Lung Structure & Function Flashcards
What is gas exchange and where does it take place?
O2 and CO2 exchange in alveoli (rich blood supply)
What part of the bronchioles keeps the airways open most of the time?
Bronchiole cartilage
Innervation of airways - how is the sympathetic nervous system involved?
SYMPATHETIC
Circulating adrenaline
Acts on beta 2 adrenoreceptor on bronchial smooth muscle to cause relaxation
Inhibition of mediator release from mast cells
Aside from innervation where else / for what are beta 2 adrenoreceptors found?
Mucous glands to inhibit secretion
Agonists = increased clearance of mucous
What is the role of parasympathetic nervous system in innervation of the airways?
Releases Ach which activates muscarinic M3 receptors - causes bronchial constriction and increased mucous secretion
What is the role of sensory nerves in the innervation of airways?
Local reflexes respond to irritants
Cause coughing, bronchoconstriction and increased mucous secretion
- rapid reaction e.g. Breathing in chilli powder = cough
What is the hypothesised method of sensory nerve local control (exercise induced asthma)
Water loss from airways in exercise thought to stimulate release of mediators and activates sensory nerves
How does surface area change as you go down the lung “tree”? What is the lung tree?
Surface area increases as you go down from trachea, main bronchi, bronchi and bronchioles to the alveoli
Sensory nerves are up regulated by inflammation (increases response to stimulus) what is an example of other sensory nerves / local control?
Cold Receptors
- detect changes in temperature eg TRPMB receptors
- present on mast cells and airway epithelium and sensory nerves
Sympathetic nervous system nerves
Ach -> nAchR -> NA -> AdrR
Parasympathetic nervous system
Ach -> nAchR -> Ach -> mAchR
Somatic nervous system
From spinal cord
Ach -> nAchR
Alpha 1 adrenoceptors are found on?
Vascular smooth muscle contraction
Alpha 2 adrenoceptors found on?
What else do they control?
Vascular smooth muscle contraction
- pre junctional regulation of NA release
Where do beta 1 adrenoceptors and what do they cause?
HEART (sino atrial node and ventricles)
Rate and force of contraction is controlled
What do beta 2 adrenoceptors do?
Relaxation of smooth muscle in the airways
Where are beta 3 adrenoceptors found?
Skeletal muscle and adipose tissue
Muscarinic subtype M1
CNS, salivary glands, gastric glands
Muscarinic subtype M2
HEART
rate of contraction, GI smooth muscle contraction, CNS
Muscarinic subtype M3
Salivary glands, smooth muscle GI AIRWAYS
Muscarinic subtype M4
CNS
Muscarinic subtype M5
CNS
Causes of breathelessness
Congenital conditions e.g. cystic fibrosis Infection e.g. chest infection / TB Inflammation e.g. asthma anaphylaxis Cancer Mental - panic attack Degeneration of lung e.g. COPD Cardiac - heart failure Pulmonary embolism Pregnancy / obesity / altitude Side effects of drugs e.g. Beta blockers / NSAIDS
Breathing In - diaphragm and pressure?
- deep and heaving breathing, what physiological changes occur.
Diaphragm expands the thoracic cavity
Decreases pressure causing air to flow into airways
Deep and heavy breathing - intercostal muscles contract and pull rib cage upwards and outwards
Breathing Out - diaphragm and pressure (during rest ?)
What happens during forced expiration
- role of abdominal muscles
During rest expiration is passive
Internal intercostal muscles contract and pull rib cage inwards during FORCED EXPIRATION
Abdominal muscles also contract to reduce thoracic volume
What is airway resistance?
What factors can affect it?
Consider how these factors could vary?
Opposition to airflow in respiratory tree
Depends on friction and airway cross section
Consider increased growth of smooth muscle /excess mucus production
What is compliance ?
Indication of lungs ability to stretch
What is elastance?
Ability of the lungs to recoil
What are the compliance and elastance properties of stiff lungs (e.g. With fibrosis)?
Low compliance and high elastance recoil I.e. Difficult to stretch and tend to return to resting position
What is fibrosis?
Caused by lung damage e.g. After TB
What can cause a loss in lung elastance?
COPD/ emphysema
Describe the central control if breathing - what happens if we stop breathing ?
Controlled by the ANS
We can stop breathing for a short period of time however a build up of CO2 is recognised by chemoreceptors in respiratory centres in brain stem
What does Spirometry measure?
Lung volume
What is Vc?
= FVC
Forced vital capacity
What is VT?
Tidal volume
What is TLC?
Total lung capacity
What is IRV?
Inspiration reserve volume
When can airways become obstructed? What changes do obstructive airways cause? Why do these changes occur?
Asthma and COPD
FEV1 is greatly reduced - cannot expel all air quickly so comes out slower
FVC can be normal if all air is expelled (may be reduced in COPD if all air cannot be reduced)
What are restricted airways? What can cause this? What changes are there as a consequence?
Restrictive airways cannot fill lungs with air e.g. Fibrosis
FEV1 and FVC is reduced (ratio is normal)
Obstructive vs Restrictive
FEV1 : FVC ratio
Obstructive - decreased
Restrictive - normal
At what Po2 does Hb release O2 and where does this occur ?
Low Po2
Tissues
At what Po2 is the lung and what happens here?
High Po2
Hb is saturated with oxygen I.e 100% oxyhemoglobin
How can respiratory acidosis arise?
Impaired / reduced lung function leads to reduced expiration of CO2
Built up CO2 leads to increased carbonic acid
Increase in pH leads to increase in plasma concentration - buffering with Hb in rbcs leads to increase in plasma HCO3-
This in turn causes rise in bicarbonate levels
pH of plasma and bicarbonate levels indicate…
Respiratory distress (see respiratory acidosis)
What happens to bicarbonate levels in chronic acidosis?
Raised due to buffering - pH normal
What other causes of respiratory acidosis / alkalosis and breathing rate?
Hyperventilation - loss of CO2 and hence alkalosis
- drop in PCO2 and increase in pH leads to inhibition of ventilation to limit hyperventilation
What is metabolic acidosis? What changes occur?
Diabetes
Drop in pH stimulates ventilation to lower blood PCO2
What is metabolic alkalosis? What changes occur?
Vomiting
Depresses ventilation
What does a reduction in ventilation lead to?
Reduced O2 for metabolism
Increased CO2 which leads to acidosis
Three factors that regulate the intake of air
Rate of respiration
Depth of inspiration
Diameter of the airways
