Human Respiratory System Questions in English

(C) The human respiratory system follows a branching pattern:
$1$. Trachea $(I)$: There is only $1$ trachea.
$2$. Secondary bronchi $(III)$: There are $2$ secondary bronchi (one for each lung).
$3$. Tertiary bronchi $(IV)$: There are approximately $8-10$ tertiary bronchi in each lung,totaling about $16-20$.
$4$. Terminal bronchioles $(II)$: These are the most numerous,numbering in the thousands.
Therefore,the correct order based on the number of structures is $II > IV > III > I$.

(A) The human respiratory system consists of a pair of lungs. Each lung is a complex structure composed of a branching network of bronchi,bronchioles,and alveoli. The bronchi enter the lungs and divide into secondary and tertiary bronchi and bronchioles,which finally terminate in very thin,terminal bronchioles associated with the alveoli,where the actual exchange of gases occurs.

(C) The lungs are covered by a double-layered membrane known as the pleura.
The space between the inner and outer pleural membranes is called the pleural cavity.
This cavity is filled with a lubricating fluid known as pleural fluid.
This fluid reduces friction on the lung surface during breathing.

(B) The human respiratory system is divided into two parts: the conducting part and the respiratory (exchange) part.
$1$. The conducting part includes the external nostrils,nasal passage,pharynx,larynx,trachea,bronchi,and bronchioles (up to the terminal bronchioles).
$2$. The primary functions of the conducting part are to transport atmospheric air to the alveoli,clear it of foreign particles,humidify it,and bring it to body temperature.
$3$. The respiratory or exchange part consists of the alveoli and their ducts,where the actual diffusion of $O_2$ and $CO_2$ between blood and atmospheric air takes place.
$4$. Option $B$ is incorrect because the conducting part transports air up to the terminal bronchioles,not directly to the alveoli. The alveoli are part of the respiratory exchange zone.

(C) The thoracic cavity is an airtight chamber formed as follows:
$1$. Dorsally: By the vertebral column.
$2$. Ventrally: By the sternum.
$3$. Laterally: By the ribs.
$4$. Lower side: By the dome-shaped diaphragm.
Therefore,the correct sequence is Vertebral column (Dorsal),Sternum (Ventral),Ribs (Lateral),and Diaphragm (Lower).

(C) The thoracic cavity is a hollow space in the body protected by the rib cage.
It contains the lungs,heart,esophagus,and major blood vessels.
The liver is a large organ located in the abdominal cavity,specifically in the upper right quadrant,just below the diaphragm.
Therefore,the liver is not located in the thoracic cavity.

(B) The human respiratory tract is supported by cartilaginous rings to prevent the collapse of the airways during breathing.
Specifically,the trachea,primary bronchi,secondary bronchi,tertiary bronchi,and initial bronchioles are supported by incomplete cartilaginous rings.
These rings are 'incomplete' ($C$-shaped) to allow for the expansion of the esophagus during swallowing and to provide structural flexibility.
Therefore,the correct option is $B$.

(A) The human respiratory system is divided into two parts based on function: the conducting zone and the respiratory (or exchange) zone.
$1$. The conducting zone includes the external nostrils,nasal passage,pharynx,larynx,trachea,bronchi,and bronchioles up to the terminal bronchioles.
$2$. The primary function of this zone is to transport atmospheric air to the alveoli,clear it from foreign particles,humidify it,and bring it to body temperature.
$3$. The respiratory zone consists of respiratory bronchioles,alveolar ducts,and alveoli,where the actual diffusion of $O_2$ and $CO_2$ between blood and atmospheric air takes place.
Therefore,the conducting zone extends from the external nostrils to the terminal bronchioles.

(B) The trachea is a straight tube extending up to the mid-thoracic cavity.
It divides at the level of the $5^{\text{th}}$ thoracic vertebra into right and left primary bronchi.
This point of bifurcation is known as the carina.

