Adaptations for Transport: Animals

Question 1

Describe an open circulatory system eg in insects

Answer 1

• Fluid is pumped at a relatively low pressure from one main long, dorsal tube-shaped heart running the length of the body
• Fluid called haemolymph bathes the tissues directly, enabling the exchange of substances
• When the heart relaxes, the haemolymph is sucked slowly back to the heart
• There is no respiratory pigment in haemolymph as oxygen diffuses directly to respiring cells through the tracheal system

Question 2

Describe a closed circulatory system eg in mammals and fish

Answer 2

• Blood circulates in a fully enclosed system of blood vessels
• The heart is a muscular pump, pushing blood at high pressure and with a rapid flow rate
• Organs are not in direct contact with the blood but are bathed in tissue fluid
• Blood contains a respiratory pigment which carries oxygen

Question 3

Describe a closed circulatory system eg in earthworms

Answer 3

• Has dorsal and ventral vessels running the length of the body
• These are connected by 5 pairs of pseudohearts
• Blood contains a respiratory pigment which carries oxygen

Question 4

Define single circulation and state where its found

Answer 4

Blood passes through the heart once in one complete circulation
Eg in fish

Question 5

Define double circulation and state where its found

Answer 5

Blood passes through the heart twice in one complete circulation
Eg in mammals

Question 6

What are the 2 circuits in double circulation?

Answer 6

Pulmonary circulation
Systemic circulation

Question 7

Define the pulmonary circulation

Answer 7

All of the blood vessels involved in transporting blood from the heart to the lungs

Question 8

Define the systemic circulation

Answer 8

All of the blood vessels involved in transporting blood from the heart to the rest of the body (excluding the lungs)

Question 9

State and explain 3 advantages of a double circulation system over a single circulation system

Answer 9

1. Maintains a high blood pressure in the systemic circulation - Increased rate of flow to the tissues = increased rate of oxygen supply to tissues for aerobic respiration
2. Allows for a lower pressure in the pulmonary circulation - reduces the build up of tissue fluid in the lungs which would reduce the efficiency of gas exchange
3. Rapid circulation in the systemic circuit

Question 10

Why is it important that the oxygenated and deoxygenated blood is kept separate in double circulation?

Answer 10

Maintains a steep concentration gradient for oxygen at the tissues and carbon dioxide in the lungs for efficient gas exchange

Question 11

State the function of arteries

Answer 11

Transport blood away from the heart

Question 12

State the function of veins

Answer 12

Transport blood to the heart

Question 13

State the function of capillaries

Answer 13

Allow gas exchange of substances with body cells

Question 14

Why is a layer of endothelium an important feature of blood vessels?

Answer 14

Smooth to reduce friction and minimal resistance to blood flow
In capillaries: short diffusion pathway as only 1 cell thick

Question 15

What is the function of smooth muscle in arteries?

Answer 15

• Withstands high blood pressure
• Can constrict to restrict blood flow (vasoconstriction)

Question 16

What is the function of elastic fibres in arteries?

Answer 16

• Sustain pressure
• Elastic recoil maintains blood pressure and aids pumping

Question 17

What is the function of collagen fibres?

Answer 17

They’re resistant to overstretching

Question 18

Describe the structure of veins

Answer 18

• Wide diameter lumen to deliver large volumes of blood back to the heart
• Thin walls as the pressure inside is much lower, due to further distance from the heart
• Thin muscle layer in the walls can be compressed easily to allow contrasting skeletal muscle to squeeze veins and push blood upwards towards the heart
• Pocket valves ensure that blood flows in one direction

Question 19

How do the valves in veins work?

Answer 19

• Blood tries to flow back
• Blood fills the pocket above the valve
• This forces the valve shut

Question 20

Why do veins above the heart have no valves?

