Why do large animals need transport systems?
Animals need transport systems because......
- Size, They are much larger than cells and this means that any diffusion which occurs at the outer layers will be used by the first few cells.
- Surface are to volume ratio, the bigger something gets the lower the surface area becomes in comparison to the volume, this means that there is less area for diffusion to take place.
- Level of activity, they do alot more than smaller animals and require more energy.
Single circulatory system - In this blood travels in only one circuit to reach all key areas and goes throught the heart once....
i.e Heart - Lungs - Body
Double circulatory system - In this system blood travels through the heart twice before it reaches everywhere in the body, this means that only de-oxygenated blood travels to the lungs, and oxygenated blood travles to the muscles.
i.e Heart - Lungs - Heart - Body
Closed and open circulatory systems
Open system - This kind of system passes out of the heart and enters the body cavity directly.
Closed system - This kind of system passes through the body only in vessels.
Structure of the heart
Walls of the heart
Atria - The muscle of the atria are very thin, because not much pressure needs to be created.
Right Ventricle - The walls of the right ventricle are thinner than that of the left because the blood does not needed to be pumped far, the lungs are very close to the heart.
Left Ventricle - This has the thickest walls because it has to pump the most blood all around the body, this means it has to withstand high pressures and provide a lot of force.
The cardiac cycle
Stages of the cardiac cycle
Filling phase (Diastole) - This is the phase were the heart relaxes and this allows blodd to flow into the heart.
Atrial contraction (Atrial sytole) - Next the atria contract and this pushes blood through the atrioventricular valves.
Ventricular contraction (Ventricular systole) - The ventricles contract, this contraction starts at the apex of the heart and moves upwards forcing blood out of the heart.
(Rinse and repeat)
The co-ordination of the heartbeat
The order of action in a heartbeat...
- At the sinoatrial node (located by the vena cava at the top of the heart) a small wave of electricity is created and this moves down the walls of the heart.
- This wave of excitement causes the atria to contract when it reaches them first.
- Next it is carried away from the Atria, moving down specialised conducting tissue called Purkyne tissue this leads it to the apex of the heart.
- It causes the apex to contract and then moves up along the walls of the ventricles causing them to contract.
On a healthy ECG (Electrocardiogram) It should show a small pulse and then a very large pulse followed by a medium sized pulse.
These carry blood away from the heart.
- They have a relatively small lumen. This is used to maintain a high pressure.
- It contains a lot of elastic fibres, and this means it can stretch and recoil easily.
- The walls are very thick and conatin a fibrous protein to give it strength.
- The endothelium is folded and can unfold when the arteries are stretched.
- The walls contain smooth muscle so blood can be moved and these can also control the flow of blood.
Veins carry blood back to the heart unlike arteries their pressure is very low and this means that the blood has to move in a different way to arteries.
In arteries bloodflow relies upon the heart, in veins this is partly true residual pressure from the blood does move it but this pressure is small and it means you cannot see the effects of a heartbeat or feel a pulse. Veins rely upon the fact that they can be easily squished and this means that when they experience skeletal pressure the blood is moved.
- Veins have a large lumen to ease blood flow.
- Thin walls so that they are easily squashed.
- Valves so blood doesnt flow back into the muscles. Arteries do not contain these.
Capillaries are where the components of bllod can be exchanged with the muscles and this means that there walls have to be very thin to ease diffusion.
- Capillaries have very thin walls to ease diffusion.
- They also very narrow.
Since they are so thin they can withstand little pressure, so pressure must have eased from that found in the arteries, this is caused by.....
- Increasing distance from the heart.
- Friction of the artery walls.
Blood and Tissue fluid and Lymph
- Erythrocytes (Red blood cells)
- White blood cells
- This is part of the blood and is formed when it is forced out of the blood through holes in the capillary walls.
- This bathes the body cells and allows diffusion to take place.
- Not all of this tissue fluid returns to the body though some drains through the lymphatic system.
- The main difference is that it contains a lot of lymphocytes which it gets from lymph nodes, it uses these to destroy bacteria and filter the blood.
Haemoglobin, the chemical that is present in blood which allows oxygen to be transported throughout your body.
Each molecule of haemoglobin is made up of four haem groups (Fe2+) , these are said to have an affinity for oxygen. Each haem group can carry one molecule of oxygen.
Oxyhaemoglobin dissociation curve
What is it?
The oxyhaemoglobin dissociation curve shows the haemoglobins affinity for oxygen when different levels of oxygen are present in the surrounding fluid.
What does it show?
The curve shows that haemoglobins affinty for oxygen isn't directly proportional, unlike in a regular fluid.
This is because at the start of the s-shaped curve, haemoglobin is not the right shape to take up oxygen easily. Though as soon as it takes up one its shape changes and it can readily take up more oxygen, until it reaches the fourth haem group and it struggles to fill the final small space so the curve levels off.
Fetal haemoglobin as a slightly higher affinity for oxygen than adult haemoglobin this is because since a foetus is inside a human body it needs to be able to take oxygen directly from the parents blood (It does this using the placenta) so it needs a higher affinity for oxygen.
Haemoglobin carrying CO2
The Bohr effect
This shows that the more C02 present, the more oxygen will be released from the blood.