Respiratory (series I)

Pharmacy/Biomedical

RESPIRATORY SYSTEM Dr Saadiah Mohd Hidir 2008/2009 Biomedical / pharmacy

TOPICS

•Functions of resp. system •Events during inspiration & expiration •Pulmonary surfactant •Lung compliance •Airway resistance •Lung volumes & capacities •Pulmonary & alveolar ventilation •Partial pressure of gases •Hyperventilation & hypoventilation •Pulmonary circulation •O2 diffusing capacity •Ventilation-perfusion ratio •A-a PO2 difference Reference books: Human Physiology; Respiratory Physiology

2 MAJOR FUNCTIONS OF RESPIRATORY SYSTEM :

1.

2.

Provides mechanisms for exchange of O2 & CO2 between atmosphere & tissues. Plays important role in the regulation of pH of extracellular fluid • Adjusting rate of removal of acidforming CO2by changes in alveolar ventilation

OTHER FUNCTIONS OF RESPIRATORY SYSTEM :

1.

2.

Defends mechanism against inhaled foreign matter •

Bronchial secretions contains Igs

•

Alveolar macrophages

Metabolic functions eg.: •

Synthesis surfactant

•

Angiotensin II

3.

Lyse small clots

4.

Productions of sounds by movement of air thro’ vocal cords

1. Respiratory airways: • Upper airways (nasal cavity/mouth, pharynx, larynx) and tracheobronchial tree which is a series of branching airways (trachea, 2 primary bronchi, smaller bronchi → each divide into secondary bronchi which then branch into smaller & smaller bronchi → bronchioles 2. Inhaled air is filtered, warmed & humidified as it passes thro’ upper airways

1. Bronchioles  • Terminal bronchioles → • Respiratory bronchioles → • Alveolar ducts which have alveoli 2. Lungs ~ 300 millions alveoli

1. Alveoli surrounded by many capillaries q(From the pulmonary artery that brings deoxygenated blood from the right ventricle) 2. Exchange of gases in the lungs by simple diffusion thro’ thin alveolarcapillary membrane q(large surface area for diffusion )

•3 important pressures involved in breathing : qIntrapleural pressure (Pip) / pleural pressure (Ppl)

1. Pleural cavity - v. thin space between the visceral & parietal pleurae - contains a thin layer of fluid (lubricates pleural surfaces as they slide past each other during respiratory movements) 2. Pressure in pleural cavity - intrapleural pressure (Pip)

3. Visceral pleura (thin membrane) is firmly attached to outer surface of each lung & parietal pleura lines the inside of the thoracic walls)

Pleural cavity

•Normal quiet breathing: Pip is always -ve (< atmospheric pressure (Patm) or subatmospheric (If P = 0 mm Hg (same as Patm). If P is +ve (> Patm)

•At eqm, the inward elastic recoil of the lungs tending to collapse the lungs exactly balances the outward elastic recoil tending to pull thoracic cage outward → q-ve Pip

-ve Pip

Apex of lungs

Base of lungs

•Upright position: Pip more negative at the apex of lung •Mean Pipat the end of normal expiration ~ - 4 mm Hg (- 4 mm Hg less than Patm)

•Pip +ve (> Patm) eg. : qDuring forced expiration qCoughing

3 IMPORTANT PRESSURES INVOLVED IN BREATHING

1

Intrapleural pressure (Pip) / pleural pressure (Ppl)

(ii) Alveolar pressure (PA) / intra-alveolar pressure / intrapulmonary pressure q pressure in alveoli

15

3 IMPORTANT PRESSURES INVOLVED IN BREATHING

1

Intrapleural pressure (Pip) / pleural pressure (Ppl)

(ii) Alveolar pressure (PA) / intra-alveolar pressure / intrapulmonary pressure q Pressure in alveoli (iii) Transpulmonary pressure (PTP) = PA minus Pip q Force acting to expand the alveoli)

