Features of a transport system
- A suitable medium, blood - carry materials.
- closed system of vessles contains blood - forms branching network for distribution.
- pump - heart - moving blood within vessels.
- valves - maintain flow in one direction.
- respiratory pigment - increases volume of oxygen to be transported.
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Open systems and closed systems
- Open blood system - blood pumped at low pressure from one main long, dorsal, tube-shaped heart running length of body.
- blood pumped out of heart into spaces - haemocoel - within body cavity.
- blood bathes tissues directly, exchange of materials takes place, little control over direction of circulation.
- blood returns slowly to heart.
- valves and waves of contraction of muscle wall move blood forward to head region - open circulation starts again.
- respiratory pigment is found rarely in insects - blood does not transport oxygen, transported directly to tissues via tracheae.
- larvae of certain midges known as a bloodworms that live in the bottom of muddy ponds do contain haemoglobin.
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Open systems and closed systems
- closed circulation system.
- blood circulates in continuous system of tubes - blood vessels.
- blood pumped by muscular heart at high pressure - rapid flow rate.
- organs not in direct contact with blood but bathed in tissue fluid - seeps out of thin walled capillaries.
- blood contains blood pigment - carries oxygen.
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- Single circulation:-
- Fish have single circulation.
- heart pumps deoxygenated blood to gills.
- oxygenated blood carried to tissues.
- deoxygenated blood returns to heart.
- blood goes once through heart during each circuit of the body.
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Transport in mammals
- Double circulatory system:-
- blood passes twice through heart for eacg complete circuit of body
- blood passed to lungs - pressure reduced - if blood pass from lungs to rest of body, circulation would be slow.
- blood returned to heart - pumped to rest of body - materials delivered quickly to body cells.
- Pulmonary circulation:-
- right side of heart pumps deoxygenated blood to lungs - oxygenated blood returns to left side of heart.
- Systematic circulation:-
- left side of heart pumps oxygenated blood to tissues - deoxygenated blood returns to tight side of heart.
- BLOOD PASSES THROUG HEART TWICE IN EACH CIRCUIT - through heart twice , once trhough right side and once through left side.
- Double circulation is more efficient than single circulation - oxygenated blood pumped around body at higher pressure.
- In fish pressure lost in capillaries of gills.
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Structure and function of blood vessels
- Arteries and Veins
- Basic three-layered structure.
- innermost layer - endothelium - one cell thick, provides smooth lining, to reduce friction and provide minimum resistance to flow of the blood.
- middle layer is made up of elastic fibres and smooth muscle - thicker in arteries than in veins to accomodate changes in blood flow and pressure as blood is pumped from heart.
- outer layer is made up of collagen fibres - resistant to over-stretching.
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Structure and function of blood vessels
- carry blood away from heart
- thick, muscular walls to withstand high pressure of blood recieved from heart.
- contraction of arterial muscles help maintain pressure as blood transported further from heart.
- Arteries branch into arterioles - subdivide into thin-walled capillaries.
- form a vast network which penetrates tissues and organs.
- blood from capillaries collects in venules.
- empty into veins - returned to heart.
- thin walled - one layer on endothelium - walls are permeable to water and dissolved substances.
- exchange of materials between blood and tissues.
- small diameter and friction with walls - slows blood flow.
- diameter is small - many capillaries in the capillary bed - large total cross-sectional area which reduces blood flow.
- low velocity in thin-walled vessels - enhances ability to exchange materials.
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Structure and function of blood vessels
- larger diameters and thinner walls than arteries - pressure flow reduced.
- veins have semi-lunar valves along their length to ensure flow in one direction.
- not present in arteries - only in aortic valves.
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- pump to circulate blood.
- consists of a relatively thin-walled collection chamber - partitioned into two, allowing separation of oxygenated and deoxygenated blood.
- heart is two separate pumps lying side by side.
- pump on left deals with oxygenated blood,
- each pump has two chambers - upper atrium and lower ventricle.
- consists largely of cardiac muscle - capable of rhythmical contraction and relaxation at own accord.
- heart muscle is myogenic.
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The cardiac cycle
- cardiac cycle describes sequence of events in one heartbeat.
- pumping action consists of alternating contractions (systole) and relaxations (diastole).
- Atrial systole:-
- right and left ventricles relax.
- tricuspid and bicuspid valves open as atria contract.
- blood flows into ventricles,
- Ventricular systole:-
- atria relax.
- right and left ventricles contract together forcing blood out of heart into pulmonary artery.
- aorta and semi-lunar valves opened.
- tricuspid and bicuspid valves closed by rise in ventricular pressure.
- pulmonary artery carries deoxygenated blood to lungs.
- aorta carries oxygenated blood to varous parts of the body.
- ventricles relax - pressure in ventricles falls.
- blood under high pressure in arteries causes semi-lunar valves to shut - prevents blood from going back to ventricles.
- blood from vena cavae and pulmonary veins enters atria - cycle starts again.
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Flow of blood throough left side of heart
- left atrium relaxed - recieves oxygenated blood from pulmonary vein.
