15.2

Question 1

What is the function of the arteries? (1)

Answer 1

they transport blood away from the heart rapidly under high pressure

Question 2

What is the function of the veins? (2)

Answer 2

(1) they carry blood slowly under low pressure
(2) from capillaries back to the heart

Question 3

What are the functions of the capillaries? (2)

Answer 3

(1) they link arterioles to veins
(2) allow exchange of substances

Question 4

What is the function of the arterioles? (2)

Answer 4

(1) they carry blood under lower pressure than arteries
(2) and control blood flow from the arteries to the capillaries

Question 5

There are 4 layers inside arteries, arterioles and veins:
1. the tough outer layer
2. the muscle layer
3. the elastic layer
4. the thin inner lining (endothelium).

What is the function of the tough outer layer? (1)

Answer 5

it resists pressure changes from both within & outside the vessel

Question 6

There are 4 layers inside arteries, arterioles and veins:
1. the tough outer layer
2. the muscle layer
3. the elastic layer
4. the thin inner lining (endothelium).

What is the function of the muscle layer? (1)

Answer 6

it contracts & controls blood flow

Question 7

There are 4 layers inside arteries, arterioles and veins:
1. the tough outer layer
2. the muscle layer
3. the elastic layer
4. the thin inner lining (endothelium).

What is the function of the elastic layer? (1)

Answer 7

it maintains blood pressure by stretching & recoiling

Question 8

There are 4 layers inside arteries, arterioles and veins:
1. the tough outer layer
2. the muscle layer
3. the elastic layer
4. the thin inner lining (endothelium).

What is the function of the endothelium? (2)

Answer 8

(1) it’s smooth to prevent friction
(2) it’s thin to allow diffusion

Question 9

How do arterioles differ from arteries? (2)

Answer 9

(1) they are smaller in diameter
(2) they have a larger muscle layer & larger lumen

Question 10

Which blood vessels carry out exchange of substances? (1)

Answer 10

capillaries (the others only transport blood)

Question 11

Arteries have a:
1. thick muscle layer
2. thick elastic layer
3. thick wall overall
4. no valves.

Why do arteries have a thick muscle layer? (2)

Answer 11

(1) To allow constriction & dilation,
(2) controlling the volume of blood passing through

Question 12

Arteries have a:
1. thick muscle layer
2. thick elastic layer
3. thick wall overall
4. no valves.

Why do arteries have a thick elastic layer? (2)

Answer 12

(1) To maintain high blood pressure
(2) by stretching & recoiling with each heartbeat

Question 13

Arteries have a:
1. thick muscle layer
2. thick elastic layer
3. thick wall overall
4. no valves.

Why are arterial walls thick overall? (1)

Answer 13

To resist bursting under high pressure

Question 14

Arteries have a:
1. thick muscle layer
2. thick elastic layer
3. thick wall overall
4. no valves.

Why do arteries not have any valves? (1)

Answer 14

Because blood in arteries is under constant high pressure, which prevents back flow

Question 15

Arterioles have a:
1. thicker muscle layer than arteries
2. larger lumen than arteries
3. thinner elastic layer than arteries

Why do arterioles have a relatively thicker muscle layer than arteries? (1)

Answer 15

To allow better control of blood flow (by constricting and dilating)

Question 16

Arterioles have a:
1. thicker muscle layer than arteries
2. larger lumen than arteries
3. thinner elastic layer than arteries

Why do arterioles have a larger lumen relative to their size? (1)

Answer 16

Because their walls are thinner than arteries

Question 17

Arterioles have a:
1. thicker muscle layer than arteries
2. larger lumen than arteries
3. thinner elastic layer than arteries

Why do arterioles have a relatively thinner elastic layer than arteries? (1)

Answer 17

Because arterioles operate under lower blood pressure

Question 18

Veins have a:
1. thin muscle layer
2. thin elastic layer
3. thin wall overall
4. valves

Why do veins have a relatively thin muscle layer? (1)

Answer 18

Because their constriction and dilation do not significantly control blood flow

Question 19

Veins have a:
1. thin muscle layer
2. thin elastic layer
3. thin wall overall
4. valves

Why do veins have a relatively thin elastic layer? (1)

Answer 19

Because blood pressure in veins is too low to require stretch and recoil

Question 20

Veins have a:
1. thin muscle layer
2. thin elastic layer
3. thin wall overall
4. valves

Why do veins have a thin wall overall? (1)

Answer 20

Because the pressure inside veins is low so they do not need thick walls

Question 21

Veins have a:
1. thin muscle layer
2. thin elastic layer
3. thin wall overall
4. valves

Why do veins have valves? (1)

Answer 21

To prevent backflow and ensure blood flows only towards the heart

Question 22

Why is the blood flow in capillaries much slower? (1)

Answer 22

to allow more time for the exchange of materials

Question 23

Capillaries have a:

1. wall that only consists of endothelium
2. are numerous & highly branched
3. narrow diameter
4. narrow lumen
5. spaces between endothelial cells.

