B7 - gas exchange & breathing

Question 1

Why don’t unicellular organisms need a gas exchange system?

Answer 1

• metabolic needs met by diffusion alone
• High SA:V ratio = quick exchange & absorption of gases
• small volume = small travel distance
• low metabolic activity (low O2 demand & CO2 production)

Question 2

Why do unicellular organisms need a transport system?

Answer 2

• higher metabolic demands
• diffusion alone too slow for survival
• small SA:V = cells in centre of organism too far from external O2 supply
• O2 diffusion would take too long

Question 3

How is the nasal cavity (in mammals) adapted for gas exchange?

Answer 3

• Large SA & good blood supply warms air as passes into lungs
• Hairy lining: secreted mucous to trap dust & bacteria, protecting lungs from infection
• Moist surfaces = increases humidity of incoming air, reducing evaporation of water in lungs due to lower water potential gradient

Question 4

Describe the structure of the trachea.

Answer 4

• wide tube surrounded by incomplete rings of cartilage to keep trachea open
• incomplete cartilage to prevent rubbing against oesophagus which is behind the trachea
• ciliated epithelium w/ goblet cells that secrete mucous to trap bacteria which cilia move away from lungs (mainly to throat, then swallowed & digested)

Question 5

Bronchus (bronchi (plural))

Answer 5

• extensions of trachea (split in 2 for left and right lung)
• similar structure to bronchi but thinner walls & smaller, FULL cartilage rings.

Question 6

Bronchioles

Answer 6

• branched off from bronchi
• no cartilage
• held open by smooth muscle
• when smooth muscle contracts, bronchioles constrict (close up), relax = bronchioles dilate. This changes the amount of air reaching the lungs
• Lined w/ thin epithelium for SOME gas exchange

Question 7

Alveoli

Answer 7

• small air sacs at end of bronchioles
• layer of SQUAMOUS epithelium, some collagen & elastic fibres (elastin)
• elastic fibres allow ELASTIC RECOIL = alveoli stretch as air drawn in, & helps squeeze out air when returning to resting size.

Question 8

Alveoli adaptations for gas exchange (4)

Answer 8

Large SA(millions in each lung):
- high O2 intake

Thin layers:
- both alveoli & surrounding capillaries are 1 epithelial cell thick
- V. short diffusion distance for O2

Good blood supply:
- maintains steep concentration gradient
- constant rich blood flow in capillaries surrounding alveoli brings in CO2 and carries of O2 to cells needing it for respiration

Good ventilation:
- breathing moves air in & out alveoli = maintain steep diffusion gradient = more efficient

Question 9

What is lung surfactant?

Answer 9

• alveoli lack cartilage structural support
• Inner lining of alveoli has thin layer of water & lung surfactant that keep alveoli open.
• alveoli would collapse w/o it.
• O2 dissolves in the water before diffusing into blood

Question 10

What are some tissues of the gas exchange system? (4)

Answer 10

• cartilage ( structural )
• ciliated epithelium
• goblet cells
• squamous epithelium (v.thin & permeable)
• smooth muscle (help regulate air flow by dilating and constricting depending on how much air is needed)
• elastic fibres (stretch & recoil)
• capillary network surrounding alveoli

Question 11

Define ventilation

Answer 11

Movement of air in & out of the lungs due to pressure changes in the thorax.

Question 12

Rib cage

Answer 12

provides semi-rigid cage within which pressure outside can be lowered with respect to the air outside it.

Question 13

Diaphragm

Answer 13

• Broad, domed sheet of muscle
• forms floor of thorax

Question 14

lungs

Answer 14

• pleural membrane lines thorax & surrounds lungs
• pleural cavity = space between plural membranes, containing thin layer of lubricating pleural fluid so membranes can slide over each other as you breathe

Question 15

Inspiration

Answer 15

• Active/ energy requiring process
• diaphragm contracts, flattens & lowers
• external intercostal muscles contract, lifting ribs up & out
• internal intercostal relax
• thorax volume increases
• pressure decreases
• thorax pressure lower than pressure in surrounding atmospheric air
• air forced into lungs to attain pressure eqm

Question 16

Expiration

Answer 16

• Normal expiration is passive
• diaphragm relaxes, moving up
• ribs move down and in
• external intercostal muscles relax
• internal intercostal muscles contract
• thorax volume decreases
• pressure increases
• more pressure in thorax than in surrounding atmospheric pressure
• air moves out lung to equalise pressure

Question 17

During an asthma attack, cells lining the bronchioles release histamines. What does this do?

Answer 17

• inflate epithelium
• cause goblet cells to secrete excess mucous
• airways fill with mucous = hard to breathe

Question 18

What does an inhaler do?

Answer 18

• asthma medicines/drugs released into breathing system using an inhaler.

Question 19

What are the two main drugs in inhalers that treat asthma?

Answer 19

relievers:
- immediate relief from symptoms
- attach to active sites on surface membranes of smooth muscle & bronchioles, causing them to dilate & open airways

Preventers (often steroids):
taken daily to reduce sensitivity of lining in the airways

Question 20

What are the 3 ways in which lung capacity can be measured?

Answer 20

Peak flow meter:
- measures air expelled from lungs

vitalographs:
- more sophisticated version of peak flow meter
- breathe out as quick as possible through mouthpiece. A graph is produced of how much & how quickly air is breathed out

spirometer:
- measures diff aspects of lung volume & investigates breathing patterns

Question 21

tidal volume

Answer 21

vol of air in & out lungs during resting breaths

Question 22

vital capacity

Answer 22

max vol of strongest inhalation & exhalation in one breath

Question 23

inspiratory reserve volume

Answer 23

max air vol inhaled (above normal inhalation)

Question 24

expiratory reserve volume

Answer 24

max vol air exhaled (above normal exhalation)

Question 25

Residual volume

Answer 25

air left in lungs after exhaling as hard as possible

Question 26

Total lung capacity

Answer 26

vital capacity + residual volume

Question 27

Breathing rate

Answer 27

breaths per unit of time (usually per min)

Question 28

Oxygen uptake

Answer 28

Rate a person used up O2 (dm^3min-1)

Question 29

How does a spirometer work?

Answer 29

lower half of tank full of water
upper (mobile) half full of O2
breathe out = upper half/lid rises
breathe in = upper half/lid falls
1) subject wears a nose clip & breathes in/out through spirometer to ensure no external O2 supply/ only O2 supply is from subject’s breathing through mouth.
2)CO2 breathed out absorbed by soda lime to prevent high CO2 concentration in re-breathed air
3) trace drawn on kymograph as lid moves up & down

(CO2 removes by lime soda, so total air volume decreases after breaths)

Question 30

Spirometer precautions

Answer 30

nose clip:
- all ventilation through mouth
- no external air source

counterweight:
- no resistance to breathing

soda lime:
absorbs CO2, so not being re-breathed

Patient must be healthy as limited O2 in chamber, but enough so that a healthy peron won’t struggle breathing

Question 31

breathing rate & ventilation rate difference

Answer 31

breathing rate = number of breaths per minute

ventilation rate = total volume of air inhaled in one min

ventilation rate = tidal volume x breathing rate