Cambridge tech the cardiovascular system


The structure of the heart

The heart is split into four quarters. The smaller top chambers are called atriums and the biger chambers are called ventricles. The heart is effectively two pumps joined in the middle. The left-hand pump is concerned with pumping the oxygenated blood from the lungs to the body. The right-hand pump is concerned with pumping deoxygenated blood from the body to the lungs.

The vessels that carry blood away from the heart are called arteries and vessels that carry blood towards the heart are called veins. The valves in the heart prevent blood from flowing backwards. The arteries that carry blood away from the heart are the aorta and the pulmonary artery. The veins that bring blood back to your heart are called the pulmonary veins and vena cava. 

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Stroke volume (SV)

The volume of blood pumped out of the heart in one contraction. A typical SV for an adult is 70ml; however it can range between 50ml and 100ml. This is dependant mainly on the size of the person. Exercise also plays a large part of this. As the heart is a muscle it can adapt with regular exercise in two ways: the ventricle can grow in size, secondly, it can contract with a greater force and eject more blood per contraction.

formula for calculating SV=

Stoke volume(SV) = Cardiac output(CO) / Heart rate (HR)

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Heart rate (HR) and Cardiac output (Q)

Heart rate is the amount of time your heart beats per minute (bpm). A typical heart rate is between 60 and 80 bpm. If we now combine the stroke volume and heart rate we are able to establish how much blood is pumped out of the heart per minute - otherwise known as the cardiac output (Q). This is mesured in litres per minute. A typical resting value for an adult cardiac output is 5 l/min

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Structure of blood vessels

Arteries - Large vessels that carry blood away from the heart. They have thick musclular walls 

Arterioles - Vessels that connect arteries to capillaries; they are smaller versions of arteries, with muscular walls 

Capillaries - Vessels that are one cell thick, which enables nutrience to pass through them

Venules - Venules connect capilliaries to veins; they are smaller versions of veins without valves 

Veins - Vessels with a large lumen, with valves inside to prevent the backflow of blood

Tunica - The general Latin term for layer or sheath

Adventia/Externia - The outside layer of an artery or vein.

Media - The middle layer of an artery or vein

Intima - The inside layer of an artery or vein; the only layer of a capillary

Lumen - The space in the inside of an artery, vein or capillary, through which blood passes

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Arteries and Arterioles

Arteries have a thicker lunica media than veins, containing smooth muscle. The muscle is able to change the lumen of the arteries. This mean that our blood pressure can be adjusted. Arteries also have much more elastin in them, which means that they are able to strech and recoil as the blood is forced out of the heart and down the arteries.

Arterioles provide the link between arteries and capillaries. They are smaller in diameter than arteries, but are still able to adjust their diameter, controlling the flow of blood into the capillary. At the end of the arteriole, just before it becomes the capillary. This is called a pre-capillary sphincter (PCS). The PCS is able to contract and divert blood away from the capillary.

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Capillaries and Venules

Capillariesare the thinest vessels, only one cell thick. It is here that oxygen, carbon dioxide and nutrients are passed from the blood into the tissue/muscle. Blood pressure in capillary vessels is much lower so that diffusion can occur.

Venules are the venous version of an arteriole. They collect the blood, drawing it together before emptying the veins. Pressure in the venules and veins is much lower than in arteries. Pressure in the venules relies on the flow of blood to keep it moving.

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Veins and pocket valves

Veins return the blood backto the heart, where the process can start again. Structurally, the veins have much smaller tunica mediae than arteries, with little smooth muscle. The tunica adventitia is the thickest layer, and veins have a larger lumen to allow increased blood volume. The tunica intima is also especially adapted to incorporate pocket valves. These improve the flow of blood back to the heart. The return of blood back to the heart is called venous return. Blood pressure in veins is much lower than arteries and the body has developed ways to improve the flow back.

Pocket valves are formed from the tunica intima, and they only allow blood to flow back towards the heart. As the flow starts to slow or stop, the valve closes until the flow increases again.

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vein placement and the respiratory pump

Vein placement - to help keep the blood moving, the veins are often located within muscles or between muscle and bones. The advantage to this is that as the muscles contract they also squeeze the veins. Combined with the pocket valves, this is an effective way to return blood back to the heart

Respirtory pump - The simple action of breathing also helps to increase the flow of blood back to the heart. The pump works as we breathe. Breathing in causes the pressure inside your thoracic cavity to decrease and it also causes the pressure inside the abdominal cavity to increase as the diaphragm contracts. The difference in pressure between the veins in the thoracic and abdominal cavity moves the blood into the thoracic area and back towards the heart

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components of blood

Oxygen O2 - A key element in the areobic production of energy

Carbon dioxide CO2 - The by-product of aerobic energy production

Haemoglobin Hb - The part of blood that carries oxygen

Oxyhaemoglobin HbO2 - The name given to haemoglobin when carrying oxygen

White blood cells - The cells in the blood responsible for protecting you from infection and disease

Platelets - The cells that stop you from bleeding should you cut yourself 

Plasma - The fluid that enables all the other cells to move around the body

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Functions of blood

One of the roles of the blood is to transport oxygen and carbon dioxide using red blood cells (haemoglobin). The oxygen attaches to the haemoglobin to form oxyhaemoglobin. The blood also carries white blood cells. These circulate around your body looking for foreign bodies to attack and distroy.

Platelets are also an essential component of blood. Their job is to stop you from bleeding. Most of the time they circulate around the body with nothing to do. However, if there is ever any damage they swarm to the area to minimise the amount you bleed.

The final component of our blood is plasma. This fluid enables all of your cells to flow around your body quickly and effectively. Plasma is also able to carry carbon dioxide, protein, gycogen and triglycerides.

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Vascular shunt mechanism

The body has a way of ensuring that blood is sent to all the areas that need it most. The redistribution of blood when exercising is called the vascular shunt mechanism (VSM). The VSM makes sure that the muscles, heart, lungs and brain have sufficent blood and oxygen to enable you to participate in exercise.

Blood distrubution at rest is fairly evenly distrubuted, however, as you start to undertake physical activity not only does the carbon dioxide level increase, but how the blood is distibuted is also altered. The body achieves this by activating the arterioles and pre capilliary sphincters to either increase or reduce blood flow depending on the area being served.

The muscles are the main beneficiary of the vascular shunt. However, it should also be noted that although the muscles get most of the blood, its increased volume can be accounted for mostly by the increase cardiac output. The brains flow remains unchanged and the heart and skin have increased flow in order to maintain blood flow and keep you cool. It is only really the kidneys, liver and bone marrow that have a reduced flow as they are non-essential during exercise.

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Short and long term effects of exercise

Participating in physical activity effects the cradiovascular system in the short term by increasing the heart rate, stroke volume and cardiac output. The increase in cardiac output is related to the increase in stroke volume and heart rate. The increase is liked to the intensity of the exercise: the harder we work the greater the rise. However, the intensity and duration by which a performer is able to perform is related to their fitness

Repeated bouts of physical activity that stress the cardiovascular system force it to adapt to these changes. The long term effects of physicala activity on the cardiovascular system is to increase the resting and exercising stroke volume of the left ventricle. This means that the resting heart rate is reduced and the maximal cardiac output is increased 

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