Breathing and Exchange of Gases Test 69

When C$$O_{2}$$ concentration in blood increases, breathing becomes faster and deeper. The effect of rising $$CO_{2}$$ concentration is due to decrease in affinity of Hb for $$O_{2}$$. Thus, the $$CO_{2}$$ released in the tissues accelerates the delivery of $$O_{2}$$ (called Bohr effect), due to-which breathing becomes faster and deeper.

The pneumotaxic center is located in the dorsal part of Pons Varolii. It is called the switch-off point of breathing since it is known to limit the duration of inspiration. This center influences the respiratory rhythm center by regulating the breathing rate.

The given graph shows the relationship between the partial pressure of oxygen with the amount of oxygen that can bind with haemoglobin. The P$$O_{2}$$ of the air within alveoli is about 100 mm Hg. As the blood travels through the systemic blood capillaries, oxygen leaves the blood and diffuses into the tissues. Consequently, the bipod that leaves the tissues in the veins has a P$$O_{2}$$ that is decreasing (in a resting person) to about 40 mm Hg. Therefore, A depicts oxygenated blood and B depicts systemic blood. The steep portion of the curve from 60 down to 20 mm Hg is ideal for unloading oxygen in the tissue, Le., for a small decrease in P$$O_{2}$$ (due to diffusion of oxygen) a large quantity of oxygen can be unloaded to the peripheral tissue capillary. During strenuous exercise, the muscles accelerated metabolism uses more oxygen from the capillary blood and thus decreases the venous blood P$$O_{2}$$, for example, the P$$O_{2}$$ of the venous blood could drop to 20 mm Hg. Hence, D, E and F show venous blood in exercise, normal venous blood and normal arterial blood respectively. As we know, in the resting person, the P$$O_{2}$$ of tissue is 40 mm Hg, which is favourable for oxygen diffusion from arterial blood to the tissues. Oxygen unloaded to the tissues by arterial blood is 5 mL/100 mL of blood (20 mL- 15 mL = 5mL/100mL, from the graph). During strenuous exercise, the muscle interstitial fluid P$$O_{2}$$ falls to 20 mm Hg, so the oxygen that unloads to the tissue Is 15 mL/100 ml of blood, (20 - 5) ml/100 mL = 15 mL/100mL, from the graph i.e., three times as much as normal.

• The tidal volume represents the volume of air inhaled or exhaled during normal respiration. The value of tidal volume in a normal healthy person is approximately 6000-8000 ml/min.

Oxygen hemoglobin dissociation curve - This curve shows the relationship between oxygen level and hemoglobin saturation or we can say it shows the affinity for hemoglobin.

• The nasopharynx is the portion of the pharynx. Other two portions of the pharynx are oropharynx and hypopharynx.
  
• The larynx is called as a cartilaginous box as it is made up of 9 cartilages which help in the production of voice.
  
• Primary and secondary bronchi are supported by incomplete hyaline cartilage c-shaped rings.
  
• The pleural fluid of pleural space reduces friction on lung surface. The pleural fluid is secreted by visceral(inside) pleura.
  

An increased concentration of carbon dioxide is the strongest stimulus to breathe more deeply and more frequently. When the carbon dioxide concentration in the blood is low, the brain decreases the frequency and depth of breath.

Due to low oxygen tension and high carbon dioxide oxyhaemoglobin at the tissue level liberates the oxygen to the cells. Oxygen dissociates from the hemoglobin and diffuses into tissue.