Why do capillary walls consist only of endothelium? (2)

Answer 23

(1) To create an extremely thin barrier,
(2) reducing the diffusion distance for rapid exchange

Question 24

Capillaries have a:

1. wall that only consists of endothelium
2. are numerous & highly branched
3. narrow diameter
4. narrow lumen
5. spaces between endothelial cells.

Why are capillaries numerous & highly branched? (1)

Answer 24

To provide a large surface area for diffusion

Question 25

Capillaries have a: 1. wall that only consists of endothelium 2. are numerous & highly branched 3. narrow diameter 4. narrow lumen 5. spaces between endothelial cells. What is the significance of the narrow diameter of capillaries? (2)

Answer 25

(1) It ensures that **no cell is far from a capillary**, (2) promoting **efficient diffusion**

Question 26

Capillaries have a: 1. wall that only consists of endothelium 2. are numerous & highly branched 3. narrow diameter 4. narrow lumen 5. spaces between endothelial cells. Why is the capillary lumen so narrow? (2)

Answer 26

(1) To **squeeze red blood cells against the capillary wall** (2) **reducing** the **diffusion distance**

Question 27

Capillaries have a: 1. wall that only consists of endothelium 2. are numerous & highly branched 3. narrow diameter 4. narrow lumen 5. spaces between endothelial cells. What is the function of spaces between endothelial cells in capillaries? (1)

Answer 27

To allow **white blood cells to escape** and ***deal with infections** within tissues

Question 28

What is tissue fluid? (2)

Answer 28

(1) A **watery liquid** that contains glucose, amino acids, salts and oxygen, providing nutrients to the tissues (2) while receiving waste products from the tissues

Question 29

What's the relationship between tissue fluid and blood plasma? (2)

Answer 29

(1) Tissue fluid is **formed** from blood plasma (2) but **lacks larger molecules** like proteins and cells

Question 30

Why is tissue fluid important for homeostasis? (2)

Answer 30

(1) It provides a **mostly constant environment** for cells, (2) ensuring their **proper function**

Question 31

What pressure forces the tissue fluid out of the blood plasma? (1)

Answer 31

**Hydrostatic pressure** at the arterial end of the capillaries

Question 32

What two forces oppose hydrostatic pressure in capillaries? (2)

Answer 32

(1) The **lower water potential** of the **blood** (due to plasma proteins), pulling **water back into capillaries** (2) the **hydrostatic pressure** of the **tissue fluid outside** the **capillaries**

Question 33

Why does hydrostatic pressure in capillaries decrease along their length? (2)

Answer 33

(1) Because some **tissue fluid is pushed out** (2) **reducing the pressure inside the capillaries**

Question 34

Explain what type of filtration occurs during the tissue fluid formation (2)

Answer 34

(1) **ultrafiltration** (2) **Small molecules are forced out of the capillaries under pressure**, leaving larger molecules and cells in the blood

Question 35

Once tissue fluid has exchanged metabolic materials with the cells that bathes, it is returned to the circulatory system. How does most tissue fluid return directly to the blood plasma? (4)

Answer 35

(1) Loss of tissue fluid from capillaries **reduces hydrostatic pressure inside** (2) **hydrostatic pressure** at the venous end of the capillary is **lower than in the tissue fluid** (3) tissue fluid is **forced back into the capillaries** due to **higher hydrostatic pressure outside** (4) **water potential of blood plasma** is **more negative** than tissue fluid, causing **water to move into plasma by osmosis**

Question 36

What changes occur in tissue fluid after it exchanges materials with cells? (2)

Answer 36

(1) It loses much of its oxygen and nutrients (2) it gains carbon dioxide & waste materials

Question 37

What happens to the tissue fluid that doesn't return directly to the capillaries? (3)

Answer 37

(1) It is carried back via the **lymphatic system** (2) the lymphatic system is a **network of vessels** that resemble capillaries, but are **dead-ends in the tissues** (3) these vessels **merge into larger vessels** that **drain into the bloodstream near the heart**

Question 38

How are the contents of the lymphatic system (lymphs) moved in the body? (3)

Answer 38

(1) by the **Hydrostatic pressure of the tissue fluid** that has **left the capillaries** (2) by the **Contraction of body muscles** that **squeeze** the lymph vessels or valves in the lymph vessels (3) **valves** in the lymph vessels **prevent backflow**

Question 39

NOTE: check figure 6 & 7 for a clearer picture of the process of the formation & return of tissue fluid on page 197

Answer 39

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