Cardiovascular System

• BP = CO x SVR
• CO = HR x SV
• SV = EDV - ESV
• the pericardium is filled with pericardial fluid which reduces friction with the hearts movement
• The heart has three layers, epicardium (outer), myocardium (middle) and endocardium (inner)
• the myocardium is the cardiac muscle tissue which is responsible for contraction
• tricuspid valve: prevents blood flowing back into the right atrium when the right ventricle contracts
• pulmonary valve: separates right ventricle and pulmonary artery, closes during ventricular diastole to prevent blood flow back into the heart, opens during systole (contraction)
• bicuspid/mitral valve: prevents blood flowing back into left atrium when left ventricle contracts
• aortic valve: separates left ventricle from aorta, closes during ventricular diastole to prevent blood flow back into the heart, opens during systole (contraction)
• de-oxygenated blood returns to the heart via the inferior and superior vena cava
• de-oxygenated blood flows into the right atrium and right ventricle, 70% of blood entering the ventricle does so passively at this stage
• atrium contracts, expels other 30% into the ventricle - "atrial kick"
• the right ventricle contracts, forcing blood upwards. this pressure causes the tricuspid valve to close, forcing blood into pulmonary artery. roughly 70ml leaves the ventricle (stroke volume) while roughly 50ml remains
• de-oxygenated blood flows through pulmonary arteries to the lungs. carbon dioxide is released and oxygen is picked up. blood then travels through the pulmonary veins to the left atrium
• oxygenated blood flows into the left atrium and left ventricle
• left ventricle contracts, causing oxygenated blood to exert pressure upwards. pressure causes bicuspid valve to close, blocking the exit to the left atrium. blood is forced into the aorta
• the amount of blood ejected from the left ventricle to the aorta is known as stroke volume
• oxygenated blood flows through the aorta and throughout the body
• cardiac output is the volume of blood pumped by the heart every minute
• diastole is the relaxation phase of the heartbeat, when the ventricles fill passively
• systole is the contraction phase of the heartbeat, when the ventricles eject their blood
• the myocardium only receives blood in diastole as the blood vessels are open, allows for perfusion
• during systole, contracted muscles of heart compress coronary arteries entering the muscle, cutting off blood supply to the heart
• the right coronary artery originates just above the aortic valve on the right side of the heart and travels along the atrioventricular groove. it supplies blood to the right ventricle and some parts of the left ventricle, and supplies blood to the sinoatrial node
• the left coronary artery originates from just above the aortic valve on the left side of the heart, the blood vessel split into circumflex artery and anterior interventricular artery
• the interventricular artery is also known as the left anterior descending artery (LAD), it supplies blood to approximately 50% (anterior and lateral aspects) of the left ventricle, supplies blood to apex and interventricular septum
• an occlusion in the interventricular/left anterior artery is known as a "widowmaker" occlusion
• the SA/sinoatrial node sits in the right atrium of the heart. the normal impulse of electrical activity is generated from here
• internodal pathways: these fibres transmit the energy generated from the SA node through the atria to the atrioventricular (AV) node. this transmission causes the atria to contract
• AV node: role is to conduct the impulse further down the electrical pathway but also to slow the speed at which the conduction travels. this gives the ventricles time to completely fill before they contract
• bundle of his: small segment before left and right bundle branches in the interventricular septum. the only pathway the impulse can travel from the atrial to the ventricles
• AV node and bundle of his: AV junction
• right bundle branch: pathway impulse travels to purkinje fibres to innervate contractions of the right ventricle
• left bundle branch: pathway impulse travels to purkinje fibres to innervate contractions of the left ventricle
• purkinje fibres: located within the myocardium. an impulse from the bundle branches travels to the purkinje fibres resulting in the contraction of the ventricles
• myocardial cells are striated muscle cells that have a high density of mitochondria, allowing them to generate ATP through aerobic respiration
• arteries: thick to withstand force, greater pressure than veins
• veins: thin walled, contain valves to direct blood flow due to lower pressure, blood squeezed towards the heart from the valves
• normal ECG looks mainly at the left ventricle