Topic 1 - Lifestyle, health and risk Flashcards
Define an open circulatory system.
a. A simple heart pumps blood out into cavities surrounding the animal’s organs. Substances can diffuse between the blood and cells.
b. When the heart muscle relaxes, blood is drawn from the cavity back into the heart through small, valved, openings along its length.
Define a closed circulatory system.
a. Many animals, including all vertebrates, have a closed circulatory system in which the blood is enclosed within tubes – blood vessels. This generates higher blood pressure as the blood is forced along fairly narrow channels instead of flowing into large cavities. This means the blood travels faster and so the blood system is more efficient at delivering substances around the body.
b. The blood leaves the heart under pressure and flows along arteries and then arterioles to capillaries. There are extremely large numbers of capillaries. These come into close contact with most of the cells in the body where substances are exchanged between blood and cells.
c. After passing along the capillaries, the blood returns to the heart by means of venules and then veins, valves ensure the blood flows only in one direction.
Define a single circulatory system.
a. Animals with a closed circulatory system have either single or double circulation. Fish, for example, have single circulation.
i. The heart pumps deoxygenated blood to the gills.
ii. Gaseous exchange takes place in the gills; there is diffusion of carbon dioxide from the blood into the water that surrounds the gills, and diffusion of oxygen from this water into the blood within the gills. The blood leaving the gills then flows round the rest of the body before eventually returning to the heart.
iii. It is known as a single circulatory system as the blood flows through the heart once for each complete circuit of the body.
Define a double circulatory system.
a. Birds and mammals have a double circulation:
i. The right ventricle of the heart pumps deoxygenated blood to the lungs where it receives oxygen.
ii. 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.
b. As the blood flows through the heart twice for each complete circuit of the body, it is known as a double circulatory system. The heart gives the blood returning from the lungs an extra ‘boost’ that reduces the time it takes for the blood to circulate round the whole body.
c. This leads to birds and mammals having a high metabolic rate.
What is mass flow?
In the circulatory system a liquid and all the particles it contains are transported in one direction due to a difference in pressure in a process known as mass flow.
What does the transport medium in animals contain?
a. In animals the transport medium is usually called 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 breakdown of proteins, are some of the other substances transported in the plasma. Cells such as red blood cells, white blood cells and platelets are also carried in the blood.
b. Blood is not only important in the transport of dissolved substances and cells, but also plays a vital role in regulation of body temperature, transferring energy around the body.
What are the properties of water that make it a good transport medium?
a. Water is a polar molecule; the hydrogen end of the molecule is slightly positive, and the oxygen end is slightly negative because the electrons are more concentrated at that end. Therefore, water is said to be a dipole. Due to this dipole nature, water contains hydrogen bonding which leads to a high boiling point.
b. Due to its polar nature, other polar substances, as well as ionic and hydrophilic substances can easily dissolve in water.
c. Non-polar, hydrophobic substances such as lipids do not dissolve in water. To enable transport in blood, lipids combine with proteins to form lipoproteins.
d. Water also has a high specific heat capacity, a large input of energy causes only 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 bodies of water in which aquatic organisms live do not change temperature rapidly.
What is the heart made of?
The heart is a double pump and is made of cardiac muscle.
Define the structure of an artery.
a. The artery contains an outer coating – connective tissue with collagen, which is a tough fibrous protein, making them strong and durable. They also contain elastic fibres that allow them to stretch and recoil. They also contain smooth muscle cells in the walls which allow them to constrict and dilate. They also contain an endothelium layer.
b. Arteries contain a narrow lumen, thicker walls, more collagen, smooth muscle and elastic fibres and no valves.
Describe the structure of a vein.
a. The vein also contains an outer coating – connective tissue with collagen, a tough fibrous protein, making them strong and durable. They also contain elastic fibres that allow them to stretch and recoil. Additionally, they also contain smooth muscle cells in the walls which allow them to constrict and dilate. Like arteries they also contain an endothelium layer.
b. Veins contain a wide lumen, thinner walls, less collagen and smooth muscle, with fewer elastic fibres. They however also contain valves.
