Topic 1 Flashcards
Why have a heart and circulation?
The heart and circulation have one primary purpose to move substances around the body.In very small organisms such as unicellular creatures where diffusion distances are short, substances such as oxygen, carbon dioxide and digestive products move around the organism by diffusion.
What is diffusion
Diffusion is the movement of molecules or ions from a region of a higher concentration to a region of a low concentration by relatively slow movement of molecules.
In unicellular creatures diffusion is usually fast enough to meet the organisms requirements.
Heart and circulation in complex organisms
Most complex multicellular organisms are too large for diffusion to substances around their bodies quickly enough. These organisms rely on a mass transport system to move substances efficiently over a long distance by mass flow. All the particles in a liquid move in one direction through tubes due to the difference in pressure.
What do animals have to move move vital substances around their body?
Animals usually have blood to carry vital substances around their bodies and a heart to pump it instead of relying on diffusion, in other words they have a Circulatory system
Open circulatory system
In insects and some other animal groups, blood circulates in large open spaces.A simple heart pumps blood out to the cavities surrounding the animals organs. Substances can diffuse between the blood and cells. When the heart muscle relaxes, blood is drawn from the cavity back into the heart through small, valved openings along its length.
Closed circulatory system
Many animals, including all verbrates, have a closed circulatory system in which blood is enclosed within tubes ( blood vessels). This generates higher blood pressures as blood is forced along fairly narrow channels instead of flowing into large cavities. This means that the blood travels faster and so the blood system is more efficient at delivering substances around the body.
How blood travels in close circulatory system
- The blood that leaves the heart is under pressure and flows along arteries and then arterioles (small arteries) to capillaries.
- These are extremely large number of capillaries. These come into contact with most the cells in the body where substances are exchanged between the blood and cells.
- After passing along the capillaries, the blood returns to the heart by the means of venules (small veins) and then veins.
- Valves ensure that blood flows in one direction.
Animals with close circulatory system are generally larger in size and often more active than those with open systems.
Single Circulatory system
Animals with a closed circulatory system have either single circulation or double circulation. Fish for example, have single circulation.
- The heart pumps deoxygentated blood to the gills.
- Gaseous exchange takes place in the gills; there’s a diffusion of carbon dioxide from the blood into to the water that surrounds the gills and a diffusion of oxygen from the water into to the blood within the gills.
- The blood leaving the gills then flows round the rest of the body before eventually returning to the heart.
Note that the blood flows through the heart once for each complete circuit of the body.
Double circulatory system
Birds and mammals have double circulation:
- The right ventricle of the heart pumps deoxygentated blood to the lungs where it receives oxygen.
- The oxygenated blood then returns to the heart to be pumped a second time (by the left ventricle) out to the rest of the body.
This means that blood flows through the heart twice for each complete circuit of the body.The heart gives the blood returning from the lungs an extra boost which reduces the time it takes for blood to circulate round the whole body.This allows birds and mammals to have a high metabolic rate, as oxygen and food substances required for metabolic processes can be delivered more rapidly to cells and meet the needs of the organism.
How does circulation work?
The transport medium
In the circulatory system a liquid and all the particles it contains are transported in one direction due to the difference in pressure in a process known as mass flow.
What is the transport medium in animals
In animals the transport medium is usually blood. The fluid plasma, is mainly water and contains dissolved substances such as digested food molecules, (e.g. glucose), oxygen and carbon dioxide.Proteins, amino acids, salts, enzymes, hormones, antibodies and urea ( the waste product from the break down of proteins) are just some of the other substances transported in the plasma.
Cells are also carried in the blood: red blood cells, white blood cells and platelets.
What other vital role does blood play apart from transport of dissolved substances and cells?
Blood is important not only in the transport of dissolved substances and cells, it also plays a vital role in the regulation of body temperature, transferring energy around the body.
Properties of water that make it an ideal transport medium:
- Water is a liquid at room temperature while most other small molecules, such as co2 and o2, are gases.
- Water is a polar molecule it has unevenly distributed electrical charge. The two hydrogens are pushed towards each other forming a V-shaped molecule. The hydrogen end of the molecules is slightly positive and the oxygen end is slightly negative beacuse the electrons are more concentrated at that end.
