Exchange Surfaces

Question 1

What factors make for an effective exchange surface?

Answer 1

• Increased SA.
• Thin diffusion pathway/layers. (Makes the process faster and more efficient)
• Good blood supply. (Creates and maintains steep concentration gradient)
• Ventilation to maintain diffusion gradient.

Question 2

What are the features of the nasal cavity?

Answer 2

• Good blood supply and large SA which warms air to body temperature.
• A hairy lining, which secretes mucus to trap dust and bacteria, protecting delicate lung tissue from irritation and infection.
• Moist surfaces, increasing humidity of incoming air, reducing evaporation from the exchange surfaces.

Question 3

What is the structure and function of the trachea?

Answer 3

• The trachea is the main airway carrying clean, warm, moist air from the nose to the chest.
• Supported by C-shaped incomplete rings of cartilage.
• Lined with ciliated epithelium, with goblet cells interspersed between and below them. Traps dust and MOs, waft.
• Elastic tissue allows for dilation and constriction.
• Smooth muscle can contract to expel air.

Question 4

What is the structure and function of the bronchi?

Answer 4

• Full rings of cartilage.
• Goblet and ciliated epithelial cells.
• Smooth muscle controls the diameter and length of bronchi, contracts during expiration.
• Elastic tissue allows for dilation and constriction. Can recoil to expel air.

Question 5

Small bronchioles: structure and function?

Answer 5

• Diameter 1mm or less.
• No cartilage
• Flattened squamous epithelial cells.
• Elastic tissue allows for dilation and constriction.
• Smooth muscle can contract to expel air. Holds them open.

Question 6

Alveoli: structure and function?

Answer 6

• Surfactant prevents sticking/collapse.
• Elastic tissue allows for dilation and constriction.
• Smooth muscle can contract to expel air.
• No cartilage.
• One cell thick epithelium.

Question 7

What events occur during inhalation?

Answer 7

• Pressure inside lungs must be lower than atm.
• External intercostal muscles contract, internal muscles relax.
• Ribs move up and out.
• Diaphragm contracts and flattens (moves down).
• This increases the volume of the thorax, so pressure inside decreases.
• Air therefore rushes in and the lungs inflate.

Question 8

What events occur during exhalation?

Answer 8

• Pressure must be higher than atm.
• External intercostal muscles relax, internal muscles contract.
  -Ribs move down and in.
• Together this decreases the volume inside the thorax, pressure increases.
• Air leaves the lungs, they deflate.
• diaphragm relaxes

Question 9

What causes asthma?

Answer 9

The cells lining the bronchioles release histamines, making the epithelial cells become inflamed and swollen and produce excess mucus. The airways therefore narrow and fill with mucus.

Question 10

What does an upwards line on a spirometer trace show?

Answer 10

Exhalation. Volume of air in the mobile, upper chamber of the spirometer increases so the trace marker moves upwards.

Question 11

What does a downwards line on a spirometer show?

Answer 11

Inhalation. Volume of air in the mobile, upper chamber of the spirometer decreases so the trace marker moves downwards.

Question 12

What is tidal volume?

Answer 12

The volume of air that moves into and out of the lungs with each resting breath. It is around 0.5dm3 in most adults at rest, around 15% of the vital capacity of the lungs.

Question 13

What is vital capacity?

Answer 13

Vital capacity is the volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath.

Question 14

What is inspiratory reserve volume?

Answer 14

The maximum volume of air you can breathe in over and above a normal inhalation.

Question 15

What is expiratory reserve volume?

Answer 15

The extra amount of air you can force out of your lungs over and above the normal tidal volume of air you breathe out.

Question 16

What is residual volume?

Answer 16

The volume of air that is left in your lungs when you have exhaled as hard as possible. This cannot be measured directly.

Question 17

How is ventilation rate calculated?

Answer 17

Tidal volume x breathing rate (per minute)

Question 18

What is total lung capacity?

Answer 18

The sum of the vital capacity and the residual volume.

Question 19

How is breathing rate calculated?

Answer 19

Number of breaths/ time (minutes)

Question 20

How is the rate of oxygen consumption calculated?

Answer 20

Air volume decrease/time (min)

Question 21

Why do insects need a specialised gas exchange system?

Answer 21

• Can be very active during parts of their life cycles.
• Tough exoskeleton through which very little/no gas exchange can occur.
• No blood pigments which can transport oxygen.
• Oxygen is therefore delivered directly to the cells via haemolymph which the tissues are bathed in.

Question 22

How is water loss from the spiracles controlled?

Answer 22

• Spiracle sphincters can open and close during periods of activity and inactivity to prevent unnecessary water loss when oxygen demand is low.

Question 23

What prevents trachaea from collapsing?

Answer 23

• Full, spiralling rings of chitin which hold them open.

Question 24

What do tracheoles consist of?

Answer 24

• Single, extremely elongated cells with no chitin lining. They are freely permeable to gases.

Question 25

How does oxygen diffuse into the cells/ CO2 diffuse out in insects?

Answer 25

The microscopic ends of the tracheoles run between the insect’s cells, this is where most of the gaseous exchange takes place between the air and the respiring cells. The vast number of tiny tracheoles give a very large surface area.

Question 26

What is the difference between how air moves into the spiracles -> tracheoles -> cells of bigger and smaller insects?

Answer 26

• Some large insects used rhythmic abdominal movements, changing air pressure in the tracheae and tracheoles to pull air in.
• Small insects often rely simply on diffusion to move air in.

Question 27

What are the adaptations of the gills that increase diffusion?

Answer 27

Many lamellae providing a large surface area, many blood vessels to create and maintain a steep concentration gradient (including the countercurrent system), and thin layers for more effective gas exchange.

Question 28

What are the afferent and efferent blood vessels?

Answer 28

The afferent blood vessel delivers deoxygenated blood to the lamellae, the efferent blood vessel carries the blood leaving the gills in the opposite direction to the oncoming water, maintaining a steep concentration gradient (countercurrent flow/exchange).

Question 29

Describe the process of gill ventilation.

Answer 29

• The mouth is opened and the floor of the buccal cavity is lowered. This increases the volume of the buccal cavity, decreasing the pressure and meaning water moves in.
• At the same time the opercular valve (on the outside of the operculum) is shut and the opercular cavity containing the gills expands, lowering the pressure.
• The floor of the buccal cavity starts to move up, increasing the pressure there so that water moves from the buccal cavity over the gills.
• The mouth then closes, the operculum opens and the sides of the opercular cavity move inwards. All of these serve to increase the pressure within the opercular cavity and force water over the gills and out of the operculum. The floor of the buccal cavity is steadily moved up, maintaining a flow of water over the gills for gas exchange.

Question 30

What is the effect of overlapping gill filaments?

Answer 30

• Increases resistance to the flow of water over the gill surfaces and slows down the movements of the water. As a result there is more time for gaseous exchange to take place.

Question 31

What is the countercurrent exchange system in gills?

Answer 31

• The water moving over the gills and the blood in the gill filaments flow in opposite directions. A steep concentration gradient is needed for fast efficient diffusion to take place. Because the blood and water flow in opposite directions, a countercurrent exchange system is set up.