Tag: breathing and exchange of gas

Lungs are never empty even after forceful expiration. There is always a certain amount of air present in the lungs which is known as residual volume which amounts to 1500 ml. 

When the intercostal muscles and the diaphragm contract they increase the size of the thoracic cavity, causing negative pressure in the lungs, causing inspiration.
So, the correct answer is option B.

• When you breathe in, or inhale, your diaphragm contract and move downward. This increases the space in the chest cavity into which lungs expand.
  
• The intercostal muscles between ribs also help enlarge the chest cavity.

Intercostal and abdominal muscle would contract if we blow up a balloon. When this occurs, you are interrupting the natural rhythm of breathing. The inhalation process is blowing up a balloon. As you this movement is facilitated by the contraction of the external intercostal muscles.

Volume of thoracic chamber increases in anteroposterior and dorso-ventral axis in human by contraction of diaphragm and external intercostal muscles.

During inspiration, the diaphragm contracts and moves downward and when the diaphragm relaxes it becomes dome shaped and moves upward during expiration. 

Nasal cavity opens to outside through external nares or nostrils. Nasal cavity occurs between palate and cranium. Nasal cavity is divisible into two nasal chambers by a nasal septum. Each nasal chamber has three parts - (a) Vestibule- It has hairs to filter out the dust particles, (b) Conditioner - respiratory region. It has bony projections and sinuses. It is abundant in blood capillaries, (c) Olfactory region- perceives sense of smell. The two nasal cavities condition the air to be received by the other areas of the respiratory tract.

During quiet breathing, there is little or no muscle contraction/relaxation involved in expiration. This process is simply driven by the elastic recoil of the lungs in healthy individuals. In certain conditions the elasticity of the lung can be lost, such as in emphysema. Forced or active expiration occurs in such individuals as well as occurring during exercise. The abdominal muscles and the internal and innermost intercostal muscles help expel air.

Coughing is an airway reflex mediated by airway receptors, that react to either pressure or chemical stimuli. The function of coughing is to assist the removal of material from the airways. This material may have been inhaled or produced in the airways. Coughing also prevents additional inhalation of material, or movement of inhaled material into the peripheral airways. Once material comes in contact with ciliated epithelium, it is transported by ciliary beating towards the trachea, where there is the highest density of cough receptors. Coughing then propels the material into the oropharynx, where it is swallowed. Coughing is an extremely important protective mechanism for the respiratory system.

Respiration is the process by which oxygen and carbon dioxide diffuse in and out of the blood. Respiration is also referred to as gas exchange, and it occurs in two areas of the body. External respiration refers to gas exchange across the respiratory membrane in the lungs. Internal respiration refers to gas exchange across the respiratory membrane in the metabolizing tissues, like your skeletal muscles. Expiration and inspiration are not the related terms of respiration. Thus, option C is correct.