1. Respiratory System Aim:
Gas exchange: O2 to the cells & CO2 out of the body.
Regulation of pH of extracellular fluid
Respiration: the different processes by which we finally obtain energy from different food stuffs

2. Respiration processes includes:
1- external respiration:
a) pulmonary ventilation; gas exchange between lung & atmosphere
b) pulmonary respiration; gas exchange between alveoli & blood
2- gas transport; O2 & CO2 transport in the blood & body fluids to & from the cells
3- internal respiration:
a) gas exchange between cells & tissue fluids
b) chemical reactions that end by release of energy

5. Mechanics of respiration
The lungs are enclosed in an air tight compartment & the only connection with atmosphere is through the mouth & nose The lungs are surrounded by minute space called pleural space that contains a film of fluid to lubricate the movement of the lungs The pleural space is lying between 2 layers of pleura; visceral pleura, attached to the lungs & parietal pleura lining the inner surface of thoracic cage and diaphragm The chest wall is formed of muscles, ribs, vertebrae, skin & subcutaneous tissue

6. Figure 22.12

7. The diaphragm
The diaphragm is a muscle, separates the thoracic cavity from the abdomen
When relaxed……. Dome shape
When contract…… It descends & become less convex

9. The ribs are connected with two layers of muscles:
External intercostal: pass downwards & forwards
Internal intercostal: pass downwards & backwards

11. When external intercostal ms contract…
When external intercostal ms contract….. They raise the upper ribs & sternum…….. Increasing the antero-posterior diameter of the chest….. 23 – 30% of volume change and slightly the transverse diameter…1-2%
When diaphragm contracts…….becomes less convex, pushes the abdominal viscera downwards…….. Increases the vertical diameter of the chest ….70% of the increase in volume

12. V2 V1 V1 < V2 Vb Va Va < Vb descent of diaphragm
elevation of rib cage V1 V2 Va Vb
V1 < V2
Va < Vb

14. Intra-alveolar pressure
These changes in the intra alveolar pressure are caused by Changes in the Volume of the lungs.
At the end of expiration with the glottis open, it is atmospheric
During inspiration, the chest size increases, the pressure falls below atmospheric(-1), air will flow into the lungs
During expiration, the lung recoils, the intra-alveolar pressure rises above atmospheric (+1), air flows out of the lungs.

15. Normal Breathing Cycle

16. The Intrapleural Pressure
Def: It is the pressure inside the pleural sacs Value: It is always Negative. at the end of normal expiration: -2 at the end of normal inspiration: -6 to -8 --During forced inspiration: -30 to During forced expiration with the glottis closed +50 (Valsalva experiment) *Functions of the intra pleural pressure 1-It helps lung expansion. 2-It helps venous and lymphatic return. *Causes of negativity of intrapleural pressure: Tendency of the lung to recoil and tendency of the chest to expand. At equilibrium, these two opposing forces lead to the negativity of intrapleural pressure Causes of the tendency of the lung to recoil 1)Elastic tissues in the lungs 2)The surface tension of the fluid lining the alveoli. At the air water interface, the attractive forces between the water molecules make the water lining like a stretched balloon that tries to shrink. This force (Surface tension) is strong enough to collapse the alveoli. * If air is introduced into the pleural space: 1- the lung will collapse 2- the chest will expand 3- the intrapleural pressure increases, becomes atmospheric 4- venous return decreases

19. Intrapleural pressure

20. Pneumothorax

21. Mechanism of air flow between lungs and atmosphere
Stimulation of the phrenic nerve, and the intercostal nerves… contraction of diaphragm & external intercostals…. Increasing the vertical & antero-posterior diameter of the chest….. Increase in chest volume …. Decrease intra-pleural pressure.. The lungs expands… decrease intra-alveolar pressure….the air flows into the lungs
It is an active process (involving muscle contraction)

22. Inspiration
The diaphragm and external intercostal muscles (inspiratory muscles) contract and the rib cage rises
The lungs are stretched and intrapulmonary volume increases
Intrapulmonary pressure drops below atmospheric pressure (1 mm Hg)
Air flows into the lungs, down its pressure gradient, until intrapleural pressure = atmospheric pressure

