Lecture 7: Body Circulation - The Heart

Lecture 7: Body Circulation - The Heart

• The cardiovascular system delivers oxygen and nutrients, removes carbon dioxide and waste, transports hormones and other molecules, maintains temperature and fluid balance, and supports immune function.

Lecture Outline

• Mean arterial pressure (MAP) can be approximated using both systolic and diastolic pressure.
• MAP regulation occurs through short-term and long-term mechanisms.
• The baroreceptor reflex is a regulatory mechanism.
• Excitation-contraction (EC) of the heart is described.
• Action potentials of the SA node are explained.
• Action potentials of cardiac muscle cells (myocardial cells) are described.
• The cardiac cycle's electrical and mechanical events are discussed.
• The Wiggers diagram's importance is noted.

Pre-class Assignment

• Micromodule Six: Why does the human heart need a pacemaker?
• Defines a pacemaker for the human heart and describes the intrinsic conduction system.

Concept Recall (Lecture 6)

• MAP (mean arterial pressure) is the driving force for blood flow in the systemic circuit.
• MAP = CO x TPR (cardiac output x total peripheral resistance)
• MAP = HR x SV x TPR (heart rate x stroke volume x total peripheral resistance)

MAP and Hypotension

• Factors causing a fall in MAP (hypotension) are illustrated in a diagram.
• Diagram shows sympathetic/parasympathetic activity, veins, venomotor tone, compliance, venous pressure, venous return, atrial pressure, end-diastolic pressure, and total peripheral resistance.

The Heart

• The heart is shaped like an inverted cone.
• The base of the heart is larger and flat.
• The apex of the heart is inferior, tapering to a blunt, rounded point.

Four Chambers

• The heart has four chambers: two atria and two ventricles.
• The direction of arrows in a diagram represents the route of blood flow.
• The diagram displays the four chambers and associated valves, arteries, and veins.

Atria

• Atria are the receiving chambers of the heart, through which blood flows from veins to ventricles.
• Atrial contraction contributes to ventricular filling, but it's not substantial.
• Atrial walls are thin and small.

Ventricles

• Ventricles are the pumping/discharging chambers of the heart.
• Contractions generate pressures that drive blood flow through the pulmonary and systemic vascular systems and return to the heart.
• Ventricles occupy most of the heart's volume.
• The right ventricle pumps blood into the pulmonary trunk.
• The left ventricle pumps blood into the aorta.
• The left ventricle has a thicker muscle wall than the right ventricle.

Cardiac Valves

• Cardiac valves ensure one-way blood flow through the heart.
• They open and close in response to pressure gradients.
• Atrioventricular (AV) valves prevent backflow into the atria when ventricles contract. Tricuspid (right AV) and mitral (left AV) valves are included in the AV valves.
• Semilunar (SL) valves prevent backflow into ventricles when ventricles relax. Aortic and pulmonary valves are included in the SL valves.

Excitation-Contraction (EC) Coupling

• EC coupling is the mechanism by which cardiac action potentials stimulate cardiac contraction.
• Two types of cardiac action potentials exist.
• Diagrams illustrate the excitation, excitation (step 2), and contraction (step 3) phases. The action potentials of the pacemaker cell (sinoatrial node) and cardiac muscle cells are displayed, showing the different phases clearly.
• Gap junctions are protein channels connecting the cytoplasm of adjacent cells. Action potentials spread from one cell to another through these junctions.

Path of Blood Flow

• Both sides of the heart pump simultaneously to maintain the same stroke volume (SV) and cardiac output (CO).
• A diagram illustrates blood flow through the heart and major vessels, showing capillaries, the superior vena cava, the inferior vena cava, the coronary sinus, right atrium, right AV valve, right ventricle, pulmonary valve, and pulmonary trunk, as well as pulmonary arteries and systemic capillaries.

Electrical Events of The Heart

• The heart depolarizes and contracts at a resting rate of 60-100 beats per minute.
• The autonomic nervous system (ANS), including sympathetic and parasympathetic input, modifies this rhythm.
• The SA node fires at an intrinsic rate of 100/min, with no extrinsic control on heart rate (HR).
• During rest, the parasympathetic system predominates, leading to a rate of 70-75 bpm.
• During stress, the sympathetic system takes over, increasing the HR.

The SA Node

• The sinoatrial (SA) node is the heart's intrinsic pacemaker.
• It spontaneously generates action potentials leading to cardiac cell depolarization.
• The intrinsic conduction system spreads depolarization throughout the heart.
• The SA node is situated in the right atrium, near the superior vena cava's entrance.
• Action potentials spread from the SA node through the atria and then into the ventricles.

Spread of Electrical Excitation

• A diagram shows electrical excitation through the heart's conduction system.
• The intrinsic conduction system involves nodal cells and conducting fibers.

Electrocardiogram (ECG)

• An ECG detects electrical excitation of the heart. Diagrams display atrial and ventricular excitation and relaxation, showing their correspondence with ECG components.
• ECG components are described with reference to waves (P, QRS, T).

Wave Components of an ECG

• P wave corresponds to atrial depolarization.
• QRS complex corresponds to ventricular depolarization.
• T wave corresponds to ventricular repolarization.

Action Potential of the SA Node

• The SA (sinoatrial) node generates action potentials in three distinct phases: pacemaker potential, depolarization, repolarization.
• Specific ions (Na+, Ca2+, K+) are involved in each phase.

Effects of Autonomic Nervous System

• Sympathetic and parasympathetic nervous system influences heart rate by modulating the frequency of action potentials generated by the SA node. Diagrams present how the activation of each system affects the SA nodal cell action potentials.

Action Potential of Cardiac Muscle Cell

• Cardiac muscle cell action potentials have five phases: depolarisation, small repolarisation, plateau, repolarisation, and resting membrane potential. Specific ions and their roles are detailed.

Mechanical Events of Cardiac Cycle (Systole)

• Mechanical events of cardiac cycle involving contraction occur during systole. Includes isovolumetric ventricular contraction and ventricular ejection.

Mechanical Events of Cardiac Cycle (Diastole)

• Mechanical events of cardiac cycle involving relaxation occur during diastole. Includes isovolumetric ventricular relaxation and ventricular filling.

Summary of Mechanical Events

• Contraction and relaxation of the heart influence blood pressure and volume within cardiac chambers and the aorta. A diagram illustrates these events.

Path of Blood Flow: Detailed Steps

• The detailed steps of blood flow are described.

Stroke Volume and Ejection Fraction

• Stroke volume (SV),end-diastolic volume, and end-systolic volume are defined in terms of the cardiac cycle phases.
• Ejection fraction (EF) is presented as the percent of end-diastolic volume pumped. A formula describes EF.

Mean Arterial Blood Pressure (MAP)

• MAP is the pressure that pushes blood to tissues. A formula describes MAP.
• Pulse pressure (PP) and MAP both decrease with increasing distance from the heart due to resistance.
• Systolic and diastolic pressures can be measured by a sphygmomanometer.

Learning Outcomes

• Learning objectives for the lecture, including definitions and descriptions of related physiology.

Explore the mechanisms of body circulation through the heart in this comprehensive quiz. Understand the cardiovascular system's functions, Mean arterial pressure, and the important role of the baroreceptor reflex. Additionally, examine the cardiac cycle and the significance of the Wiggers diagram.