Human Respiratory System – Diagram, Function and Disease

Human Respiratory System - Diagram, Function and Disease

Respiratory system are following organs :-

  1. Nasal cavity
  2. Naso pharynx
  3. Oropharynx
  4. Larynx
  5. Trachea
  6. Right and left principal bronchi
  7. Bronchioles
  8. Lungs
Respiratory System - Diagram, Parts, Function and Disease

Larynx or voice box (स्वरयन्त्र)

(1) Introduction-

  • The larynx is the organ for production of voice. It is also an air passage and acts as a sphincter at the inlet of the lower respiratory passage.
  • The upper respiratory passage include the nose, the nasopharynx and the oropharynx.

(2) Situation-

  • The larynx lies in the anterior midline of the neck.
  • The larynx is a short passageway that connects the laryngo- pharynx (Root of the tongue) to the trachea.
  • It lies infront of the C3-C, vertebrae.

(3) Measurement-

Length – 44 m.m. in male.
36 m.m. in female.

  • At puberty male larynx grows rapidly and become larger than the female larynx.
  • The pubertal growth of the female larynx is negligible.

(4) Constitution of larynx-

The larynx is made up of a skeletal framework of cartilages. The cartilages are connected by joints, ligaments and me branes. And are moved by a number of muscles. The cavity of the larynx is lined by muscous membrane.

(5) Cartilage of larynx or skeleton of larynx-

  • The wall of the larynx is composed of 9 pieces of cartilages
  • Three are unpaired and three are paired.
  • Unpaired cartilage-
    1. Thyroid cartilage 2. Cricoid cartilage 3. Epiglottic cartilage
  • Paired cartilage-
  1. Arytenoid cartilage
  2. Corniculate cartilage
  3. Cuneiform cartilage

Unpaired Cartilage

1. Thyroid cartilage or adam’s apple-

  • The thyroid cartilage consists of two fused plates of hyaline
  • cartilage that formn the anterior wall of the larynx and give it.
  • Triangular in shape.
  • It is usually larger in males than females.
  • Due to the influence of male sex hormones during puberty.
  • The ligament that connects the thyroid cartilage to the hyoid bone is called the thyrohyoid membrane.
  • ‘V’ shaped in cross section.

2. Cricoid cartilage- Ring shape.
3. Epiglottic cartilage- Leaf shape.

Paired cartilage-

  1. Arytenoid cartilage- Two small pyramid shaped. The arytenoid cartilage are most important since they influence the positions and tensions of the vocal cord.
  2. Corniculate cartilage- Two small conical nodules.
  3. Cuneiform cartilage- Two small rod shaped.

(6) Laryngeal joints-

  1. Cricothyroid joint
  2. Cricoarytenoid joint

Intrinsic muscles of larynx-

S.No.MusclesNerve supply
1.Posterior cricoarytenoidRecurrent laryngeal nerve
2.Lateral cricoarytenoidRecurrent laryngeal nerve.
3.Transverse arytenoidRecurrent laryngeal nerve.
4.Oblique arytenoidRecurrent laryngeal nerve.
5.ThyroarytenoidRecurrent laryngeal nerve.
6.ThyroepiglotticusRecurrent laryngeal nerve.
7.AryepiglotticusRecurrent laryngeal nerve.
8.VocalisRecurrent laryngeal nerve.
9.Cricothyroid – Lying on external aspect of larynxExternal laryngeal nerve.

(8) Arterial supply-

  • Superior and inferior laryngeal artery.

(9) Venous drainage-

  • Superior and inferior laryngeal vein.

(10) Lymphatic drainage-

  • Deep cervical nodes.
  • Prelaryngeal nodes.

(11) Nerve supply-

  • Recurrent laryngeal nerve.