(B) $Statement-I$ is incorrect because the epiglottis prevents the entry of food into the trachea (glottis), not the oesophagus.
$Statement-II$ is incorrect because the internal lining of the trachea is composed of ciliated pseudostratified columnar epithelium, which also contains goblet cells for mucus secretion, not just ciliated epithelium.

(A) The pharynx is divided into three parts: nasopharynx,oropharynx,and laryngopharynx. The nasopharynx is the superior part,the oropharynx is the middle part,and the laryngopharynx is the inferior part. Therefore,the oropharynx communicates with the nasopharynx above,not below. Thus,option $A$ is the incorrect statement.

(D) Statement $i$ is correct: The air sacs of terminal bronchioles contain $10-12$ alveoli.
Statement $ii$ is correct: Each alveolus is surrounded by a dense network of pulmonary capillaries for efficient gas exchange.
Statement $iii$ is incorrect: Alveoli are lined by thin,simple squamous epithelium to facilitate diffusion,not ciliated pseudostratified epithelium.
Statement $iv$ is correct: Alveoli significantly increase the surface area available for the exchange of $O_2$ and $CO_2$.
Statement $v$ is correct: The human lungs contain approximately $700$ million alveoli,providing a massive surface area for respiration.
Therefore,statements $ii, iv,$ and $v$ are correct.

(C) The air passage in the respiratory system follows a specific anatomical order.
Starting from the upper respiratory tract,the air enters the $II.$ Larynx (voice box).
From the larynx,it moves into the trachea,which then branches into the $I.$ Bronchi.
The bronchi further divide into smaller tubes called $III.$ Bronchioles.
Finally,the air reaches the $IV.$ Alveolus,where gas exchange occurs.
Therefore,the correct sequence is $II \rightarrow I \rightarrow III \rightarrow IV$.

(D) The $larynx$ is a cartilaginous box which helps in sound production and is hence called the sound box.
During swallowing,glottis can be covered by a thin elastic cartilaginous flap called epiglottis to prevent the entry of food into the larynx.
Vocal cords are present in the larynx,which vibrate to produce sound.

(A) The alveoli of the lungs are the primary sites of gaseous exchange.
To facilitate efficient diffusion of gases ($O_2$ and $CO_2$),the wall of the alveoli must be extremely thin.
This is achieved by a single layer of flat,scale-like cells known as simple squamous epithelium.
Therefore,the alveolus of the lungs is lined by squamous epithelium.

(C) The human respiratory system is divided into the upper and lower respiratory tracts.
$1$. The upper respiratory tract includes the nose,nasal cavity,pharynx (throat),and nasopharynx.
$2$. The lower respiratory tract begins with the larynx,followed by the trachea,bronchi,and lungs.
$3$. Therefore,the larynx is considered the first part of the lower respiratory system,not the upper respiratory system.

(B) In humans,the lungs are the primary organs of respiration. The right lung is larger and is divided into three lobes: superior,middle,and inferior. The left lung is smaller to accommodate the heart and is divided into two lobes: superior and inferior. Therefore,the correct statement is that the right lung is divided into three lobes and the left lung is divided into two lobes.

(B) The $larynx$,also known as the voice box,is a cartilaginous structure located in the upper part of the respiratory tract.
It contains vocal cords that vibrate as air passes through them,producing sound.
Therefore,the $larynx$ is the sound-producing organ in the human respiratory system.

(D) In human beings,the lungs are the primary organs of respiration.
The right lung is larger and is divided into $3$ lobes: superior,middle,and inferior lobes.
The left lung is smaller to accommodate the heart and is divided into $2$ lobes: superior and inferior lobes.
Therefore,the number of lobes in the right and left lungs are $3$ and $2$ respectively.

(D) The epiglottis is a thin,leaf-shaped cartilaginous flap located at the entrance of the larynx.
During the process of deglutition (swallowing),the epiglottis folds down to cover the glottis (the opening of the windpipe).
This action effectively prevents food and liquid from entering the respiratory tract,directing them instead into the esophagus.