Anatomy and Physiology of the Heart: Structure, Blood Flow, and Cardiovascular Physiology

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Heart Anatomy

Major Structures of the Heart

The heart is a muscular organ responsible for pumping blood throughout the body. Its anatomy includes chambers, valves, and associated vessels that direct blood flow in a specific sequence.

Superior & Inferior Vena Cava: Large veins that return deoxygenated blood from the body to the right atrium.
Right Atrium: Receives blood from the vena cavae and pumps it into the right ventricle.
Right Atrioventricular/Tricuspid Valve: Prevents backflow of blood from the right ventricle to the right atrium.
Right Ventricle: Pumps blood into the pulmonary trunk.
Right/Pulmonary Semilunar Valve: Prevents backflow from the pulmonary trunk into the right ventricle.
Pulmonary Trunk: Splits into pulmonary arteries carrying blood to the lungs.
Pulmonary Arteries: Transport deoxygenated blood to the lungs.
Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium.
Left Atrium: Receives oxygenated blood from the pulmonary veins.
Left Atrioventricular/Bicuspid/Mitral Valve: Prevents backflow from the left ventricle to the left atrium.
Left Ventricle: Pumps oxygenated blood into the aorta.
Left/Aortic Semilunar Valve: Prevents backflow from the aorta into the left ventricle.
Ascending Aorta: Distributes oxygenated blood to the body.
Aortic Arch: Curved portion of the aorta that branches to supply the head, neck, and arms.

Other Key Structures

Right & Left Auricle: Ear-like extensions of the atria that increase atrial volume.
Apex of Heart: The pointed end of the heart, directed downward and to the left.
Coronary Sulcus: Groove marking the border between atria and ventricles.
Anterior & Posterior Interventricular Sulcus: Grooves on the heart surface marking the position of the interventricular septum.
Fossa Ovalis: Remnant of fetal foramen ovale in the right atrium.
Interventricular Septum: Wall separating the right and left ventricles.
Chordae Tendineae: Tendinous cords anchoring AV valves to papillary muscles.
Papillary Muscles: Muscles that contract to prevent AV valve prolapse.
Trabeculae Carneae: Irregular muscular columns on the inner ventricular walls.
Myocardium: Thick muscular layer of the heart wall responsible for contraction.
Coronary Arteries: Supply blood to the heart muscle itself.
Coronary Sinus: Collects deoxygenated blood from the myocardium and returns it to the right atrium.

Additional info: The heart's structure is similar in humans and adult pigs, making pig hearts useful for anatomical study.

Order of Blood Flow Through the Heart

Pathway of Circulation

Blood flows through the heart in a specific sequence, ensuring separation of oxygenated and deoxygenated blood.

Superior/Inferior Vena Cava → Right Atrium
Right Atrium → Tricuspid Valve → Right Ventricle
Right Ventricle → Pulmonary Semilunar Valve → Pulmonary Trunk → Pulmonary Arteries
Pulmonary Arteries → Lungs (gas exchange)
Lungs → Pulmonary Veins → Left Atrium
Left Atrium → Bicuspid/Mitral Valve → Left Ventricle
Left Ventricle → Aortic Semilunar Valve → Ascending Aorta → Aortic Arch → Body

Example: Oxygen-poor blood enters the right atrium, is pumped to the lungs for oxygenation, returns to the left atrium, and is then pumped to the body.

Cardiovascular Physiology

Cardiac Cycle

The cardiac cycle describes the sequence of events in one heartbeat, including contraction and relaxation of the atria and ventricles.

Atrial Systole: Contraction of the atria, pushing blood into the ventricles.
Atrial Diastole: Relaxation of the atria, allowing them to fill with blood.
Ventricular Systole: Contraction of the ventricles, ejecting blood into the pulmonary trunk and aorta.
Ventricular Diastole: Relaxation of the ventricles, allowing them to fill with blood from the atria.

Example: During ventricular systole, the left ventricle generates the highest pressure to pump blood into the aorta.

Pressure Changes in the Cardiac Cycle

Pressure within the heart chambers varies during the cardiac cycle, influencing blood flow and valve function.

Highest Pressure: Occurs during ventricular systole, especially in the left ventricle.
Relative Thickness: The left ventricle has the thickest wall to withstand high pressure needed for systemic circulation.

Blood Pressure Measurement

Blood pressure is the force exerted by circulating blood on the walls of blood vessels, measured using a sphygmomanometer.

Sphygmomanometer: Device used to measure blood pressure.
Systolic Pressure: Maximum pressure during ventricular contraction (systole).
Diastolic Pressure: Minimum pressure during ventricular relaxation (diastole).
Korotkoff Sounds: Sounds heard while measuring blood pressure, indicating systolic and diastolic values.

What to Listen For: The first Korotkoff sound marks systolic pressure; disappearance of sound marks diastolic pressure.

Pulse and Blood Pressure Changes

Pulse and blood pressure vary with activity level.

Resting: Lower heart rate and blood pressure.
Exercising: Increased heart rate and blood pressure to meet higher oxygen demand.

Why: Exercise increases sympathetic nervous system activity, raising cardiac output and arterial pressure.

Pressure-Volume Relationships in the Cardiac Cycle

Graphical Representation

The pressure-volume graph illustrates changes in pressure within the left atrium, left ventricle, and aorta during the cardiac cycle.

Atrial Contraction: Begins the cycle, increasing atrial pressure.
Ventricular Systole: Rapid rise in ventricular pressure, opening the aortic valve and ejecting blood.
Ventricular Diastole: Pressure falls, mitral valve opens, and passive ventricular filling occurs.
Dicrotic Notch: Brief rise in aortic pressure following closure of the aortic valve.

Example: The graph shows that ventricular pressure peaks during systole, corresponding to blood ejection into the aorta.

Phase	Valve Status	Pressure Change
Atrial Systole	Mitral valve open	Atrial pressure rises
Ventricular Systole	Aortic valve opens	Ventricular pressure peaks
Ventricular Diastole	Mitral valve opens	Ventricular pressure falls

Key Equations

Blood pressure is typically recorded as systolic over diastolic pressure:

Cardiac output is the volume of blood pumped by the heart per minute:

Additional info: The pressure-volume graph is essential for understanding the timing and magnitude of pressure changes in the heart chambers and major vessels.