12.10a Mass Transport in Humans

Question 1

Function of the heart

Answer 1

Pumps blood around the body

Question 2

Define closed double circulatory system.

Answer 2

• Closed- the blood remains within the blood vessels.
• Double circulatory system- the blood passes through the heart twice in each circuit. There is one circuit that delivers deoxygenated blood to the lungs and the other delivers oxygenated blood to the rest of the body.

Question 3

Veins- towards or away from the heart?

Answer 3

Towards the heart.

Question 4

Arteries- towards or away from the heart?

Answer 4

Away from the heart.

Question 5

Define pulmonary circulation.

Answer 5

Blood passes through the heart and is pumped to the lungs, returning to the heart.

Question 6

Define systematic circulation

Answer 6

The blood passes through the heart a second time (and is repressurised) and it pumped around the body organs, before returning to the heart.

Question 7

Which are the highest, high, lowest and low pressure arteries/veins?

Answer 7

Highest pressure- Aorta (Heart to Body)
High pressure- Pulmonary Artery (Heart to Lungs)
Lowest pressure- Vena Cava (Body to Heart)
Low pressure- Pulmonary Vein (Lungs to Heart)

Question 8

Explain mass flow.

Answer 8

• The bulk movement of blood due to a pressure difference.
• Essential for efficient transport of blood around the body.
• Easier to generate and maintain a pressure gradient.
• Blood moves due to the pressure difference in the heart (high) & in the blood vessels (low)

Question 9

What is the wall of the heart made of and what are the heart cells called?

Answer 9

• Wall is made of cardiac muscle which is myogenic (can contract/relax without nervous/hormonal stimulation)
• Cells are cardiomyocytes.

Question 10

Explain the movement of blood in the heart.

Answer 10

• Deoxygenated blood returns from the body in the vena cava and enters the right atrium.
• The blood then passes into the right ventricle via an atrioventricular valve.
• Then passes out into the pulmonary artery via a semi-lunar valve.
• The blood now passes through the lungs and returns to the left atrium via the pulmonary vein.
• The blood passes through the second atrioventricular valve into the left ventricle.
• Then passes through the semi-lunar valve into the aorta and then to body tissue.

Question 11

Why are the walls of the left ventricle much thicker than the right ventricle?

Answer 11

• The right ventricle is pumping blood through pulmonary arteries only.
• Left ventricle is pumping blood through a larger number of capillaries (which branch off from the aorta) around the body.
• Left ventricle requires more pressure.

Question 12

Why does pressure change in each of the heart chambers?

Answer 12

Due to changes in the volume of blood and contractions of the heart muscle.

Question 13

Explain the cardiac cycle in terms of pressure and volume changes and associated valve movements, to maintain a unidirectional flow of blood.

Answer 13

• When blood enters the atrium, blood volume increases, and pressure increases in atrium. The pressure in the atrium is greater than in the ventricle so the atrioventricular valve opens.
• The atrium muscles systole (contract), so the remaining blood is forced into the ventricle from the atrium.
• When the blood enters the ventricle, the pressure increases in the ventricle due to volume of blood. The pressure in the ventricle is now greater than in the atrium, so the atrioventricular valve closes.
• The ventricle muscles systole, atrial muscles diastole (relaxes) which further increases pressure in ventricle until it is greater than in the aorta/pulmonary artery. The semi-lunar valve opens.
• Blood will then enter the aorta/pulmonary artery and is either pumped to the body (left) or to the lungs (right).
• Ventricle muscles diastole and the pressure in the ventricle is less than in the aorta/pulmonary artery, so the semi-lunar valve now closes.
• The process happens again for the other side of the heart.

Question 14

Function of the heart valves

Answer 14

• Atrio-ventricular valves and semi-lunar valves ensure the blood flows in one direction through the heart.
• The valves will only open in one direction, and open and close due to pressure differences on either side of the valve.

Question 15

When do atrioventricular valves open and close in terms of pressure?

Answer 15

• Open- greater pressure in atria than ventricles.
• Close- greater pressure in ventricles than atria.

Question 16

When do semi-lunar valves open and close in terms of pressure?

Answer 16

• Open- greater pressure in ventricles than arteries (pulmonary arteries and aorta)
• Close- greater pressure in arteries than ventricles.

Question 17

What is the equation to measure the activity of the heart?

Answer 17

Cardiac output= stroke volume x heart rate
* Cardiac output- volume of blood pumped out from the left ventricle per minute.
(dm3 min-1)
* Stroke volume- volume of blood pumped out from left ventricle in one cardiac cycle.
* Heart rate- number of cardiac cycles/beats per minute.

Question 18

What are the coronary arteries and what happens if they become blocked?

Answer 18

• Branch from the aorta and take blood to the cardiac muscle from the heart. The heart muscle needs its own capillary supply for rapid delivery of oxygen.
• If they become blocked, cardiac muscle will not receive oxygen and wont be able to respire and the cells will die (heart attack)

Question 19

What are the veins and arteries of the kidney called?

