Respiration

Respiratory System Functions

Provide oxygen

Remove CO₂

Maintain blood pH

Mechanics of respiration

Inspiration

Expiration

From Lung’s perspective – passive

Skeletal muscles contract, increasing size of thoracic cavity

Diaphragm and external intercostals

Gas exchange via passive diffusion

Ventilation Control (Homeostasis)

Regulated through the rate and depth of breathing

Basic rate established in respiratory centers in the medulla (12-14 cycles/min)

Ventilation affected by:

Higher centers in the brain

Stretch receptors in the lungs

Chemoreceptors

Aortic and Carotid bodies

Measure CO₂ rise and pH fall

Other receptors in the body

Hyperventilation – rapid breathing

CO₂ lost at a fast rate; H⁺ lost so pH increases

Chemoreceptors cause depressed ventilation until normal blood levels return

Hypoventilation – shallow and/or slow breathing

CO₂ retained in blood

Forms carbonic acid

H⁺ retained so pH decreases

Chemoreceptors cause ventilation to increase

Elevated CO₂ results in:

· Confusion

· Diminished sensory acuity

· Coma

· Death

Lung Capacities

Measured with a spirometer; measures volumes of air

Total lung capacity (TLC) – total lung volume (6 L)

Tidal volume – air inspired (or expired) during single breath at rest (450-500 ml)

Inspiratory reserve volume (IRV) – volume of air maximally inhaled at end of tidal respiration (1900-3300 ml)

Expiratory reserve volume (ERV) – volume of air that can be maximally exhaled at the end of tidal expiration (700-1000 ml)

Vital capacity (VC) – total volume of air that can be forced into (or out of) lungs (3000-5000 ml)

Residual volume (RV) – volume of gas remaining after maximal expiration (1100-1200 ml)

Pulmonary Capacities

Capacity	Calculation
Inspiratory Capacity	IC = TV + IRV
Expiratory Capacity	EC = TV + ERV
Functional Residual Capacity	FRC = ERV + RV
Vital Capacity	VC = IRV + TV + ERV
Total Lung Capacity	TLC = IRV + TV + ERV + RV

Pulmonary Disorders

Obstructive vs. Restrictive disorders

Obstructive

Reduced airflow due to increased resistance

Emphysema

Bronchitis

Asthma

Show increased residual capacity

Restrictive

Actual lung damage limiting vital capacity

Pulmonary fibrosis

Normal FEV

Emphysema

Decreased FEV