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Circulatory System
Circulatory System of Mammals
| Question | Answer |
|---|---|
| What is meant by double circulation? | Blood passes twice through the heart in each complete circuit of the body. |
| These blood vessels carry blood away from the heart. | Arteries Arterioles - smaller arteries |
| These blood vessels carry blood towards the heart. | Veins Venules - smaller veins |
| The blood vessels link arteries to veins. | Capillaries |
| State the 3 main layers of blood vessels. | 1) Tunica intima (lining layer) 2) Tunic media ( middle layer) 3) Tunica adventitia (outer layer) |
| Describe the structure of the tunica intima. | A single layer of endothelial cells attached to a basement membrane. |
| Describe the structure of the tunica media. | A layer of smooth muscle and elastic fibres which vary in size depending on the type of blood vessel. |
| Describe the structure of the tunica adventitia. | A layer composed mainly of collagen fibres. |
| How does the thickness of the tunica media support the function of arteries? | This enables the artery to withstand high pressure of blood flowing within it. |
| How do the collagen fibres of the tunica adventitia support the function of arteries? | It enables the artery to stretch as blood flows through it. |
| How does the small lumen of arteries support their function? | This allows for greater thickness of the outer wall which prevents the arteries from bursting under pressure. |
| The tunica media of veins is thin. How does this support function? | Veins carry low pressure blood so they don't require thick walls to prevent bursting. |
| What is the function of collagen fibres in the tunica adventitia of veins? | To prevent bursting of the veins (mostly from external forces) than the blood within. |
| What is the purpose of semi-lunar valves in veins? | To prevent the backward flow of blood due to the low pressure of the blood. |
| State 5 key characteristics of capillaries. | 1) Their walls consist only of endothelium (one cell thick) 2) They are numerous and highly branched 3) They have a narrow diameter 4) Their lumen is narrow 5) There are spaces(pores/fenestrations) between endothelial cells |
| What makes up blood? | Plasma - 55% Blood cells (red, white and platelets) - 45% |
| What makes up blood plasma? | Water - 90% Chemicals (nutrients, waste products, mineral ions, hormones, plasma proteins and respiratory gases) - 10% |
| What is the function of blood plasma? | To transport chemicals (nutrients, waste products, mineral ions, hormones, plasma proteins and respiratory gases) from where they are produced or absorbed to the cells that use or excrete them. |
| What is the lifespan of a red blood cells? | Approx. 120 days. |
| Where are red blood cells made? | Bone marrow of certain bones (cranium, sternum, vertebrae and ribs) |
| State 4 organelles which are absent in mature red blood cells. | Nucleus, mitochondria, rough endoplasmic reticulum and Golgi body. |
| The absence of certain organelles gives RBCs a short life span. Give 3 ways this makes them more effective in transporting oxygen. | 1) Thin middle allows formation of a bi-concave shape giving larger surface area to volume ratio. 2) They can easily change shape, flatten against the capillary walls and shorten diffusion distance. 3) Greater room for haemoglobin which carries O2. |
| T or F. Red blood cells cannot pass through the pores of capillaries into the fluid that surrounds the cells of tissues but white blood cells can pass through even though they are usually larger. | T |
| Where are white blood cells made? | Marrow of limb bones |
| What is the main function of white blood cells? | Protect the body against infection |
| These white blood cells have a spherical shape and a large, compact spherical nucleus. | Lymphocytes |
| These white blood cells have irregular shape, multilobed nucleus and granular cytoplasm. | Neutrophils |
| There large white blood cells have an irregular shape with a large, kidney shaped nucleus. | Monocytes These later mature into macrophages with granular cytoplasm. |
