Download 1. Types of respiration and functions of resp system-1

Types of Respiration and Functions of
Respiratory Passageways
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Primary functions of respiratory system
1. Exchange of gases between the atmosphere and
the blood. The body brings in O2 for distribution to the
tissues and eliminates CO2 produced by metabolism.
2. Homeostatic regulation of body pH by the lung
selectively retaining or excreting CO2.
3. Protection from inhaled pathogens and irritating
substances. The respiratory epithelium is supplied
with defense mechanisms to trap & destroy pathogens
(secretory IgA and macrophages) .
4. Vocalization. Air moving across the vocal cords
creates vibrations used for speech or singing
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2. Homeostatic regulation of body pH
The lungs play a crucial role in regulating the pH of the body by
selectively retaining or excreting carbon dioxide (CO2). Carbon
dioxide is produced as a waste product of cellular respiration,
and it can combine with water to form carbonic acid
(H2CO3), which can then dissociate into bicarbonate ions
(HCO3-) and hydrogen ions (H+).
When the pH of the blood becomes too acidic (low pH), the
lungs can selectively retain carbon dioxide by decreasing the
rate of breathing, which allows carbon dioxide to build up in the
blood. This increase in carbon dioxide causes the formation of
more carbonic acid, which then leads to an increase in
bicarbonate ions and hydrogen ions. This, in turn, increases the
pH of the blood, bringing it back to the normal range.
Conversely, when the pH of the blood becomes too alkaline
(high pH), the lungs can selectively excrete carbon dioxide by
increasing the rate of breathing, which helps to remove excess
carbon dioxide from the blood. This decrease in carbon dioxide
causes a decrease in the production of carbonic acid, which
then leads to a decrease in bicarbonate ions and hydrogen ions.
This, in turn, decreases the pH of the blood, bringing it back to
the normal range.
3. Protection from inhaled pathogens and
irritating substances.
the respiratory epithelium is supplied with immune cells
such as macrophages, which can engulf and destroy
pathogens that are not trapped by the mucus layer.
These macrophages are located in the airway walls and
can also move to the surface of the respiratory
epithelium to engulf and eliminate pathogens. Another
important defense mechanism is the secretion of
secretory IgA (sIgA), which is an antibody that can bind
to and neutralize pathogens, preventing them from
entering the body.
Furthermore, the respiratory epithelium can respond to
pathogens and irritants by triggering an inflammatory
response, which involves the release of cytokines and
other immune cells to the site of infection or irritation.
This inflammatory response can help to clear pathogens
and promote tissue repair but can also lead to airway
hyperresponsiveness and respiratory symptoms in some
individuals.
Primary functions of respiratory system
5. Air conditioning:
The Airways Warm, Humidify, and Filter Inspired Air.
Conditioning has 3 components:
A. Warming air to body temperature (37 °C), so that
core body temperature does not change and alveoli
are not damaged by cold air;
B. Adding water vapor until the air reaches 100%
humidity, so that the moist exchange epithelium does
not dry out; and
C. Filtering out foreign material, so that viruses,
bacteria, and inorganic particles do not reach the
alveoli.
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Primary functions of respiratory system
Filtering out foreign material:
Particles > 6 Um or more are impacted at the nose.
Particles 1-5 Um are impacted at bronchioles.
Particles 1 Um adhere to alveolar surface while
Particles < 0.5 Um remain suspended in air.
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Primary functions of respiratory system
6. Mucociliary escalator:
Air is filtered both in the trachea and in the bronchi.
These airways are lined with ciliated epithelium whose
cilia are bathed in a watery saline layer (sol layer).
The saline is produced by epithelial cells when Clsecreted into the lumen by apical anion channels
draws Na+ into the lumen.
Movement of solute from the ECF to the lumen
creates an osmotic gradient, and water follows the
ions into the airways.
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The mucociliary escalator is an important mechanism in the respiratory system that helps to clear the airways of mucus,
debris, and foreign particles, including pathogens. The ciliated epithelium lining the trachea and bronchi is covered with a
layer of watery saline, called the sol layer. This sol layer is essential for the function of the mucociliary escalator.
