The document summarizes the structure and function of the human respiratory system. It describes that the respiratory system consists of respiratory tract and lungs. The respiratory tract includes the nose, nasal passages, pharynx, larynx, trachea, and bronchial tree. The lungs are located in the thoracic cavity and contain bronchioles and alveoli where gas exchange takes place. The diaphragm and intercostal muscles help in the mechanism of breathing by contracting and relaxing during inhalation and exhalation.

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2. Respiratory System
 Respiratory system is a complex organ system
consisting of various organs essential for carrying
out respiration.
 The process of exchange of gases between the body
and atmosphere is known as respiration.
 Respiration is for energy liberation.

3. Steps of respiration
1. Pulmonary ventilation
2. Diffusion of gases across the alveolar membranes
3. Transport of gases by blood
4. Diffusion of oxygen and carbon dioxide between
blood and tissues
5. Utilization of oxygen by the cells for catabolic
reactions and resultant release of Carbon dioxide.

4. Types of respiration
 Internal
 External
 Cellular

5. Respiratory organs
Respirato
ry organs
General
body
surface
Moist
cuticle
Tracheal
tubes
Gills Lungs
Examples Sponges,
coelentrates
, flatworms
Earthworm
s, Frogs
Insects Aquatic
arthropods,
molluscs,
fishes
Reptiles,
birds,
mammals

6. Human respiratory system
 Human respiratory system is divided into two main
parts
1. Respiratory tract
2. Lungs

7. Respiratory tract
 Nose and nasal passage
 Bucco-paharyngeal cavity
 Larynx
 Trachea
 Bronchial tree

8. Respiratory tract

9.  When trachea enters into the thoracic cavity it
divides into two branches called as the primary
bronchus at the level of fifth thoracic vertebra.
 Branches of primary bronchus upto terminal
bronchioles make bronchial tree.
 In bronchial tree cartilage rings are present, while
these are absent in respiratory tree.

10.  Gaseous exchange occurs in respiratory tree while it
is absent in bronchial tree.
 Exchange zone is the actual site of diffusion of
oxygen and carbon dioxide between blood and
atmoshphere.
 The conducting transports the atmosphere air of the
alveoli clears, clears it from foreign particles,
humidifies and also brings the air to the body
tempreature.

11. Nose and nasal passage
 Paired external nostrils
 Open in vestibular
region
 Vestibules are
posteriorly connected
with nasal chambers

12.  Nasal passage is functionally divided into three
regions
1. Vestibular region- skin, hair, sebaceous glands
2. Respiratory region- lined by PSCCGE
3. Olfactory region-lined by scheidarian membrane

13. Bucco-phayngeal cavity
 Divided in two parts:
1. Buccal cavity
2. Pharyngeal cavity

14. Larynx
 Larynx is a cartilagenous box which helps in sound
production.
 Larynx is made up of following cartilages
1. Thyroid cartilage
2. Cricoid cartilage
3. Arytenoid cartilage
4. Cartilage of santorini

16.  In larynx two pair of vocal cords are present for
production:
 False vocal cords
 True vocal cords

17. Trachea
 10-12 cm long straight tube extending upto mid
thoracic cavity.
 In trachea 16-20’C’ shaped cartilagenous rings are
present.
 The rings are incomplete at dorsal surface of
trachea.

19. Bronchial tree
 Branches of primary bronchus upto terminal
bronchioles makes bronchial tree.
 Terminal bronchioles divide to form respiratory
bronchioles & branches of respiratory brochioles
makes respiratory tree.

20.  In the bronchial tree catrilagenous rings are present,
while these are absent in respiratory tree.
 Gaseous exchange occurs in respiratory tree while
absent in bronchial tree.
 Volume of air which is filled in bronchial tree is
dead space volume, which doesnot take part in
gaseous exchage.

22. Lungs
 Paired and located inside thoracic cavity
 Covered by double pleural membranes.
1. Outer one is the parietal pleura
2. Inner one is the visceral pleaura
 In between both the membranes pleuaral cavity is
present.

24. Alveoli
 Alveoli are the structural
and functional units of lungs.
 Approx.300million alvcelolar
cells are present in the lungs.
 Squamous cells of alveoli
are called as Pneumocytes

25. Diaphragm
 A muscular septum which is found only in mammals
and crocodiles.
 Normal shape of Diaphragm is dome like which
divides body into two parts
1. Upper thoracic cavity
 Lower abdominal cavity

26.  radial muscles are present in Diaphragm.
 Diaphragm contracts and
relaxes during inhalation and
exhalation.

27. Mechanism of breathing
Inspiration:
 Inspiration is an active process.
 At the time of inspiration contraction in diaphragm
and external intercostal muscles muscles takes place.
 Diaphragm becomes flat and is pushed towards
abdominal cavity.
 Sternum moves towards ventral and anterior
direction.

28. Expiration:
 Normal expiration is an passive process.
 During expiration relaxation in diaphragm and
external intercostal muscles takes place.
 We have the ability to increase the strength of
inspiration and expiration with the help of additional
muscles, this is called forceful breathing.

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