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The Circulatory System: The Heart

Course: Anatomy & Physiology II, Chapter 19

Overview of the Circulatory System

Cardiology: The scientific study, diagnosis, and treatment of heart disorders encompasses various conditions affecting the heart, including congenital defects, heart failure, and coronary artery disease.

Major Divisions:

• Pulmonary Circuit: Involves the right side of the heart, responsible for carrying deoxygenated blood to the lungs via the pulmonary arteries, where carbon dioxide is exchanged for oxygen through gas exchange in the alveoli.

• Systemic Circuit: Involves the left side of the heart, delivering oxygenated blood to tissues throughout the body via the aorta and receiving deoxygenated blood to return to the heart.

Anatomy of the Heart

• Apex: The pointed lower end of the heart, located near the 5th rib, plays a crucial role in the direction of blood flow.

• Arteries (red): Carry oxygen-rich blood away from the heart to the body's tissues and organs.

• Veins (blue): Transport oxygen-poor blood back to the heart. Most arteries generally carry oxygenated blood, while most veins carry deoxygenated blood.

• The right side of the heart is responsible for carrying deoxygenated blood, while the left side handles oxygenated blood.

Blood Circulation Paths

• Left Heart (Systemic): Oxygenated blood from the lungs travels through the pulmonary veins into the left atrium, then moves into the left ventricle, where it is pumped through the aorta to supply body organs.

• Right Heart (Pulmonary): Deoxygenated blood from the body enters the right atrium through the superior and inferior vena cavae, moves to the right ventricle, and is pumped via the pulmonary trunk to the lungs for gas exchange.

• Blood circulation occurs seamlessly, with gas exchange in capillary beds, facilitating oxygen delivery and carbon dioxide removal between different systems.

Heart Function as a Double Pump

• Right Side: Responsible for pumping oxygen-poor and carbon dioxide-rich blood to the lungs for reoxygenation (Pulmonary Circuit).

• Left Side: Pumps oxygen-rich blood to body tissues (Systemic Circuit) to support cellular functions and metabolism.

Position, Size, and Shape of the Heart

• The heart is located within the mediastinum, the central compartment of the thoracic cavity, between the lungs, and tilts slightly to the left.

• The base is the superior, wide portion where major vessels attach, while the apex is the inferior point and weighs approximately 10 ounces.

Heart Wall Structure

• Epicardium: The outer layer, also known as the visceral pericardium, is a serous membrane coating the heart.

• Myocardium: Composed of cardiac muscle, the myocardium is responsible for heart contractions, enabling effective pumping of blood.

• Endocardium: A smooth inner lining of the heart and heart valves that reduces friction as blood flows through. It contains specialized Purkinje fibers that facilitate conduction.

Serous Pericardium

• This double-layered membrane covers the heart and lines the fibrous pericardium to provide protection and ensure smooth heart movements.

Pericardium Anatomy

• Consists of a double-walled sac providing a space that allows the heart to beat freely within the thoracic cavity.

  • Parietal Pericardium: The outer wall contains two layers: a tough fibrous layer and a smooth serous layer.

  • Visceral Pericardium: Also known as the epicardium, covers the heart's surface.

  • Pericardial Cavity: The space between the two layers is filled with serous fluid that prevents friction during heartbeats. Pericarditis is the inflammation of this cavity, causing chest pain.

Blood Vessel Types

Three Types of Blood Vessels:

• Arteries: Carry oxygen-rich blood away from the heart to the body's tissues and organs.

• Capillaries: Tiny blood vessels where the exchange of gases, nutrients, and waste occurs between blood and tissues.

• Veins: Transport oxygen-poor blood back to the heart.

  • Arterioles: Smaller branches of arteries that lead to capillaries.

  • Venules: Small veins that drain blood from capillaries and merge into larger veins.

Four Heart Chambers

• Right Atrium: Receives deoxygenated blood returning from the body via the superior and inferior vena cavae.

• Left Atrium: Receives oxygen-rich blood coming from the lungs through the pulmonary veins.

• Right Ventricle: Responsible for pumping blood to the lungs for gas exchange.

• Left Ventricle: Responsible for pumping oxygenated blood to the rest of the body, requiring strong muscular contraction.

