Respiratory System - Study Notes

Human
Respiratory
system
BIOLOGY
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Human respiratory system

The process of exchange of O2 from the atmosphere with CO2 produced by the cell is
called breathing. It occurs in two stages of inspiration and expiration. During inspiration
air enters the lungs from atmosphere and during expiration air leaves the lungs.
Anatomy of Respiratory system

 The human respiratory system comprised of a pair of nostrils openings out above
the upper lips.
 The nasal passage starts from the nostrils ends in the nasal chamber.
 This passage opens into the pharynx. It is the common passage for food and air
and connected with the mouth and nose.
 This pharynx connected with trachea via Larynx.
 Larynx or sound box, consist of two vocal cords, is a cartilaginous box which is re-
sponsible for the sound production.
 During the time of swallowing glottis is covered by epiglottis, a thin elastic cartilagi-
nous flap and it prevent the entry of food particles into the larynx.
 Trachea, a straight tube-like structure extending up to the middle of the thoracic

cavity. • This trachea then divides at the level of 5th thoracic vertebra into a right
and left primary bronchi.
 Each bronchus then farther divided into repeated divisions to form the secondary
and tertiary.
BIOLOGY | Human respiratory system PAGE 2

 Those tertiary bronchi then finally ending up in very thin terminal bronchioles.
 Many incomplete cartilaginous rings are present in the passage between the
trachea and the initial bronchioles to support the structure.
 Alveoli, a very thin, irregular-walled and vascularized saclike structures are present
at the end of each terminal bronchioles.
 The branching network of bronchi, bronchioles and alveoli are comprising the lungs.
 Humans have two lungs, the left and the right lung.
 Both are covered by a double layered membrane, called Pleura. Between the
double layer membrane, a jelly like fluid is also present for lower the friction on the
lung-surface.
Human Respiratory System

 There are two main part in the human respiratory system:-
 The conducting part: From the external nostrils up to the terminal bronchioles. It
transports the atmospheric air to the alveoli, remove the foreign particles,
humidifies the air and brings the air to body temperature.
 The exchange part: The alveoli and their ducts. In this part the actual diffusion of
O2 and CO2 between blood and atmospheric air takes place.
 The lungs are situated in the air-tight chamber known as the thoracic chamber.
 The vertebral column is present in the back or dorsal position of the thoracic
chamber and the sternum is present in front side, the ribs formed the lateral walls
and on the lower side it is guarded by the dome-shaped diaphragm, a muscular
membrane
Steps in Respiration
1) Pulmonary ventilation or Breathing by
which atmospheric air is drawn in and
CO2 rich alveolar air is released out.
Diffusion of gases (O2 and CO2) across
alveolar membrane.
2) Transport of gases by the blood.
3) Diffusion of O2 and CO2 between blood

and tissues.
4) Utilization of O2 by the cells for catabolic

reactions like cellular respiration and
release of CO2 as a waste product Exchange of O2 and CO2

Mechanism of Respiration
 Breathing involves inspiration and expiration. During inspiration atmospheric air is
drawn in and during expiration, alveolar air is released out.
 Movement of air in and out takes place due to difference in pressure gradient.
 Inspiration occurs when pressure inside the lung is less and expiration occurs when
pressure is more in lungs than outside.
 The diaphragm and external and internal intercostal muscles between the ribs
help in developing pressure gradient due to change in volume.
 The contraction of intercostal muscles lifts the ribs and sternum causing an
increase in volume of thoracic cavity that results in decrease in pressure than the
atmospheric pressure. This causes inspiration.
 Relaxation of the diaphragm and intercostal muscles reduce the thoracic volume
and increase the pressure causing expiration.
 The volume of air involved in breathing movements is estimated by

using spirometer for clinical assessment of pulmonary functions. volume.
Inspiration Expiration

Exchange of gases
 Exchange of gases takes place at two sites

1) Alveoli to blood
2) Between blood and tissues.
 Exchanges of gases occur by simple diffusion due to pressure/ concentration

gradient, solubility of the gases and thickness of membrane.
 Pressure contributed by individual gas in a mixture of gas is known as partial

pressure represented by pC and p .
 The partial pressure of Oxygen and carbon dioxide at different parts involved in
diffusion varies from one part to another and moves from higher partial pressure to
lower partial pressure.
 The solubility of C is 20-25 times more than the solubility of , so C diffuses much
faster through the membrane.
 The diffusion membrane is three-layered thick, that is the alveolar squamous

epithelium, endothelium of alveolar capillaries, and basement substance between
them.
Exchange of gases

Chloride shift
 The chloride shift is defined as the movement of chloride ions from the plasma into
RBCs as the blood undergoes the transition from arterial to venous gas.
 The chloride shift is also known as the Hamburger shift. It is the process that takes
place in a cardiovascular system where the exchange of bicarbonate HCO−3 and
chloride Cl– across the membrane of RBCs.
 Following are the times when does the chloride shift occur:
1) When the chloride moves into erythrocytes and bicarbonate moves out into the
venous blood.
2) When chloride moves out and bicarbonate moves into the pulmonary capillaries.
Chloride shift

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Human

Human respiratory system

Anatomy of Respiratory system

 This pharynx connected with trachea via Larynx.

 Trachea, a straight tube-like structure extending up to the middle of the thoracic

BIOLOGY | Human respiratory system PAGE 2

Human Respiratory System

BIOLOGY | Human respiratory system PAGE 3

 There are two main part in the human respiratory system:-

2) Transport of gases by the blood.

3) Diffusion of O2 and CO2 between blood

4) Utilization of O2 by the cells for catabolic

BIOLOGY | Human respiratory system PAGE 4

 The volume of air involved in breathing movements is estimated by

BIOLOGY | Human respiratory system PAGE 5

 Exchange of gases takes place at two sites

 Exchanges of gases occur by simple diffusion due to pressure/ concentration

 Pressure contributed by individual gas in a mixture of gas is known as partial

 The diffusion membrane is three-layered thick, that is the alveolar squamous

BIOLOGY | Human respiratory system PAGE 6

BIOLOGY | Human respiratory system PAGE 7

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