23. Alveolar Pressure Changes

24. Inspiration
Figure

25. Expiration
When inspiration ends, the muscles relax…. Decrease in the diameters of the chest…. The thoracic wall recoils …. The intra-pleural pressure rises…the elastic lungs recoil… compressing the air… rising of the intra-alveolar pressure… air is forced out
It is a passive process (relaxation of muscles & recoil of elastic fibers)

26. Expiration
Figure

28. Accessory muscles of respiration
During quiet breathing, only 1/10 of the external intercostal muscles & diaphragm are active & expiration is a passive process
With more powerful respiration, all fibers of intercostal & diaphragm are active, this increases the pulmonary ventilation 10 folds
More forced respiration, there is accessory ms of inspiration (sternomastoid, serratus anterior, scaleni) & expiration (internal intercostal, abdominal recti ms), these make respiration more deep & decrease airway resistance

29. Ventilation
It is the movement of air between lungs & atmosphere

30. Lung volumes Lung volumes:
1- Tidal volume (TV or Vt): it is the volume of air inspired or expired each cycle during normal quiet breathing, it is 500 mL
2- Inspiratory reserve volume (IRV): it is the maximum volume of air can be inspired after normal inspiration, it is 3000 mL
3- Expiratory reserve volume (ERV) it is the maximum volume of air can be expired after normal expiration, it is 1100 mL
4- Residual volume (RV): it is the volume of air remaining in the lungs after maximal expiration, it can not be expired, it prevent lung collapse & aerates the blood between breaths, it is 1200 mL

32. Spirometer and Lung Volumes/Capacities

33. Lung volumes
Vital capacity (sum total of all except RV)

34. Lung capacities A capacity is two or more volumes added together
1- Inspiratory capacity (IC): it is the maximum volume of air can be inspired after normal expiration.
IC= TV+ IRV= 3500mL
2- Functional residual capacity (FRC): it is the volume of air remained in the lung after normal expiration
FRC=ERV+RV= 2300mL.

35. Lung capacities
3-Vital capacity: (VC) it is the maximum volume of air can be expired after maximal inspiration.
VC=IRV+ERV+TV=4600mL
Total lung capacity: (TLC) it is the volume of air contained in the lung after deep inspiration.
TLC=IRV+ERV+TV+RV= 5800mL
All lung capacities are 20-25% more in males than females, more in athletes, less in recumbent position

36. Work of Breathing
Energy required during normal respiration is 2-3% of the total energy expenditure, it increases in heavy exercise, but the ratio to total energy expenditure remains nearly the same.
Work is done only in inspiration, but normal expiration is a passive process depending on the elastic recoil of the lung and chest wall.
*Contraction of expiratory muscles occurs when air way resistance or tissue resistance increases as in asthma. (expiration needs work)

37. Work of breathing
Energy are needed for contraction of respiratory muscles. Increase when accessory ms contracts in deep& forced breathing
1- overcome the viscosity of the expanding lung (non elastic tissue resistance)
2- stretch the thoracic & lung elastic fibers & overcome the surface tension in the alveoli. This energy increase if surfactant is deficient
3- overcome airway resistance. This increase in bronchial asthma or obstructive emphysema

38. Compliance It is the ability to expand or stretch
It is the reciprocal of elasticity (recoil of stretched elastic fibers)
It is a useful measurement for diagnosis of respiratory diseases
It is the change in length or volume per unit change in stretching force.
Normal compliance of lungs & thorax = 0.11L/cmH2O pressure
Normal compliance of lungs alone = 0.2 L/cmH2O pressure

39. Compliance
High compliance means a given change in pressure moves a larger volume of air in the lungs
Low compliance in fibrosis, congestion, oedema, bronchial obstruction or in increased surface tension
The compliance is small in newborn, increases gradually with age, decreases in old age
The main factors affect compliance are: congestion, size, surface tension

40. 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.
H20 molecules at the surface are attracted to other H20 molecules by attractive forces.
Force is directed inward, raising pressure in alveoli.

