The Respiratory System

Question 1

What is the basic structure of the lungs

Answer 1

• lungs are inside the ribcage
• 23 generations of airways between alveoli and outside air
• around 300 million alveoli in adult lungs creating a surface area for gas exchange around 60-80m2
• trachea and primary bronchi held open by c-shaped rings of cartilage, smaller bronchi by overlapping plates of cartilage and no cartilage in bronchioles
• smooth muscle is present in the walls of airways

Question 2

What is Boyle’s law

Answer 2

• the pressure exerted by a gas is inversely proportional to its volume

inspiration: increased lung volume —> pressure in lungs falls below atmospheric pressure —> air flows in

expiration: reduction of lung volume —> pressure in lungs rises —> air flows out

Question 3

How are the lungs held open

Answer 3

• interpleural pressure holds the lungs open

the elastic recoil of the chest wall tries to pull chest wall outwards

the elastic recoil of the lungs creates an inwards pull

the pull in opposite directions creates a negative/sub atmospheric pressure

Question 4

What are the muscles used in respiration

Answer 4

main muscles in pulmonary ventilation are intercostal muscles and diaphragm

inspiration: active process, muscles contract
expiration: passive process, muscles relax

inspiration: thoracic cavity expands, external intercostal muscles contract, diaphragm contracts

expiration: thoracic cavity reduces, external intercostal muscles relax, diaphragm relaxes

Question 5

What are the factors affecting pulmonary ventilation

Answer 5

• elastic recoil/pulmonary ventilation
• airway resistance

Question 6

What is elastic recoil/lung compliance

Answer 6

elastic recoil
- the ease in which the lung rebounds after stretching

compliance
- ease in which the lungs stretch/expands
- these are inversely related

compliance is mainly determined by elastic fibres in lung tissue and alveolar surface tension, the fibres are present in connective tissue

alveolar surface tension is reduced by surfactant secreted by alveolar type ii cells

Question 7

What is air way resistance

Answer 7

• airflow is inversely proportional to resistance
• resistance depends on tube diameter and type of flow
• resistance highest at medium-sized bronchi, as even though small airways have greater resistance the combined surface-area means a lower resistance

Question 8

What are the pressure changes during breathing

Answer 8

at rest: interpulmonary pressure =atmospheric pressure, negative interpleural pressure

inspiration: as thoracic cavity expands, interpleural pressure decreases, causing lungs to expand, decreasing intrapulmonary pressure. air then flows into the lungs and intrapulmonary pressure slowly reaches atmospheric pressure

expiration: decrease of thoracic cavity volume, increases intrapleural pressure, lung volume decreases due to elastic recoil, intrapulmonary pressure then increases and air flows out of the lungs until intrapulmonary pressure = atmospheric pressure

Question 9

What does a spirometry do

Answer 9

• measures lung volume

when using a bell spirometry

inspiration: air from bell, upwards movement on chart

expiration: lifts inverted bell, downwards on chart

Question 10

How are gases exchanged for respiration

Answer 10

• gas exchange between alveoli and capillaries occurs by diffusion
• gases diffuse from a region of high partial pressure to a region of low partial pressure

Question 11

What is Fick’s law of diffusion

Answer 11

• describes the rate of transfer of a gas through a sheet of tissue

dV/dT = A/T x D x (P1-P2)

Question 12

How is oxygen transported in the blood

Answer 12

• oxygen solubility in blood is low 3ml O2/l blood so not enough to support the body
• haemoglobin increases capacity of blood to transport oxygen to 5 litre/ minute so sufficient supply to the body

Question 13

What is the structure of haemoglobin

Answer 13

2 alpha-chain and 2 beta-chains with a heme group
- each Fe2+ can reversibly bind one molecule of oxygen (oxyhaemoglobin)

Question 14

What is a haemoglobin oxygen-dissociation curve

Answer 14

sigmodial shaped curve from cooperative O2 binding
- binding of one O2 molecule leads to conformational change of haemoglobin that increases binding affinity of remaining heme group for additional O2

high partial pressure: flat curve —> drop in PO2 leads to little change in saturation

low partial pressure: steep curve —> facilitates release of O2 for diffusion into tissues

Question 15

How is carbon dioxide transported into the blood

Answer 15

• CO2 diffuses from tissues into blood vessels —> some CO2 binds to haemoglobin —> this releases carbonic anhydrase in red blood cells which catalyses C02 + H2O <—> H2CO3 reaction
• H2CO3 dissociates into HCO3- and H+, HCO3- is exchanged for Cl- and H+ is buffered by haemoglobin

in the body
CO2 gas, HCO3- and carbamino (CO2 + amino acid from haemoglobin)