- Water is said to be a dipole it is this polarity that accounts for many of its biological important properties.
- The slightly positively charged end of the water molecule is attracted to the slightly negative ends of the surrounding water molecules. This hydrogen bonding holds the water molecules together and results in many of water including being liquid at room temperature.
Water also has solvent and thermal properties that make it an ideal transport medium
Solvent Properties of water
- Many chemicals dissolve easily in water due to their dipole nature allowing vital biochemical reactions to occur in the cytoplasm of cells.Free to move around in an aqueous environment, the chemicals can often react with water itself being involved in the reaction (hydrolysis and condensation reactions) . The dissolved substances can also be transported around organisms, in animals via the blood and lymph systems and in plants via the xylem and phloem.
- Ionic substances such as sodium chloride dissolve easily in water as the negative cl- ions are attracted to the positive ends of the water molecules while the positive Na+ ions are attracted to the negative ends of the surrounding water molecules. The chloride and sodium ions are hydrated in aqueous solution, they become surrounded by water molecules.
- Polar molecules also dissolve easily in water. Their polar groups, for example the -OH group in sugars or the amine group, -NH2, in amino acids become surrounded by water and go into the solution. Such polar molecules are hydrophilic ( Water attracting)
- Non- polar, hydrophobic substances, such as lipids, do not dissolve easily in water. To enable transport in the blood, lipids combine with proteins to form lipoproteins.
Thermal properties of water
The specific heat capacity of water the amount of energy joules required to raise the temperature of 1cm^3 of water by 1°C is very high. This is because in water a large input of energy is required to break the hydrogen bonds. A large input of energy only causes a small increase in temperature, so water warms up and cools down slowly.This is useful for organisms, helping them to avoid rapid changes in their internal temperature and enabling them to maintain a steady temperature even when the temperature in their surroundings varies considerably. This also means that the bodies of water in which aquatic organisms live do not change temperature rapidly.
Water also has a high boiling point because there are so many hydrogen bonds and a lot of them is needed to break them all.
The structure of blood vessels
-The walls of both arteries and veins contain collagen, a tough fibrous protein, which makes them strong and durable.
- They contain elastic fibres that allow them to stretch and recoil.
-Smooth muscles cells in the walls allows them to constrict and dilate.
The structure of Arteries, veins and capillaries
Arteries:
- narrow lumen
-thicker walls - more collagen smooth muscle and elastic fibres
- no valves
Veins:
- wide lumen
- thinner walls
- less collagen smooth muscle and fewer elastic fibres
- valves
Structure of Capillaries
The Capillaries that join the smaller arteries (arterioles) and smaller veins (venules ) are very narrow, with walls that are only one cell thick.
These features can directly relate to the function of blood vessels.
How does blood move through vessels ?
Every time the heart contracts ( systole), blood is forced into arteries and their elastic walls stretch to accommodate the blood.The thick artery walls can withstand the high blood pressure generated as blood is forced against the walls.
During diastole (relaxation of the heart) , the elasticity of the artery walls causes them to recoil the blood, helping to push the blood forward and smoothing blood flow. The blood moves along the length of the artery as each section in series stretches and recoils in this way.The pulsing flow of flow through arteries can be felt anywhere an artery passes over a bone close to the skin.
By the time the blood reaches the smaller arteries and capillaries there is a steady flow of blood.Blood flows more slowly in the capillaries due to their narrow lumen causing more of the blood to be slowed down by friction against the capillary wall. This slower steady flow allows exchange between the blood and the surrounding cells through the one-cell thick capillary walls. The network of capillaries that lies close to every cell ensures that there is a rapid diffusion between the blood and the surrounding cells.
The heart has less direct on the flow of blood through veins. Blood flows steadily and without pulses in veins where it is under relatively low pressure. In the veins blood flow is assisted by the contraction of skeletal muscles during the movement of limbs and breathing. Low pressure developed in the thorax ( chest cavity) when breathing in also helps draw blood into the heart from the veins. Backflow is prevented by the semilunar valves within the veins.