Components of Oxygenation

Oxygenation is the distribution of oxygen to the body’s cells via internal and external respiration.

Heart

A cone-shaped, hollow, muscular organ location in the mediastinum between the lungs. It pumps ~5L/min (Cardiac Output) or ~60mL/beat (Stroke Volume).

• It is covered by a thin covering called the pericardium, made up of the parietal pericardium, the visceral pericardium, and the pericardial cavity/space that sits in between them, containing pericardial fluid normally around ~20mL.
• There are three layers of cardiac muscle tissue: the epicardium, myocardium, and endocardium (from outermost to innermost).

Chambers and Valves of the Heart

1. Right Atrium: entry point of unoxygenated blood into the heart from the SVC, IVC, and Coronary Sinuses.
   • Exit Point: tricuspid valve (when closing, it produces S1)
2. Right Ventricle: exits into pulmonary circulation.
   • Exit Point: pulmonary semilunar valve (when closing, produces S2/P2)
3. Left Atrium: entry point of oxygenated blood into the heart from the four pulmonary veins.
   • Exit Point: mitral/bicuspid valve
4. Left Ventricle: exits into systemic circulation.
   • Exit Point: aortic semilunar valve (when closing, produces S2/A2)

Coronary Artery Disease

The coronary arteries are the main oxygen supply of the heart. When they are blocked by plaque formed from deposition and damage caused by fat/lipids, atherosclerosis occurs, which leads to angina pectoris, where the oxygen supply and oxygen demand of the heart is mismatched. This leads to necrosis, which leads to myocardial infarction.

1. Left Coronary Arteries
   • Left Anterior Descending Artery (LADA): supplies the LV and Ventricular Septum, Chordae Tendinea, Papillary Muscle, and to a lesser extent, the RV.
   • Circumflex Coronary Artery: supplies the LA, Lateral and Posterior Surfaces of the LV, Some of the Ventricular Septum, and the SA/AV Nodes.
2. Right Coronary Artery: supplies the RA, RV, and the lower portion of the LV.

Electrophysiologic Properties of the Heart

1. Automaticity: spontaneous and automatous repetitive impulse.
2. Excitability: depolarization, the response to a stimulus.
3. Conductivity: transmission of impulses across the heart.
4. Contractility: physical contractile ability of the heart.
5. Refractoriness: inability to respond until repolarization.
6. Elasticity/Distensibility: ability of the heart to compensate increased pressure and volume.
7. Rhythmicity: standard and continuous repolarization and depolarization of the heart.

Conduction System of the Heart

1. Sinoatrial Node: the pacemaker of the heart (because it’s the fastest), which sends impulses at around 60 to 100 BPM, the normal adult heart rate.
   • Sends impulses to the two atria (via the internodal tracts) initiating their contractions (P Wave).
   • The impulse also reaches the AV Node, where the impulse is delayed to wait for the atria to finish contracting.
2. Atrioventricular Node: secondary pacemaker if the SA Node fails, sending impulses at around 40 to 60 BPM.
3. Bundle of His
4. Right and Left Bundle Branches
5. Purkinje Fibers: ends in ventricular depolarization (QRS Complex)

NOTE

Disturbances in the conduction system of the heart is called “Heart Block”.

Mechanical Properties of the Heart

1. Cardiac Output: the product of an individual’s heart rate and stroke volume ($\text{HR}\times \text{SV}$).
   • Increased by stimulation of the autonomous nervous system and increased release of endogenous catecholamines (epinephrine, norepinephrine, dopamine).
   • Decreased by the parasympathetic nervous system (vagus nerve), Beta-Adrenergic Blockers (-olols), Calcium Channel Blockers (-dipines), Digitalis (Digoxin).
2. Stroke Volume: amount of blood pumped in one beat of the heart.
   • Preload: the amount of blood distending the ventricles just before contraction.
   • Afterload: the resistance the ventricles must overcome to eject blood.
   • Contractility

Vascular System

Hmm 🤔