The Cardiovascular System

Key Components:
- Sinoatrial (SA) Node: Pacemaker of the heart located in the right atrium; initiates heartbeat
- Atrioventricular (AV) Node: Located at the junction of the atria and ventricles, delays impulses to allow atrial contraction
- Atrioventricular (AV) Bundle (Bundle of His): Transmits impulses from the AV node
- Bundle Branches: Right and left branches in the interventricular septum
- Purkinje Fibers: Spread within the ventricular myocardium
Function:
- The SA node generates electrical impulses that cause heart muscle depolarization and contraction from the atria to the ventricles in a coordinated manner.
- The intrinsic conduction system influences a standard heart rate of approximately 75 beats per minute.

Overall Functionality:
- The heart performs continuous contractions, pumping approximately 6 liters of blood through the vessels over 1,000 times per day, which accumulates to about 6,000 quarts (1,500 gallons) daily.
Unique Properties of Cardiac Muscle Cells:
- Cardiac muscle cells can contract independently and spontaneously without nerve impulses, unlike skeletal muscle.
- Specific rhythms in different areas:
- Atrial cells: ~60 beats/min
- Ventricular cells: ~20-40 beats/min

Definitions:
- Systole: Contraction phase of the heart
- Diastole: Relaxation phase of the heart
- Cardiac Cycle: A complete heartbeat comprising contraction and relaxation periods; lasts about 0.8 seconds at a normal heart rate of 75 beats/min.

Atrial Diastole:
- Heart is relaxed; blood flows passively into ventricles through open AV valves.
- Semilunar valves remain closed.
Atrial Systole:
- Atria contract; pressure increases, pushing blood into the ventricles.
- Ventricles remain in diastole.
Isovolumetric Contraction:
- Ventricles begin to contract (systole); AV and semilunar valves closed.
Ventricular Systole (Ejection Phase):
- Ventricles contract, pressure rises; semilunar valves open as blood is ejected into arteries.
Isovolumetric Relaxation:
- Ventricles relax; pressures drop, semilunar valves close. AV valves remain closed until ventricular pressure falls below atrial pressure.

Heart Sounds:
- Produces two distinct sounds:
- Lub: Closing of AV valves at the beginning of ventricular systole
- Dup: Closing of semilunar valves at the end of ventricular systole.

Overview:
- Records electrical activity of the heart, detecting impulse flow.
Normal Waves:
- P Wave: Atrial depolarization
- QRS Complex: Ventricular depolarization (also conceals atrial repolarization)
- T Wave: Ventricular repolarization
Clinical Implications:
- Abnormalities indicate potential heart issues (e.g., myocardial infarct).
- Fibrillation results in loss of coordinated heart function and severe risks.

Definition:
- Cardiac Output (CO): Amount of blood pumped by each side (ventricle) of the heart per minute.
- Formula: CO = HR imes SV
  where HR = heart rate (beats/min), SV = stroke volume (ml/beat).
Normal Values:
- At resting values:
  - HR = 75 beats/min
  - SV = 70 ml/beat
  - Calculated CO = 75 imes 70 = 5250 ext{ml/min} = 5.25L/min

Key Components:
- Sinoatrial (SA) Node: Pacemaker of the heart located in the right atrium; initiates heartbeat.
- Atrioventricular (AV) Node: Located at the junction of the atria and ventricles, delays impulses to allow atrial contraction.
- Atrioventricular (AV) Bundle (Bundle of His): Transmits impulses from the AV node.
- Bundle Branches: Right and left branches in the interventricular septum.
- Purkinje Fibers: Spread within the ventricular myocardium.
Pathway of Impulses:
1. The SA node generates electrical impulses that spread throughout the atria, causing them to contract.
2. The impulse reaches the AV node, where it is momentarily delayed to ensure that the atria have fully contracted before the ventricles begin to contract.
3. The AV node transmits the impulse down the AV bundle, which divides into the bundle branches and extends into the Purkinje fibers, causing the ventricles to contract in a coordinated manner.

Overview:
- Records electrical activity of the heart, detecting impulse flow.
Information Provided:
- P Wave: Atrial depolarization.
- QRS Complex: Ventricular depolarization (also conceals atrial repolarization).
- T Wave: Ventricular repolarization.
- Abnormalities can indicate potential heart issues (e.g., myocardial infarct) and conditions like fibrillation, which results in a loss of coordinated heart function.

Systole: Contraction phase of the heart.
Diastole: Relaxation phase of the heart.
Stroke Volume: The amount of blood pumped by each ventricle of the heart per heartbeat.
Cardiac Cycle: A complete heartbeat comprising contraction (systole) and relaxation (diastole) periods; lasts about 0.8 seconds at a normal heart rate of 75 beats/min.
Heart Sounds: Produces two distinct sounds:
- Lub: Closing of AV valves at the beginning of ventricular systole.
- Dup: Closing of semilunar valves at the end of ventricular systole.
Heart Murmur: An abnormal heart sound often indicative of turbulent blood flow due to faulty valves or congenital defects.

Vagus Nerve Stimulation: Slows heart rate by releasing acetylcholine, which reduces the heart's pacing.
Exercise: Increases heart rate due to sympathetic nervous system activation, allowing faster blood circulation to meet metabolic needs.
Epinephrine: A hormone that increases heart rate and contractility by stimulating beta receptors in the heart.
Ions:
- Calcium: Increased calcium levels can enhance heart muscle contraction and increase heart rate.
- Potassium: High levels can reduce heart rate and irritability; low levels can lead to arrhythmias.