Transport in Animals

Question 1

What is the need for transport systems in multicellular animals?

Answer 1

o Size – larger organisms (2+ levels of cells) need a way to supply cells deep inside
o Surface Area to Volume Ratio – small organisms have a large SA:V ratio, but larger organisms have a smaller SA:V ratio, so diffusion alone is inadequate, the diffusion distance is too far/would take too long, to supply substances to cells, deep within the organism
o Metabolic Rate – more metabolically active organisms need more energy from respiration and so, require a constant supply of oxygen and glucose (remove waste)

Question 2

Describe the features of a single circulatory system.

Answer 2

o Speed of blood flow to the body is reduced – due to lower pressure of blood (passes through capillaries of gills)
o Rate of oxygen and other substances being delivered to respiring cells is limited
o Blood flows once through the heart for each circuit of the body
o Present in fish, who have only two chamber in the heart
o One in which the blood flows through the heart once for each circuit of the body

Question 3

Describe the features of a double circulatory system.

Answer 3

o Two separate circuits – blood flows through the heart twice (very efficient)
o Present in mammals, including humans
o Heart increases pressure of blood after it picks up oxygen in the lungs
o Systemic circulation (body) carries blood at a higher pressure than pulmonary circulation (lungs)
o Reduced pressure is necessary in the capillaries of lungs to avoid damage
o High blood pressure in the systemic circulation is needed to pump the blood all around the body, fast enough

Question 4

Describe the features of an open circulatory system.

Answer 4

o Present in insects
o Blood fluid circulates through the body cavity (haemocoel) so tissues and cells are bathed directly in haemolymph (insect blood)
 Haemolymph does not carry oxygen or carbon dioxide but hold food and nitrogenous waste
o A long, muscular organ, like a heart, pumps this blood fluid
o Movement, or lack of, can affect the circulation
o Blood pressure is slow and blood flow is slow

Question 5

Describe the features of a closed circulatory system.

Answer 5

o Blood is held in blood vessels

o Present in mammals and fish

Question 6

Describe the structure and function of arteries/arterioles and the distribution of different tissues within the vessel walls.

Answer 6

o Relatively small lumen – to maintain blood pressure
o Relatively thick wall – to withstand high pressure of the blood
o Very smooth endothelium on the inner lining – allows blood to flow freely (no friction)
o Large amount of smooth muscle in the tunica media, especially in arterioles/small arteries – contraction of muscle in the arterioles reduces the size of the lumen, diverting blood from one area to another (vasoconstriction)
o Large amount of elastic tissue/collagen in the tunica adventitia, especially in the arteries close to the heart – allows wall to stretch/recoil as high pressure blood pushes through
o Valves are not present – except in the aorta/pulmonary artery (leaving the heart)

Question 7

Describe the structure and function of veins/venules and the distribution of different tissues within the vessel walls.

Answer 7

o Relatively large lumen – less resistance to blood flow allowing blood at low pressure to move through more easily
o Relatively thin walls
o Very smooth endothelium
o Small amount of elastic tissue/collagen/smooth muscle – low pressure and therefore, there is no need to stretch/recoil, nor divert blood
o Valves are present – prevent backflow and due to low blood pressure

Question 8

Describe the structure and function of capillaries and the distribution of different tissues within the vessel walls.

Answer 8

o Very narrow lumen, one cell thick – short diffusion distance
o Leaky walls with small spaces between cells and very thin endothelium walls – allow blood plasma and dissolved substances to leave
o No smooth muscle/elastic tissue in wall, nor any valves present
o Form a vast network for vessels – large surface area for exchange
o Permeable to water and dissolved substances
o Gaps between endothelial cells that make up the capillary walls
o Low pressure, slow movement – time for exchange of substances

Question 9

How is the dissection of a heart carried out?

Answer 9

1. Feel the arteries (feel thicker) and veins.
2. Cut along the line where the right atrium and coronary artery meet.
3. Look at the atria and ventricles - the latter have thicker walls. The left ventricle will be thicker than its right counterpart because it needs to pump blood to the whole body.

Question 10

How is tissue fluid made?

Answer 10

• Tissue fluid formed because:
o Pressure high at the arterial end ;
o Heart contractions generating hydrostatic pressure ;
o Hydrostatic pressure is greater than oncotic pressure ;
o Capillary wall, is leaky
o Water / plasma passes through & dissolved substances (e.g. glucose, amino acids) ;
o Red blood cells / plasma proteins / some WBC’s cannot get out because they are too large ;
o Net outflow / tissue fluid formed at arterial end ;
• Some fluid returns to capillary as:
o Hydrostatic pressure lower at venous end ;
 As tissue fluid spreads out in the capillaries
o Ref. to increased distance from the heart ;
o Ref. to osmotic effect / oncotic pressure ;
o Oncotic pressure caused by soluble plasma proteins (high concentration in blood) which could not leave capillary;
 Oncotic pressure gradient encourages movement of water back into the capillaries from the tissue fluid
o Some return of fluid at venous end ;
• Some tissue fluid enters the lymphatic system, which drains excess tissue fluid into lymph vessels and returns it to the blood in the subclavian vein

Question 11

Tissue fluid

Answer 11

fluid that permeates the spaces between individual cells, is in osmotic contact with blood and lymph, and that serves as a transport of metabolic requirements and waste

Question 12

What are the components of blood?