•Normally, no air in pleural cavity •If air enters pleural cavity e.g. due to stab wound or broken rib, hole in lung → qPip = Patm (0 mm Hg) q→ PTP = 0 mm Hg q→ lung on that side collapses (atelectasis) & thoracic wall spring outward qCondition is called PNEUMOTHORAX

PRESSURES AT THE END OF QUIET EXPIRATION

Pleural cavity

PTP

(= Patm)

(0 – (4) (mean Pip) 20

1. Inspiration – active process •

•

Initiated by the contractions of the diaphragm (main muscle of inspiration) & the external intercostal muscles → thorax expands Skeletal muscles

Main muscle of inspiration

External intercostal muscles

Force acting to expand lung

(Boyle’s law)

until Pavl = atmpres (0 mm Hg) & airflow ceases

Main muscle of inspiration

External intercostal muscles

Force acting to expand lung

(Boyle’s law) until Pavl = atmpres (0 mm Hg) & airflow ceases

Changes in Pavl, Pip, PTP& tidal volume (TV) / during a respiratory cycle

1. Normal breathing 2. Referred to as negative -pressure breathing (during inspiration, air moves into the lungs because the PA< Patm) 3. Positive-pressure breathing eg. mouth to mouth breathing

Accessory muscles of inspiration

Changes in Pavl, Pip, PTP & tidal volume during a respiratory cycle

1. During forced expiration, expiration is active •

Muscles of expiration (internal intercostal muscles, abdominal muscles) contract which ↓ thoracic dimension

COMPLIANCE 1. change in volume per unit change in pressure

Compliance =   Lung compliance ( •the magnitude of the change in lung volume produced by a given change in the transpulmonary pressure

Normal CL 0.2 L / cm H2O





•High CL eg. in emphysema → easier to expand the lungs (loss of elastic tissues) •    



 

SOME FACTORS AFFECTING CL: Pathological states P    ↑    3. Posture – CL higher in standing position 4. Lung volumes 5. Surface tension of alveoli : High alveolar surface  

• 



•Type II alveolar cells secrete pulmonary surfactant - a mixture of phospholipids & proteins  alveolar surface tension

FUNCTIONS OF PULMONARY SURFACTANT ↓

alveolar surface tension

3

↑ lung compliance (easier to expand the lungs) &  

(ii) Stabilises alveoli of different sizes - it prevents small alveoli from collapse at the end of expiration

FUNCTIONS OF PULMONARY SURFACTANT ↓

alveolar surface tension

3

↑ lung compliance (easier to expand the lungs) &  

(ii) Stabilises alveoli of different sizes - it prevents small alveoli from collapse at the end of expiration (iii) Helps to prevents pulmonary oedema

•Lack of pulmonary surfactant in premature infants → respiratory distress syndrome of the newborn (RDS) / infant respiratory distress syndrome / hyaline membrane disease after birth •Lack of pulmonary surfactant in premature infants → high alveolar surface tension → CL , alveoli collapsed, difficulty in inspiration → respiratory failure •Administration of glucocorticoid to mother ↑ rate of maturation of foetal lungs

•Chest wall compliance •Total compliance •Dynamic compliance



•Breathing 100 % O2for prolonged period •Atelectasis •Pulmonary oedema

↓ Surfactant pulmonary

•Hypoxia •Shallow breathing •Cigarette smoking 40

•25-40% of total resistance to airflow - in upper airways – nose, pharynx, larynx •In the tracheobroncial tree, most resistance in medium -sized bronchi (24 mm) •Normally, resistance is low

•Main determinant of airway (bronchi & bronchioles) R is radius of airways (R      

•  

↑ parasympathetic nerve activity, smoke, histamine, → smooth muscles contraction → bronchoconstriction → 

Adrenaline (through  ), ß2-agonists relaxation of smooth muscles of airways

(wheezing – due turbulent airflow thro’ narrowed airways- more prominent during expiration)

•Less dense gas such as helium can be used to replace N2in air to reduce airway resistance