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Human Respiratory System Structure and Parts

Introduction:

The human respiratory system is a physiological system consisting of respiratory organs and structures involved in gaseous exchange.
The human respiratory system involves:

  • Nose
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi and bronchioles
  • Alveoli
  • Lungs
     

human-respiratory-system


Topics covered:

  • Nose
  • Pharynx
  • Larynx
  • Bronchial
  • Alveoli
  • Conduction and Exchange Zone
  • Lungs


Nose

Has the following components:

External nares/ nostrils -

  • It is the first part of the respiratory tract.
  • A pair of external nostrils are present just above the lips.
  • These are the anterior openings of our nose that lead to the nasal chamber.

Nasal chambers -

  • Present above the palate and separated by the nasal septum
  • It has a lining of pseudostratified ciliated columnar epithelium
  • Each nasal chamber can be divided into three parts:
    1. Vestibular
    2. Respiratory
    3. Olfactory
  • Function:
    1. Mucus from goblet cells helps in trapping dust particles present in the air and makes the air humid.
    2. Ciliated epithelial lining also acts as an air filter.
    3. It regulates the temperature of inspired air as per the body temperature.

Internal nares -

  • Posterior opening of nasal cavities leading to the nasopharynx.
     

internal-nares


Pharynx

  • The pharynx is the common passage for both air and food
  • It has three parts:
    a. Nasopharynx - Opening of the nasal cavity into the pharynx
    b. Oropharynx - Opening of the oral cavity into the pharynx c. Laryngopharynx / Hypopharynx -
  • Passage for both food and air.
  • The posterior end has 2 openings i.e., gullet and glottis
  • Glottis is ventral, slit-like opening which leads to the larynx and has a thin leaf-like cartilaginous flap called epiglottis attached, to prevent the entry of food into the larynx
  • Gullet is a dorsal opening that opens into oesophagus.
     

pharynx


Larynx

a. Thyroid cartilage-

  • C-shaped, unpaired cartilage
  • Prominent in males and is called Adam’s apple or Poma’s Adami.

b. Cricoid cartilage -

  • Ring-shaped cartilage

c. Arytenoid cartilages -

  • Paired, pyramid-shaped cartilage

d. Corniculate -

  • Paired, conical nodules of elastic cartilage

e. Cuneiform -

  • Paired, small club-shaped nodules of elastic cartilage.
  • Connects arytenoid cartilage to the epiglottis.

f. Epiglottis -

  • Leaf-shaped cartilage

larynx-anatomy

Bronchial Tree

  • The trachea along with the two primary bronchi is known as the bronchial tree.
     

bronchial-tree

Trachea

  • It is also called windpipe.
  • A straight cartilaginous tube extending up to the mid-thoracic cavity (chest cavity).
  • It divides into left and right primary bronchi at the level of 5th thoracic vertebra.
  • Its function is to conduct air to bronchi.
  • It is surrounded by C-shaped/ incomplete cartilaginous (hyaline) rings which prevent the trachea from collapsing due to pressure change during breathing.
     

trachea

Bronchi

  • The trachea divides into primary bronchi.
  • Each primary bronchus enters into the lung
  • Each bronchus further divides into secondary and tertiary bronchi and bronchioles.
  • Bronchioles are terminal branching of bronchi.
  • Primary, secondary and tertiary bronchi and initial bronchioles are supported by incomplete cartilaginous rings.
  • These cartilaginous rings prevent bronchi from collapsing during the gaseous exchange.
  • Bronchioles give rise to numerous sac-like structures called alveoli.
     

bronchi

Alveoli

  • Terminal bronchioles end in alveolar duct
  • Alveolar ducts are tube-like structures and each alveolar duct leads to numerous alveoli.
  • Alveoli are very small, highly vascularised air sacs with a very thin, irregular membrane and rich blood supply.
  • Alveoli are the primary site for gaseous exchange.
  • Gaseous exchange takes place between alveoli and blood capillaries surrounding them.
  • There are millions of alveoli in a lung which increase the surface area for gaseous exchange.
  • Oxygen present in the inhaled air moves from the alveolus to the blood in the capillaries and carbon dioxide moves from the blood capillaries to the air in the alveolus.
     

alveoli


alveolus

Conduction and Exchange Zone

  • The respiratory system can be divided into two parts/ zones:
    1. Conducting part/ conduction zone
    2. Respiratory or exchange zone
  • The conduction zone extends from the nose to the terminal bronchioles
    - It transports air to the alveoli
    - Removes foreign particles from the air
    - Humidifies air and brings it to body temperature
  • The respiratory or exchange zone includes alveoli and their ducts
    - It is the site of gaseous exchange (diffusion of CO₂ and O₂) with blood
     

conduucting-part
It is the site of gaseous exchange (diffusion of CO and O₂) with blood

Lungs

  • A pair of lungs lie in an air-tight chamber called thoracic cavity or chest cavity.
  • Thoracic cavity is formed:
    - Dorsally by the vertebral column
    - Ventrally by the sternum
    - Laterally by the ribs
    - Anteriorly by clavicle
    - Posteriorly by the dome-shaped diaphragm
  • The anatomical setup of lungs in the thorax is such that any change in the volume of the thoracic cavity will be reflected in the cavity of lung
  • Each lung is covered by a two-layered membrane called pleura or pleural membrane.
    (a) Parietal pleura - Outer pleural membrane, that is in close contact with the thoracic cavity
    (b) Visceral pleura - Inner pleural membrane, that is in contact with the lung surface.
  • A narrow space is present between the outer and inner pleural membranes called pleural cavity.
  • Pleural cavity is filled with a fluid called pleural fluid, which keeps the pleura moist and lubricates the membranes to reduce the friction between them during breathing.
     
  • Structure of Lungs:

          (a) Left lung -

  • Left lung is two-lobed,
  • Smaller than the right lung as it contains a cardiac notch for accommodating the heart.

          (b) Right lung -

  • Right lung is three-lobed
  • It is broader but shorter in length than the left lung, due to the raised position of the diaphragm on the right side, to accommodate the liver.
  • Internally, lungs comprise a branching network of bronchi, bronchioles and alveoli.  

lungs


Frequently Asked Questions - FAQs

Q1. What is glottis?
Ans. Glottis is a ventral, slit-like opening that leads pharynx to the larynx.

Q2. What prevents entry of food into the respiratory tract while swallowing?
Ans. Epiglottis, a thin leaf-like cartilaginous flap, is located just above the larynx.
This flap covers the glottis while swallowing food, preventing food from entering the larynx.

Q3. What keeps the trachea from collapsing?
Ans. Trachea is surrounded by C-shaped/ incomplete cartilaginous rings which prevent the trachea from collapsing.

Q4. Which is the common passage for both air and food?
Ans. The pharynx is the common passage for both air and food

Q5. Why is the left lung smaller than the right?
Ans. Left lung is slightly smaller than the right because it has a cardiac notch to accommodate the heart.

Q6. Which part of the respiratory tract helps in the production of sound?
Ans.True vocal cords are present within the larynx which help in the production of sound.

Q7. At which level of thoracic vertebra, trachea divides?
Ans. Trachea divides into left and right primary bronchi at the level of 5th thoracic vertebra.

Q8. What is the function of pleural fluid?
Ans. Pleural cavity is filled with a fluid called pleural fluid, which keeps the pleura (lungs membranes) moist and lubricates the membranes to reduce the friction between them during breathing.

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