Heart Anatomy and Physiology

Purpose & Function of the Cardiovascular System

  • The cardiovascular system's primary purpose is to circulate blood throughout the body, delivering essential substances and removing waste products.

  • Its key functions include:

    • Transport of Oxygen and Nutrients: Delivers O2_2 from the lungs and nutrients from the digestive system to all body tissues.

    • Removal of Metabolic Wastes: Carries carbon dioxide (CO2_2) to the lungs for exhalation and metabolic wastes (e.g., urea, lactic acid) to the kidneys for excretion.

    • Transport of Hormones: Moves hormones from endocrine glands to target organs.

    • Regulation of Body Temperature: Helps distribute heat throughout the body and facilitates heat loss or conservation.

    • Maintenance of pH Balance: Buffers H+^+ ions to maintain optimal blood pH.

    • Immune Defense: Transports immune cells (e.g., white blood cells) and antibodies to fight infections and protect the body.

Heart Location & Pericardium

  • Heart sits in the mediastinum of the thoracic cavity, slightly left of the mid-sagittal plane.

  • Entire heart is enclosed within the pericardial cavity, a potential space formed by the pericardium (serous membrane of the heart).

  • Filled with serous fluid whose lubricating action ↓ friction generated by continual muscular contractions.

  • Serous Fluid: clear to pale yellow, watery fluid found in body cavities and surrounding organs.

  • Serous Fluid Function is to acts as a lubricant, reducing friction between membranes during movement.

  • Two pericardial layers:

    • Parietal pericardium:

    • External “anchor”; fuses to surrounding connective tissues and helps tether the heart to the mediastinum.

    • Visceral pericardium (≡ epicardium)

    • Directly covers the external surface of the heart and embryologically counts as the heart’s outer-most tissue layer.

What do arteries carry?

Arteries carry oxygenated blood away from the heart to various tissues and organs throughout the body, with the exception of the pulmonary arteries, which transport deoxygenated blood to the lungs for oxygenation.

What do veins carry?

Veins carry deoxygenated blood back to the heart from the tissues and organs, with the exception of the pulmonary veins, which transport oxygenated blood from the lungs to the heart for systemic circulation.

Layers of the Heart Wall

  • Three concentric layers (superficial ➞ deep):

    • Epicardium

      Epicardium Function: Protective “skin” of the heart, secretes lubricating fluid to reduce friction as the heart beats.

    • Same tissue as visceral pericardium.

    • Thin, slippery serous membrane; houses coronary vessels & some fat.

    • Myocardium

      Myocardium Function: Thick cardiac muscle that actually contracts and pumps blood.

    • Bulk of the wall; composed of cardiocytes (cardiac muscle cells) arranged in spiral bundles that generate the pumping force.

    • Thickness varies (LV wall > RV wall) in proportion to workload.

    • Endocardium

            Endocardium Function: Smooth lining of the heart chambers and valves—keeps blood flowing smoothly and prevents clots.

    • Thin, smooth, endothelial layer lining all heart chambers & covering valves; continuous with tunica interna of vessels to provide a low-friction surface that discourages clotting.

Chambers, Sulci & Septa

  • Four chambers:

    • Right atrium (RA), Left atrium (LA) = receiving chambers.

    • Right ventricle (RV), Left ventricle (LV) = discharging chambers.

  • One drop of blood must be pumped twice to finish a systemic loop:

    • RA (right atrium) ➞ RV (right ventricle)➞ pulmonary circuit ➞ LA (left atrium) ➞ LV (left ventricle) ➞ systemic circuit.

Right Atrium

  • Purpose: Receives deoxygenated blood from the body

  • Blood type: Deoxygenated

Right Ventricle

  • Purpose: Pumps deoxygenated blood to the lungs

  • Blood type: Deoxygenated

Left Atrium

  • Purpose: Receives oxygenated blood from the lungs

  • Blood type: Oxygenated

Left Ventricle

  • Purpose: Pumps oxygenated blood to the body

  • Blood type: Oxygenated

💡 Tip to remember:
"Right = to lungs (deoxygenated)"
"Left = to body (oxygenated)"

  • Pulmonary Circuit:

  • The pathway through which deoxygenated blood is carried from the right ventricle to the lungs for oxygenation. Consists pulmonary arteries that transport blood to the lungs and pulmonary veins that return oxygenated blood to the left atrium.

  • Systemic Circuit:

  • The pathway that carries oxygenated blood from the left ventricle to the rest of the body, delivering essential nutrients and oxygen to tissues. It includes the aorta, which branches into smaller arteries that distribute blood to various organs, and then returns deoxygenated blood via veins to the right atrium.

    what is purpose of these two circuits?: Together, these two circuits function in a continuous loop, ensuring the body receives a steady supply of oxygen while removing carbon dioxide and other metabolic wastes.

  • Surface landmarks

    • Each atrium bears an ear-shaped auricle (expands capacity during ↑ venous return).

    • Grooves between the atria and ventricles is called the coronary sulcus, which serves as a pathway for blood vessels that supply the heart muscle.

    • Coronary sulcus (atrioventricular groove) encircles the heart, demarcating atria from ventricles and sheltering major coronary vessels.

    • Anterior / Posterior interventricular sulcus trace the position of the muscular septum between ventricles.

  • Internal partitions

    • Interatrial septum separates RA & LA.

