Study Guide: The Cardiovascular System – The Heart (Chapter 18)

The Cardiovascular System: The Heart

Overview

The heart is a muscular organ responsible for pumping blood throughout the body via the circulatory system. It consists of four chambers, valves, and specialized tissues that coordinate its function. Understanding the heart's anatomy and physiology is essential for comprehending cardiovascular health and disease.

Heart Anatomy

Chambers of the Heart

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

• Right Ventricle: Pumps deoxygenated blood to the lungs through the pulmonary trunk.

• Left Atrium: Receives oxygenated blood from the lungs via the pulmonary veins.

• Left Ventricle: Pumps oxygenated blood to the body through the aorta.

Valves ensure unidirectional blood flow:

• Atrioventricular (AV) Valves:

  • Tricuspid Valve: Between right atrium and right ventricle.

  • Bicuspid (Mitral) Valve: Between left atrium and left ventricle.

• Semilunar Valves:

  • Pulmonary Valve: Between right ventricle and pulmonary trunk.

  • Aortic Valve: Between left ventricle and aorta.

Layers of the Heart Wall

• Epicardium: Outermost layer; also called the visceral pericardium.

• Myocardium: Middle layer; composed of cardiac muscle tissue responsible for contraction.

• Endocardium: Innermost layer; lines the heart chambers and valves.

Coronary Circulation

Definition and Importance

Coronary circulation refers to the heart's own blood supply system, essential for nourishing the heart muscle (myocardium). Blockage of coronary arteries can lead to myocardial infarction (heart attack).

Electrical Activity of the Heart

Pathway of Electrical Signal

1. Sinoatrial (SA) Node: Located in the right atrium; initiates the heartbeat (pacemaker).

2. Atrioventricular (AV) Node: Receives impulse from SA node; delays signal to allow atria to contract.

3. AV Bundle (Bundle of His): Conducts impulse from AV node to ventricles.

4. Right and Left Bundle Branches: Carry impulses through the interventricular septum.

5. Purkinje Fibers: Distribute impulse throughout ventricular myocardium, causing contraction.

Electrocardiogram (ECG) Phases

• P wave: Atrial depolarization initiated by SA node; lasts ~0.08 seconds.

• QRS complex: Ventricular depolarization; precedes ventricular contraction; lasts ~0.08 seconds.

• T wave: Ventricular repolarization; slower process; lasts ~0.16 seconds.

Heart Sounds

First and Second Heart Sounds (S1 and S2)

• S1 ("lub"): Caused by closure of AV valves at the beginning of ventricular systole.

• S2 ("dup"): Caused by closure of semilunar valves at the beginning of ventricular diastole.

Cardiac Muscle and Specialized Structures

Cardiac Muscle Features

• Cardiomyocytes: Specialized muscle cells responsible for heart contraction.

• Intercalated Discs: Specialized cell junctions that allow rapid electrical communication between cells.

Heart Rate and Cardiac Output

Definitions

• Bradycardia: Resting heart rate slower than 60 beats per minute.

• Tachycardia: Resting heart rate exceeding 100 beats per minute.

• Resting Heart Rate: For young adults, typically 72–80 beats/min; for young adult males, 64–72 beats/min. Heart rate generally declines with age.

• Cardiac Output: The volume of blood pumped by each ventricle per minute. Formula: $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$

Cardiac Centers and Regulation

Medulla Oblongata

• Cardiac centers in the medulla regulate heart rate and force of contraction.

• Baroreceptors: Detect changes in blood pressure; send signals to cardiac centers.

• Chemoreceptors: Detect changes in blood levels of CO2, O2, and pH; influence heart rate accordingly.

Heart Failure

Congestive Heart Failure

• Definition: The heart's inability to pump blood efficiently, leading to inadequate circulation.

• Symptoms: Fatigue, shortness of breath, fluid retention.

• Common Causes: Coronary atherosclerosis, persistent high blood pressure, multiple myocardial infarctions, dilated cardiomyopathy.

Vocabulary Table

Key Terms and Definitions

Vocab Term	Use in a Sentence	Synonym	Reminds me of
Myocardium	The myocardium is the muscle layer of the heart located between the endocardium and epicardium.	Heart muscle	"Reminds me of meat muscle"
Coronary circulation	The left and right coronary arteries supply oxygenated blood to the heart muscle.	Heart blood supply	"Reminds me of blocked artery in heart attack"
Cardiomyocytes	Cardiomyocytes are specialized cells found only in the heart; they are critical for heart function.	Heart muscle fibers	"Muscle highway"
Intercalated discs	Intercalated discs contain gap junctions, a type of electrical junction.	Cell junctions	"Power line"
Systole	A phase in the cardiac cycle, where the heart's ventricles contract to pump blood out of the heart.	Contraction	"Squeezing a sponge"
Diastole	The heart muscle relaxes, allowing chambers to fill with blood, otherwise known as diastole.	Relaxation	"Filling a water balloon"
Cardiac cycle	The cardiac cycle involves the mechanical events that occur during one heart beat.	Heartbeat steps	"Pumping a tire"
Tachycardia	An abnormally fast heartbeat is considered tachycardia.	Rapid heartbeat	"Anxiety"
Bradycardia	Bradycardia is a heart rate less than 60 beats/min.	Slow heartbeat	"Runner's heartbeat"
Cardiac output	Cardiac output is the volume of blood pumped by each ventricle, each minute.	Blood flow	"Pump fuel"

Additional info:

• Cardiac muscle cells are interconnected by intercalated discs, which allow for rapid transmission of electrical impulses, ensuring coordinated contraction.

• Baroreceptors and chemoreceptors play a crucial role in short-term regulation of heart rate and blood pressure.

• Heart failure can be classified as left-sided, right-sided, or congestive, depending on the affected chambers and symptoms.