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The primary function of the cardiovascular system is to provide continuous and controlled movement of blood through the system to reach every cell in the body.
The SA node, or sinoatrial node, is the natural pacemaker of the heart that generates electrical impulses, initiating the heartbeat and regulating the heart rate.
If the SA node loses its ability to generate impulses, pacemaker activity shifts to another part of the conduction system, which will fire more slowly, potentially leading to an ectopic pacemaker.
The autonomic nervous system modifies heart rhythm through cardiac centers in the medulla, with the sympathetic nervous system acting as an accelerator and the parasympathetic nervous system (via the vagus nerve) acting as brakes.
The P wave represents depolarization of the atria, the QRS complex represents depolarization of the ventricles (while the atria are repolarizing), and the T wave represents repolarization of the ventricles.
During atrial diastole, blood flows from the veins into the right and left atria, allowing the heart to fill with blood before the next contraction.
The heart is cone-shaped, fist-sized, weighs about 1 pound, has an apex located just above the diaphragm, and a base located just below the second rib, slightly left of the midline in the mediastinum.
The pericardium is a double-walled sac around the heart that consists of an outer fibrous portion for protection and anchoring, and an inner serous portion that reduces friction through serous fluid in the pericardial cavity.
The three layers of the heart wall are the epicardium (visceral pericardium), myocardium (cardiac muscle), and endocardium (endothelium that is continuous with blood vessel endothelium).
Contractility affects stroke volume by increasing the strength of heart muscle contractions, which can be enhanced by sympathetic nerve stimulation, hormones like epinephrine/norepinephrine, and medications like digitalis.
Afterload is the back pressure of arterial blood that the ventricles must overcome to eject blood. In individuals with hypertension, higher afterload decreases the ventricles' ability to eject blood effectively.
In untrained individuals, cardiac output initially increases due to rises in heart rate and stroke volume, but as exercise intensity increases, stroke volume plateaus and heart rate must increase. In trained athletes, improved heart muscle efficiency leads to greater stroke volume, allowing for increased cardiac output and potentially lower resting heart rates.
Baroreceptors detect changes in blood vessel stretch and send signals to the cardiac control centers in the medulla, which adjust the heart rate accordingly to maintain blood pressure.
The fibrous skeleton of the heart consists of connective tissue fibers that tether cardiac muscle cells together, reinforce the myocardium, anchor muscle fibers, decrease stretch on vessels and valves, and limit the spread of action potentials to specific pathways.
The four chambers of the heart are the right atrium, left atrium, right ventricle, and left ventricle.
The myocardium is the cardiac muscle layer responsible for the contraction of the heart chambers, enabling the pumping of blood throughout the body.
Heart valves are made of smooth tissue that forms folds, allowing them to open and close effectively, ensuring unidirectional blood flow through the heart and preventing backflow.
The endocardium is the innermost layer of the heart that provides a smooth lining for the heart chambers and is continuous with the endothelium of blood vessels, facilitating efficient blood flow.
Autorhythmicity refers to the ability of cardiac muscle cells to generate their own electrical impulses without external stimulation, allowing the heart to maintain a consistent rhythm.
The apex of the heart is the pointed bottom part located above the diaphragm, while the base is the flat top part located just below the second rib.
The heart's position in the mediastinum, between the two lungs and slightly left of the midline, allows for optimal space for expansion and contraction while being protected by the rib cage.
Anatomy: Thick-walled arteries near heart Contain more elastin Physiology: Expand/Recoil as blood ejected from heart provides continuous blood flow (pressure-smoothing effect
Anatomy: Thickest tunica media-more smooth muscle, less elastic tissue Physiology: More active in vasoconstriction, less distensible (stretchy)
Anatomy: Lose tunica externa as they get smaller Tunica media mainly sm. ms. Cells w/ few scattered elastic fibers Physiology: Determine blood flow into capillary beds Vary in response to neural/hormonal/local chemical influences