Heart I(1)

Lecture Overview

• Lecture Title: The Heart

• Course: Anatomy and Physiology (Ch20)

• Instructor: Dr. Christopher Potter

• Copyright: ©2018 Pearson Education, Inc.

Important Figures

• The physiology of the heart is depicted in various important figures:

  • Fig 20-10: Conducting system of the heart

  • Fig 20-11: Impulse conduction through the heart

  • Fig 20-12: Electrocardiogram (ECG)

  • Fig 20-15: Action potentials in skeletal and cardiac muscle

  • Fig 20-16: Phases of the cardiac cycle

  • Fig 20-17: Pressure and volume relationships in the cardiac cycle

  • Fig 20-21: Autonomic innervation of the heart

  • Fig 20-22: Autonomic regulation of pacemaker cells

  • Fig 20-23: Factors affecting stroke volume

  • Fig 20-24: Summary of factors affecting cardiac output

Overview of the Cardiovascular System

• The heart plays a vital role by pumping blood throughout the pulmonary and systemic circuits, ensuring oxygenation and nutrient delivery to the body.

• Systemic Circuit: Involves capillaries in the head, neck, abdominal organs, and limbs, working in conjunction with the systemic arteries and veins.

• Pulmonary Circuit: Focuses on the capillaries in the lungs, associated with pulmonary arteries and veins, crucial for gas exchange.

Anatomy of the Heart

Location of the Heart

• The heart is located in the thoracic cavity, specifically in the mediastinum between the lungs, with anatomical landmarks including:

  • Right lung

  • Left lung

  • Sternum

  • Diaphragm

Structural Components

• Key layers of the heart:

  • Pericardium: The fibrous sac surrounding the heart, including:

    • Fibrous Pericardium: Tough connective tissue outer layer.

    • Serous Pericardium: A double-layered layer with parietal and visceral components (the epicardium).

  • Myocardium: The thick, muscular middle layer responsible for heart contractions.

  • Endocardium: The smooth inner layer of the heart chambers and vessels.

  • Pericardial Cavity: Contains serous fluid, which reduces friction between the heart and pericardium during heartbeats.

Pericardium Details

• Composed of:

  • Fibrous Pericardium: Provides protection and maintains position.

  • Serous Pericardium:

    • Parietal Pericardium: A layer that lines the interior of the fibrous pericardium.

    • Visceral Pericardium (Epicardium): Directly covers the heart muscle.

• Serous Fluid: Acts as a lubricant, allowing smooth motion during heart activity.

Heart Wall Structure

• The heart wall consists of:

  • Epicardium: Same as visceral pericardium; protects and lubricates the heart.

  • Myocardium: The thickest layer made of cardiac muscle cells, enabling the heart to pump effectively.

  • Endocardium: Lines the heart's chambers and is continuous with blood vessel linings.

Heart Musculature

• Atrial musculature forms bands that wrap in a figure-eight pattern, while ventricular musculature wraps around in spirals, allowing efficient contraction.

• The left ventricle has thicker walls compared to the right due to the higher pressure it generates for systemic circulation.

Heart Contraction Mechanism

• Cardiac muscle cells feature:

  • Intercalated Discs: Structures that connect cardiac fibers, enabling synchronized contraction.

  • Gap Junctions: Allow electrical impulses to flow and propagate quickly between cells, facilitating coordinated heart contractions.

  • Desmosomes: Structures that anchor cells together, preventing separation during contractions.

Cardiac Valves

• The heart contains several valves crucial for unidirectional blood flow:

  • Atrioventricular Valves: (Tricuspid and Mitral) open when ventricles relax, and close when ventricles contract.

  • Semilunar Valves: (Aortic and Pulmonary) open during ventricular contraction and close when the ventricles relax.

Heart Sounds

• The first heart sound ("lub"): Associated with the closing of atrioventricular valves.

• The second heart sound ("dub"): Associated with the closure of semilunar valves.

Summary of Cardiac Structure

• The heart is a complex organ featuring multiple layers and structures that work in unison to maintain effective blood circulation throughout the body. Understanding these components is essential for studying cardiovascular physiology.