Describe the structure of a capillary.
The capillaries that join the small arteries (arterioles) and small veins (venules) are very narrow, about 10um in diameter, with walls that are only one cell thick.
How does the blood move through the vessels?
a. As 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 pressure generated as the blood is forced against the walls.
b. During diastole (relaxation of the heart), the elasticity of the artery walls causes them to recoil behind 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 blood through the arteries can be felt anywhere an artery passes over a bone close to the skin.
c. By the time the blood reaches the arterioles and capillaries there is a steady flow of blood. Blood flows more slowly in the capillaries due to their narrow lumens 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 rapid diffusion between the blood and surrounding cells.
d. The heart has a less direct effect on the flow of blood through the 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 back into the heart from the veins. Backflow is prevented by the semilunar valves within the veins.
How does the heart obtain a blood supply?
Since the heart is a muscle, it needs a constant supply of fresh blood carrying oxygen and glucose for aerobic respiration. The heart muscle does not obtain oxygen and nutrients from the blood inside its pumping chambers due to the large diffusion distances involved. Instead, the heart muscle is supplied with blood through its own coronary circulation; two vessels called the coronary arteries, a network of capillaries, and two coronary veins.
What is atrial systole?
a. Blood returns to the heart due to the action of skeletal and muscles involved in breathing as you move and breathe.
b. Blood under low pressure flows into the left and right atria from the pulmonary vein and vena cava.
c. As the atria fill, the increasing pressure of blood against the atrioventricular valves pushes them open and blood begins to leak into the ventricle.
d. The atria walls contract forcing more blood into the ventricles. The contraction of the atria is known as atrial systole.
What is ventricular systole?
a. After a slight delay, atrial systole is followed by ventricular systole. The ventricles contract from the base of the heart upwards, increasing the pressure in the ventricles.
b. The pressure forces open the semilunar valves and pushes blood up and out through the pulmonary arteries and aorta.
c. The pressure of blood against the atrioventricular valves closes them and prevents blood flowing backwards into the atria.
What is cardiac diastole?
a. The atria and ventricles then relax during cardiac diastole. Elastic recoil of the relaxing heart walls lowers pressure in the atria and ventricles. Blood under higher pressure in the pulmonary arteries and aorta is drawn back towards the ventricles, closing the semilunar valves and preventing further backflow in the ventricles.
b. The coronary arteries fill during diastole.
c. Low pressure in the atria helps draw blood into the heart from the veins.
How to calculate beats per minute from a graph?
a. Calculate the time it takes to complete one cardiac cycle.
b. Beats per minute = 60 / cycle time.
What is atherosclerosis?
a. Atherosclerosis is the disease process that leads to coronary heart disease and strokes.
b. In atherosclerosis fatty deposits can either block an artery directly or increase its chance of being blocked by a blood clot (thrombosis). The blood supply can be blocked completely. If it is not restored very quickly, the affected cells are permanently damaged. In the coronary arteries this results in a heart attack (myocardial infarction).
c. In the arteries supplying the brain it results in a stroke. The supply of blood to the brain is restricted or blocked, causing damage or death to cells in the brain.
d. Narrowing of arteries to the legs can result in tissue death and gangrene (decay).
e. An aneurysm can also form where an artery bursts due to a build-up of blood behind an artery that has been narrowed as a result of atherosclerosis.
