Chapter 8: Transport in Humans

Question 1

Explain the difference between the lumen size of arteries and veins

Answer 1

Arteries have smaller lumen than that of veins (note: vena cava has the largest lumen)
- Blood pressure in veins is relatively low
- Large lumen reduces resistance to facilitate the blood flow inside the veins

2017DSE
Veins have large lumen, HENCE (NOT because) the blood pressure inside them is low

Question 2

Explain the difference between the thickness of the walls of the arteries and veins

Answer 2

Walls of arteries are thicker than that of veins
Reason:
More direct pumping action of the heart drives the blood flow inside arteries
Blood pressure inside arteries is higher than that in veins
Arteries have a thicker wall to withstand high blood pressure due to the more direct pumping action of the heart

Question 3

Why do arterial walls have a thicker elastic tissue than the walls of veins?

Answer 3

Allows the arteries to distend and recoil → provides force for blood to move forward
Maintaining a high blood pressure for maintaining continuous blood flow along arteries

Question 4

Why do walls of arteries have thicker layers of smooth muscle than walls of veins?

Answer 4

Contract or relax to change the diameter of the lumen of the artery → regulate the amount of blood flow to different body parts

Question 5

Why is the rate of blood flow higher in arteries than veins?

Answer 5

Arteries:
(direct) pumping action of the heart → Elastic muscllar wall distends and recoils → provides recoiling force to push blood forward

Veins:
Blood pressure dropps after blood passes through capillaries

Question 6

Which of the following are responsible for the periodic chage in the blood pressure of the aorta?
1. Pumping of heart
2. Thickness of wall of aorta
3. Elasticity of the wall of the aorta

A. (1) only
B. (2) only
C. (1) and (3) only
D. (1), (2) and (3)

Answer 6

(1) and (3)

Question 7

Force for blood flow (Source)

Answer 7

Arteries: Pumping action of the heart
Veins: contraction of adjacent skeletal muscles lying next to the veins

Question 8

Blood pressure - Arteries and arterioles

Answer 8

Blood pressure is high
Reasons:
- (Direct) pumping force of the heart
- Elastic muscles distend and recoil to provide recoiling force to push the blood forward

Question 9

Explain the significance of the presence of valves in veins

Answer 9

• Contraction of adjacent skeletal muscles lying next to the veins pushes blood in veins forward, which squeezes the blood along
• Valves are closed to prevent the backflow of the blood
• Significance: Ensures that blood flows in one direction back to the heart

Question 10

Valves in arteries

Answer 10

No valves EXCEPT for the base of the aorta and pulmonary artery

Question 11

Why is water potential of blood contant in arteriole/venule?

Answer 11

• The vessel walls of the arteriole and venule are wrapped with fibrous tissue, smooth muscles and elastic
• tissue.
• This outer layer is too thick for water or dissolved substances to pass through as the distance for diffusion is too long. (1)
• There is therefore no exchange of materials between the blood in the arteriole and venule and the surrounding tissue fluid. (1)
• Thus the blood content and hence the water potential remains unchanged.

Question 12

Capillaries: features

Answer 12

1. Small lumen (slightly larger than the diameter of a RBC)

2. Highly branched capillaries network
Each artery branches into a large number of capillaries
Large surface area for the exchange of materials
Large total cross-sectional area
→ reduce rate of blood flow in capillaries
→ longer and hence sufficient time for exchange of materials (such as oxygen, nutrients and waste) between body cells and blood cells
DO NOT write diffusion, because active transport is also involved

3. Capillary wall:
- One-cell thick endothelium → Short diffusion distance for the exchange of materials
- Differentially permeable
- No muscular wall → cannot constrict or dilate

Question 13

Blood pressure in arteries and arterioles

Answer 13

• Blood pressure is high due to the more direct pumping action of the heart.
• The increase in blood pressure increases blood flow, and hence travelling distance.
• Pressure in arteries and arterioles decreases rapidly because the decreasing size of lumen increases frictional resistance to blood flow.

Question 14

Blood pressure in capillaries

Answer 14

• Significant drop (compared to arteries) of blood pressure along the capillaries
• small diameter of the capillaries → high resistance to blood flow

Question 15

Blood pressure in veins

Answer 15

The blood pressure in the vein is much lower than that in the artery
● The blood in the artery is under more direct pumping action of the heart, while that of the vein is not
● The blood in the vein has overcome great resistance after travelling over a long distance
● There is a loss of fluid from the blood during the formation of the tissue fluid

Question 16

Explain how the rhythmic changes in blood pressure are related to the heart activity.

