4. Breathing
Breathing is the exchange of gases. The
respiratory and cardiovascular systems
combine to provide an efficient delivery
system that carries oxygen to our body tissues
and removes carbon dioxide from them. This
transportation involves four separate
processes:
5. -
1. Pulmonary ventilation (breathing), which is the
movement of gases into and out of the lungs
2. Pulmonary diffusion, which is the exchange of
gases between the lungs and the blood
3. Transport of oxygen and carbon dioxide via the
blood
4. Capillary gas exchange, which is the exchange of
gases between the capillary blood and the
metabolically active tissue.
6. -
The first two processes are referred to as external
respiration because they involve moving gases
from outside the body into the lungs and then
the blood. Once the gases are in the blood they
must travel to the tissues. When blood arrives at
the tissues, the fourth step of respiration occurs.
This gas exchange between the blood and the
tissues is called internal respiration. Thus
external and internal respiration are linked by the
circulatory system.
7. Pulmonary Ventilation
Pulmonary ventilation, commonly referred to as
breathing, is the process by which we move air
into and out of our lungs. Air is typically drawn
into the lungs through the nose, although the
mouth must also be used when the demand for
air exceedes the amount that can comfortably be
brought in through the nose. Bringing air in
through the nose has certain advantages over
mouth breathing. The air is warmed and
humidified as it swirls through the irregular
surfaces (turbinates) inside the nose.
8. -
Of equal importance, the turbinates churn the
inhaled air, causing dust and other particles to
contact and adhere to the nasal mucosa. This
filters out all but the tiniest particles, minimizing
irritation and the threat of respiratory infections.
From the nose and mouth, the air travels through
the pharynx, larynx, trachea, bronchi, and
bronchioles, until it finally reaches the smallest
respiratory units: alveoli. The alveoli are the sites
of gas exchange in the lungs
9. -
• The lungs are not directly attached to the ribs.
Rather, they are suspended by the pleural sacs. These
sacs envelop the lungs and contain a thin layer of
pleural fluid that reduces friction during respiratory
movements. In addition, these sacs are connected to
the lungs and to the inner surface of the thoracic
cage, causing the lungs to take the shape and size of
the cage as the chest expands and contracts.
• These relationships between the lungs, the pleural
sacs, and the thoracic cage determine air flow into and
out of the lungs. There are two phases: inspiration and
expiration
10. Inspiration
• Inspiration is an active process involving the diaphragm and
the external intercostal muscles. The ribs and sternum are
moved by the external intercostal muscles. The ribs swing
up and out. The sternum swings up and forward. At the
same time. the diaphragm contracts, flattening down
toward the abdomen. When the lungs are expanded, the
air within them has more space to fill, so the pressure
within the lungs decreases. As a result, the pressure in the
lungs (intrapulmonary pressure) is less than pressure of the
air outside the body. Because the respiration tract is open
to the outside, air rushes into the lungs to reduce this
pressure difference. Thus air is brought into the lungs
during inspiration.
14. Expiration
• At rest, expiration is usually a passive process
involving the relaxation of the inspiratory
muscles and elastic recoil of the lung tissue.
As the external intercostal muscles relax, the
ribs and sternum lower back into their resting
position. This increases the pressure in the
thorax, so air is forced out of the lungs. Thus
expiration is accomplished. During forced
breathing, expiration becomes a more active
process.
15. Pulmonary Diffusion
• Gas exchange in the lungs, called pulmonary
diffusion, serves two major functions:
1. It replenishes the blood oxygen supply that
has been depleted at the tissue level where it
is used for oxidative energy production.
2. It removes carbon dioxide from returning
venous blood.
17. -
• Pulmonary diffusion has two requirements: air
that brings oxygen into the lungs and blood to
receive the oxygen and give up carbon dioxide
and give up carbon dioxide. Air was brought
into the lungs during pulmonary ventilation;
now gas exchange must occur between this air
and the blood.
18. The Respiratory Membrane
Gas exchange between the air in the alveoli and
the blood in the pulmonary capillaries occurs
across the respiratory membrane (also called
the alveolar-capillary membrane) which is
composed of
a) the alveolar wall
b) the capillary wall, and
c) their basement membranes.
20. Partial Pressure of Gases
• The air we breathe is a mixture of gases. Each
exerts pressure in proportion to its
concentration in the gas mixture. The
individual pressures from each gas in a
mixture are referred to as partial pressures.
According to Dalton`s law, the total pressure
equals the sum of the partial pressures of the
individual gases in that mixture.