Applied aspect-

1. Laryngitis- Infection or inflammation of the larynx is called laryngitis.
It is characterized by hoarseness of voice.

2. Laryngeal oedema- Obstruction to breathing.

3. The larynx (glottis) is the narrowest part of the respiratory passage, foreign bodies are usually lodged here.

4. Laryngoscopy- Examination of larynx.


1. Introduction –

  • The trachea is a mobile cartilaginous and membranous tube. Formed by ‘C shaped rings.
  • The rings are about 16-20 in number and make the tube convex anterolaterally.
  • The trachea is a wide tube lying in the midline.
  • The upper end of the trachea lies at the lower border of the cricoid cartilage (opposite 6h cervical vertebrae) of the larynx. And extends downwards in the midline of the neck.
  • In the thorax, it ends by dividing into two main bronchi at the level of lower border of 4 thoracic vertebrae.
* Vertebral level- C-T,- In cadaver
*Vertebral level- C-T- In living erect posture.

(2) Measurement-

  • Length- 4-6 inches (10-15 cm.)
  • External diameter- 2 cm. in males, 1.5 cm. in females.
  • Lumen is smaller in the living than in the cadaver.
    3 mm.- At I year.
    12 mm.- In adult.

(3) Relations-

Cervical partThoracic part
1. Anteriorly-1. Anteriorly-
Skin, fascia, isthmus of the thyroid gland.
Sternohyoid and sternothyroid muscles.
Left brachiocephalic vein and inferior thyroid vein.
Manubrium sterni, sternothyroid muscle, left brachiocephalic vein and inferior thyroid vein, left common carotid artery-
2. Posteriorly- Esophagus, vertebral column.2. Posteriorly– Esophagus, vertebral column.
3. Laterally (Side to side)- Lobe of thyroid gland.3. Right side- Right lung and pleura, azygos vein, right vagus nerve.
Left side- Arch of aorta, left common carotid artery, left subclavian artery.

(4) Arterial supply-

  • Inferior thyroid artery.

(5) Venous drainage-

  • Inferior thyroid vein.
  • Left brachiocephalic vein.

(6) Lymphatic drainage-

  • Pretracheal nodes.

(7) Nerve supply-

  • Sympathetic- Fibres from the middle cervical ganglion.
  • Parasympathetic- Vagus- through recurrent laryngeal nerve.

(8) Applied aspect-

  1. Clinically the trachea is palpated in the suprasternal notch.
  2. Tracheal tug.
  3. The trachea may get compressed by pathological enlargements of the thyroid, thymus, lymph nodes and the aortic arch. This causes dyspnoea, irritable cough and often a husky voice.
  4. Tracheostomy- Surgical creation of an opening into the trachea.
  5. Tracheotomy- An incision of the trachea.


(1) Situation-

  • The lungs are a pair of respiratory organs situated in the thoracic cavity.
  • Each lung invaginates the corresponding pleural cavity.
  • The right and left lungs are separated by the mediastinum.
  • The lungs are spongy in texture.

(2) Colour-

  • In the child- Pink colour.
  • In the young- Brown or grey in colour.
  • Gradually they become mottled black because of the deposition of inhaled carbon particles.

(3) Weight-

  • Right lung- 625 gm.
  • Left lung- 575 gm.

(4) External feature- Each lung is conical in shape. It has-

  1. Apex
  2. Base
  3. Borders – (Anterior border, Posterior border, Inferior border)
  4. Surfaces – {Costal surface, Medial surface (Vertebral part, Mediastinal part)}

1. Apex (Cupola)- The apex is blunt and lies above the level of the anterior end of the first rib. It reaches nearly an one inch above the medial 1/3 of the clavicle. Just medial to the supraclavicular fossa.

2. Base-

  • The base is semilunar and concave.
  • It rests on the diaphragm which separates the right lung from the right lobe of the liver and the left lung from the left lobe of the liver, the fundus of the stomach and the spleen

3. Borders-

(i) Anterior border- is very thin.

  • Anterior border of the left lung shows a wide cardiac notch below the level of 4th costal cartilage.
  • The heart and pericardium are uncovered by the lung in the region of this notch.

(ii) Posterior border- is thick and ill defined.

  • It extends from the C,-T,, spine.

(iii) Inferior border- It separate the base from the costal and medial surfaces.

4. Surfaces-

(i) Costal surface- is large and convex.
(ii) Medial surface- is divided into two parts.

  • Vertebral part or posterior part.
  • Mediastinal part or anterior part.