Answer 16

Note: Answer is in terms of the LEFT side of the heart (because blood pressure → oxygenated blood → LEFT)

● When the wall of the left ventricle of the heart contracts, (+ pressure is higher than that in aorta → semilunar valves open) blood is forced into the aorta → blood pressure increases
[Ventricular systole]
● Blood in aorta flows forwards along blood vessels while the wall of the left ventricle relaxes → blood pressure drops
[Diastole]

Question 17

Which has the total cross sectional area, blood capillaries, arteries or veins?

Answer 17

Capillaries have the highest total cross-sectional area
- Highly-branched network → number of capillaries is large
- Provides a large surface area for rapid exchange of materials between the blood and body cells
- Blood flow rate is small to provide sufficient time for nutrients exchange

Question 18

Rate of blood flow: arteries and arterioles

Answer 18

• Rate of blood flow in the arteries is high under the direct pumping force of the heart. The elastic muscular wall provides recoiling force to increase the heart pumping force.
• When the arteries branch into arterioles, the total cross-sectional area of the arterioles increases, so the flow rate drops.

Question 19

Rate of blood flow: capillaries

Answer 19

• Greatest total cross-sectional area
• The rate of blood flow drops to nearly zero
• more time for the exchange of materials between body cells and blood

Question 20

Rate of blood flow: veins

Answer 20

• Rate of blood flow increases due to the contraction of skeletal muscles lying next to the veins. When the muscles contract, force is exerted on the wall of the veins/venules. The extra force partially restores the blood flow rate in veins/venules/vena cava (to a level near to that of the aorta) (despite its low blood pressure)
• Veins have large lumens to reduce resistance to blood flow to maintain blood flow.
• The total cross-sectional area of the veins is smaller than that of the capillaries.
• Since the volume of blood passing through each section of the blood vessel per unit time is the same, the rate of blood flow increases.

Question 21

Septum

Answer 21

• Separates the left side and the right side of the heart
• Prevents the mixing of oxygenated blood and deoxygenated blood

Question 22

What will happen if there is a hole in the septum?

Answer 22

• Oxygenated blood mixes with deoxygenated blood
• Oxygen content of blood pumped out of the heart decreases
• The heart has to pump more to meet the demand of body cells

Question 23

Coronary arteries

Answer 23

Supply oxygen and nutrients to the cardiac muscles

Question 24

Reason for formation of the cholesterol plaque in the artery

Answer 24

Formation of the cholesterol plaque in the artery is partly due to a low fibre, high fat diet.

Question 25

What will happen if fatty substances (e.g. (cholestrol plague) are deposited on the inner wall of the coronary artery?

Answer 25

Block the coronary vessel
- block supply of oxygen and nutrients to the cardiac muscles
- Heart muscles will die/risk of heart attack increases since blood supply to the cardiac
muscle is reduced
- Larger fatty substances (e.g. cholestrol plague), higher blood pressure (reason: smaller lumen)

Question 26

What can be done if cholestrol deposits on the coronary artery and obstructs it?

Answer 26

• Formation of the cholesterol plaque in the artery is partly due to a low fibre, high fat diet.
• Inserting an inflated balloon helps to widen the lumen in the artery and may restore normal blood flow through the artery.

Question 27

Bicuspid valves and tricuspid valves

Answer 27

Separate the atria from the ventricles
- They are held in place by tough heart tendons, which prevent the valves from turning inside
out when the ventricular walls contract
- The closure of heart valves is due to an increase in pressure of the ventricles (just higher than the atria), but not an increase in pressure of heart tendons

Question 28

Bicuspid VS tricuspid valves

Answer 28

Bicuspid:
- Left side of the heart (oxygenated blood)
- 2 flaps (bi)
From the left ventricle to the left atrium when the left ventricular walls contracts

Tricuspid:
- Right side of the heart (deoxygenated blood)
- 3 flaps (tri)
- From the right ventricle to the right atrium when the right ventricular walls contracts

Question 29

Semilunar valves

Answer 29

Present at the base of the aorta and the
pulmonary artery to prevent the backflow of blood from the aorta into the ventricles when the ventricles relax.
- NOT held by heart tendons

Question 30

What will happen if the bicuspid valve cannot close properly?

Answer 30

When the wall of the left ventricle contracts, oxygenated blood will flow back from the left
ventricle to the left atrium through the opened valve.
- Unidirectional flow of blood in the heart cannot be maintained.
- Less oxygenated blood is pumped out of the left ventricle through the aorta in each heart beat.
- The heart cannot pump blood to the rest of the body efficiently and the rate of blood flow
decreases

Question 31

Structures protecting the heart

Answer 31

1. Rib cage (does NOT include the intercostal muscles)
2. Pericardium filled with pericardial fluid (reduces friction within the pericardium by allowing the
   membranes to glide over each other with each heartbeat)

Question 32

Ventricles: features (in general)

Answer 32

Ventricular WALL contract

• The ventricles receive blood from the atria and are connected to the arteries which carry blood away from the heart to all parts of the body.
• They have a thicker muscular wall than the atria to generate a greater force of contraction to pump blood over a longer distance to all parts of the body; When the ventricular walls contract, they pump blood out of the heart at high pressure.

