Circulatory System

• The heart is made out of muscle and is the primary organ of the circulatory system. It is powered by electrical impulses and directed by the brain and nervous system. Its role is to move blood through the body as well as controlling the rhythm and speed of the heart rate and maintaining a stable blood pressure
• The deoxygenated partition of the heart is on the right side and receives deoxygenated blood from the rest of the body
• The oxygenated partition of the heart is on the left side and receives oxygenated blood from the lungs to transport to the rest of the body
• Heart walls are muscles that contract and relax to send blood around the body. The atria (top) has thinner walls than the vetricles (bottom), because the ventricles have to pump blood around to the rest of the body and the pressure of the blood flowing through is higher
• The right atrium is the top right chamber of the heart and receives oxygen poor blood from the superior and inferior vena cava to pump it to the right ventricle

  
• The inferior vena cava is the largest vein in the body and returns oxygen poor blood from the lower parts of the body (below the diaphragm) to the right atrium

  
• The superior vena cava is the second largest vein in the body and returns oxygen poor blood from the upper parts of the body to the right atrium

  
• The right ventricle is the bottom right chamber of the heart and pumps oxygen poor blood to the lungs through the pulmonary artery to produce oxygen rich blood

  
• The left atrium is the top left chamber of the heart and receives oxygen rich blood from the lungs through the pulmonary vein, to pump it to the left ventricle

  
• The left ventricle is the bottom left chamber of the heart and pumps oxygen rich blood to the rest of the body through the aorta, therefore it is slightly larger than the right ventricle as it needs more muscle

  
• Heart valves separate the different heart chambers and create a one-way path for blood. They open to let blood flow through and close to prevent backflow
• Atrioventricular valves separate the atria from the ventricles
• Semilunar valves separate the ventricles from the arteries
• The tricuspid valve is an atrioventricular valve and is located between the right atrium and right ventricle. It has 3 cusps, hence the name.

  
• The bicuspid/mitral valve is an atrioventricular valve and is located between the left atrium and left ventricle. It has 2 cusps, hence the name.

  
• The aortic valve is a semilunar valve and opens when blood flows out of the left ventricle and to the aorta

  
• The pulmonary valve is a semilunar valve and opens when blood flows out of the right ventricle and to the pulmonary arteries

  
• Arteries are a type of blood vessel and carries oxygen rich blood away from the heart and to the body's tissues. The only exception to this is the pulmonary artery as it carries oxygen poor blood away from the heart and to the lungs. The blood is high pressure, hence the lumen are narrow/small. It feeds into the capillaries and does not have valves.

  
• Lumen is the diameter/space inside a blood vessel. Smaller lumen maintain high pressure as blood is transported

  
• Veins are a type of blood vessel that carries oxygen poor blood from the body's tissues to the heart. The blood is transported at low pressure and therefore the lumen are wide/large. The blood enters the veins from capillaries. Valves are interspersed throughout them to prevent backflow

  
• Blood vessels carry blood around the body and all except for capillaries are made out of smooth muscles and connective tissue

  
• The aorta is the largest artery and the main one that carries oxygenated blood from the heart to the rest of the body

  
• Capillaries are small blood vessels that organize material exchange between blood and body tissue, by delivering oxygen to organs/tissues and carries CO2 from organs/tissues to blood cells (hemoglobin). They also form a connection between arteries and veins, and have thin walls and narrow lumen.

  
• Systole is the phase of the cardiac cycle where the muscle contracts and pumps blood from the ventricles to the arteries
• Diastole is the phase of the cardiac cycle where the muscle relaxes and allows the atria to fill with blood
• Sinoatrial nodes generate an electrical signal that causes the atria to contract. Regulates the pace/rhythm/rate of the heartbeat
• Atroventricular nodes transmit the impulse from the atria to the ventricles to cause the ventricles to contract
• Cellular components of blood include red blood cells, which transport oxygen and CO2 to/from the lungs and around the body, white blood cells which fight infections, and platelets, which are cell fragments in blood that help it clot to stop/prevent bleeding. This makes up 45% of cellular components in blood
• Plasma makes up 55% of the cellular components of blood and is the liquid portion. It redistributes water, hormones, nutrients, and proteins around the body, exchanges oxygen and CO2, prevents blood vessels from collapsing or clogging, and maintains blood pressure and circulation
• Systolic blood pressure measures the pressure in the arteries when the heart beats/during systole
• Diastolic blood pressure measures the pressure in the arteries when the heart is relaxed between beats/during diastole
• Cardiac cycle is the time between systole and diastole, or the time between the start of a heart beat and the start of the next
• Atrial pressure is the pressure measured in the atrium
• Ventricular pressure is the pressure measured in the ventricle
• Blood pressure is when the blood exerts force on the muscular walls of blood vessels. It rises and falls with the heartbeat
• Systolic blood pressure is high blood pressure during systole as the heart contracts to force blood through the arteries
• Diastolic blood pressure is low blood pressure between beats of the heart
• Normal blood pressure is around 120/80mm Hg
• Increased blood pressure can be caused by thicker blood, higher volumes of blood and/or stress, all which causes the heart to pump harder