Heart notes

Chapter 15.1-15.2 Notes: The Heart

Size and Location of the Heart

  • Size of the Heart: The heart is approximately the size of a fist and weighs between 250 to 350 grams in adults.

  • Location of the Heart:

    • The apex of the heart is located on the inferior surface.

    • The base of the heart is located on the superior surface.

Coverings of the Heart

  • Layers of the Heart from the Outside In: The layers are named as follows:

    1. Fibrous Pericardium: The outermost layer that protects and anchors the heart.

    2. Serous Pericardium: Divided into two layers—parietal and visceral; the parietal layer lines the fibrous pericardium, and the visceral layer (epicardium) adheres to the heart.

  • Function of Pericardial Fluid: Reduces friction of the heart moving in the pericardial sac during the cardiac cycle.

  • Layer Containing Cardiac Muscle: The middle layer is called the ** myocardium**, which is composed of cardiac muscle tissue.

  • Layer Covering the Chambers of the Heart: The inner layer is referred to as the endocardium, which lines the chambers and valves of the heart.

Structure of the Heart: Valves, Chambers, Blood Vessels

  • Separation of the Heart's Sides: The septum separates the right and left sides of the heart.

  • Ventricle with Larger Myocardium: The left ventricle has a thicker myocardium compared to the right ventricle due to its role in pumping blood to the entire body.

  • Valves with Heart Strings (Chordae Tendineae): The AV (atrioventricular) valves are attached to the chordae tendineae, which help prevent backflow of blood into the atria during ventricular contraction.

Blood Flow through the Heart

  • Path of Blood Flow:

    • Oxygenated Blood: The left side of the heart contains oxygenated blood.

    • Deoxygenated Blood: The right side of the heart contains deoxygenated blood.

  • Systemic Circuit: Blood flow from the heart to the body.

  • Pulmonary Circuit: Blood flow from the heart to the lungs for oxygenation.

Coronary Circulation

  • Importance of Coronary Circulation: The heart requires coronary circulation to supply the myocardium with oxygen and nutrients.

  • Pathways of Coronary Circulation:

    • Coronary arteries branch off from the aorta to supply blood to the heart muscle.

    • Coronary veins return deoxygenated blood from the heart muscle to the right atrium through the coronary sinus.

Cardiac Events

  • Differentiation of Conditions:

    • Angina: Chest pain due to temporary decreased blood flow to the heart muscle.

    • Ischemia: A condition characterized by insufficient blood supply to the tissues, affecting heart function.

    • Myocardial Infarction: Commonly known as a heart attack, occurring when blood flow to a part of the heart is blocked long enough that part of the heart muscle is damaged or dies.

  • Causes/Risk Factors of Heart Attacks: Common risk factors include high blood pressure, high cholesterol, smoking, obesity, sedentary lifestyle, and diabetes.

External Features of the Heart

  • Auricles: These are small, ear-shaped structures located on the anterior part of the atria used to increase atrial volume and capacity.

Cardiac Cycle and Heart Sounds

  • Cardiac Cycle: The sequence of events in one complete heartbeat.

    • Difference between Systole and Diastole:

    • Systole: The phase of contraction of the heart muscle.

    • Diastole: The phase of relaxation of the heart muscle.

    • Order of Events: Blood flows through the heart during diastole (relaxation) as the chambers fill with blood, and is pumped out during systole (contraction).

  • Heart Sounds: The characteristic sounds of a heartbeat, "LUB-DUP", created by the closure of heart valves.

    • The first sound (LUB) is produced by the closure of the AV valves at the beginning of systole, while the second sound (DUP) is produced by the closure of the semilunar valves at the end of systole.

Anatomical and Physiological Effects of Birth Defects

  • Foramen Ovale Defect: A condition where the foramen ovale, a small opening in the atrial septum, fails to close after birth leading to potential mixing of oxygenated and deoxygenated blood.

  • Transposition of the Great Arteries: A congenital heart defect where the aorta and pulmonary arteries are switched, leading to two separate blood circuits.

Fetal Blood Circulation

  • Fetal Blood Supply: A fetus does not need to breathe while growing inside the mother because it receives oxygen and nutrients from the maternal blood through the placenta.

  • Structures Involved in Fetal Circulation:

    • Ductus arteriosus: A blood vessel connecting the pulmonary artery to the aorta, shunting blood away from the lungs.

    • Ductus venosus: A blood vessel that allows oxygenated blood from the placenta to bypass the liver to the fetus.

    • Foramen ovale: Allows blood to flow directly from the right atrium to the left atrium.

Skeletal vs Cardiac Muscle

  • Differences and Similarities:

    • Similarities: Both are striated muscle types and are involved in involuntary and voluntary movements (although skeletal is primarily voluntary).