| State the two groups into which white blood cells (leucocytes) can be subdivided. | 1) Phagocytes - these mainly include monocytes and neutrophils 2) Lymphocytes OR granulocytes and agranulocytes |
| Describe the composition of cardiac muscle. | Actin and myosin proteins. Many mitochondria to supply ATP. Muscle fibres made of myofibrils. |
| The thin walled elastic chambers which expand and collect blood. | Atria Sing. atrium |
| These chambers have thick muscular walls. | Ventricles |
| Why is the wall of the left ventricle thicker than the right? | The left ventricle has to contract more forcefully to pump high pressure blood to longer distances in systemic (body) circulation whereas the right ventricle pumps blood at lower pressure a short distance to the lungs (pulmonary circulation). |
| These valves are made of two cup shaped flaps, are found on the left side of the heart and prevent backflow of blood into the left atrium. | Left atrioventricular (bicuspid) valve |
| These valves are made of three cup-shaped flaps, are found in the right side of the heart and prevent the backflow of blood into the right atrium. | Right atrioventricular (tricuspid) valve |
| These special pillars of muscle are attached to the valves in the heart to prevent them from turning inside out under pressure. | Papillary muscle |
| These special heart wall fibres attach to papillary muscle which attach to valves. | Tendinous cords (chordae tendinae) |
| This blood vessel is connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs. | Aorta |
| This blood vessel is connected to the right atrium and brings deoxygenated blood back from the tissues of the body. | Vena cava |
| This blood vessel is connected to the right ventricle and carries deoxygenated blood to the lungs. | Pulmonary artery (unusual since arteries do not usually carry deoxygenated blood) |
| This blood vessel is connected to the left atrium and brings oxygenated blood back from the lungs. | Pulmonary vein (unusual since veins do not usually carry oxygenated blood) |
| What is the cardiac cycle? | One complete rhythmic cycle of pumping and filling of the heart i.e. a heartbeat. |
| What is cardiac output? | It is the volume of blood pumped by the ventricles each minute. Unit : dm3/min. Cardiac output = heart rate x stroke volume |
| What is heart rate (i.e. rate of contraction of heart)? | The number of beats per minute |
| What is stroke volume? | Volume of blood pumped by a ventricle during a single contraction. |
| Give a general outline the systole (contraction) and diastole (relaxation) actions of the heart in one cardiac cycle. | 1) Both left and right atria contract (ventricles relax) 2) Both left and right ventricles contract (atria relax) 3) Atria and ventricles rest/relax. |
| What does myogenic mean in describing cardiac muscle? | Its contraction is initiated from within the muscle itself rather than by nervous impulses from outside (neurogenic), as is the case other muscles |
| This is a group of cells in the right atrium of the heart that stimulates the initiation of the heartbeat. | Sinoatrial node (SAN) / pacemaker |
| Outline the events which occur in the initiation and control of the cardiac cycle. | 1) Wave of excitation spreads from the sinoatrial node. 2) It reaches atria causing contraction then spreads to AVN 3) AVN passes wave of excitation down septum along Purkyne fibres to apex and up through the ventricle walls causing contraction. |
| This is a visual trace representation of the electrical current changes in the heart picked up by a cathode ray oscilloscope. | Electrocardiogram |
| What is a myocardial infarction? | Heart attack |
| What is fibrillation? | Irregular, disorganized contraction of heart. |
| If a heart stops, a defibrillator can be used to restart it. What does this do? | It aims to restore the natural rhythm of the heartbeat by electrical shock. |
| Name the 2 nerves which carry impulses from the brain to the SAN. | 1) Vagus nerve - which releases acetylcholine 2) Sympathetic nerve - which releases noradrenaline |
| What is the effect of acetylcholine on the cells in the SAN? | It makes the cells beat more slowly thus reducing heart rate. |
| What is the effect of noradrenaline (and adrenaline) on the cells in the SAN? | It makes the cells beat more rapidly thus increasing heart rate. |
