Module 3: Section 2 - Transport in Animals

Question 1

Talk me through the circulatory system in fish

Answer 1

In fish, the heart pumps blood to the gills (to pick up oxygen) and then on through the rest of the body (to deliver the oxygen in a short circuit)

Question 2

Talk me through the circulatory system in mammals

Answer 2

In mammals, the heart is divided down the middle, so it’s really like two hearts joined together.

1) the right side of the heart pumps the blood to the lungs (to pick up oxygen)
2) from the lungs it travels to the left side of the heart, which pumps it to the rest of the body
3) when blood returns to the heart, it enters the right side again

Question 3

What is an advantage of the mammalian double circulatory system?

Answer 3

An advantage of the mammalian double circulatory system is that the heart can give the blood an extra push between the lungs and the rest of the body. This makes the blood travel faster, so oxygen is delivered to the tissues more quickly.

Question 4

What is the pulmonary and systemic system?

Answer 4

Our circulatory system is really two linked loops. One sends blood to the lungs - this is called the pulmonary system, and the other sends blood to the rest of the body - this is called the systemic system

Question 5

Talk me through a closed circulatory system

Answer 5

The blood is enclosed inside blood vessels

1) the heart pumps blood into arteries. These branch out into millions of capillaries
2) substances like oxygen and glucose diffuse from the blood in the capillaries into the body cells, but the blood stays inside the blood vessels as it circulates
3) veins take the blood back to the heart

Question 6

Talk me through a closed circulatory system

Answer 6

Some invertebrates (e.g insects) have an open circulatory system - blood isn’t enclosed in blood vessels all the time. Instead, it flows freely through the body cavity:

1) the heart is segmented. It contracts in a wave, starting from the back, pumping the blood into a single main artery.
2) that artery opens up into the body cavity
3) the blood flows around the insect’s organs, gradually making its way back into the heart segments through a series of valves

Question 7

What does a closed circulatory system supply?

Answer 7

The closed circulatory system supplies the insect’s cells with nutrients, and transports things like hormones around the body. It doesn’t supply the insect’s cells with oxygen though - this is done by a system of tubes called the tracheal system

Question 8

What is the purpose of arteries?

Answer 8

Arteries carry blood from the heart to the rest of the body. Their walls are thick and muscular and have elastic tissue to stretch and recoil as the heart beats, which helps maintain the high pressure. All arteries carry oxygenated blood except for the pulmonary arteries, which takes deoxygenated blood to the lungs.

Question 9

What is the purpose of arterioles?

Answer 9

Arteries branch into arterioles, which are much smaller than arteries. Like arteries, arterioles have a layer of smooth muscle, but they have less elastic tissue. The smooth muscle allows them to expand or contract, thus controlling the amount of blood flowing to the tissues

Question 10

What is the purpose of capillaries?

Answer 10

Arterioles branch into capillaries, which are the smallest of the blood vessels. Substances like glucose and oxygen are exchanged between cells and capillaries, so they’ve adapted for efficient diffusion. e.g. their cell walls are only one cell thick

Question 11

What is the purpose of venules?

Answer 11

Capillaries connect to venules, which have very thin walls that can contain some muscle cells. Venules join together to form veins.

Question 12

What is the purpose of veins?

Answer 12

Veins take blood back to the heart under low pressure. They have a wider lumen than equivalent arteries, with very little elastic or muscle tissue. Veins contain valves to stop the blood flowing backwards. Blood flow through the veins is helped by contraction of the body muscles surrounding them. All veins carry deoxygenated blood, except for pulmonary veins, which carry oxygenated blood to the heart from the lungs.

Question 13

What is tissue fluid and briefly how is it made?

Answer 13

Tissue fluid is the fluid that surrounds cells in tissues. It’s made from a substances that leave the blood plasma, e.g. oxygen, water and nutrients.

Question 14

What does the tissue fluid not contain and why?

Answer 14

Unlike blood, tissue fluid does not contain red blood cells or big proteins, because they’re too large to be pushed out through the capillary walls.