What happens in atherosclerosis?
a. The endothelium, a delicate layer of cells that lines the inside of an artery and separates the blood that flows along the artery from the muscular wall, becomes damaged and dysfunctional for some reason. This endothelial damage can result from high blood pressure, which puts an extra strain of the layer of cells, or it might occur due to some of the toxins from cigarette smoke in the bloodstream.
b. Once the inner lining of the artery is breached there is an inflammatory response. White blood cells leave the blood vessel and move into the artery wall. These cells accumulate chemicals from the blood, particularly cholesterol. A fatty deposit builds up, called an atheroma.
c. Calcium salts and fibrous tissue also build up at the site, resulting in a hard swelling called a plaque on the inner wall of the artery. The build-up of fibrous tissue means that the artery wall loses some of its elasticity; in other words, it hardens.
d. Plaques cause the lumen of the artery to become narrower. This makes it more difficult for the heart to pump blood around the body and can lead to a rise in blood pressure. Now there is a dangerous positive feedback building up. Plaques lead to raised blood pressure and raised blood pressure makes it more likely that further plaques will form, as damage to endothelial tissue in other areas become more likely.
e. The person may be unaware of any problem at this stage, but if the arteries become very narrow or completely blocked, they cannot supply enough blood to bring oxygen and nutrients to the tissues. The tissue can no longer function normally, and symptoms will soon start to show.
Describe the clotting cascade reaction.
a. Rapid blood clotting is vital when a blood vessel is damaged. The blood clot seals the break in the blood vessel and limits blood loss and prevents entry of pathogens through any open wounds.
b. When platelets, a type of blood cell without a nucleus, come into contact with the damaged vessel wall they change from flattened discs to spheres with long thin projections. Their cell surfaces change, causing them to stick to the exposed collagen in the wall and to each other to form a temporary platelet plug. They also release substances that activate more platelets.
c. The direct contact of blood with collagen within the damaged blood vessel wall also triggers a complex series of chemical changes in the blood.
i. Platelets stick to damaged wall and to each other, forming a platelet plug. Platelets and damaged tissue release a protein called thromboplastin.
ii. Thromboplastin activates an enzyme that catalyses the conversion of the protein prothrombin into an enzyme called thrombin. A number of other protein factors, vitamin K and calcium ions must be present in the blood plasma for this conversion to happen.
iii. Thrombin then catalyses the conversion of the soluble plasma protein, fibrinogen, into the insoluble protein fibrin.
iv. A mesh of fibrin forms that traps more platelets and red blood cells to form a clot.
What happens inside arteries to cause blood clotting?
a. Usually blood does not clot inside blood vessels. Platelets do not stick to the endothelium (inner lining) of blood vessels. It is very smooth and has substances on its surface that repel the platelets.
b. However, if there is atherosclerosis and the endothelium is damaged, the platelets come into contact with the damaged surface and any exposed collaged. The clotting cascade will be triggered with the vessel resulting in a clot.
What are the consequences of atherosclerosis?
a. Coronary heart disease is one of the consequences of atherosclerosis.
i. Narrowing of the coronary arteries limits the amount of oxygen-rich blood reaching the heart muscle. The result may be a chest pain called angina. Angina is usually experienced during exertion when the cardiac muscle is working harder and needs to respire more. Because the heart muscle lacks oxygen, it is forced to respire anaerobically. It is thought that this results in chemical changes which trigger pain, but the detailed mechanism is still not known. Usually these symptoms will ease with rest.
ii. If a fatty plaque in the coronary arteries ruptures, collagen is exposed which leads to rapid clot formation. The blood supply to the heart may be blocked completely. The heart muscle supplied by these arteries does not receive any blood, so it is said to be ischaemic (without blood). If the affected muscle cells are starved of oxygen for long, they will be permanently damaged. This is what we call a heart attack or myocardial infarction. If the zone of dead cells occupies only a small area of tissue the heart attack is less likely to prove fatal.
b. A stroke is another consequence that could occur as a result of atherosclerosis.
i. If the supply of blood to the brain is only briefly interrupted, then a mini-stroke may occur. A mini stroke has all the symptoms of a full stroke but the effects last for only a short period, and full recovery can happen quite quickly. However, a mini stroke is a warning of problems with blood supply to the brain that could result in a full stroke in the future.
ii. If a blood clot blocks one of the arteries leading to the brain, a full stroke will result. If brain cells are starved of oxygen for more than a few minutes they will be permanently damaged, and it can be fatal.