[16DSE]
● The ventricles pump out a larger volume of blood than atria

Question 33

Right ventricle

Answer 33

pumps deoxygenated blood to the lungs via the pulmonary artery
● Because the distance between the lungs and the heart is close, the heart
pumping force is adjusted to prevent damage to capillaries and lungs by
exceptionally high blood pressure.

Question 34

Left ventricle

Answer 34

pumps oxygenated blood to the rest of the body via the aorta

● The muscular wall of the left ventricle is thicker than that of the right ventricle
because the walls of the left ventricle has to generate greater force of
contraction to pump blood over a long distance to all parts of the body (except
the lungs) whereas the right ventricle pumps blood for only a short distance to the lungs.
● Increase in blood pressure ⇒ increase in blood flow rate ⇒ increase in travel distance

Question 35

Atria: features

Answer 35

The atria are connected to the veins which carry blood from different parts of the body of the heart.
They have a thinner muscular wall than the ventricles; receive blood at low pressure from the veins.
- Right atrium: receives deoxygenated blood from the anterior vena cava and the posterior vena cava. The anterior vena cava carries blood from the head and arms. The posterior vena cava carries blood from the legs and abdomen.
- Left atrium: receives oxygenated blood from two pulmonary veins from the lungs.

Question 36

Components of tissue fluid

Answer 36

Similar to blood
Present: WBCs, plasma, glucose, amino acids
Absent: RBCs, plasma proteins (water-soluble; will decrease water potential of blood), platelets

Question 37

Importance of tissue fluid

Answer 37

• All body cells are bathed in tissue fluid, relatively constant environment (e.g. temperature) for the normal functions of the body cells
• Important link for the exchange of materials between the blood in the capillaries and body cells

Question 38

Factors that govern the movement of fluid between the capillary netweok and tissue fluid

Answer 38

1. Water potential gradient between blood and tissue fluid
[Tissue fluid → capillaries, venous]
- Water potential of tissue fluid is higher than that of blood due to the presence of water-soluble plasma proteins in blood, which is absent in tissue fluid.
- Tends to force water back in capillary due to the presence of water-soluble plasma proteins in blood

2. Difference between hydrostatic poressure of blood and tissue fluid
[Capillaries → tissue fluid, arterial]
- highest at arterial end due to the pumping action of heart

Question 39

Arteriole end of blood capillary network

Answer 39

• At the arterial end of the capillary bed, the hydrostatic pressure of blood in the capillaries is higher than that of the fluid surrounding the body cells/tissue fluid AND the water potential gradient between the blood and the tissue fluid.
• This forces some components of the plasma (e.g. water, minerals, sugars, lipids, antibodies and hormones) out of the capillary walls to form tissue fluid.
• Plasma proteins, red blood cells and blood platelets are too large to pass through the capillary walls. They remain in the blood and drain to the venous end.
• White blood cells can squeeze through the capillary walls. Thus, the composition of tissue fluid is similar to blood except for the absence of red blood cells, plasma proteins, and blood platelets.

Question 40

Venous end

Answer 40

As plasma proteins (X rbc/blood platelets because they are insoluble in water and wouldn’t affect
water potential) remain in the blood, the water potential of the blood at the venule end of the capillaries is lower than that of tissue fluid. [Note: WP gradient is unchanged]

As fluid is forced out the blood at the arterial end the blood volume also decreases, and the hydrostatic pressure decreases

High resistance at venous end, lower blood pressure, lower hydrostatic pressure
Water potential gradient > difference in hydrostatic pressure
The water in the tissue fluid is drawn into the capillaries by osmosis.
- Most tissue fluid returns to the blood at the venule end of the capillaries.

Question 41

Formation of lymph

Answer 41

• Excess tissue fluid will enter the lymph vessels to form the lymph
• due to the higher hydrostatic pressure in the tissue spaces than in the lymph vessel.
• Contraction of skeletal muscles squeezes the lymph vessels and the presence of valves in the lymph vessels prevents the backflow of lymph.
• Thus, the lymph will flow along the lymph vessels and eventually joins the
• vein near the neck region,
• then to the vena cava and returns to the heart.

Question 42

Lymph vessels

Answer 42

Lymph capillaries are blind-ended vessels. These lymph vessels are connected to two
large veins (vena cava) near the neck region, where the lymph is returned to the blood circulation.

Different from veins:
- Lymph vessels are usually found deep inside the body.