41. Surfactant Def: It is the surface active agent
Composition: Phospholipid (dipalmitoyl lecithin), protein and Carbohydrates
Secretion: produced by alveolar type II cells.
Action: Lowers surface tension.
Functions of surfactant:
Facilitates lung expantion
Prevent lung collapse As alveoli radius decreases, surfactant’s ability to lower surface tension increases.
Prevent pulmonary oedema
Surfactant Deficiency:
RDS of the newborn. The lung is rigid and oedematous and the alveoli collapse

43. What is surface tension?
air
What is surface tension?
How do we deal with surface tension??

44. Alveolar Ventilation The inspired air is distributed between:
1- The anatomical Dead Space: It is the part of the respiratory system where no gas exchange takes place. It extends from the mouth to the terminal bronchioles. Ventilation of dead space is said to be wasted ventilation.=1/3 of the resting tidal volume
2- the rest of air occupies the respiratory bronchioles, the alveolar ducts, alveoli and alveolar sacs, gas exchange takes place
Minute Ventilation= VT (ml/breath) x Respiratory rate (breath/min) =500 x 12
=6000 ml/min.
Alveolar ventilation= 2/3 x 500 x12
=4000 ml/min.
Dead space ventilation= 1/3 x 500 x 12
= 2000ml/min.

47. Measurement of the dead space
Bohr`s equation:
Anatomical dead space= tidal volume x (alveolar CO2- expired CO2)
Alveolar CO2

48. Physiological dead space
The anatomical dead space + unperfused alveoli
In Normal person the anatomical dead space= the physiological dead space
In certain diseases the physiological dead space may be 10 times anatomical dead space or more.

49. Gas exchange
Alveolar air contains less O2 & more CO2 than inspired air (mixed with air that was in the dead space)
Expired air constitute a mixture of alveolar air and dead space (which is atmospheric)
The exchange of oxygen & CO2 between alveoli & blood is passive by diffusion

50. Comparison between the respiratory gases
Expired air
Alveolar air
atmospheric air
120mmHg
104mmHg
159mmHg O2
27mmHg
40mmHg
0.3mmHg
CO2
47mmHg
variable
H2O
566mmHg
569mmHg
597mmHg N2
760mmHg
Total pressure

51. Gas exchange
O2 of air is higher in the lungs than in the blood, O2 diffuses from air to the blood.
C02 moves from the blood to the air by diffusing down its concentration gradient.
Gas exchange occurs entirely by diffusion.
Diffusion is rapid because of the large surface area and the small diffusion distance.

54. Diffusion is determined by several factors:
1- Alveolar- capillary membrane:
Semi-permeable: separates alveolar air from pulmonary capillary blood
Layers:
Fluid film lining the alveoli
Alveolar membrane
Interstitial fluid
Capillary wall

55. Total AREA available for diffusion of gases is large
The respiratory membrane:
Total AREA available for diffusion of gases is large
in human 70 m2
Diffusion PATH LENGTH is very small, =2µm
Pulmonary Epithelium

56. 2- Partial pressure gradient of gases across the alveolar capillary membrane:
The partial pressure of oxygen in mixed venous blood is 40mmHg
The partial pressure of oxygen in alveolar air is 100mmHg
O2 diffuses from the alveoli to the capillary blood along a partial pressure gradient of 60mmHg
The partial pressure of CO2 in mixed venous blood is 46mmHg
The partial pressure of CO2 in alveolar air 40 mmHg
CO2 diffuses along pressure gradient of 6 mmHg

57. 3- the physical properties of gases:
Solubility: the more soluble the gas, the faster its diffusion (CO2 is 23 fold more soluble than O2)
Molecular weight: the higher the molecular weight of the gas, the slower its diffusion
The solubility of a gas & its MW determine diffusion coefficient (the rate of diffusion through a unit area of a given membrane per unit pressure difference.
Diffusion coefficient = solubility / √molecular size
The diffusion coefficient of O2 = 1.0
The diffusion coefficient of CO2 = 20
CO2 can diffuse 20 times faster than O2
Diffusion failure affects O2 before affecting CO2
4- surface area of the alveolar capillary membrane: 70square meter
When increased, gas exchange increases

58. 5-Ventilation- blood flow ratio:
Effective surface area means the functional alveoli in contact with functioning capillaries, where the alveolar air comes in contact with capillary blood
Ventilation / perfusion ratio = alveolar ventilation/ pulmonary blood flow
In a normal adult male at rest
Alveolar ventilation is 4L/min
Pulmonary blood flow is 5L/min
Ventilation / perfusion ratio=0.8
Diseases that affects the alveolar capillary membrane will lower the diffusion capacity of O2
Fatal levels of O2 diffusion impairment is reached long before CO2 diffusion is affected

