Dr: Ayub Abdulcadir Sheikh:
Postgraduate MBBS, at University of Somalia.
Resident physician at Sureya Medical Center.
A lecturer physiology at Frontier University.
To all my family especially may parents (Allah may bless you), also my student
in frontier university.
TABLE OF CONTENTS
1. Introduction to Respiratory system ……………………...……………..…………. 1 - 2
2. Mechanism of Respiration …………………………………………………….…… 3 - 4
3. Lung Volume and capacity changes ………………………………………………...… 5
4. Pulmonary Circulation ……………………………….……………………………...… 6
5. Diffusion of gases across respiratory membrane …….………………………...…..… 7
6. Transport of Gases (O2 & CO2) …………………………………………….…….. 8 - 10
7. Regulation Of Respiration …………………………………………...……….… 11 – 15
8. High altitude, Avian, Space physiology …………………………………...……. 16 - 17
9. Deep Sea Physiology ………………………………………………...…………… 17 - 18
Page 1 of 18
The respiratory system starts from the nose and ends to the alveoli
The lungs are contained in a space with a volume of approximately 4 L (~ 6-8L).
The respiratory system dividedinto:
1. Upper respiratory system: includes all
structures from nose to larynx.
2. Lower respiratory system: includes
trachea, bronchi, and lungs.
The Types Of Respiration:
1. External respiration: that involvesexchange of respiratory gases,
i.e. (oxygen and carbon dioxide between lungs and blood).
2. Internal respiration: that involves exchange of gases between
blood and tissues).
The Phases Of Respiration:
1. Inspiration: air enters the lungs
2. Expiration: air leaves the lungs.
The Stages Of Respiration:
1. Ventilation stage.
2. Transport stage.
3. Exchange stage.
4. Tissue stage.
The Respiratory zone:
1. Conductive zone: no gas
exchange, but humidified
air and prevent foreign
2. Respiratory zone: site for
1. Cough reflexes.
2. Sneezing reflex.
3. Swallowing reflex.
Autonomic nervous system on bronchial conductive zone:
1. Sympathetic “Adrenergic receptor”: Adrenaline (relaxation and
dilation of smooth muscle cells) – Nor adrenaline (decrease
2. Parasympathetic “Cholinergic Muscarinic receptor”:
Acetylcholine (Contraction and Constriction of smooth muscle
cell) – Acetylcholine (increase mucosal secretion).
Mechanism of Cough Reflexes:
1. Pick up to 2.5 liters of air are rapidly
2. The epiglottis closes, and the vocal
cords shut tightly to entrap the air
within the lungs.
3. The abdominal muscles contract
forcefully, pushing against the
diaphragm while other expiratory
muscles, such as the internal
intercostals, also contract
4. The vocal cords and the epiglottis
suddenly open widely, so that air
under this high pressure in the lungs
Page 2 of 18
1. Inner Visceral Layer: that attached
firmly to the surface of the lungs.
2. Outer Parietal Layers: that attaches to
the wall of thoracic cavity.
A. Intrapleural Space or Pleural Cavity:
the narrow space in between the two
layers of pleura.
B. Intrapleural Fluid: thin film of serous
fluid, which is secreted by the visceral
B 1. Serve as lubricant to prevent
friction between two layers of pleura
B2. Serve creating the negative
pressure called intrapleural pressure
within intrapleural space.
Alveolar Cells or Pneumocytes:
A. Type I alveolar cells: Site of gaseousexchange between the
alveolus and blood.
B. Type II alveolar cells: Secrete alveolar fluid and surfactant.
Page 3 of 18
Inspiration & Expiration depends:
A) Changes of these Pressures:
1. intrapleural or intrathoracic pressure.
2. Alveolar or intrapulmonary pressure.
3. Transpulmonary pressure.
B) Respiratory Muscles:
1. Primary & accessory inspiratory muscle.
2. Primary & accessory expiratory muscle.
Two recoils of respiratory system:
1. The Lungs recoil.
2. The chest wall recoils.
Three ways to increase lung volume:
1- Anterioposterior diameter.
