Circulatory System

The three main types of blood vessels are arteries, veins, and capillaries.

• Arteries have thick, muscular walls that are capable of withstanding high pressure.
• They have elastic fibers which allow them to stretch and recoil with each heartbeat.

Arteries carry oxygenated blood away from the heart to supply oxygen and nutrients to the body’s tissues and organs.

• Veins have thinner walls compared to arteries.
• They have valves that prevent the backflow of blood.

Veins carry deoxygenated blood back to the heart from the body’s tissues and organs.

• Capillaries are very thin-walled vessels.
• They allow for the exchange of nutrients, oxygen, and waste products between the blood and the body’s cells.

The exchange of oxygen, nutrients, and waste products between the blood and the body’s tissues takes place at the capillaries.

The major artery associated with oxygenated blood leaving the heart is the aorta.

The blood vessel that transports oxygenated blood from the lungs to the heart is the pulmonary vein.

The major vein associated with deoxygenated blood entering the heart is the superior vena cava.

The vein which transports deoxygenated blood from the heart to the lungs is the pulmonary artery.

• The atria are the upper chambers of the heart, receiving blood.
• The ventricles are the lower chambers, responsible for pumping blood out of the heart.

• Deoxygenated blood enters the right atrium from the superior and inferior vena cava.
• It then passes through the tricuspid valve into the right ventricle.
• The right ventricle pumps deoxygenated blood through the pulmonary valve into the pulmonary artery, which carries it to the lungs for oxygenation.
• Oxygenated blood returns from the lungs through the pulmonary veins into the left atrium.
• It then passes through the bicuspid (mitral) valve into the left ventricle.
• Finally, the left ventricle pumps oxygenated blood through the aortic valve into the aorta for distribution to the rest of the body.

The cardiac cycle refers to the contraction and relaxation of the heart during one heart beat, including systole and diastole.

Diastole is the phase of the cardiac cycle when the heart muscle relaxes and chambers fill with blood.

Systole is the phase of the cardiac cycle when the heart muscle contracts and pumps blood out of the chambers.

• Valves in the heart open and close to ensure one-way flow of blood. They prevent backflow and ensure that blood moves in the correct direction.

Heart rate is the number of times the heart beats per minute.

• Stroke volume is the volume of blood ejected by the left ventricle in one contraction.

Cardiac output is the total volume of blood pumped by the heart per minute.

• Cardiac output is determined by multiplying stroke volume (the amount of blood pumped by the heart in one beat) and heart rate (the number of beats per minute).
• An increase in either stroke volume or heart rate will lead to an increase in cardiac output.

• Anticipatory rise refers to the increase in heart rate that occurs in anticipation of physical activity or stress. It is a response preparing the body for increased demand / work.
• On a heart rate graph, anticipatory rise appears as a gradual, steady increase in heart rate prior to the start of activity.

• Higher levels of activity intensity will be represented by higher peaks on the heart rate graph, indicating an increased heart rate.
• Lower levels of intensity will result in smaller peaks or plateaus on the graph, reflecting a steadier heart rate.

Vasoconstriction refers to the narrowing of blood vessels, reducing blood flow.

• Vasoconstriction occurs in response to various factors, such as cold temperature or stress, in order to conserve body heat and redirect blood flow to vital organs.
• During exercise, blood is directed to the working muscles and vasodilation restricts blood away from organs in the body.

Vasodilation refers to the widening of blood vessels, increasing blood flow to the working muscles.

Vasodilation occurs in response to increased demand for oxygen during exercise, allowing more blood to flow to active tissues and muscles.