3.1.2 Transport in animals

Question 1

What is the need for transport systems in multicellular animals?

Answer 1

-single celled organisms can use diffusion across outer membrane to get substances but as organisms get bigger, the distance between cells and the outside gets greater and diffusion would be too slow

Question 2

What are the 4 main reasons animals have a specialised transport system?

Answer 2

1) to meet their high metabolic demands(need more O2+food and remove more waste products)
2) overcome smaller SA:V they have to absorb substances
3) maintain steep concentration gradients(rapid supply of glucose + oxygen and removal of CO2 especially for active animals)
4) allow diffusion across large distances(need energy from food for respiration+other metabolic processes)

Question 3

What do most circulatory systems have in common?

Answer 3

-liquid transport medium that circulate around the body(blood)
-vessels to carry transport medium
-pumping mechanism to move fluid around the system

Question 4

What is the circulatory system in mammals used for?

Answer 4

-to carry glucose and oxygen around the body
-to carry hormones antibodies(to fight disease) and waste products like CO2

Question 5

What happens in an open circulatory system?

Answer 5

• blood is pumped from the heart into cavities surrounding organs
  -in the haemocoel* the blood is under low pressure(pulmonary) so can come into direct contact with the with tissues and cells where exchange can take place between transport medium and cells and then medium truths to heart through open ended vessel
  *open body cavity

Question 6

Example of open circulatory system

Answer 6

some invertebrates have open circulatory system i.e insect:
-has segmented heart that contracts in a wave starting from the back—> pumps blood into a single main artery
-artery opens up into the body cavity
-blood flows around the insect’s organs, gradually making its way back into the heart segments through a series of valves
(haemolymph/blood doesn’t carry oxygen, only nutrients and white blood cells etc)

Question 7

What happens in a closed circulatory system?

Answer 7

-blood is continuously contained in vessels and doesn’t come directly into contact with body cells
-heart pumps blood under high pressure (systemic)
-substances leave and enter via diffusion through blood vessel walls(widening and narrowing control blood flow)

Question 8

Example of a closed circulatory system

Answer 8

all vertebrates i.e fish:
-heart pumps blood into arteries which branch out into millions of capillaries
-substances like oxygen and glucose diffuse from blood in capillaries to body cells BUT blood stays inside the blood vessels as it circulates
-veins take blood back to the heart

Question 9

What is a single closed circulatory system?

Answer 9

• blood passes through the heat once for each complete circuit of the body
  passes through 2 sets of capillaries before returning to heart:
  -1st, exchanges O2 and CO2
  -2nd, substances exchanged between blood + cells in other organ systems
• narrow vessels causes blood pressure to drop + blood returns to heart slow = limits efficiency so tend to have low activity levels

Question 10

Why do fish have an effective single circulatory system even though they are very active?

Answer 10

-have a countercurrent mechanism in gills that allows them to take a lot of O2 from the water = efficient gas exchange
-do not have to maintain own body temp because body weight supported by the water they’re in = reduces metabolic deman

Question 11

What is a double circulatory system?

Answer 11

(most efficient system to transport substances around the body)
- blood passes through the heart twice for each complete circuit of the body
-each circuit only passes through 1 capillary network; relatively high pressure + fast blood flow can be maintained

Question 12

Example of how double closed circulatory system works?

Answer 12

-birds and most mammals have this which allows them to be very active and maintain own body temp
- RIGHT SIDE: blood pumped from heart to lungs to pick up O2 and unload CO2 and returns to LEFT SIDE of heart
-LEFT SIDE: blood flows through the heart and is pumped out to travel all around the body before returning to the RIGHT SIDE of the heart again
(heart can give an extra push between lungs and rest of the body to make blood travel faster, so oxygen is delivered to tissues quicker)

Question 13

Elastic fibres

Answer 13

-composed of elastin and can stretch and recoil to maintain BP and provide vessel walls with flexibility

Question 14

Smooth muscle

Answer 14

contracts/relaxes, which changes size of the lumen and controls flow of blood

Question 15

Collagen

Answer 15

provides structural support to maintain shape + volume of blood vessel and resist changes in BP

Question 16

Artery

Answer 16

• carry blood from heart to rest if the body and have elastic tissue that recoils to maintain high pressure and overcome resistance of circulatory system
  -thick muscle layer which contacts and relaxes control blood flow
  -thick elastic fibres stretch and recoil to maintain high bp
  -thick arterial wall(with collagen to resist changes in pressure) to prevent bursting from high bp
  -no valves because bp is too high