2- Vertical diameter.
3- Transverse diameter.
Dalton Law: is the sum of all partial pressure of
gasses equal total pressure.
Atmospheric pressure = 760 mmHg or 1 Atm.
Pressure gradient: is movement of gases from
highest pressure to lowest pressure.
Boyle’s law: whenlung volumes increase the
pressure decrease and vice verse.
Atmospheric pressure = 760 mmHg or 1 Atmosphere.
Intrapulmonary or (intra-alveolar) pressure: during
inspiration less than Atmosphere (-1mmHg), during
expiration more than Atmosphere (=1mmHg).
Intrapleural or (intrathoracic) pressure: normally less
than atmosphere (-4mmHg), during inspiration (-7
mmHg), during expiration (-4mmHg).
Transpulmonary pressure: intrapulmonary pressure –
During normal quiet breathing:
Inspiration is the “active process”.
Expiration is the “passive process”.
Page 4 of 18
Process of Inspiration (quite or heavy state):
1- Contraction of diaphragm, external intercostals
mus., and accessory muscles leads
2- Increases lung volume & decrease pressure.
3- Then the intra-pleural pressure becomes more
negatively from (-4 mmHg to -7mmHg) and
4- The intrapulmonary pressure also decreases
(760 mmHg - 1 mmHg = 759 mmHg) means less
than atmospheric pressure.
5- Due to these changes the air in the
atmosphere will enter the lungs.
Process of Expiration(quite or heavy state):
1. Relaxation of diaphragm, & contraction of internal
intercostals mus., and accessory muscles leads
2. Decrease lung volume & increase pressure.
3. Then the intra-pleural pressure becomes back to
its normal (-4 mmHg) and
4. The intrapulmonary pressure also increase (760
mmHg +1 mmHg = 760 mmHg) means more than
5. Due to these changes the air in the lungs will exit
to the atmosphere.
Compliance: is the ability of the lungs and thorax
to expand or it is the expansibility of lungs and
A. Static and Dynamic compliance.
B. Old age & emphysema increases lung compliance.
C. Kyphosis, pleural fibrosis, paralysis of respiratory
muscles, pleural effusion all will decrease lung
Collapsing Tendency of Lungs:
Tendency of Lungs:
1. Elastic property of lung tissues.
2. Surface tension.
Factors Preventing Collapsing
Tendency of Lungs:
1. Intrapleural pressure.
1. Mixture of several
2. Reduces the surface
tension of water.
3. Defense within the
lungs against infection
WORK OF BREATHING: Is work done by respiratory
muscles during breathing (inspiration) to
overcome the resistance in thorax and respiratory
Three types of resistance:
1. Airway resistance.
2. Elastic resistance of lungs and thorax.
3. Non-elastic viscous resistance.
Page 5 of 18
DEAD SPACE: is some of the air a person
breathes never reaches the gas exchange areas
but simply fills respiratory passages where gas
exchange does not occur, such as the nose,
pharynx, and trachea. Normal range = 150 mL.
1. Tidal volume (TV) = 500ml.
2. Inspiratory reserve (force) volume (IRV) = 1.9 -3.3ml.
3. Expiratory reserve (force) volume (ERV) = 0.7–
4. Residual volume (RV) = 1.1 -1.2ml.
Factors that affects lung
volume andlung capacities are:
E. Level of physical training.
RESPIRATORY MINUTE VOLUME:
Also called; Pulmonary ventilation or
Is the volume of air breathed in and out
of lungs every minute.
Is the amount of air utilized for gaseous
exchange every minute.
TYPES OF DEAD SPACE :
1- Anatomical Dead Space:
It includes nose, pharynx, trachea,
bronchi and branches of bronchi up to
Gaseous exchange does not take place in
2- Physiological Dead Space:
Air in the alveoli, which are non-
Air in the alveoli, which do not receive
adequate blood flow
These two types of respiratory diseases are determined by
lung functions tests; particularly Force Expiratory Volume
FEV (has great diagnostic value).
