The document discusses the structure and function of the respiratory system. It can be summarized as follows: 1) The respiratory system is divided into an upper and lower portion. The upper portion includes the nose, nasal cavity and pharynx, while the lower portion includes the larynx, trachea, bronchi and lungs. 2) Gas exchange occurs in the lungs through diffusion of oxygen and carbon dioxide between the alveoli and blood in the pulmonary capillaries. The partial pressures of oxygen and carbon dioxide drive this diffusion. 3) Respiration is regulated by both nervous and chemical mechanisms. The brain stem contains centers that control automatic breathing, while voluntary control occurs in the cerebral cortex.

2. Introduction:
Body’s cell continually use oxygen (O2) for the
metabolic reactions that release energy from
nutrient molecules and produce ATP, at the same
time, these reactions release carbon dioxide
(CO2).
This system also participates in regulating blood
pH
This system helps to contributes to homeostasis
by providing for the exchange of gases oxygen &
carbon dioxide between air, blood and tissue cells.

3. Structure:
Respiratory system parts can be classified
according to either structure or function.
Structurally the respiratory system consist of two
parts:
1) Upper respiratory system( Nose, Nasal cavity,
Pharynx and associated structure)
2) Lower respiratory system (Larynx, Trachea,
Bronchi and Lungs)

4. Structure:
Functionally the respiratory system consist of
two parts:
1) Conducting zone: (Nose, Nasal cavity, Pharynx,
Larynx, Trachea, Bronchi, Bronchioles and
terminal Bronchioles).
2) Respiratory zone: (Respiratory bronchioles,
Alveolar ducts, Alveolar sacs, Alveoli).
Branch of medicine that deals with diagnosis and
treatment of disease of ear, nose & throat is called
otorhinolaryngology.
Pulmonologist is a specialist in the diagnosis &
treatment of diseases of the lungs.

5. Structure's of the Respiratory System

6. Functions of Respiratory System:
1) Provides for gas exchange: intake of O2 for
delivery to body cells and removal of Co2
produced by blood cells.
2) Helps regulate blood pH.
3) Contains receptors for sense of smell, filters
inspired air, produces vocal sounds (phonation)
and excrete small amount of water and heat.

7. 1.NOSE:
It is divided into external portion and internal portion called nasal
cavity.
External nose is the portion of the nose visible on the face consist
of bone & hyaline cartilage covered by muscle & skin and lined by
mucous membrane.
On the undersurface of external nose are 2 openings called
External nares (nostrils).
Interior structure of external nose have 3 functions (warming,
moistening & filtering).
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8. 2.NASAL CAVITY:
It is a deep hollow cavity, stretching from over
the hard palate at the back to between the eye
sockets.
It is divided into two almost symmetrical halves
by the nasal septum.

9. 2.NASAL CAVITY:
Structure forming the boundaries of nasal cavity:
1) Roof: Formed by cribriform plate of ethmoid
bone & sphenoid, frontal & nasal bones.
2) Floor: Formed by roof of mouth & consist of
hard palate in front & soft palate behind.
3) Medial wall: Formed by nasal septum which
consists of ethmoid & vomer posteriorly and
hyaline cartilage anteriorly.
4) Lateral wall: Formed by maxilla, ethmoid bone
& inferior conchae.
5) Posteriorly: Opens into nasopharynx

10. 2.NASAL CAVITY:
Openings of Nasal cavity:
1) Nostrils opening from the exterior into the nasal
cavity contains hair.
2) Posterior nares openings from the nasal cavity
into the pharynx.
3) Paranasal sinuses are cavities in the bone
forming the nasal cavity which contain air. The
main sinuses are: (maxillary sinuses, frontal and
sphenoidal sinuses & ethmoidal sinuses)
4) Nasolacrimal ducts extend from the lateral walls
of the nose to the conjunctival sacs of the eyes,
they drain tears from the eyes.
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11. 3.PHARYNX:
1) Pharynx (Throat) is 12-14cm long tube lies
behind nasal and mouth cavities & larynx. It
belongs to both respiratory and digestive.
2) During swallowing epiglottis covers the
entrance to the larynx completely, at rest and
during breathing epiglottis stand up &
oesophagus is closed allowing air to pass into
respiratory tract.

13. 3.PHARYNX:
1) Pharynx is divided into three parts: (Naso, Oro,
Laryngopharynx).
Nasopharynx: It lies behind the nose. Lateral
structure is pharyngotympanic tube, posteriorly
structure is pharyngeal tonsils (adenoids).
Oropharynx: It lies behind the mouth, lateral
structure is collection of lymphoid tissue called
palatine tonsil, during swallowing nasal & oral
part is separated by soft palate & uvula.
Laryngopharynx: It extend from oropharynx
above & continues as esophagus below.