    • Houses the fossa ovalis, a thin, oval depression—remnant of the fetal foramen ovale that once shunted blood RA ➞ LA to bypass non-functional fetal lungs.

    • Interventricular septum forms the muscular wall between RV & LV.

Internal Musculature & Conduction-Related Structures

  • Pectinate muscles: comb-like ridges lining the anterior wall & auricle of the RA; increase surface area without massively thickening the wall.

  • Trabeculae carneae: irregular muscular folds lining the inner surfaces of both ventricles; thought to prevent suction that would impair pumping efficiency.

  • Moderator band (septomarginal trabecula) in RV: a muscular bridge carrying part of the conduction pathway (right bundle branch) from septum to anterior papillary muscle—ensures synchronous RV activation.

Heart Valves & One-Way Flow

  • Two classes (total 4 valves): two atrial ventricular (AV)/Mitral valves and two semilunar valves to control direction of blood flow.\

  1. Atrioventricular (AV) valves

    • Tricuspid valve: RA ➞ RV (three cusps).

    • Bicuspid / Mitral valve: LA ➞ LV (two cusps).

    • Valve cusps tethered by chordae tendineae to papillary muscles anchored in ventricular walls; when ventricles contract, papillary muscles pull cords taut preventing cusp prolapse/backflow into atria.

      what do AV valves prevent: prevent backflow of blood from ventricles into the atria

  2. Tricuspid Valve: right AV valve

    Functions: ensures blood flows in the correct direction, preventing backflow from the ventricle to the atrium

  3. Bicuspid Valve: Left AV valve

    Functions similarly to the tricuspid valve, ensuring unidirectional blood flow from the left atrium to the left ventricle.

  4. Pulmonary Valve: This valve is located between the right ventricle and the pulmonary artery. Functions: It opens to allow blood to be pumped from the right ventricle into the pulmonary artery, and closes to prevent backflow of blood into the ventricle.

  5. Chordae Tendineae: cusps of valves have small cords. attached to the papillary muscles within the ventricles, which help maintain the valve position and prevent dysfunction during ventricular contraction.

    1. Semilunar (SL) valves

    • Pulmonary valve at RV outflow tract ➞ pulmonary trunk.

    • Aortic valve at LV outflow tract ➞ ascending aorta.

    • Three pocket-like cusps each; fill with blood when ventricles relax, sealing the lumen and preventing regurgitation into ventricles.

    • These are each located at the base of the artery

  • Functional reciprocity: AV open⇒SL closed\text{AV open} \Rightarrow \text{SL closed} and vice-versa, enforcing unidirectional flow.

Coronary Circulation (Blood Supply for Myocardium)

what is coronary circulation?: flow of blood to and from the tissues of the heart, primarily through the coronary arteries that supply oxygen-rich blood, and the cardiac veins that return deoxygenated blood to the right atrium.

  • Coronary arteries are the first branches of the systemic circuit; originate at the base of the ascending aorta behind the SL cusps so they receive blood during ventricular diastole.

  • Main trunks:

    • Right coronary artery (RCA)

    • Courses in coronary sulcus to supply RA, RV, and portions of conduction system.

    • Posterior interventricular branch (a.k.a. posterior descending artery, PDA) travels in posterior IV sulcus supplying adjacent posterior ventricular walls & septum.

    • Left coronary artery (LCA) quickly bifurcates:

    • Circumflex artery: follows coronary sulcus to supply LA & posterior LV.

    • Anterior interventricular artery (left anterior descending, LAD): descends in anterior IV sulcus, irrigating anterior LV, RV apex, and anterior 2/3 of septum.

  • Cardiac veins mirror arteries; most converge into the coronary sinus lodged in the posterior coronary sulcus.

  • Coronary sinus empties deoxygenated blood directly into RA, completing the coronary circuit.

Intrinsic Conduction System (Nodal & Conducting Cells)

  • Specialized, self-excitable nodal cells generate & propagate electrical impulses, orchestrating the heartbeat without neural input (autorhythmicity).

  • Major components (pacemaker ➞ ventricles):

  1. Sinoatrial (SA) node

    • Located where the superior vena cava empties into right atrium

    • Fastest rate of spontaneous depolarization (≈ 60!–!100~\text{beats·min}^{-1} at rest); sets the sinus rhythm.

    • Spreads impulse through both atria & to AV node.

    • stimulates both atria and AV Node and is crucial for synchronizing the contractions of the heart chambers, ensuring efficient blood flow throughout the cardiovascular system.

    1. Atrioventricular (AV) node

      Located in lower medial floor of the right atrium , the AV node serves as a critical relay station by slowing the electrical impulse before it travels to the ventricles, allowing sufficient time for the atria to contract and fill the ventricles with blood.

    • Situated on the lower interatrial septum adjacent to the tricuspid valve.

    • Provides a brief conduction delay (~0.1 s0.1\text{ s}) allowing ventricular filling.

    1. AV bundle (Bundle of His)

    • Only electrical connection between atria & ventricles; penetrates fibrous skeleton, entering interventricular septum.

    1. Right & Left bundle branches

    • Travel down septum; left branch is broad & subdivides earlier because LV mass > RV mass.

    1. Purkinje fibers

    • Extensive sub-endocardial network rising from bundle branches; deliver rapid depolarization to ventricular cardiocytes from apex upward, ensuring efficient blood ejection.