6.4 Gas Exchange

Question 1

what are the processes of physiological respiration? (3)

Answer 1

• ventilation: exchange of air between atmosphere and lungs
• gas exchange: exchange of O2 and CO2 between alveoli and bloodstream
• cell respiration: release of energy ATP from organic molecules (enhanced by presence of O2)

Question 2

what is the structure of lung? (5)

Answer 2

• air enters respiratory system through mouth and nose and passes through pharynx to trachea
• air travels down trachae and divides into 2 bronch which connect to lungs
• right lung is comprised of 3 lobes and left lung
• bronchi split into smaller bronchioles (increase SA)
• bronchiole terminated w/ cluster of alveoli and gas exchange w/ bloodstream occurs

Question 3

what is structure of alvolus? (4)

Answer 3

• thin epithelial layer minimise (1 cell) diffusion distance for respiratory gases
• surrounded by rich capillary to increase capacity for gas exchange w/ blood
• roughly spherical to maximise gas exchange
• internal surface is covered w/ moist surface so gases can diffuse better

Question 4

what are the 2 types of alveolar cells?

Answer 4

type I pneumocyte
type II pneumocyte

Question 5

what are type I pneumocytes and what do they do? (4)

Answer 5

• involved in gas exchange between alveoli and capillaries
• are squamous and extremely thin
• type I pneumocyte are connected by occluding junctions which prevent leakage of tissue fluid into alveolar air space
• type I pneumocyte are amitotic and unable to replicate, but type II pneumocyte can differentiate into type I cells if required

Question 6

what are type II pneumocytes and what do they do? (3)

Answer 6

• type II pneumocytes are responsible for secretion of pulmonary surfactant which reduces surface tension in alveoli
• in cuboida; shape and possess granules
• type II pneumocyte comprise a fraction of alveolar surface

Question 7

what is surface tension and what causes it?

Answer 7

• elastic force created by fluid surface that minimises the surface area (via cohesion of water molecules)

Question 8

what reduces surface tension?

Answer 8

pulmonary surfactant
- as alveoli expands with gas intake the surfactant becomes more spread out across the moist alveolar lining
- increases surface tension slows rate of expansion (ensures all alveoli inflate at same rate)

Question 9

what does the mechanism of breathing occur according to?

Answer 9

Boyle’s Law (pressure is inversely proportional to volume)

Question 10

how does the mechanism of breathing occur? (4)

Answer 10

• when the volume of thoracic cavity increases, pressure in the thorax decreases
• when volume of thoracic cavity decreases, pressure in the thorax increases
• when the pressure of chest is less than the atmospheric pressure, air will move into lungs (inspiration)
• when the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs (expiration)

Question 11

How do respiratory muscles contract to change the volume of the thoracic cavity and alter the pressure in the chest? (3)

Answer 11

• Changing chest volume creates a pressure differential between the chest and atmosphere – with air then moving to equalise
• Muscles that increase the volume of the chest cause inspiration (as chest pressure is less than atmospheric pressure)
• Muscles the decrease the volume of the chest cause expiration (as chest pressure is greater than atmospheric pressure)

Question 12

what kind of muscles groups are involves in breathing?

Answer 12

antagonistic muscle groups

Question 13

what is the process of inspiration? (4)

Answer 13

• muscles are responsible for inspiration = diaphragm and external intercostals
• diaphragm muscles contract cause diaphragm to flatten and increase volume of thoracic cavity
• external intercostals contract pulling ribs upwards and outwards (expanding chest)
• additional muscle groups help pull ribs up and out

Question 14

what is the process of expiration? (4)

Answer 14

• muscles responsible for expirations = abdominal muscles and internal intercostal
• internal intercostal muscles contract, pulling ribs inwards and downwards (reduce breadth of chest)
• abdominal muscles contract and push the diaphragm upwards during forced exhalation
• additional muscles groups may help pull ribs upwards

Question 15

what is lung cancer? (3)

Answer 15

• uncontrolled proliferation of lung muscles, leading to abnormal growth of lung tissue
• can impact on normal tissue function
• can be benign to malignant

Question 16

what are the symptoms of lung cancer?

Answer 16

• coughing up blood, wheezing, respiration distress and weight loss

Question 17

what is emphysema? (3)

Answer 17

• lung conditions where walls of alveoli lose their elasticity due to damage alveolar wall
• loss of elasticity results in abnormal enlargement of alveoli leading to to a lower SA for gas exchange
• degradation of alveolar walls can cause holes to develop and alveoli to merge into huge air space (pulmonary bullae)

Question 18

how does emphysema occur? (5)

Answer 18

• smoking damage alveolar walls
• damage to lung tissue leads to recruitment of phagocytes to the region which produce elastase (enzyme)
• elastase released as part of inflammatory response, breaks down elastic fibres in alveolar wall
• elastase activity can be blocked by enzyme inhibitor but no when elastase concs are increased
• small proportion of emphysema cases due to hereditary deficiency in enzyme inhibitor due to gene mutation

Question 19

what are symptons of emphysema? (5)

Answer 19

shortess of breath, phlegm production, expansion of ribcage, cyanosis, increased susceptibility to chest infections

Question 20

what changes ventilation in humans? (3)

Answer 20

• ATP production produce CO2 and waster product
• changes in blood CO3 levels are detected by chemosensors in walls of arteries which send signals to brainstem
• exercise intensity increase, so does gas exchange, increase levels of ventilation

Question 21

what is spirometry?

Answer 21

measuring the amount (volume) and / or speed (flow) at which air can be inhaled or exhaled