Breathing and Exchange of Gases (NEET Biology)

Breathing and Exchange of Gases

Respiratory Process

• Last product of respiration to obtain energy in animals: CO2
• Respiration is helpful in producing energy within the body and removing waste
• Pulmonary respiration is found in reptiles, aves, mammals, and all of these

Respiratory Organs

• Presence of respiratory organs in animals depends on habitat and level of organization
• A respiratory surface must be thin, moist, and have a large surface area
• Respiratory organs of insects: tracheal tubes
• Earthworms exchange O2 and CO2 through moist cuticle
• Branchial respiration is respiration by gills

Trachea and Bronchi

• Trachea terminates in bronchi
• Air is breathed in through nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
• Vocal cords occur in the larynx
• Bronchus gives passage to air towards alveoli
• Trachea is supported by cartilaginous rings, which are C-shaped

Lung Structure

• Lungs have a number of small balloon-like air sacs called alveoli
• Alveoli have a large surface area for diffusion of gases
• Wall of alveoli is composed of simple squamous epithelium

Thoracic Cage and Breathing

• Thoracic cage of man is formed of ribs, sternum, and thoracic vertebrae
• During inspiration, diaphragm and external intercostal muscles contract
• Abdominal breathing refers to forceful breathing
• Intercostal muscles regulate the movement of ribs

Respiratory Volumes

• Functional residual capacity = expiratory reserve volume + residual volume
• Air filled in dead space is approximately 150 cc

Blood Transport

• De-oxygenated blood from heart comes to the lungs by pulmonary artery
• Oxygen-containing blood is transported from lungs to heart by pulmonary vein
• Partial pressure of carbon dioxide in alveoli, atmospheric air, and tissues: 40 mmHg, 0.3 mmHg, 45 mmHg
• Oxygen diffuses from atmospheric air into alveoli with a partial pressure of 104 mmHg

Respiratory Membrane

• Respiratory membrane is composed of three major layers and has an average thickness of less than 1 mm
• Rate of gaseous exchange at lungs will be decreased upon increasing the thickness of the respiratory membrane
• One hemoglobin can carry 4 molecules of O2

CO2 Transport

• H2CO3 is converted into CO2 and H2O with the help of the enzyme carbonic anhydrase
• The largest amount of CO2 is transported in blood as bicarbonates
• CO2 reacts with water to form carbonic acid

Oxygen Transport

• Maximum amount of O2 is transported in humans by RBCs
• The metal ion present in hemoglobin is iron
• Oxygen-hemoglobin dissociation curve will shift to the right on decrease of pH

Respiratory Centre

• Respiratory centre of the brain is stimulated by carbon dioxide content in arterial blood
• Respiratory rhythm centre is present in the medulla oblongata
• Pneumotaxic centre is present in the pons
• Asthma is a respiratory disease caused due to allergy of lungs