cardiovascular system

• The function of the cardiovascular system is to pump blood around the body, delivering oxygen and offloading waste products.
• The cardiovascular system consists of the heart and blood vessels.
• The function of the heart is to pump blood and the function of blood vessels is to transport blood.
• The heart is a muscular organ consisting of four chambers surrounded by muscular walls, four valves, a handful of so-called great vessels, and a number of minor vessels.
• Blood returns to the heart in its deoxygenated state through the right atrium, which can be reached via the superior vena cava, the inferior vena cava, or the coronary sinus.
• From the right atrium, blood travels through a valved opening called the tricuspid valve into the right ventricle.
• From the right ventricle, blood travels through another valve called the pulmonary valve into the pulmonary artery, which carries the still deoxygenated blood to the right and left lungs where carbon dioxide will be offloaded and oxygen will be picked up.
• The oxygenated blood returns to the heart via one of four pulmonary veins, bringing it to the left atrium.
• From the left atrium, blood travels through the mitral valve into the left ventricle.
• From the left ventricle, blood exits the heart through the aortic valve, which is hidden behind the pulmonary valve, and then travels via the aorta to the rest of the body.
• The sequence of steps from the vena cava to the aorta is separated into two segments by the lung, with the right side of the heart containing deoxygenated blood and the left side of the heart containing oxygen.
• The right and left atria are separated by a relatively thin inter atrial septum, hidden behind the right ventricular outflow tract, while the left and right ventricles are separated by the relatively thick and muscular interventricular septum.
• The endocardium, partly composed of endothelial cells, forms the lining of the heart valves and is the location of the purkinje fibers.
• Cardiomyocytes are connected to one another via porous bridges called intercalated discs which allow for the free movement of electrolytes which is necessary for rapid transmission of electrical signals from one cell to the next through the muscle tissue.
• Pathologic conditions of the cardiovascular system can usually be mapped to just one of these components: the heart, the valves, the pericardium, the conduction system, or the coronary arteries.
• Lymphatic vessels are responsible for returning interstitial fluid that is extra vascular fluid that surrounds the cells and sits in the connective tissue back to the bloodstream.
• The heart is composed of three layers: the thin inner endocardium, the sub endocardium, and the thick myocardium.
• The thick myocardium, composed predominantly of cardiomyocytes, contains long myofibrils that contain a repeating microstructure called sarcomeres which are the fundamental contractile units of the cell.
• Lymphatic capillaries merge into ever larger vessels until eventually most feed into a conduit called the thoracic duct which empties into large veins of the thorax.
• The sub endocardium, composed of loose connective tissue, is also the location of the purkinje fibers.
• The potential space between the two serous layers is called the pericardial space and is normally much thinner than it is in this image it contains a thin film of fluid that allows the heart to beat in a near frictionless environment.
• The pericardium is a fibrosyrus structure that encases the heart and the roots of the great vessels, composed of a tough outer fibrous pericardium which is tethered to the diaphragm in the sternum and which keeps the heart in place and a inner smooth serous pericardium that's folded over on itself to make two separate layers containing a potential space between them.
• The blood vessels can be subdivided into arteries including arterioles which are impacted by peripheral artery disease and veins including venials which are impacted by a condition called venous insufficiency.
• Capillaries, which are rarely the primary site of pathology but which can be the site of manifestations of sepsis and lymphatics which cause a condition called lymphedema when obstructed.
• Cardiomyocytes contain a high density of mitochondria necessary for the continuous production of energy containing atp.
• The rapid increase in pressure within the ventricles causes the AV valves to quickly snap shut, triggering the first heart sound in the cardiac cycle, known as S1.
• There are five basic types of vessels starting from the heart, all blood leaves the left ventricle via the aorta, from the aorta branch off large and medium-sized arteries which are thick-walled with significant elastic tissue and smooth muscle allowing them to handle high pressure, arteries divide into smaller arterioles which are the site of greatest resistance to blood flow through the circulation, and arterioles eventually divide and divide again into microscopic networks of extremely small vessels called capillaries which are so small as to be lined by a single layer of endothelial cells
• The tricuspid valve is slightly larger and a little bit more round than the bicuspid valve.
• The heart is only one half of the cardiovascular system, the other half is the blood vessels which are the conduits through which blood is pumped around the body, moving from the heart to the peripheral tissues and from the peripheral tissues back to the heart.
• After the capillaries, blood moves to the venules which are analogous to the arterials and from there to the veins, in contrast to arteries, veins are relatively thin walled and lack much elastic tissue resulting in significant distensibility, this distensibility allows veins to act as a reservoir for blood volume.
• The capillaries are where blood travels the most slowly through the circulation, which is of course helpful for the exchange of gas, nutrients, and waste.
• The entrance of the coronary sinus, where the coronary sinus drains into the right atrium, is superior to the tricuspid valve.
• Arteries and veins are typically named for either the part of the body they travel through or which organ they bring blood to or away from, and they often exist as matching pairs.
• Blood is moving from the atria to the ventricles throughout all diastole, so both before and during atrial contraction, the final point about the cardiac cycle, systole is always shorter than diastole, although the relative fraction of the cardiac cycle each takes up is dependent on the heart rate.
• After the electrical signal reaches the AV node and undergoes the brief AV delay, allowing time for filling of the ventricles, the signal propagates through the His-Purkinje system and triggers ventricular contraction.
• The signal triggers the right and left atria to contract, squeezing blood through the already open tricuspid and mitral valves into the right and left ventricles, this period of atrial contraction is formally referred to as atrial systole but is more commonly referred to as the atrial kick.
• The intraventricular blood is ejected through the now open semilunar valves after a brief period of time, the ventricles relax again, and there is higher pressure in the pulmonary artery and aorta than in the right and left ventricles, so the semilunar valves snap shut, resulting in the second heart sound known as S2.
• The cardiac cycle is a sequence of all events within the heart that occur from one heartbeat to the next, each cycle is triggered by the SA node firing an electrical signal.
• The superior and inferior vena cava bring blood from the body to the right atrium.
• The electrical signal will next reach the atrioventricular or AV node within the inferior part of the interatrial septum.