Heart Valves

• Atrioventricular Valves: Include the tricuspid valve (between right atrium and ventricle) and mitral (bicuspid) valve (between left atrium and ventricle), crucial for preventing backflow during contraction.

• Semilunar Valves: Pulmonary and aortic valves that control blood flow from the ventricles into the major arteries, preventing backflow when the heart relaxes.

Properties of the Heart

• Myocytes: The cardiac muscle cells responsible for the mechanical function of the heart.

• Myogenic Nature: The heart can contract without external nerve stimulation, driven by its own pacemaker cells.

• Autorhythmic Cells: Specialized heart cells initiate action potentials, creating the heart's intrinsic rhythm.

Cardiac Conduction System

• Electrical Impulses: Stimulate heart contractions beginning from the Sinoatrial (SA) Node, the natural pacemaker that sets the heart rhythm.

• Atrioventricular (AV) Node: Acts as a gatekeeper for electrical impulses before they reach the ventricles, ensuring proper pacing and coordination.

This comprehensive revision adds further clarity about the heart's anatomy and physiology, including deeper explanations and terminology relevant to anatomy and functions of the circulatory system.

Systole and diastole refer to the two phases of the cardiac cycle in the heart's functioning:

• Systole: This is the phase when the heart muscles contract, pumping blood out of the chambers. In this phase, both the atria contract to fill the ventricles with blood, and then the ventricles contract to push blood into the pulmonary artery and aorta.

• Diastole: This is the relaxation phase of the heart, during which the heart chambers fill with blood. After systole, the heart muscles relax, allowing the atria to fill with blood from the veins, and subsequently the ventricles fill with blood from the atria.

The proper functioning of systole and diastole is crucial for maintaining blood circulation and ensuring that oxygenated blood reaches the body while deoxygenated blood is sent to the lungs for oxygenation.

Anastomoses and Their Role in Heart Protection

Definition

• Anastomoses: Connections or interconnections between blood vessels.

Importance in the Heart

• Provide alternative pathways for blood flow within coronary arteries.

• Protect the heart from damage due to blockage in any single coronary artery.

Mechanism of Protection

1. Redirection of Blood Flow

   • When an artery becomes narrowed or blocked (e.g., during a heart attack), blood can be redirected through collateral circulation.

2. Maintaining Blood Supply

   • Areas of the heart that may be deprived of adequate blood supply can still receive oxygen and nutrients through alternate routes.

Benefits

• Ensures continued perfusion of the heart muscle.

• Reduces the risk of ischemia (insufficient blood flow) and myocardial infarction (heart attack).

• Critical role in maintaining cardiac function and overall heart health, particularly in individuals with risk factors for coronary artery disease.

Myogenic: Definition and Significance

Definition

• Myogenic: Refers to the property of heart muscle tissue (myocardium) that allows it to contract and generate action potentials without requiring external nerve stimulation.

Reason the Heart is Described as Myogenic

1. Intrinsic Regulation

   • The heart possesses specialized cells known as pacemaker cells that can initiate electrical impulses independently.

   • These impulses lead to contractions of the heart muscle without external signals.

2. Sinoatrial (SA) Node

   • The SA Node acts as the natural pacemaker of the heart, setting the rhythm for heartbeats.

3. Independent Function

   • The heart can maintain a consistent heartbeat even when disconnected from the nervous system, showcasing its myogenic nature.

4. Importance for Circulation

   • Myogenic functionality is essential for the continuous circulation of blood throughout the body.

Nodes Responsible for Contraction of Heart Chambers

Atrial Contraction

• Node Responsible: Sinoatrial (SA) Node

  • Function: Initiates electrical impulses that cause the atria to contract, facilitating the filling of the ventricles with blood.

Ventricular Contraction

• Node Responsible: Atrioventricular (AV) Node

  • Function: Acts as a gatekeeper for electrical impulses before they reach the ventricles, ensuring proper timing and coordination for ventricular contraction.

Causes of Heart Sounds "Lubb Dupp"

First Heart Sound (Lubb)

• Caused by: Closure of the atrioventricular (AV) valves

  • Valves Involved: Tricuspid valve (between right atrium and ventricle) and mitral (bicuspid) valve (between left atrium and ventricle).