| Name a few drugs which increase heart rate. | Digoxin, Advil (Ibuprufen), Caffeine etc |
| Name a few drugs which decrease heart rate. | Propanadol (a beta blocker drug usually given to people with angina) etc |
| What is angina? | Chest pain which signals that the coronary arteries are not supplying enough oxygen to the heart muscle. |
| What is blood pressure? | The force of circulating blood against the walls of the arteries (force acting on blood vessels). Both systolic and diastolic pressure are taken into account. |
| What is systolic pressure? | The maximum pressure produced as a result of the contraction of the left ventricle of the heart. |
| What is diastolic pressure? | The lowest pressure caused by the relaxation of the ventricular muscle in the heart. ( More significant in indicating the condition of heart health than systolic pressure) |
| A persistently high diastolic pressure in a person at rest is known as | hypertension (high blood pressure) |
| This device is used to measure blood pressure | sphygmomanometer |
| What is the value for normal blood pressure (systolic/diastolic) in mmHg at rest? | 120/80 mmHg |
| What is the value for pre-hypertension (systolic/diastolic) in mmHg at rest? | 120-139/80-89 mmHg |
| What is the value for high blood pressure (systolic/diastolic) in mmHg at rest? | 140-159/90-99 mmHg |
| State 3 factors which influence blood pressure. | 1) Cardiac output - how much blood the ventricles pump in a given time. 2) Resistance to blood flow - e.g. narrowing of blood vessels during vasoconstriction 3) Total volume of blood being pumped |
| State 3 ways in which blood pressure is increased. | 1) Increased cardiac output e.g. during exercise 2) Increased resistance to blood flow e.g. by narrowing of arteries during vasoconstriction OR reduced elasticity due to atherosclerosis. 3) Increased blood volume e.g. due to water retention by ADH |
| State 3 ways in which blood pressure is decreased. | 1) Decreased cardiac output e.g. rest or sleep 2) Decreased resistance to blood flow e.g. during widening of arteries in vasodilation 3) Decreased blood volume e.g during loss of blood due to haemorrhage or water loss. |
| State 4 conditions for which hypertension is a risk factor. | 1) Heart disease 2) Atherosclerosis 3) Stroke 4) Kidney failure |
| List 6 factors which can lead to hypertension. | 1) Smoking 2) Excessive alcohol intake 3) Excess salt in diet 4) Stress 5) Obesity 6) Lack of exercise |
| What is a pulse? | These are pressure bulges, passing in sequence along arteries. It is the stretch and recoil of arteries as blood is forced into them by the contraction of the heart; can be felt at pressure points e.g. at the wrist. |
| What is pulse rate? | The number of heart beats in one minute |
| What is haemoglobin? | The pigment in red blood cells which is primarily responsible for carrying oxygen. |
| List 3 roles of haemoglobin. | 1) Transporting O2 2) Transporting CO2 3) Buffering the blood |
| How many oxygen atoms can combine with haemoglobin molecule (each contains 4 haem groups)? | 8 atoms 4 (O2 molecules) Reaction of one haem group shown: Hb + O2 -> HbO2 deoxyhaemoglobin + oxygen -> oxyhaemoglobin |
| What is the partial pressure of a gas ? | The amount of a gas present in a mixture of gases (i.e. the concentration of a gas) Unit: kPa |
| What is loading of haemoglobin and where does it occur? | The collection/picking up of oxygen at the lungs (gaseous exchange surface). |
| What is unloading of haemoglobin and where does it occur? | The release/donation of oxygen to tissues which need it. |
| What is the Bohr effect? | The property of haemoglobin to change its affinity for oxygen in different concentrations of carbon dioxide. The greater the concentration of carbon dioxide, the more readily haemoglobin releases oxygen to tissues in need. |
| What is an oxygen dissociation curve? | It is a graph showing oxygen saturation of haemoglobin (loading and unloading) against different partial pressures of oxygen |
