A&P 2 Classwork 2 Cardiovascular System PDF

**[A&P 2 Classwork 2:] Cardiovascular System: The heart** --------------------------- **Location of the Heart** --------------------------- The human heart is located within the thoracic cavity, medially between the lungs in the space known as the mediastinum.  Within the mediastinum, the h...

**[A&P 2 Classwork 2:] Cardiovascular System: The heart** --------------------------- **Location of the Heart** --------------------------- The human heart is located within the thoracic cavity, medially between the lungs in the space known as the mediastinum.  Within the mediastinum, the heart is separated from the other mediastinal structures by a tough membrane known as the **pericardium**, or pericardial sac, and sits in its own space called the **pericardial cavity**. The dorsal surface of the heart lies near the bodies of the vertebrae, and its anterior surface sits deep to the sternum and costal cartilages. The great veins, the superior and inferior venae cavae, and the great arteries, the aorta and pulmonary trunk, are attached to the superior surface of the heart, called the **base**. The base of the heart is located at the level of the third costal cartilage. The inferior tip of the heart, the **apex**, lies just to the left of the sternum between the junction of the fourth and fifth ribs near their articulation with the costal cartilages. The right side of the heart is deflected anteriorly, and the left side is deflected posteriorly. It is important to remember the position and orientation of the heart when placing a stethoscope on the chest of a patient and listening for heart sounds, and also when looking at images taken from a midsagittal perspective. The slight deviation of the apex to the left is reflected in a depression in the medial surface of the inferior lobe of the left lung, called the **cardiac notch**. This diagram shows the location of the heart in the thorax. **Figure: Position of the Heart in the Thorax **The heart is located within the thoracic cavity, medially between the lungs in the mediastinum. It is about the size of a fist, is broad at the top, and tapers toward the base. **[EVERYDAY CONNECTION]: CPR**  **Figure:** **CPR Technique **If the heart should stop, CPR can maintain the flow of blood until the heart resumes beating. By applying pressure to the sternum, the blood within the heart will be squeezed out of the heart and into the circulation. Proper positioning of the hands on the sternum to perform CPR would be between the lines at T4 and T9. ---------------------------- **Structure of the Heart** ---------------------------- **Heart Wall Layers** **The pericardium:** the out layer, is made up of squamous epithelial cells verifying connective tissue **The myocardium:** the middle layer, forms most of the heart wall. It has striated muscle fibers that cause the heart to contract. **The endocardium:** the heart's inner layer, consists of endothelial tissue with small blood vessels and bundles of smooth muscle **Pericardium** The membrane that directly surrounds the heart and defines the pericardial cavity is called the **pericardium** or **pericardial sac**. It also surrounds the "roots" of the major vessels, or the areas of closest proximity to the heart. The pericardium, which literally translates as "around the heart," consists of two distinct sublayers: the sturdy outer fibrous pericardium and the inner serous pericardium. The fibrous pericardium is made of tough, dense connective tissue that protects the heart and maintains its position in the thorax. The more delicate serous pericardium consists of two layers: the parietal pericardium, which is fused to the fibrous pericardium, and an inner visceral pericardium, or **epicardium**, which is fused to the heart and is part of the heart wall. The pericardial cavity, filled with lubricating serous fluid, lies between the epicardium and the pericardium. **Figure below:** **Pericardial Membranes and Layers of the Heart Wall ** The pericardial membrane that surrounds the heart consists of three layers and the pericardial cavity. The heart wall also consists of three layers. The pericardial membrane and the heart wall share the epicardium.  **Heart Chambers** Within the heart lie four hollow chambers: two atria and two ventricles: The right and left **atria** serve as volume reservoirs for blood being sent into the ventricles. The **interatrial septum** divides the atrial chambers, helping them to contract and force blood into the ventricles below. The **Ventricles** serve as the pumping chambers of the heart The **interventricular septum** separates the ventricles and also helps them to pump  In this figure the top panel shows the image of the heart with the major parts labeled. The bottom left panel shows a photo of the heart with the surface layer peeled off. The images on the bottom right show detailed musculature inside the heart. The thickness of a chamber wall depends on the amount of high-pressure work the chamber does. a -- Because the atria only have to pump blood into the ventricles, their walls are relatively thin b -- The wall of the right ventricles are thicker because it pumps the blood against the resistance of the pulmonary circulation. c -- The walls of the left ventricles are the thickest of all because it pumps blood against the resistance of the systemic circulation. The top panel shows the human heart with the arteries and veins labeled. The bottom panel shows the human circulatory system. **Heart valves and their function** A transverse section through the heart slightly above the level of the atrioventricular septum reveals all four heart valves along the same plane. The valves ensure unidirectional blood flow through the heart. 1 -- The **right atrioventricular valve**, or **tricuspid valve is** between the right atrium and the right ventricle. It typically consists of three flaps, or leaflets, made of endocardium reinforced with additional connective tissue. The flaps are connected by chordae tendineae to the papillary muscles, which control the opening and closing of the valves.  2 -- The **pulmonary valve** or the [right semilunar valve] is the [pulmonary semilunar valve] that emerges from the right ventricle at the base of the pulmonary trunk. It is comprised of three small flaps of endothelium reinforced with connective tissue. When the ventricle relaxes, the pressure differential causes blood to flow back into the ventricle from the pulmonary trunk. This flow of blood fills the pocket-like flaps of the pulmonary valve, causing the valve to close and produce an **audible sound**. Unlike the atrioventricular valves, there are no papillary muscles or chordae tendineae associated with the pulmonary valve. 3 -- The **mitral valve,** also called the **bicuspid valve** or the **left atrioventricular valve** is located at the opening between the left atrium and left ventricle Structurally, this valve consists of two cusps, compared to the three cusps of the tricuspid valve. In a clinical setting, the valve is referred to as the mitral valve, rather than the bicuspid valve. The two cusps of the mitral valve are attached by chordae tendineae to two papillary muscles that project from the wall of the ventricle. 4 -- The **aortic valve** or the aortic semilunar valve is at the base of the aorta and prevents backflow from the aorta. It normally is composed of three flaps. When the ventricle relaxes and blood attempts to flow back into the ventricle from the aorta, blood will fill the cusps of the valve, causing it to close and produce an **audible sound**. #### Heart: Heart Defects This diagram shows the structure of the heart with different congenital defects. The top left panel shows patent foramen ovale, the top right panel shows coarctation of the aorta, the bottom left panel shows patent ductus ateriosus and the bottom right shows tetralogy of fallot. **Figure:** **Congenital Heart Defects ** a. A patent foramen ovale defect is an abnormal opening in the interatrial septum, or more commonly, a failure of the foramen ovale to close. b. Coarctation of the aorta is an abnormal narrowing of the aorta. c. A patent ductus arteriosus is the failure of the ductus arteriosus to close. d. Tetralogy of Fallot includes an abnormal opening in the interventricular septum. **Blood Flow Through the Heart** The valves open to allow forward flow of blood through the heart. They immediately snap closed to prevent backward flow**.** **Under pressure:** pressure changes within the heart affect the opening and closing of the valves. The amount of blood stretching the chamber and the degree of contraction of the chamber wall determine the pressure. For example: as blood fills a chamber, the pressure rises; then as the chamber wall contracts, the pressure rises further. This increase in pressure causes the valve to open and blood to flow out into an area of lower pressure, leading to an equal pressure state.  **Cardiac Muscles and Electrical Activity** ### Structure of Cardiac Muscle The top left panel of this figure shows the cross structure of cardiac muscle with the major parts labeled. The top right panel shows a micrograph of cardiac muscle. The bottom panel shows the structure of intercalated discs. **Figure: Cardiac Muscle ** \(a) Cardiac muscle cells have myofibrils composed of myofilaments arranged in sarcomeres, T tubules to transmit the impulse from the sarcolemma to the interior of the cell, numerous mitochondria for energy, and intercalated discs that are found at the junction of different cardiac muscle cells. \(b) A photomicrograph of cardiac muscle cells shows the nuclei and intercalated discs. \(c) An intercalated disc connects cardiac muscle cells and consists of desmosomes and gap junctions. ### Conduction System of the Heart  **Figure:** **Conduction System of the Heart **Specialized conducting components of the heart include the sinoatrial node, the internodal pathways, the atrioventricular node, the atrioventricular bundle, the right and left bundle branches, and the Purkinje fibers. This image shows the different stages in the conduction cycle of the heart. **Figure:** **Cardiac Conduction ** \(1) The sinoatrial (SA) node and the remainder of the conduction system are at rest. \(2) The SA node initiates the action potential, which sweeps across the atria. \(3) After reaching the atrioventricular node, there is a delay of approximately 100 ms that allows the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle. \(4) Following the delay, the impulse travels through the atrioventricular bundle and bundle branches to the Purkinje fibers, and also reaches the right papillary muscle via the moderator band. \(5) The impulse spreads to the contractile fibers of the ventricle. \(6) Ventricular contraction begins. **Pacemakers of the heart**  The SA node is the heart's primary pacemaker. Pacemaker cells in lower areas, such as the junctions tissue and the Purkinje fibers, initiate an impulse only when they don't receive one from above, such as when the SA node a damaged from a myocardial infarction. 1 -- The SA node has a firing rate of 60 to 100 beats/minutes. 2 -- The AV node has a firing rate of 40 to 60 beats/minutes. 3 -- The Purkinje fibers have a firing rate of 20 to 40 beats/minutes. **Generation and Transmission of electrical impulses depend on four characteristics of cardiac cells:** **Automaticity:** ability to spontaneously initiate an impulse (pacemaker cells have the ability). **Excitability:** a cell's response to an electrical stimulus (results from ion shifts across the cell membrane). **Conductivity:** ability of a cell to transmit an electrical impulse to another cardiac cell. **Contractility:** ability of a cell to contract after receiving a stimulus. #### Membrane Potentials and Ion Movement in Cardiac Conductive Cells This graph shows the change in membrane potential as a function of time. **Figure:**  **Action Potential at the SA Node **The prepotential is due to a slow influx of sodium ions until the threshold is reached followed by a rapid depolarization and repolarization. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarization and contraction of the cell. Note the lack of a resting potential. #### #### #### #### #### #### Membrane Potentials and Ion Movement in Cardiac Contractile Cells  **Figure:** **Action Potential in Cardiac Contractile Cells **(a) Note the long plateau phase due to the influx of calcium ions. The extended refractory period allows the cell to fully contract before another electrical event can occur. (b) The action potential for heart muscle is compared to that of skeletal muscle. ### Electrocardiogram **Figure:** **Standard Placement of ECG Leads ** 12-lead ECG, six electrodes are placed on the chest, and four electrodes are placed on the limbs.  **Figure:** **Electrocardiogram **A normal tracing shows the P wave, QRS complex, and T wave. Also indicated are the PR, QT, QRS, and ST intervals, plus the P-R and S-T segments. This diagram shows the different stages of heart contraction and relaxation along with the stages in the QT cycle. **Figure:** **ECG Tracing Correlated to the Cardiac Cycle **This diagram correlates an ECG tracing with the electrical and mechanical events of a heart contraction. Each segment of an ECG tracing corresponds to one event in the cardiac cycle. #### #### #### #### #### #### #### #### ECG Abnormalities  **Figure 19.25** **Common ECG Abnormalities **(a) In a second-degree or partial block, one-half of the P waves are not followed by the QRS complex and T waves while the other half are. (b) In atrial