RESPIRATORY SYSTEM

Respiration is the process of exchange of gas between the atmosphere and the body cells.

Organs involved in respiratory system are:

Upper Respiratory Tract:

1. Nose and nasal cavity
2. Pharynx
3. Larynx

Lower Respiratory Tract:

4. Trachea
5. Bronchi
6. Lungs
7. Alveoli

1. Nose and nasal cavity:

• It is the organ for olfaction
• Nose is a part of respiratory tract lying above mouth. It is made by hyaline
cartilage.
• It is divided into right and left nasal cavity by nasal septum. Its anterior part is
cartilaginous and posterior portion is bony.
• The nasal cavity opens outside through nostrils or external nares.
• The nasal cavity opens posteriorly into the nasopharynx through internal nares.

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 • The opening of paranasal sinuses and nasolacrimal ducts lie in the nasal cavities,
internally, nasal cavity is lined with mucous membrane and ciliated columnar
epithelium. It contains nasal hairs.

Function
▪ It prevents the entry of dust particles into the lungs.
▪ Mucus secretory glands i.e. goblet cells are found in nasal chamber that produce
mucus. Smoke or dust particles attached with mucus.
▪ The ciliated epithelium prevents infection by sweeping out microorganism.
▪ It warms the cold air and moistens the dry air.
▪ It detects smell.
▪ Internal nares: these are openings of nasal chambers in the root of nasopharynx and
are closed uvula during the swallowing.

2. Pharynx
• It is both digestive and respiratory organ.
• It is a tube of 12-14cm that extends the base of skull to the level of 5th cervical
vertebra.
• It lies behind the mouth, nose and larynx.
• It is connected to nasal cavity through the internal opening of nares and to the
mouth.

It is divided into below 3 parts

1. Nasopharynx
It is the nasal part of pharynx. Lies behind the nose and superior to the
soft palate. Lined with ciliated epithelium that helps in cleaning inspired air. On the
lateral wall, there are two openings of auditory tubes and on posterior wall, there is a
pharyngeal tonsil, consisting of lymphoid tissues.
2. Oropharynx
Oral part of pharynx. Lies at the posterior part of mouth, extends from soft palate to
epiglottis. It is separated from mouth by a pair of membranous narrow passage
called fauces.

3. Laryngopharynx
It is the lower most portion of pharynx and has a slit like aperture called glottis. This
can be closed by leaf like bilobed cartilage, epiglottis, during swallowing of the food.

Function of pharynx
▪ Pharynx helps in passage of air from nose to trachea.

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 ▪ The air is further warmed and moistened as it passes through pharynx.
▪ There are olfactory nerve endings of the sense of smell.
▪ Protection: the lymphatic tissue of the pharyngeal and laryngeal tonsils produces
antibodies in response to antigen.
▪ Hearing: The auditory tube, extending from the nasopharynx to each middle ear,
allows air to enter the middle ear.

Larynx
• Also called sound box or voice box.
• It is situated in the anterior neck.
• It is a small, thin walled, tubular part present in the neck at the apex of trachea.
• It connects the lower part of pharynx and trachea.
• Pharynx opens in larynx through glottis which is guarded by a leaf like unpaired
cartilage which is called epiglottis. It prevents the entrance of food into trachea.

The size of larynx is similar in boys and girls before puberty. After puberty, the larynx in male
becomes larger and is called Adam’s apple in male.

Function
▪ It plays important role in sound production.
▪ It links pharynx with trachea; thus, it allows passage of air.
▪ Humidifying, filtering and warming of air occurs in larynx.
▪ Speech is produced when sound produced by vocal cords are manipulated by tongue,
cheeks and lips.
▪ During swallowing the larynx moves upward, blocking the opening into it from the
pharynx. In addition, the epiglottis also closes over the larynx. This ensures the food
passes into oesophagus and not into trachea.

Trachea (wind pipe)

• It is a hollow tube of about 11-12cm in length and 2.5 in diameter.
• It extends from the base of larynx to thoracic cavity. It runs in the neck in front of
esophagus.
• It is supported by 16-20 C-shaped cartilaginous tracheal ring. These rings prevent the
trachea from collapsing due to continuous relaxation and expansion.
Internally, the wall of trachea is lined by pseudo stratified ciliated epithelium with mucus
secreting goblet cells. The secretion of mucus cells keeps the wall of tube moist and trap
dust particles.

Function
▪ The mucus lubricates the passage and cilia help to filter out dust.

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 ▪ The constant beating of cilia carries mucous and debris upward into pharynx where
upon it is swallowed or coughed up.
▪ Helps in cough reflex.
▪ It supports head and neck.

