This document provides an overview of respiratory physiology, covering the definition and function of respiration, the steps of respiration, the structure and function of the conducting and respiratory zones of the lungs, lung volumes and capacities, mechanics of breathing, gas exchange, transport of oxygen and carbon dioxide in the blood and tissues, and control of breathing. Key points include that respiration involves the exchange of oxygen and carbon dioxide between the environment and body cells, occurring in five steps including ventilation, diffusion, transport, and cellular respiration. Gas exchange takes place in the alveoli via differences in partial pressures and is facilitated by a large surface area and thin diffusion barrier. Oxygen is transported in both dissolved and hemoglobin-bound forms in the blood, while carbon

1. Respiratory Physiology
LECTURE

2. LECTURE OUTLINE
1. Respiration: Definition, Function. The Steps of respiration.
2. Conducting zone and Respiratory zone.
3. Lung Volumes and Capacities.
4. Mechanics of Breathing.
5. Gas exchange. Partial pressure. Fick’s law.
6. Gas transport in the lungs.
7. Exchange of O2 and CO2 between air –blood and blood-tissue barriers
8. Transport of oxygen in the blood.
9. Control of breathing.

3. RESPIRATION
• Respiration is the exchange of oxygen and
carbon dioxide between the environment
and the body cells.
The goals of respiration are to provide oxygen to the
tissues and to remove carbon dioxide.

4. The Stages (Steps) of
Respiration

5. Respiration in humans can be
divided into 5 steps:
1. Pulmonary Ventilation.
2. Diffusion of O2 and CO2 through the Air-Blood
barrier. Oxygen diffuses from the lungs to the blood,
and carbon dioxide diffuses from the blood to the
lungs.
3. Transport of O2 and CO2 in Blood. Oxygen is
transported from the lungs to the tissue cells of the
body, and carbon dioxide is transported from the
tissue cells to the lungs.
4. Diffusion of O2 and CO2 through the Blood–Tissue
barrier. Oxygen diffuses from blood to tissue cells,
and carbon dioxide diffuses from tissue cells to
blood.
5. Cellular respiration.

6. What is External Respiration and
Internal Respiration?
• External respiration is the first and second
stages of respiration.
• Internal respiration is the third, fourth and
fifth stages of respiration.

7. Physical Processes of
Gas Transport System

8. Organization of the Respiratory
System

9. The respiratory system includes:
• the nose
• nasal cavity
• the pharynx
• the larynx
• the trachea
• the bronchi and their smaller branches
• the lungs, which contain tiny air sacs called alveoli

10. The Components of the Respiratory System

12. The Components of the Respiratory System
1. Conducting Zone
2. Respiratory Zone
Functionally, the respiratory
system consists of two zones:

13. The Components of the Respiratory System
• The conducting zone includes respiratory
passage-ways (trachea, bronchus, bronchioles)
which provide fairly rigid conduits for air to reach
the gas exchange sites. The conducting zone
organs also cleanse, humidify, and warm
incoming air. As a result, air reaching the lungs
has fewer irritants (dust, bacteria, etc.) than when
it entered the body, and it is warm and damp.
• The respiratory zone, the actual site of gas
exchange, is composed of the respiratory
bronchioles, alveolar ducts, and alveoli.

14. • Region of gas
exchange
between air
and blood.
• Includes
respiratory
bronchioles
and alveolar
sacs.
Conducting zone &Respiratory Zone

15. The Bronchi and Lobules of the Lung

16. The Air-Blood barrier
(Respiratory Membrane)
This air-blood barrier is composed of:
• Alveolar and capillary walls
• Their fused basal laminas
Together, the capillary and alveolar walls and their fused basement
membranes form the respiratory membrane, a 0.5-μm-thick blood air
barrier that has blood flowing past on one side and gas on the other.
•Alveolar walls are a single layer that consists of type I
epithelial cells (permit gas exchange by simple
diffusion) and type II cells that secrete surfactant

17. Respiratory Membrane

18. Pulmonary Volumes
and Capacities

19. Recording Changes in Pulmonary Volume
— Spirometry
A simple method for studying pulmonary
ventilation is to record the volume movement of air
into and out of the lungs, a process called
spirometry.
There are 4 pulmonary volumes and 4 pulmonary capacities.

20. Respiratory Volumes
1. Tidal volume (Vt) is the volume inspired
or expired with each normal breath.
2. Inspiratory reserve volume (IRV) is the
volume that can be inspired over and
above the tidal volume. It is used during
exercise.
3. Expiratory reserve volume (ERV) is the
volume that can be expired after the
expiration of a tidal volume.
4. Residual volume (RV) is the volume that
remains in the lungs after a maximal
expiration. It cannot be measured by
spirometry.

21. Respiratory Capacities
1. Inspiratory capacity (IC) – total amount of air that can be inspired
after a tidal expiration (IRV + TV)
2. Functional residual capacity (FRC) – amount of air remaining in
the lungs after a tidal expiration
(RV + ERV)
3. Vital capacity (VC) – the total amount of exchangeable air (TV + IRV
+ ERV)
4. Total lung capacity (TLC) – sum of all lung volumes (approximately
6000 ml in males)

22. Dead Space
The volume of the airways that does not participate
in gas exchange
Anatomical dead space – volume of the
conducting respiratory passages (150 ml)
Functional dead space – alveoli that cease to act
in gas exchange due to collapse or obstruction
Physiological dead space – sum of alveolar and
anatomical dead spaces

23. Normal Respiration Cycle
(Normal Breathing Pattern)

24. Normal Respiration Cycle
(Normal Breathing Pattern)
1. Inhalation
2. Exhalation
3. Automatic Pause

25. Mechanics of Breathing

26. Inspiration
• Inspiration is active process:
• Diaphragm contracts -> increased thoracic
volume vertically.
• Intercostals muscles contract, expanding rib
cage -> increased thoracic volume laterally.
• More volume -> lowered pressure -> air in.

