mass transport in animals

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

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
- 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

how does haemoglobin transport O2 efficiently?

- readily associate with O2 at the lungs (gas exchange surface)
- readily dissociated with oxygen at the respiring cells

oxygen and carbon dioxide concentrations at gas exchange surfaces:

oxygen: high

carbon dioxide: 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 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

measured in kiloPascals (kPa)

two factors that affect Hb’s affinity

1. pO2 or pCO2
2. saturation of the Hb with O2

oxygen dissociation curve

shows the relationship between the pO2 and saturation of Hb with O2

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

dissociation curve has an s-shape

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)

% 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

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

low partial pressure of oxygen

curve goes left

high rate of respiration

curve goes right

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

- 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

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

contains lots of mitochondria and myoglobin

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

right atrium: receives deoxygenated blood via the superior and inferior vena cava

right ventricle: pumps deoxygenated blood to the lungs

left atrium: receives oxygenated blood from the lungs

left ventricle: pumps blood from the left atrium to the aorta

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

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

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

aorta: carries oxygenated blood from left ventricle to body
pulmonary artery: carries deoxygenated blood from right ventricle to the lungs
hepatic artery: carries oxygenated blood to the liver
mesenteric artery: carries oxygenated blood to the gut
renal artery: carries oxygenated blood to the kidneys

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

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

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

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

vena cava: brings deoxygenated blood from tissues to right atrium

superior vena cava: receives deoxygenated blood from the head and body

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

tissue fluid

- fluid that bathes the tissue
- water, glucose, amino acids, oxygen, etc.
- allows the exchange of materials into and out of the cell

formation:
- 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

what are the events of the cardiac cycle?

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

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

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

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

- always relatively low cuz the thin walls of the atrium can’t 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

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

the three different valves in the heart:
(1) atrioventricular valves
- between the atria and ventricles
- prevent back flow of blood in to the atria
- left AV valve (bicuspid)
- right AV valve (tricuspid)

(2) semi-lunar valves
- in the pulmonary artery and aorta
- prevent blood flowing back in the ventricles

(3) pocket valves
in the venal system prevent the blood from flowing backwards, when the veins are squeezed by muscles

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

- risk factors: 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

capillaries:
- water re-enters from a high to low hydrostatic pressure
- water re-enters via osmosis from a high to low WP
- water brings carbon dioxide and other waste products with it, back into the capillary

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

give the pathway a RBC takes when travelling in the human circulatory system from a kidney to the lungs

1. renal vein

2. vena cava to right atrium

3. right ventricle to pulmonary artery

explain how water from tissue fluid is returned to the circulatory system

1. plasma proteins remain
2. creates WP gradient
3. water moves to blood by osmosis
4. returns to blood by lymphatic system

describe two precautions a student should take when clearing away after a heart dissection

1. disinfect instruments/surfaces

2. disinfect hands

explain how an arteriole can reduce the blood flow into capillaries

1. muscle contracts

2. constricts lumen

which blood vessel carries blood at the lowest blood pressure

the vena cava

describe the advantage of the Bohr effect during intense exercise

increases dissociation of oxygen for aerobic respiration at the tissues

EPO is another performance-enhancing drug. It can increase the haematocrit (the percentage of red blood cells in blood).

A heart attack is caused by a lack of glucose and oxygen being delivered to cardiac muscle via the coronary arteries. The overuse of EPO can increase the risk of a heart attack.

Suggest how.

1. EPO causes blood to thicken

2. the thickened blood could block the coronary arteries

The normal haematocrit for human males is 47(±5)%. For professional male cyclists, the maximum haematocrit allowed is 50%.

A student suggested that professional male cyclists should be allowed to use EPO until their haematocrit is 50%.

Give two reasons why this suggestion is not valid.

1. some cyclists will gain a bigger advantage

2. there are health risks associated with taking EPO

describe and explain the effect of increasing carbon dioxide conc on the dissociation of oxyhemoglobin

1. increases oxygen dissociation

2. by decreasing blood pH

name valve A and chamber B

valve A - left AV valve

chamber B - left ventricle

explain how AV valve maintains a unidirectional flow of blood

1. pressure in left atrium is higher than in ventricle causing valve to open
2. pressure in left ventricle is higher than in atrium causing valve to close

name the blood vessels that carry blood to the heart muscle

coronary arteries

explain the role of the heart in the formation of tissue fluid

1. contraction of ventricles produces high hydrostatic pressure
2. this forces water and some dissolved substances out of blood capillaries

Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system.

Suggest how a blockage in the lymphatic system could cause lymphoedema.

excess tissue fluid cannot be reabsorbed