(5) Fissures and lobes of the lungs-

  • The right lung is divided into three lobes by two fissures.
  • Lobes-
    1, Superior lobe 2. Middle lobe 3. Inferior lobe
  • Fissures- 1, Oblique fissure 2. Horizontal fissure

The left lung is divided into two lobes by one fissure.

  • Lobes – 1. Superior lobe 2. Inferior lobe
  • Fissure – Oblique fissure.

Lingula- The tongue shaped projection of the left Iung below the cardiac notch is called the lingula. It corresponds to the middle lobe of the right lung.

(6) Root of the lungs

  • It is short, broad pedicle which connects medial surface of the lung to mediastinum.
  • The roots of the lungs lie opposite the bodies of 5-6-7 thoracic vertebrae.


  1. Principal bronchus on the left side and eparterial and hyparterial bronchi on right side.
  2. One pulmonary artery.
  3. Two pulmonary vein- Superior and inferior.
  4. Bronchial arteries- One on right side and two on left side.
  5. Bronchial veins.
  6. Anterior and posterior pulmonary plexuses of nerves.
  7. Bronchiopulmonary lymph nodes and lymphatics of lungs.
  8. Areolar tissue.

(7) Surface marking of the lungs-

1. Apex-

  • One inch above the medial 1/3 of the clavicle.
  • Above the level of anterior end of first rib.

2. Anterior border of right lung-

Corresponds very closely to the anterior margin of the pleura and is obtained by joining-

  • A point at the- Sternoclavicular joint.
  • Another point in the- Median plane at the sternal angle.
  • A third point in the- Median plane just above the xiphisternal joint.

Anterior border of left lung- Corresponds to the anterior margin of the pleura up to the level of 4th costal cartilage.

Cardiac notch- Below the level of 4th costal cartilage, from the level of 4th costal cartilage. It passage laterally for 3.5 cm. from the sternal margin and then curves downwards and medially to reach the 6th costal cartilage 4 cm. from median plane.

3. Posterior border- It extend from the level of C,-T,, spine.

4. Inferior border- Lower border of each lung lie two ribs higher than the pleural reflection.

LungsSurface marking of pleura
Midclavicular line up to 6h rib)8h rib
Midaxillary line- up to 8h rib 10th rib
Lateral border of the erector spinae. – up to 10th rib
8th rib
10th rib
12th rib

5. Oblique fissure-

  • A point 2 cm. lateral to the – 3rd thoracic spine.
  • Another point on the – 5th rib in the midaxillary line.
  • A third point on the – 6th costal cartilage, 7.5 cm from median line

6. Horizontal fissure-

  • A point on the anterior border of right lung at the level of 4th costal cartilage.
  • A second point on the 5th rib in the midaxillary line.

(8) Structures related to the mediastinal surface of right and left lung

Right LungLeft Lung
1. Rt. atrium and auricle
2. A small part of right ventricle
3. Lower part of right brachiocephalic vein
4. Oesophagus
5. Right vagus nerve
6. Right phrenic nerve
7. Superior venacava
8. Azygous vein
9. Inferior venacava
10. Trachea
1. Left auricle
2. Left ventricle
3. Left brachio cephalic vein
4. Oesophagus
5. Left vagus nerve
6. Left phrenic nerve
7. Pulmonary trunk
8. Arch of aorta
9. Descending thoracic aorta
10. Thoracic duct

(9) Difference B/w the lungs

Right lungLeft lungs
1. It has two fissures and three lobes.
2. Anterior border is straight
3. Larger and heavier, weight about 625 gm.
4. Shoter and wider.
5. Right lung lies slightly above than left due to liver
1. It has only one fissure and two lobes. Third lobe- Lingula- Accomadation of heart.
2. Anterior border is interrupted by the cardiac notch.
3. Smaller and lighter, weight about 575 gm.
4. Longer and narrower.
5. Left lung lies slighlty be low than right due to small spleen.