Bronchi
• As the trachea reaches into the thoracic cavity, it divides into two branches called
bronchi; right and left bronchus.
• Each bronchus has the structure similar to trachea.
• The right bronchus is wider and shorter than left bronchus.
• Each bronchus when enter into corresponding lungs, it divides into smaller secondary
bronchi and then into tertiary bronchi.
• These bronchi progressively subdivided into smaller and smaller tube called bronchioles
and then into tertiary bronchioles.
• Bronchioles continue to branch, and open into respiratory bronchioles which in turn
branch into alveolar duct that lead to alveoli (microscopic air sac).
Function
▪ Bronchi connect the trachea to the lungs, allowing air from external respiratory
openings into the lungs.

Alveoli
▪ Bronchioles continue to branch, and open into respiratory bronchioles which in turn
branch into alveolar duct that lead into microscopic air sac called alveoli.
▪ Gaseous exchange takes place in alveoli. The alveoli are richly supplied with blood
capillaries.
Function
▪ Alveoli help in purification of blood.
▪ Allows exchange of oxygen and carbon dioxide in the lungs.

Lungs
• Lungs are a pair of conical organs situated one on either sides of thoracic cavity.
• They are hollow, soft, spongy, elastic, light and pink coloured.
• There are one pair of lungs- right lung and left lung.
• Lungs are externally surrounded by two layers called pleural membrane.
• The outer membrane is called parietal pleural membrane and the inner layer is
called visceral pleural membrane. These membranes protect lungs and stop leaking
of air into thoracic cavity.
• The space between two layers is called pleural cavity.

Function
▪ Allow free/smooth frictionless movement of lungs.

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 ▪ Protects the lungs from mechanical shocks.
▪ Keeps the pleura together and lungs expanded

Lobes of lungs
• Lungs are divided into distinct lobes.
• Right lung has three lobes i.e.; superior, middle, inferior lobe.
• Left lung has two lobes i.e.; superior and inferior lobes. The left lung is smaller than
right lung and has a cardiac notch to accommodate heart.
• Internally, lung is composed of numerous alveoli.
• Alveoli are extremely thin walled and vascular structure.
• The alveoli are richly supplied with blood capillaries. Alveoli are the primary
structures which facilitate the exchange of gases.
• Alveoli helps in purification of blood.

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 Diseases related to respiratory system
Asthma: It is an inflammatory disease of the airway to the lungs.
It occurs when the lining of your airways swells and the muscles around them tighten.
Mucus then fills the airways, further reducing the amount of air that can pass through.
Symptoms include episodes of wheezing, coughing, chest tightness, and SOB.

Chronic obstructive pulmonary disease: COPD, is an umbrella term that encompasses

several respiratory illnesses that cause breathlessness, or the inability to exhale normally.
Emphysema and chronic bronchitis are the most common conditions that contribute to
COPD.
Symptoms include breathing difficulty, cough, mucus (sputum) production and wheezing.

Emphysema: It affects the air sacs at the end of the airways in your lungs. They break down
and the lungs become baggy and full of holes which trap air.

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Emphysema evolves slowly over the years, and there is no cure.
Bronchitis: It means the airways are inflamed and narrowed. People with bronchitis often
produce sputum, or phlegm
Pneumonia: It is an inflammatory condition of the lung affecting primarily the small air sacs
known as alveoli. It can be a serious life-threatening disease. It normally starts with a
bacterial, viral or fungal infection. The lungs become inflamed, and the tiny air sacs or
alveoli, inside the lungs fill up with fluid.
The most common symptoms of pneumonia can include coughing that may produce phlegm
(mucus), fever, sweating, chills, SOB & chest pain.

Bronchiectasis: It is a condition where the bronchial tubes of the lungs are permanently
damaged, widened, and thickened. These damaged air passages allow bacteria and mucus
to build up and pool in your lungs. This resulted in frequent infections and blockages of the
airways.
There is no cure for bronchiectasis, but it is manageable.

Pleural effusion: A pleural effusion is excess fluid that accumulates in the pleural cavity, the
fluid-filled space that surrounds the lungs

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Atelectasis: It is a complete or partial collapse of the entire lung or area (lobe) of the lung. It
occurs when the tiny air sacs (alveoli) within the lung become deflated or possibly filled with
alveolar fluid. Atelectasis is one of the most common breathing (respiratory) complications
after surgery.
Respiratory failure: it results from inadequate gas exchange by the respiratory system,
meaning that the arterial oxygen, carbon dioxide or both cannot be kept at normal levels. A
drop in the oxygen carried in blood is known as hypoxemia; a rise in arterial carbon dioxide
level is called hypercapnia.
Acute Respiratory distress syndrome (ARDS): It is type of respiratory failure characterised
by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of
breath, rapid breathing, and bluish discoloration.

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