The respiratory system has several key functions including supplying oxygen to the body and removing carbon dioxide. It consists of breathing, which has two phases - inhalation that draws air into the lungs and exhalation that forces air out. Gas exchange occurs externally between the lungs and blood and internally between blood and tissues. Regulation of respiration maintains appropriate oxygen and carbon dioxide levels in the blood by adjusting breathing to meet metabolic demand.

1. PHYSIOLOGY OF
RESPIRATORY SYSTEM

2. Respiratory System Functions
1. Supplies the body with oxygen and
disposes of carbon dioxide
2. Filters inspired air
3. Produces sound
4. Clears the body from excess water and
heat
5. Control blood pH

3. • Primary function is to obtain oxygen for use
by body's cells & eliminate carbon dioxide
that cells produce

4. Breathing
• Breathing (pulmonary ventilation). consists
of two cyclic phases:
• Inhalation, also called inspiration - draws gases
into the lungs.
• Exhalation, also called expiration - forces gases
out of the lungs.

5. Respiratory events
• Pulmonary ventilation = exchange of gases
between lungs and atmosphere
• External respiration = exchange of gases
between alveoli and pulmonary capillaries
• Internal respiration = exchange of gases
between systemic capillaries and tissue cells

7. Phases of pulmonary ventilation
• Inspiration, or inhalation - A very active process
that requires input of energy. The diaphragm
contracts, moving downward and flattening.
• Expiration, or exhalation - A passive process that
takes advantage of the recoil properties of elastic
fiber. The diaphragm relaxes. The elasticity of the
lungs and the thoracic cage allows them to return
to their normal size and shape.
• This two processes are happens when phrenic
nerves Stimulates.

8. LUNG VOLUMES
• Minute ventilation (MV): MV 12 breaths/min 500 mL
/breath = 6 liters/min. total lung capacity.
• TIDAL VOLUME (TV): Volume inspired or expired with each
normal/breath. = 500 ml
• INSPIRATORY RESERVE VOLUME (IRV): Maximum volume that
can be inspired over the inspiration of a tidal volume/normal
breath. Used during exercise/exertion.= Male 3100 ml/ Female
1900 ml
• EXPIRATRY RESERVE VOLUME (ERV): Maximal volume that
can be expired after the expiration of a tidal volume/normal
breath. = Male 1200 ml/ Female 700 ml
• RESIDUAL VOLUME (RV): Volume that remains in the lungs
after a maximal expiration. Male 1200 ml/ Female 1100 ml

9. • Inspiratory capacity is the sum of tidal volume and
inspiratory reserve volume, IRV + TV (500 ml 3100 ml
3600 ml in males and 500 ml 1900 ml 2400 ml in
females).
• Functional residual capacity is the sum of residual
volume and expiratory reserve volume, ERV + RV (1200 ml
1200 ml 2400 ml in males and 1100 ml 700 ml 1800 ml in
females).
• Vital capacity is the sum of inspiratory reserve volume,
tidal volume, and expiratory reserve volume, IRV + TV +
ERV = IC + ERV (4800 ml in males and 3100 ml in females).
• Total lung capacity is the sum of vital capacity and
residual volume IRV+ TV + ERV + RV = IC + FRC (4800 ml
1200 ml 6000 ml in males and 3100 ml 1100 ml 4200 ml
in females).

11. Physiology of respiration
The process of gas exchange in the body, called respiration, it has three
basic steps:
1. Pulmonary ventilation or breathing
– It is the inhalation (inflow) and exhalation (outflow) of air and
involves the exchange of air between the atmosphere and the alveoli
of the lungs.
2. External (pulmonary) respiration
– It is the exchange of gases between the alveoli of the lungs and the
blood in pulmonary capillaries across the respiratory membrane.
– In this process, pulmonary capillary blood gains O2 and loses CO2.
3. Internal (tissue) respiration
– It is the exchange of gases between blood in systemic capillaries
and tissue cells. In this step the blood loses O2 and gains CO2. Within
cells, the metabolic reactions that consume O2 and give off CO2
during the production of ATP are termed cellular respiration

12. Inhalation
• Breathing in is called inhalation (inspiration)
• Each inhalation, the air pressure inside the lungs is equal
to the air pressure of the atmosphere, which is about 760
mmHg.
• Air to flow into the lungs, the pressure inside the alveoli
must become lower than the atmospheric pressure.
• This condition is achieved by increasing the size of the
lungs.