The sol layer is produced by epithelial cells lining the airways. These cells secrete chloride ions (Cl-) into the lumen of the
airway through apical anion channels. This secretion of chloride ions creates an electrochemical gradient that draws
sodium ions (Na+) into the lumen. The movement of solute from the extracellular fluid (ECF) to the lumen of the airway
creates an osmotic gradient, and water follows the ions into the airways.
The movement of water into the airways increases the depth of the sol layer and creates a thin layer of fluid that covers
the cilia. The cilia then beat in a coordinated manner, moving the sol layer and its contents towards the pharynx, where it
can be swallowed or expectorated. The movement of the sol layer and the cilia is called the mucociliary escalator, and it
helps to remove mucus, debris, and foreign particles from the airways.
Primary functions of respiratory system
A sticky mucus layer (gel layer) floats over the cilia
to trap most inhaled particles > 2 mm. The mucus
layer is secreted by goblet cells in the epithelium. The
beating action of cilia (10-20 beats/sec) causing flow
of mucus few mm/min towards the pharynx to be
swallowed or expectorated.
This is called mucociliary escalator.
Mucus contains immunoglobulins (secretory IgA) that
can disable many pathogens. For swallowed mucus,
stomach acid and enzymes destroy any remaining
microorganisms.
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Primary functions of respiratory system
Secretion of the watery saline layer beneath the
mucus layer is essential for a functional mucociliary
escalator.
In cystic fibrosis, inadequate ion secretion decreases
fluid movement in the airways. Without the saline
layer, cilia become trapped in thick, sticky mucus and
can no longer move. Mucus cannot be cleared, and
bacteria colonize the airways, resulting in recurrent
lung infections
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Primary functions of respiratory system
7. Nervous control of bronchioles:
Sympathetic:
Stimulation of beta-adrenergic receptors causes
dilatation of bronchioles caused by norepinephrine
and epinephrine released from adrenal medulla.
Parasympathetic:
Stimulation of cholinergic receptors (vagal) causes
constriction of bronchioles caused by acetylcholine
Primary functions of respiratory system
8. Cough reflex:
Cough is a part of innate immunity
It is a reflex defense mechanism that tend to
clear the respiratory passages from secretions
and irritating matters whether exogenous or
endogenous.
9. Sneezing reflex:
Forced expiratory effort against open glottis.
It is mediated by the trigeminal nerve.
What is Respiration?
1. Cellular respiration:
It refers to the intracellular reaction of O2 with organic
molecules at the mitochondria to produce CO2, water,
and energy in the form of ATP
2. External respiration:
It is the movement of gases between the environment
and the body’s cells.
External respiration can be subdivided into four
integrated processes, illustrated
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External Respiration
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External respiration
1. The exchange of air between atmosphere & lungs.
This process is known as ventilation, or breathing.
Inspiration (inhalation):
It is the movement of air into the lungs.
Expiration (exhalation):
It is the movement of air out of the lungs.
2. The exchange of O2 & CO2 between lungs & blood
3. The transport of O2 & CO2 by the blood.
4. The exchange of gases between blood and cells.
The respiratory and circulatory systems coordinate
transfer of O2 & CO2 between atmosphere & cells.
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Anatomy: lung & thoracic cavity
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Anatomy: lung & thoracic cavity
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Respiratory tract
The respiratory system can be divided into two parts.
1. Upper respiratory tract:
Mouth, nasal cavity, pharynx, and larynx.
2. Lower respiratory tract:
Trachea, two primary bronchi, their branches, and
the lungs.
The lower tract is also known as the thoracic
portion of the respiratory system because it is
enclosed in the thorax.
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Pleural sacs
Pleura is a double-walled sac surrounding the lungs
whose membranes line the inside of the thorax
(parietal layer) and cover the outer surface of the
lungs (visceral layer).
Each pleural membrane, contains several layers of
elastic connective tissue and numerous capillaries.
The opposing layers of pleural membrane are held
together by a thin film of pleural fluid whose total
volume is only about 25–30 mL in a 70-kg man.
