1.6 - 1.9 : circulation (not definitions) unit 1

why do large multicellular organisms need transport systems

they have small surface area to volume ration and high metabolic rate,therefore the rate of diffusion alone would not be fast enough to transport substances to where they are needed

give 4 examples of substances transport within organisms

• oxygen is transported in for respiration

• CO2 is transported out from respiration

• dissolved food molecules from digestion

• waste products such as urea in humans

give features of a mass transport system

• vessels

• transport medium

• a mechanism for maintaining a flow

what is the difference in function between veins , arteries , and capillaries

arteries carry blood away from the heart

veins carry blood towards the heart

capillaries flow close to tissues for exchange

describe the structure of arteries

they have thick walls made of muscle and elastic tissue and a small lumen to transport blood under high pressure

describe the structure of capillaries

they have thin walls about one cell thick to allow for the easy exchange of substance at the tissues

describe the structure of veins

veins have less muscle and elastic issue than arteries and they have a larger lumen as the blood is at lower pressure they also have valves to prevent backflow

what is the cardiac cycle

the sequence of events involved in one cycle of contraction and relaxation of the heart it involves 3 stages : atrial systole , ventricular systole and diastole

describe what happens during cardiac diastole

the heart is relaxed, blood enters the atria, increasing the pressure and pushing open the atrioventricular valves, this allows blood to flow into the ventricles , pressure in the heart is lower than in the arteries , so semilunar valves remain closed

which side of the heart receives blood from the body and pumps it to the lungs

the right side of the heart

which side of the heart receives blood from the lungs and pumps it to the body

the left side of the heart

why is the wall of the left ventricle thicker than the wall of the right ventricle

the left ventricle has to pump blood around the whole body so the blood needs to be at a higher pressure

describe the blood flow through the right side of the heart

• deoxygenated blood flows into the right atrium from the vena cava

• this blood passes through the right AV valve into the right ventricle

• the blood is then pumped out of the heart to the lungs through the right Sl valve and into the pulmonary artery

describe the blood through the left side of the heart

• blood enters into the left atrium from the pulmonary vein

• the blood is then pumped through the left AV valve into the left ventricle

• the blood is then pumped out through the left SL valve and into the the aorta

what is the function of the valves in the heart

the valves prevent backflow of the blood so that is only flows in one direction

relate the structure of the chambers to their function

• atria : thin walled and elastic, so they can stretch when filled with blood

• ventricles : thick muscular walls pump blood under high pressure the left ventricle is thicker than the right because it has to pump blood all the way around the body

relate the structure of arteries to their function

thick muscular walls to handle high pressure without tearing, elastic tissue allows recoil ,narrow lumen to maintain pressure

why are two pumps (left and right) needed instead of one ?

to maintain blood pressure around the whole body, when blood passes through the narrow capillaries of the lungs, the pressure drops sharply and therefore would not be flowing strongly enough to continue around the whole body , therefore it is returned to the heart to increase the pressure

describe the structure of erythrocytes and their function

biconcave shape, no nucleus , contain lots of haemoglobin, function is to carry oxygen

describe the structure of haemoglobin

haemoglobin is a globular conjugated protein which has a quaternary structure consisting of 2 alpha chains and 2 beta chains which each contain a haem prosthetic group which have iron ions that can bind to oxygen

describe the role of haemoglobin

present in red blood cells, oxygen molecules bind to the haem groups and are carries around the body to where they are needed in respiring tissues

how does partial pressure of oxygen affect oxygen haemoglobin binding

as partial pressure of oxygen increases , the affinity of haemoglobin for oxygen also increases , so oxygen binds tightly to haemoglobin, when partial pressure is low , oxygen is released from haemoglobin

state 3 ways that CO2 is transported in the blood

• some is transported combined with haemoglobin as carbaminohaemoglobin

• dissolved in the plasma

• as hydrogencarbonate ions (HCO-3) from the dissociation of carbonic acid

explain the bohr effect

as partial pressure of carbon dioxide increases , the conditions become acidic causing haemoglobin to change shape, the affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin

what do oxyhaemoglobin dissociation curves show

saturation of haemoglobin with oxygen (in %) , plotted against partial pressure of oxygen (in kPa) , curves further to the left show the haemoglobin has a higher affinity for oxygen

explain the role of carbonic anhydrase in the bohr effect

• carbonic anhydrase is present in red blood cells

• converts carbon dioxide to carbonic acid, which dissociates to produce H+ ions

• these combine with the haemoglobin to form haemoglobinic acid

• encourages oxygen to dissociate from haemoglobin

explain the role of bicarbonate ions (HCO-3) in gas exchange

produced alongside carbonic acid, 70% of carbon dioxide is carried in this form, in the lungs, bicarbonate ions are converted back into carbon dioxide which we breathe out

describe the chloride shift

the intake of chloride ions across a red blood cell membrane, this repolarises the cell after bicarbonate ions have diffused out