• Expiration is a mechanism in which air which contains carbon dioxide release out from the lungs of the body.
  
• This air is dry and contains more moisture from the lungs.
• Lungs can never be empty even after force full expiration some amount of air remains in it known as residual volume.
• The exchange of gases occurs only at cellular and alveolar site, not in expiration.
  

During inspiration, the diaphragm contracts and flattens to increase the volume of the the thoracic cavity. This increase in volume leads to a decrease in intra-alveolar pressure, which is a pressure lower than atmospheric pressure and creates the pressure gradient. Due to the gradient the air is from the atmosphere is forced inside the lungs through nasal cavity.

The diaphragm is the muscular organ situated between the thoracic cavity and the abdominal cavity. It contracts and moves downwards due to which the volume in the lungs increases and the air is inhaled. When it relaxes, the volume of the lungs decreases and the air is expelled out.

When the gaseous exchange occurs due to a difference in the partial pressure of gases between alveoli of lungs and capillaries it is termed as an external exchange as it involves air that ix either inhaled or exhaled from the environment outside the body while when the exchange occurs between capillaries and tissue it is known as the internal exchange.

In the alveoli, the oxygen is continuously absorbed by the blood and CO$ _{2}$ is continuously added by the blood. So, the alveolar air has more CO$ _{2}$ concentration than the expired air.

The gas which we exhale or breath out is carbon-dioxide. 

Air can be forced to move from one place to another by creating a pressure gradient. In the human body, the contraction of the diaphragm allows it to move down to abdomen cavity slightly. This increases the area in the thoracic cavity and the lungs expand. The intercostal muscles between the ribs also contract and allow the rib bones o come upwards and outward. Due to this, volume in the lungs increases and the pressure decreases. The pressure in the lungs is less than that of atmospheric pressure, so the air is drawn in and inspiration occurs.

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.

Inhalation involves a contraction of the muscles, an increase in the size or volume of thoracic cavity, an expansion of the lungs with a drop of pressure inside them and entrance of atmospheric air into lungs through the air passages. Thus during inspiration the lungs act as suction pump. Inhalation is followed by exhalation, which is effected by the contraction of the lungs.

The diaphragm, located below the lungs, is the major muscle of respiration. It is a large, dome-shaped muscle that contracts rhythmically and continuously, and most of the time, involuntarily. Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs. Upon exhalation, the diaphragm relaxes and returns to its dome like shape, and air is forced out of the lungs. Thus, option B is correct. 

External respiration occurs in the lungs where oxygen diffuses into the blood and carbon dioxide diffuses into the alveolar air. Internal respiration occurs in the metabolizing tissues, where oxygen diffuses out of the blood and carbon dioxide diffuses out of the cells. Inspiration and expirations are breath in and breath out processes. 

Inhaled air contains more oxygen used to create energy and less CO$ _2$. It contains 21% O$ _2$, 0.04% CO$ _2$ and 79% Nitrogen. Exhaled air contains 16% O$ _2$, 4% CO$ _2$ and 79% Nitrogen. Thus, option C is correct. 

Inhaled air contains more oxygen used to create energy and less CO$ _2$. It contains 21% O$ _2$, 0.04% CO$ _2$ and 79% Nitrogen. Thus, option A is correct. 

The diaphragm, located below the lungs, is the major muscle of respiration. It is a large, dome-shaped muscle that contracts rhythmically and continuously, and most of the time, involuntarily. Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs. Upon exhalation, the diaphragm relaxes and returns to its dome like shape, and air is forced out of the lungs. Diaphragm contracts, moves down and flattens during inhalation and diaphragm relaxes and curves upwards during exhalation. So, when diaphragm of man is completely dome shaped, it shows that beginning of expiration and end of inspiration. Thus, option B is correct. 

Inhalation (also known as inspiration) is the flow of air into an organism. It is a vital process for all human life. In humans it is the movement of air from the external environment, through the airways, and into the alveoli. Inhalation begins with the contraction of the muscles attached to the rib cage. This causes an expansion in the chest cavity. Then takes place the onset of contraction of the diaphragm, which results in expansion of the intrapleural space and an increase in negative pressure according to Boyle's Law. This negative pressure generates airflow because of the pressure difference between the atmosphere and alveolus. Air enters, inflating the lung through either the nose or the mouth into the pharynx (throat) and trachea before entering the alveoli. 

External respiration also known as breathing refers to a process of inhaling oxygen from the air into the lungs and expelling carbon dioxide from the lungs to the air. Exchange of gases both in and out of the blood occurs simultaneously. External respiration is a physical process during which oxygen is taken up by capillaries of lung alveoli and carbon dioxide is released from blood. Internal respiration or tissue respiration/cellular respiration refers to a metabolic process in which oxygen is released to tissues or living cells and carbon dioxide is absorbed by the blood. Once inside the cell the oxygen is used for producing energy in the form of ATP or adenosine triphosphate. Therefore, the correct answer is option D.

Chloride shift is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO$ _{3-}$) and chloride (Cl-) across the membrane of the red blood cells (RBCs).
Therefore, the correct answer is option C.

Inhaled air contains more oxygen used to create energy and less carbon dioxide. Exhaled air which contains more carbon dioxide produced as a waste product of energy production and less oxygen as it has been used in respiration. Inhaled air contains 21% oxygen, 0.04% CO$ _2$ and 79% N$ _2$. Exhaled air contains 16% oxygen, 4% CO$ _2$ and 79% N$ _2$.

The diaphragm is located below the lungs and is the major muscle of respiration. It is large, dome-shaped muscle that contracts rhythmically and continually. upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs. Upon exhalation, the diaphragm relaxes and returns to its dome-like shape, and is forced out of the lungs.
Therefore, the correct answer is option B.

