Cardiovascular System: The Heart

Describe the structure, position, and functions of the fibrous pericardium and serous pericardium.

- The heart is enclosed a pericardial sac, the outermost layer of which is covered in dense irregular tissue called the fibrous pericardium. This attaches inferiorly to the diaphragm and superiorly to the base of the great arterial trunks to restrict movement of the heart and prevents it from overfilling with blood. - The serous pericardium is the inner portion of the pericardium. It is composed of the parietal and visceral layers. The parietal pericardium is just deep to the fibrous pericardium. The visceral pericardium adheres tightly to the heart and is also known as the epicardium. It is separated by the parietal pericardium by a cavity filled with serous fluid, this space is called the pericardial cavity.

Identify and locate the 5 groups of the autorhythmic cardiac cells.

1. Sinoatrial node: posterior wall of right atrium, adjacent to entrance of superior vena cava. 2. Atrioventricular node: located in the floor of the right atrium between the right av valve and the opening for the coronary sinus. 3 & 4. Atrioventricular bundle (of his): extends from AV node into and through the interventricular septum. Divides into left and right. 5. Purkinje fibers extend from left and right bundles from the apex of the heart and continue through the walls of the ventricles.

Identify 2 ways in which cardiac autorhythmic cells differ from cardiac contractile cells.

Autorhythmic cells, also called nodal cells, generate action potentials on their own since they have unstable resting potentials that spontaneously move toward threshold and trigger action potentials.

Identify the 3 layers of the heart wall. Describe their primary composition and functions.

Epicardium (visceral pericardium): composed of simple squamous epithelium tissue and areolar connective tissue. This, along with the parietal epicardium secrete serous fluid into the pericardial cavity to reduce friction around the heart. Myocardium: thick middle layer of the heart. Composed of cardiac muscle tissue it is the muscle that contracts the ventricles. Endocardium: composed of simple squamous tissue called endothelium and an underlying layer of areolar connective tissue.

Describe the cardioacceleratory center and its effect on the SA node's depolarization rate.

Housed within the cardiac center of the medulla oblongata, along with the cardioinhibitory center, the cardioacceleratory center is responsible for sympathetic innervation which speeds up the rate at which the SA node depolarizes and thus increases heart rate.

Identify the 3 vessels that empty into the right atrium. Identify what body regions they drain and describe their O2 and CO2 content.

Inferior vena cava: deoxygenated blood from below the diaphragm Superior vena cava: deoxygenated blood from above the diaphragm Coronary sinus: deoxygenated blood from the coronary circuit.

Identify the 4 vessels that empty into the left atrium. Identify the organs they drain and describe their O2 and CO2 content.

Left and right superior and inferior pulmonary veins empty into the left atrium. The blood they carry is fully oxygenated, as it is returning directly from the lungs.

Compare the pulmonary and systemic circuits in terms of length, pressure, volume, resistance, arterial gas content, and venous gas content.

Length: pulmonary is much shorter than systemic. Pressure: pressure is higher in the systemic since the length is much greater and the left ventricle pumps with much more power. Volume: is the same Resistance: Arterial gas content: deoxygenated in the pulmonary circuit, oxygenated in the systemic circuit. Venous gas content: pulmonary circuit contains oxygenated blood, systemic circuit has deoxygenated blood

Describe the location of the atrioventricular node

On the floor of the right atrium in between the tricuspid valve and the opening for the coronary sinus.

Define Pulmonary and Systemic Circuits

Pulmonary circulation: includes the pumping of blood by the right side of the heart to the lungs and the return of blood to the left side of the heart. Systemic: includes the pumping of blood by the left side of the heart to the body's cells and the return of blood to the right side of the heart.

Describe the pathway of blood as it completes a round trip through the pulmonary and systemic circuits beginning and ending in the right atrium

SVC/IVC/Coronary Sinus>> R Atrium>> Tricuspid valve>> R Ventricle>> Pulmonary semilunar valve>> Pulmonary trunk >> R/L Pulmonary Arteries>> Lung Capillaries>> R/L Pulmonary Veins>>L Atrium >> Bicuspid Valve >>L Ventricle>> Aortic Semilunar Valve>>Ascending Aorta>> Brachiocephalic A Aortic Arch >>L Common Carotid A Aortic Arch >> L Subclavian A Aortic Arch>> Descending A

Explain how the cardioacceleratory and cardioinhibitory centers differ in terms of divisions of the autonomic nervous system and regions of the heart innervated.

The CA center is responsible for sympathetic innervation and the CI center is responsible for parasympathetic innervation. The CI center innervates the heart via the right and left vagus nerves. The right vagus nerve innervates the SA node and the left nerve innervates the AV node The CA center innervates the heart via neurons within the T1-T5 segments of the spinal cord extend to the SA node, AV node, and the myocardium section. This innervation has direct effect on the force of contraction. There is also some parasympathetic innervation to the coronary arteries which causes dilation.

Describe the location of the SA node and explain why it is the pacemaker of the heart.

The SA node lies on the posterior wall of the right atrium and has the fastest rate of spontaneous depolarization thus it sets the rate for the rest of the heart.

Describe the structure and function of the atria.

The atria are where blood return from either the pulmonary circuit (left atrium) or the systemic circuit (right atrium). They both have pectinate muscles within their auricles. After enough blood pools in the atria, they flow into the ventricles via the atrioventricular valves.

Describe the cardioinhibitory center and its effect on the SA node's depolarization rate.

The cardioinhibitory center, responsible for parasympathetic innervation, decreases the rate of depolarization of the SA node.

Describe the hearts position in the mediastinum. Describe the position of the heart relative to the lungs, diaphragm, vertebral column, sternum and esophagus.

The heart is located in the mediastinum in between the lungs, anterior to the vertebral column, superior to the diaphragm, inferior to the esophagus and just deep, and most of it lateral, to the sternum

Identify the 4 heart chambers and describe their relative positions.

The heart is said to be divided into two pumps. The left side pumping to the systemic circuit and the right side to the pulmonary circuit. Each side is composed of a superior atrium, which receives blood, and an inferior ventricle, which pumps to either pulmonary or systemic circuit, right and left, respectively. The atria are separated by the interatrial septum and the ventricles by the interventricular septum.

Describe the structure and function of the ventricles.

The internal wall surface of the ventricles display irregular muscular ridges called the trabeculae carneae. In the right ventricle extending from the external wall are three muscular projections called papillary muscles (there are two in the left ventricle). These anchor to the chordae tendineae, collagen fibers that attach to the atrioventricular valves. The ventricles pump blood to their appropriate circuits. The left to the systemic circuit via the aorta, and the right to the pulmonary circuit via the pulmonary trunk.

Define coronary circulation. Describe the location and function of the left and right coronary arteries and coronary sinus.

The right and left coronary arteries travel within the coronary sulcus. They originate from immediately superior to the aortic semilunar valve. The coronary vein lies in the posterior portion of the coronary sulcus. It collects venous blood and drains deoxygenated blood from the heat and delivers it to the right atrium.

Explain the significance of the delay in impulse conduction at the AV node.

The slight delay allows the atria enough time to complete contraction and the ventricles to fill with blood before themselves contracting.