Question 17

Arterioles

Answer 17

(smaller branches of arteries, from arteries to capillaries under low pressure)
-thicker muscle layer to reduce blood flow to capillaries(vasoconstriction to prevent blood flow and vasodilation to allow blood flow to capillary bed)
-thinner elastic tissue because they don’t need to maintain a high bp
-have intermediate collagen to resist bp
-no valves

Question 18

Capillaries

Answer 18

(arterioles branch into capillaries which are the smallest of the blood vessels, link arterioles and venules)
-substances are exchanged between blood and tissue fluid
-only have a thin endothelium and a narrow lumen
-provides a short diffusion distance
-they come in a large number(network) and are highly branched so they have a large SA for exchange

Question 19

How are capillaries adapted for their role?

Answer 19

-large SA for diffusion of substances in and out of the blood
-total cross sectional area is always greater than arteriole supplying them to lower rate of blood flow to give more time for diffusion
-walls are one cell thick, giving a very thin layer for diffusion

Question 20

Venules

Answer 20

(transport blood from capillary to veins under low pressure)
-has the same stricte and function of veins but are much smaller
-very thin walls that contain some muscle cells

Question 21

Veins

Answer 21

(carry mostly deoxygenated blood back to the heart under low pressure)
-lower bp—> valves prevent blood flowing backwards
-have relatively thin muscle layer as there is no need to control blood flow
-thin elastic wall as low bp needed
-venal wall is thin
-more collagen than arteries for structural support as they carry large volumes of blood

Question 22

How is the body adapted to pump blood under low pressure after veins return blood to heart?

Answer 22

-majority of veins have one way valves at intervals—> open so blood can pass through when blood flows in the direction of the heart + prevent back flow
-many of the bigger veins run between active muscles which squeeze veins when they contact, forcing blocks to the heart + valves prevent back flow when the muscles relax
-breathing movements of chest acts as a pump—> pressure changes and the squeezing actions move blood in the veins of the chest + abdomen towards heart

Question 23

What are the 4 main blood vessels in double closed circulatory systems?

Answer 23

-Pulmonary artery + aorta(away)
-Pulmonary vein + vein(towards)

Question 24

What kind of tissue is blood and how does that affect its role?

Answer 24

Blood is a connective tissue:
-connects all organs and transports substances(vitamins, minerals, ions, hormones, glucose, amino acids, oxygen + CO2 to respiring cells, waste products, antibodies, food molecules from storage compounds etc) between them
-contributes to maintenance of steady body temp and acts as a buffer to minimise pH change

Question 25

What does blood consist of?

Answer 25

-plasma
-platelets
-red blood cells
-white blood cells(leucocytes)–} neutrophils/lymphocytes

Question 26

Red blood cells

Answer 26

-4 to 6 mil per ml of blood
-45% of blood volume
-transports 02 in the blood via haemoglobin(carries iron)
-biconcave disc to increase SA and allow it to squeeze through gaps(flexible)
-no nucleus for more space to carry oxygen
-surface is covered with antigens integrally linked to membrane proteins/lipids that determine blood group

Question 27

White blood cells(leucocytes)

Answer 27

-around 1% of blood vol
-NEUTROPHILS: type of phagocytes, engulf and destroy pathogens and send signals to lymphocytes, contain digestive enzymes and multilobed nucleus
-LYMPHOCYTES: produce antibodies + antitoxins, T lymphocytes attach to and destroy cells that have been take over by viruses/are cancerous, B lymphocytes are a memory cell which retains which retains which antibody it produces is for what pathogen

Question 28

Platelets(thrombocytes)

Answer 28

-around 1% of blood
-small cell fragments made in the bone marrow
-cause blood clots by trapping blood cells
-contains enzymes released at the site of a cut
-converts soluble protein fibrinogeninto insoluble fibrinogen to form blood clot(prevent entry of microorganisms)

Question 29

Plasma

Answer 29

-55% of total blood vol(90% water)
-transports substances around the body
-CO2 from cells to lungs; urea from liver to kidneys; carries nutrients, hormones and proteins to parts of the body
-filtered blood plasma makes tissue fluid

Question 30

Tissue fluid

Answer 30

-fluid that surrounds cells in tissues to facilitate substance exchange between cells + blood
-made from substances that leave blood plasma i.e water, oxygen, glucose + ions
-doesn’t contain red blood cells or big/plasma proteins because they’re too large to be pushed out through capillary walls
-controls exchange of substances between blood and cells