- when full pressure forces open bicuspid valve between atrium and ventricle.
- relaxation of left ventricle draws blood from left atrium.
- left atrium contracts - pushing blood into left ventricle through valve.
- left atrium relaxed and bicuspid valve closed - left ventricle contracts.
- strong muscular walls exert strong pressure - push blood away from heart through semi-lunar valves through pulmonary arteries and aorta.
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Characteristics of cardiac cycle
- both sides of heart work together.
- both ventricles contract at the same time - both atria contract together - one complete contraction is a heart beat.
- after contraction and compartment has been emptied of blood, it relaxes, to be filled with blood once more.
- ventricles contain more muscle than atria - generate more pressure to force blood a greater distance.
- left ventricle has a thicker muscular wall than right ventricle as it pumps blood all round the body whereas right ventricle only pumps blood a shorter distance to the lungs.
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- prevent backflow of blood.
- atrio-ventricular valves - bicuspid and tricuspid.
- semi-lunar valves.
- valves in veins
- all have the same design and operate in the same way.
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Pressure changes in the heart
- highest pressure occurs in aorta/arteries that show rhythmic rise and fall corresponding to ventricular contraction.
- friction with vessel walls causes progressive drop in pressure - arterioles have large total surface area and narrow bore causing a substantial reduction from aortic pressure, there pressure depends on whether they are dilated or contracted.
- the extensive capillary beds have a large cross-sectional area, these beds create and even greater resistance to blood flow.
- there is a relationship between pressure and speed and pressure drops further due to leakage from capillaries and tissues.
- the return flow to heart is non-rhythmci and pressure in veins is low but can be increased by massaging effect of muscles.
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Control of heartbeat
- caridac muscle is myogenic.
- within wall of right atrium is region of specialised cardiac fibres called sino-atrial node - acts as pacemaker.
- wave of electrical stimulation arises at SAN, spreads over two atria causing them to contract more or less at the same time.
- electrical stimulation is prevented by spreading to ventricles by thin layer of connective tissue - acts as layer of insulation - important muscles of ventricles do not start contracting until muscles of atria have finished contracting.
- stimulation reaches another specialised region of cardiac fibres atrio-ventricular node - lies between two atria, passes on excitation to specialised tissues in ventricles.
- from AVN excitation passes down bundle of His to apex. Bundle of branches into Purkinje fibres in ventricle walls carry wave of excitation upwards through ventricle muscle.
- impulses cause cardiac muscle in each ventricle to contract simultaneously from apex upwards.
- ensures ventricles are emptied properly.
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- blood is a tissue made up of cells 45% in fluid plasma 55%
- Red Blood Cells:-
- red blood cells/erythrocytes contain pigment haemoglobin - transports oxygen from lungs to respiring tissue.
- bioconcave in shape - increases surface area of cell, enabling oxygen to diffuse quickly into or out of the cell.
- have no nucleus - more room for haemoglobin, maximising oxygen to be carried by each cell.
- White Blood Cells:-
- white blood cells/leurocytes larger than red blood cells, possess a nucleus, are either spherical or irregular in shape.
- Granulocytes - phagocytic, granular cytoplasm, lobed nuclei, engulf bacteria.
- Agranulocytes - produce antibodies and antitoxins, clear cytoplasm, spherical nuclei.
- 90% water, with soluble food molecules, waste products, hormones, plasma proteins, mineral ions and vitamins dissolved in it.
- transports CO2, digested food products, hormones, plasma proteins, fibrinogen, antibodies
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Transport of oxygen
- to be efficient at transporting oxygen haemoglobin needs to readily associate with oxygen at surfaces where gas exchange is taking place - lungs.
- readily dissociate from oxygen at tissues - muscle.
- change its affinity for oxygen in presence of CO2 by changing its shape - altered shape binds loosely with oxygen and releases it.
- when exposed to increasing partial pressure of oxygen haemoglobin shows an oxygen dissociation curve.
- at low concentration difficult for haemoglobin to absorb oxygen - once loaded associates readily with oxygen.
- at high partial pressures of oxygen - percentage saturation of oxygen is very high.
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Transport of oxygen
- Red Blood cells:-
- load oxygen in lungs where partial pressure is high and haemoglobin becomes saturated with oxygen.
- cells carry oxygen as oxyhaemoglobin to respiring tissues e.g. muscle - partial pressure is low, oxygen used up in respiration to create energy.
- oxyhaemoglobin unloads oxygen - dissociates.
- Graph of oxygen dissociation curve:-
- small decrease in partial pressure of oxygen leads to a lot of oxygen becoming dissociated from haemoglobin.
- the more the dissociation curve of haemoglobin is displaced to the left - more readily picks up oxygen, less readily it releases it.
- the more the dissociation curve of haemoglobin is displaced to the right - less readily picks up oxygen, more easily it releases it.
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Effects of carbon dioxide concentration
- at higher partial pressure of carbon dioxide the oxygen dissociation curve shifts to the right.
- this is known as the Bohr effect.
