Cardiovascular System and Pharmacology

• Cardiac conduction and the autonomic nervous system are key to circulation.
• The autonomic nervous system includes the effects of various emergency drugs.

Blood Flow Through the Heart:

• Deoxygenated blood enters from the body through the superior vena cava (upper body) and inferior vena cava (lower body).
• The SA node fires an impulse, causing the atria to contract.
• Blood flows into the ventricles through valves.
• Both ventricles contract, sending blood to the lungs (right ventricle via the pulmonary artery) and oxygenated blood to the body (left ventricle via the aorta).
• The top arch and the bottom half of the aorta provide blood to the body.

Cardiac Electrical Conduction

• The electrical wiring transfers voltage/energy through conduction.
• The Sinoatrial (SA) node is the "chunkiest" and fires the highest voltage electrical impulse, sending a branch to the left atrium.
• The impulse travels to the atrioventricular (AV) node, which has lesser voltage and does not branch to the left atrium.
• Impulses travel down the Bundle of His and Purkinje fibers, which stimulate ventricular wall contraction.
• Pacemaker cells are electrically powered and initiate impulses automatically (automaticity).
• Cells are excited by ion movement, causing more positive charges inside than outside (excitability).
• Pacemaker cells transmit electrical impulses to cardiac muscle cells (conduction).
• Healthy muscles only contract upon receiving a stimulus (contractility).

Action Potential

• Action happens in the heart via CARDIAC muscle or NEURONAL networks.
• NEURONAL involves nerves, electrical communication, ions, and voltages.
• At number 4 (REST) during an Action Potential: Positive potassium (K+) enters, and sodium (Na+) exits the cell.
• At number 0 (DEPOLARISATION): Potassium exits, and Calcium ++ enters, increasing positive charge inside the cell.
• At number 3 (REPOLARISATION): Calcium channels close as potassium continues to exit the cell.
• At number 4 (REST): Potassium re-enters the cell.
• Calcium++ triggers contraction by increasing voltage, while potassium contributes to rest and resting potential.
• Drugs such as amiodarone can block potassium leakage, increasing resting potential and calming arrhythmias.
• Increased voltage enables the depolarization of contraction cells.

Heart Rate and Failure

• The QRS complex on an EKG relates to the ventricular rate, used to calculate heart rate.
• If the SA node fails, the AV node takes over, but with less strength, resulting in a slower heart rate and less effective contractions.
• If both SA and AV nodes fail, the Bundle of His takes over, further lowering heart rate.
• When the Bundle of His fails, Purkinje fibers attempt to maintain rhythm, resulting in an even slower heart rate.
• Typical BPM (Beats Per Minute) for heart tissues: SA Node (60-100), AV Node (40-60), Bundle of His (40), Purkinje Fibers (15-20).

Autonomic Nervous System

• Sympathetic and vagal responses can increase heart rate.
• The autonomic nervous system (sympathetic/fight or flight and parasympathetic/rest and digest) acts on the SA node to affect depolarization and heart rate.
• It operates unconsciously on smooth muscles/glands.
• The response is either sympathetic or parasympathetic, dictated by neurotransmitters.

Neurotransmitters

• Pre-Ganglionic Neurotransmitter: Uses Acetylcholine (Ach) in both Sympathetic and Parasympathetic divisions.
• Pre-Ganglionic Receptor: Uses Nicotinic receptors in both Sympathetic and Parasympathetic divisions.
• Post-Ganglionic Neurotransmitter: Sympathetic uses Noradrenaline/Adrenaline; Parasympathetic uses Acetylcholine (Ach).
• Post-Ganglionic Receptor: Sympathetic uses Adrenoreceptors (Alpha/Beta); Parasympathetic uses Muscarinic receptors.

Sympathetic vs. Parasympathetic

• In a sympathetic response, the ganglion decides to release noradrenaline/adrenaline, which binds to adrenergic receptors.

• In a parasympathetic response, acetylcholine is released binding to muscarinic receptors.

• Key points to remember include the following:

• Sympathetic: Vasoconstriction

• Parasympathetic: Vasodilation

Adrenaline Dosage

• The effect of adrenaline/noradrenaline depends on whether it has an ALPHA or BETA effect.
• At lower doses (e.g., anaphylaxis treatment), adrenaline has a BETA effect, which increases HR/cardiac output and dilates the bronchus.
• At high doses (e.g., cardiac arrest), adrenaline has a mainly ALPHA effect.
• Alpha increases BP, whereas BETA can lower BP due to vasodilation; in anaphylaxis, bronchodilation is the primary goal.

Drug Classifications

• Agonist: A drug that mimics a neurotransmitter (e.g., succinylcholine acts like acetylcholine), creating a hyperactive response.
• Antagonist: A drug that obstructs the receptor site where the neurotransmitter should act, blocking its effect.
• CATHECHOLAMINE: A copy of adrenaline/noradrenaline, acting on adrenergic receptors.
• Inotrope: A drug that improves heart contractility.
• Although noradrenaline is an inotrope, it mainly effects ALPHA receptors.
• Chronotrope: A drug that increases heart rate (BETA).

Explore the cardiovascular system, including blood flow, heart function, and electrical impulses. Learn about the sinoatrial node, adrenaline effects, agonists, antagonists, and autonomic nervous system control. Understand heart rate regulation and neurotransmitter functions.