Cardiac Physiology Lecture Notes Lecture 1

This lecture focuses on the intricate anatomy and physiology of the circulatory system and the heart. Presented by Dr. Matt Parker at the University of Surrey, this session delves deeper into how the cardiovascular system functions, emphasizing its essential role in maintaining homeostasis through blood circulation.

The course includes various assessments such as practical reports, which provide hands-on experiences, and a final examination composed of multiple-choice questions (MCQ) to evaluate understanding.

Learning Objectives

Students will:

• Understand in detail the arrangement and interaction of the circulatory system, including the distinct roles of systemic and pulmonary circulations in oxygen transport and waste elimination.

• Describe the complex anatomy of the heart, including its chambers, valves, and associated structures, assessing how these components work synergistically.

• Explain the intricate blood flow through the heart, detailing the path through each chamber and valve, and understanding the significance of this flow in cardiovascular health.

• Outline the structure and function of different types of blood vessels, including arteries, veins, and capillaries, and their roles in systemic and pulmonary circulation.

• Discuss the coronary circulation, essential for nourishing the heart muscle, as well as the electrical conduction system that regulates heartbeats.

• Interpret Electrocardiogram (ECG) readings to assess heart health and diagnose potential cardiovascular disorders.

Circulatory System Structure

The cardiovascular system consists of:

• Heart: The main organ responsible for pumping blood throughout the body, divided into four chambers.

• Blood Vessels: A distribution network that is divided into:

  • Arterial System: Comprising arteries that carry oxygenated blood away from the heart to the body tissues, aiding in the delivery of oxygen and nutrients.

  • Venous System: Comprising veins which carry deoxygenated blood from the body back to the heart for reoxygenation in the lungs.

Circulation Types

Systemic Circulation

Systemic circulation refers to the pathway in which blood is pumped from the left ventricle to the entire body, providing oxygen and nutrients while removing carbon dioxide and waste products. The process can be broken down as follows:

• Left Ventricle → Pumps oxygen-rich blood into the Aorta → This blood travels through the arterial branches to the Body (organs and tissues) → Returns to the Right Atrium via the Superior/Inferior Vena Cava.

Pulmonary Circulation

Pulmonary circulation is responsible for sending deoxygenated blood from the right ventricle to the lungs for oxygenation. The process is as follows:

• Right Ventricle → Pumps deoxygenated blood into the Pulmonary Artery → Blood travels to the Lungs where it releases carbon dioxide and absorbs oxygen → Returns to the Left Atrium via the Pulmonary Veins.

Anatomy of the Heart

The heart is approximately the size of a fist and is located in the thoracic cavity, superior to the diaphragm and to the left of the midline, sitting anterior to the vertebral column and posterior to the sternum.

• Weight: Approximately 300 grams in adults, varying with body size and fitness level.

• Chambers: The heart consists of four chambers - two atria (the left atrium and right atrium) that serve as receiving chambers, and two ventricles (the left ventricle and right ventricle) which act as discharging chambers.

Heart Chambers and Their Functions

Atria

• Right Atrium: Receives deoxygenated blood from the body through the venae cavae.

• Left Atrium: Receives oxygenated blood from the lungs through the pulmonary veins.

Ventricles

• Right Ventricle: Pumps deoxygenated blood to the pulmonary artery for reoxygenation in the lungs.

• Left Ventricle: Pumps oxygenated blood into the aorta, distributing it to the body.

Heart Valves

The heart valves ensure unidirectional blood flow through the heart, preventing backflow, and include:

• Tricuspid Valve: Located between the right atrium and right ventricle.

• Bicuspid (Mitral) Valve: Located between the left atrium and left ventricle.

• Aortic Valve: Situated between the left ventricle and the aorta.

• Pulmonary Valve: Located between the right ventricle and the pulmonary artery.

Coverings of the Heart

The heart is protected by the pericardium, a double-walled sac which includes:

• Fibrous Pericardium: The outermost layer that provides mechanical support.

• Serous Pericardium: Composed of two layers (parietal and visceral) that secrete pericardial fluid to reduce friction during heartbeats.

Heart Walls

The heart wall consists of three layers:

• Epicardium: The visceral layer of the serous pericardium that is the outermost layer of the heart.

• Myocardium: The thick layer of cardiac muscle responsible for pumping action.

• Endocardium: The inner layer lining the heart chambers and valves.

Major Vessels of the Heart

Returning Blood to the Heart

• Superior and Inferior Venae Cavae: The major veins returning deoxygenated blood from the body to the right atrium.

• Right and Left Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium.

Conveying Blood Away from the Heart

• Pulmonary Trunk: Splits into right and left pulmonary arteries for transporting deoxygenated blood to the lungs.

• Aorta: The main artery that branches into several arteries (Brachiocephalic, Left Common Carotid, Subclavian) distributing oxygenated blood to the rest of the body.

Coronary Circulation

Coronary circulation supplies blood to the heart muscle itself. Blood flow primarily occurs during relaxation phases (diastole), allowing the myocardium to receive oxygen and nutrients.

• Myocardial Ischemia: A condition where blood flow is reduced due to various factors such as arterial spasm or atherosclerosis, potentially leading to myocardial infarction (heart attack).

Cardiac Muscle Features

Cardiac myocytes, the muscle cells of the heart, exhibit unique features:

• Self-excitable: Capable of initiating their own contraction without external signals.

• Contracting as a Unit: All cardiac cells work together to contract simultaneously, allowing for efficient pump function.

• Absolute Refractory Period: A longer refractory period (~250 ms) prevents tetanus (sustained contraction), ensuring rhythmic pumping.

Electrical Conduction System

1. Sinoatrial (SA) Node: Serves as the primary pacemaker, setting the rhythm of the heartbeat.

2. Atrioventricular (AV) Node: Delays the impulse, allowing the atria to contract and fill the ventricles before they contract.

3. Bundle of His: Transmits impulses from the AV node to the ventricles.

4. Purkinje Fibers: Spread the electrical impulse rapidly throughout the ventricles, ensuring coordinated contraction.

Cardiac Action Potential Steps

The cardiac action potential is crucial for maintaining a normal heartbeat and consists of several phases:

1. Depolarization: Sodium channels open, allowing Na+ ions to enter the cell and initiate contraction.

2. Sustained Depolarization: Calcium channels open, maintaining contraction through influx of Ca2+.

3. Repolarization: Potassium channels open, allowing K+ ions to exit, returning the cell to its resting state.

ECG (Electrocardiogram)

ECGs measure the overall electrical activity of the heart over time, providing vital information about heart health. Key components include:

• P Wave: Represents atrial depolarization.

• QRS Complex: Represents ventricular depolarization.

• T Wave: Represents ventricular repolarization.

Normal Values:

• P-R Interval: 0.12-0.20 seconds

• QRS Width: 0.08-0.12 seconds

• Q-T Interval: 0.35-0.43 seconds

Heart Rate Measurement

Heart rate can be calculated using the R-R interval on an ECG.

• Normal Heart Rate Range: Between 55-75 beats per minute, varying on factors like fitness level and stress.

Summary of Learning Outcomes

By the end of this course, students will have a comprehensive understanding of:

• The intricacies of systemic and pulmonary circulations.

• Detailed heart anatomy and the course of blood flow.

• The structure and functional significance of various blood vessels.

• An understanding of coronary circulation and the conduction pathways of the heart.

• Proficient skills in ECG interpretation and assessment of cardiac function.

Upcoming Topics

The next session will cover essential topics such as cardiac output, blood pressure regulation, and autonomic control of the heart during stress and exercise conditions.