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Cigarette smoking damages alveolar walls due to alveolar sacs remaining filled with air leading to decreased respiratory surface for exchange of gases.

Emphysema is a chromic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. One of the major causes of this is cigarette smoking.

Alveoli is primary site of respiratory gas exchange.

Insects have a network of tubes through which air is transported within the body. These tubes are called tracheae. The tracheae open on the lateral surface of the animal through minute pores; called spiracles.

Insects have a network of tubes (tracheal tubes) to transport air within the body. Air enters the spiracles during inspiration and reaches the tracheoles which contain tissue fluids. Oxygen in the air dissolves in those fluids and reaches the cells.

There is a fall of PO₂ level at high altitudes. This lowers alveolar PO₂ and consequently reduces the diffusion of oxygen from the alveolar air to the blood. So oxygenation of blood is decreased progressively. After some time, the affected person gets adjusted to the surroundings due to which the heart rate are accelerated, RBC count in the blood is increased, haemoglobin level and oxygen-carrying capacity are also increased.

Lack of adequate oxygen supply to whole body or a part is called hypoxia. Hypoxia generally happens because of a mismatch between oxygen demand and supply.

(ii)  PO₂ higher, PCO₂ lesser

(ii) pO₂ higher, pCO₂ lesser

After tissue respiration, PO₂ and PCO₂ in deoxygenated blood are 40 mm Hg and 45mm Hg respectively.

Binding of oxygen with haemoglobin is mainly related to the partial pressure of O₂. Partial pressure of CO₂, hydrogen ion concentration and temperature are the other factors which can interfere with this binding. Increased partial pressure of CO₂ can increase haemoglobin’s affinity towards oxygen and vice-versa is also true.

External respiration – intake of oxygen by the blood from water or air in the respiratory organs and elimination of carbon dioxide. 

Internal respiration – involves uptake of oxygen by tissue cells via tissue fluid, oxidation of food in tissue cells leading to production of carbon dioxide, water and energy, storage of energy in the form of ATP and release of CO₂ from tissue cells into blood via tissue fluid. 

First step of respiration, refers to the movements that send fresh air or with dissolved in water to the respiratory organs (inspiration) and removes foul air or water from them (expiration). 

The  Alveoli

Haemoglobin.

The apparatus used in measuring the amount of air exchanged during breathing & the rate of ventilation is the Spirometer.

Alveoli is last part of the bronchiole tree.

Trachea is a common passage for both air and food in man.

Carbonic Anhydrase.

Low PO₂, high PCO₂, high H⁺ concentration and high temperature.

1. Trachea

2. Gills.

Four is the maximum number of molecules of oxygen which one molecule of haemoglobin can carry.

Larynx is a cartilaginous box which helps in sound production and hence called the sound box.

Four molecules. 

Glottis is the opening of pharynx into larynx while epiglottis is a leaf-like cartilage that covers the wind-pipe or trachea.

Aquatic molluscs: Gills, Insects : Trachea.

Alveoli are number of very thin, irregular walled and vascularised bag like structures into which terminal bronchioles end.

When the diaphragm muscles contract, it moves down towards abdomen, increasing the volume of thoracic cavity, but decrease in air pressure. So air is drawn into the lungs.

Entry of air into alveoli of the lungs is called inspiration or inhalation.

Carbamino haemoglobin is the complex formed when carbon dioxide combines with the amine radical of the globin of haemoglobin.

carbamino-haemoglobin is the complex formed when carbon dioxide combines with the globin part of haemoglobin.

Carbonic anhydrase is found in RBC. It catalyses the formation of carbonic acid from carbon dioxide and water.

Amino group of reduced haemoglobin combines with CO₂ forming carbaminohaemoglobin to transport CO₂.

The two lungs are covered by a double layered membrane called pleura, with pleural fluid between them. The fluid reduces the friction on the lung surface. The outer pleural membrane is in close contact with the thoracic lining whereas the inner pleural membrane is in contact with the lung surface.

• Asthma: It is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.
• Emphysema: It is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. This is mainly caused by cigarette smoking. 
• Occupational Respiratory disorders: In certain industries, involving grinding and stone breaking the dust produced results in inflammation leading to fibrosis and this causing serious lung damage.

Larynx (Sound box)

Movement or exit of air from the alveoli of the lungs to outer atmosphere is called expiration or exhalation.

Blood is the medium of transport for O₂ and CO₂. About 97% of O₂ is transported by RBCs in the blood. The remaining 3% of O₂ is carried in a dissolved state through the plasma. Nearly 20-25 percent of CO₂ is transported by RBCs whereas 70% of it is carried as bicarbonate. About 7% is carried in a dissolved state through plasma.

Pleural fluid reduces the friction on the lung surface.

• Oxygen binds to the Fe²⁺ part of haemoglobin and is transported as oxyhaemoglobin through the RBCs of the blood.
• Each molecule of haemoglobin can transport a maximum of four oxygen molecules.
• CO₂ combines with the amine radial of haemoglobin to form carbamino haemoglobin and about 20 – 25% of CO₂ is transported in this form.

Only alveolar region is made up of squamous epithelium which is favorable for diffusion of gases.

In the tissues, PCO₂ is high, PO₂ is low and there is high concentration of H+ ions and high temperature. Since the PO₂ is lower than that of the blood, oxyhaemoglobin dissociates and releases the oxygen into the tissues.

Oxygen binds with haemoglobin in reversible manner to form oxyhaemoglobin. About 97% of O₂ is transported as oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four molecules of O₂. Binding of O₂ with haemoglobin depends on partial pressure of oxygen primarily and also on partial pressure of carbon dioxide, hydrogen ion concentration and temperature. In the alveoli, where there is high pO₂, low pCO₂, lesser H⁺ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, whereas in the tissues, where low PO₂, high PCO₂, high H⁺ concentration and higher temperature exist the conditions are favourable for dissociation of oxygen from the oxyhemoglobin. This indicates that O₂ gets bound to haemoglobin in the lung surface and gets dissociated at the tissues.

Exchange part is the actual site of diffusion of oxygen and carbon dioxide between blood and atmosphere.

Tidal Volume (TV): The volume of air inspired or expired during a normal respiration is called Tidal Volume. It is approximately 500 ml in a healthy man. This means that a healthy adult can inspire or expire about 6 to 8 litre of air per minute. 

Tidal Volume = 500 ml

Respiration rate = 12 per minute

Hence, Tidal Volume in 1 hour = 500 ml x 12 x 60 minute = 360000 ml = 360 litre.

Diaphragm and intercostal muscles.

• Squamous epithelium of alveoli
• Endothelium of alveolar capillaries
• Basement substance.

The solubility of CO₂ is 20-25 times higher than that of O₂. So more CO₂ diffuses across the respiratory membrane.

Pressure gradient between the lungs and the atmosphere.

In a closed room, there is no provision of fresh air coming into the room. The oxygen already present in the air of that room shall be gradually consumed. If more number of people are sitting in a room the percentage of oxygen will go on decreasing and the percentage of carbon dioxide would go on increasing. Thus it is not a healthy sign to breath in a closed room for a very long time.