CARDIOVASCULAR system BLOOD & VESSELS Learning Objectives To be able to describe the structure of components within the cardiovascular system. To be able to explain how the cardiovascular system is able to adapt, particularly during increased exercise. Content 1.2.3 Structure of arteries, capillaries and veins and how this relates to function and importance during physical activity and sport in terms of: blood pressure; oxygenated and deoxygenated blood; and changes due to physical exercise 1.2.4 The mechanisms required (vasoconstriction, vasodilation) and the need for redistribution of blood flow (vascular shunting) during physical activities compared to when resting 1.2.5 Function and importance of red and white blood cells, platelets and plasma for physical activity and sport

Blood Vessels Blood vessels are responsible for carrying blood to and from the living cells in the body. There are 3 types of blood vessel: Arteries Capillaries Veins Each is structured differently to perform its specific job effectively.

Arteries Arteries carry blood Away from the heart. The main artery is the Aorta! They have 3 layers: A tough outer layer A middle layer of muscle A smooth inner layer to make it easy for blood to pass through. They carry blood at higher pressure than veins and capillaries. They pulsate: When the heart relaxes, the artery muscle contracts, continuing to push the blood forward. They carry oxygenated blood from the heart, with ONE exception. What is it?

Veins Veins carry blood back towards the heart. The main vein is the Vena Cava! Important things to remember about veins: They carry blood towards the heart. They carry blood at low pressure. They have thin walls. They have valves. They have a larger internal lumen (space in the middle of the vessel) than arteries. They carry deoxygenated blood back to the heart, with one exception. What is it?

Capillaries Arteries take blood away from the heart and veins bring the blood back – capillaries are the link between the two! It is in the capillaries that carbon dioxide diffuses from the tissue into the blood and oxygen diffuses from the blood to the tissue. Capillaries are one cell thick and very fragile. Blood cells pass through them one cell at a time. This allows time for the exchange of gases to take place.

The Blood Adults have around 5.5 litres of blood circulating their bodies. Blood is made up of the following components: Plasma This is the liquid part and is mainly made up of water. It is essential to allow the solid cells to flow around the body (think of a water slide). Red Blood Cells These are vital as they contain haemoglobin, which allows the transportation of oxygen around the body. White Blood Cells These seek out and destroy infections. White cells can slide through vessel walls and attack bacteria at the site of infection. Platelets These aid clotting, which can be particularly important for sports performers. If a performer receives a cut or graze, platelets are dispatched to the site to act as a plug and prevent further loss of blood.

Blood Pressure As blood moves through our arteries, veins and capillaries it exerts force on the sides of the vessel it is travelling through. The strength of this force is your blood pressure. It is greatest nearer the heart and least furthest from the heart. Blood pressure is checked because if it is too high it puts under extra strain on your arteries and your heart, which could lead to heart attack or stroke. When the left and right ventricles contract to pump blood out of the heart, blood pressure is at its highest. This is called systolic blood pressure. When the ventricles are filling with blood from the atria, blood pressure is at its lowest. This is called diastolic blood pressure. Blood pressure measurement is given as two numbers e.g 120/80 mmHG. The first number is your systolic blood pressure (120) and the second is your diastolic blood pressure (80).

Heart Rate Heart rate (HR) refers to the number of times the heart beats per minute. With every beat, the ventricles contract and squeeze blood out of the heart to either the lung or the rest of the body. During exercise we need to increase the amount of oxygen being delivered to working cells and the speed at which waste products are removed. This is achieved by increased blood flow, which increasing HR helps with. It is possible for people to achieve a HR of around 200 beats per minute during extremely intense exercise.

Stroke Volume This is the amount of blood ejected from the heart every beat. When the ventricles contract only about 60% of the blood within them is squeezed out, they aren’t completely emptied. With exercise the muscles of the heart become stronger so they can contract with more force. As they contract more forcibly, they are able to squeeze a larger volume of blood out of the heart. Because fitter individuals have stronger hearts, and are therefore able to pump more blood per beat, they tend to have a lower resting heart rate.

Cardiac Output This is the amount of blood ejected from the heart per minute. Cardiac Output = Stroke Volume X Heart Rate At rest we need about 5 litres of blood to circulate our bodies per minute. However, as we exercise and require more oxygen, this can rise to 30 litres per minute.

Vascular Shunting At rest there is around 5 litres of blood circulating our body, but how we use that blood flow can vary. If we have just eaten, a large proportion of the blood will be directed to our kidneys and liver to allow digestive functions to be carried out. At rest this isn’t a problem as the small percentage being directed to skeletal muscles is sufficient while we aren’t exercising. If we start to exercise, requiring more blood flow to skeletal muscles ,we can: Increase cardiac output from 5.5L to 30L per minute. Redistribute blood flow so that a greater proportion of blood leaving the heart is being directed to the working muscles.

Vascular Shunting The process to allow us to redistribute blood is called vascular shunting and is achieved through: Vasodilation The relaxation of the muscle wall in the vessel causing the internal space to become wider, allowing more blood to flow though. Vasoconstriction The muscular walls of the vessel contract, making the internal space narrower and restricting blood flow.

Questions Explain the major differences, in both structure and function, between arteries and veins. (4 marks) Blood pressure is given as two numbers, for example 120/80 mm/Hg. Explain what the two numbers represent. (4 marks) Define the term vasodilation. (1 mark)