Question 15

Cells take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it. In a capillary bed (the network of capillaries in an area of tissue), substances move out of the capillaries, into the tissue fluid, by pressure filtration. What is the first step of pressure filtration?

Answer 15

1) At the start of the capillary bed, nearest the arteries, the hydrostatic (blood) pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid. This difference in hydrostatic pressure forces fluid out of the capillaries and into the spaces around cells, forming tissue fluid.

Question 16

What is the second step of pressure filtration?

Answer 16

2) As fluid leaves, the hydrostatic pressure reduces in the capillaries - so the hydrostatic pressure is much lower at the end of the capillary bed that’s nearest to the venules.

Question 17

What is the third step of pressure filtration?

Answer 17

3) There is another form of pressure at work here called oncotic pressure - this is generated by plasma proteins present in the capillaries which lower the water potential. At the venule end of the capillary bed, the water potential in the capillaries is lower than than the water potential in the tissue fluid due to the fluid loss from the capillaries and the high oncotic pressure. This means some water re-enters the capillaries from the tissue fluid at the venule end by osmosis

Question 18

Not all of the tissue fluid re-enters the capillaries at the venule end of the capillary bed - some excess tissue fluid is left over. This extra fluid eventually gets returned to the blood through the lymphatic system - a kind of drainage system, made up of lymph vessels. What are the four steps in the process of excess tissue fluid draining into the lymph vessels?

Answer 18

1) the smallest lymph vessels are the lymph capillaries
2) excess tissue fluid passes into lymph vessels. Once inside, it’s called lymph
3) valves in the lymph vessels stop the lymph going backwards
4) lymph gradually moves towards the main lymph vessels in the thorax (chest cavity). Here, it’s returned to the blood, near the heart

Question 19

Draw and label a diagram of the heart

Answer 19

see page 80 for answer

Question 20

The atrioventricular valves link the atria to the ventricles, and the semi-lunar valves link the ventricles to the pulmonary artery and aorta - they all stop blood flowing the wrong way. How do they work?

Answer 20

1) the valves only open one way - whether they’re open or closed depends on the relative pressure of the heart chambers
2) if there’s higher pressure behind a valve, it’s forced open
3) if pressure is higher in front of the valve, it’s forced shut

Question 21

Briefly, explain what the cardiac cycle is

Answer 21

The cardiac cycle is an ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body. The volumes of the atria and ventricles change as they contract and relax, altering the pressure in each chamber. This causes valves to open and close, which directs the blood flow through the heart. The cardiac cycle can be simplified into three stags: atria contract, ventricles contract and atria and ventricles relax.

Question 22

Explain the first step of the cardiac cycle: ventricles relax, atria contract

Answer 22

1) the ventricles are relaxed. The atria contract, which decreases their volume and increases their pressure. This pushes blood into the ventricles through the atrioventricular valves. There’s a slight increase in ventricular pressure and volume as the ventricles receive the ejected blood from the contracting atria

Question 23

Explain the second step of the cardiac cycle: ventricles contract, atria relax

Answer 23

2) the atria relax. The ventricles contract (decreasing their volume), increasing their pressure. The pressure becomes higher in the ventricles than the atria, which forces the atrioventricular valves shut to prevent back-flow. The high pressure in the ventricles opens the semi-lunar valves - blood is forced out into the pulmonary artery and aorta

Question 24

Explain the third step of the cardiac cycle: ventricles relax, atria relax

Answer 24

3) the ventricles and the atria both relax. The higher pressure in the pulmonary artery and aorta causes the semi-lunar valves to close, preventing backflow. The atria fill with blood (increasing their pressure) due to the higher pressure in the vena cava and pulmonary vein. As the ventricles continue to relax, their pressure falls below the pressure in the atria. This causes the atrioventricular valves to open and blood flows passively (without being pushed by atrial contraction) into the ventricles and from the atria. The atria contract, and the whole process begins again

Question 25

Draw a diagram of the cardiac cycle

Answer 25

see page 81 for answer

Question 26

Where does the 'lub-dub' sound of a heartbeat come from?

