physiology cardiovascular physiology 3

Cardiac Cycle

• Overview: The cardiac cycle is the sequence of events that occur during one complete heartbeat, involving the contraction and relaxation of the heart chambers to pump blood effectively.

• Phases of Cardiac Cycle: - Atrial Systole: Atria contract, pushing blood into ventricles. - Ventricular Systole: Ventricles contract, increasing pressure to eject blood into the pulmonary artery and aorta. - Ventricular Diastole: Ventricles relax, pressure drops, and the cycle begins again.

• Ventricular Pressure and Volume Changes: - Diastole: Ventricles fill with blood; volume increases, pressure low. - Systole: Ventricular pressure rises, volume decreases as blood is ejected.

• Heart Sounds: - First Heart Sound (S1): Occurs with the closing of the atrioventricular (AV) valves (mitral and tricuspid). - Second Heart Sound (S2):Occurs with the closing of the semilunar valves (aortic and pulmonary).

• Valve Function: - Valves ensure one-way blood flow. - AV Valves: (Mitral and tricuspid) open during diastole, close during systole. - Semilunar Valves: (Aortic and pulmonary) open during ventricular systole, close during diastole.

Blood Flow

• Overview: Blood flow is the circulation of blood throughout the body, delivering oxygen and nutrients while removing waste. It involves pulmonary and systemic circulation, ensuring efficient gas exchange in the lungs and tissues.

• Path of Blood Flow Through the Heart: - Blood enters the heart through the superior and inferior vena cava into the right atrium. - Blood passes through the tricuspid valve into the right ventricle. - From the right ventricle, blood goes through the pulmonary valve and into the pulmonary arteries. - Blood travels to the lungs for oxygenation. - Oxygenated blood returns to the heart via the pulmonary veins, entering the left atrium. - Blood passes through the bicuspid valve into the left ventricle. - The left ventricle pumps blood through the aortic valve into the aorta for systemic circulation.

• Pulmonary Circulation: - Deoxygenated blood flows from the right ventricle through the pulmonary arteries to the lungs. - In the pulmonary capillaries, blood releases carbon dioxide and picks up oxygen. - Oxygenated blood returns to the left atrium via the pulmonary veins.

• Systemic Circulation: - Oxygenated blood flows from the left ventricle through the aorta and systemic arteries to the body's tissues. - In systemic capillaries, blood delivers oxygen and nutrients while picking up carbon dioxide and waste. - Deoxygenated blood returns to the right atrium via the superior and inferior vena cava.

• Gas Exchange in Capillaries: - In pulmonary capillaries: blood releases CO2 and gains O2 - In systemic capillaries: blood loses O2 and gains CO2.

Cardiac Control System

• Overview: The cardiac control system regulates heart function through the autonomic nervous system, primarily involving the medulla oblongata, which integrates signals from baroreceptors and influences the heart rate and contractility via the vagus and cardiac accelerator nerves, affecting the SA and AV nodes and the ventricular myocardium.

• Medulla Oblongata:

  • Acts as the cardiovascular control center in the brainstem.

  • Receives and integrates sensory information.

  • Controls heart rate and contractility through the autonomic nervous system.

• Baroreceptors:

• Sensory receptors that detect changes in blood pressure.

• Located in the carotid sinus and the aortic arch.

• Send signals to the medulla oblongata to regulate heart function.

• Nerves:

  • Vagus Nerve (Parasympathetic):

    • Slows heart rate.

    • Innervates the SA and AV nodes.

  • Cardiac Accelerator Nerves (Sympathetic):

    • Increase heart rate and contractility.

    • Innervate the SA node, AV node, and ventricular myocardium.

• SA Node (Sinoatrial Node):

  • The heart's primary pacemaker.

  • Generates electrical impulses that initiate the cardiac cycle.

  • Heart rate is increased by sympathetic stimulation and decreased by parasympathetic stimulation.

• AV Node (Atrioventricular Node):

  • Relays electrical impulses from the atria to the ventricles.

  • Can slow the conduction of impulses.

  • Influenced by both sympathetic and parasympathetic nervous systems.

• Ventricular Myocardium:

  • The heart muscle of the ventricles.

  • Contracts to pump blood out of the heart.

  • Sympathetic stimulation increases contractility.

Autonomic Nervous System (ANS)

• Overview: The Autonomic Nervous System (ANS) regulates involuntary bodily functions through the sympathetic and parasympathetic nervous systems. It exerts significant control over cardiovascular function, influencing heart rate and stroke volume, and ultimately cardiac output.

• Autonomic Innervation of the Heart:

  • The cardiovascular control center is in the medulla oblongata (brainstem).

  • Increased sympathetic activity increases heart rate (chronotropic effect) and contractility (ionotropic effect).

  • Increased parasympathetic activity decreases heart rate.

  • Parasympathetic innervation has a negligible effect on the contractility of the heart muscle.

• Cardiovascular Control Center:

  • Located in the Medulla Oblongata.

  • Receives sensory input from baroreceptors in the carotid sinus and aortic arch.

  • Integrates information and initiates appropriate responses via sympathetic and parasympathetic pathways.

• Sympathetic Activity:

  • Increases heart rate (chronotropic effect).

  • Increases contractility (ionotropic effect), leading to a higher stroke volume for any given end-diastolic volume (EDV).

  • Increases cardiac output.

• Parasympathetic Activity:

  • Primarily influences heart rate, decreasing it.

  • Has minimal direct effect on myocardial contractility.

• Effects of ANS on Heart Rate:

  • Sympathetic activity increases heart rate.

  • Parasympathetic activity decreases heart rate.

• Effects of ANS on Stroke Volume:

  • Primarily affected by sympathetic activity, which increases contractility.

  • Increased contractility leads to higher stroke volume for a given EDV.