Lung Structure & Function Flashcards by My Revision

What is gas exchange and where does it take place?

O2 and CO2 exchange in alveoli (rich blood supply)

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What part of the bronchioles keeps the airways open most of the time?

Bronchiole cartilage

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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

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Aside from innervation where else / for what are beta 2 adrenoreceptors found?

Mucous glands to inhibit secretion

Agonists = increased clearance of mucous

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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

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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

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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

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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

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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

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Sympathetic nervous system nerves

Ach -> nAchR -> NA -> AdrR

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Parasympathetic nervous system

Ach -> nAchR -> Ach -> mAchR

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Somatic nervous system

From spinal cord

Ach -> nAchR

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Alpha 1 adrenoceptors are found on?

Vascular smooth muscle contraction

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Alpha 2 adrenoceptors found on?

What else do they control?

Vascular smooth muscle contraction

- pre junctional regulation of NA release

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Where do beta 1 adrenoceptors and what do they cause?

HEART (sino atrial node and ventricles)

Rate and force of contraction is controlled

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What do beta 2 adrenoceptors do?

Relaxation of smooth muscle in the airways

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Where are beta 3 adrenoceptors found?

Skeletal muscle and adipose tissue

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Muscarinic subtype M1

CNS, salivary glands, gastric glands

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Muscarinic subtype M2

HEART

rate of contraction, GI smooth muscle contraction, CNS

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Muscarinic subtype M3

Salivary glands, smooth muscle GI AIRWAYS

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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