13. Exhalation
Breathing out or exhalation starts when the inspiratory muscles relax. As
the diaphragm relaxes, its dome moves superiorly owing to its elasticity.
As the external intercostals relax, the ribs are depressed.
• The pressure in the lungs is greater than the pressure of the
atmosphere. Normal exhalation during quiet breathing
• It is a passive process because no muscular contractions are involved.
Instead, exhalation results from elastic recoil of the chest wall and
lungs, both of which have a natural tendency to spring back after they
have been stretched.
• Two inwardly directed forces contribute to elastic recoil:
a. The recoil of elastic fibers that were stretched during inhalation
b. The inward pull of surface tension due to the film of alveolar fluid.

15. External respiration or pulmonary
gas exchange
• It is the diffusion of O2 from air in the alveoli of the lungs to blood in
pulmonary capillaries and the diffusion of CO2 in the opposite
direction.
• External respiration in the lungs converts deoxygenated blood
(depleted of some O2) coming from the right side of the heart into
oxygenated blood (saturated with O2) that returns to the left side of
the heart.
• As blood flows through the pulmonary capillaries, it picks up O2 from
alveolar air and unloads CO2 into alveolar air, this process is called an
“exchange” of gases, this process is carried by diffusion.

16. Internal respiration
The left ventricle pumps oxygenated blood
into the aorta and through the systemic
arteries to systemic capillaries. The exchange
of O2 and CO2 between systemic capillaries
and tissue cells is called internal respiration
or systemic gas exchange

17. Oxygen Transport
• Oxygen does not dissolve easily in water, so only about
1.5% of inhaled O2 is dissolved in blood plasma, which is
mostly water. About 98.5% of blood O2 is bound to
hemoglobin in red blood Cells. Each 100 mL of oxygenated
blood contains the equivalent of 20 mL of gaseous O2.
• The heme portion of hemoglobin contains four atoms of
iron, each capable of binding to a molecule of O2. The
98.5% of the O2 that is bound to hemoglobin. Oxygen and
hemoglobin bind in an easily reversible reaction to form
oxyhemoglobin. O2 +Hgb = 4HgbO2
• As blood flows through tissue capillaries, the iron–oxygen
reaction reverses. Hemoglobin releases oxygen, which
diffuses first into the interstitial fluid and then into cells.

18. Factors Affecting the Affinity of
Hemoglobin for Oxygen
• Although PO2 is the most important factor
that determines the percent O2 saturation of
hemoglobin. The following four factors
affect the affinity of hemoglobin for O2 :
1. Acidity (pH).
2. Partial pressure of carbon dioxide
3. Temperature.
4. 2,3-bisphosphoglycerate (BPG)

19. Acidity
• As acidity increases (pH decreases), the
affinity of hemoglobin for O2 decreases, and
O2 dissociates more readily from
hemoglobin.
• When H+ ions bind to amino acids in
hemoglobin, they alter its structure slightly,
decreasing its oxygen-carrying capacity.
Thus, lowered pH drives O2 off hemoglobin,
making more O2 available for tissue cells.

20. Oxygen–hemoglobin dissociation curves
showing the relationship of pH

21. Partial pressure of carbon dioxide
• CO2 enters the blood it is temporarily
converted to carbonic acid (H2CO3).
• It dissociates and form hydrogen ions and
bicarbonate ions. So in red blood cells the
H+ concentration increases, pH decreases.
Thus, an increased PCO2 produces a more
acidic environment, which helps release O2
from hemoglobin.