fibrillation, the electrical pattern is abnormal prior to the QRS complex, and the frequency between the QRS complexes has increased. (c) In ventricular tachycardia, the shape of the QRS complex is abnormal. (d) In ventricular fibrillation, there is no normal electrical activity. (e) In a third-degree block, there is no correlation between atrial activity (the P wave) and ventricular activity (the QRS complex). **The Cardiac Cycle** This pie chart shows the different phases of the cardiac cycle and details the atrial and ventricular stages. **Figure:** **Overview of the Cardiac Cycle **The cardiac cycle begins with atrial systole and progresses to ventricular systole, atrial diastole, and ventricular diastole, when the cycle begins again. Correlations to the ECG are highlighted.  **Figure:** **Relationship between the Cardiac Cycle and ECG **Initially, both the atria and ventricles are relaxed (diastole). The P wave represents depolarization of the atria and is followed by atrial contraction (systole). Atrial systole extends until the QRS complex, at which point, the atria relax. The QRS complex represents depolarization of the ventricles and is followed by ventricular contraction. The T wave represents the repolarization of the ventricles and marks the beginning of ventricular relaxation. ### Heart Sounds This image shows a graph of the blood pressure with the different stages labeled. Under the graph, a line shows the different sounds made by the beating heart. **Figure: Heart Sounds and the Cardiac Cycle **In this illustration, the x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure. The term **murmur** is used to describe an unusual sound coming from the heart that is caused by the turbulent flow of blood. Murmurs are graded on a scale of 1 to 6, with 1 being the most common, the most difficult sound to detect, and the least serious. The most severe is a 6. Phonocardiograms or auscultograms can be used to record both normal and abnormal sounds using specialized electronic stethoscopes. **During auscultation**, it is common practice for the clinician to ask the patient to breathe deeply. This procedure not only allows for listening to airflow, but it may also amplify heart murmurs. Inhalation increases blood flow into the right side of the heart and may increase the amplitude of right-sided heart murmurs. Expiration partially restricts blood flow into the left side of the heart and may amplify left-sided heart murmurs. indicates proper placement of the bell of the stethoscope to facilitate auscultation.  **Figure: Stethoscope Placement for Auscultation **Proper placement of the bell of the stethoscope facilitates auscultation. At each of the four locations on the chest, a different valve can be heard. ------------------------ **Cardiac Physiology** ------------------------ The autorhythmicity inherent in cardiac cells keeps the heart beating at a regular pace; however, the heart is regulated by and responds to outside influences as well. Neural and endocrine controls are vital to the regulation of cardiac function. In addition, the heart is sensitive to several environmental factors, including electrolytes. ### Resting Cardiac Output It can be represented mathematically by the following equation: **CO = HR × SV** **Cardiac output (CO)** is a measurement of the amount of blood pumped by each ventricle in one minute. To calculate this value, multiply **stroke volume (SV)**, the amount of blood pumped by each ventricle, by **heart rate (HR)**, in contractions per minute (or beats per minute, bpm). This figure lists the different factors affecting the heart rate and stroke volume. It also shows how they both affect the cardiac output. **Figure:** **Major Factors Influencing Cardiac Output **Cardiac output is influenced by heart rate and stroke volume, both of which are also variable. **Factors influencing Stroke Volume:** The three primary factors to consider are: - **preload**, or the stretch on the ventricles prior to contraction. - the **contractility**, or the force or strength of the contraction itself. - and **afterload**, the force the ventricles must generate to pump blood against the resistance in the vessels.  **Figure: Autonomic Innervation of the Heart **Cardioaccelerator and cardioinhibitory areas are components of the paired cardiac centers located in the medulla oblongata of the brain. They innervate the heart via sympathetic cardiac nerves that increase cardiac activity and cranial nerve 10, Vagus ( (parasympathetic) nerves that slow cardiac activity.