Question 31

Oncotic pressure

Answer 31

-tendency of water to move into blood via osmosis due to the presence of proteins/solutes
-generated by plasma proteins i.e albumin cause a difference in water potential between the blood and tissue fluid therefore osmosis can occur(osmotic effect)
-ALWAYS -3.3kPa(positive pressure= move out of the blood, negative pressure= moves into the blood)

Question 32

Hydrostatic pressure

Answer 32

-exerted by fluid
-generated by heart contraction
changes according to location:
-arterial= 4.6kPa
-venous= 2.3 kPa
-pressure gradient because elastic tissue stretches to increase lumen size= reduces resistance to blood flow

Question 33

Pressure filtration

Answer 33

-Artery to arteriole has a high BP from the surge of blood every time heart ventricle contracts
-causes blood moving into arterial end of capillary to have a high hydrostatic pressure of around 4.6 kPa, greater than the oncotic pressure, around -3.3kPa, formed by plasma proteins(and greater than tissue fluid)
-the difference between hydro and oncotic pressure in capillaries forces(filtration pressure of 1.3kPa) fluid out of capillaries through fenestrations(open due to pressure) and into spaces between the cells to form tissue fluid
As fluid leaves, the hydrostatic pressure is much lower at the venule end of the capillaries
As water leaves, conc of plasma proteins increase and water potential decreases(generates oncotic pressure)
-As blood moves through capillaries towards venous system, hydro pressure falls lower than the oncotic pressure(-1kPa), because of the loss of fluid, so water/ net fluid moves back into the capillaries via osmosis because water potential in capillaries is lower than in the tissue fluid

Question 34

Lymph vessels

Answer 34

-some tissue fluid does not return to capillaries and gets returned to the blood via lymphatic system
-around 10% of liquid drains into capillaries called lymph which is similar to blood plasma but with less oxygen + nutrients (fatty acids absorbed from villi in small intestine), has more proteins because of antibody production via lymphocytes in the lymph nodes(enlarge when fighting off pathogen)
-capillaries join up to form larger vessels and have valves stop the lymph backflowing
-lymph gradually moves towards main vessels in the thorax where it is returned to the blood

Question 35

Red blood cell components

Answer 35

-has blood
-no tissue fluid
-no lymph
-red blood cells are too big to get through capillary walls into tissue fluid

Question 36

White blood cell components

Answer 36

-has blood
-very few tissue fluids
-has lymph
-most white blood cells are in lymph system, only enter tissue fluid when there’s an infection

Question 37

Proteins

Answer 37

-has blood
-very few tissue fluid
-only antibody lymph
(most plasma proteins are too but to get through capillary walls)

Question 38

Water

Answer 38

-has blood
-has tissue fluid
-has lymph
(tissue fluid and lymph have a higher water potential than blood)

Question 39

Dissolved solutes

Answer 39

-has blood
-has tissure fluid
-has lymph
(solutes i.e salts can move freely between blood, tissue fluid and lymph)

Question 40

The human heart

Answer 40

-consists of two muscular pumps that are joined and work together
-deoxygenated blood from the body flows in the right side of the heart which pumps it into the lungs
-oxygenated blood from the lungs returns to the left side of the heart which pumps it to the body(blood from 2 sides don’t mix)

Question 41

Features of the heart

Answer 41

-superior and inferior vena cava
-coronary artery(supply cardiac muscle with blood it needs to keep contracting and relaxing)
-right + left arteries
-right + left ventricle
-aorta
-vena cava
-pulmonary vein
-pulmonary artery

Question 42

Extra internal structures of the heart

Answer 42

-cardiac muscle
-tricuspid(right atrioventricular valve) + bicuspid(left atrioventricular valve), between atria and ventricles
-semilunar valves(sit between blood vessels and ventricles)
-septum(wall of tissue which separates heart in two halves)
-cartoid arteries
-cords(valve tendons)

Question 43

Specialised features of the heart

Answer 43

-muscular wall left side of the heart(especially ventricle) is much thicker and more muscular than the right, to push the blood around the body(force to overcome resistance of aorta and all arterial systems)
- lungs are close to the heart and is small so blood can be pumped a short distance
-septum is the inner dividing wall of the heart which prevents the mixing of deoxygenated and oxygenated blood

Question 44

Atrioventricular and semi lunar valves

Answer 44

-AV links the atria and the ventricles, and the semi lunar valves
SL link the ventricles to the pulmonary artery
-both stop blood flowing the wrong way so blood is unidirectional:
valves only open one way and closing + opening depend on the pressure of the heart chambers
-higher pressure behind valve= forced open
-higher pressure in front of valve= forced shut

