The document summarizes the anatomy and physiology of the respiratory system. It describes the major components of the respiratory tract including the nose, pharynx, larynx, trachea, bronchi, bronchioles and lungs. It explains the functions of these structures in conducting air, warming, humidifying, and filtering air as well as the gas exchange that occurs in the alveoli. It also discusses the muscles involved in breathing and the process of inhalation and exhalation.

1. RESPIRATORY SYSTEM
Prepared by:
Ms. Dhruvi A. Prajapati
Assistant Professor
Babaria Institute of Pharmacy
BITS Edu campus - Vadodara

2. Respiratory system 2
GTU Syllabus

3. What is breathing

4. Respiration
The cells of human body require a constant stream of oxygen to
stay alive !!
• Respiratory system is the system through which every cell in
the body receives oxygen and excretes carbon dioxide.
• Respiratory tract forms the path through which air passes
from the nose to the lungs.

5. Respiration
• Bresthing in (inspiration) and breathing out (expiration) of air
through lungs is External respiration.
• The air exchanged in for oxygen and out for CO2 in the alveoli and
through capillaries is carried to each and every cell of the body.
This exchange of gases at the cellular level is Internal Respiration.

6. Respiratory system 6

7. Functions of the Respiratory System
1. Interchange of Gases
2. Maintenance of pH: carried out by balancing excretion of CO2
3. Maintenance of circulation: affects the heart rate & cardiac
output. BP also changes during respiration.
4. Excretion
5. Metabolic function: helps in maintaining homeostasis of
metabolism in tissue.
6. Temperature regulation
7. Water regulation: Water vapour is partly excreted
Respiratory system 7

8. Respiratory system can be divided
based on its function
Conducting zone
(Nose to Bronchioles):
It transports atmospheric air to
the alveoli, discrards foreign
particles from inhaled air, also
humidifying and maintaining its
temperature
Respiratory zone
(Alveolar duct to alveoli):
It forms the site where O2 and
CO2 gases are exchanged between
the blood capillaries and alveoli.

9. Respiratory system can be divided based on
its anatomical structure
Upper Respiratory Tract
This zone consists of the
organs outside the chest cavity
(thorax) i.e. nose, pharynx and
larynx.
Lower Respiratory Tract
This zone consists of the
organs within the chest cavity
i.e trachea, bronchi,
bronchiole, alveolar duct and
alveoli.

10. Respiratory system 10

11. Respiratory system 11

12. The Anatomy and Physiology of the
Respiratory System

13. Divisions of the Respiratory System
 Upper respiratory tract (outside thorax)
 Nose
 Nasal Cavity
 Pharynx
 Larynx
Respiratory system 13

14. Nose (nasal cavity)
First organ of the respiratory tract which receives the inhaled air
and forms a passage for the air to reach the nasal cavity or nasal
chamber.
• Performs the process of warming, moistening and filtering of the
inhaled air.
• Nasal cavity is a large irregularly shaped cavity, divided into two
equal halves by a septum.

15.  The posterior bony part of septum
is formed by ethmoid and vomer
bones. Anteriorly, it consists of
hyaline cartilage.
 Nose is a bony and catilagenous
structure.
 Bony part – Frontal, nasal and
maxillae bones.
 Cartilaginous part
 Anterior portion  septal
cartilage
 Inferior portion  lateral
cartilage
 Nostril portion  Alar cartilageRespiratory system
15

16. Nasal cavity
• Anterior nares - opening to exterior
• Posterior nares - opening to pharynx
• Nasal conchae - folds in the mucous membrane that
increase air turbulence and ensures that most air contacts the
mucous membranes

17. Respiratory system 17

18. Paranasal Air Sinuses
“Paranasal Sinuses are cavities in the bones of the face and the
cranium, containing air.”
•Main Sinuses:
Ethmoidal sinuses
Frontal sinuses
Spenoidal sinuses
Maxillary sinuses
•Function: in speech and also lighten the skull

19. Respiratory system 19

20. Function of Nose
• Provides an airway for respiration
• Moisten and warms air / Humidification: As air travels over the
moist mucosa, it becomes saturated with water vapour.
• Filters and cleans inspired air: This occurs due to hairs which trap
larger particles.
• Resonating chamber for speech
• Houses of olfactory receptors

21. Pharynx
The pharynx is the part of the throat that is behind the
mouth and nasal cavity and above the esophagus and
the larynx.
• Length:12-14 cm
• Common space used by both the respiratory and
digestive systems.

22. Walls of Pharynx
• Walls are lined by a mucosa and contain skeletal
muscles that are primarily used for swallowing.
• Flexible lateral walls are distensible in order to force
swallowed food into the esophagus.

