mass transport

haemoglobin

• a group of chemically similar molecules found in many different organisms

• hundreds packed into one RBC

• 2alpha and 2beta polypeptide chains

• quaternary structure

• 4 heme groups, each has an Fe2+

• each Fe+ combines with O2 to form oxyhaemoglobin

how is haemoglobin able to associate and dissociate with O2?

• by changing its affinity for O2 in different conditions

• by changing its shape in the present of some substances, e.g. CO2

how many O2 can bind to a haemoglobin molecule?

4

association and dissociation

• Hb + O₂ associated in lungs to make oxyhaemoglobin

• oxyhaemoglobin undergoes dissociation at respiring tissue to produce Hb + O₂

• in the presence of CO₂, the new shape of the Hb molecule binds more loosely to O₂ → therefore, Hb releases O₂

• binding of first O₂ changes tertiary/quaternary structure of Hb (conformational shift cause)

• uncovers another haem group to bind to

• allows more O₂ to bind more readily

how does haemoglobin transport O2 efficiently?

• readily associate with O2 at the lungs (gas exchange surface)

• readily dissociated with oxygen at the respiring cells

O2 concentration at gas exchange surfaces

high

CO2 concentration at gas exchange surfaces

low

the Bohr effect

• pCO2 affects oxygen dissociation

• when pCO2 is high (rapidly respiring cells) → pH decreases (acidic) → affinity of Hb to O2 is lower and low concentration of O2 → more O2 dissociated and can enter cells for aerobic respiration → curve shifts right

• (lungs) when pCO2 is lower → affinity of Hb to pO2 is greater and there’s a high concentration of O2 → less O2 dissociated → the curve shifts left

the Bohr effect - the more active a tissue is, the more O2 is unloaded

higher rate respiration → more CO2 tissues produce → lower pH → greater Hb shape change → more readily O2 unloaded → more oxygen available for respiration

partial pressure

the pressure of a gas compared to the total pressure of a mixture of gases

what is partial pressure measured in?

kiloPascals (kPa)

two factors that affect Hb’s affinity

1. pO2 or pCO2

2. saturation of the Hb with O2

what does an oxygen dissociation curve show?

the relationship between the pO2 and saturation of Hb with O2

oxygen dissociation curve

• at different partial pressures, haemoglobin doesn’t bind to O2 evenly

1. the first O2 doesn’t bind easily with the Hb (due to closely united polypeptide chains) → little O2 associates with Hb → the gradient of the curve is shallow

2. binding of the first O2 changes the tertiary and quaternary structure, making it easier for 2nd and 3rd O2 to associate to the haem group because more binding sites are exposed - positive cooperativity. a small increase in pO2 causes a big change in O2 saturation → the gradient is very steep

3. after the 3rd O2 is associated, the majority of the binding sites are occupied and the Hb is saturated → less likely that an O2 will find an empty binding site - a matter of probability → the curve plateaus

shape of dissociation curve

s-shape

% saturation of Hb with O2

(oxygenated haemoglobin / maximum saturation) x 100

respiring tissue

• low pO2

• haemoglobin has a low affinity for oxygen

• more O2 released to respiring cells

lungs

• high pO2

• high affinity for O2

• more O2 associated with haemoglobin

two rules for O2 dissociation curves

1. the further left the curve is, the greater the affinity of Hb for O2 (loads O2 readily, unloads it less easily)

2. the further right the curve is, the lower the affinity of Hb for O2 (loads O2 less readily, unloads it easily)

how much O2 will Hb release to resting tissues?

1

how much O2 will Hb release to very active tissues?

about 3

why are there many different oxygen dissociation curves?

1. the shape of a Hb can change under different conditions, so affinity changes

2. different species have different Hbs with different affinities to O₂ - pO₂ (altitude) and respiration

the shape of a haemoglobin can change under different conditions, so affinity changes

• pCO2 also affects oxygen dissociation

• when pCO2 is high (rapidly respiring cells)

• curve shifts right

• affinity of Hb to O2 is lower

• more O2 dissociated

different species have different haemoglobin with different affinities to oxygen

• because they have different amino acid sequences

• so different tertiary and quaternary structure

• different oxygen binding properties, so different affinities of Hb to O₂

different species have different haemoglobins with different affinities to oxygen - respiration

