Download Physiology of Respiratory system

Physiology of Respiratory system
General physiology
By Assist. Prof.Dr. Majida Alqayim
Departement of physiology and pharmacology College
of veterinary medicine
University of baghdad
Respiration
Exchange of gases between the air and the cells of the
body, in the followings steps:
• Pulmonary ventilation :The physical movement of air into
and out of the lungs.
• External Respiration: Movement of respiratory gases
from the lung into the blood. Involves diffusion across a
respiratory membrane.
• Internal respiration: The use of oxygen by the
mitochondria to produce ATP by oxidative
phosphorylation with production of carbon dioxide as a
waste product.
Introduction:Respiratory
System
The respiratory system is made up of a gas-exchanging organ (the
lungs) and a "pump" that ventilates the lungs. The pump consists of
the chest wall; the respiratory muscles, which increase and
decrease the size of the thoracic cavity; the areas in the brain that
control the muscles; and the tracts and nerves that connect the
brain to the muscles. At rest, a normal human breathes 12 to 15
times a minute. About 500 mL of air per breath, or 6 to 8 L/min, is
inspired and expired. This air mixes with the gas in the alveoli, and,
by simple diffusion, O2 enters the blood in the pulmonary capillaries
while CO2 enters the alveoli. In this manner, 250 mL of O2 enters the
body per minute and 200 mL of CO2 is excreted. Traces of other
gases, such as methane from the intestines, are also found in
expired air. Alcohol and acetone are expired when present in
appreciable quantities in the body.
Lungs are cone-shaped organs situated in the thoracic cavity. The left
lung is divided by an oblique fissure into superior and inferior lobes. The
right lung is divided by oblique and horizontal fissures into superior,
middle and inferior lobes. Each lobe receives a secondary (lobar)
bronchus from the primary bronchi. Inside the lungs, the secondary
bronchi give rise to smaller bronchi called 'tertiary (segmental) bronchi',
which in turn divide into smaller tubes called 'bronchioles'. Bronchioles
branch repeatedly to form the terminal bronchioles that divide into
respiratory bronchioles.
GROSS AND MICROSCOPIC STRUCTURE OF THE LUNGS
Between the trachea and the alveolar sacs,
the airways divide 23 times.
The first 16 generations of passages form the
conducting zone of the airways that
transports gas from and to the exterior.
They are made up of bronchi, bronchioles,
and terminal bronchioles.
The remaining seven generations form the
respiratory zones where gas exchange
occurs; they are made up of respiratory
bronchioles, alveolar ducts, and alveoli.
These multiple divisions greatly increase
the total cross-sectional area of the
airways, from 2.5 cm2 in the trachea to
11,800 cm2 in the alveoli . Consequently,
the velocity of air flow in the small airways
declines to very low values.
Blood gas barrier
•
•
•
•
1. A layer of fluid lining the alveolus and containing
surfactant that reduces the surface tension of the
alveolar fluid
2. The alveolar epithelium composed of thin
epithelial cells
3. An epithelial basement membrane
4. A thin interstitial space between the alveolar
epithelium and the capillary membrane 5. A capillary basement membrane that in many
places fuses with the alveolar epithelial basement
membrane
6. The capillary endothelial membrane
Alveolar wall
•
The alveoli are lined by two types of epithelial
cells. Type I cells are flat cells with large
cytoplasmic extensions and are the primary
lining cells of the alveoli, covering
approximately 95% of the alveolar epithelial
surface area. Type II cells (granular
pneumocytes) are thicker and contain
numerous lamellar inclusion bodies. A primary
function of these cells is to secrete surfactant;
however, they are also important in alveolar
repair as well as other cellular physiology.
