cusps.
Left AV valve:
- Has two names: Bicuspid and Mitral.
- Also known as the mitral valve.
- Has two cusps.
- Resembles a miter (archbishop's hat).

Papillary muscles: Muscles within the ventricles that hold the AV valves closed via heartstrings.
Chordae tendineae: Heartstrings that attach the papillary muscles to the AV valve cusps.
Trabeculae carneae: Located within the ventricles.

Atrial septal defect (ASD): A hole in the interatrial septum due to incomplete closure of the foramen ovale.
Ventricular septal defect (VSD): A hole in the interventricular septum.

AV valve: Open to allow blood flow from the atrium into the ventricle.
Ventricular pressure: Low.
Chordae tendineae: Loose; tension is low.
Papillary muscles: Relaxed.
Semilunar valves: Closed to prevent backflow of blood from arteries into the ventricles.

Ventricular pressure: High to push blood forward into the arteries.
AV valve: Closed to prevent backflow of blood into the atrium.
Chordae tendineae: Tense due to contraction of papillary muscles.
Papillary muscles: Contracted to pull on chordae tendineae and keep AV valves closed.
Semilunar valve: Open to allow blood to flow into the great vessels.

Right atrium:
- Receives blood from the superior vena cava, inferior vena cava, and coronary sinus.
Right ventricle:
- Blood moves through the tricuspid valve (right AV valve).
Pulmonary trunk:
- Blood moves through the pulmonary semilunar valve.
Pulmonary arteries:
- The pulmonary trunk branches into the left and right pulmonary arteries, which carry blood to the lungs.
Lungs:
- Blood picks up oxygen and releases carbon dioxide.
Left atrium:
- Blood returns to the heart via the four pulmonary veins.
Left ventricle:
- Blood moves through the bicuspid (mitral, left AV) valve.
Aorta:
- Blood moves through the aortic semilunar valve.
- Blood is then distributed to the systemic and coronary circuits.

Right Atrium: Blood received from superior vena cava, inferior vena cava, and coronary sinus.
Atrial Depolarization: P wave on EKG; contraction occurs, moving blood to the right ventricle with the AV valve open.
Right Ventricle: Ventricles depolarize (QRS complex), contract, moving blood to the pulmonary trunk through the pulmonary semilunar valve.
Lungs: Blood picks up $O<em>2$ and releases $CO</em>2$ .
Left Atrium: Blood returns via four pulmonary veins.
Left Ventricle: Blood moves through the bicuspid (mitral) valve.
Aorta: Blood moves through the aortic semilunar valve to systemic and coronary circuits.

Ascending aorta: The initial, upward-moving portion.
Aortic arch: The arch formed at the top of the ascending aorta.
Descending aorta: The portion moving downwards towards the abdominal cavity, consisting of the thoracic and abdominal aorta.
Thoracic aorta: Located superior to the diaphragm, within the thoracic cavity.
Abdominal aorta: Located inferior to the diaphragm, within the abdominal cavity.
Order: Ascending aorta → Aortic arch → Thoracic aorta → Abdominal aorta

Right marginal artery: A branch that makes its way towards the right margin of the heart.
Posterior interventricular artery: Runs along the groove between the two ventricles on the posterior side.

Anterior interventricular artery: Located on the anterior face, moving between the ventricles.
Circumflex artery: The second branch.
Left marginal artery: The third branch. Makes its way towards the left margin of the heart.

Occlusion of coronary vessels leads to a lack of blood supply to the heart muscle, causing cell death.
Most common cause: Occlusion of the anterior interventricular artery (the "widow's maker").
Second most common cause: Occlusion of the posterior interventricular artery.

A procedure to bypass blocked coronary arteries using a harvested vein (often from the leg).
Also known as a "cabbage."

Major veins run parallel to major arteries.
- Great cardiac vein: Runs parallel to the anterior interventricular artery.
- Small cardiac vein: Runs parallel to the right marginal artery.
- Posterior vein of the left ventricle: Runs parallel to the left marginal artery.
- Middle cardiac vein: Runs parallel to the posterior interventricular artery.
All veins drain into the coronary sinus, which then drains into the right atrium.