59. Exchange of gases Alveolar air Atmospheric air pressure % 40mmHg 5.6%
0.04%
CO2
105mmHg
14.8%
159mmHg
20.95% O2
568mmHg
79.6%
600mmHg
79.00% N2

61. Gas Transport by The Blood
Oxygen transport:
O2 is transported in the blood in two forms:
1- Attached in loose combination with Hb
Over 98% of arterial O2 is carried in the form of oxyhemoglobin. PO2 in systemic arterial blood is usually below 100mmHg eventhough it may be 100mmHg in the pulmonary capillary blood, because some venous blood mixes with arterial blood
2- Physically dissolved: less than 2% of O2 in the arterial blood. At PO2 100mmHg, about 0.3ml O2 dissolve in 100ml blood. In venous blood, PO2 is 40mmHg, about 0.12ml O2 /100ml blood is dissolved.

62. Oxyhaemoglobin Haemoglobin has great affinity for O2
It combines loosely & reversibly with O2 by process called oxygenation (not oxidation)
The reaction is very fast, less than 10 msec
The reaction increases with the increase in PO2
The relation between oxyHb formation and PO2 is studied in the Oxyhaemoglobin dissociation curve

63. Hemoglobin Each hemoglobin has 4 polypeptide chains and 4 hemes.
In the center of each heme group is 1 atom of iron that can combine with 1 molecule 02.
Fe remains in the ferrous form (Oxygenation and not oxidation)
Hb carries 65 times as much as plasma at PO2 of 100mmHg
Insert fig
Figure 16.32

64. Hemoglobin dissociation curves:
Def:It is a relationship between PO2 and %HbO2 saturation (and not content)
Characteristics:
1-It is not linear, it is sigmoid (S shaped) with flat part and steep part.
Causes of S shaped curve
Hb is formed of 4 sub units which load or unload with different affinity.
Oxygenation of one haem unit leads to configurational change in the Hb molecule, increasing affinity of the second, and oxygenation of the 2nd , increasing affinity of the 3rd ,etc..
The dissociation curve starts slowly, but rapidly gained sigmoid shape
2-there is steep rise in the percentage saturation of Hb between PO2 0& 75mmHg
3- above 75mmHg, there is slow rise of the curve, becoming more or less flat at PO2 of 80mmHg

67. 1gm of Hb binds up to 1.34ml O2
The partial pressure of O2 in the arterial blood is about 95mmHg,Hb is 97% saturated (Hb concentration is 150gm/L, O2 content is 195ml/l of blood)
At PO2 40mmHg, Hb saturation is 75% saturated.
At rest, Arterio-venous difference (O2 uptake by tissues) is about 40-45ml /L of blood
During exercise, oxygen uptake by tissues increase, PO2 drops to 15 mmHg, % saturation 20%, O2 content=40ml
During exercise, the arterio-venous O2 difference, 150ml/L
Quantity of O2 carried in a volume of blood is dependent on PO2 & Hb concentration.

69. Factors which affect Oxy-Hb dissociation curve
Shift to the right: (facilitate the release of O2 at tissues) →↓ affinity of Hb for O2→ easier giving O2 to the tissues
1- ↑ PCO2: Bohr effect
2-↓ pH :due to lactic acid during exercise, more CO2 production
3-↑ temperature: active tissues during oxidative processes more heat is released, more O2 supply to the tissues
4- ↑ 2,3 DPG: found in RBCs & increases in cases of hypoxia & high altitudes

70. S-shaped hemoglobin curve
Advantages of “S-shaped” curve for Hb-O2 association 20
High affinity only
Can’t release much
O2 to tissues 15
S-shaped hemoglobin curve
Releases much Becomes saturated
O2 at tissues with O2 at lungs
ml O2/100 ml blood 10
Low affinity only
Doesn’t hold on to But can’t pick up
much O2 at tissues much O2 at lungs 5
Active cell

