C6 Combined SAMS Notes Part 5 PDF

Pulmonary circulation: Deoxygenated blood is transported to the lungs for oxygenation and then returned to the heart. The deoxygenated blood enters the right atrium and flows into the right ventricle. The deoxygenated blood exits the heart through the pulmonary trunk. The pulmonary trunk divides int...

Pulmonary circulation: Deoxygenated blood is transported to the lungs for oxygenation and then returned to the heart. The deoxygenated blood enters the right atrium and flows into the right ventricle. The deoxygenated blood exits the heart through the pulmonary trunk. The pulmonary trunk divides into left and right pulmonary arteries. The deoxygenated blood travels to the right and left lung where gas exchange occurs. Oxygenated blood travels in the left or right pulmonary veins and enters the left atrium. Systemic circulation: oxygenated blood is transported to body tissues and then returned to the heart. The Oxygenated blood enters the left atrium. The oxygenated blood flows into the left ventricle. The left ventricle contracts and pushes blood out of the heart through the aorta. The aorta branches into the ascending aorta, the aortic arch and the descending aorta. The oxygenated blood is delivered to all cells and tissues in the body for gas/nutrient/fluid exchange. The deoxygenated blood travels back to the heart and re-enters the right atrium through the vena cava. Contraction of the heart produces the pressure Blood moves through the circulatory system from areas of higher to lower pressure The Cardiac cycle: The repetitive contraction (systole) and relaxation (diastole) of heart chambers move the blood through the heart and body. Blood flow is proportional to the metabolic needs of tissues. The brain, kidneys, liver, exercising skeletal muscle have very high needs for blood. Cardiac output is heart rate x stroke volume Nervous control system: The nervous control system maintains blood pressure and thus blood flow. It controls the re-routing of blood flow e.g., an increase in BP with exercise. It controls the re-routing of blood flow away from skin and viscera towards the brain and cardiac muscle in response to blood loss/injury Hormonal Control: Epinephrine (adrenaline) from the adrenal gland – increases HR and SV, Vasoconstriction in response to stress Conducting system: The cardiac conduction system is an internal pacemaker & nerve-like pathway through the myocardium. An action potential is a rapid change in membrane potential. Action potential acts as an electrical signal /impulse. Action potentials spread through the conducting system of the heart to all cardiac muscle cells. This causes the cardiac muscle cells to contract. Blood is ‘pumped’. The heart can generate its own action potentials. Auto-rhythmicity is the repetitive contractions caused by autorhythmic contractile cells. The conducting system process steps: Step one: Action potential originates in the sinoatrial (SA) node (the pacemaker) and travels across the wall of the atrium from the SA node to the atrioventricular (AV) node. Step 2: Action potentials pass through the AV node and along the atrioventricular (AV) bundle which extends from the AV node, through the fibrous skeleton, into the interventricular septum. Step 3: The AV bundle divides into right and left bundle branches, and action potentials descend to the apex of each ventricle along the bundle branches. Step 4: Action potentials are carried by the Purkinje fibres from the bundle branches to the ventricular walls and papillary muscles.