Describe various parts of the human respiratory system.

(N/A) The human respiratory system consists of the nose,pharynx,larynx,trachea,bronchi,and lungs.
$(1)$ Nose: The nose is a raised structure on the face. It is divided into external nostrils,nasal chamber,and internal nostrils.
$(a)$ External nostrils: $A$ pair of openings located above the upper lip.
$(b)$ Nasal chamber: The internal cavity divided by a nasal septum. It is categorized into three regions: $(i)$ Vestibular,$(ii)$ Respiratory,and $(iii)$ Olfactory.
$(2)$ Pharynx: $A$ $13 \ cm$ long tube acting as a common passage for food and air. It is divided into $(a)$ Nasopharynx,$(b)$ Oropharynx (bucco-pharynx),and $(c)$ Laryngopharynx.
$(3)$ Larynx: Known as the sound box. It contains the glottis,which is covered by a cartilaginous flap called the epiglottis to prevent food entry during swallowing. It contains vocal cords for sound production.
$(4)$ Trachea: $A$ straight tube,$12.5 \ cm$ long and $2.5 \ cm$ in diameter. It extends to the mid-thoracic cavity and divides at the level of the $5^{th}$ thoracic vertebra into right and left primary bronchi. It is supported by '$C$'-shaped cartilaginous rings.
$(5)$ Bronchi and Bronchioles: The primary bronchi branch into secondary and tertiary bronchi,which further divide into bronchioles,eventually leading to alveoli. This network is called the bronchial tree.
$(6)$ Lungs: $A$ pair of cone-shaped organs in the thoracic cavity,protected by the rib cage and diaphragm.

Feature	Right Lung	Left Lung
Size	Thick,short,heavy	Thin,narrow,long,light
Lobes	Three lobes	Two lobes
Aortic arch	Absent	Present

Internal Structure: Lungs are covered by a double-layered pleural membrane with pleural fluid in between to reduce friction. The system is divided into the conducting part (nostrils to terminal bronchioles) and the respiratory/exchange part (alveoli and their ducts). The thoracic chamber is an air-tight space formed by the vertebral column,sternum,ribs,and diaphragm,allowing for breathing through volume changes.