Answer 19

Renal vein and Renal artery

Question 20

What are the veins and arteries of the liver called?

Answer 20

Hepatic vein and Hepatic artery

Question 21

Explain the structure of arteries in relation to its function.

Answer 21

• Transports blood at high pressure from heart to organs- wall is very thick to withstand this pressure.
• Has an endothelial layer which is only one cell thick- this gives a smooth layer to reduce friction and give a smooth flow.
• Contains a large thick elastic protein fibre layer- maintains hydrostatic (blood) pressure of blood as the walls stretch as blood flows past and once it has passed it will recoil.
• Has a thick muscle layer- constricts the vessel and reduces volume of blood passing which increases blood pressure.
• The outer layer is made of fibrous proteins- giving support and strength to wall, which helps it resist damage from high pressure of blood inside.

Question 22

Explain the structure of arterioles in relation to its function.

Answer 22

• Smaller vessel diameter than arteries (and connect artery to capillaries)- greater friction between blood and wall, so lower blood pressure.
• Wall is thinner- pressure is slightly lower.
• Elastic layer is thinner than artery- blood pressure is lower so there is no need for the same elasticity as arteries to let the pulse of blood pass.
• Muscle layer is thicker than artery- restricts blood flow into capillaries

Question 23

Explain the structure of the veins in relation to its function.

Answer 23

• Carries blood back to the heart from the tissues, low pressure, so relatively thin.
• Relatively thinner muscle layer than artery- no need for vaso-constriction, as blood flow cannot be controlled.
• Elastic layer is thin as the pressure is very low- no need to stretch and recoil.
• Has valves which only allow blood to flow in one direction to ensure the blood returns to the heart.
• Bigger lumen

Question 24

Explain the structure of the capillary in relation to its function.

Answer 24

• Only has endothelial layer which is one cell thick- short diffusion distance for exchanging material between blood and tissue cells.
• Small diameter but large number of capillaries- creates greater friction and high surface area, reducing blood pressure and blood flow as it passes through the capillary.
• Narrow diameter- ensures RBC is in contact with the wall.

Question 25

What is tissue fluid?

Answer 25

Fluid containing water, glucose, amino acids, fatty acids, ions and oxygen which surrounds body cells.

Question 26

Define ultrafiltration.

Answer 26

Hydrostatic (fluid) pressure of blood is greater than hydrostatic pressure of tissue fluid meaning there is a net force pushing the fluid containing water, glucose, amino acids and other small molecules out of the capillary fenestrations.

Question 27

Describe how tissue fluid is formed and how it is returned to the circulatory system.

Answer 27

Formation * High blood/hydrostatic pressure * Forces tissue fluid and other small molecules out * Large proteins remain in capillary Return * Lower water potential in capillary * Due to large number of plasma proteins and less tissue fluid * Water enters the capillary at the venous end * By osmosis * Excess water is removed from the tissue via lymph vessel.

Question 28

What happens to the rest of the tissue fluid which isnt reabsorbed?

Answer 28

* Lymphatic system has lymph vessels which surround blood vessels. * Any liquid that doesn’t get reabsorbed into capillary is absorbed into lymph vessels. * It will eventually empty back to blood near neck region.

Question 29

How can a blockage in the lymphatic system cause swelling?

Answer 29

Excess tissue fluid cannot be reabsorbed/ builds up.

Question 30

Risk factors in Coronary Heart disease

Answer 30

-high cholesterol diet -high lipid diet -lack of exercise -smoking CAUSES -high blood pressure -increase blood toxins -increase level of cholesterol in blood LEADS TO -damage to endothelium wall -increase in lipid uptake

Question 31

Explain how an arteriole can reduce the blood flow into capillaries.

Answer 31

1. Muscle contracts; 2. Constricts/narrows arteriole/lumen;

Question 31

Explain how an arteriole can reduce the blood flow into capillaries.

Answer 31

1. Muscle contracts; 2. Constricts/narrows arteriole/lumen;

Question 32

Describe the pathway taken by an oxygen molecule from an alveolus to the blood

Answer 32

1. (Across) alveolar epithelium; 2. Endothelium of capillary;

Question 33

Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions. (6)

Answer 33

Elastic tissue 1 Elastic tissue stretches under pressure/when heart contracts; 2 Recoils/springs back; 3 Evens out pressure/flow; Muscle 4 Muscle contracts; 5 Reduces diameter of lumen/vasoconstriction/constricts vessel; 6 Changes flow/pressure; Epithelium 7 Epithelium smooth; 8 Reduces friction/blood clots/less resistance;

Question 34

The thickness of the aorta wall changes all the time during each cardiac cycle. Explain why. (5)

Answer 34

1. (Aorta wall) stretches; 2. Because ventricle/heart contracts / systole / pressure increases; 3. (Aorta wall) recoils; 4. Because ventricle relaxes / heart relaxes /diastole / pressure falls; 5. Maintain smooth flow / pressure;

Question 35

Heart rate equation

Answer 35

Heart rate = cardiac output ÷ stroke volume