14. Functions of Pharynx:
1) It acts as passageway for, both air and food.
2) It is useful in warming and humidifying the air.
3) The pharyngotympanic tube plays an important
role in hearing.
4) The pharyngeal & laryngeal tonsils produce
antibodies in response to antigen.
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15. 4.LARYNX:
1) Larynx or voice box lies in the neck, anterior to
esophagus. At puberty it grows larger in males,
prominence of the Adam’s apple and deeper
voice, larynx consist of cartilages, connected by
ligaments & skeletal muscles.

16. 4.LARYNX:
1) It is connected to hyoid bone with help of connective
tissue.
2) Thyroid cartilage consist of two flat pieces of hyaline
cartilage fused anteriorly to form laryngeal prominence
(Adam's apple).
3) Epiglottis is elastic plate of cartilage it is attached to
thyroid cartilage by ligaments, during swallowing base
of tongue presses the epiglottis with this food is
prevented from entering into the trachea.
4) Cricoid cartilage consist of hyaline cartilage lies below
to thyroid cartilage, it separates of air tract and food
tract.
5) Arytenoid cartilage two in number influence position
and tension in vocal cords.

17. Functions of Larynx:
1) Larynx helps in production of sound.
2) Pitch (frequency) of the voice depends upon the
length and tension of vocal cords.
3) Volume or loudness of voice depends upon the
force with which the cord vibrate.
4) It is a passageway for air between the pharynx
& trachea.
5) It protects the lower respiratory tract during
swallowing.
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18. 5.TRACHEA:
Trachea (windpipe) is a tubular passageway of
air, it is about 12 cm long 2.5 cm in diameter,
located anterior to esophagus, extend from larynx
to 5th thoraxic vertebra, where it divide into right
& left bronchi

19. 5.TRACHEA:
Trachea is having 4 layers (mucosa, submucosa,
hyaline cartilage & adventitia (composed of
areolar connective tissue).
Consist of 16-20 incomplete rings of hyaline
cartilage resemble letter “C”.
Inner wall of trachea lined by mucous membrane
containing numerous mucus secreting goblet
cells.

20. 6.BRONCHI:
Trachea divides into right and left primary
bronchus which goes to lungs.
Point where trachea divides into left & right
primary bronchi an internal ridge called “carina”
is formed, its mucous membrane is very sensitive
and it trigger the cough reflex.
Trachea primary bronchi secondary
bronchi tertiary bronchi bronchioles
terminal bronchioles respiratory
bronchioles alveolar ducts
alveolar sacs alveoli

21. 7.LUNGS:

22. 7.LUNGS:
There are two cone-shaped lungs, one lying on each side
of the midline in thoracic cavity.
Apex is rounded & base of lung is concave and semi-
lunar in shape, it rests on diaphragm.
Medial surface having hilum structures which enter and
leave hilum include (1 bronchus, 1 pulmonary artery, 2
pulmonary vein, 1 bronchial artery, bronchial vein,
parasympathetic & sympathetic nerves.
Area between lung is mediastinum, it is occupied by
heart, great vessels, trachea, bronchi, oesophagus, lymph
nodes, lymph vessels & nerves.
Right lung divided into 3 lobes (superior, middle &
inferior), left lung into 2 lobes (superior & inferior).

23. 7.LUNGS:
Air in the alveoli is separated from blood in pulmonary
capillaries by a wall called respiratory membrane which
consist of alveolar wall and capillary wall.
Lungs are enveloped by pleura which has 2 layers
parietal pleura (superficial layer) and visceral pleura
(deep inside layer), this space is filled with approx. 2 ml
of serous lubricating fluid called pleural fluid.
Lungs receives blood via 2 sets of arteries (pulmonary &
bronchial arteries), oxygenated blood to the heart occur
by 4 pulmonary vein which drains into left atrium
(heart).

24. MECHANISM OF RESPIRATION:
Eupnoea means rhythmic breathing at rest. It consists of
inspiration and expiration.
Inspiration: It is a active process during which size of
thoracic cavity is increased by contraction of appropriate
muscles. Parietal pleura follows the expanding chest
wall, expansion of lung is associated with a fall in
pressure in the lung parenchyma & atmospheric air.
Expiration: It is a passive process. At the end of
inspiration, the muscle which contracts actively during
inspiration relaxes & the elastic recoil of thoracic wall &
lungs cause passive expiration.

