1. The Respiratory System

2. The Respiratory System
Cells produce energy:
for maintenance, growth, defense, and division
through mechanisms that use oxygen and produce carbon dioxide

3. Oxygen
Is obtained from the air by diffusion across delicate exchange surfaces of lungs
Is carried to cells by the cardiovascular system which also returns carbon dioxide to the lungs

4. 5 Functions of the Respiratory System
Provides extensive gas exchange surface area between air and circulating blood
Moves air to and from exchange surfaces of lungs
Protects respiratory surfaces from outside environment
Produces sounds
Participates in olfactory sense

5. External & Internal Respiration
External Respiration
Mechanics of breathing
The movement of gases into & out of body
Gas transfer from lungs to tissues of body
Maintain body & cellular homeostasis
Internal Respiration
Intracellular oxygen metabolism
Cellular transformation
Krebs cycle – aerobic ATP generation
Mitochondria & O2 utilization

6. Organization of Respiratory System
Nose
Nasal cavities
Paranasal sinuses
Pharynx
Larynx
Trachea
Bronchi and lungs
Bronchioles
Alveoli

8. Airway Branching Trachea Main Bronchi 1 Lobar Bronchus 2
Main Bronchi 1
Lobar Bronchus 2
Segmental Bronchus
3-4
Bronchioles
5-15
Terminal Bronchioles 16
Resp. Bronchioles
17-19
Alveolar Ducts
20-22
Alveolas Sacs 23
Source: SEER Training Website (training.seer.cancer.gov)

10. Alveoli ~ 300 million air sacs (alveoli). 2 types of cells:
Large surface area (60–80 m2).
Each alveolus is 1 cell layer thick.
2 types of cells:
Alveolar type I:
Structural cells.
Alveolar type II:
Secrete surfactant.

11. Alveolar Organization
Respiratory bronchioles are connected to alveoli along alveolar ducts
Alveolar ducts end at alveolar sacs:
common chambers connected to many individual alveoli

12. Respiratory Mechanics
Multiple factors required to alter lung volumes
Respiratory muscles generate force to inflate & deflate the lungs
Tissue elastance & resistance impedes ventilation
Distribution of air movement within the lung, resistance within the airway
Overcoming surface tension within alveoli

13. The Breathing Cycle Airflow requires a pressure gradient
Air flow from higher to lower pressures
During inspiration alveolar pressure is sub-atmospheric allowing airflow into lungs
Higher pressure in alveoli during expiration than atmosphere allows airflow out of lung
Changes in alveolar pressure are generated by changes in pleural pressure

14. diaphragm-most important External intercostals Accessory muscles :
Muscles of inpiration
Muscles of expiration
diaphragm-most important
External intercostals
Accessory muscles :
Sternocleidomastoid
Serratus anterior
scaleni
Abdominal recti
Internal intercostal muscles

15. The Respiratory Muscles
Most important are:
the diaphragm
external intracostal muscles of the ribs
accessory respiratory muscles:
activated when respiration increases significantly

16. The Respiratory Muscles
Figure 23–16c, d

17. The Mechanics of Breathing
Inspiration:
always active
Expiration:
active or passive

18. 3 Muscle Groups of Inspiration
Diaphragm:
contraction draws air into lungs
75% of normal air movement
External intracostal muscles:
assist inhalation
25% of normal air movement
Accessory muscles assist in elevating ribs:
sternocleidomastoid
serratus anterior
pectoralis minor
scalene muscles

19. Muscles of Active Expiration
Internal intercostal and transversus thoracis muscles:
depress the ribs
Abdominal muscles:
compress the abdomen
force diaphragm upward

20. Movement of Thorax During Breathing Cycle

21. Movement of Diaphragm

22. Pleura and Pleural Cavities
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.

23. Pleural Cavities
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.
Pleural effusion – pleuritis with too much fluid

24. Intrapleural Pressure
Pressure in space between parietal and visceral pleura
Averages —4 mm Hg
Maximum of —18 mm Hg
Remains below Patm throughout respiratory cycle

25. Intrapulmonary Pressure
Also called intra-alveolar pressure
Is relative to Patm
In relaxed breathing, the difference between Patm and intrapulmonary pressure is small:
about —1 mm Hg on inspiration or +1 mm Hg on expiration

26. Transpulmonary Pressure
The pressure difference between the alveolar pressure & pleural pressure on outside of lungs
The alveoli tend to collapse together while the pleural pressure attempts to pull outward
The elastic forces which tend to collapse the lung during respiration is Recoil Pressure

27. Physical Properties of the Lungs
Ventilation occurs as a result of changes in lung volume of given pressure difference
Physical properties that affect lung function:
Compliance.
Elasticity.
Surface tension.