- when oxygen reaches respiring tissues, high partial pressure of carbon dioxide there enables haemoglobin to unload oxygen even more readily.
- when haemoglobin is exposed to a gradual increase in oxygen tension it absorbs oxygen rapidly at first but more slowly as tension continues to rise.
- release of oxygen from haemoglobin facilitated by presence of carbon dioxide - partial pressure of oxygen high, in lung capillaries, oxygen combines with haemoglobin to form oxyhaemoglobin.
- when partial pressure of oxygen is low - found in respiring tissues, oxygen dissociates from haemoglobin.
- when partial pressure of carbon dioxide is high - heamoglobin less efficient at associating with oxygen, more efficient at releasing it.
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Dissociation curve of foetal haemoglobin
- blood of foetus and mother flow closely together in placenta, rarely mix.
- to enable foetal haemoglobin to absorb oxygen from maternal haemoglobin in placenta and foetus has haemoglobin that differs from haemoglobin of adult.
- structural difference (two of four polypeptide chains) makes foetal haemoglobin dissociation curve shift to left od adults.
- foetal haemoglobin combines with oxygen more readily than mother's haemoglobin.
- foetal haemoglobin has a greater affinity for oxygen.
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Transport of oxygen in other animals
- many organisms possess haemoglobin and often have different forms of haemoglobin - this is related to the habitat in which they live, some animals have adapted to places of low O2.
- the lugworm has a low metabolic rate, lives in the sand on the seashore, lugworm pumps seawater through its burrow, giving access to limited amount of dissolved oxygen present, to load oxygen more readily it has haemoglobin with a dissociation curve, very much to the left compared with human haemoglobin dissociation curve.
- increase in altitude, drop in atmoshpheric pressure - significant in the llama, because partial pressure of oxygen in atmosphere is less at high altitude, to compensate for this the llama possesses haemoglobin which loads more readily with oxygen in the lungs. Haemoglobin has a dissociation curve to the left of normal haemoglobin.
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- far more stable than haemoglobin - will not release oxygen unless partial pressure of oxygen is extremely low.
- dissociation curve of myoglobin is far to the left of that of haemoglobin.
- at each partial pressure of oxygen, myoglobin has a higher percentage oxygen saturation than haemoglobin.
- if oxygen partial pressure becomes very low, when exercising, oxymyoglobin unloads its oxygen.
- oxygen held by myoglobin acts as a reserve - to be used in conditions of particular oxygen demand, sucg as sustained activity.
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Transport of carbon dioxide
- transported in blood cells and plasma in three ways:
- in solution in plasma 5%
- as hydrogen carbonate 85%
- in combination with haemoglobin to form carbamino-haemoglobin 10%
- Some carbon dioxide is transported in red blood cells, most is converted in red blood cells to hydrogen carbonate, the dissolved in the plasma.
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- Carbon dioxide diffuses into red blood cell and combines with water to form carbonic acid. Reaction is catalysed by carbonic anhydrase.
- Carbonic acid dissociates into H+ and HCO3- ions, HCO3- ions diffuse out of RBC into plasma where they combine with Na+ ions from the dissociation of sodium chloride to form sodium hydrogen carbonate.
- H+ ions provide conditions for oxyhaempglobin to dissociate into oxygen and haemoglobin.
- H+ ions are buffered by their combination with haemoglobin and the formation of haemoglobiniv acid - HHb.
- oxygen diffuses out of RBC into the tissues.
- to balance outward movement of negatively charged ions, chloride ions diffuse in.
- it is by this means that the electrochemical neutrality of the RBC is maintained.
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- capillaries are site of exchange between blood and cells of the body. They are adapted to allow exchange of materials between blood and the cells.
- thin permeable walls.
- provide large surface area for exchange of materials.
- blood flows very slowly through the capillaries allowing time for exchange of materials.
- blood consists of fluid plasma that carries blood cells, dissolved materials and large molecules, plasma proteins.
- blood contained in closed system but fluid from plasma escapes through walls of capillaries - tissue fluid bathes cells, supplying them with glucose, amino acids, fatty acids, salts and oxygen.
- tissue fluid also removes waste materials from the cells.
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- factors of movement of solutes and water in and out of capillaries are blood pressure and diffusion.
- blood reaches arterial end of a capillary under pressure due to pumping action heart and resistance to blood flow of capillaries, hydrostatic pressure forces fluid of blood through capillary walls into spaces between cells.
- outward flow is opposed by reduced water potential of blood, created by presence of plasma proteins.
- hydrostatic pressure of blood greater than osmotic forces, net flow of water and solutes out of blood.
- at arterial end of capillary bed diffusion gradient for solutes such as glucose, oxygen and ions favours movement from the capillaries to tissue fluid, substances used during cell metabolism.
- at venous end of capillary bed, blood pressure is lower and water passes into capillaries by osmosis, reduced water potential of blood created by presence of plasma proteins causes a net inflow of water.
- at venous end tissue fluids pick up CO2 and other excretory substances, some fluid flows back to capillaries, some drains into lymphatic system, returned eventually to venous system via thoracic duct, empties near the heart.
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