1- Restrictive respiratory disease: difficulty in inspiration (FEV-
slightly reduced), but expiration not affected.
2- Obstructive respiratory disease: difficulty inexpiration
(FEV- very much decreased).
Page 6 of 18
Lung (pulmonary) vessels:
1- Bronchial artery (High-pressure, low-flow
A. Branch of aorta,
B. Less than aortic pressure.
C. Supplies: trachea bronchus, supportive
connective tissue of lung,& outer coat of vessels.
2- Pulmonary artery (low-pressure, high-flow
A. 1/3 thickness of that aorta.
B. Large compliance, larger diameters.
C. Carries deoxygenated blood from heart to lungs.
3- Lymphatic vessels:
A. Present in all the supportive tissues of the lung.
B. Empties to right thoracic lymph duct
C. Prevent pulmonary edema.
Physiological shunt: A diversion through which the venous blood is
mixed with arterial blood (1-5% of cardiac output).
The Lungs Serve as a Blood Reservoir.
Cardiac Pathology May Shift Blood From the
Systemic Circulation to the Pulmonary Circulation
Increases fluid filtration out of
the pulmonary capillaries.
Impedes pulmonary lymphatic
Page 7 of 18
Diffusion: is simply the random motion of molecules in all directions through
the respiratory membrane and adjacent fluids.
Respiratory (Pulmonary) Membrane:
1) A layer of fluid containing surfactant.
2) The alveolar epithelium.
3) An epithelial basement membrane.
4) A thin interstitial space.
5) A capillary basement membrane.
6) The capillary endothelial membrane.
7) Blood plasma.
8) Red blood cell membrane.
9) Red blood cell cytoplasm.
• For diffusion to occur these factors mast be done:
A. A source of energy provided by the kinetic motion of the molecules.
B. A constant temperature.
“Partial Pressures” of Individual Gases: Is the pressure
of a single type of gas in a mixture of gases.
Henry’s law: is the solubility of gases in a liquid and
Factors that affect the rate of gas diffusion
through the respiratory membrane:
1. The thickness of the membrane.
2. The surface area of the membrane.
3. The diffusion coefficient of the gas
4. The partial pressure difference of the gas
between the two sides of the membrane.
Multiple breaths are required to
exchange most of the alveolar air.
Page 8 of 18
• Transport of oxygen from alveoli to the tissue:
1. As simple physical solution(3%).
2. In combination with hemoglobin (97%) as Oxyhemoglobin.
Poor solubility of oxygen in water content of plasma as in simple
Oxygen Carrying Capacity of Hemoglobin & Blood:
Each Hb can carry 4 oxygen.
One RBC contains 250 million Hb molecules: 250 X 4 =
1 billion oxygen (one RBC).
1g of Hb combines 1.34ml of Oxygen.
100ml of blood contains 15g of Hb, so
15g X 1.34ml/g = 20 ml of oxygen.
OXYGEN-HEMOGLOBIN DISSOCIATION CURVE:
Hemoglobin’s affinity for oxygen.
Under normal conditions, oxygen-hemoglobin
dissociation curve is ‘S’ shaped or sigmoid shaped.
A. Upper part of the curve indicates the uptake of
oxygen by hemoglobin depending upon partial
pressure of oxygen (shift to left).
B. Lower part of the curve indicates dissociation of
oxygen from hemoglobin (shift to right).
Christian Bohr in 1904.
Is the effect by which presence of carbon
dioxide decreases the affinity of hemoglobin
Due to continual metabolic activity in the
tissue there is high P co2 and Low P o2 in
Oxygen dissociation curve is shifted to right.
