The Heart and Circulation - Pumping Blood
Blood flows around your body in blood vessels which make up the circulatory system.
Blood is pumped through by your heart, when it contracts blood is forced out and when it relaxes, blood fills up the blood.
Blood is pumped out in blood vessels called arteries.
The arteries branch out into capillaries which are the width of a red blood cell and go into organs.
When they leave the all come back together to form veins, pushing the blood to the heart.
The Heart and Circulation - The Heart
The heart is divided into two sides.
Each side has an upper atrium and a lower ventricle.
Each side has a valve allowing blood to flow from the atrium to the ventricle while preventing back flow.
Blood is returned to the heart by two veins the superior (from the brain) and inferior (from the rest of the body) vena cava and the pulmonary vein.
Blood is pumped out of the heart through two arteries, the aorta and pulmonary artery.
The Heart and Circulation - Double Circulation
The double circulation of the blood is as follows (it is called double circulation as the blood goes through the heart twice):
1. Blood from the right ventricle is pumped out to the lungs via the pulmonary artery.
2. In the lung tissue, oxygen diffuses in and carbon dioxide out of the blood making the blood from deoxygenated to oxygenated.
3. The blood the returns to the left atrium via the pulmonary vein.
4. Blood is pumped through the aorta and to the rest of the body.
5. Oxygen diffuses into cells for respiration and carbon dioxide is diffuses into the blood, making the blood from oxygenated to deoxygenated.
6. Deoxygenated blood is returned via the vena cava to the atrium.
Arteries have thick walls made of muscle and elastic tissue mostly. The arteries have high pressures.
The muscles contract to move the blood along and the elastic tissue expands so blood forced from the ventricles can get through. However the elastic tissue then recoils to keep the high pressures.
We can take people's pulse because when the heart contracts a surge of blood passes through the arteries causing the walls to bulge then relax. We can feel this in our wrists.
Veins have thinner walls and have low pressures. They have valves to stop flow-back
Capillaries are the smallest. Their walls are one cell thick so substances (carbon dioxide and other wast products, glucose and oxygen)can pass in and out of body cells easily .
Surgery of the Heart - Bypass and Stents
Oxygnated blood is caried to the eart muscles through the conorary arteries.
When someone has conorary heart disease they have a fatty layer making the arteries thinner, reducing the blood flow. Therefore the heart gets less oxygen.
In severe cases, blood flow ceases to part of the heart and the affected muscle tissues die, this is what is known as a heart attack.
There are two treatment methods; one is, bypass surgery where a vein from the arm, chest or leg is taken and creates a bypass around the blocked portion. The operation requires general anesthetic, up to seven days in hospital and three months for full recovery.
The second treatment is stents, stents are wires used to open an artery. At the beginning a balloon (attatcched to a tube called a catheter) is in inside the wire. It is inserted into a leg blood vessel and manipulated to the blocked conorary artery. The balloon inflates, the stent expands, locks into place and forms a scaffold, holding the artery open. The catheter is then removed. the stent then stays there permanently. Inserting the stent takes 1-2 hours under a local anesthetic, with just one night in hospital and patients can resume normal routine in a week. However, fatty substances are more likely to build up than in the bypass.
Surgery of the Heart - Replacing Heart Valves and
Heart Valves may become faulty through either the tissue stiffening, preventing the valve opening fully or a development of a leak.
Valaves can be replaced using other organism's valves or mechanical valves.
Mechanical valves have two semicircular carbon leaflets that pivot on hinges which swing open, parallel to the direction of the blood flow. They are strong and last a lifetime so are often used on young patients, however, they damage the red blood cells and increase the risk of a blockage, so to decrease this risk the patients must take drugs permanently after.
Biologically replacing the valve usually replaces the valve in the aorta with the patients pulmonary valve which is then given to the donor. Biological valves tend to harden with calcium deposits meaning after a while they do not open fully.
Some patients with heart disease canot be treated with stents or bypasses, for these patients there are two choices, a heart transplant or an artificial heart, artificial hearts have not been very successful and require both internal and external power supplies.
Transport Systems in Plants - Movement of Water in
Solutes in soil move to the cytoplasm of the plant roots by osmosis, moving from a high to low concerntration. The water then moves from the cells to others through the same process, moving the water to through the root to the centre of the root, the xylem tissue.
Evapourated qater moves out of the leaves through the cells by the air spaces, and diffueses from the stomata into the air. Once the water is removed from these cells, cells next to it diffuse their water. This continues until it gets to the xylem vein at the centre of the leaf.
Water travels through the xylem vessels, formed by the breakdown of the end walls of dead xylem cells forming long tubes and have thick rigid walls stopping them from collapsing.
The transpiration stream is where water is pulled all the way up the plant by water leaving the xylem to the leaf so that the water columns are pulled upwards as water molecules stick together.
The energy to do all of this comes from the sun which evapourates the water from the leaves.
Transport Systems in Plants - Vascular Bundles
The phloem, a plant tissue, transorts the sugar in a plant and is found next to the xylem tissue in vascular bundles.
Most of the suger is carried through sieve tubes which are similar to xylem vessels but the end walls don't break down completely. Instead form structures called sieve plates which don't have nuclei and are associated with living cells called companion cells. Companion cells assist in the movement of sugars through active transport.
Sugar is made through photosynthesis in the leaves and is then transported to all parts of the plants. It is then used in respiration for growth at the root of shoot tips.
Most plants store carbohydrates in underground roots or stems, like patatoes.
The phloem was discovered by Marcello Malphighi 300 years ago as he cut of the bark of a tree and after three weeks, there was swelling above the ring. The swelled tissue was rich in sugars. He said this showed that sugar was travelling down from the leaves to the roots.
He repeated the experiment in the winter and this time there was no swelling which he correctly said was because there were any leaves so no sugars could be transported.