Chapter 21: The Heart

Introduction to the Cardiovascular System

• The cardiovascular system is essential for maintaining homeostasis by supplying oxygen and nutrients through blood circulation.

  • Proper heart function adjusts pumping capacity to meet tissue demands.

  • The Heart is the primary organ in the cardiovascular system, it never stops contracting, ensuring blood stays in motion and efficiently delivers essential substances to various tissues while also aiding in the removal of waste products.

    • Controlled by the autonomic nervous system

  • Cardiac Output: volume of blood pumped per minute— worries between 5 and 30 liters per minute

Overview of the Cardiovascular System

• Two Closed Circuits:

  • The heart has 4 muscular chambers, acting together as one muscle:

    • R & L Atria (2)

    • R & L Ventricles (2)

  • The heart acts as a double pump:

    1. Pulmonary Circuit: Oxygen-deficient blood is pumped from the right atrium to the right ventricle, transported to the lungs for oxygenation, and then returned to the left atrium, where it is distributed to the left ventricle before being pumped into the systemic circuit.

       • Short, low-pressure citculation

    2. Systemic Circuit: Oxygen-rich blood is pumped from the left ventricle into the aorta, which delivers it to the rest of the body, providing essential nutrients and oxygen to tissues before returning deoxygenated blood to the right atrium.

       • Long, High-pressure circulation

         • There is also the Coronary Circuit: Which supplies the heart muscle with oxygenated blood, and then back to the R side of the heart

• Blood Vessels:

  • Arteries: A vessel that transports blood away from the heart.

  • Veins: A vessel that transports blood to the heart.

  • Capillaries: Thin-walled vessels that interconnect for nutrient and gas exchange “exchange vessels”

    • This is the only place where things can leave the CVS, as it is a closed system

• Heart Chambers:

  • Four chambers:

    1. Right Atrium

    2. Right Ventricle,

    3. Left Atrium

    4. Left Ventricle.

  • Atria collect incoming blood

  • Ventricles pump blood out.

Structure of the Heart Wall

• Layers of the Heart Wall:

  • Epicardium: Visceral layer of serous pericardium.

  • Myocardium: Muscular layer, facilitating contraction.

  • Endocardium: Linings inside of heart chambers (covers 2 AV valves, 2 Semilunar valves, 2 atria, and 2 ventricles)

• Cardiac Muscle Tissue:

  • Cardiac muscle cells are small, depend on aerobic respiration.

  • Intercalated Discs connect cardiac muscle cells, conducting impulses and forces of contraction.

The Pericardium

• Pericardium:

  • The Body Cavity that surrounds the heart, located in the mediastinum.

  • Contains pericardial fluid for lubrication.

  • Visceral Pericardium (inner, epicardium) covers the heart; Parietal Pericardium (outer) lines the cavity.

  • Fibrous Pericardium— Fibrous sac that anchors pericardial cavity to the diaphragm

The Cardiac Skeleton

• Function of Fibrous Cardiac Skeleton:

  • Stabilizes contractile cells and valves, providing physical support

  • Supports blood vessels and nerves, adds strength and elasticity, isolates atria from ventricles.

Orientation and Superficial Anatomy of the Heart

• Heart Orientation:

  • Rotated slightly to the L

  • Anterior Surface:

    • R Atrium, R Ventricle, L Ventricle

  • Posterior Surface:

    • L Atrium, a small portion of R Atrium

  • Positioned at an angle, base at the top (great vessels connection) and apex at the bottom.

  • Major surfaces include: anterior (sternocostal), posterior, and diaphragmatic surfaces.

• External Landmarks:

  • Grooves mark chamber separations:

    • Interatrial Groove— Separates L & R atria

    • Coronary Sulcus— Separates the atria and the ventricles

    • Anterior Interventricular Sulcus— Separates L & R ventricles

    • Posterior Interventricular Sulcus— Separates L & R ventricles

    • Auricle of R Atrium— Small, ear-shaped muscular pouch that increases capacity for blood collection

    • Auricle of L Atrium— Small, ear-shaped muscular extension functioning as a reservoir for blood returning from the pulmonary veins

      • Auricles are extensions of atria.

Internal Anatomy and Organization of the Heart

• Separation of Chambers:

  • The interventricular septum separates atria, interventricular septum separates ventricles.

  • Valves maintain one-way blood flow between chambers.