Question 45

General cycle of the heart

Answer 45

-Deoxygenated blood enters right atrium from superior vena cava(upper body and head) and inferior vena cava(lower body) at low pressure BUT atria have thin muscular walls which builds up pressure as blood flows in
-AV(tricuspid) valve opens to let blood pass into right ventricle, when both filled the cardiac cycle occurs on right side(blood leaves through pulmonary artery)
-At the same time oxygenated blood enters left atrium through pulmonary vein, pressure forces AV(bicuspid) valve to let blood pass in, cardiac cycle occurs on left side(blood leaves through aorta)

Question 46

What is the cardiac cycle?

Answer 46

-ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body
-changes in volume and pressure maintain unidirectional movement of blood
-lasts about 0.8 seconds in a human adult

Question 47

Cardiac cycle stages

Answer 47

1)Ventricles are relaxed with relatively low pressure. Atria contracts(atrial systole) which increases pressure and decreases volume of chambers–} pushes blood through open AV valves. Slight increase in ventricular pressure and volume as it fills with blood and stretches ventricle walls.
2)Atria relax but ventricles contract which decreases volume and increases pressure higher than in the atria which forces AV to shut(prevents backflow). Pressure in the ventricles is higher than in aorta/pulmonary artery which forces SL valves open and blood is forced out arteries.(to capillary beds in lungs for right side)
3) Ventricles and atria relax. Higher pressure in pulmonary artey/aorta closes SL valves to prevent backflow into ventricles. The atrial pressure increases more than relaxed ventricle because blood returns to heart and enters atria again. AV valves open which allows blood to flow passively(without any contractions) into the ventricles, atria contracts and cycle restarts.

Question 48

What happens in the diastole?

Answer 48

-the heart relaxes–} atria and ventricles are relaxed and fill with blood, volume + pressure build up as blood fills but pressure in arteries is at a minimum

Question 49

What happens in the systole?

Answer 49

-the atria contact(atrial systole), which decreases the vol in the atria and increases pressure and remaining blood enters ventricles
followed by ventricles contracting(ventricular systole), ventricles contract which decreases vol and increases pressure
-pressure in heart increases dramatically and blood is forced out of the right side of the heart to lungs and out left side to main body circulation.
-Volume + pressure of the blood are low by the end of systole but BP in the arteries is at a max

Question 50

What causes the ‘Lub-Dub sound’?

Answer 50

-made by BP closing heart valves
-Lub= AV valves closing
-Dub= SL valves closing

Question 51

Reading a pressure changes graph

Answer 51

Aortic pressure= below the pressure in the ventricles until SL opens(lub) as ventricles contract and blood flows flows in the aorta. SL closes and pressure slightly dips(blood flows out)
Ventricular pressure= increases above aorta as ventricles fill with blood + AV close(thick muscle walls contract). Decreases below aortic when SL closes because ventricles empty and walls relax and falls below atrial when AV opens
Atrial pressure= always relatively low because thin walls can’t create much force. At its highest when it is contracting but drops when AV closes and walls relax, fills with blood and gradually increases in pressure until AV opens and blood moves in to ventricles

Question 52

Heart dissection PAG

Answer 52

-wear apron and gloves to maintain mess
-Place heart on dissecting tray and look at the outside of it to identify 4 main veins(pulmonary artery/vein, vena cava, aorta), veins feel much thinner than thick and rubbery arteries
-Identify right and left atria and ventricles and coronary arteries to draw external drawing of the heart(LABELLED)
-cut along lines of the heart with a clean scalpel
-can measure + record thickness of the ventricle walls and note differences
-cut open atria walls and compare thickness to ventricle walls
-find AV + SL valves and observe structure and how they open one way.
-Draw internal structure of heart and label it
-wash hands and disinfect surfaces once done

Question 53

Cardiac output(cm cubed min -1)

Answer 53

-volume of blood pumped by a ventricle in 1 minute
stroke volume x heart rate
-stroke volume= volume of blood pumped during each heartbeat in cm cubed
-heart rate= number of bpm

Question 54

How to read ventricular volume

Answer 54

-rises as the atria contract and the ventricles fill with blood, and then drops suddenly as blood is forced out into the aorta when the SL valve opens.
Volume increases again as the ventricles fill with blood again

Question 55

Endothelium

Answer 55

-smooth to reduce friction with the blood
-one cell thick to allow rapid diffusion

Question 56

How is the cardiac muscle myogenic?

