multicellular organisms - mammalian circulatory system

Question 1

functions of the double circulatory system

Answer 1

-transportation of water, oxygen and carbon dioxide
-distribution of nutrients and removal of wastes
-maintenance of body temperature
-circulation of hormones

Question 2

plasma

Answer 2

-55% of blood, the liquid aspect
-pale-yellow fluid component of the blood with which the solid blood components, along with body heat, dissolved gases, nutrients, wastes and hormones, are transported around the body

Question 3

erythrocytes (red blood cells)

Answer 3

-contains haemoglobin, a molecule that enables the cell to bind oxygen molecules
-do not have a nucleus in their mature stage, allowing the cell to carry more haemoglobin

Question 4

leukocytes (white blood cells)

Answer 4

-function mainly to protect the body against invading micro-organisms and toxins
-some types destroy micro-organisms by engulfing them and then using enzymes to digest the micro-organism and the leukocyte itself; others are specialised in producing antibodies that are an important part of the body’s immune system

Question 5

platelets

Answer 5

-function primarily to initiate blood clotting; when the platelet membrane breaks, the platelet releases a substance that reacts with proteins in the plasma to create a mesh of fibres, preventing further blood loss

Question 6

red blood cells and oxygen transport

Answer 6

-red blood cells are produced in the bone marrow. just before they are released from the bone marrow and move into the circulatory system, their nucleus breaks down
-this makes them pliable and elastic so that they can twist and flex as they move through blood vessels that are sometimes narrower than their unbent size, lack of nuclei also allows more space to carry oxygen
-main function of red blood cells is to carry oxygen and, to a lesser extent, carbon dioxide
-normally only about 0.3 mL of oxygen can dissolve in 100 mL of blood. however, red blood cells have an iron-containing pigment called haem and a special protein called globin, which gives them their red colour
-haemoglobin enables blood to carry about 20 mL of oxygen per 100 mL of blood. This is about the same as the proportion of oxygen in air

Question 7

blood and carbon dioxide transport

Answer 7

-cellular respiration in each cell produces carbon dioxide as a waste product. its removal ensures the cell pH level is maintained for optimal function
-just as the bloodstream can deliver oxygen to every cell in the body, it can also remove carbon dioxide from every cell in the body
-carbon dioxide is quite soluble and reacts with water to form carbonic acid. normally a slow reaction, however, in red blood cells the enzyme carbonic anhydrase speeds up the reaction
-carbonic acid produced diffuses into the plasma. approximately 70% of the carbon dioxide produced by cells is carried as carbonic acid in the plasma back to the lungs
-rest is either carried in the plasma as carbon dioxide (7%) or attaches to haemoglobin in red blood cells (23%)
-as the blood passes through the lungs, the concentration gradient for carbon dioxide between the lungs and the blood causes the previous reactions to reverse. carbonic acid reverts back to carbon dioxide and water
-the carbon dioxide leaves the internal environment of the blood, passing into the external environment of the lungs where it and the water are exhaled

Question 8

major organs of blood vessels

Answer 8

-driving force behind the blood flow around the mammalian body is the heart, so all vessels must be connected to this organ. three main types of blood vessels
-arteries take blood away from the heart
-veins carry blood towards the heart
-capillaries are found between these two blood vessels
-arterioles are smaller arteries and venules are smaller veins; both act as continuous bridges between the larger vessels and capillaries
-therefore, the major organs of the circulatory system are the heart, arteries, arterioles, veins, venules and capillaries

Question 9

arteries

Answer 9

-walls of the artery are thicker than those of the vein. this is because arteries have a lot more muscle and elastic fibres than veins
-muscle and fibre tissues of the arteries lead to the production of blood pressure as the heart beats, and forces the blood through the narrow central cavity
-arteries swell as each wave of blood is ejected from the heart, then recoiling elastically to propel the blood further on

Question 10

veins

Answer 10

-have valves in them to help keep the blood flowing towards the heart. this knowledge can be applied, by people who have to stand still for a long time in hot weather (such as soldiers on parade)
-sometimes feel faint, because too much blood is staying in the veins in their legs. because the blood is not returning to the heart quickly enough, the brain is deprived of enough oxygenated blood
-by continually contracting and relaxing the muscles in their legs (e.g. by wiggling their toes), they can move the blood up to their hearts and avoid fainting

Question 11

capillaries

Answer 11

-have very thin walls and are very narrow. in fact, their walls are only one cell thick.
-makes it possible for diffusion of all the nutrients that a cell needs, such as glucose and oxygen, to occur
-wastes, such as carbon dioxide and urea, are also able to pass through their walls, but in the other direction – from the cells to the blood
-diameter of capillaries is about the same as or smaller than a red blood cell, which further increases the diffusion rate of gases
-capillaries are so numerous and so small that every cell in the body is only a few millimetres away from a capillary

Question 12

circulatory pump - the heart

Answer 12

-blood is pumped around the body by the heart. heart is made of muscle and, in humans, it can contract continuously about 70 times a minute, day and night, for as long as we are alive
-cardiac tissue is found only in the heart, the coordinated contractions of cardiac muscle that provide the pumping action of the heart
-heart has four chambers. two are thin-walled atria (singular atrium) and the other two are the more muscular ventricles
-when you use a stethoscope to listen to the heart, it is the sound of the valves closing and the sudden stop of blood flow that you hear as ‘heart beats’. trained listeners can determine if particular valves are not shutting completely and if the timing of valve closure is abnormal

Question 13

process of the heart pumping

Answer 13

-deoxygenated blood enters the right atrium, via the vena cava, from the general body system of blood vessels, the systemic circulation, and passes into the right ventricle
-when the right ventricle contracts, blood is forced into the pulmonary artery, which leads to the lungs, called pulmonary circulation
-here, oxygen diffuses into the blood and carbon dioxide passes out from the blood into the air in the lungs. the now oxygen-rich or oxygenated blood passes back into the heart through the left atrium and then into the left ventricle
-when this ventricle contracts, the blood is forced into the aorta, the largest artery. through its many branches, the aorta takes blood to all parts of the body
-septum is the dividing wall that separates the right and left chambers of the heart, keeping the deoxygenated blood on the right side of the heart from mixing with the oxygenated blood on the left side
-blood is kept flowing in one direction in the heart by the presence of four valves: one between each atrium and ventricle (the two atrioventricular valves) and one between each ventricle and the artery it leads to (the pulmonary valve and the aortic valve)
-the two ventricles contract at the same time and the two atria contract at the same time, but the ventricles and atria contract at different times from each other. This leads to the two atrioventricular valves snapping shut at the same time as the ventricles contract
-pulmonary and aortic valves close when the ventricle finishes contracting, so that blood under pressure from the enlarged, elastic arteries does not flow back into the heart

Question 14

lymphatic system

Answer 14

-gases and small molecules entering the internal environment are not the only substances to pass through capillary walls
-blood pressure forces some fluid and some small protein molecules out of the capillaries at the arterial end
-most of the water from this fluid passes back into the capillaries at the venous end, where the blood pressure is lower, by osmosis
-some water and proteins would be left in the spaces between the cells if it were not for the lymph vessels
-lymphatic capillaries are small, blind-ending tubes that allow the fluid and protein to enter through tiny flaps between the cells in their walls that act as one-way valves
-fluid flows in the lymph vessels towards the heart to re-join the blood circulation. it is pushed along in much the same way as blood in the veins is moved, by contracting muscles. valves in the lymph vessel walls maintain a unidirectional flow to the heart