28. Compliance Compliance describes the dispensability of the system
Ease with which the lungs can expand
Thus the lung compliance describes how volume changes for the given change in pressure
Change in lung volume per change in transpulmonary pressure.
DV/DP

29. Compliance of the lungs
Measurement of lung compliance requires simultaneous measurement of lung pressure & volume .

30. Compliance of the lungs(continued)
The characteristics of the compliance diagram are determined by the elastic forces of the lungs .these can be divided into two parts
Elastic forces of lung tissue itself
Elastic forces caused by surface tension .

31. Surface Tension
Force exerted by fluid in alveoli to resist distension.
Lungs secrete and absorb fluid, leaving a very thin film of fluid.
This film of fluid causes surface tension.
The attractive forces between adjacent molecules of liquid are stronger than forces between molecule of liquid and a molecule of gas in the alveoli
H20 molecules at the surface are attracted to other H20 molecules by attractive forces.
Force is directed inward, that tends to collapse the alveoli

32. Surface Tension (continued)
Law of Laplace:
Pressure in alveoli is directly proportional to surface tension; and inversely proportional to radius of alveoli.
Pressure in smaller alveolus would be greater than in larger alveolus, if surface tension were the same in both.
Insert fig

33. Surfactant
Surfactant is surface active agent in water that greatly reduces the surface tension .
Secreted by type II alveolar epithelial cells , it lines the alveoli & reduces their surface tension.
Complex mixture of phospholipids, dipalmotylphophotidylcholine & surfactant apoprotien

34. Role of surfactant

35. Role of surfactant Surfactant provides two functions
Reduces the surface tension thereby reducing the collapsing forces in alveoli
It increases the lung compliance .
In neonatal distress syndrome, surfactant is lacking
Surfactant not begin to secret normally before gestational ages of 24 to 28 week

36. 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

37. tidal volume — anatomic dead space  respiratory rate
Alveolar Ventilation
Amount of air reaching alveoli each minute
Calculated as:
tidal volume — anatomic dead space  respiratory rate
Alveoli contain less O2, more CO2 than atmospheric air:
because air mixes with expiration air

38. Alveolar Ventilation Rate
Determined by respiratory rate and tidal volume:
for a given respiratory rate:
increasing tidal volume increases alveolar ventilation rate
for a given tidal volume:
increasing respiratory rate increases alveolar ventilation

39. 4 Calculated Respiratory Capacities
Inspiratory capacity:
tidal volume + inspiratory reserve volume
Functional residual capacity (FRC):
expiratory reserve volume + residual volume
Vital capacity:
expiratory reserve volume + tidal volume + inspiratory reserve volume
Total lung capacity:
vital capacity + residual volume

40. Diffusion of Gases

41. Gas Movement due to Diffusion
Diffusion - movement of gas due to molecular motion, rather than flow.
Akin to the spread of a scent in a room, rather than wind.
Random motion leads to distribution of gas molecules in alveolus.

42. Gas Movement due to Diffusion
Source: Jkrieger (wikimedia.org)

43. Diffusion Driven by concentration gradients:
differences in partial pressure of the individual gases.
Movement of O2 and CO2 between the level of the respiratory bronchiole and that of the alveolar space depends only on diffusion.
The distances are small, so diffusion here is fast.

