BSC 2086 Lesson 7

Introduction to the Cardiovascular System

• Cardiovascular system: heart and blood vessels.

• Cardiology is the study of the heart and disorders related to it.

Overview of the Cardiovascular System

• Expected 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 that encloses the heart.

• Components:

  • Heart: Functions as a pump maintaining blood flow.

  • Vessels:

    • Arteries: Carry blood away from the heart.

    • Veins: Carry blood towards the heart.

    • Capillaries: Connect smallest arteries to veins.

• Circulatory system includes heart, vessels, and blood.

Circuits of the Cardiovascular System

• Two Major Divisions:

  • Pulmonary Circuit:

    • Carries blood to the lungs for gas exchange.

    • Managed by the right side of the heart.

  • Systemic Circuit:

    • Supplies oxygenated blood to body tissues, returns deoxygenated blood to the heart.

    • Managed by the left side of the heart.

Detailed Description of the Circuits

• Pulmonary Circuit:

  • Oxygen-poor blood arrives from body tissues to the right atrium.

  • Blood is sent to the lungs via the pulmonary trunk, picks up oxygen, and returns via the pulmonary veins.

• Systemic Circuit:

  • Oxygenated blood is sent to body tissues from the left ventricle via the aorta.

  • Deoxygenated blood returns to the heart via vena cavae.

• Great Vessels: Major arteries and veins entering/leaving the heart.

Anatomy of the Heart

• Position: Located in the mediastinum between the lungs.

• Shape:

  • Base: Wide superior portion where major vessels attach.

  • Apex: Tapered end tilting left.

• Size: Approximately the size of a fist, averaging 10 ounces.

The Pericardium

• Encloses the heart in a double-walled sac.

• Functions:

  • Allows for heart movement without friction.

  • Provides space for expansion and limits excessive expansion.

  • Anchors to diaphragm and sternum.

• Structure:

  • Fibrous Pericardium: Tough outer sac.

  • Serous Pericardium: Contains parietal and visceral layers (epicardium).

  • Pericardial Cavity: Contains fluid to reduce friction.

  • Pericarditis: Inflammation may cause friction rubbing.

Gross Anatomy of the Heart

• Layers of the Heart Wall:

  • Epicardium: Serous membrane covering the heart.

  • Myocardium: Muscle layer that contracts.

  • Endocardium: Smooth lining covering chambers and valves.

  • Fibrous Skeleton: Collagen and elastic fibers supporting heart structure and electrically isolating atria from ventricles.

Heart Chambers and Valves

• Chambers: Four in total, two atria (upper) and two ventricles (lower).

• Atria: Thin-walled, receive blood from veins.

• Ventricles: Thick-walled, pump blood into arteries.

• Heart Valves:

  • Atrioventricular (AV) Valves:

    • Right AV (tricuspid) & Left AV (mitral) regulate flow between atria and ventricles.

  • Semilunar Valves: Control blood flow from ventricles to arteries (pulmonary and aortic).

Blood Flow Pathways

• Pathway of Blood through Heart:

  • Enter right atrium from superior and inferior venae cavae.

  • Flows through right AV valve to right ventricle, then to lungs via pulmonary valve.

  • Returns oxygenated blood to left atrium, flows through left AV valve into left ventricle, and ejected into aorta.

Coronary Circulation

• Function: Supplies heart muscle (myocardium) with blood.

• Arterial Supply: Left coronary artery branches supply anterior aspects, right coronary artery supplies posterior aspects.

• Flow: Greatest during heart relaxation; obstructed during contraction.

Cardiac Muscle Structure and Function

• Unique Features: Striated, short fibers with intercalated discs forming cell connections for synchronized contraction.

• Cardiac Muscle Metabolism: Primarily aerobic respiration; fatigue resistant with reliance on various organic fuels.

Cardiac Conduction System

• Heartbeat Initiation: Myogenic and autorhythmic characteristics; rhythm is controlled by SA node.

• Signal Pathway: SA node → AV node → bundle branches → Purkinje fibers.

• Action Potential Dynamics: Unique plateau phase in cardiomyocytes prevents tetanus, sustaining contractions.

Electrocardiogram (ECG)

• Basics: Records electrical activity of the heart.

• Components: P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization).

Cardiac Arrhythmias

• Indicators of Abnormalities: Deviations from normal ECG may signal issues like myocardial infarction or conduction pathologies.

• Types of Arrhythmias: Include ventricular fibrillation, atrial fibrillation, heart block, and premature ventricular contractions.