Answer 26

The first 'lub' sound is caused by atrioventricular valves closing. The second 'dub' sound is caused by the semi-lunar valves closing

Question 27

The heart is myogenic - what does this mean?

Answer 27

Cardiac muscle is myogenic - it can contract and relax without receiving signals from nerves. This pattern of contractions controls the regular heartbeat

Question 28

You're probably going to want to make a poster of this - this is going to be a nasty one. Very sorry dearest J dawg. How does cardiac muscle control the regular beating of the heart?

Answer 28

1) the process starts in the sino-atrial node (SAN), which is in the wall of the right atrium 2) the SAN is like a pacemaker - it sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls 3) this causes the right and left atria to contract at the same time 4) a band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles 5) instead, these waves of electrical activity are transferred from the SAN to the atrioventricular node (AVN) 6) the AVN is responsible for passing the waves of electrical activity on the bundle of His. But, there's a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied 7) the bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right and left ventricle walls, called the Purkyne tissue 8) The Purkyne tissue carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from the bottom up

Question 29

An electrocardiograph records these changes in electrical charge using electrodes placed on the chest. What changes is an ECG recording?

Answer 29

The heart muscle depolarises (loses electrical charge) when it contracts, and repolarises (regains charge) when it relaxes. An ECG records these changes

Question 30

Draw and label a normal ECG wave

Answer 30

see pg 82 for answers

Question 31

What is the P wave on an ECG caused by?

Answer 31

The P wave is caused by contraction (depolarisation) of the atria

Question 32

What is the main peak of a heartbeat on an ECG known as?

Answer 32

The main peak of the heartbeat, together with the dips at either side, is called the QRS complex - it's caused by contraction (depolarisation) of the ventricles

Question 33

What is the T wave on an ECG caused by?

Answer 33

The T wave is due to relaxation (repolarisation) of the ventricles

Question 34

What does the height of a wave on an ECG indicate?

Answer 34

The height of the wave indicates how much electrical charge is passing through the heart - a bigger wave means more electrical charge, so (for the P and R waves) a bigger wave means a stronger contraction.

Question 35

Define tachycardia and bradycardia

Answer 35

Tachycardia is when the heart is beating too quickly - around 120 bpm Bradycardia is below 60 bpm

Question 36

What is an ectopic heartbeat and what causes it?

Answer 36

An ectopic heartbeat - an 'extra' heartbeat. Can be caused by too early contraction of atria or ventricles. Occasionally, in healthy people ectopic heartbeats don't cause a problem.

Question 37

What is fibrillation and what causes it?

Answer 37

Fibrillation - a really irregular heartbeat. The atria or ventricles completely lose their rhythm and stop contracting properly. It can result in anything from chest pain and fainting to no pulse and death.

Question 38

What does affinity for oxygen mean?

Answer 38

Affinity for oxygen means tendency to combine with oxygen

Question 39

Tell me five pretty cool facts about haemoglobin

Answer 39

1) Hb is a large protein with a quaternary structure - it's made up of more than one polypeptide chain (four of them actually) 2) Each chain has a haem group which contains iron and gives haemoglobin its red colour 3) Hb has a high affinity for oxygen - each molecule can carry four oxygen molecules 4) In the lungs, oxygen joins to the iron in Hb to form oxyHb 5) This is a reversible reaction - when oxygen leaves oxyHb (dissociates from it) near the body cells, it turns back to Hb Cool!!!!!

Question 40

What is the partial pressure of oxygen and how do you increase this?

Answer 40

1) The partial pressure of oxygen (pO2) is a measure of oxygen concentration. The greater the concentration of dissolved oxygen in cells, the higher the partial pressure

Question 41

What is the partial pressure of carbon dioxide?

