Blood and Blood Vessels
- Created by: Emily Cartwright
- Created on: 29-05-14 17:02
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- Blood and blood vessels
- Blood
- An average adult has 4-6 litres of blood. Blood it made up of';
- Plasma (55%)
- Consists of 90% water. The other 10% is made up of dissolved solutes e.g. CO2, hormones, fibrinogen and antibodies
- Plasma also has a role in the distribution of heat throughout the body
- Consists of 90% water. The other 10% is made up of dissolved solutes e.g. CO2, hormones, fibrinogen and antibodies
- Cells (45%)
- Plasma (55%)
- Large diameter of red blood cells going through a small diameter capillary means there is a large surface area of contact and more diffustion
- An average adult has 4-6 litres of blood. Blood it made up of';
- White blood cells
- Granulocyte
- These are phagocytic and engulf bacteria to fight infection. They have lobed nuclei
- Agranulocyte
- These produce antibodies and antitoxins to fight infection and provide immunity to diseases. They have spherical nuclei
- Granulocyte
- Platelet cells are involved with blood clotting
- Types of blood vessels
- Arteries
- Small, round lumen
- Increases resistance to blood flow, which in turn helps to maintain a high pressure as the blood gets furthur away from the influence of the heart
- Thick layer of smooth muscle in walls
- Needed to withstand the high pressure of blood coming from the heart
- Can contract to narrow the lumen furthur, helping to maintain pressure
- Needed to withstand the high pressure of blood coming from the heart
- Thick layer of elastic tissue fibres in walls
- These allow the artery walls to expand with each pulse of blood
- They undergo elastic recoil which pushes the blood onwards. This produces a unidirectinal flow, so the arteries don't need valves
- These allow the artery walls to expand with each pulse of blood
- All arteries carry deoxygenated blood except the pulmonary artery
- All arteries have blood with high pressure
- No arteries have valves (except aorta and pulmonary artery)
- Small, round lumen
- Arterioles
- Aterioles branch off from arteries and are similar in structure but have less elastic tissue and more smooth muscle
- This enables them to constrict and reduce blood flow through the tissue so it can be directed to where it is needed most
- During exercise more blood is required by the working muscle, blood is therefore redistributed around the body
- When the smooth muscle contracts this causes vasoconstriction (the lumen of the arteriole become narrower and restricts the blood flow through to the capillaries) - this happens in the gut
- When the smooth muscle relaxes, this is called vasodilation (the lumen become wider) and increases the blood flow through to the capillaries - happens in muscle and skin surface
- When the smooth muscle contracts this causes vasoconstriction (the lumen of the arteriole become narrower and restricts the blood flow through to the capillaries) - this happens in the gut
- During exercise more blood is required by the working muscle, blood is therefore redistributed around the body
- This enables them to constrict and reduce blood flow through the tissue so it can be directed to where it is needed most
- Aterioles branch off from arteries and are similar in structure but have less elastic tissue and more smooth muscle
- Capillaries
- Arterioles furthur subdivide into thin walled capillaries. The capillaries form a vast network which will penetrate all the tissues and organs of the body
- It is at capillaries that the exchange of materials between the blood and tissues actually takes place
- Blood from the capillaries collects in venules, which in turn empty blood into veins which return it to the heart
- It is at capillaries that the exchange of materials between the blood and tissues actually takes place
- There are millions of capillaries, they form a dense network of tissues
- Capillary walls have just one single layer of endothelial cells forming their structure so they are permeable to water and other dissolved substances like glucose
- The capillaries have a narrow lumen. This causes friction between the blood and the capillary walls which slows down the rate of blood flow
- Although capillaries are small in diameter, there are lots of them, so overall there is a large cross sectional area. This furthur reduces the rate of blood flow
- The capillaries have a narrow lumen. This causes friction between the blood and the capillary walls which slows down the rate of blood flow
- Capillary walls have just one single layer of endothelial cells forming their structure so they are permeable to water and other dissolved substances like glucose
- Arterioles furthur subdivide into thin walled capillaries. The capillaries form a vast network which will penetrate all the tissues and organs of the body
- Venules
- Veins
- Large, irregular shaped lumen
- Wide lumen offers less resistance to blood flow and since the blood the veins is under low pressure, it is not prevented from returning to the heart
- Thin walls with a thin layer of smooth muscle
- Less muscle to contract, so the lumen will not be narrowed and there will be no increase in resistance to blood flow
- Thin layer of elastic tissue fibre in wall
- No need to expand as there are no surges of blood and no need to contract
- Large, irregular shaped lumen
- Arteries
- Venous return
- As skeletal muscles contract, blood beyond the site of contraction is forced towards the heart, opening the valves
- Valves behind the site of contraction prevent blood from being forces away from the heart
- As skeletal muscles relax, blood pushes back against the valves, causing them to close and prevent the blood from being forced away from the heart again
- Valves behind the site of contraction prevent blood from being forces away from the heart
- Blood is returned to the heart due to;
- Residual pressure of blood during ventricular systole
- Massaging effect of skeletal muscles on veins
- Negative pressure in the pressure during inspiration
- Negative pressure due to atrial diastole
- As skeletal muscles contract, blood beyond the site of contraction is forced towards the heart, opening the valves
- Exchange of materials from capillary to tissue fluid is possible because;
- Blood entering the capillary network through arterioles is under high pressure
- The endothelial cells 'fit' together loosely, leaving small spaces through which materials in the blood can be forces out by the high hydrostatic pressure of the blood
- The leakage furthur decreases the rate of blood flow
- Blood
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