Answer 12

• Erythrocytes (too large to pass capillary walls)
• Plasma proteins (too big to leave the capillaries)
• Leukocytes – i.e. phagocytes, neutrophils, lymphocytes
• Platelets
• Hormones
• Water and dissolved solutes
• High hydrostatic pressure
• More negative oncotic pressure
• In blood vessels
• Glucose, amino acids, O2

Question 13

What are the components of tissue fluid?

Answer 13

• No RBC (too large to pass capillary walls)
• Plasma with dissolved nutrients – i.e. glucose, oxygen
• Some leukocytes, during infection – i.e. neutrophils
• No platelets
• Very few proteins and some hormones
• Water and dissolved solutes
• Low hydrostatic pressure
• Less negative oncotic pressure
• Not in vessels
• Less glucose, amino acids, O2 than blood

Question 14

What are the components of lymph?

Answer 14

• No RBC (too large to pass capillary walls)
• In the liver, have a particularly high concentration of proteins
• Many lymphocytes
• No platelets
• High concentration of lipids
• Few proteins – only antibodies
• Water and dissolved solutes
• Low hydrostatic pressure
• Less negative oncotic pressure
• In lymph vessels
• Less glucose, amino acids, O2 than tissue fluid

Question 15

Systole

Answer 15

describes contracting

Question 16

Diastole

Answer 16

describes relaxing

Question 17

Cardiac cycle

Answer 17

the sequence of events taking place, during one heartbeat

Question 18

Describe the steps of the cardiac cycle

Answer 18

o Atrial systole – atria contract
o Blood flows into the left and right atria from the pulmonary vein and vena cava
o Atrial muscles contract pushing blood past atrioventricular valve into the ventricles
o Ventricular systole from the base upwards, increasing the pressure
o Pushes blood upwards into the aorta and pulmonary artery
o Semi-lunar valves open
o Increases pressure above atrial pressure, closing the atrioventricular valves – preventing backflow
o Atrial and ventricular diastole
o Semilunar valves (in the aorta/pulmonary artery) close – preventing backflow
o Elastic recoil of relaxing heart muscle lowers pressure in the atria and ventricles
o At low blood pressure, blood flows from the veins into the atria
o Blood under high pressure in the arteries is drawn back towards the ventricles
o Coronary arteries fill
o Atrial muscles contract and the cycle begins again

Question 19

Describe pressure changes in the heart

Answer 19

o Semi-lunar valves open
 Aortic pressure rises when ventricles contract as blood is forced into the aorta
 Recoiling produces a temporary rise in pressure
o The dip between AV closing and opening
 Atrial pressure is relatively low as the thin atrial walls cannot create much force
 Pressure drops when the left AV valve closes and its walls relax but rises when the atria is filled with blood
o Ventricular pressure
 Increases as ventricles fill with blood and as the atria contract
 Pressure rises above that of the aorta, forcing blood into the aorta
 Pressure drops when the ventricles are empty and walls relax

Question 20

Describe pressure changes in the blood vessels

Answer 20

o Pressure of blood in the aorta is high
o Artery walls close to the heart have lots of elastic tissue – they stretch when blood enters/recoil when it leaves
o This maintains blood pressure
o The further blood flows along the arteries, the more the pressure drops
o A pressure gradient is required between arteries and arterioles to maintain blood flow

Question 21

How is heart action initiated and coordinated?

Answer 21

• Heart muscle is myogenic – it contracts and relaxes involuntarily
o The SAN contracts, generating electrical activity that spreads along membranes of muscle tissue of the atria, causing atrial systole
o Impulses spread rapidly through the atrial wall and the cardiac muscle responds to the excitation waves by contracting (same rhythm and pace as SAN to set the heartbeat)
o The electrical activity is picked up by the atrio-ventricular node (AVN) in the wall between the atrium and ventricle
o Delay of impulse – important so blood can enter the ventricles before they contract
o The AVN passes the wave of excitation to the Purkyne tissue (run down the septum), which transmit the excitation to the base of the septum where it then spreads out/up through the ventricular walls
o The ventricular muscles respond to the impulses by contracting, from the base upwards, to push the blood up and into the arteries

Question 22

What is fibrillation?