25. MECHANISM OF RESPIRATION:
At rest an adult breathes at a respiratory rate of 12-14
breaths per minute & the amount of air inspired or
expired per breath (i.e. tidal air) is approx. 500 mL, thus
6-7 litres of air is breathed in or out of the lungs per
minute called pulmonary ventilation..

26. MECHANISM OF INSPIRATION:
1) RIB MOVEMENTS: On inspiration ribs move
upwards to assume a more horizontal position due to
contraction of external intercostal muscles to cause
increase in anteroposterior diameter of the chest.
2) DIAPHRAGMATIC MOVEMENTS: During
inspiration as a result discharge in phrenic neuron
(c3,4,5), muscle fibre contract & draw the central
tendon downwards by 1.5cm in eupnoea & by 7cm in
deep inspiration. This causes increase in diameter of
thoracic cage, for each 1cm descent 200-300 ml air is
sucked.
3) ACCESSORY MUSCLE OF INSPIRATION: Scalene,
Sternocleidomastoid muscles & intrinsic muscles of
larynx.

27. MECHANISM OF EXPIRATION:
1) CONTRACTION OF ANTERIOR ABDOMINAL
WALL MUSCLES increases intra-abdominal pressure
& draws the lower rib down & medially, thereby
diaphragm is relaxing.
2) INTERNAL INTERCOSTAL MUSCLES: they pass
obliquely downwards & posteriorly from rib to rib. On
contraction they pull the upper ribs down so that ribs
acquire the position
3) ACCESSORY MUSCLES OF EXPIRATION are
adductor muscles of vocal cords. They begin to
contract early in expiration. Their main function is
protective i.e. prevent entry of food & fluid into
trachea.

28. LUNG VOLUMES & CAPACITIES:
Lung volumes & capacities can be divided into 2 major
headings:
1) Static lung volumes and capacities (here time factor
is not involved, therefore expressed in ml or L.)
2) Dynamic lung volumes and capacities (these are time
dependent, therefore it is expressed in ml/ minute or
L/minute).

29. STATIC LUNG VOLUMES &
CAPACITIES:
VOLUMES:
1) Tidal volume (TV): Is the air breathed in or out of lung
during quiet respiration. Normal: 500 ml.
2) Inspiratory reserve volume (IRV): maximum volume of
air which can be inspired in normal inspiration.
Normal: 2000-3200 ml.
3) Expiratory reserve volume (ERV): maximum volume
of air which can be expired after normal expiration.
Normal: 750-1000 ml.
4) Residual volume (RV): It is the volume of air which
remains in lungs after maximal expiration.
Normal: 1200 ml

30. STATIC LUNG VOLUMES &
CAPACITIES:
CAPACITIES:
1) Inspiratory capacity (IC): It is the maximum volume of
air which can be inspired after completing tidal
expiration. It can be computed as: (TV + IRV)
Normal: 2500-3700 ml.
2) Expiratory capacity (EC): It is the maximum volume of
air which can be expired after completing tidal
inspiration. It can be computed as: (TV + ERV),
Normal: 1250-1500 ml.
3) Vital capacity (VC): vital capacity is the maximum
volume of air which can be expelled from lungs by
forceful effort following a maximal inspiration. It is
computed as: TV+ IRV+ ERV. Normal: 4.8 litres in
males & 3.2 litres in females.

31. STATIC LUNG VOLUMES &
CAPACITIES:
CAPACITIES:
4) Functional residual capacity (FRC): It is the volume of
air which is contained in the lungs after completion of
tidal expiration. It can be computed as: RV+ ERV,
Normal: 2.5 litres. It is act as buffer & allows
continuos exchange of gases to occur even during
expiration, it also prevent collapse of the alveoli.
5) Total lung capacity (TLC): It is the volume of air
contained in lungs after a maximal inspiration. It can
be computed as: VC+ RV, Normal: 6 litres.

32. DYNAMIC LUNG VOLUMES &
CAPACITIES:
1) Timed Vital Capacity (TVC) or Forced Vital Capacity
(FVC): It is the maximum volume of air which can be
breathed out as forcefully & rapidly as possible
following a maximum inspiration.
2) Minute Ventilation (MV) or Pulmonary Ventilation
(PV): This is the volume of air expired or inspired by
the lungs in 1 minute.
PV= TV x RR per minute
= 500 x 12
= 6L/minute, normally.