27. Expiration
• Expiration is passive process:
• Due to recoil of elastic lungs.
• Less volume -> pressure within alveoli is
above atmospheric pressure -> air leaves
lungs.
• Note: Residual volume of air is always left
behind, so alveoli do not collapse.

28. Mechanisms of Pulmonary Ventilation

29. Gas Exchange

30. • Daltons Law and partial pressure
Individual gases in a mixture exert
pressure proportional to their abundance
Partial pressure = Total pressure ×
Fractional
Ex: Gas concentration PO2 =760mm
Hg×0.21 =160mm Hg
Gas Exchange

31. Gas Exchange
The diffusion rates of O2 and CO2 depend on the partial
pressure differences across the membrane and the area
available for diffusion.
For example, the diffusion of O2 from alveolar air into the
pulmonary capillary depends on the partial pressure difference
for O2 between alveolar air and pulmonary capillary blood.
Normally, capillary blood equilibrates with alveolar gas; when
the partial pressures of O2 become equal, there is no more net
diffusion of O2.
Gas diffusion across the alveolar–pulmonary capillary barrier
occurs according to Fick’s law: Vx =DL×ΔP
where:
Vx = volume of gas transferred per minute (mL/min)
DL = lung diffusing capacity (mL/min/mm Hg)
P = partial pressure difference of gas (mm Hg)

32. • Gas exchange across respiratory
membrane is efficient due to:
• Differences in partial pressure
• Small diffusion distance
• Lipid-soluble gases
• Large surface area of all alveoli
• Coordination of blood flow and airflow
Diffusion and respiratory function

33. Gas Pickup and Delivery

34. An Overview of Respiratory Processes and
Partial Pressures in Respiration

35. Gas Exchange in the Lungs and Tissues: Oxygen

36. Gas Transport in the Blood: Oxygen
• dissolved in
plasma (2%)
• in combination
with hemoglobin
(Hb)( 98%)
Blood holds O2
reserve
Oxygen is transported
from alveoli to the tissue by blood
in two forms:

37. Hemoglobin Transport of Oxygen
• 4 binding sites per Hb molecule
• 98% saturated in alveolar arteries
• More unloaded with more need
• 75% in reserve at normal activity

38. Hemoglobin Saturation Curve

39. • Temperature, pH, PCO2, and DPG
• Increase of temperature, PCO2, and DPG and
decrease of pH :
• Decrease hemoglobin’s affinity for oxygen
• Enhance oxygen unloading from the blood
• Decreases of temperature, PCO2, and DPG and
the increase of pH act in the opposite manner
• These parameters are all high in systemic
capillaries where oxygen unloading is the goal
Factors Influencing Hemoglobin Saturation

41. • 7% dissolved in plasma
• 70% carried as becarbonate
• 23% bound to hemoglobin
(carbaminohemoglobin)
Carbon dioxide transport
Co2 is transported
from the tissue to alveoli by blood
in three forms:

42. A Summary of the Gas Transport Mechanisms
Air-Blood barrier

43. A Summary of the Gas Transport Mechanisms
Tissue-Blood Barrier

44. Control of Respiration

45. • Medullary centers
• Respiratory rhythmicity centers set pace
• Dorsal respiratory group (DRG)– inspiration
• Ventral respiratory group (VRG)– forced
breathing
Respiratory centers of the brain

46. • Pons
• Apneustic and pneumotaxic centers:
● regulate the respiratory rate and the
depth of respiration in response to
sensory stimuli or input from other centers
in the brain
Respiratory centers of the brain

47. Respiratory Centers and Reflex Controls

48. Chemoreceptors
• Chemoreceptors are located throughout the
body (in brain and arteries).
• chemoreceptors are more sensitive
to changes in PCO2
(as sensed through
changes in pH).
• Ventilation is adjusted to maintain
arterial PC02 of 40 mm Hg.

49. Medullary Respiratory Centers

50. QUESTIONS
1. Respiration: Definition, Function. The Steps of respiration.
2. Structure of the Conducting zone. Respiratory zone.
3. Site of Gas Exchange: The Alveoli.
4. Lung Volumes and Capacities.
5. Dead space. Anatomic dead space. Functional dead space..
6. Mechanics of Breathing.
7. Sequence of events during inspiration and expiration.
8. Gas exchange. Partial pressure.
9. Diffusion of gases. Form gases in solution.
10. The diagram of the changes in Po2 and Pco2 in the lungs and tissues.
11. O2- hemoglobin dissociation curve.
12. Transport of oxygen in the blood. Form of O2 in the blood.
13. Carbon dioxide transport in blood. Forms CO2 in the blood.
14. Exchange of O2 and CO2 between alveolar air and blood in lung capillaries.
15. Exchange of O2 and CO2 between blood in tissue capillaries and cells in
tissues.
16. Control of breathing.