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Respiratory
physiology
Functions of respiratory system


Respiratory function.
Protective functions.
Functions of the Respiratory System:

Exchange O2
Air to blood
 Blood to cells


Exchange CO2
Cells to blood
 Blood to air




Regulate blood
pH
Vocalizations
Protect alveoli
Figure 17-1: Overview of external and cellular respiration
Protective functions
A.
Air conditioning.
B.
Trapping & elimination of
foreign particles.
C.
Protective reflexes:
 Cough reflex .
 Sneeze reflex.
Respiration & Ventilation
Four Stages:
1. Pulmonary ventilation; air into lungs
2. External respiration; gas exchange from
lungs to blood
3. Internal respiration; exchange of gas from
blood to cells
4. Cellular respiration; utilization of oxygen by
cells to produce energy
Respiratory System Divisions
Airways
Respiratory Airways
(Respiratory tract or Air passages)
Anatomically:


Upper respiratory tract.
Lower respiratory tract.
Functionally:


Conducting zone (no gas exchange =
dead space).
Respiratory zone (Gas exchange).
Nasal Cavity and Pharynx
Nose and Pharynx

Nose
 External nose
 Nasal cavity
 Functions
 Passageway for air
 Cleans the air
 Humidifies, warms air
 Smell
 Along with paranasal
sinuses are resonating
chambers for speech

Pharynx
Common opening
for digestive and
respiratory
systems
 Three regions
 Nasopharynx
 Oropharynx
 Laryngopharynx

Larynx

Functions
Maintain an open passageway for air movement
 Epiglottis and vestibular folds prevent
swallowed material from moving into larynx
 Vocal folds are primary source of sound
production

Respiratory zone

Respiratory
bronchioles,
alveolar
ducts, atria, alveolar sacs & alveoli.

Gas exchange.
Conducting zone

Nose, pharynx, larynx, trachea, bronchi,
bronchioles & terminal bronchioles.

Cartilaginous rings, smooth muscles,
columnar ciliated epithelium (escalator) &
mucous glands.

Warms and humidifies inspired air.
Filters and cleans:
 Mucus secreted to trap particles in the inspired air.
 Mucus moved by cilia to be expectorated

Pleura






2 layers (visceral & parietal).
Thin layer of fluid (lubricant).
Pressure difference across the wall
of the lung to expand lung
Positive air pressure = MORE than 760 mmHg
Intrapleural pressure is the pressure within the pleural sac
which surrounds the lung
Intrapulmonary pressure is the pressure within the alveoli of
the lung itself
Pleura

Pleural fluid produced by pleural membranes


Acts as lubricant
Helps hold parietal and visceral pleural
membranes together
Ventilation
Mechanical process that moves air in and out of
the lungs.
[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
Breathing rate is 10-16 breaths / minute at rest, 40 45 at maximum exercise in adults
Ventilation
Movement of air
into and out of
alveoli
Inhalation: The
lungs inflate with air,
bringing oxygen into
the body
Exhalation: The
lungs let go of air,
releasing carbon
dioxide out into the
environment



Movement of air into and out of lungs
Air moves from area of higher pressure to
area of lower pressure
Pressure is inversely related to volume
Inspiration

Active process.

Contraction of the inspiratory muscles.

Diaphragm (75%) & External intercostal muscles.
Inspiration
Mechanism of inspiration
1.
Contraction of the inspiratory
muscles.
2.
.snoisnemid tsehC
3.
PPI.
4.
Lungs expansion.
5.
6.
Intrapulmonary pressure.
Rush of 500 ml air into the lungs
(Inflation).
Expiration
Expiration

A passive process

No muscle contraction

Only relaxation of inspiratory muscles
Mechanism of Expiration
1.
Relaxation of the inspiratory muscles.
2.
snoisnemid tsehC.
3.
PPI.
4.
Lungs recoil.
5.
6.
Intrapulmonary pressure.
Rush of 500 ml air outside the lungs
(Deflation).
Inspiration
Inspirato
ry
muscles
contract
Thoraci
c cavity
size
increase
I.Pulm
on
volume
increas
e
Thoracic
cavity
size
Decrease
I.Pulmon
volume
decrease
I.P
Decreas
e than
atmosph
ric
Air
Rush
into
lung
Expiration
Inspiratory
muscles
Relax
expiratory
muscles
Contract
I.P
inecrease
than
atmosphri
c
Air Rush
out the
lung
W Paul Segars Johns Hopkins
W Paul Segars Johns Hopkins
Alveoli