22. Oxygen–hemoglobin dissociation curves
showing the relationship of PCO2

23. Temperature
• Heat is a by-product of the metabolic
reactions of all cells, and the heat released
by contracting muscle fibers tends to raise
body temperature. Metabolically active cells
require more O2 and liberate more acids and
heat.

24. Oxygen–hemoglobin dissociation curves
showing the effect of temperature changes.

25. 2,3-bisphosphoglycerate (BPG)
(Diphosphoglycerate)
• BPG is formed in red blood cells when they
break down glucose to produce ATP in a
process called glycolysis. When BPG
combines with hemoglobin, it unloads or
decreases the bonding with oxygen.

26. CO2 Transportation
• Normal resting conditions, each 100 mL of
deoxygenated blood contains the equivalent
of 53 mL of gaseous CO2, which is
transported in the blood in three main
forms
1. Dissolved CO2. The smallest percentage—
about 7%—is dissolved in blood plasma. On
reaching the lungs, it diffuses into alveolar air
and is exhaled.

27. 2. Carbamino compounds:- About 23% of
CO2, combines with the amino groups of
amino acids and proteins in blood to form
carbamino compounds. The main CO2
binding sites are the terminal amino acids
in the two alpha and two beta globin
chains. Hemoglobin that has bound CO2 is
termed carbaminohemoglobin (Hb—CO2):

28. 3. Bicarbonate ions. The greatest percentage
of CO2 about 70%—is transported in blood
plasma as bicarbonate ions (HCO3
-).
• CO2 diffuses into systemic capillaries and
enters red blood cells, it reacts with water in
the presence of the enzyme carbonic
anhydrase (CA) to form carbonic acid, which
dissociates into H+ and HCO3
-.

29. CO2 Dissociation Curve
The arterial point (a) and the venous point (v)

31. Regulation of respiration
• Regulation of respiration control is the rate and
depth of respiration as per the physiologic
demand. Control of respiration primarily
involves neurons in the reticular formation of
the medulla and pons. Because the medulla sets
the respiratory rhythm. The purpose of
Regulation of respiration are
1. To maintain a constant O2 and CO2 level in blood
2. It adjust the O2 supply as per the metabolic
demand of the body.
3. It helps to regulate acid base balance or pH.

32. • The size of the thorax is altered by the action of the
respiratory muscles, which contract as a result of nerve
impulses transmitted to them from centers in the brain and
relax in the absence of nerve impulses. This impulses travels
along the phrenic and intercostal nerves to excite the
diaphragm and external intercostal muscles
• These nerve impulses are sent from clusters of neurons
located bilaterally in the medulla oblongata and pons of the
brainstem.
• This widely dispersed group of neurons, collectively called
the respiratory center.

33. Mechanism of Regulation of
respiration
• There are two major mechanisms
1. Nervous regulation of respiration
2. Chemical regulation of respiration

34. 1. Nervous regulation of respiration
Respiratory Center
The respiratory centers are divided into four
major groups, two groups in the medulla and two
in the pons.
The two groups in the medulla are
a. The dorsal respiratory group
b. The ventral respiratory group.
The two groups in the pons are the pneumotaxic
center and the apneustic center also known as
the pontine respiratory group.

36. • Respiratory centers can be divided into
three areas on the basis of their functions:
1. The medullary rhythmicity area in the medulla
oblongata
2. The pneumotaxic area in the pons
3. The apneustic area, also in the pons

38. Medullary Rhythmicity Area
• The function of the medullary
rhythmicity area is to control the
basic rhythm of respiration. It includes
two areas
a. Inspiratory medullary rhythmicity area or
inspiratory centre
b. Expiratory medullary rhythmicity area or
expiratory centre

39. a. Inspiratory centre:
It establish the basic rhythm of breathing. When
its inspiratory neurons fire, a burst of
impulses travels along the phrenic and
intercostal nerves to excite the diaphragm
and external intercostal muscles.
b. Expiratory centre:
Impulses from the expiratory area cause
contraction of the internal intercostal and
abdominal muscles, which decreases the size of
the thoracic cavity and causes forceful
exhalation.