23. Parts of Pharynx
• Pharynx - (throat)
• Base of skull to esophagus
• 3 divisions
– Nasopharynx - behind nose to soft
palate.
– Oropharynx - behind mouth, soft
palate to hyoid bone.
– Laryngopharynx - hyoid bone to
esophagus.
Respiratory system
23

24. Respiratory system 24

25. Function of Pharynx
• Passageway for air and food.
• Warming and humidifying.
• Taste : There are olfactory nerve endings.
• Hearing : The auditory tube, extending from the nasopharynx to each
middle ear.
• Protection: The lymphatic tissue of the pharyngeal tonsils produces
antibodies.
• Speech : Act as a resonating chamber for sound ascending from the
larynx.

26. Larynx
 The larynx or voice box extends from the root of the tongue.
 It lies in front of the laryngopharynx at the level of 3rd, 4th, 5th and 6th
cervical vertebra.
 Until the puberty there is little difference in the size of the larynx
between the sexes.
 It grows larger in the male.
Position:
 Superiorly - The hyoid bone & roof of the tongue.
 Inferiorly - Continuous with the trachea.
 Anteriorly - The muscle of the neck.
 Posteriorly - The laryngopharynx and 3rd to 6th cervical vertebra.

27. Larynx
The larynx is composed of several irregularly shaped cartilages
attached to each other by ligaments and membranes.
 The main cartilages are:
 1 thyroid cartilage
 1 cricoid cartilage hyaline cartilage
 2 arytenoid cartilage
 1 epiglottis elastic fibrocartilage

28. Cartilages of Larynx
• THE THYROID CARTILAGE: This is the most prominent & consists of 2 flat
pieces of hyaline cartilage & fused anteriorly forming the Adam’s apple.
• THE CRICOID CARTILAGE: This lies below the thyroid cartilage &
composed of hyaline cartilage.
• THE ARYTENOID CARTILAGES: These are two roughly pyramid-shaped
hyaline cartilages situated on top of the broad part of the cricoid cartilage.
• THE EPIGLOTTIS: This is a leaf-shaped fibroelastic cartilage attached to the
inner surface of the anterior wall of the thyroid cartilage.

29. 29
View
from
front
View
from
behind

30. Function of Larynx
• Production of sound
• Speech
• Protection of the lower respiratory tract: During swallowing the larynx
moves upwards and hinged epiglottis closes over the larynx.
• Passageway for air
• Humidifying
• Filtering

31. Respiratory system 31

32. Trachea
The trachea or windpipe is a continuation of the larynx &
extends downwards to about the level of T - 5 where it divides
into right & left primary bronchi.
• Length: 10 - 11 cm
Position:
 Superiorly - the larynx
 Inferiorly - the right & left bronchi
 Anteriorly - upper part - the thyroid gland.
lower part - the arch of aorta & the sternum.
 Posteriorly - the oesophagus
 Laterally- the lungs

33. 33

34. Trachea
STRUCTURE: Composed of 3 layers of tissue.
(i) Fibrous & Elastic Tissue
(ii) Smooth Muscle
(iii) Ciliated Columnar Epithelium
 Held open by between 16-20 incomplete cartilage rings (C-shaped)
 BLOOD SUPPLY: Inferior thyroid artery, Bronchial artery
 VENOUS DRAINAGE: Inferior thyroid veins
 NERVE SUPPLY: Laryngeal nerve

35. Function of Trachea
• Support and patency
• Mucociliary escalator
• Cough reflex
• Warming
• Humidifying
• Filtering

36. Bronchi & Bronchioles
Bronchi: Tubes that branch off trachea and enter into lungs
• Branches of Bronchi:
Primary bronchi  secondary bronchi  tertiary bronchi 
bronchioles
 Bronchioles branch into microscopic alveolar ducts.

37. Bronchi & Bronchioles
The two primary bronchi when the trachea divides about the level of
T-5.
The right bronchus:
 This is wider, shorter and more vertical than the left bronchus.
 Length - 2.5 cm
 After entering the right lung, it divides into 3 branches, one to each lobe.
The left bronchus:
 This is narrower than the right.
 Length – 5 cm
 After entering the left lung, it divides into 2 branches, one to each lobe.

