7.2 - Mammalian Gaseous Exchange System

Question 1

What 2 issues posed by the human body requires a mammalian gas exchange system?

Answer 1

• Mammals have small SA:V ratio due to large size and cell volume
• High metabolic rate - need lots of oxygen for cellular resp. and CO2 must be removed as metabolic waste

Gas exchange occurs in lungs

Question 2

Name the key structures in the human gas exchange system.

Answer 2

Nasal cavity
Trachea
Bronchus
Bronchioles
Alveoli

Question 3

Describe the features, functions and structure of the nasal cavity.

Answer 3

• Large SA, good blood supply - warms the air to body temperature
• Hair lining that secretes mucus to trap dust and bacteria - protects lung tissue from infection
• Moist surfaces - increasing incoming air’s humidity, reducing evaporation from exchange surfaces

Question 4

Describe the features, functions and structure of the trachea.

Answer 4

Airways - carries clean, warm, moist air from nose to chest
- Wide tube supported by incomplete rings of flexible cartilage stopping trachea collapsing.
(Rings are incomplete to allow oesophagus, situated behind trachea, to transport food. )

• Lined with ciliated epithelium with goblet cells in between.

Question 5

What are the functions of goblet cells?

Answer 5

• Secrete mucus onto the trachea to trap dust and microorganisms that escape the nasal lining.
• Most of mucus is swallowed and digested, some gets beat and moved along by cilia away from the lung.

Question 6

Describe the features, functions and structure of the bronchi and bronchioles.

Answer 6

Trachea divides to form LEFT and RIGHT BRONCHUS (each leading to left and right lung)
- Similar structure to trachea, but smaller (has rings of supporting cartilage)

Bronchi divide into smaller bronchioles
- Diameter <1mm
- Walls have smooth muscle which contract - bronchioles constrict.
, when wall relax - bronchioles dilate

Question 7

Describe the features, functions and structure of the alveoli (singular alveolus).

Answer 7

• Tiny air sacs, main site of gas exchange in body
• Diameter 200-300 micrometers
• Layer of thin, flattened epithelial cells with collagen (provides strength to stop bursting) and elastin (allows elastic recoil)

Question 8

When referring to the ‘expansion’ and ‘contraction’ of either MUSCLES or AIRWAYS, what terminology is used.

Answer 8

MUSCLES:
Contraction
Relaxation

AIRWAYS:
Constriction
Dilation

Question 9

Give adaptations of alveoli for gaseous exchange.

Answer 9

Good blood supply - maintain steep concentration gradient between CO2 and O2 in air and in blood of capillaries

Good ventilation - maintains conc. gradient

Large SA (300-500million alveoli per adult lung) - speed up diffusion

Thin layers - shorter diffusion distance

Alveoli & surrounding capillaries are 1 cell thick, shortening diffusion distance.

Question 10

What exists on the inner alveolar surface?

Answer 10

• Thin layer of water, salts and lung surfactant

Lung surfactants stop the lungs from collapsings - keeps alveoli inflated.

Question 11

Define lung ventilation.

Answer 11

Movement of air into and out of lungs

Question 12

Describe the structure of the rib cage and thorax.

Answer 12

Rib cage: Semi-rigid case within which pressure can be lowered with respect to outside air

Diaphragm - broad domed sheet of muscle - floor of thorax

Thorax lined by pleural membrane - surround the lung
Space between pleural membrane and lung - pleural cavity is filled with layer of lubricating fluid so membranes can easily slide over one another, as you breath.

Question 13

Describe the process of inspiration.

Answer 13

Breathing in - energy using process
1) Dome shaped diaphragm contracts (flattens and lowers)
2) External intercostal muscles contract - moves ribs UP AND OUT
3) Volume of thorax increases, lowering pressure in thorax. (Lower than atmospheric air)
4) Therefore, air is drawn in through nasal passage, trachea and bronchi/bronchioles.
Equalising pressure in and out of chest

Question 14

Describe the process of expiration.

Answer 14

Normal expiration is a passive process

1) Diaphragm muscles relax, moving up into resting domed shape
2) External intercostal muscles relax - moves rib DOWN and IN under gravity.
3) Elastic fibres of alveoli in lung return to normla length
4) 1-3 reduces thorac volume and increases pressure in thorax to be > than atmospheric air.
Air moves out of lungs until pressure in and out of chest is equal

Question 15

Describe the process of forced expiration.

Answer 15

Energy using process

Internal intercostal muscles contract, pulling ribs down hard and fast
- Abdominal muscles contract forcing diaphragm forcing diaphragm up to increase lung pressure rapidly.