Although these cells make up approximately 5%
of the surface area, they represent
approximately 60% of the epithelial cells in the
alveoli. The alveoli also contain other
specialized cells, including pulmonary alveolar
macrophages (PAMs, or AMs), lymphocytes,
plasma cells, neuroendocrine cells, and mast
cells. The mast cells contain heparin, various
lipids, histamine, and various proteases that
participate in allergic reactions
Cells within airway
Airway wall
Pulmonary and bronchial circulation
Pulmonary and bronchial circulation
Pulmonary and bronchial circulation
Air ways divisions
Volume of conducting
zone is about 150 ml
volume of respiratory
zone is 3 litters
Dead space
•
•
•
•
•
Definition - It is the volume of the respiratory tract that does not participate in gas
exchange. It is approximately 300 ml in normal lungs. It is important to distinguish
between the anatomic dead space (respiratory system volume exclusive of alveoli) and
the total (physiologic) dead space (volume of gas not equilibrating with blood; ie,
wasted ventilation).
Physiological dead space= Anatomical dead space + Alveolar dead space
Normally, the volume (in mL) of this anatomic dead space is approximately equal to the
body weight in pounds. As an example, in a man who weighs 150 lb (68 kg), only the
first 350 mL of the 500 mL inspired with each breath at rest mixes with the air in the
alveoli.
Air that reaches the alveoli, but for one reason or other does not take part in gas
exchange, is not considered as Alveolar dead space (for example, air that goes to an
unperfused alveolus). influencing alveolar dead space:Low cardiac output can increase alveolar dead space (increasing West's zone 1)
Pulmonary embolism.
Alveolar ventilation (VA) is the volume of air reached the alveoli in per minute that (1)
reaches the alveoli and (2) takes part in gas exchange.
• Rapid shallow breathing produces much less
alveolar ventilation than slow deep breathing
at the same respiratory minute volume (Table
).
Regions lacking gas exchange constitute
alveolar dead space.
10/min
30/min
Respiratory rate
600 mL
200 mL
Tidal volume
6L
6L
Minute volume
(600 – 150) x 10 = 4500 mL (200 – 150) x 30 = 1500 mL Alveolar ventilation
Mechanics of ventilation (breathing)
Pulmonary ventilation:-The physical movement of air into and out of the lungs. A
mechanical process that depends on volume changes in the thoracic cavity,
lead to pressure changes( Boyle's law ), which lead to the flow of gases in
and out of the thoracic cavity to equalize pressure.
Ventilation results from bulk flow of air as the result of pressure gradients which
created between alveoli and atmospheric pressure as a result of volume
changes.
Boyle's law :-This law states that the pressure of gas in any container is inversely
related to the volume of the container. In other words, when volume
increases, pressure decreases and when volume
decreases, pressure increases.
P1V1 = P2V2
P = pressure of a gas in mm Hg
V = volume of a gas in cubic millimeters
Mechanics of
Breathing
As the external intercostals &
diaphragm contract, the lungs
expand. The expansion of the
lungs causes the pressure in the
lungs (and alveoli) to become
slightly negative relative to
atmospheric pressure. As a result,
air moves from an area of higher
pressure (the air) to an area of
lower pressure (our lungs &
alveoli). During expiration, the
respiration muscles relax & lung
volume descreases. This causes
pressure in the lungs (and alveoli)
to become slight positive relative
to atmospheric pressure. As a
result, air leaves the lungs.
Pulmonary ventilation
The factors limiting the pulmonary ventilation :• 1- - ve Intraplueral pressure
• 2--Elastic recoil ( elastine proteins , collagen fiber, intraplueral fluid)
• 3- lung surface tension
During inspiration, alveolar volume
increases and intra-alveolar
pressure falls causing air molecules
to enter down the pressure
gradient created by the inspiration.
The air flow stops when pressure is
equal to atmospheric pressure (0
mm Hg). During expiration,
alveolar volume decreases and
intra-alveolar pressure increases
causing air molecules to leave
down a pressure gradient in the
reverse direction until the pressure
returns to 0 mm Hg. The movement
of air into and out of the alveoli is
due to the changes in the volume
of the thoracic cavity produced by
the muscles of ventilation.