Answer 56

-it can contract and relax without receiving signals from the nerves–} it has its own intrinsic rhythm around 60 bpm
-rhythm prevents body wasting resources to maintain basic heart rate

Question 57

Control of the heartbeat

Answer 57

(the pattern of contractions is maintained by a wave of electrical excitation)
- wave of electrical excitation starts in the pacemaker area called the Sino-atrial node(SAN) which sets out rhythm of the heartbeat by sending regular waves of electricity over atrial walls
- causes right and left atria to contract at the same time to initiate heartbeat
- layer of non-conducting collagen tissue prevents waves of electrical activity from being passed directly from atria to ventricles
- waves of electrical activity transferred to atrioventricular node (AVN) (responsible for passing waves to the bundle of His/ BOH)
- slight delay before AVN reacts to stimulate BOH, to make sure ventricles contract after atria empty
- BOH is a group of conducting tissue made up of muscle fibres(Purkyne fibres), which penetrate through septum between ventricles
- BOH splits into 2 branches and conducts wave to the apex(bottom of heart)
- There, the P fibres spread out through walls of both ventricles causing them to contract simultaneously from the bottom up(efficient emptying of the ventricles)

Question 58

What is an electrocardiograph?

Answer 58

-a machine that records the electrical activity of the heart(doctor can check someone’s heart function)
-heart muscle depolarises(loses electrical charge) when it contracts, and repolarises when it relaxes.
-records these changes in charge using electrodes placed on the chest

Question 59

Electrocardiograms(ECGs)

Answer 59

-the trace produced by an electrocardiograph that measures electrical charge differences which result from electrical activity of heart
-the signal from each electrode is fed into the machine to produce ECG
-can be used to help diagnose heart problems by comparing patient’s ECGs to a normal trace

Question 60

P wave, QRS complex and T wave

Answer 60

-P: represents contraction(depolarisation) of the atria in response to SAN
-QRS complex: represents ventricular contraction triggered by AVN
-T: represents relaxation(repolarisation) of ventricles
(height of a wave represents how much electrical charge is passing through the heart)

Question 61

Calculating heart rate

Answer 61

-can calculate this with an ECG and the equation:
heart rate(bpm)= 60 / time taken for one heartbeat (s)
-time taken for one heart beat is done by working out time between one wave i.e R wave and the next

Question 62

Heart rhythm abnormalities

Answer 62

-Tachycardia= heart beat is too fast at resting rate(around 120bpm)–} heart isn’t pumping blood efficiently
-Bradycardia= heart beat is too slow below 60bpm (may happen due to being fit as training makes heart beat more slow and efficient)–} severe cases may need an artificial pacemaker to keep heart beating steadily
-Ectopic heartbeat= extra heartbeat that interrupts normal rhythm. can happen occasionally but become serious when frequent
-Fibrillation= really irregular heartbeat, normally rapid. Atria or ventricles completely lose their rhythm and stop contracting properly so heart doesn’t pump blood very effectively

Question 63

Haemoglobin structure

Answer 63

-human Hb found in erythrocytes
-large globular conjugated protein made up of 4 polypeptide chains each containing a haem group(gives off iron and gives pigment)
-each molecule of human Hb can carry 4 oxygen molecules
-2 alpha and 2 beta subunits

Question 64

Advantages of carrying Hb in erythrocytes

Answer 64

-Hb is close to enzymes that maintain/vary pigment’s biding property
-Hb won’t affect osmotic pressure of plasma

Question 65

How are erythrocytes specialised for transporting oxygen?

Answer 65

-biconcave shape to have a larger SA for diffusion of gases + helps them pass through narrow capillaries
-have approximately 300 mill Hb for carrying oxygen
-formed continuously in the red bone marrow and by the time they mature + enter circulation they have lost their nuclei to maximise Hb that fits into the cells
-lasts around 120 days in the bloodstream

Question 66

How is oxyhaemoglobin formed?

Answer 66

-In the lungs, oxygen joins to the iron in haemoglobin to form oxyhaemoglobin loosely(association/loading)
reversible reaction
-near the body cells, oxygen leaves oxyhaemoglobin and turns back into haemoglobin(dissociation/unloading)
Hb + 4O2 ⇌ Hb(O2)4

Question 67

How is O2 transported in the blood?