    • Differences: Cardiac muscle is branched, contains intercalated discs, and operates involuntarily, while skeletal muscle is non-branched, striated, and can be controlled voluntarily.

  • Functional Enhancements of Cardiac Muscle: The presence of intercalated discs allows for rapid transmission of electrical impulses and coordinated contraction, crucial for effective pumping of the heart.

Cardiac Conduction System

  • Order of Conduction Pathway:

    1. SA Node (Sinoatrial Node): The heart's natural pacemaker located in the right atrium.

    2. AV Node (Atrioventricular Node): Located at the junction of the atria and ventricles; it delays the impulse allowing for atrial contraction before ventricular contraction.

    3. AV Bundle (Bundle of His): Conducts impulses from the AV node to the bundle branches.

    4. Bundle Branches: Left and right branches that spread the impulse to the ventricles.

    5. Purkinje Fibers: End of the conduction pathway that spreads impulses throughout the ventricles, causing them to contract.

Electrocardiogram (EKG)

  • Events Recorded During EKG: The EKG displays electrical activity relating to:

    • P Wave: Represents atrial depolarization (atrial contraction).

    • QRS Complex: Represents ventricular depolarization (ventricular contraction) and is the largest part of the EKG spike.

    • T Wave: Represents ventricular repolarization (ventricular relaxation).

  • Drawing and Labeling an EKG: Be prepared to illustrate and label the EKG wave components.

  • Calculating Heart Rate: Heart rate can be calculated from the EKG by counting the number of R waves in a specific time interval, usually one minute, or using the formula:
    extHeartRate=rac60extR−RInterval(inseconds)ext{Heart Rate} = rac{60}{ ext{R-R Interval (in seconds)}}

Defects of the Cardiac Conduction System

  • Arrhythmias: Defined as irregular heartbeats; two types include:

    • Tachycardia: Fast heart rate over 100 beats per minute.

    • Bradycardia: Slow heart rate under 60 beats per minute.

  • Cardiac Arrest: A sudden stop of heart function, commonly caused by arrhythmias.

    • Treatment: Use of a Defibrillator (AED) to restore normal heart rhythm.

Regulation of Heart Rate

  • Need for Regulation: To ensure that the heart adapts to the body's changing metabolic demands and maintains blood pressure.

  • Sympathetic vs. Parasympathetic:

    • Sympathetic Division: Increases heart rate via norepinephrine release.

    • Parasympathetic Division: Decreases heart rate via acetylcholine release.

  • Factors Affecting Heart Rate: Various factors include:

    1. Hormones (e.g., adrenaline).

    2. Electrolyte levels.

    3. Temperature fluctuations.

Vocabulary

  • Angina: Chest pain due to decreased blood flow.

  • Aorta: The largest artery in the body.

  • Aortic Valve: Regulates blood flow from the left ventricle to the aorta.

  • Arrhythmias: Irregular heart rhythms.

  • Atria/Auricles: Upper chambers of the heart; auricles are small pouches on top of the atria.

  • Atrioventricular (AV) Bundle: Connects the atria and ventricles.

  • AV Node: Atrioventricular node that delays impulses.

  • Bradycardia: Slower than normal heart rate.

  • Chordae Tendineae: Fibrous cords that anchor the AV valves to the papillary muscles.

  • Coronary Veins: Vessels that drain blood from the heart muscle back to the right atrium.

  • Coronary Arteries: Supply oxygenated blood to the heart muscle.

  • Defibrillator: Device that delivers electrical shocks to restore heart rhythm.

  • Diastole: Phase of relaxation of the heart.

  • Ductus Arteriosus: Fetal blood vessel connecting the aorta and pulmonary artery.

  • Ductus Venosus: Fetal blood vessel that shunts blood away from the liver.

  • Electrocardiogram (EKG): A test that records the electrical signals in the heart.

  • Fibrillations: Rapid, irregular heartbeats.

  • Foramen Ovale: An opening in the fetal heart that allows blood to bypass the lungs.

  • Ischemia: Insufficient blood flow to a part of the body.

  • Inferior Vena Cava: Carries deoxygenated blood from the lower body to the heart.

  • Lub-Dup: Sounds of heartbeats associated with valve closure.

  • Mitral Valve: Regulates blood flow from the left atrium to the left ventricle.

  • Myocardial Infarction: Heart attack due to obstruction of blood flow.

  • Myocardium: The muscular layer of the heart.

  • P Wave: Represents atrial depolarization.

  • QRS Complex: Large spike representing ventricular depolarization.

  • T Wave: Represents ventricular repolarization.

  • Tachycardia: Fast heart rate.

  • Tricuspid Valve: Regulates blood flow from the right atrium to the right ventricle.

  • Ventricles: Lower chambers of the heart.