Circulatory System

Question 1

Mammals have a closed double circulatory system, what does “closed” and “double” mean in this context?

Answer 1

Closed = blood is confined to vessels
Double = blood passes twice through the heart for each complete circuit of the body

Question 2

What does the blood transport?

Answer 2

• respiratory gases
• products of digestion eg glucose, amino acids, monoglycerides and fatty acids
• metabolic waste products eg urea
• hormones

Question 3

What does the pulmonary artery do?

Answer 3

Carries blood from the heart to the lungs

Question 4

What does the pulmonary vein do?

Answer 4

Caddies blood from lungs to the heart

Question 5

What does the aorta do?

Answer 5

Carries blood from the heart to the body

Question 6

What does the vena cava do?

Answer 6

Carries blood from the body to the heart

Question 7

What does the renal artery do?

Answer 7

Carries blood from the aorta/body to the kidneys

Question 8

What does the renal vein do?

Answer 8

Carries blood from the kidneys to the heart/vena cava

Question 9

Label the internal structure of the human heart

Answer 9

Question 10

Why do the ventricles have thicker muscle walls then the atria?

Answer 10

Ventricles need to push blood out of the heart to the rest of the body whereas atria just need to push blood a short distance into the ventricles

Question 11

Why is the left ventricle muscle much thicker than the right ventricle?

Answer 11

Allows it to contract more powerfully and pump blood all the way around the body. The right side is less muscular so it’s contractions are only powerful enough to pump blood to the nearby lungs

Question 12

What does the septum do?

Answer 12

Separates the two sides of the heart so oxygenated and deoxygenated blood do not mix. It also enables there to be differnt pressures each side of the heart

• the right side of the heart pumps deoxygenated blood to the lungs
• the left side of the heart pumps oxygenated blood to the whole body

Question 13

Label the external structure of the heart

Answer 13

Question 14

What is the hearts blood supply?

Answer 14

Left and right coronary arteries

Question 15

What do arteries do?

Answer 15

Arteries carry blood from the heart to the rest of the body. They divide into smaller blood vessels called arterioles which form a network throughout the body

Question 16

What is the structure of arteries?

Answer 16

• lumen is small to maintain blood pressure
• collagen fibres and fibrous proteins mean the thick wall can withstand high pressure
• elastic tissue allows the wall to stretch and then recoil - maintains the diastolic blood pressure
• endothelium is smooth to reduce friction and is also folded so can unfold when the artery stretches
• smooth muscle allows contraction thin and vasoconstriction, narrowing lumen of artery

Question 17

What is the blood pressure like in the arteries?

Answer 17

Very high pressure due to the contraction of the left ventricle muscle

Question 18

What does the muscles in arterioles allow?

Answer 18

Enables blood to be directed to different areas of demand in the body - muscle contracts to restrict blood flow and relaxes to allow full blood flow

Question 19

What do veins do?

Answer 19

Veins carry blood back to the heart. Have valves to prevent the back flow of blood

Question 20

What is the structure of veins?

Answer 20

• lumen is large to ease the flow of blood
• walls have less collagen, smooth muscle and elastic tissues as they do not need to perform the roles of the artery. The wall is therefore thin but still strong

Question 21

What is the pressure like in the veins?

Answer 21

Blood is at a lower pressure than the artery, arterioles or capillaries.

There is residual pressure from the contraction of the left ventricle muscle wall

Question 22

What do capillaries do?

Answer 22

Arterioles branch into capillaries which are the smallest of blood vessels. Molecules are exchanged between capillaries and cells

Question 23

What is the structure of capillaries?

Answer 23

• walls are made up of a single layer of flattened endothelial cells which reduces the diffusion distance
• narrow lumen which is the same diameter as a RBC ensures that the cells are squeezed as they travel through the capillaries so reduces diffusion distance, it also slows the RBCs so more time for diffusion
• smooth endothelium which reduces friction for blood flow
• gaps between the endothelial cells allows movement of nutrients proteins cannot pass
• has a large total surface area/ cross sectional area allowing for more exchange

Question 24

What is the blood pressure like in capillaries?

Answer 24

Blood is at high pressure at the arteriole end due to the contraction of the left ventricle wall but the pressure falls as it goes towards the venous end

Question 25

Describe what happens at each of the 3 stages on this graph in regards to pressure changes in blood vessels

Answer 25

1) high pressure in arteries due to contraction of left ventricles
2) fluctuation is due to stretching and recoiling of elastic fibres
3) pressure decreases through arterioles and capillaries and venues and veins due to moving further from the heart, splitting into more blood vessels

Question 26

What are the 3 stages of the cardiac cycle?

Answer 26

1. Atrial systole - ventricles relax, atria contracts
2. Ventricular systole - ventricles contract, atria relax
3. Diastole - ventricles and atria relax

Question 27

What is systole?

Answer 27

Contraction of cardiac muscle

Question 28

What is diastole?

Answer 28

Relaxation of cardiac muscle

Question 29

How long does the cardiac cycle last?

Answer 29

Around 0.8 seconds giving a heart rate of 75 beats per minute

Question 30

Describe atrial systole

Answer 30

• atria fill with blood
• atria contract decreasing the volume of the atria and increasing the pressure inside the chambers
• blood is squeezed into ventricle via atrioventricular valve
• pressure is greater in the atria than the ventricle causing the atrioventricular valve to open

Question 31

Describe ventricular systole

Answer 31

• ventricles contract decreasing their volume and increasing the pressure inside the chambers
• the pressure inside the ventricle became higher than the pressure inside the atria forcing the atrioventricular valves shut to prevent back flow
• the pressure in the ventricles is also higher than taht of the arteries which forces the semi lunar valves open

Question 32

Describe ventricular and atrial diastole

Answer 32

• ventricles and atria both relax
• the higher pressure in the arteries then ventricles causing the semi-lunar valves to close to prevent back flow of blood into the ventricles
• atria fill with blood
• cycle starts again

Question 33

What causes valves to open?

Answer 33

Valves open when the pressure above the valve is greater than below it.

• atrioventricular valves open when the pressure in the atria is greater than the ventricles
• semi-lunar valves open when the pressure in the ventricles is greater than the arteries

Question 34

What causes valves to close?

Answer 34

Valves close when the pressure beneath the valve is greater than above it. Valves close to prevent the back flow of blood

The lub dub sound the heart makes is due to the closing of the atrioventricular valve followed by the closing of the semilunar valve

Question 35

Learn:

Answer 35

Question 36

What is an electrocardiogram? (ECG)

Answer 36

Monitors the electrical activity of the heart. Electrical activity generated by the heart spreads through the tissue nearby. Sensors on the skin pick up the electrical excitation created by the heart and turn it into a trace

P- excitation of the atria
Q,R,S - excitation of the ventricles
T - diastole

Question 37

What is the equation for cardiac output?

Answer 37

Cardiac output = stroke volume x heart rate

• Cardiac output - volume of blood pumped by the heart per minute

• Heart rate - the number of beats per minute

• stroke volume - volume of blood pumped during each heartbeat