11+heart
Physiology of the Cardiovascular System
Overview
Understand the structure and function of the cardiovascular system, with focus on the heart and blood flow.
Anatomy of the Heart
Location and Orientation
Sits in the mediastinum of the thoracic cavity.
May vary in position with individual height, obesity, or pregnancy.
Chambers of the Heart
Four Chambers:
Right and left atrium (plural: atria)
Right and left ventricle
External Features
Superior point of maximal intensity (PMI): where the heartbeat is strongest.
Major arteries include the aorta and pulmonary trunk, connecting the heart to systemic and pulmonary circulation.
Blood Flow Through the Heart
Deoxygenated Blood Flow
Enters the right atrium via the superior and inferior vena cava, indicating low oxygen levels (less than 50%).
Oxygenated Blood Flow
After passing through the lungs, oxygenated blood returns to the left atrium via pulmonary veins:
Essential for systemic circulation from the left ventricle through the aorta.
Blood Pressure and Valve Function
Atrioventricular (AV) Valves:
Located between atria and ventricles, preventing backflow during contraction.
Right AV valve: Tricuspid; Left AV valve: Bicuspid (Mitral).
Papillary Muscles and Chordae Tendinae:
Prevent valve prolapse during ventricular contraction by maintaining tension on valve leaflets.
Cardiac Cycle Phases
Diastole (Filling Phase)
Atria fill with blood; ventricles relax, preparing for next contraction.
AV valves open, allowing blood flow into ventricles from atria, aided by gravity.
Systole (Contraction Phase)
Ventricular Systole:
Ventricles contract, pushing deoxygenated blood to the lungs and oxygenated blood to the body.
Semi-lunar valves open during this phase to allow blood ejection.
Heart Sounds
First Heart Sound (S1 - Lub):
Occurs when AV valves close at the onset of ventricular contraction.
Second Heart Sound (S2 - Dup):
Occurs when semi-lunar valves close at the onset of ventricular relaxation.
Myocardial Contraction and Action Potentials
Cardiac Muscle Characteristics
Cardiac muscle contains 99% contractile cells and 1% autorhythmic cells (pacemaker cells).
Mitochondria-rich cells enable aerobic metabolism to support sustained contractions.
Pacemaker Cells
Located in sinoatrial (SA) node; responsible for initiating action potentials autonomously.
AV node acts as a secondary pacemaker if SA node fails.
Action Potential Phases
Resting Membrane Potential:
Stable at -90 mV for contractile cells.
Depolarization:
Rapid influx of Na+ followed by Ca2+ entry during contraction.
Repolarization:
Ca2+ channels close, K+ channels open to reset the resting potential.
Clinical Considerations
Myocardial Infarction
Occurs due to inadequate blood flow (ischemia) leading to muscle death.
Plaque buildup in coronary arteries can lead to heart attacks.
Atherosclerosis
Characterized by plaque buildup in arteries, influenced by cholesterol levels.
HDL (High-Density Lipoprotein): "Healthy" cholesterol.
LDL (Low-Density Lipoprotein): "Lethal" cholesterol.
Electrocardiogram (ECG)
ECG Basics
Reflects electrical activity across the heart, interpretable through surface electrodes.
Waveforms:
P Wave: Atrial depolarization.
QRS complex: Ventricular depolarization.
T Wave: Ventricular repolarization.
Clinical Interpretation
Assess heart rate, rhythm, and the relationship between components (e.g., each P wave followed by QRS complex).
Influence of Autonomic Nervous System
Sympathetic stimulation increases heart rate.
Parasympathetic (via acetylcholine) decreases heart rate.
Summary of Blood Flow Dynamics
Blood flow is influenced by:
Hydrostatic pressure gradients.
Resistance due to vessel radius.
Poiseuille’s Law: Resistance increases with a decrease in radius, dramatically affecting blood flow.
Conclusion
The understanding of cardiovascular physiology is integral to recognizing heart function, potential pathological states, and overall health.