Answer 20

Gravity will draw blood down towards the heart

Question 21

Describe the structure of arteries

Answer 21

• Thick layer of smooth muscle to withstand high blood pressure
• Thick layer of elastic fibres for elastic recoil to maintain high blood pressure

Question 22

Describe the structure of capillaries

Answer 22

• Walls are one cell thick, some have pores in their walls
• Walls are permeable to water and dissolved substances eg glucose, amino acids, urea, oxygen and carbon dioxide
• Thin capillary walls allow for a more efficient exchange of materials and gases as there is a shorter diffusion pathway and a large cross sectional area
• Narrow lumen restricts blood flow, slowing down the blood to allow more time for exchange of materials at the tissues

Question 23

Give the function of the tendinous chords in the heart

Answer 23

They prevent the inversion of the valves by becoming tense, thus pulling the valves, holding them in closed position, preventing back flow

Question 24

Describe blood flow through the heart from the lungs

Answer 24

1. Oxygenated blood travels from the lungs to the heart in the pulmonary vein
2. Blood leaves the pulmonary vein and enters the left atrium
3. The left atrium contracts and forces blood into the left ventricle through the left atrio-ventricular valve
4. The ventricle contracts and the left atrio-ventricular valve closes, forcing blood upwards into the aorta through the semi-lunar valve
5. Oxygenated blood leaves the heart via the aorta to travel to body tissues

Question 25

Describe blood flow through the heart from the body tissues to the lungs

Answer 25

1. Deoxygenated blood from the body returns to the heart in the **vena cava** 2. Deoxygenated blood moves from the superior and inferior vena cava into the **right atrium** 3. The right atrium contracts and blood moves into the **right ventricle** through the **right atrio-ventricular valve** 4. The right ventricle contracts, closing the right atrio-ventricular valve and forcing blood into the **pulmonary artery** through the **semi-lunar** valve 5. Deoxygenated blood travels in the pulmonary artery toward the lungs

Question 26

What 3 stages make up the cardiac cycle?

Answer 26

1. Atrial systole 2. Ventricular systole 3. Diastole

Question 27

Describe atrial systole

Answer 27

Both atria contract forcing the tricuspid and bicuspid valves open. Blood flows from the atria (higher pressure) to the ventricles (lower pressure) Back flow of blood into the veins is prevented by closure of the valves in the veins

Question 28

Describe ventricular systole

Answer 28

Both ventricles contract forcing the blood up and out of the heart (higher pressure) into the arteries (lower pressure) The bicuspid and tricuspid valves close due to pressure from blood in the ventricles. This prevents the back flow of blood into the atria The semi-lunar valves in the aorta and pulmonary artery open

Question 29

Describe diastole

Answer 29

Atria and ventricles relax creating a low pressure in the heart The semi-lunar valves in the aorta and pulmonary artery close due to blood in the aorta (higher pressure) attempting to flow backwards into the ventricles (lower pressure) Blood flows from the veins through the atria and into the ventricles as there is higher pressure in the veins

Question 30

Why is the mean pressure in the lung capillary lower than the muscle capillaries?

Answer 30

- Reduced flow rate which allows for more time for gas exchange - Less tissue fluid produced

Question 31

What causes a drop in pressure in blood vessels?

Answer 31

Friction with vessel walls

Question 32

The heartbeat is initiated from within the heart muscle itself and not due to external stimulation. What is this called?

Answer 32

Myogenic

Question 33

Describe how the heartbeat is controlled

Answer 33

- The sino-atrial node (SAN) acts as a pacemaker - A wave of depolarisation arises at the SAN and electrical impulses spread over the 2 atria causing them to contract simultaneously - The electrical stimulation is prevented from spreading to the ventricles by a thin layer of connective tissue which acts as a layer of insulation - After a short delay the nerve impulse reaches the atrio-ventricular node (AVN). This passes on the impulse to the ventricles - From the AVN the impulse passes down the Bundle of His to the apex of the heart - The bundle branches off into Purkinje fibres in the ventricular walls which carry the wave of depolarisation upwards through the ventricle muscle - The impulses cause the cardiac muscle in each ventricle to contract simultaneously from the apex upwards, forcing blood up and out of the heart

Question 34

What does ECG stand for?

Answer 34

Electrocardiogram

Question 35

What does the **P wave** show?

Answer 35

The depolarisation of the atria during **atrial systole**

Question 36

What does the **QRS wave** show?

Answer 36

The spread of depolarisation through the ventricles, resulting in **ventricular systole**

Question 37

What does the **T wave** show?

Answer 37

The relaxation and repolarisation of the ventricular muscles during **ventricular diastole**

Question 38

What does the length of the PR interval indicate?

Answer 38

Time taken for the electrical impulses to spread from the atria to the ventricles through the atrioventricular nodes

Question 39

Why is the QRS wave bigger than the P wave?

Answer 39

Ventricles have more muscle than the atria so the amplitude is bigger than the P wave

Question 40

Suggest the change in the QRS wave of a person with enlarged ventricle walls

Answer 40

A QRS complex showing greater voltage range