(10) Bronchial Tree –

  • The trachea divides at the level of lower border of the 4s thoracic vertebrae into two primary bronchi.
  • One for each lungs. The right principal bronchus is shorter (1 inch) wider and vertical than the left principal bronchus.
  • Inhaled particles, therefore, tend to pass more frequently to the right lung. With the result than infection are more common on the right side than on the left.
  • The left principal bronchus is longer (2 inches), narrower and more oblique than the right bronchus.
  • Each principal bronchus enters the lung through the hilum and divides into secondary (lobar) bronchi one for each lobe of the lungs. (3 on the right and 2 on the left side)
  • Each lobar bronchus divides into tertiary (segmental) bronchi.

One for each bronchopulmonary segment (10 on the right side and8 on the left side). The segmental bronchi divide repeatedly to form very small branches called terminal bronchioles. Still smaller branches are called respiratory bronchioles.

  • Each respiratory bronchiole aereates a small part of the lung known as a pulmonary unit.
  • The respiratory bronchiole ends in microscopic passages which are termed-
  • Alveolar ducts
  • Atria
  • Air saccules
  • Pulmonary alveoli

Gaseous exchanges take place in the alveoli


Rt. and left principal bronchi (primary)

Secondary bronchi (Lobar)

Tertiary bronchi (Segmental)
↓ → Divides repeatedly
Terminal bronchioles
↓ → Still smaller
Respiratory bronchioles
↓ → ends in microscopic passage

  • Alveolar ducts
  • Atria
  • Air saccules
  • Pulmonary alveoli

[Gaseous exchanges take place in the alveoli]

Pulmonary unit – Each respiratory bronchioles aereates a small part of lung known as pulmonary unit

(11) Bronchio Pulmonary Segments-

Definition- There are well defined sectors of the lung.

Right Lung – Lobes & SegmentsLeft Lung – Lobes & Segments
1. Upper lobe – 3 segment
2. Middle lobe- 2 segment
3. Lower lobe- 5 segment
Superior or apical
Anterior Basal
Posterior Basal
Lateral Basal
Medial Basal
1. Upper lobe- Upper division
Lower division
Supesrior lingular
Inferior lingular
2. Lower lobe-
Anterior Basal
Medial Basal
Posterior Basal
Lateral Basal
3+2+5 = 10 Segments2+2+4 = 8 segments or
3+2+5 = 10 segment

Arterial Supply-

  • Bronchial arteries – Right side one bronchial artery.
    Left side two bronchial artery.
  • Pulmonary artery – DO2 blood

Venous Drainage

  • Bronchial veins- Right bronchial vein drains into-Azygos vein.
    Left bronchial vein drains into-Hemiazygos vein.

Nerve Supply

  • Sympathetic nerve- T1 – T5
  • Parasympathetic nerve- Vagus.

Applied Aspect

  1. C.O.P.D. – Chronic obstructive pulmonary disease. Disease such as asthma, bronchitis, emphysema have in common degree of obstruction of the air ways.
    Air flow obstruction- Coughing, wheezing, dyspnea.
  2. Pneumonia – Acute infection or inflammation of the alveoli.
  3. Bronchogenic carcinoma – A common lung cancer. Start in the wall of the bronchí.
  4. Tuberculosis (T.B.)- Mainly occur in apices of lungs.
  5. Haemoptysis – The spitting of blood from the respiratory tract.
  6. Pulmonary embolism / Pulmnonary oedema – is a blood clot or other foreign body substance in a pulmonary blood vessels that obstructs circulation to lung tissue. (Heart diseases)
  7. Haematemesis- Vomiting of blood.
  8. Epistaxix– Bleeding from the nose.
  9. Pneumothorax- Presence of air in pleural cavity.
  10. Haemothorax – Presence of blood in pleural cavity.
  11. Empyema – Presence of pus in pleural cavity.
  12. Hydropneumothorax- Presence of ” both-fluid and air “ in pleural cavity.
  13. Pleurisy – Inflammation of pleura. It may be dry.
  14. Pleural effusion – Collection of fluid in the pleural cavity.
  15. Parencentesis – Aspiration of fluid.
  16. Bronchioscopy – Examination of bronchi
  17. Bronchiography or bronchiogram or chest X-ray- Picture of bronchial tree.
  18. Pneumonectomy – Surgical removal of a lung.
  19. Segmnental resection – Surgical removal of a segment.

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