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Describe the human respiratory system.

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Respiratory Organs of Human beings: The respiratory passage includes the following organs – 

Nostrils: 

1. There is a pair of external nares which are situated obliquely at the tip of the snout. This condition is called as diaphanous. 

2. Their cavities are called as fossae or nasal passage. Both the fossae remain separated by a nasal septum which is made up of mesethmoid cartilage. 

Nasal Cavities: 

1. The external nares open into nasal cavities which are situated dorsally to the palate. The nasal cavities open into the nasopharynx through a pair of internal nares or choanae.

2. Nasal cavities are formed as an invagination of the skin and it contains a turbinal bone which is a scrolled & porous bone, 

3. The projections of the turbinal bones are called as conchae. 

4. The nasal cavities remain lined by pseudo-stratified epithelium which is ciliated & glandular. 

5. There are Bowmann’s glands to secrete the mucus. 

6. The nasal epithelium is electroreceptors and it is also called as Schneiderian epithelium. 

7. Functions of nasal cavities – 

  • It filters the inspired air 
  • It acts as electroreceptor 
  • According to new researches, it is provided with pheromones receptors. 
  • It maintains the temperature of inspired air by cooling’warming the air. 
  • It makes the inspired air moist. 

Pharynx: 

1. Its a dorsal part is called as nasopharynx & ventral part as oro-pharynx. 

2. Posteriorly, it has two openings viz.-gullet (dorsal) & glottis (ventral). The gullet leads into an oesophagus & the glottis opens into a larynx. 

3. The glottis remains covered by a cartilaginous flap which is called as epiglottis. The epiglottis prevents the entry of food & water into the larynx. 

Larynx: 

1. It is located in the anterior end of the throat which is formed by the modification of the anterior end of the trachea. 

2. It is also called a sound-producing organ. 

3. Formation of larynx involves 

4 cartilages which are of 3 types viz., 

  • Thyroid-one largest, C-shaped & forms ventrolateral sides. 
  • Cricoid-one, ring-like, broad dorsally & forms base of the larynx. 
  • Arytenoid-Two small & from the dorsal side. 

4. The anterior end of the arytenoid cartilage is knob-like and it is called as the cartilage of Santorini. 

5. The larynx has two pairs of elastic vocal cords which remain stretched between the thyroid and arytenoid cartilages: 

  • Anterior or False vocal cords 
  • Inelastic & pinkish in colour. 
  • Posterior or True vocal cords

Lungs: 

1. Man has a pair of lungs which are situated in the thoracic cavity on both the sides of the heart. 

2. The lungs are elastic, spongy, light pink, unequal & without muscles. 

3. In the human being, the left lung consists of two lobes viz., left superior lobe & left inferior lobe. Whereas, the right lung includes three lobes viz.-superior lobe, middle lobe & inferior lobe. 

4. Each lung is bounded by two pleural membranes viz., 

  • External or Parietal pleuron. 
  • Internal or Visceral pleuron. 

5. Both the pleura remain closely applied to each other. 

6. The space between the lung and the pleura is called a pleural cavity. 

7. Each bronchus enters into the lung of own side & divide to form secondary or lobular bronchi (4 secondary bronchi in right lung & 2 secondary bronchi in the left lung). 

8. Each secondary bronchus divides to form tertiary or segmental bronchi, which further divide to form intrapulmonary bronchi. The ends of intrapulmonary bronchi divide to form terminal bronchioles which further form respiratory bronchioles. 

9. These bronchioles lack cartilaginous rings. Each respiratory bronchiole gives out 2 to 11 alveolar ducts. Each alveolar duct gives out small ducts, the atria. Each atrium forms small baglike alveoli or air sacs which are made up of squamous epithelium. 

10. Internally, the alveolus is lined by mucous & there is a network of blood capillaries outside. The alveoli provide more surface for the exchange of gases.

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