72. Factors shift the curve to the left: (increases Hb affinity to O2, Easier picking up O2, Difficult release of O2)
1- ↓ PCO2 at lungs
2- ↑pH
3- ↓ temperature
4- foetal Hb: as it binds to 2,3 DPG less effectively

73. Dissolved O2:
↑ PO2….↑ dissolved O2
O2 is poorly soluble
In 100ml blood, 0.003ml O2 dissolve /1mmHg PO2
In arterial blood, 0.3 ml/100ml
In venous blood, 0.12 ml/100ml
The dissolved O2 is at equilibrium with the O2 combined with Hb
It is the dissolved O2 gets transferred to tissues & become replaced from O2 carried by Hb
Although dissolved O2 is less than 2% of total O2 transport, it is essential for tissues that do not have blood supply, as cartilage & cornea which depend on O2 dissolved in tissue fluids
↑ dissolved O2 by breathing pure or hyperbaric O2 (this is the base of O2 therapy)

74. CO2 transport
It is transported from tissues that produce CO2 to the lungs, where it is unloaded, removed to the atmosphere
It is transported by plasma & RBCs

75. Transport of CO2 in the blood:
1- dissolves in the plasma & RBCs: 5%, it is important because it determines the tension (40mmHg in arterial blood & 46 mmHg in venous blood) & determine the direction of flow
2- chemically combined: 95% of CO2
a-carbamino compounds: carried by plasma proteins & hemoglobin
b- bicarbonates:
In the form of KHCO3 & NaHCO3
43ml/100ml in arterial blood
56ml/100ml in venous blood

76. Tidal CO2 transport
It is the volume of CO2 added to each 100ml of arterial blood during its flow through the tissues
CO2 produced by active cells as a result of metabolism
Normally 4ml/100ml blood during rest (52-48)
CO2 carried in 3 forms in plasma:
1- dissolves in the plasma
2- Bicarbonates:
3- Carbamino proteins:

77. How is CO2 carried by the blood?? Plasma: dissolved HCO3-
Tissues
CO2
HbO2  Hb.H + O2 +
C.A.
slow
CO2 + H2O  H2CO3  H+ + HCO3- O2
HCO3-
Hb + CO2 Hb.CO2 (carbamino cmpd.)
How is CO2 carried by the blood??
Plasma: dissolved
HCO3-
carbamino proteins
RBCs: dissolved
Carbamino Hb

78. Control of ventilation
Mechanism of regulation involves:
Nervous & chemical
The respiratory centre:
In the medulla & pons.
Can be divided into 4 groups;
1- dorsal respiratory group: (Rhythmicity centre)
In the medulla, they are inspiratory neurons, they discharge rhythmically during resting & forced inspiration
2- ventral respiratory group:( expiratory neurons)
In the medulla, they are inactive during resting breathing
Activated in forced ventilation as in exercise

79. 3- Apneustic centre:
In the pons
It sends excitatory impulses to dorsal respiratory group, potentiates the inspiratory drive. Section to remove the apneustic impulses…. Gasping breathing( shallow inspiration followed by long expiration)
Receives inhibitory impulses from vagus nerve during inflation of the lungs (Hering Breuer reflex)
Receives inhibitory impulses from Pneumotaxic centre in the upper pons
Section of vagus & abolishing the impulses from pneumotaxic centre, results in apneustic breathing (prolonged inspiration)

80. 4-Pneumotaxic centre: in the upper pons
It sends inhibitory impulses to apneustic center & to inspiratory areas to switch off respiration

82. Both inspiratory & expiratory areas are influenced by impulses from pneumotaxic & apneustic center & higher centers
DRG are the integrating site for different inputs

83. Nervous control of ventilation
The rhythmicity centre sends sends excitatory impulses via phrenic & intercostal nerves to diaphragm, external intercostal muscles
The rhythmicity center receives impulses from higher brain centers, brain stem, special receptors
Higher brain centers:
1- impulses from cerebral cortex: voluntary hyperventilation, voluntary apnea
2- impulses from cerebellum: coordinates breathing with other activities as swallowing, talking, coughing
3- Impulses from hypothalamus: centers of emotions & temperature regulation, breathing modified during emotional stress, changes of temperature, (panting of dogs)