Similar to veins:
- Lymph is kept flowing very slowly by the contraction of skeletal muscles lying
next to the lymph vessels.
- Valves are present in the lymph vessels to prevent the backflow of lymph.

Question 43

Lymph nodes

Answer 43

• Located at intervals along the lymph vessels
• Many white blood cells accumulate there
• Lymph is filtered through lymph nodes before it returns to the blood circulation. When lymph passes through lymph nodes, the white blood cells kill the germs in the lymph.

Question 44

Explain why lymph nodes may become enlarged when a person has a sore throat.

Answer 44

• Lymph nodes contain many white blood cells. When a person has a sore throat, an infection occurs.
• White blood cells in the lymph node are stimulated to multiply to kill the bacteria or virus.
• The accumulation of white blood cells and dead germ cells enlarges the node.

Question 45

Blood vessels deoxygenated blood in veins has to pass through in order to become oxygenated again

Answer 45

Vein→ vena cava→ right atrium→ right ventricle→ pulmonary artery→ blood
capillaries surrounding air sacs in the lungs→ pulmonary vein→ left atrium→ left ventricle→ aorta → artery

Question 46

2024 HKDSE [Part A]
https://drive.google.com/file/d/1vtWxHW6klt5xdB29U9JMF7ZujSDE5-Kl/view?usp=drive_link

Answer 46

• Black arrow: water potential gradient between blood and tissue fluid
• White arrow: difference in hydrostatic pressure between blood and tissue fluid

Question 47

2024 HKDSE [Part B]
https://drive.google.com/file/d/1vtWxHW6klt5xdB29U9JMF7ZujSDE5-Kl/view?usp=drive_link

Answer 47

• The difference in hydrostatic pressure between blood and tissue fluid decreases
• As fluid is forced out of the blood at the end of capillaries near P
• the blood volume in the capillaries decreases and hence decreases hydrostatic pressure

Question 48

1986 HKCEE [ALL]
https://drive.google.com/file/d/15DI4vTgT9anBb7eJ1wgG-_xRUQA8cMUE/view?usp=sharing

Answer 48

i) valves
ii) veins
iii)
- movement of finger B pushed blood away from the segment
- valves at Q close to prevent the backflow of blood and ensure unidirectional flow of blood back to the heart
iv)
1. make the vein more conspicious by stopping/slowing down the blood flow
2. to allow normal blood flow in the arm again

Question 49

Importance of increasing heart rate during exercising [HKCEE]

Answer 49

During exercise, the heart beats rapidly to supply more blood to the skeletal muscle. This provides an
abundant supply of oxygen and glucose to the muscles so that a larger amount of energy can be released in respiration for the vigorous contraction of the skeletal muscles. At the same time, more blood supply to the muscles also helps to rapidly remove the carbon dioxide produced by the muscles in respiration.

Question 50

When a person with a narrowed coronary artery exercises

Answer 50

Risk of heart attack is higher
The workload of the heart muscle cells is increased during vigorous exercise.
Narrowing of the coronary artery’s results in a reduced blood flow to the heart muscles, and thus reducing the supply of oxygen and glucose to the heart muscle cells. Some heart muscle cells may die.
Risk of fainting is higher
During vigorous exercise, the oxygen consumption of the skeletal muscles is very high. The blood flow rate will not be high enough to carry a sufficient supply of oxygen to the body cells for rapid respiration. When the brain is not supplied with enough oxygen, the person faints.
Risk of cardiac muscle fatigue is higher
A smaller volume of blood is pumped out of the heart. To ensure the same supply of blood to body cells, cardiac muscles need to contract stronger and more rapidly, which results in cardiac muscle fatigue.

Question 51

A man’s bicuspid valve cannot close properly. Explain why he would faint easily during exercise.

Answer 51

• If the bicuspid valve cannot close properly, oxygenated blood in the LEFT ventricle will flow back to the LEFT atrium during exercise
• Less oxygenated blood can be pumped out of the heart in each beat
• During vigorous exercise, the rate of consumption of oxygen by skeletal muscles is very high
• Increases the risk of insufficient oxugen supply to the brain

Question 52

Why does Mabel’s lower legs become swollen after she takes a 16-hour flight?

Answer 52

Sedentary -> contraction of skeletal muscles in the lower legs decreases -> tissue fluid is drained from the legs more slowly

Question 53

What should Mabel do if her lower legs are swollen after a 16-hour flight?

Answer 53

• stretch legs more (1)
• swollen feet in lower legs are due to the accumulation of tissue fluid (1)
• stretching legs more often helps since skeletal muscles contraction can squeeze the lymph vessels and more lymph flows away from the legs back to the circulatory system (1)
• This reduces the accumulation of tissue fluid (1)