• mammals with a larger SA:V lose heat more rapidly

• cells must respire more to maintain heat and body temp

• so, their Hb has a lower affinity for O2

• Hb can dissociate from O2 more easily

• therefore, faster rate of respiration

low partial pressure of oxygen

curve goes left

high rate of respiration

curve goes right

haemoglobin - different species

• different species have evolved and adapted to different conditions and environments

• e.g. species living in lower pO2 have evolved Hb with a higher affinity for O2

• different Hb from each species can be represented on their own oxygen dissociation curves

describe the role of haemoglobin (Hb) in the loading, transport and unloading of oxygen

1. Hb associates oxygen in the lungs

2. at high partial pressure of oxygen

3. binding of an O₂ molecule to Hb makes binding of another O₂ molecule easier

4. oxygen transported as oxyhaemoglobin in RBCs

5. Hb dissociates oxygen in the respiring cells

6. at low partial pressure of oxygen

myoglobin

• similar to Hb, but only 1 haem group

• found in muscle cells, acts as an oxygen reserve

• myoglobin has a very high affinity for oxygen, even at low pO2

• oxymyoglobin will only dissociate when pO2 is very low (during intense activity)

• humans don’t have myoglobin

• much higher % O2 saturation than haemoglobin

• it can deliver O2 when levels are low during periods of intense muscular activity

• diving mammals such are able to remain submerged for long periods because they have greater amounts of myoglobin in their muscles compared to other animals

other species

• different species have slightly different amino acid sequences

• they produce different Hb molecules

• the Hb of different species has: different tertiary and quaternary structures, and different oxygen binding properties - some have a high affinity, others have a low affinity

lugworm

• covered with sea water

• when the tide goes out, there is no longer a fresh supply of oxygenated water to flow through the burrow

• water in the burrow progressively loses oxygen

• evolved to have Hb with a high affinity, even in conditions of low pO2

llama

• lives at high altitude

• pO2 is much lower

• difficult to load Hb with O2

• evolved a special type of Hb with a higher affinity for O2

• curve has shifted LEFT

highly active species

• organisms that are highly active (fish/birds) require a large amount of O2 for respiration

• their dissociation curves are shifted to the RIGHT

• therefore, Hb is able to dissociate O2 and deliver it to muscles more readily

foetal Hb

• in the womb, the pO2 is lower

• foetal Hb has a higher affinity for O2

• therefore, association of O2 occurs more readily

• this allows the foetus to respire

SA:V

• smaller mammals have a larger SA:V

• therefore they lose heat more rapidly

• the dissociation curve is shifted RIGHT

• the affinity is LOWER

• O2 is more easily dissociated from Hb to tissues

• tissues can respire more and produce more heat

• this helps to maintain their body temp

mass transport systems

• diffusion allows the transport of substances across a short distance

• the supply of substances over a larger distance requires a mass transport system

• the lower the SA:V and the more active the organism, the greater the need for a specialised transport system with a pump

features of transport systems

1. a suitable medium in materials can dissolve and be transported (usually water based)

2. a closed system of tubes to contain the medium and connect different parts of the organism

3. a mechanism for moving the medium around, involving pressure changes in different parts of the organism

4. ensuring the medium flows in one direction, e.g. valves

5. ability to control where the medium flows, changing amount of flow to different parts depending on the demand

the heart

• muscular organ located between lungs

• made of cardiac muscle

• contains lots of mitochondria and myoglobin

circulatory system

• carries raw materials from gas exchange surface to body cells

• closed system - confined to vessels

• vessels - arteries, veins and capillaries

• double circulatory - passes twice through heart for each complete cycle

why is the mammalian circulatory system double circulatory?

• mammals have a high metabolism

• as blood travels through the lungs, its pressure is reduced

• allows blood to flow slower for efficient diffusion across alveoli

• pressure needs to be increased to transport blood to the body quickly - so it pumps through the heart again

what is the mammalian circulatory system made up of?

arteries, veins and capillaries

blood vessels

• tough fibrous outer layer resists pressure changes from within and outside

• muscle layer contracts to control blood flow by constricting/dilating

• elastic layer maintains blood pressure by stretching and recoiling

• endothelium is smooth to reduce friction and thin to allow diffusion

artery structure

• elastic tissue to allow stretching/recoil/maintain pressure

• muscle for vasoconstriction

• thick walls withstand pressure

• smooth endothelium reduces friction

• muscle layer is thick so the artery can constrict and dilate to control the volume of blood passing through