  • Timing: Occurs at the beginning of systole, when the ventricles contract to pump blood out of the heart.

Second Heart Sound (Dupp)

• Caused by: Closure of the semilunar valves

  • Valves Involved: Pulmonary valve (between right ventricle and pulmonary artery) and aortic valve (between left ventricle and aorta).

  • Timing: Occurs at the beginning of diastole, when the ventricles relax and fill with blood.

Overall Significance

• The "lubb dupp" sounds are crucial indicators of heart health and function, reflecting the proper closing of heart valves during the cardiac cycle.

The Circulatory System: The Heart

Course: Anatomy & Physiology II, Chapter 19

EKG and Heart Electrical Activity

• EKG (Electrocardiogram): Measures the electrical activity of the heart.

  • P Wave: Represents atrial depolarization.

  • QRS Complex: Represents ventricular depolarization.

  • T Wave: Represents ventricular repolarization.

Thicker Myocardium

• The left ventricle has a thicker myocardium compared to the right ventricle. This is because the left ventricle is responsible for pumping oxygenated blood to the rest of the body, requiring greater force and pressure than the right ventricle, which only pumps blood to the lungs.

Stroke Volume (SV), End Systolic Volume (ESV), and End Diastolic Volume (EDV)

• Stroke Volume (SV): The amount of blood pumped by the left ventricle in one contraction.

  • Calculation: SV = EDV - ESV.

• End Systolic Volume (ESV): The volume of blood in the ventricle at the end of contraction.

• End Diastolic Volume (EDV): The volume of blood in the ventricle at the end of filling.

• Cardiac Output (CO): The amount of blood the heart pumps in one minute.

  • Calculation: CO = SV x Heart Rate (HR).

Bradycardia vs. Tachycardia

• Bradycardia: A slow heart rate, typically below 60 beats per minute.

• Tachycardia: A fast heart rate, typically above 100 beats per minute.

Edema Types

• Pulmonary Edema: Accumulation of fluid in the lungs, causing shortness of breath and oxygen exchange issues.

• Peripheral Edema: Swelling due to excess fluid in the body's tissues, generally seen in extremities like legs and feet.

Cardiac Conduction System

• Sinoatrial (SA) Node: Located in the right atrium, it is the natural pacemaker of the heart that initiates electrical impulses leading to atrial contraction.

• Atrioventricular (AV) Node: Located between the atria and ventricles; it regulates impulses to the ventricles.

• Bundle of His: A pathway that conducts impulses from the AV node to the ventricles.

• Purkinje Fibers: Located throughout the ventricles; they spread the electrical signal rapidly, causing ventricular contraction.

Atrioventricular Valves

• Purpose: The atrioventricular (AV) valves include the tricuspid valve (between the right atrium and ventricle) and the mitral (bicuspid) valve (between the left atrium and ventricle). Their primary purpose is to prevent backflow of blood into the atria during ventricular contraction, ensuring that blood flows in one direction from the atria to the ventricles.

Coronary Arteries

• Function: The coronary arteries supply blood to the heart muscle (myocardium) itself, providing the necessary oxygen and nutrients for cardiac function.

• Blocked Coronary Arteries: If the coronary arteries become blocked, it can lead to reduced blood flow to the heart. This can cause symptoms such as chest pain (angina) and can result in heart muscle damage, leading to conditions such as myocardial infarction (heart attack).

Angina Pectoris vs. Myocardial Infarction

• Angina Pectoris: This is a type of chest pain caused by reduced blood flow to the heart muscle, often triggered by physical exertion or stress. Symptoms can include discomfort in the chest, shortness of breath, and fatigue. Angina is usually temporary and can be relieved by rest or medication.

• Myocardial Infarction: Also known as a heart attack, it occurs when blood flow to a part of the heart is blocked for an extended period, leading to permanent damage to the heart muscle. Symptoms typically include severe chest pain, often described as pressure, squeezing, or fullness, and may also include pain radiating to the arms, jaw, or back, as well as shortness of breath, sweating, nausea, and lightheadedness.