Chap 19 The circulatory system - Heart- part 1 of 2 (1)

Chapter 19: Circulatory System - The Heart (Part 1 of 2)

Learning Outcomes

• Define and distinguish between the pulmonary circuit and systemic circuit.

• Describe the general location, size, and shape of the heart.

• Describe the pericardium and the three layers of the heart wall.

• Identify and describe the four chambers of the heart.

• Identify the surface features of the heart and correlate them with its internal four-chambered anatomy.

• Identify the four valves of the heart and explain their function.

• Trace the flow of blood through the four chambers, valves of the heart, and adjacent blood vessels.

Overview of the Cardiovascular System

• Components: The cardiovascular (CV) system consists of the heart and blood vessels.

  • Functions: The heart acts as a muscular pump to keep blood moving through the blood vessels, which deliver blood to organs and return it to the heart.

• Divisions of the CV system:

  • Pulmonary Circuit: Carries blood to the lungs for gas exchange and returns it to the heart.

  • Systemic Circuit: Supplies blood to every organ of the body, including the lung tissues and heart wall.

  • Oxygenation: Each circuit's relative concentration of oxygen (O2) and carbon dioxide (CO2) varies; pulmonary carries deoxygenated blood, while systemic carries oxygenated blood.

Position, Size, and Shape of the Heart

• Location: The heart is located in the mediastinum, a thick partition between the lungs.

• Shape: Triangular.

• Dimensions:

  • Base: Wide, superior portion.

  • Apex: Tapered inferior end, tilts to the left.

  • Weight: Approximately 10 ounces for adults, about the size of a fist.

  • Measurement: 3.5 inches wide at the base, 5 inches from base to apex, situated between ribs 2-6.

Structure of the Pericardium

• Definition: The heart is enclosed in a double-walled sac called the pericardium.

• Components:

  1. Fibrous Pericardium: Forms the outer wall, anchoring the heart to the diaphragm and sternum.

  2. Serous Pericardium: Comprised of two layers:

     • Parietal Layer: Lies next to the fibrous pericardium.

     • Visceral Layer (Epicardium): Adheres to the heart surface, forming the outermost layer of the heart wall.

• Pericardial Cavity: The space between the parietal and visceral layers, containing 5 to 30 mL of pericardial fluid, which reduces friction and can become inflamed (pericarditis).

Layers of the Heart Wall

1. Epicardium: The visceral layer of serous pericardium, acting as a covering.

   • Contains larger coronary blood vessels.

2. Endocardium: Smooth inner lining of the heart and blood vessels, consisting of simple squamous epithelium.

   • Covers valve surfaces and continues with the endothelium of blood vessels.

3. Myocardium: Composed of cardiac muscle tissue, it's the thickest layer due to its workload.

   • Cardiac muscle is organized into bundles that produce a wringing motion during contraction to enhance blood pumping.

Fibrous Skeleton of the Heart

• Defined as dense connective tissue concentrated between the heart's upper and lower chambers.

• Structure: Arranged in fibrous rings surrounding the base of two valves and two blood vessels.

• Functions: Provides structural support and anchors cardiomyocytes, giving them a force to pull against.

Internal Heart Anatomy

• Chambers: There are four heart chambers:

  • Two Superior Chambers: Right atrium and left atrium; receive blood returning to the heart.

    • Each atrium contains an ear-like flap (auricle) that increases volume.

    • Atria are separated by the interatrial septum.

  • Two Inferior Chambers: Right and left ventricles; pump blood into arteries.

    • Ventricles are separated by the interventricular septum which has trabeculae carneae (ridges) to prevent wall collapse.

    • The left ventricle wall is much thicker than the right ventricle wall due to higher pressure needs.

Surface Features of the Heart

• Anterior View: Coronary sulcus separates atria from ventricles; interventricular sulcus marks the boundary between ventricles.

• Posterior View: Structures include the aorta, left pulmonary artery and veins, right atrium, and right ventricle, outlining major blood flows.

Heart Valves and Blood Flow

• Functions of Heart Valves: Ensure one-way blood flow:

  • Atrioventricular Valves (AV): Control blood flow between the atria and ventricles.

    • Right AV (Tricuspid Valve): Three fibrous flaps.

    • Left AV (Mitral Valve): Two flaps (bicuspid).

    • Chordae Tendineae: Connect AV valves to papillary muscles to stabilize valve positions during contraction.

  • Other Valves: Include the pulmonary valve (between the RV and pulmonary trunk) and the aortic valve (between LV and aorta).

Blood Flow Through the Heart

• The flow of blood through the heart chambers is sequential, with steps related to the pulmonary circuit and systemic circuit.