Ventilation

Mediastinum

area in the thorax, between the lungs where the heart, large blood vessels, trachea and oesophagus lie

Pleural membranes (2)

• epithelial membrane lining the thoracic wall and lungs

• very thin membrane

Pleural cavity

sealed compartment

Parietal (=wall) pleura location

=costal

lines the inside of the thoracic wall

Visceral (organ) pleura ‘location’

covers surface of the lungs

Cross-section of the thorax (photo)

Intrapleural Space (5)

• Both pleura continuously forming a potential space between them - FLUID

• maintains negative pressure:

  • air from outside flow into the lungs

  • during inhalation chest, lungs expands → creates a pressure difference

  • air flows into the conducting zone to the terminal bronchioles and alveoli

Intrapleural pressure

subatmospheric

potential space

small air in the intrapleural space

parietal pleura function (4)

• Secrete FLUID

• serves as a lubricant

• forms from the blood capillaries

• drains in the lymphatics

lubricant definition

a substance used to reduce friction between two surfaces in contact, allowing them to move smoothly over one another

Transpulmonary / transmural pressure (2)

Intrapleural space pressure:

• lower than that in the lungs

• Low p pulls the lungs outwards

Higher pressure in the lungs what does it do?

pushes the lungs outwards against the chest wall

Pneumothorax (2)

air leaks between the lungs and the chest wall in the intrapleural space

pressure ↑s → the lung collapses

Pneumothorax caused by (2)

• spontaneous (no obvious cause)

• injury

Pneumothorax treatment

Chest drains - to remove air out

Chest drains used for (4)

• post-op

• trauma

• to drain pleural effusion

• pneumothorax

Pleuritis

inflammation of the pleural membranes with an increase of fluid in the intrapleural space (Painful with breathing)

Pleuritis caused by (5)

• viral or bacterial infections of the pleura

• lung infections (pneumonia)

• cancer

• autoimmune conditions:

  • SLE (Systemic lupus erythematosus)

  • RA (rheumatoid arthritis)

Pleural Effusion

Increase in fluid between the lungs, causing pressure on the lungs and difficulty with breathing (May be painless)

Pleural Effusion caused by (7)

• Heart failure

• kidney and liver disease

• inflammatory conditions

  • Pleuritis

  • Pneumonia

  • Tuberculosis

  • Lupus

inflammatory conditions

in which inflammatory fluid is increased

Air flow into the lungs depends on (4)

• Pressure gradient

• Physical properties of the lung

• Airways resistance

• Volume changes

Physical properties of the lung in ventilation (4)

• Compliance of the lung

• Elasticity

• Surfactant

• Surface Tension

Compliance (4)

=distensibility

• The change in lung volume per change in pulmonary pressure

• Lung compliance is changed in conditions

  • lung fibrosis: where there is infiltration of connective tissue proteins which decrease lung compliance

• inspiration

Elasticity (3)

• refers to the tendency of the lungs to return to their initial size after being distended, aiding expiration by facilitating the collapse of the lungs

  • bc/ elastin proteins present in lung tissue

• allows respiration

elastic tension is counteracted by

intrapleural pressure

Surface Tension (7)

• The lungs secrete and absorb fluid, leaving a thin film on the alveolar surface

  • the thin film of fluid has a surface tension

  • the film squeezes the alveolus → produce recoil

• pulls the alveoli inward → increasing the tendency to cause the lungs to collapse → increases the pressure of the air inside the alveolus

• allows alveolus to resist expansion

• coat pulmonary surfactant → prevents alveoli from collapsing from this tension

• lining fluid

Insuffiecient pulmonary surfactant produce

newborn respiratory distress syndrome

Surfactant (5)

= Surface Acting Agent

• Secreted by Type II alveolar cells

• Consists of Phospholipids and hydrophobic surfactant proteins

  • primarily phosphatidylcholine and phosphatidylglycerol

• It is interspersed between the H₂O molecules at the water-air interface, reducing the H bonds between the H₂O molecules at the surface, reducing the surface tension

Effect of surfactant on smaller alveoli (3)

• improves as the alveoli get smaller during expiration

  • due to the increase in concentration

  • preventing the alveoli from collapse

Type I alveolar cells secretes

Epithelial cells

Airways resistance

Determined by airway diameter

Pressure Gradient

Air moves in and out of the lungs as a result of the pressure differences created by changes in the lung volumes

Air flow (2)

• Directly proportional to the pressure difference induced by changes in lung volume

• Inversely proportional to friction resistance

Boyles’ Law (2)

P₁V₁ = P₂V₂

If the size of a container is reduced → the collisions between the gas molecules and the walls become more frequent → the pressure ↑

Inspiration pressure (2)

• Alveolar pressure ↓ as the volume ↑

• Air flows into the lungs

Expiration pressure (2)

• Alveolar pressure ↑ as the volume ↓

• Air is pushed out of the lungs

Cystic Fibrosis (3)

• inherited, genetic condition

• the lung fluid is viscous (thick and sticky) - difficult to clear

• The higher surface tension affects lung function - making it more difficult to expand

Premature Babies

Immature lungs –lack of surfactant

Factors affecting airways resistance (5)

• Length of conducting system (constant)

• Viscosity of air (usually constant but may be slightly altered by humidity and altitude)

• Diameter of Airways (main determinant)

  • Upper airways – physical obstruction, mucus, spasm

  • Bronchioles constriction/dilatation

Anatomy and Structure of the Bronchial Tree and lobules of the Lung (7 + photo)

• Trachea

• Right + left primary bronchi

• Secondary bronchi 2x left, 3x right

• Bronchioles

• Terminal bronchioles

• Respiratory bronchioles

• Alveoli

Gas exchange location

At Respiratory bronchioles + Alveoli

Airways of the lower respiratory tract

are kept open by cartilage and smooth muscle

Cartilage - Lower Respiratory Tract (3)

• found down to the small bronchi

• In the trachea they are C-shaped rings of hyaline cartilage

• In the bronchi the cartilage takes the form of plates

Smooth muscle - Lower Respiratory Tract (2)

• found from the trachea down to the bronchioles

• In asthma the smooth muscle contracts narrowing the lumen of the bronchial tree, causing obstruction to air flow

Bronchi and bronchioles are made from

elastic tissue

Physiological changes in bronchial airways diameter - Airways Resistance (5)

• Bronchoconstriction

• Bronchodilation

• Sympathetic Influence

• Salbutamol

Bronchoconstriction (4)

• Narrowing of the airways

• Caused by:

  • Parasympathetic stimulation via muscarinic receptors

  • Histamines and leukotrienes (allergens)

Bronchodilation

Occurs when CO₂ levels in expired air ↑

Sympathetic Influence (2)

• no direct sympathetic nerve control of the airways

• epinephrine (adrenaline) from the bloodstream can cause bronchodilation by stimulating β2 receptors

Salbutamol

a β2 receptor agonist that mimics epinephrine, causing bronchodilation and reducing airway resistance

Obstructive Lung Disease (5)

• External pressure from enlarged thyroid gland other masses

• Physical obstruction of bronchial lumen

  • fx.: tumours, inhaled foreign bodies

• Narrowing of airways from smooth muscle spasm or inflammation

  • fx.: asthma

Restrictive Lung Disease (photo)