• elastic layer is thick, this stretches at each systole and recoils at each diastole. the stretching and recoiling action maintains a high pressure so blood can reach extremities

• overall thickness is large to resist bursting of the vessels under pressure

• no valves

arteries

• the blood vessels that carry blood away from the heart to the capillaries within the tissues

• arteries branch out into arterioles

• resistance to blood flow is altered by vasoconstriction or vasodilation of the blood vessel walls, especially in arterioles

vasoconstriction

• contraction

• increases resistance

• leads to an increase in blood pressure

vasodilation

• relaxation

• decreases resistance

• leads to a decrease in blood pressure

capillaries

• link arteries and veins

• exchange substances/metabolic materials between blood and cells (O₂, CO₂, glucose)

• proteins and RBCs can’t leave capillaries to make tissue fluid because they’re too big

capillary structure and function

• thin, so short diffusion distance

• pores, so material can leave (inc. WBC)

• large SA, so rapid exchange

• narrow lumen, so RBCs squeezed against capillary wall and creates a short diffusion pathway

vein structure

• wider diameter so lower pressure

• central thin layer of elastic and muscle tissue (the smaller venules lack this inner layer)

• valves at regular intervals to prevent backflow

• inner thin layer of simple squamous epithelium lines the vein (endothelium)

• thinner layer of elastic connective tissue compared to arteries due to low pressure of the blood (too low to create a recoil action)

• muscle layer thinner than arteries, no control of blood flow

veins

• the blood vessels that return blood to the heart from the tissues

• the smallest veins (venules) return blood from the capillary bed to the larger veins

tissue fluid

• fluid that bathes the tissue

• water, glucose, amino acids, oxygen, etc.

• allows the exchange of materials into and out of the cell

how is tissue fluid formed?

• arteriole end

• higher hydrostatic pressure in capillary than in tissue fluid (due to heart pumping)

• outward pressure forces fluid out forming tissue fluid

• this reduces the hydrostatic pressure in the capillaries

• WP at the venule end is lower than in the tissue fluid

• so some water re-enters the capillaries by osmosis

• excess tissue fluid is drained into the lymphatic system

left pump

oxygenated blood from lungs

right pump

deoxygenated blood from body

atrium

thin-walled, elastic and stretches to collect blood

ventricle

thicker muscular walls, contracts to pump blood

aorta

carries oxygenated blood from left ventricle to body

vena cava

brings deoxygenated blood from tissues to right atrium

superior vena cava

receives deoxygenated blood from the head and body

right atrium

receives deoxygenated blood via the superior and inferior vena cava

right ventricle

pumps deoxygenated blood to the lungs

inferior vena cava

receives deoxygenated blood from the lower body and organs

hepatic vein

carries deoxygenated blood from the liver

hepatic portal vein

carries deoxygenated, nutrient rich blood from the gut for processing

renal vein

carries deoxygenated blood from the kidneys

pulmonary vein

carries oxygenated blood back from lungs to left atrium

pulmonary artery

carries deoxygenated blood from right ventricle to the lungs

left atrium

receives oxygenated blood from the lungs

left ventricle

pumps blood from the left atrium to the aorta

hepatic artery

carries oxygenated blood to the liver

mesenteric artery

carries oxygenated blood to the gut

renal artery

carries oxygenated blood to the kidneys

what are the events of the cardiac cycle?

• the cardiac cycle is the sequence of events that take place during one heartbeat

• it can be divided into three phases: atrial systole, ventricular systole, and diastole

diastole

• blood from the pulmonary vein and vena cava return to the atria

• atria are relaxed and fill with blood, increasing pressure

• when the atrial pressure is higher than the pressure in ventricles, AV valve opens

• blood enters (aided by gravity)

• atria and ventricles are relaxed

• pressure in ventricle lower than pressure in aorta/pulmonary artery

• semi-lunar valve closes

• “dub” sound

atrial systole

• atrial walls contract, pushing blood into the ventricles

• ventricle walls remain relaxed

ventricular systole

• after a short delay…

• ventricles fill, and walls contract simultaneously

• increases blood pressure

• this forces AV valves shut (no back flow)

• “lub” sound

• further increase in blood pressure

• ventricle pressure higher than pressure in aorta/pulmonary artery

• semi-lunar valves open so blood forced out into vessels

• thick muscular ventricle walls allow blood to be pumped at high pressure

• atria relax

ventricular pressure

• is low at first, but gradually increases as the ventricles fill with blood as the atria contract