Inhaled air contains more oxygen used to create energy and less carbon dioxide. Exhaled air which contains more carbon dioxide produced as a waste product of energy production and less oxygen as it has been used in respiration. Inhaled air contains 21% oxygen, 0.04% CO$ _2$ and 79% N$ _2$. Exhaled air contains 16% oxygen, 4% CO$ _2$ and 79% N$ _2$. 

Increase in volume of thoracic cavity is seen in case of inspiration. Inspiration results in flattened diaphragm. The volume of thoracic cavity decreases during expiration and the diaphragm relaxes and comes to its original dome shape. 

Component       Inspired air     Expired air

The most important muscles of forced expiration are those of the abdominals. When these muscles contract, intra-abdominal pressure is raised, and the diaphragm is pushed upward. These muscles also contract forcefully during coughing, vomiting, and defecation. The internal intercostal muscles assist active expiration by pulling the ribs downward and inward thus decreasing the thoracic volume. 

In respiration, the human body exhales about 15% of the oxygen that is not utilized by the body. 

During the process of inhalation, the lung volume expands as a result of contraction of the diaphragm & intercostal muscles, thoracic cavity expands, due to this increase in volume, the pressure is decreased.

When the internal intercostal muscles contract and diaphragm relax, the ribs move .downward and inward and diaphragm becomes convex {dome shaped), thus decreasing the volume of thoracic cavity and increasing the pressure inside as compared to the atmospheric pressure outside. This will cause the air to move out (expiration).

Vital capacity is the maximum volume of air a person can breathe in after a forced expiration or the maximum volume of air a person can breathe out after a forced inspiration.This equals the inspiratory reserve volume (IRV) + expiratory reserve volume (ERV) + tidal volume (TV). Its value is 3400 mL - 4800 mL..

 Corrected statements:

(ii) Lungs do not become empty after a forceful expiration.

(iii) The exchange of gases in the lungs is not interrupted during expiration.

So, the correct answer is '(ii) and (iii)'.

During inspiration external intercoastal muscles and diaphragm contract because it allows air to be moved into the lungs and requires the contraction of various musceles; the diaphragm and external intercoastal muscles contract.

Sum of the partial pressure of all gases is 760 mm of Hg.

The amount gases in exhaled air are 4% to 5% by volume more carbon dioxide and 4% to 5% by volume less oxygen than was inhaled. This expired air typically composed of: 78.04% nitrogen; 13.6% - 16% oxygen; 4% - 5.3% carbon dioxide; 1% other gases.

When the diaphragm relaxes, air is exhaled by elastic recoil of the lung and the tissues lining the thoracic cavity in conjunction with the abdominal muscles which act as an antagonist paired with the diaphragm's contraction. The internal intercostals assist in expiration by pulling the ribcage down.

When we breathe in, or inhale, the diaphragm contracts (tightens) and moves downward. This increases the space in the chest cavity, into which the lungs expand. The intercostal muscles between the ribs also help enlarge the chest cavity. They contract to pull the rib cage both upward and outward when we inhale. As the lungs expand, air is sucked in through the nose or mouth. The air travels down the windpipe and into the lungs. After passing through the bronchial tubes, the air finally reaches and enters the alveoli (air sacs).

Carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin. This form transports about 10 percent of the carbon dioxide. When carbon dioxide binds to hemoglobin, a molecule called carbaminohemoglobin is formed. Binding of carbon dioxide to hemoglobin is reversible. Therefore, when it reaches the lungs, the carbon dioxide can freely dissociate from the hemoglobin and be expelled from the body. About 30% of CO$ _2$ is transported as carbamino haemoglobin. 

Internal respiration refers to gas exchange across the respiratory membrane in the metabolizing tissues. External respiration refers to gas exchange across the respiratory membrane in the lungs. Pulmonary ventilation is the process by which oxygen enters and carbon dioxide exits the alveoli. Respiration is the process by which oxygen and carbon dioxide diffuse in and out of the blood. 

What most people don’t know is that it is, in fact, the level of CO$ _2$ rather than oxygen that usually drives breathing rate. Your body’s ability to detect specific concentrations of CO$ _2$ is extremely sensitive. If the level of CO$ _2$ in your blood increases by a mere 10%, your rate of breathing will double. The answer comes from the way CO$ _2$ is transported. Instead of being bound to hemoglobin, the CO$ _2$ mostly just dissolves in your blood. When the CO$ _2$ dissolves, it combines with the water in your blood to form carbonic acid. As this acid builds up, it dramatically decreases the pH of your blood, throwing it out of balance. Your brainstem detects this pH change, and speeds up your breathing rate in order to to get rid of the extra CO$ _2$. 

The correct sequence of events in the initiation of respiration is:
(i)    The contraction of external intercostal muscles raises the ribs and sternum
(ii)    The volume of thorax increases in the dorsoventral axis
(iv)    Diaphragm contraction
(vi)    The volume of thorax increases in the anterior-posterior axis
(iii)    Intrapulmonary pressure decreases

The relaxation of external intercostal muscles and diaphragm leads to return of diaphragm, ribs, and sternum to resting position thus restoring thoracic cavity to pre-inspiratory volume. The pressure in the lungs increases and the air is exhaled.
So, the correct answer is option A.

During inspiration, the diaphragm contracts and pulls downward while the muscles between the ribs contract and pull upward. This increases the size of the thoracic cavity and decreases the pressure inside. As a result, air rushes in and fills the lungs.

During expiration, the diaphragm relaxes, and the volume of the thoracic cavity decreases, while the pressure within it increases. As a result, the lungs contract and air is forced out.