300 million.
80 - 100 m2.
0.2 micron.
Single layer of flat epithelium cells (Type I).
Granular pneumocytes (Type II) → Surfactant.
Lined by thin film of fluid (surface tension ).
Surfactant decreases the surface tension of alveolar fluid
Pulmonary Alveolar macrophages.
Pulmonary Interstitial tissue (elastin & collagen).
Surrounded by extensive network of capillaries.
Alveolar structure




Type I cells  gas
exchange
Type II cells  secrete
surfactant (lipoproteins)
 decrease surface
tension  allowing for
easier alveoli inflation
Surfactants start to be
secreted by the 7th
month of pregnancy 
risk of lung disease in
premature babies
Presence of
macrophages in alveoli
Anatomical Dead Space

No gas exchange (dead space).

Not all of the inspired air reached the alveoli.
As fresh air is inhaled it is mixed with air in
anatomical dead space.



Conducting zone and alveoli where [02] is lower
than normal and [C02] is higher than normal.
Alveolar ventilation = F x (TV- DS).
F = frequency (breaths/min.).
 TV = tidal volume.
 DS = dead space.

HOW THE BODY GET OXYGEN AND GET RIDE
OF CO2 DURING RESPIRATION
Gas exchange at Tissue levels
Gas exchange at Lung levels
Pulmonary Capillary
Co2 transport






Some fraction of carbon dioxide is dissolved and
carried in blood. Some reacts reversibly with Hb to
form carbamino Hb.
CO2 + Hb ↔ HbC02
Some carbon dioxide is converted to bicarbonate.
Carbonic
CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+
anhydrase
The enzyme, carbonic anyhydrase, is present in
erythrocytes where the reaction takes place after
which the bicarbonate moves out into the plasma.
Minute and Alveolar Ventilation
1. Tidal volume:Volume of air inspired or expired
during a normal inspiration or expiration=500
mL
2. Respiratory rate or frequency: Number of
breaths taken per minute= 12-16
3. Minute ventilation: Total amount of air moved
into and out of respiratory system per minute
=500x12=6 L
4. Anatomic dead space: Part of respiratory system
where gas exchange does not take place=150 mL
5. Alveolar ventilation: How much air per minute
enters the parts of the respiratory system in
which gas exchange takes place=
Hypoxia
O2 deficiency at the tissue level
Deficiency in either the delivery or
utilization of oxygen at the tissue
level, which can lead to changes in
function, metabolism and even
structure of the body
1) Hypoxic hypoxia
2) Anemic hypoxia
3) Stagnant hypoxia
4) Histotoxic hypoxia
Hypoxia
1. Shortness of
breath
2. Restlessness
3. Headache
4. Nausea
5. Fatigue
6. Tachycardia
7. Tachypnea and
Hyperpnea
8. Cyanosis
9. Coma
10. Death
types of hypoxia
I.
1. Hypoxic hypoxia
II.
Anemic hypoxia
III. 3. Stagnant hypoxia
IV. 4. Histotoxic hypoxia
Hypoxic hypoxia:
It is the hypoxia in which arterial PO2 is reduced
Causes:
1. Decreased O2 tension in the atmosphere: high
altitude.
2. Defective pulmonary ventilation
3. Defective gas exchange
4. Venous-to-arterial shunts.
Anemic hypoxia
This is due to reduction of the amount of hemoglobin available to
carry O2.
Causes:
1.
All types of anemia
2.
Carbon monoxide (CO) poisoning
Stagnant hypoxia:
This is the hypoxia in which the blood flow to the tissues is slow,
O2 delivered to the tissues is not adequate despite a normal PO2
and hemoglobin concentration
Causes:
1. Hypotension
2. Polycythemia.
(localized).
2. Heart failure.
3. V.C. on exposure to cold
Histotoxic hypoxia
This is the hypoxia in which tissue is unable to use O2 due
to inhibition of enzyme responsible for internal respiration.
Causes:
1. Cyanide poisoning: the most common cause
2. Alcohol and barbiturate which prevent dehydrogenase enzyme.