• the left AV valves close and pressure rises dramatically as the thick muscular walls of the ventricle contract

• as pressure rises above that of the aorta, blood is forced into the aorta past the semi-lunar valves

• pressure falls as the ventricles empty and the walls relax

atrial pressure

• is always relatively low because the thin walls of the atrium cannot create much force

• it is higher when they’re contracting, but drops when the left AV valve closes and its walls relax

• the atria then fill with blood, which leads to a gradual build-up of pressure until a slight drop when the left AV valve opens and some blood moves into the ventricle

aortic pressure

• rises when ventricles contract as blood is forced into the aorta

• it then gradually falls, but never below around 12kPa, because of the elasticity of its wall, which creates a recoil action - essential is blood is to be constantly delivered to the tissues

• the recoil produces a temporary rise in pressure at the start of the relaxation phase

ventricular volume

• 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 semilunar valve opens

• volume increases again as the ventricles fill with blood

name the three different valves in the heart

1. atrioventricular valves

2. semi-lunar valves

3. pocket valves

atrioventricular valves

• between the atria and ventricles

• prevent back flow of blood in to the atria

• left AV valve (bicuspid)

• right AV valve (tricuspid)

semi-lunar valves

• in the pulmonary artery and aorta

• prevent blood flowing back in the ventricles

pocket valves

in the venal system prevent the blood from flowing backwards, when the veins are squeezed by muscles

valves

• tough, flexible, fibrous tissue

• cusp-shaped

• when pressure is greater on the convex side, they move apart allowing blood to flow through

• when pressure is greater on the concave side, blood collects pushing them together and preventing the passage of blood

coronary arteries

• the heart is supplied with oxygenated blood by its own blood vessels - coronary arteries

• these are small extensions of the aorta

• blockage of these (e.g. a clot) can lead to myocardial infarction (heart attack) or coronary heart disease

• cells of the heart become deprived of an oxygen supply, so can’t respire and therefore start to die

arterioles

• carry blood under lower pressure than arteries

• muscle layer is relatively thicker than in arteries, contraction allow constriction of the lumen

• elastic layer is relatively thinner than in arteries as blood is at a lower pressure

cardiovascular disease

• a number of risk factors increase the risk or probability of cardiovascular disease, e.g. smoking, high blood pressure, blood cholesterol, diet

• when risk factors are combined, the risk increases greatly

cardiac output

• the volume of blood pumped by 1 ventricle of the heart in 1 minute (dm³min^-1)

• cardiac output = heart rate x stroke volume

stroke volume

volume pumped out per heartbeat

what is 1000cm³ in dm?

1dm³

return of tissue fluid (1 - capillaries)

1. water re-enters from a high to low hydrostatic pressure

2. water re-enters via osmosis from a high to low WP

3. water brings carbon dioxide and other waste products with it, back into the capillary

return of tissue fluid (2 - lymph)

• some fluid enters the lymph vessels to form lymph

• these vessels form a network (lymphatic system) which connect to the blood system nearer the heart at the vena cava, via the thoracic duct

• lymph circulates via hydrostatic pressure and muscle contraction

symbol equation for photosynthesis

CO2 + H2O → O2 + C6H12O6

symbol equation for respiration

O2 + C6H12O6 → CO2 + H2O

structure and function of xylem

• long cells with no end walls, to allow movement of a continuous column of water

• no organelles or cytoplasm, to allow easier water flow (no obstruction)

• supported by rings of lignin, to withstand the tension of water and provide strength

• contains pits in walls, to allow lateral movement (side to side) of water

transpiration (cohesion-tension theory)

• water vapour lost from mesophyll cells due to evaporation of water through stomata

• lowers WP of mesophyll cells

• hydrogen bonds stick water molecules together - cohesion

• forming a continuous water column

• adhesion of water molecules to walls of xylem

• water pulled up xylem creating tension

• water from xylem replaces water lost from mesophyll cells

• via osmosis from soil with higher WP, to root hair cells with lower WP

what is the opposite of tension?

pressure

evidence for the cohesion-tension theory

1. diameter of trunks is narrower at midday because tension stretches trunks. this coincides with highest rates of transpiration and evaporation

2. when xylem breaks there is a lack of cohesion, as a result water no longer reaches top leaves

3. when xylem breaks, water does not leak out of a broken vessel, instead air is drawn in due to tension