Question 16

How is breathing controlled

Answer 16

• respiratory muscles have NO intrinsic rhythmic control
• a group of neurones located in the pons and medulla (brainstem) discharge action potential with an intrinsic rhythm corresponding to respiratory cycle. neurons activate neurons of the phrenic and intercostal nerves and activate intercostal muscles and the diaphragm

Question 17

What is the effect of blood gases on breathing

Answer 17

• peripheral and central chemoreceptors sense changes in PO2 + PCO2 and pH
• signals are sent to respiratory centers to adjust rate and depth of ventilation

Question 18

How do peripheral chemoreceptors work

Answer 18

• carotid and aortic bodies are main peripheral chemoreceptors

i. glomus cells in carotid bodies detect low PO2 in blood vessles
ii. K+ channels close in response to the low PO2
iii. cell depolarisation occurs
iv. voltage-gates calcium channels open
v. Ca2+ enters the cell
vi. the influx of Ca2+ triggers exocytosis of vesicles containing neurotransmitters
vii. neurotransmitters bind to receptors on sensory neurons, leading to cation potential generation
viii. sensory neurons stimulate neurones of respiratory centres to increase ventilation rate and depth

Question 19

How do central chemoreceptors work

Answer 19

• located on ventral surface of medulla, respond to changes in pH of cerebrospinal fluid (CFS)
• CO2 can diffuse from blood to CFS, in CFS reactions lead to the formation of H+
• higher partial pressure of CO2 in CFS, more H+ produced which causes a lower pH
  -H+ stimulates central chemoreceptors which sends signals to respiratory centres increasing ventilation

Question 20

How is breathing controlled

Answer 20

higher brain centres modulate respiratory activity for non-respiratory activities eg. swallowing

streton receptors in smooth muscles of upper airways protect lungs from overinflation

irritant receptors respond to chemical/mechanical irritation, activation induced coughing and bronchoconstriction

receptors in muscles and joints that are activated when muscles contract have stimulatory effect on ventilation

ventilation can also be modulated as a response to emotional stimuli and pain

Question 21

What are the pulmonary defense mechanisms

Answer 21

• mucus produced by mucous cells inside ciliated columnar epithelial and movement of cilia slowly moves mucus to pharynx where it is swallowed. any particles reaching alveoli are phagocytosed by alveolar macrophages
• some material is also trapped in the nasal cavity

Question 22

What are the two different types of lung disease

Answer 22

obstructive
- airway obstruction increases resistance to air flow eg. COPD (chronic obstructive pulmonary disease)

restrictive
- reduced compliance limits expansion eg. pulmonary fibrosis

Question 23

What is COPD and the effects of COPD

Answer 23

• causes tobacco smoke, air pollution, some genetic factors

continual bronchial irritation and inflammation —> CHRONIC BRONCHITIS (excessive mucus, chronic productive cough) —> airway obstruction, dyspena, frequent infection —> respiratory failure

breakdown of elastin in connective tissue of lungs —> EMPHYSEMA (destruction of alveolar walls, loss of elasticity) —> airway obstruction, dyspena, frequent infection —> respiratory failure

Question 24

What is the cause of pulmonary fibrosis and the effects

Answer 24

• cause is unknown in most cases, but thought to be from infection or autoimmune disorders

scars form in lung tissues causing a thickening of the alveolar walls which impairs O2 diffusion
- the stiffness leads to decreased compliance (stretch and expansion of lungs)

Question 25

How does forced vital capacity (FVC) and forced expiratory volume at 1 second FEV1) change

Answer 25

• forced vital capacity (FVC) and forced expiratory volume at 1 second FEV1) are used to assess lung function
• in healthy function FVC around 0.8
• patients with obstructive lung disease FEV1 reduced as increased resistance takes longer for air to leave lungs
• in patients with a restrictive disease FVC is affected more as it is more difficult to get air into the lungs

Question 26

What is a treatment for COPD

Answer 26

In COPD increased contraction of airway smooth muscle contributes to airway obstruction
- to treat COPD drugs are used to lead relaxation of airway smooth muscle
- B2-adrenergic receptor agonists lead to smooth muscle relaxation
- Salbutamd is the drug used