Answer 22

• Myogenic tissue can cause inefficient pumping because the atrial muscles contract at a higher frequency than their ventricular counterpart
• If the chambers are not synchronised, there is uncoordinated contraction of the chambers – this is fibrillation

Question 23

Where is the SAN found?

Answer 23

The sino-atrial node (SAN) is in the wall of the right atrium and is the heart’s natural pacemaker

Question 24

Why is an ECG used?

Answer 24

The electrical impulses travelling in the cardiac muscle can be recorded in an ECG, where electrodes on the body can detect the electrical currents

Question 25

How is oxygen transported in the body?

Answer 25

• Each haemoglobin molecule binds to 4 oxygen molecules to form oxyhaemoglobin
• Hb + 4O2 Hb(O2)4
• Haemoglobin has a high affinity for oxygen and they reversibly bind
• The oxygen molecules enter the blood from the alveoli and become associated with haemoglobin, taking oxygen out of the solution and maintains a steep concentration gradient
• At the body tissues, oxygen must be release from oxyhaemoglobin – this is dissociation

Question 26

Explain the oxygen dissociation curve

Answer 26

• The ability of haemoglobin to associate with/release oxygen depends on the partial pressure of oxygen (pO2) in the surrounding tissues
• At low partial pressures of O2 (pO2) haemoglobin does not carry much oxygen ; (low saturation)
• In high pO2 (e.g. the lungs) haemoglobin combines with oxygen to form oxyhaemoglobin
• When an erythrocyte circulates in the bloodstream to areas of low pO2 (e.g. muscles, body tissues) the oxyhaemoglobin dissociates, releasing the oxygen transported to the respiring tissues, as the pO2 in the cytoplasm of the body cells is lower than in the erythrocytes so the oxygen moves out of the erythrocytes down a concentration gradient
o Once the first oxygen molecule is released from the haemoglobin, the molecule again changes shape and it becomes easier to remove the remaining oxygen molecules

Question 27

Describe the oxygen dissociation curve

Answer 27

• The affinity of haemoglobin for oxygen changes at different pO2 ;
• As the first O2 molecule binds (low saturation of Hb) it changes the 3D shape of the Hb molecule, making it much easier for the second and third O2molecules to bind ;
• This is shown by the change in steepness of dissociation curve between 2kPa & 6kPa;
• As the haemoglobin becomes saturated it becomes more difficult to add more O2; (plateau)
• The significance of this is that a small drop in pO2 (e.g. moving from 6kPa to 2kPa) causes the release of a large number of oxygen molecules

Question 28

Discuss foetal haemoglobin

Answer 28

• A foetus gets its oxygen from the mother’s placenta and the pO2 in the placental blood is quite low, as the foetus is respiring
• Therefore, foetal has a higher affinity for oxygen than adult haemoglobin, allowing the foetus to gain oxygen from maternal blood across the placenta
• At any partial pressure of oxygen, the foetal haemoglobin is more saturated than adult haemoglobin
• After birth, adult Hb eventually replaces foetal Hb, otherwise the affinity for oxygen would be too high and not release oxygen to respiring tissues

Question 29

Describe how carbon dioxide is transported.

Answer 29

• Carbon dioxide can be transported in solution within the blood plasma, bound to haemoglobin – forming carbaminohaemoglobin in erythrocytes or diffused into erythrocytes, forming hydrogen carbonate ions (HCO3-) that travel in the blood plasma
• Carbonic anhydrase (enzyme) in the cytoplasm of red blood cells catalyses the reaction:
o CO2 + H2O  H2CO3 (carbonic acid)
o This dissociates: H2CO3  H+ + HCO3- (hydrogencarbonate ions)
o The increase in H+ ions causes oxyhaemoglobin to unload its oxygen so it can take up H+ to form haemoglobinic acid (acts as a buffer)
• Hydrogencarbonate ions diffuse out of the RBCs in the plasma and to compensate for this, Cl- ions move in from the blood plasma into the erythrocyte - chloride shift
o The dissociation curve for haemoglobin in high carbon dioxide concentrations lies to the right and below the standard curve (maintains balance of charge)
o Increased pCO2 causes Hb to release more O2 than it would otherwise – the Bohr effect ;

Question 30

Arterioles

Answer 30

small blood vessels that distribute blood from an artery to the capillaries

Question 31

Hydrostatic pressure

Answer 31

Hydrostatic pressure that a fluid exerts when pushing against the sides of a vessel or container

Question 32

Oncotic pressure

Answer 32

pressure created by the osmotic effects of the solutes

Question 33

Lymph

Answer 33

fluid held in the lymphatic system

Question 34

Bradycardia

Answer 34

slow heartbeat

Question 35

Tachycardia

Answer 35

fast heartbeat

Question 36

Atrial fibrillation

Answer 36

atria beating more frequently than ventricles (no clear P wave seen)

Question 37

Ectopic heartbeat

Answer 37

A heartbeat is early - feels like the heart has skipped a beat