40. Pneumotaxic Area
• It transmits inhibitory impulses to the
inspiratory area. The major effect of these
nerve impulses is to help turn off the
inspiratory area before the lungs become
too full of air.

41. Apneustic area
• This area sends stimulatory impulses to the
inspiratory area that activate it and prolong
inhalation. The result is a long, deep
inhalation.

42. 2. Chemical regulation of respiration
• There are three important chemical factors
controlling respiration
1. Concentration of CO2 in blood
2. Concentration of H+ ions or pH
3. Concentration of oxygen In blood

43. Concentration of CO2 in blood
• When CO2 concentration in blood increases,
it stimulates the chemoreceptors. There are
two group of chemoreceptors
1. Peripheral chemoreceptors – situated at the
carotid body and aortic body
2. Central chemoreceptors – situated at the
medulla oblongata

44. When CO2 concentration in blood increases
Stimulates the chemoreceptors
Transmission of sensory impulses to respiratory centers
Activation of respiratory centers
Increases the activities of respiration (rate and Depth)
Increase alveolar ventilation
Expulsion of CO2 and decreases the level of CO2 in blood

45. Concentration of H+ ions or pH
When Concentration of H+ ions increases, it
stimulates the peripheral chemoreceptors.
H+ ions diffuses with CO2 and form carbonic acid, to
cross the blood brain barrier then dissociates into
H+ and HCO3. There by H+ ions stimulates the
central chemoreceptors then the respiratory centers,
resulting a reduction in the level of CO2 in blood. This
will inturn decrease concentration of H+ in blood or
increase the pH in to normal.

46. Concentration of oxygen In blood
When O2 concentration in blood decreases
Stimulates the peripheral chemoreceptors
Transmission of impulses to respiratory centers
Activation of respiratory centers
Increases the activities of respiration (rate and Depth)
Increase alveolar ventilation
Increases the uptake of O2
Thereby increases the level of O2 in blood

47. Respiratory System Terminologies
• Apnea: temporary cessation of breathing
• Tachypnea: abnormally rapid respirations
• Bradypnea: abnormally slow respiration
• Dyspnea: labored breathing or shortness of breath
• Hypoxemia: decrease in arterial oxygen tension in the blood
• Hypoxia: decrease in oxygen supply to the tissues and cells
• Hypercapnia: an increase in the partial pressure of carbon
dioxide in the blood.
• Hypocapnia: a decreased amount of carbon dioxide in the blood.
• Physiologic dead space: portion of the tracheobronchial tree that
does not participate in gas exchange.
• Central cyanosis: bluish discoloration of the skin or mucous
membranes due to hemoglobin carrying reduced amounts of
oxygen.
• Intrapleural (intrathoracic) pressure: pressure between the
two pleural layers in the pleural cavity.

48. • Alveolar (intrapulmonic) pressure: The pressure within the
tiny gas-exchanging structures of the lungs.
• Diffusion: exchange of gas molecules from areas of high
concentration to areas of low concentration.
• Osmosis: The passage of solvent through a semipermeable
membrane that separates solutions of different concentrations.
• Dalton’s law: (John Dalton, Brit. chemist, 1766–1844) A law
that states that, in a mixture of gases, the total pressure is equal
to the sum of the partial pressures of each gas.
• Henry’s law: (William Henry, Brit. chemist, 1774–1836) The
weight of a gas dissolved by a given volume of liquid at a
constant temperature is directly proportional to the pressure.
• Boyle’s law: (Robert Boyle, Brit. physicist, 1627–1691) A law
stating that, at a constant temperature, the volume of a gas
varies inversely with the pressure.

49. Normal Values
• Normal respiration: 12 – 16 breaths/min
• Normal Arterial blood gas values
– pH: 7.35 – 7.45
– Pa O2 : (80 to 100 mm Hg) and Sa O2 (95% to
98%)
– P CO2 : 35 – 45 mm Hg
– HCO3 : 22 – 27 mEq/L