38. Respiratory system 38

39. Bronchi & Bronchioles
STRUCTURE:
 The bronchi are composed of the same issues as the trachea.
 Are lined with ciliated columnar epithelium.
DIVISION OF BRONCHI:
Bronchioles
Terminal bronchioles
Respiratory bronchioles
Alveolar ducts
Alveoli

40. Respiratory system 40

41. Bronchi
 Ciliated columnar mucous membrane changes gradually to
non-ciliated cuboidal-shaped cells in the distal bronchioles.
 The wider passages are called conducting airways.
 Conducting airways, bring air into the lungs & their walls are too
thick to permit gas exchange.
 BLOOD SUPPLY: Bronchial arteries
 VENOUS DRAINAGE: Bronchial veins
 NERVE SUPPLY: Vagus nerve
 LYMPH DRAINAGE: The Thoracic duct

42. Function of Bronchi & Bronchioles
 Control of air entry
 Warming & humidifying
 Support & patency
 Removal of particulate matter
 Cough reflex

43. Alveoli
 Each lobule is supplied with air by a terminal bronchiole, which further
subdivides into respiratory bronchioles, alveolar ducts and large numbers of
alveoli (air sacs).
 About 150 million alveoli are found in the adult lung.
 In these structures, process of gas exchange occurs.
 As airways progressively divide and become smaller & smaller, their walls
gradually become thinner.
 These distal respiratory passages are supported by a loose network of
elastic connective tissue.
 Exchange of gases in the lungs takes place in alveoli.

44. Respiratory system 44

45. Respiratory system 45

46. Function of Alveoli
 EXTERNAL RESPIRATION: This is exchange of gases by
diffusion between the alveoli and the blood.
 DEFENCE AGAINST MICROBES: Protective cells present
within the lung tissue, include lymphocytes & plasma cells,
which produce antibodies.
 EXCHANGE OF GASES

47. Lungs
 There are two lungs, one lying on each side.
 Shape : cone
 Weight : 600 - 700 gm
 Length : 20 - 24 cm
 Colour : Pinkish
 Lobes : three lobes in the right lung
two lobes in the left lung
 Lobes are separated by the fissures.
 The area between the lungs is the mediastinum.

48. Lobes of the Lungs
Respiratory system 48

49. Surfaces of Lungs
Apex : Rounded and rises into the root of the neck.
A base : This is concave & semilunar in shape, lies on the
thoracic surface of the diaphragm.
Costal surface :This surface is convex & lies against the costal
cartilages.
Medial surface :This surface is concave & has a roughly triangular
- shaped area, called the hilum. The pulmonary artery
supplying the lung & two pulmonary veins draining it.

50. Respiratory system 50

51. Pleura
The outer surface of each lung and the adjacent internal thoracic wall
are lined by a serous membrane called pleura.
 The outer surface of each lung is tightly covered by the visceral
pleura.
 While the internal thoracic walls, the lateral surfaces of the
mediastinum and the superior surface of the diaphragm are lined
by the parietal pleura.
 The parietal and visceral pleural layers are continuous at the hilus
of each lung.

52. Pleural Cavity
 The potential space between the serous membrane layers is a
pleural cavity.
 The pleural membranes produce a thin, serous pleural fluid that
circulates in the pleural cavity and acts as a lubricant, ensuring
minimal friction during breathing.
 The serous fluid is secreted by the epithelial cells of the
membrane.

53. The Pleural Cavities
Respiratory system 53

54. RESPIRATION
 The term respiration means the exchange of gases between body cells
and the environment.
BREATHING OR PULMONARY VENTILATION
 This is movement of air into and out of the lungs.
 Exchange of gases: This takes place:
 In the lungs: external respiration.
 In the tissues: internal respiration

55. BREATHING
 Breathing supplies oxygen to the alveoli and eliminates carbon
dioxide.
MUSCLES OF BREATHING:
 The main muscles used in normal quiet breathing are the
INTERCOSTAL MUSCLES and the DIAPHRAGM.
 Expansion of the chest during inspiration occurs as a result of
muscular activity, partly voluntary and partly involuntary.
 During difficult or deep breathing they are assisted by muscles of
the neck, shoulders and abdomen.

56. INTERCOSTAL MUSCLES
 There are 11 pairs of intercostal muscles that occupy the spaces
between the 12 pairs of ribs.
 They are arranged in two layers, the external and internal intercostal
muscles.
 The first rib is fixed.
 Therefore, when the intercostal muscles contract they pull all the other
ribs towards the first rib. Because of the shape and sizes of the ribs
they move outwards when pulled upwards, enlarging the thoracic cavity.

58. DIAPHRAGM
 The diaphragm is a dome - shaped muscular structure separating
the thoracic and abdominal cavities.
 It forms the floor of the thoracic cavity and the roof of the
abdominal cavity and consists of a central tendon from which
muscle fibres radiate to be attached to the lower ribs and sternum
and to the vertebral column by two crura.
 When the muscle of the diaphragm is relaxed ,the central tendon
is pulled downwards to the level of the T - 9, enlarging the thoracic
cavity in length.
 This decreases pressure in the thoracic cavity and increases it in
the abdominal and pelvic cavities.