| The oxygen dissociation curve is sigmoid (S-shaped). Why is the initial part of the curve shallow (not very steep)? | Haemoglobin's shape makes it difficult for the first O2 molecule to bind to any haem group on its four polypeptide chains as they are closely united. At low oxygen concentration, little oxygen binds to haemoglobin. |
| Why does the curve steepen? | After 1st O2 is added, shape of haemoglobin molecule changes so the rest of the O2 molecules bind easier (positive cooperativity). |
| Why does the curve flatten again? | At high oxygen concentrations, most of the haemoglobin molecules are completely loaded with oxygen. It is less likely for a single O2 molecule to find an empty site to bind to. |
| T or F. It is relatively easy for the first three O2 molecules to dissociate as the partial pressure of oxygen decreases but it is much harder for the final molecule to dissociate therefore the % saturation of Hb never reaches 0% | T |
| What does the oxygen dissociation curve tell us about the nature haemoglobin? | Hb is an ideal molecule to load oxygen in the lungs, where the partial pressure of O2 is high, and unload oxygen to the respiring tissues, where the O2 partial pressure is low. |
| carbon dioxide (CO2) + water (H20) ->(carbonic anhydrase enzyme above arrow) | carbonic acid (H2CO3) |
| T or F. Carbonic acid lowers the pH of blood. | T |
| This effect is characterized by greater unloading of oxygen from haemoglobin when carbon dioxide production is increased. | Bohr effect |
| What is a buffer? | A substance that consists of an acid and a base and which forms a solution that minimizes changes in pH when other acids and bases are added to the solution. |
| How does haemoglobin act as a buffer in the blood? | H+ ions from the dissociation of carbonic acid (H2CO3 -> H+ + HCO3- ) bind to amino acids in haemoglobin and thus minimizes changes in pH of the blood. |
| carbon dioxide + haemoglobin -> | carbaminohaemoglobin |
| carbon monoxide + haemoglobin -> | carboxyhaemoglobin |
| Why does haemoglobin have a reduced affinity for oxygen in the presence of carbon dioxide? | CO2 reacts with water to form carbonic acid which later dissociates into hydrogen and bicarbonate ions. The H+ ions combine with Hb to form haemoglobinic acid. This causes Hb to release the O2 which it was carrying. |
| What is the significance of the oxygen dissociation curve shifting to the LEFT? | Haemoglobin is binding to O2 (loading) at the lungs Factors in favour of left shift: High partial pressure of O2 Low partial pressure of CO2 /normal - high pH Decreased temp. |
| What is the significance of the oxygen dissociation curve shifting to the RIGHT? | Haemoglobin is releasing O2 (unloading) to body tissues Factors in favour of right shift: Low partial pressure of O2 High partial pressure of CO2/ low pH Increased temp. |
| T or F. Foetal haemoglobin has a much higher affinity for O2 than mother's haemoglobin and this allows sufficient O2 to be transferred. | T |
| What is the effect of increasing altitude on haemoglobin? | Increased altitude means reduced pressure. This makes loading haemoglobin more difficult. |
| T or F. Sudden increase in altitude can result in hypoxia (insufficient oxygen supply) and death. | T |
| What is acclimatisation with respect to haemoglobin and alititude? | It is the gradual adjustment of the body over a period of time (days to weeks) to maximize oxygen delivered to tissues as altitude increases. |
| Increase in the number of red blood cells occurs during acclimatization due to high altitude. State 2 ways in which this is achieved. | 1) After a few days, water is absorbed from the blood, concentrating the red blood cells and thickening the blood. 2) After 1-2 weeks, kidneys increase production of erythropoietin hormone which stimulates the formation of more RBCs from bone marrow. |
| Apart from an increase in RBCs, state 5 other ways in which the body can become acclimatized to high altitudes. | 1) Increase in cardiac output 2) Hyperventilation - increase in depth and rate of breathing 3) Increase in rate of exchange between alveoli and lung capillaries 4) Increase in haemoglobin concentration 5) Increase in level of myoglobin in muscles |
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CAPE Biology Unit 2
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