Page 9 of 18
• Transport of carbon dioxide from tissue to the alveoli:
1. As dissolved form (7%)
2. As carbonic acid(negligible)
3. As bicarbonate (63%)
4. As carbamino compounds (30%).
Carbonic acid is very unstable immediately dissociates into
bicarbonate and hydrogen ions.
CARBON DIOXIDE DISSOCIATION CURVE:
Is the curve that demonstrates the
relationship between the 1) partial pressure
of carbon dioxide and the 2) quantity of
carbon dioxide that combines with blood.
John Scott Haldane in 1860.
Is the effect by which combination of
oxygen with hemoglobin displaces carbon
dioxide from hemoglobin.
Excess of oxygen content in blood & Highly
acidic hemoglobin has low tendency to
combine with carbon dioxide
Carbon dioxide dissociation curve is
shifted to right.
Page 11 of 18
Regulation of Respiration:
Nervous or neural
Nervous or neural
Afferent nerves Respiratory centers Efferent nerves
A. Medullary centers:
1. Dorsal respiratory group of
2. Ventral respiratory group of
B. Pontine centers:
3. Apneustic center
4. Pneumotaxic center.
1. Phrenic nerve fibers (C3,
C4, C5), which supply the
Phrenic nerve: motor,
2. Intercostals nerve fibers
(T1 to T11), which supply
the intercostals muscles.
Intercostals nerve: Right
& Left internal
intercostals , Right & Left
1. Peripheral chemoreceptors
and baroreceptors via
branches of glossopharyngeal
and vagus nerves.
2. Stretch receptors of lungs via
Page 12 of 18
A= MEDULLARY CENTERS:
1. Dorsal Respiratory Group of Neurons:
a) Situated in the nucleus of tractus solitarius
b) Inspiratory neurons and generate inspiratory
c) During quite breathing (2 second inspiration
followed 3 second expiration).
2. Ventral Respiratory Group of Neurons:
a) Present in nucleus ambiguous and nucleus
b) Earlier, expiratory center.
c) Both inspiratory and expiratory neurons.
d) During forced breathing.
B= PONTINE CENTERS:
1. Apneustic Center:
a) Situated in the reticular formation of lower
b) Increases depth of inspiration.
2. Pneumotaxic Center:
a) Situated in the dorsolateral part
of reticular formation.
b) Neurons of medial parabrachial and
subparabrachial (kölliker-fuse) nuclei.
c) Inhibits the apneustic center, so inspiration
stops and expiration starts.
Page 14 of 18
Changesin Chemical Constituents of
Blood which Stimulate Chemoreceptors:
1. Hypoxia (decreased pO2)
2. Hypercapnea (increased pCO2)
3. Increased hydrogen ion concentration.
A) Central Chemoreceptors:
Present in the brain.
Deeper part of medulla oblongata,
close to the (DRGN).
In close contact with blood and
cerebrospinal fluid (CSF).
Sensitive for CO2 , H+
B) Peripheral Chemoreceptors:
Carotid and aortic region (glomus cells).
Sensitive for Oxygen.
• Mechanism action OfGLOMUS CELLS:
Decreased PO2 in blood.
Activation of O2 sensor and closure of K
Entrance of Ca+2
ions and depolarization of
Release of neurotransmitter in synaptic cleft
then taking by sensory fiber to respiratory
Page 15 of 18
• Mechanism action OfCentral Chemoreceptors:
CO2 enters the extracellular fluid of the brain.
CO2also is permeable across the brain-CSF barrier and enters the CSF.
CO2 is converted to H+ and HCO3−, thus increases in arterial PCO2
produce increases in the PCO2 of CSF, which results in an increase in H+
concentration of CSF (decrease in pH).
The central chemoreceptors are in close proximity to CSF and detect the
decrease in pH. A decrease in pH then signals the inspiratory center to
increase the breathing rate (hyperventilation).
Page 16 of 18
High altitude: Is the region of earth located at an altitude of above
8,000 feet from mean sea level.
Partial pressure of gases, particularly oxygen proportionally
Carbon dioxide in high altitude is very much negligible and it does
not create any problem.