59.  The intercostal muscles and the diaphragm contract simultaneously,
enlarging the thoracic cavity in all directions.
CYCLE OF BREATHING
 The average respiratory rate is 12 to 15 breaths/minute.
 Each breath consists of three phases:
A. Inspiration
B. Expiration
C. Pause

60. Inspiration
 When the capacity of the thoracic cavity is increased by simultaneous
contraction of the intercostal muscles and the diaphragm.
 The parietal pleura moves with the walls of the thorax & the diaphragm.
 This reduces the pressure in the pleural cavity to a level considerably
lower than atmospheric pressure.
 The visceral pleura follows the parietal pleura, pulling the lungs with it.
 This expands the lungs and the pressure within the alveoli and in the air
passages, drawing air into the lungs in attempt to equalise the
atmospheric and alveolar air pressure.
 The process of inspiration is ACTIVE, as it needs energy for muscle
contraction.
 Inspiration lasts about 2 seconds.

61. Expiration
 Relaxation of the intercostal muscles and the diaphragm results in
upward and inward movement of the rib cage and elastic recoil of the
lungs.
 As this occurs, pressure inside the lungs exceeds that in the
atmosphere and so air is expelled from respiratory tract.
 The still contain some air, are prevented from collapse by the intact
pleura.
 This process is PASSIVE as it does not require the expenditure of
energy.

62. Respiratory system 62

63. Respiratory system 63

64. Lung Volumes and capacities
Tidal volume (TV) - The amount of air involved in one normal
inhalation and exhalation.
Average TV: about 500 ml
• Alveolar Volume: Reaches upto the alveoli (350 ml)
• Dead space volume: Remains in the tract (150 ml)
Inspiratory Reserve volume (IRV) - The volume of air which
can be taken in/inhale forcefully after normal inhalation (deep
breath).
Average IRV: 2500-3000 ml.
Respiratory system 64

65. Inspiratory capacity (IC): The total volume of air that can be
inspired by contraction of the diaphragm and external
intercoastal muscles.
 It is the sum of TV + IRV = 3000 – 3500 ml
Expiratory Reserve volume (ERV): The volume of air exhaled
forcefully after normal exhalation.
Average ERV: 1000 - 1500 ml.
Respiratory system 65

66. Residual volume (RV): The volume of air that remains in the
lungs after forcefull exhalation.
Average RV: about 1200-1500 ml.
Functional residual Volume (FRC): The amount of air that is
usually retained in the lungs while at rest.
It is the sum of RV + ERV = 2500 ml
Respiratory system 66

67. • Vital capacity (VC): The volume of air forcefully exhaled
after forceful inhalation.
• Vital capacity = sum of TV + IRV + ERV
= 500 ml + (2000-3000) ml + 1100 ml
= 3500 – 4500 ml
• Total lung capacity: It is the maximum amount of air the
lungs can hold.
• VC + RV = 5000 – 6000 ml ( 5 – 6 lit.)
Respiratory system 67

68. Respiratory system 68

69. EXCHANGE OF GASES
 Inhaled oxygen enters the lungs and reaches the alveoli. The layers of
cells lining the alveoli and the surrounding capillaries are each only one
cell thick and are in very close contact with each other.
 Oxygen passes quickly through air - blood barrier into the blood in the
capillaries.
 Similarly, CO2 passes from the blood into the alveoli & is then exhaled.
 Diffusion of oxygen & carbon dioxide depends on pressure
differences.

70. DIFFUSION OF GASES
EXTERNAL RESPIRATION
 External respiration refers to gas exchange across the respiratory
membrane in the lungs.
 Each alveolar wall is one cell thick and sourrounded by a network of tiny
capillaries.
 Carbon dioxide diffuses from venous blood down its concentration
gradient into the alveoli.
 By the same process, oxygen diffuses from the alveoli into the blood.

71. Diffusion of oxygen
FROM ATMOSPHERE TO THE ALVEOLI:
 The partial pressure of O2 in the atmosphere is 159 mmHg and in the
alveoli 104 mmHg.
 O2 easily enter alveoli from atmospheric air.
FROM ALVEOLI TO BLOOD:
 The partial pressure of O2 in the alveoli is 104 mmHg and that in
pulmonary capillary is 40 mmHg.
 Thus, diffusion of O2 takes place from alveoli into the blood.