44. Diffusion of Gas Through the Alveolar Wall
Alveolar airspace
Pathway of diffusion
Source: Undetermined

45. Diffusion of Oxygen Across the Alveolar Wall
Pulmonary Surfactant
Diffuses/Dissolves
Alveolar Epithelium
Diffuses/Dissolves
Alveolar Interstitium
Diffuses/Dissolves
Capillary Endothelium
Diffuses/Dissolves
Plasma
Diffuses/Dissolves
Red Blood Cell
Binds
Hemoglobin

46. Fick’s Law for Diffusion
Vgas = A x D x (P1 – P2) T
Vgas = volume of gas diffusing through
the tissue barrier per time, in ml/min
A = surface area available for diffusion
D = diffusion coefficient of the gas (diffusivity)
T = thickness of the barrier
P1 – P2 = partial pressure difference of the gas

47. Gas Exchange Occurs between blood and alveolar air
Across the respiratory membrane
Depends on:
partial pressures of the gases
diffusion of molecules between gas and liquid

48. Oxygen Transport
Due to low solubility, only 1.5 % of oxygen is dissolved in plasma
98.5 % of oxygen combines with hemoglobin

50. Each Hb consists of a globin portion composed of 4 polypeptide chains
Each Hb also contains 4 iron containing pigments called heme groups
Up to 4 molecules of O2 can bind one Hb molecule because each iron atom can bind one oxygen molecule
There are about 250 million Hb hemoglobin molecules in one Red Blood Cell
When 4 oxygen molecules are bound to Hb, it is 100% saturated, with fewer, it is partially saturated
Oxygen binding occurs in response to high partial pressure of Oxygen in the lungs

51. Oxygen + Hb  Oxyhemoglobin (Reversible)
Cooperative binding  Hb’s affinity for O2 increases as its saturation increases (similarly its affinity decreases when saturation decreases)
In the lungs where the partial pressure of oxygen is high, the rxn proceeds to the right forming Oxyhemoglobin
In the tissues where the partial pressure of oxygen is low, the rxn reverses. OxyHb will release oxygen, forming again Hb (or properly said deoxyhemoglobin)

52. Hemoglobin Saturation Curve

53. BOHR EFFECT

54. Bohr Effect
Bohr Effect refers to the changes in the affinity of Hemoglobin for oxygen
It is represented by shifts in the Hb-O2 dissociation curve
Three curves are shown with progressively decreasing oxygen affinity indicated by increasing P(50)

55. SHIFT to the RIGHT
Decreased affinity of Hb for Oxygen
Increased delivery of Oxygen to tissues
It is brought about by
Increased partial pressure of Carbon Dioxide
Lower pH (high [H+])
Increased temperature
Increased levels of 2,3 DPGA
Ex: increased physical activity, high body temperature (hot weather as well), tissue hypoxia (lack of O2 in tissues)

56. SHIFT to the LEFT
Increased affinity of Hb for Oxygen
Decreased delivery of Oxygen to tissues
It is brought about by
Decreased partial pressure of Carbon Dioxide
Higher pH (low [H+])
Decreased temperature
Decreased levels of 2,3 DPGA
Ex: decreased physical activity, low body temperature (cold weather as well), satisfactory tissue oxygenation

57. The Effect of pH and Temperature on Hemoglobin Saturation

58. A Functional Comparison of Fetal and Adult Hemoglobin

59. Carbon Dioxide Transport
Produced by cells thru-out the body
CO2 diffuses from tissue cells and into the capillaries
7% dissolves in plasma
93% diffuses into the Red Blood Cells
Within the RBC ~23% combines with Hb (to form carbamino hemoglobin) and ~ 70% is converted to Bicarbonate Ions which are then transported in the plasma

60. In the lungs, which have low Carbon Dioxide partial pressure, CO2 dissociates from CarbaminoHemoglobin, diffuses back into lungs and is exhaled
Within the RBC, CO2 combines with water and in the presence of carbonic anhydrase it transforms into Carbonic acid
Carbonic acid then dissociate into H+ and HCO3-
In the lungs CO2 diffuses out into the alveoli. This lowers the partial press. Of Co2 in blood, causing the chemical reactions to reverse

62. Summary: Gas Transport
Figure 23–24

63. Control of Respiration

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

65. Respiratory centers of the brain
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

66. Respiratory Centers and Reflex Controls

67. Mechanism of rhythmic breathing

68. Respiratory reflexes Hering-breuer reflexes
Hering-breuer inflation reflex
Hering-breuer deflation reflex
Reflex from lung irritant receptors
Reflex from J receptors

69. Chemical regulation of respiration
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.

70. Central chempreceptors
Peripheral chemoreceptors
Presence of hypoxia together with rise in pCO2
Hypoxia

71. Medullary Respiratory Centers