Physiology of the Cardiovascular System

Overview

• The cardiovascular system includes the heart, blood vessels, and blood functioning to circulate oxygen and nutrients throughout the body.

Anatomical Perspectives

Key Structures

• Mediastinum: The central compartment of the thoracic cavity that contains the heart, major blood vessels, trachea, esophagus, and more.

• Maximal Point of Vena Cava Intensity (PMI): Location where the heartbeat can be maximally detected, generally corresponds to the apex of the heart.

• Heart Orientation: The heart can be positioned leftward (left axis deviation), be displaced due to obesity/pregnancy, or be centrally located in tall individuals.

Heart Structure

Chambers of the Heart

• The heart has four chambers:

  • Right and Left Atria (plural of atrium)

  • Right and Left Ventricles

Blood Flow Through the Heart

Pathway of Blood

• Deoxygenated Blood enters the Right Atrium via the superior and inferior vena cava, meaning it has less than 50% oxygen saturation.

• Blood flows through the tricuspid valve to the right ventricle, where it is pumped into the pulmonary trunk.

• Oxygenated Blood returns to the left atrium via the pulmonary veins, flows through the bicuspid (mitral) valve into the left ventricle, and is then pumped into the aorta.

• Key Heart Sounds: The closure of AV valves produces the "Lub" sound, while closure of the semilunar valves produces the "Dup" sound.

Cardiac Muscle

Myocardium

• The heart muscle, or myocardium, is responsible for the heart's contractions.

• Composed mostly of contractile myocytes with a small percentage of pacemaker (autorhythmic) cells, which initiate action potentials.

Heart Valves

• Atrioventricular (AV) Valves: Tricuspid (Right) and Mitral (Left) valves regulate blood flow between atria and ventricles.

• Chordae Tendineae and Papillary Muscles: Prevent valve prolapse and regulate blood flow during contractions.

Contraction Phases

Diastole and Systole

• Diastole: Heart at rest, atria fill with blood from the veins, AV valves open due to gravity.

• Systole: Ventricles contract, forcing blood into arteries; this includes isovolumetric contraction where all valves are temporarily closed.

Cardiac Electrical Conduction

Autorhythmicity

• Heartbeat initiated by pacemaker cells located primarily in the sinoatrial (SA) node, followed by atrioventricular (AV) node firing.

• Action potentials propagate through the heart muscle via specialized conduction pathways (Bundle of His, Purkinje fibers).

ECG Basics

• Electrocardiogram (ECG): Reflects the heart's electrical activity, crucially showing depolarization of the atria (P wave) and ventricles (QRS complex).

• Waveforms indicate cardiac rhythm and can reveal conditions like myocardial infarctions or arrhythmias.

Pathologies

Myocardial Infarction

• Caused by plaque buildup in coronary arteries, severely decreasing blood flow.

• Leads to muscle damage as the lack of oxygenated blood prevents normal electrical activity.

Atherosclerosis

• Characterized by the buildup of cholesterol plaques in arteries, with differing impacts based on the type of lipoproteins involved (HDL vs. LDL).

Hemodynamics

Blood Flow Dynamics

• Governed by pressure gradients (blood flows from high to low pressure), resistance, and vessel diameter (Poiseuille’s law).

• Hydrostatic Pressure: Key driving force for blood flow, measured in mmHg.