72. Diffusion of carbon dioxide
FROM BLOOD INTO ALVEOLI:
 The partial pressure of O2 in the alveoli is 40 mmHg and in the blood 45
mmHg.
 Thus, it facilitates the diffusion of CO2 from blood into alveoli.
FROM ALVEOLI TO ATMOSPHERE:
 In the atmospheric air, the partial pressure of CO2 is 0.3 mmHg and that
in alveoli is 40 mmHg.
 Hence, CO2 leaves alveoli easily.

73. INTERNAL RESPIRATION
 Internal respiration refers to gas exchange across the respiratory
membrane in the metabolizing tissues, like your skeletal muscles, for
example.
 Blood arriving at the tissues has been cleansed of it’s CO2 & saturated
with O2 during it’s passage through the lungs, therefore has a higher O2
& lower CO2 than the tissues.
 This concentration gradients between capillary blood and the tissues
lead gase exchange.
 O2 diffuses from the blood stream through the capillary wall into the
tissues.
 CO2 diffuses from the cells into the extracellular fluid, then into the
bloodstream towards the venous.

74. DIFFUSION OF OXYGEN FROM BLOOD INTO TISSUES:
 The partial pressure of O2 in the arterial blood is 95 mmHg and in the
tissue 40 mmHg.
 Thus, due to a pressure gradient of about 55 mm Hg, O2 can easily
diffuse in the tissue.
DIFFUSION OF CO2 FROM TISSUES INTO BLOOD:
 The partial pressure of CO2 is high in the cells (46 mmHg) and that in
arterial blood is 40 mmHg.
 Thus, CO2 diffuses from tissues to the blood.

75. TRANSPORT OF GASES IN THE BLOODSTREAM
Transport of blood oxygen & carbon dioxide is essential for internal
respiration to occur.
OXYGEN: Oxygen is carried in the blood in as combination with
haemoglobin as oxyhaemoglobin.
CARBON DIOXIDE: It is excreted by the lungs & transported by combined
with haemoglobin as carbaminohaemoglobin.
CONTROL OF RESPIRATION:
The respiratory centre: Medulla oblongata

76. REGULATION OF RESPIRATION
• Respiration is normally involuntary. Voluntary control of respiration is
possible only for short period about 40 seconds.
• The pattern of respiration is regulated by two mechanism:
1. Nervous or Neural mechanism
2. Chemical mechanism

77. Nervous Mechanism
• This involves respiratory centers, afferent nerves and efferent nerves.
Respiratory centers
Medullary centers
Inspiratory
center
Expiratory center
Pontine centers
Pneumotaxic
center
Apneustatic center

78. Medullary centers: Situated in
medulla oblongata
i.Inspiratory center: also known as
dorsal group of respiratory neurons.
They are concerned with normal
inspiration.
ii.Expiratory center: also known as
ventral group of respiratory system. They
are normally inactive during quite
breathing. When inspiratory center is the
active center, expiratory center is a
passive process. Expiratory centers
becomes active during forced breathing
when the inspiratory center is inhibited
Pontine centers: Situated in
pons region of the brain stem
i.Pneumotaxic center: Primary
function is to control the medullary
respiration center through apneustic
center. It inhibits the activity inspiratory
center. So that the duration of
inspiration is controlled.
ii.Apneustic center: This center
accelerates the depth of inspiration by
acting directly on the inspiratory center.

79. Chemical Mechanism
• The chemical mechanism of regulation of respiration is operated through
the chemoreceptors.
• Chemoreceptors are the receptors, which give response to change in
partial pressure of O2 and CO2 in blood and cerebrospinal fluid.
They are classified as:
1. Central chemoreceptors
2. Peripheral chemoreceptors

80. Central chemoreceptor:
Situated in medulla oblongata
 This area is known as
chemosensitive area. They are in
close contact with blood and
cerebrospinal fluid.
 When arterial pO2 rises, they
stimulate respiratory center,
increasing ventilation of lungs
and reducing arterial pO2.
Peripheral chemoreceptor:
Situated in the arch of aorta
 They are more sensitive to small
rise in arterial pO2 than to similarly
low arterial pO2 levels.
 Nerve impulse generated in
peripheral chemoreceptors are
conveyed by vagus nerves to
medulla and stimulate the
respiratory centers.

81. Respiratory system 81

82. Other factors that influence respiration:
 Speech, singing
 Emotional displays – crying, laughing, fear
 Drugs – sedatives, alcohol
 Sleep
 Body temp.

83. Reference
• Waugh A, Grant A. Ross & Wilson, Anatomy and physiology in health
and illness E-book, Elsevier Health Sciences; page no..
• Jani G.K., Elements of human anatomy, physiology & health education,
Atul prakashan; page no. 171-190.

84. THANK YOU !!! 