84. Centers in the medulla & pons:
1- the rhythmicity center interconnected with the cardiac & vasomotor centers located in the medulla
2- apneustic center sends excitatory impulses to rhythmicity center to produce deep inspiration
3- pneumotaxic center to rhythmicity center to inhibit deep inspiration & to apneustic center

85. Special receptors:
1- sensory vagal fibers: when lung is inflated, stretch receptors are stimulated, send inhibitory impulses through vagus to inhibit the apneustic center (Hering Breuer inflation reflex) protects the lung from over-inflation. There is a weaker Hering Breuer deflation reflex
2- active & passive movement of joints & muscles: propioceptive stimulation stimulate breathing in exercise
3- skin receptors: noxious stimuli stimulate breathing
4- baroreceptors in aortic arch & carotid sinus modify breathing

86. Chemical control of ventilation
Central & peripheral chemoreceptors:
Peripheral chemoreceptors:
Site: in the carotid & aortic bodies
Stimuli: ↓ in arterial PO2, ↑PCO2, ↓pH
Stimulation: send stimulatory impulses to rhythmicity center via glossopharyngeal & vagus nerves

87. Central chemoreceptors
Site: medulla
Stimuli: H+ ion concentration in the CSF
H+ ion can not cross the blood brain barrier, but it increases in the CSF secondary to ↑PCO2 in the blood, which pass through BBB to the CSF
It sends simulatory impulse to stimulates ventilation

88. Plasma BBB CSF CO2 HCO3 + H+ CO2  HCO3 + H+ When pHCNS
returns to norm
(HCO3 pumped out)
VE is less restrained
Respiratory
Alkalosis
high pHCSF limits
Hyperventilation

89. Chemoreceptors Monitor changes in blood PC02, P02, and pH. Central:
Medulla.
Peripheral:
Carotid and aortic bodies.
Control breathing indirectly.
Insert fig
Figure 16.27

90. Hypoxia It means deficient O2 supply to the tissues Causes:
1- interference with O2 in the lungs
2- interference with O2 transport in blood
3- interference with O2 delivery to the tissues

91. Hypoxia Types: 1- hypoxic hypoxia: low PO2 in the arterial blood
2- anaemic hypoxia: lowering O2 carrying capacity of the blood
3- stagnant hypoxia: slow circulation
4- histotoxic hypoxia: disturbed uptake of O2 by tissues
Treatment:
O2 therapy, correcting underlying cause

92. Hypoxic hypoxia
Causes: Any interference with normal oxygenation of the arterial blood leading to low PO2 as in:
1- low atmospheric PO2 as in high altitude
2- ventilation defects: as in paralysis of respiratory ms, airway obstruction, poisons that inhibits the
respiratory center as morphine & barbiturates (high CO2)
2- interfere with normal O2 diffusion in the lung
3- mixing of arterial blood with venous blood as in veno-arterial shunts & congenital heart disease
Low PO2, low % saturation of Hb, low O2 content in the arterial &venous blood

93. Anaemic hypoxia Causes: anaemia, abnormal hemoglobins, CO poisoning
PO2 is normal in the arterial &venous blood
% saturation is normal in the arterial &venous blood
(except in CO poisoning)
Low O2 content in the arterial &venous blood

94. Stagnant hypoxia Types:
1- localized: e.g. disturbed circulation in a limb
2- generalized as in heart failure
normal arterial blood PO2, % saturation,O2 content
↓Venous blood PO2, ↓ % saturation, ↓Content of O2

95. Histotoxic hypoxia
Disturbance of O2 uptake due to poisoning of cellular enzymes e.g. cyanide poisoning or tissue oedema
normal arterial blood PO2, % saturation,O2 content
↑Venous blood PO2, ↑% saturation, ↑Content of O2

96. Venous blood Arterial blood Types of hypoxia %O2 %sat PO2 low Hypoxic
normal
Anaemic
Stagnant
high
histotoxic

97. Cyanosis Def: blue coloration of the skin & mucous membrane
Cause: reduced Hb more than 5gm/100ml
Types:
Localized type: in the tips of fingers in cold
Generalized: in veno-arterial shunts, severe hypoxia in the newborn, or at very high altitude
It is more common seen in polycythemia
it s very rare in anaemia (the person already has low Hb, so he cannot have 5gm reduced Hb)