Describe risk perception.
a. People will overestimate a risk if the risk is:
i. involuntary (not under their control)
ii. not natural
iii. unfamiliar
iv. dreaded
v. unfair
vi. very small
What are the different factors that contribute to health risks?
a. age
b. heredity
c. physical environment
d. social environment
e. lifestyle and behavioural choices
Define a cohort study.
a. Cohort studies follow a large group of people over time to see who develops the disease and who does not. These types of studies are prospective; at the start of the study none of the participants have the disease.
b. These types of studies may take a long time and can take years, so can be very expensive.
c. There are two ways a cohort study may be carried out. The first is where a large population of people are followed over a large period of time, and their exposure to certain risk factors are studied. Researchers then compare exposure to risk factors and look for correlations and draw conclusions between the group who develop the condition and who do not.
d. The second method is where a population is exposed to a specific risk factor is follow over a period of time and the population who is not exposed to the risk factor is followed over the same period of time. For each group there is usually a group who develops the condition and who do not develop the condition, outcomes are compared, and conclusions are drawn by researchers so any correlation between the risk factors and disease development can be identified.
Define a case-control study.
a. In a case-control study, a group of people with a disease (cases) are compared with a control group of individuals who do not have the disease. Information is collected about the risk factors that they have been exposed to in the past, allowing factors that may have contributed to development of the disease to be identified.
b. These types of studies are retrospective.
c. The control group should also be representative of the population from which the case group was drawn. Sometimes controls are individually matched to cases; known disease-risk factors, such as age and sex, are then similar in each case and control pair. This allows scientists to investigate the potential role of unknown risk factors.
d. The factors used to match the cases and controls cannot be investigated within the study, so it is important not to match any variables which could potentially turn out to be risk factors.
What must a study have?
A study must have:
i. A clear aim
ii. A representative sample
iii. A large sample
iv. Controlled Variables
v. Valid and Reliable results
What are some of the risk factors for CVD?
a. high blood pressure
b. obesity
c. blood cholesterol and other dietary factors
d. smoking
e. inactivity
f. genetic inheritance.
What is used to measure blood pressure?
A sphygmomanometer
What determines your blood pressure?
a. Contact between blood and the walls of the blood vessels causes friction and this impedes the flow of blood. This is called peripheral resistance.
b. The arterioles and capillaries offer a greater total surface area than the arteries, resisting flow more, slowing the blood down and causing the total blood pressure to fall. The greatest drop in pressure occurs in the arterioles. The fluctuations in pressure in the arteries are caused by contraction and relaxation of the heart.
c. As blood is expelled from the heart, pressure is higher. During diastole, elastic recoil of the blood vessels maintains the pressure and keeps the blood flowing.
What determines increasing or decreasing resistance in the blood vessels?
a. If the smooth muscles in the walls of an artery or an arteriole contract, the vessels constrict making the lumen narrower and increasing resistance. In turn, your blood pressure is raised. If the smooth muscles relax, the lumen is dilated, so peripheral resistance is reduced and blood pressure falls.
b. Any factor that causes arteries or arterioles to constrict can lead to elevated blood pressure.
Describe oedema.
a. One sign of high blood pressure is oedema – fluid building up in tissues and causing swelling. Oedema may also be associated with kidney or liver disease, or with restricted body movement.
b. At the arterial end of the capillary, blood is under pressure. This forces fluid and small molecules normally found in plasma out through fenestrations in the capillary wall into the intercellular space, forming tissue fluid, also known as the interstitial fluid.
c. Blood cells and larger plasma proteins stay inside the capillary; their larger size prevents them passing through the gaps in the capillary wall.
d. Tissue fluid moves back into the capillaries by osmosis. 20% of tissue fluid drains into blind-ended lymph capillaries. It flows through lymph vessels and returns the lymph fluid to the blood via the thoracic duct in the neck, which empties into the vena cava.