.
• Alveolar ventilation
Alveolar ventilation (VA) is
the volume of air reached
the alveoli in per minute
that (1) reaches the alveoli
and (2) takes part in gas
exchange
• Pulmonary ventilation
Different regions of ventilation
There is regional differences
of ventilation in the lower
regions are better
ventilated from upper This
differences in the
intrapleural -ve pressure
between upper and lower
due to the gravity and the
lung mass.
.
Regional blood flow in the Lung
The uneven distribution of blood flow can
be explained by the hydrostatic pressure
differences within the blood vessels.
Causes of Un even Blood flow
1- Gravity. 2- mass of the lung
3-Non gravitational resistance
Ventilation- perfusion ratio
Ventilation – the amount of gas reaching the alveoli
Perfusion – the blood flow reaching the alveoli
Ventilation and perfusion must be tightly regulated for efficient gas exchange
Changes in PCO2 in the alveoli cause changes in the diameters of the pulmonary
arterioles
Alveolar CO2 is high/O2 low: vasoconstriction
Alveolar CO2 is low/O2 high: vasodilation
Gas exchange is dependent on local matching of regional ventilation-to-perfusion ratio
( ˙ VA/ ˙Q), where Well ventilated regions ideally have high capillary blood flows.
Poorly ventilated regions ideally have little capillary blood flow. Three regions or 3
zones in standing position and 2 zones in laying and animals
Effect of Ventilation-Perfusion
Inequality on Overall Gas Exchange
ventilation-perfusion inequality. When ventilation
and blood flow are mismatched in various
regions of the lung, impairment of both O2 and
CO2 transfer results.
Different regions for gas exchange
This diagram explain the
causes of regional
distribution for different
microbial infections in
the lung
Gases
diffusion and
transportation
• Diffusion of any gas is judged by the Fick’s law of diffusion ,
in which transfer of any gas ( v• )through a sheet of tissue is
proportional to tissue surface area (A) and the difference in
gas partial pressure (P1- P2) between the two sides of the
tissue , and inversely to thickness of the tissue(T )
• Lung is big A( 50-100 m2 ) and Low T( microne)
• D :- diffusion coaffeciant of any gas it depends on :-a.
property of tissue
• b. molecular of gas
• c. solubility of gas
Gas Exchange in the Lungs
O2 transport in the blood
Oxygen–hemoglobin dissociation curve.
Oxygen transported in two forms:
1. Dissolved in the solution (> 2%) – oxygen is
not very soluble.
2. Bound to hemoglobin (< 98%) – much more
important.
Factors Affecting the Affinity of Hemoglobin for
Oxygen
Three important conditions affect the oxygen–
hemoglobin dissociation curve: the pH, the
temperature, and the concentration of 2,3biphosphoglycerate (BPG; 2,3-BPG). A rise in
temperature or a fall in pH shifts the curve to
the right (Figure 36–3). When the curve is
shifted in this direction, a higher PO2 is
required for hemoglobin to bind a given
amount of O2. Conversely, a fall in
temperature or a rise in pH shifts the curve to
the left, and a lower PO2 is required to bind a
given amount of O2. A convenient index for
comparison of such shifts is the P50, the PO2 at
which hemoglobin is half saturated with O2.
The higher the P50, the lower the affinity of
hemoglobin for O2.
Factors affect on Hb-O2 association
curve
Carbon Dioxide transporting:-
Fate of CO2 in Blood.
In plasma
1. Dissolved
2. Formation of carbamino compounds with plasma protein
3. Hydration, H+ buffered, HCO3– in plasma
In red blood cells
1. Dissolved
2. Formation of carbamino-Hb
3. Hydration, H+ buffered, 70% of HCO3– enters the plasma
4. Cl– shifts into cells; mOsm in cells increases