08 Respiration and Circulation - part 02 - Human Respiratory system

 

08 Respiration and Circulation - part 02 - Human Respiratory system


Human Respiratory system:
  • The respiratory system brings about- 
  1. Inspiration
  2. Expiration and 
  3. Exchange of gasesin the lungs. 
  • These are then transported by blood from the lungs to the different tissues and parts of the body. 
  • The respiratory system and be divided into - 
                         A. Upper respiratory system 
                         B. Lower respiratory system

  • Upper respiratory system having - 
  1. External nares
  2. Nasal cavities
  3. Internal nares
  4. Nasopharynx
  5. Nose
  6. Throat and 
  7. Associated structures. 
  • The lower respiratory system refers to the - 
  1. Larynx
  2. Trachea
  3. Bronchi
  4. Bronchioles and 
  5. Lungs.

Nose :
  • A pair of slit like openings called external nares or nostrils for entry of air into the nasal cavity. 
  • The nasal cavity is divisible into right and left nasal chambers by a mesethmoid cartilage. 
  • Each nasal chamber is further divided into three regions.
  1. Vestibule
  2. Respiratory part (conditioner)
  3. Olfactory or sensory chamber 

1. Vestibule : 
  • It is the proximal part about the nostrils. 
  • Its skin has hair for filtering the air and traping the dust and suspended particles in the inhaled air.
2. Respiratory part (conditioner) : 
  • The middle thin walled highly vascular part for warming and moistening the inhaled air.
3. Olfactory or sensory chamber :  
  • The uppermost part is lined by olfactory epithelium for detection of smell.
Pharynx :
  • It is divisible into three parts -
  1. Nasopharynx   
  2. Oropharynx 
  3. Laryngopharynx
  • The nasopharynx is the uppermost part from the nasal chamber it leads into oropharynx (common passage for food and air). 
  • This continues below as the laryngopharynx.
  • Between the nasopharynx and oropharynx is the palate bone. 
  • The pharynx has a set of lymphoid organs called tonsils.
Larynx :

  • It is called voice box. 
  • It is the part of the respiratory tract which contains vocal cords for producing sound. 
  • The larynx extends from the laryngopharynx and the hyoid bone to the trachea. 
  • It is a hollow, tubular structure. 
  • Its wall is made up of cartilage plates held by membranes and muscles. 
  • Internally, it is lined by a pair of folds of elastic vocal cords (true vocal cords). 
  • Voice is produced by passage of air between the vocal cords and modulations created by tongue, teeth, lips and nasal cavity.
  • The larynx opens into the layngopharynx through a slit like opening called glottis. 
  • This opening of the trachea or wind pipe is guarded by a leaf like flap called epiglottis. 
  • It prevents the entry of food into trachea.
Trachea (wind pipe) :
  • It is a long tube 10 to 12 cm in length. 
  • Runs through the neck in front of the oesophagus and extends into and upto the middle of thoracic cavity. 
  • Supported by ‘C’ shaped 16 to 20 rings of cartilage which prevent the collapse of trachea. 
  • Lined internally with ciliated, pseudostratified epithelium and mucous glands that trap the unwanted particles preventing their entry into the lungs.
Bronchi :
  • The trachea divides into right and left primary bronchi as it reaches the middle of the thoracic cavity. 
  • The bronchi are supported internally by ‘C’ shaped incomplete rings of cartilage. 
  • The primary bronchi divide to form secondary and tertiary bronchi which lead into terminal bronchioles ending into alveoli.
Lungs :
  • Main respiratory organs of humans. 
  • One pair of spongy and elastic lungs are present in the thoracic cavity. 
  • Each lung is enclosed and protected by a double pleural membrane, outer parietal and inner visceral membrane. 
  • Between the two pleura is a pleural cavity filled with a lubricating fluid called pleural fluid. 
  • It is secreted by the membranes.
  • The right lung is larger and divided into 3 lobes.
  • Left lung is smaller and divided into 2 lobes. 
  • Each lobe of the lung has the terminal bronchioles ending in a bunch of air sacs, each with 10 to 12 alveoli.
Alveoli :
  • Thin walled lobulated structures, like a bunch of grapes. 
  • Each alveolus is surrounded by a network of capillaries  of pulmonary artries and veins. 
  • Have highly elastic wall made up of a single layer of squamous epithelium resting on a basement membrane of connective tissue. 
  • About 700 million alveoli in the lungs 
  • Provide the surface area for exchange of gases.
Diaphragm : 
  • Muscular septum that separates the thoracic and abdominal cavity. 
  • Dome shaped 
  • On contraction it becomes flattened.

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