Right Atrium

• Receives deoxygenated blood from systemic circulation via the:

  • Superior Vena Cavae— everything above the diaphragm

  • Inferior Vena Cavae— everything below the diaphragm

    • Coronary sinus— collects deoxygenated blood from the heart muscle

• Contains pectinate muscles (pectinate describes muscle pattern) and the fossa ovalis (remnant of foramen ovale).

Right Ventricle

• R ventricle receives oxygen-poor blood from the R atrium

• Blood flows through the R Atrioventricular (tricuspid) or (R AV Valve) to the right ventricle.

• The R ventricle contracts, forcing blood toward the Pulmonary (Semilunar) Valve, which opens due to the increased ventricular pressure.

• The blood then exits to the Pulmonary Trunk, a large artery that carries deoxygenated blood to the R & L pulmonary arteries and then lungs.

  • Papillary Muscles hold the valve shut to prevent backflow of blood into the right atrium during ventricular contraction, ensuring one-way flow through the heart.

  • Chordae tendineae— the chords that hold the papillary muscles in place and prevent the inversion of the valves

• Moderator band— a fibrous band of muscle tissue that helps synchronize the contraction of the heart's chambers due to pressure differences

  • Found only in R ventricle

• Trabecular carneae— Muscle pattern found on the inner walls of the ventricles that assist in the contraction

• Interventricular septum— separates L & R ventricles, preventing overexpansion of the thin-walled R ventricle

Left Atrium

• Receives oxygenated blood from Pulmonary Veins

  • The L atrium has thicker walls than the R atrium because of the greater pressure it must withstand while pumping blood into the left ventricle.

• Blood flows to the left ventricle through the L Atrioventricular (mitral or bicuspid) or AV valve.

Left Ventricle

• Largest and thickest chamber; pumps blood to the systemic circuit via the Aortic Valve (aortic semilunar valve), and the Aorta which has three branches servicing the upper body

  1. Brachiocephalic Trunk— supplies blood to the right arm and head, splitting into the right subclavian and right common carotid arteries.

  2. L Common Carotid Artery— supplies blood to the left side of the head and neck

  3. L Cubclacarian Artery— supplies blood to the left arm and shoulder

• Pumps at high pressure necessary for systemic distribution.

Structural Differences Between Right and Left Ventricles

• R ventricle has thin walls for low-pressure function.

• L ventricle has thick muscular walls for high-pressure output throughout the body.

Heart Valves

• Components of AV Valves :

  • R & L AV Valves— Have CT cusps (flaps) attached to chordae tendineae and papillary muscles, which prevent backflow into the atria.

    • Lubb— AV valves closing during ventricular contraction, beginning of ventricular systole (contracting), resulting in the first heart sound.

• Semilunar Valves:

  • Aortic and Pulmonary valves have three crescent-shaped cusps but no chordae tendineae or papillary muscles.

  • The cusps open passively due to blood pressure changes and snap shut to prevent backflow.

    • Dubb— semilunar valves closing creates the second heart sound, signaling the end of ventricular systole and the beginning of ventricular diastole (not contracting).

• Function: Supplies blood to the heart muscle; high oxygen demand due to aerobic metabolism.

• Coronary Sinus: A large vein that collects deoxygenated blood from all coronary veins, and empties it into the R atrium for the pulmonary circuit.

• Coronary Arteries and Branches:

  • Right coronary artery (RCA) gives rise to right marginal and posterior interventricular branches

    • Passes between the R auricle & pulmonary trunk and supplies blood to the right atrium, right ventricle, and parts of the left ventricle

  • Left coronary artery (LCA) gives rise to circumflex and anterior interventricular branches.

    • Branches into the anterior interventricular artery and the circumflex artery, supplying blood to the left atrium and left ventricle.

      • RCA & LCA originate at the aortic sinus

Coronary Veins

• Drain blood from the myocardium into the coronary sinus.

• Includes great cardiac vein, middle cardiac vein, and others draining the heart's surface.

Coordination of Cardiac Contractions

• Autorhythmicity: Cardiac muscle contracts independently of neural inputs.

• Nodal Cells:

  • Set the heart rate (mainly SA node) and distribute impulses.

Cardiac Cycle

• Consists of the phases of contraction (systole) and relaxation (diastole).

• Impulse conduction progresses through SA node, AV node, AV bundle, and Purkinje fibers.

Autonomic Control of Heart Rate

• Heart Rate Modulation:

  • Basic rhythm set by pacemaker cells but modulated by the autonomic nervous system (ANS).

  • Norepinephrine increases heart rate; acetylcholine decreases it.

  • Cardiac centers in medulla oblongata respond to pressure and gas concentrations.