The result is similar to an air-filled balloon (the lung)
surrounded by a water-filled balloon (the pleural sac).
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Pleural sacs
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Pleural sacs
Function of the pleural fluid:
1.It creates a moist, slippery surface so that the opposing
membranes can slide across one another
2. It holds the lungs tight against thoracic wall.
Intrapleural Pressure Changes during ventilation
The lungs are enclosed in the fluid-filled pleural sac. The
surface of the lungs is covered by the visceral pleura, and
the portion of the sac that lines the thoracic cavity is
called the parietal pleura. Cohesive forces of the
intrapleural fluid cause the stretchable lung to adhere to
the thoracic cage. When the thoracic cage moves during
breathing, the lungs move with it.
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The IPP pressure is normally subatmospheric. This
pressure arises during fetal development, when the
thoracic cage with its associated pleural membrane
grows more rapidly than the lungs.
The elastic lungs are forced to stretch to conform to
the larger volume of the thoracic cavity. At the same
time, elastic recoil of the lungs creates an inwardly
directed force that tries to pull the lungs away from the
chest wall.
The outward pull of the thoracic cage and inward
recoil of the elastic lungs creates a subatmospheric
intrapleural pressure -3 mm Hg
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Intrapleural (intrathoracic) pressure
At the beginning of inspiration: -3 mmHg
At the end of inspiration: -6 mmHg
During exercise or other powerful inspirations,
intrapleural pressure may reach -8 mm Hg
Causes of negative intrapleural pressure
1.The recoil tendency of the lungs
2.The expansion tendency of the chest wall
Importance of negative intrapleural pressure :
. It is an index of physical fitness
. It helps venous return: from IVC to right atrium
The negative intrapleural pressure helps venous return by facilitating blood flow back to the heart. Specifically, during inspiration, the diaphragm
contracts and moves downward, creating a negative pressure within the thoracic cavity. This negative pressure gradient helps to decrease the
pressure within the vena cava and other large veins, promoting blood flow from the lower extremities and abdomen back to the right atrium of the
heart.
The negative intrapleural pressure also helps to prevent the collapse of the thin-walled veins in the thorax, which could impede blood flow and
reduce venous return. This is especially important during physical activity when blood flow and venous return are increased, and the negative
intrapleural pressure helps to maintain adequate blood flow to the heart.
Transpulmonary pressure
. It is the difference between alveolar pressure and
pleural pressure.
. It is a measure of elastic forces in the lung that
tend to collapse the lung at each instant of
inspiration.
. It is called recoil pressure.
Airways Connect Lungs to the External Environment
As a result, the total cross-sectional area increases
with each division of the airways.
Total cross-sectional area is lowest in the upper
respiratory tract and greatest in the bronchioles,
analogous to the increase in cross-sectional area that
occurs from the aorta to the capillaries in the
circulatory system.
Velocity of air flow is inversely proportional to total
cross-sectional area of the airways. This is similar to
the velocity of blood flow through different parts of the
circulatory system, and means that the velocity of air
flow is greatest in the upper airways and slowest in
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the terminal bronchioles.
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Alveoli Are the Site of Gas Exchange
Each tiny alveolus is composed of a single layer of
epithelium.
. Type I alveolar cells:
They form 95% of the alveolar surface area used for
gas exchange. These cells are very thin so that gases
can diffuse rapidly through them.
. Type II alveolar cells:
They are smaller but thicker synthesize and secrete a
chemical known as surfactant.
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Alveoli Are the Site of Gas Exchange
The thin walls of alveoli do not contain muscle, but
connective tissue between the alveolar epithelial cells
contains many elastin & collagen fibers that create
elastic recoil when lung tissue is stretched
The close association of the alveoli with an extensive
network of capillaries demonstrates the intimate link
between the respiratory and cardiovascular systems.
Blood vessels fill 80–90% of the space between
alveoli, forming an almost continuous “sheet” of blood
in close contact with the air-filled alveoli. The proximity
of capillary blood to alveolar air is essential for the
rapid exchange of gases.
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