Answer 41

The partial pressure of carbon dioxide (pCO2) is a measure of the concentration of CO2 in a cell

Question 42

How does haemoglobin's affinity for oxygen vary depending on the partial pressure of oxygen?

Answer 42

Oxygen loads onto Hb to form oxyHb where there's a high pO2. OxyHb unloads its oxygen where there's a lower pO2. 1) oxygen enters blood capillaries at the alveoli in the lungs. Alveoli have a high PO2 so oxygen loads onto Hb to form oxyHb 2) when cells respire, they use up oxygen - this lowers the pO2. Red blood cells deliver oxyHb to respiring tissues, where it unloads its oxygen 3) the Hb then returns to the lungs to pick up more oxygen

Question 43

An oxygen dissociation curve shows how saturated the Hb is with oxygen at any given partial pressure. What does it mean when pO2 is high (e.g. in the lungs) and low (e.g. in respiring tissue)

Answer 43

1) where pO2 is high (e.g. in the lungs), Hb has a high affinity for oxygen (i.e. it will readily combine with oxygen), so it has a high saturation of oxygen 2) where pO2 is low (e.g. in respiring tissues), Hb has a low affinity for oxygen, which means it releases oxygen rather than combines with it. That's why it has a low saturation of oxygen

Question 44

Talk me through the S shape of a dissociation curve

Answer 44

1) the graph is 'S-shaped' because when Hb combines with the first O2 molecule, its shape alters in a way that makes it easier for other molecules to join too 2) but as the Hb starts to become saturated, it gets harder for more oxygen molecules to join 3) as a result, the curve has a steep bit in the middle where it's really easy for oxygen molecules to join, and shallow bits at each end where it's harder. When the curve is steep, a small change in pO2 causes a big change in the amount of oxygen carried by Hb

Question 45

Adult Hb and fetal Hb have different affinities for oxygen. Fetal Hb has a higher affinity for oxygen (the fetus's blood is better at absorbing oxygen than its mother's blood) at the same partial pressure of oxygen. Explain in four steps why this is really important.

Answer 45

1) the fetus gets oxygen from its mother's blood across the placenta 2) by the time the mother's blood reaches the placenta, its oxygen saturation has decreased (because some has been used up by the mother's body) 3) for the fetus to get enough oxygen to survive its Hb has to have a higher affinity for oxygen (so it takes up enough) 4) if its Hb had the same affinity for oxygen as adult Hb its blood wouldn't be saturated enough

Question 46

What is the Bohr effect?

Answer 46

When carbon dioxide levels increase, the dissociation curve 'shifts' right, showing that more oxygen is released from the blood (because the lower the saturation of Hb with with O2, the more O2 is released). This is called the Bohr effect.

Question 47

Carbon dioxide concentration affects oxygen unloading. Hb gives up its oxygen more readily at higher partial pressures of carbon dioxide (pCO2). It's a cunning way of getting more oxygen to cells during activity. When cells respire they produce carbon dioxide, which raises the pCO2, increasing the rate of oxygen unloading. The reason for this is linked to how CO2 affects blood pH. Give me the 6 steps in how CO2 is removed from respiring tissues.

Answer 47

1) most of the CO2 from respiring tissues diffuses into red blood cells. Here it reacts with water to form carbonic acid, catalysed by the enzyme carbonic anhydrase 2) the carbonic acid dissociates to give H= ions and HCO3- ions 3) this increase in H+ ions causes oxyHb to unload its oxygen so that Hb can take up the H+ ions. This forms a compound called haemoglobinic acid. (this process also stops the hydrogen ions from increasing the cell's acidity) 4) the HCO3- ions diffuse out of the red blood cells and are transported in the blood plasma. To compensate for the loss of HCO3- ions from the red blood cells, Cl- ions diffuse into the red blood cells. This is called the chloride shift and it prevents any change in pH that could affect the cells 5) when the blood reaches the lungs the low pCO2 causes some of the HCO3- and H+ ions to recombine into CO2 (and water) 6) the CO2 then diffuses into the alveoli and is breathed out