33. X
Y

34. EXCHANGE OF GASES (o2 & Co2):
Exchange of gases takes place between alveoli and blood
across the respiratory membrane (External respiration)
and between blood and tissue across capillary membrane
(Internal respiration) by the process of diffusion.
Diffusion is movement of any substance (Solute) from
higher concentration to lower concentration until
equilibrium is established.
Exchange of gases occurs when a difference in partial
pressure exists.
Partial pressure (PP): the pressure exerted by the
individual gas in a mixture of gases.

36. Partial Pressure of Gases:
Condition Po2 PCo2
Atmospheric air 159mmHG 0.3mmHG
Alveolar air 104mmHG 40mmHG
Pulmonary
capillary
40mmHG 46mmHG
Arterial end 95mmHG 40mmHG
Tissues 40mmHG 46mmHG
Pressure Gradient: Difference between partial
pressure of two gases.
= Po2 (Atm) – Po2 (Alveoli)
= 159-104
= 55mmHG

38. REGULATION OF RESPIRATION:
The normal rate of respiration in adults is 12- 16 breaths
per minute. With tidal volume of approx. 500 ml. the rate
& depth of respiration, i.e. total pulmonary ventilation
can be adjusted to the requirement. This requirement is
adjusted by brain by two mechanism:
1) Nervous Regulatory Mechanism
2) Chemical Regulatory Mechanism

39. 1. Nervous regulation of
respiration:
Nervous regulation of respiration is brought about by
two system. They are:
A. System responsible for automatic control of
respiration that is located in the brain stem (upper
medulla & pons).
B. System responsible for voluntary control of
respiration that is located in cerebral cortex.

40. 1. Nervous regulation of
respiration:
A. Automatic control of respiration:
The collection of certain groups of neurons in medulla &
pons constitutes medullary & pontine respiratory centres
respectively.
Medullary respiratory centre: Here neuron shows
rhythmic discharge with varying frequencies. They are of
two type.
1) Those which discharge during inspiration only, i.e. I-
neurons.
2) Those which discharge during expiration only, i.e. E-
neurons.
They both have inhibitory connections to each other, i.e.
their exist reciprocal innervation between the two.

41. 1. Nervous regulation of
respiration:
Pontine respiratory centre:
1) An area in the lower pons contains
neurons which are tonically active and
activate the I- neuron in medulla. This
area is referred to as apneustic centre.
2) An area in the upper pons that contains
both I and E neurons is called
pneumotaxic centre. It inhibits the
neurons of the apneustic centre in the
lower pons.

42. 1. Nervous regulation of
respiration:
B. Voluntary control of
respiration:
Respiration can be modified both
in rate/depth at will for a specific
period only. For e.g. voluntary
hyperventilation, breath holding
and forceful inspiratory or
expiratory efforts. The pathway for
such a control is via corticospinal
tract which originates from cerebral
cortex to end on spinal neuron
innervating respiratory group of
muscles.

43. 1. Nervous regulation of
respiration:
A. Genesis of inspiration:
Inspiratory centre (contains I-neuron) although has its own
rhythmicity, is activated by apneustic centre, inspiratory
centre discharges over pathways in spinal cord to C3,4,5 &
T1,2. therefore inspiration starts.
B. Genesis of expiration:
The inspiration must be inhibited for expiration to proceed.
1) I-neurons to medulla send excitatory impulses to
pneumotaxic centre which, in turn, discharges
inhibitory impulses to apneustic centre.

44. 1. Nervous regulation of
respiration:
2) The pulmonary stretch receptors in lungs which get
stimulated during inspiration send inhibitory impulses
via vagus (X) nerve to apneustic centre.
3) The pneumotaxic centre stimulates expiratory centre
(contains E-neurons) which reciprocally inhibits
inspiratory centre.

45. 2. Chemical regulation of
respiration:
The chemical regulatory mechanism adjusts ventilation
in such a way that alveolar pCO2 is kept constant at
normal value of 40 mmHG. It also maintains the tension
of O2, Co2 and H+ of blood. These changes are mediated
via respiratory chemoreceptors.
The respiratory chemoreceptors are of two types:
1) Peripheral chemoreceptors
2) Medullary (or central) chemoreceptors.

46. 2. Chemical regulation of
respiration:
1) Peripheral chemoreceptors: Carotid body near carotid
artery and aortic bodies near arch of the aorta.
2) Medullary (central) chemoreceptors: It is located in the
medulla near the respiratory centre, they get stimulated
by H+ concentration in brain.