WHY DO ANIMALS NEED A CIRCULATORY SYSTEM?
REFER TO SIZE, SA:V AND ACTIVITY.
- It is needed because of the size activity and SA:V ratio
- SIZE: AS the size of an organism increases so does the layer of cells. So if diffusion was to be used it would be used up by the first few cells. Therefore, to ensue every cell is reached a transport system is required.
- ACTIVITY: Animals release energy by respiration. Active mammals require large supplies of nutrients and O2 for movement and for keeping warm.
STATE THE KEY FEATURES OF A CIRCULATORY SYSTEM.
- Liquid transport medium.
- Vessels to carry the medium.
- Pumping mechanism to pump the fluid around.
- Open systems are found in insects etc, basically no closed vessels.
DESCIRIBE HOW AN ARETRY IS ADAPTED FOR ITS FUNCTION.
Small lumen maintains high pressure.
Thick walls with collagen to withstand high pressure.
Elastic fibres allows stretch and recoil.
Contraction is called vasoconstriction and relaxation is called vasodilation.
ARTERIOLES
Branch of arteries, they have thinner and less muscular walls. They have more smooth muscle and less elastin. Smooth muscles can enable vessel to vary blood flow. Lined with smooth endothelium to reduce friction and ease blood flow. They feed blood into the capillaries.
CAPILLARIES
Smallest blood vessels, site of metabolic exchange, only one cell thick for fast exchange of substances. This means red blood cells have to travel in a single file. Made of one layer of endothelial cells. Tiny holes allows water and certain solutes to pass through. Single cell diffusion
VENULE
Larger than capillaries but smaller than veins. Very thin walls with just a little smooth muscle. Feed blood out of capillary and back into veins.
VEINS
Carry blood to the heart. contains a wide lumen to maximise volume. Made of endothelium cells so the blood flows easier. Thin walled as blood is under lower pressure. Contains semilunar valves to prevent backflow of blood. Since there is no pulse there is little elastic tissue or smooth muscle as there is no need for stretching or recoiling.
SEMILUNAR VALVES
- Blood is pushed upwards by muscle contraction squeezing the blood upwards. This forces the valves to open. When the blood loses energy and moves back down and forces the valves to close. This ensures the prevention of backflow. sadness kills like any poison, penetrating deep into every crack, forcing open long forgotten wounds, creating new scars and sucking away every drop of life
COMPONENTS OF BLOOD
- Blood consists of a yellow liquid called plasma. This carried all the component of the blood including dissolved glucose, amino acids, mineral ions, hormones and plasma proteins. It also transports red blood cells and white blood cells, platelets.
FUNCTION OF BLOOD
The blood helps to transport:
- Oxygen and carbon dioxide to and from respiring cells.
- Digested food from the small intestine
- Nitrogenous waste products
- Hormones
- Food molecules from storage compounds to target cells.
- Platelets to damaged areas
- Cells and antibodies involved in immune response.
The blood also acts as a buffer to steady body temperature and pH buffer.
TISSUE FLUID
- The dissolved substances within the plasma can diffuse through the capillary walls expect for the large plasma proteins.
- The plasma proteins have an osmotic effect - gives a relatively high solute potential (low water potential - basically there’s more solutes than water because the rest of the stuff including the water will diffuse out)
- Therefore, water will move into the blood from the surrounding fluid by osmosis. The tendency for water to water to move in though osmosis is termed oncotic pressure.
- As blood flows from the arterioles into the capillaries it is still under pressure - hydrostatic pressure. This high pressure forces fluid out of the capillaries and into the surrounding fluid. So the fluid that is forced out and surrounds the cells is called the tissue fluid.
- As the blood moves along from the arterial end to the venous end the hydrostatic pressure drops making the oncotic pressure higher. This forces water into the capillaries.
LYMPH
- Some of the tissue fluid does not return to the capillaries and instead drains into another system known as the lymph capillaries. Here it is known as lymph. It is similar to tissue fluid but has less oxygen and fewer nutrients and more fatty acids that have been absorbed from the villi of the small intestine.
- The lymph is transported around by muscle contractions. Valves prevent backflow of the lymph. It eventually reaches back into the veins from the right and left subclavian.
- Along the lymph vessels are lymph nodes. Here lymphocytes build up when necessary and produce antibodies. These are then passed into the blood.
- Lymph nodes also intercept bacteria and debris from the lymph these are then ingested by the phagocytes.
TRANSPORTING OXYGEN
Erythrocytes are specialised to transport oxygen.
- Biconcave shape maximises surface area and allows them to pass through narrow capillaries. - No nucleus maximises amount of haemoglobin that fits into the cells. But it limits their life so they only last for 120 or so days. - They contain haemoglobin: red pigment that carries oxygen. This is a large globular protein made of four peptide chains each with an iron containing haem group. - When oxygen enters the capillaries in the lungs it has low oxygen levels. This makes a steep concentration gradient between the air in the lungs and the blood. - The haemoglobin molecules is packed very tightly so for the first oxygen to attach it is relatively difficult. However, as soon as the first is attached the quaternary structure loosens slightly making it easier for the third and fourth oxygens to enter - Positive Cooperation. The fourth oxygen does not usually bind because the structure becomes too 'full'. Because the oxygen binds to haemoglobin to form oxyhaemoglobin the free oxygen levels remain low in the blood mainlining a steep concentration gradient. - The reverse happens when the blood reaches the respiring cells. Because of the steep concentration gradient the first oxygen is released making it easier to remove the remaining oxygen.
THE EFFECT OF CARBON DIOXIDE
- As the partial pressure of CO2 increases, haemoglobin gives up oxygen more easily. This change is known as the Bohr Effect. This is useful in active tissues and in the lungs. In the lungs where carbon dioxide in the air is relatively low haemoglobin binds to the oxygen more easily.
- When the hydrogen ions are released from the disassociation of carbonic acid, it will compete for space on the haemoglobin. So when the carbon dioxide is present hydrogen ions will be released. H+ will displace oxygen and bind itself to the haemoglobin. This causes more oxygen to be displaced into respiring cells.
FOETAL HAEMOGLOBIN
- When the foetus is developing it is completely dependent on the mothers oxygen. The mothers oxygenated blood runs close to the baby’s deoxygenated blood in the placenta. If the foetal blood had the same affinity for oxygen that adults did little or no oxygen would diffuse through. To aid in development, foetal blood is specialised to have a greater affinity for oxygen allowing it to diffuse from the mothers blood to the placenta.