Answer 67

-combined with Hb in red blood cel(more than 98%)
-dissolved in blood plasma(less than 2%)

Question 68

Co operative binding

Answer 68

likelihood to bind
-when 4 O2s are bound to Hb, it is 100% saturated and with less O2s it is less saturated
-Hb’s affinity for O2 increases as its saturation increases

Question 69

Affinity for O2 and pO2

Answer 69

-when RBC’s enter capillaries in the lungs, there is a higher pO2 in the alveoli than in the RBC which creates a steep conc gradient
-O2 loads onto Hb to form oxyhaemoglobin and there is a conformational change in shape of Hb as soon as the first O2 molecule binds to a haem group(positive cooperativity)
-steep conc gradient maintained until fully saturated but when cells respire, they use up oxygen which lowers pO2
-RBC’s deliver oxyhaemoglobin to respiring tissues, where conc of O2 in cytoplasm of body cells is lower than RBC so it unloads
-once first oxygen moleculeis released by Hb, molecule changes shape and it becomes easier to remove remaining oxygen molecules
-Hb then returns to lungs to pick up more O2

Question 70

What is partial pressure?(pO2)

Answer 70

-measure of oxygen conc
-the greater dissolved oxygen, the higher the pO2 so more affinity
-measured in kPA

Question 71

What Hb’s affinity depend on?

Answer 71

-partial pressure of O2(higher= takes on CO2)
-partial pressure of CO2(higher= takes on O2)

Question 72

Alveoli vs Respiring tissue

Answer 72

-Alveoli: high oxygen conc, high pO2, high affinity, oxygen loads
-Respiring tissue: low oxygen conc, low pO2, low affinity, oxygen unloads

Question 73

Oxygen dissociation curve

Answer 73

• shows how saturated Hb is with oxygen at any given partial pressure
  -at lower pO2, Hb has a lower affinity for O2 so difficult to load oxygen to haems
  -at higher pO2, Hb affinity increases because once one O2 molecule has attached, conformational shape occurs and it is easier for other molecules to join(positive cooperativity)
  -at very high pO2, Hb has a very high affinity so it becomes more saturated + it becomes harder for oxygen molecules to join and eventually plateaus when fully saturated(steep= small change in pO2 causes big change in amount of O2 carried by Hb)

Question 74

Fetal Hb

Answer 74

-when a fetus is developing in the uterus is completely dependent on its mother to supply it with oxygen for growth
-oxygenated blood from the mother runs close to the deoxygenated fetal blood in the placenta
-fetal Hb has a higher affinity for oxygen than adult Hb at each point along the dissociation curve
-by the time, the mother’s blood reaches the placenta, its oxygen has decreased because some has been used up by the mother’s body so the placenta has a low pO2
-removes oxygen from maternal blood as they move past each other

Question 75

The effect of CO2(Bohr effect)

Answer 75

-at higher pO2, oxyHb gives up more oxygen more readily at high pCO2 areas (gets more O2 to cells during activity)
-O2 curve shifts to the right
-this change is known as the bohr effect
-when cells respire, they produce CO2 which raises the pCO2 and therefore increases oxygen unloading(dissociation curve shifts right)
-Hb has lower affinity for O2 in areas of high pO2
important because:
-means that in active tissues with a high partial pressure of CO2, Hb releases oxygen more readily and has lower affinity(efficient aerobic respiration)
-in the lungs, where the proportion of CO2 in the air is relatively low, oxygen binds to Hb molecules easily and has higher affinity(transporting oxygen around the body)

Question 76

Transporting CO2

Answer 76

transported from the tissues to the lungs in 3 different ways:
-5% dissolved in plasma
-10-20% combined with amino groups on the polypeptides chains on Hb to form carbaminohaemoglobin
- 75-85% is converted into hydrogen carbonate ions then transported in plasma

Question 77

Carbon dioxide

Answer 77

-most of CO2 from respiring tissues diffuses into RBC
-some CO2 reacts with water and forms carbonic acid, catalysed protein carbonic anhydrase
-remaining 10% binds to Hb and carried to the lungs
-the carbonic acid is weak so it dissociates to form hydrogen and hydrogen carbonate ions(happens in blood plasma slowly but faster in RBC’s where there is more carbonic anhydrase)
-causes oxyhaemoglobin to unload oxygen so it takes up H ions forming haemoglobonic acid(reduce cell acidity, acts as buffer)
-hydrogen carbonate ions diffuse out of RBCs to the plasma so RBC maintains steep donc gradient
-Chloride shift: loss is compensated by chloride ions diffusing into red blood cells to maintain balance of charge between red blood cells and plasma(because hco3- is negative)
-opposite in the lungs