Cardiovascular System Spring 2024 Lecture Notes

Cardiovascular System Overview

• The cardiovascular (or circulatory) system consists of two main circuits:

  • Pulmonary circulation: Closed loop of vessels carrying blood between the heart and lungs.

  • Systemic circulation: Circuit of vessels carrying blood between the heart and other body systems.

Circulatory Pathways

Pulmonary Circuit

• Right Atrium

  • Receives oxygen-poor, CO₂-rich blood from systemic circulation via the venae cavae.

• Right Ventricle

  • Pumps oxygen-poor blood to the lungs through the pulmonary arteries.

• Gas Exchange

  • Occurs in the capillary beds of the lungs, where blood releases CO₂ and picks up O₂.

• Pulmonary Veins

  • Return oxygen-rich, CO₂-poor blood to the left atrium of the heart.

Systemic Circuit

• Left Atrium

  • Receives oxygen-rich blood from the lungs via the pulmonary veins.

• Left Ventricle

  • Pumps oxygen-rich blood to the rest of the body through the aorta and its branches.

• Blood undergoes gas exchange in the capillary beds of various tissues, returning CO₂-rich, oxygen-poor blood to the heart.

Heart Anatomy

• The heart is a hollow, muscular organ roughly the size of a fist:

  • Location: Superior surface of diaphragm, left of midline in mediastinum, anterior to the vertebral column, and posterior to the sternum.

Coverings of the Heart

• Pericardium: A double-walled sac surrounding the heart.

  • Superficial fibrous pericardium: Provides protection.

  • Serous Pericardium: Divided into two layers:

    • Parietal layer: Lines the internal surface of the fibrous pericardium.

    • Visceral layer (epicardium): Covers the heart surface, separated by the pericardial cavity filled with serous fluid.

Functions of the Pericardium

• Protects and anchors the heart.

• Prevents overfilling of the heart with blood.

• Provides a friction-free environment for heart movement.

Heart Wall Structure

• Composed of three layers:

  • Epicardium: Outermost layer, which is the visceral layer of the serous pericardium.

  • Myocardium: Thick cardiac muscle forming the bulk of the heart.

  • Endocardium: Endothelial layer lining the heart's inner surface.

Cardiac Skeleton

• A crisscrossing connective tissue framework:

  • Anchors cardiac muscle fibers.

  • Supports major vessels and valves.

  • Regulates the spread of action potentials within the heart.

Heart Chambers and Valves

• The heart functions as a double pump made up of four main chambers:

  • Atria: Receiving chambers (Right and Left Atria).

    • Right atrium receives deoxygenated blood from the body.

    • Left atrium receives oxygenated blood from the lungs.

  • Ventricles: Discharging chambers (Right and Left Ventricles).

    • Right ventricle pumps blood to the lungs.

    • Left ventricle pumps blood to the body.

• Heart Valves:

  • Atrioventricular (AV) Valves: Prevent backflow into the atria during ventricular contraction.

    • Tricuspid Valve (right side)

    • Mitral Valve (left side)

  • Semilunar Valves: Prevent backflow into the ventricles after contraction.

    • Aortic Valve (between left ventricle and aorta)

    • Pulmonary Valve (between right ventricle and pulmonary trunk)

Cardiac Cycle

• Refers to the sequence of events in one heartbeat:

  • Systole: Contraction phase of heart muscles.

  • Diastole: Relaxation phase.

• Phases:

  1. Ventricular Diastole: Heart fills with blood.

  2. Ventricular Systole: Blood is pumped out of the heart.

  3. Isovolumetric relaxation: Ventricles relax, preparing for the next cycle.

Electrical Activity of the Heart

• Heart's rhythmic beating originates from action potentials generated by its own pacemaker cells.

  • Sinoatrial (SA) Node: Primary pacemaker, generates impulses at about 75 beats per minute.

  • Atrioventricular (AV) Node: Delays impulse transmission to ensure the atria finish contracting prior to ventricular contraction.

  • Bundle of His and Purkinje Fibers: Conduct impulses through the ventricles for coordinated contraction.

Blood Vessels

General Structure

• Composed of three layers (tunics):

  • Tunica Intima: Endothelium lining the inside of blood vessels.

  • Tunica Media: Middle layer consisting of smooth muscle.

  • Tunica Externa: Outermost layer providing structural support.

Types of Blood Vessels

• Arteries: Carry blood away from the heart; thicker walls to handle high pressure.

• Veins: Carry blood toward the heart; thinner walls; contain valves to prevent backflow.

• Capillaries: Exchange vessels where oxygen, carbon dioxide, nutrients, and wastes are exchanged with tissues.

Capillary Exchange

• Movement of substances across capillary walls occurs via:

  • Endothelial cell cytoplasm.

  • Intercellular clefts between cells.

  • Fenestrations in capillaries.

Starling Forces

• Govern the movement of fluids across capillaries, consisting of:

  1. Blood hydrostatic pressure: Pushes fluids out of capillaries.

  2. Colloid osmotic pressure: Pulls fluids into capillaries.

Venous Return Mechanisms

• Venous pressure is low; assisted by:

  • Muscular pump: Contraction of muscles helps push blood toward the heart.

  • Respiratory pump: Pressure changes during breathing aid venous return.

Coronary Circulation

• About 5% of blood pumped by the heart is specifically directed to supply the heart muscle via:

  • Left Coronary Artery (LCA)

  • Right Coronary Artery (RCA)

• These arteries branch off the ascending aorta to nourish the heart tissue.