CHANGES IN THE BODY AT HIGH ALTITUDE:
b) Expansion of gasesin Alveoli, and Gastrointestinal.
c) Fall in atmospheric temperature (-400
d) Injury from Light rays especially (skin, eye).
MOUNTAIN SICKNESS (Condition characterized by adverse
effects of hypoxia at high altitude) like:
a) Loss of appetite, nausea and vomiting
b) Heart rate and force of contraction of heart increases.
c) Increase pulmonary blood pressure & pulmonary edema.
d) Headache, depression, disorientation, irritability, lack of sleep,
weakness and fatigue (cerebral edema).
Adaptations or the adjustments by
the body in high altitude despite a
low oxygen tension.
Changes during cclimatization:
RBC count increases and packed
cell volume rises from normal
value of 45% to about 59% (Hb15g-
Increase in rate and force of heart
contraction & vascularity.
Pulmonary ventilation increases
and pulmonary hypertension.
Elevation both cellular oxidative
enzymes and mitochondria.
does not create any
AVIATION PHYSIOLOGY: Is the study of physiological
responses of the body in aviation environment.
Flyingexerts great effects on the body through accelerative
forces (velocity) and gravitational forces.
GRAVITATIONAL FORCE: Is the major factor that develops
Increase inG unit is called positive G (acceleration).
Decrease inG unit is called negative G (deceleration).
EFFECTS OF GRAVITATIONAL FORCES ON THE BODY:
Effects of Positive G:
When G unit increases to about 4 to 5 G, blood is pushed toward
the lower parts of the body including abdomen.
Reduced blood supply to the brain and eyes leads:
1. Graying of vision that occurs when blood flow to eyes starts
2. Complete loss of vision.
3. Loss of consciousness.
4. When force increases to about 20 g, bones, particularly the spine,
becomes susceptible for fracture even during sitting posture.
Effects of Negative G:
Negative G develops while flying downwards (inverted flying).
1. The blood is pushed towards head.
2. Blurring of vision and sudden reddening of visual field.
3. Loss of consciousness (it increases the pressure in the blood
vessels of chest and neck).
Page 17 of 18
SPACE AND SPACECRAFTS: Is the study of physiological
responses of the body in space and spacecrafts.
Major differences between the environments of earth and space are:
Astronauts also wear launch and entry suit (LES: is a pressurized suit)
that protects the body from space environment.
Another factor which affects the body in the space is
WEIGHTLESSNESS due to absence of gravity.
EFFECTS OF WEIGHTLESSNESS IN SPACECRAFT ARE:
1. Accumulation of blood and other fluid in the head and upper trunk,
firstly the heart enlarged and after a while times it become gradually
shrinking and small in size.
2. The kidney compensate the excess fluid in the body by excreted the
fluid and electrolyte, so the person not feel thirst.
3. Space anemia due to decrease both blood volume and RBC.
4. Suppression of immune system in the body.
5. Decrease in muscle mass and muscle strength, also osteoclast
activity increased. Astronauts move by floating instead of using their
6. Abnormal stimulation of vestibular apparatus and fluid shift causes
space motion sickness - It is characterized by nausea, vomiting,
headache and malaise.
Deep Sea Physiology:
In deepsea or mines, the problem is with high barometric
Increased pressure creates two major problems:
1. Compression effect on the body and internal organs.
2. Decrease in volume of gases.
Page 18 of 18
As the person going more depth in the sea his may suffer a
condition knowing as nitrogen narcosis which is means
Nitrogen narcosis is common in deep sea divers, who breathe
compressed air (air under high pressure).
Mechanism of nitrogen narcosis:
Nitrogen is soluble in fat.
Nitrogen escapes from blood vessels and gets dissolved in
neuronal membranes and act like anesthetic agent.
Nitrogen narcosis can be prevented by mixing helium with
Nitrogen narcosis may be prevented by limiting the depth of