All questions of Breathing and Exchange of Gases for NEET Exam

Alveoli are very thin, irregular walled bag like structures for gaseous exchange. Tracheae bronchi and bronchioles are supported by incomplete cartilaginous rings. Double layered pleural membrane surrounds the lungs with pleural fluid between them. It reduces friction on the lung surface.

Inspiration is initiated by contraction of diaphragm which increases volume of thoracic chamber in antero-posterior axis and contraction of external inter –costal muscles which lifts up the ribs and sternum causing increases in volume of thoracic chamber in dorsoventral axis.

The formation of oxyhemoglobin in the alveoli is primarily influenced by the partial pressure of oxygen ( pO₂ ), partial pressure of carbon dioxide ( pCO₂), hydrogen ion concentration ( H⁺ ), and temperature. Understanding these factors will help in selecting the right option that describes the conditions favorable for maximizing the binding of oxygen to hemoglobin in the lungs.
1. Oxygen Partial Pressure ( pO₂ ): High pO 2 enhances the formation of oxyhemoglobin. In the alveoli, where gas exchange occurs, the pO₂ is relatively high, making it a favorable condition for oxyhemoglobin formation as oxygen molecules bind readily to hemoglobin.
2. Carbon Dioxide Partial Pressure ( pCO₂ ): Lower pCO₂ is favorable in the alveoli for oxyhemoglobin formation. High pCO₂ leads to a lower pH (due to formation of carbonic acid), which can cause the release of O₂ from hemoglobin (Bohr effect), reducing hemoglobin's affinity for oxygen.
3. Hydrogen Ion Concentration ( H⁺): Lesser H⁺ concentration, or higher pH, increases the affinity of hemoglobin for oxygen. In alkaline conditions (higher pH), hemoglobin is more likely to bind oxygen, thus forming oxyhemoglobin.
4. Temperature: Temperature also affects oxygen binding. Lower temperatures generally enhance the uptake of oxygen by hemoglobin. However, since the lung environment maintains a stable temperature, significant fluctuations in temperature are less of a consideration in this context compared to pO₂ , pCO₂ , and H⁺ concentration. Given these points, Option B - High pO₂ and Lesser H⁺ concentration - best describes the conditions that are favorable for the formation of oxyhemoglobin in the alveoli. High pO₂ ensures that more oxygen molecules are available to bind with hemoglobin, and a lower H⁺ concentration (higher pH) reduces the release of oxygen from hemoglobin, thereby increasing oxygen uptake.

Vital capacity of lungs is largest possible expiration after largest possible inspiration that is greatest. Volume of air can be exchanged in single respiration or amount of air breath in and out with greatest  possible efforts.
VC = TRV +TV + ERV 
      = 3000 + 500 + 1100 
      = 4600 ml.

(a) and (c) . Neural signals from pneumotaxic center in pons region of brain can limit the duration of inspiration. About 25% of carbodioxide (CO₂) is carried by haemoglobin as carboxyhaemglobin.

Expiratory capacity is the total volume of air a person can expire after normal inspiration. It includes tidal volume and expiratory reserve volume.
EC = TV + ERV = 500 + 1000 = 1500 mL

Asthma is a difficulty in breathing, causing wheezing due to inflammation of bronchi and bronchioles. 

Emphysema is a chronic disorder in which abnormal distension of the bronchioles or alveolar sacs of the lungs occurs due to which respiratory surface is decreased for the exchange of oxygen and carbon dioxide.

Excess CO₂ mainly stimulates the respiratory centre of the brain and increases the inspiratory and expiratory signals to the respiratory muscles. O₂ does not have a significant direct effect on the respiratory centre of the brain in controlling respiration. 

Intrapleural pressure is the pressure of air within the pleural cavity. Intrapleural pressure is always negative, which acts like a suction to keep the lungs inflated and prevent them from collapsing. The negative intrapleural pressure is due to three main factors: surface tension of the alveolar fluid; elasticity of lungs; elasticity of thoracic wall. Normally, there is a difference between intrapleural and intrapulmonary pressure, which is called transpulmonary pressure. This transpulmonary pressure creates the suction to keep the lungs inflated. If there is no pressure difference, there is no suction and lungs will collapse.

Residual volume is the volume of air which remains in the lungs after the most forceful expiration. This residual air enables the lungs to continue exchange of gases even after maximum exhalation. Due to this, lungs do not collapse even after forceful expiration.

The number of spiracles in cockroach is 10-pairs (2-pairs in thoracic and 8-pairs in abdominal region).  The thoracic pairs of spiracles are present on pleuron between prothorax - mesothorax and metathorax. Each spiracle opens into a chamber called atrium.  After atrium the tracheal tube ramifies into fine branches of tracheae, and then tracheoles.

A is Pulmonary vein which takes pure blood from lungs to heart. B is dorsal aorta  which takes pure blood from heart to various body parts. C is Vena cava which takes impure blood from various body pars to right auricle of heart. D is pulmonary artery which takes impure blood from heart to lungs.