23. -
• The air we breathe is composed of 79.04%
nitrogen (N2), 20.93% oxygen (O2), and
0.03% carbon dioxide (CO2). If the total
atmospheric pressure is 760 mmHg, then the
partial pressure of nitrogen (PN2) in air is
600.7 mmHg (79.04% of the total 760 mmHg
pressure). Oxygen`s partial pressure (PO2) is
159.0 mmHg (20.93% of 760 mmHg ), and
carbon dioxide`s partial pressure (PCO2) is
0.03% of 760 mmHg ).
24. Gas Exchange in the Alveoli
• Differences in the partial pressures of the
gases in the alveoli and the gases in the blood
create a pressure gradient across the
respiratory membrane. This forms the basis of
gas exchange during pulmonary diffusion
26. Oxygen Transport
• Oxygen is transported by the blood either
combined with hemoglobin (Hb) in the red blood
cells (>98%) or dissolved in the blood plasma
(<2%). Each molecule of hemoglobin can carry
four molecules of oxygen. When oxygen binds to
hemoglobin, it forms oxyhemoglobin;
hemoglobin that is not bound to oxygen is
referred to as deoxyhemoglobin. The binding of
oxygen to hemoglobin depends on the Po2 in the
blood and the bonding strength or
affinity, between hemoglobin and oxygen.
28. -
There are other factors which affect this bonding
affinity, such as the level of pH and blood temperature
– higher pH and lower blood temperature increase the
bonding affinity between hemoglobin and oxygen. The
The pH in the lungs is generally high, so hemoglobin
passing through the lungs has a strong affinity for
oxygen, encouraging high saturation. At the tissue
level, however, the pH is lower, causing oxygen to
dissociate from hemoglobin, thereby supplying oxygen
to the tissues. In the lungs, where the blood might be a
bit cooler, hemoglobin`s affinity for oxygen is
increased. This encourages oxygen binding.
29. Carbon Dioxide Transport
• Carbon dioxide also relies on the blood for
transportation. Once carbon dioxide is released from
the cells, it is carried in the blood primarily in three
forms:
1) Dissolved in plasma (7-10%)
2) As bicarbonate ions resulting from the dissociation of
carbonic acid (60-70%)
3) Bound to hemoglobin (20-30%) – when carbon
dioxide binds to hemoglobin, they form a compound
called carbaminohemoglobin. Carbon dioxide binding
depends on the oxygenation of the hemoglobin and
the partial pressure of CO2
31. The Regulation of Pulmonary
Ventilation
• The respiratory muscles are under the direct
control of motor neurons, which are in turn
regulated by respiratory centers located within
the brainstem (in the medulla oblongata and
pons). These centers establish the rate and depth
of breathing by sending out periodic impulses to
the respiratory muscles. However, the respiratory
centers don`t act alone in controlling breathing.
Its regulation is also determined by a changing
chemical environment in the body
32. Voluntary Control
• We can exert some voluntary control over our
breathing through the cerebral motor cortex.
However, this voluntary control can be
overridden by the involuntary control of the
respiratory centerIf we try to hold our breath, at
some point, regardless of our conscious decision
to suppress breathing, our carbon dioxide and H+
levels become quite high, our oxygen level
drops, and our inspiratory center decides that
breathing is imperative and it forces us to inhale,.
33. Respiratory System – Anatomy and
Physiology
The respiratory system is made up of the organs involved
in the interchanges of gases and consists of the:
• nose
• mouth (oral cavity)
• pharynx (throat)
• larynx (voice box)
• trachea (windpipe)
• bronchi
• lungs
38. Nose and Nasal Cavity
The nose is the uppermost part of the respiratory
tract. It is made up to two bones and cartilage. It
forms a hollow passage that connects the nostrils
and the top of the throat. This passage is called
the nasal cavity . It is lined with a mucous
membrane which bears tiny hairs. The function of
the nose is to filter, warm and moisten the air
before it moves on to other parts of the
respiratory tract. The tiny hairs trap the dust
particles, bacteria and other foreign bodies that
enter the nose. These hairs also induce sneezing
to remove foreign bodies lodged in the nose.
40. Mouth and Pharynx
The pharynx is a passageway from the back of the
mouth (oropharynx) and nose (nasopharynx) to
the upper part of the esophagus
(laryngopharynx) and into the voice box, or
larynx. The pharynx acts like a station where the
food tube and the air tube meet. Food beings
swallowed is prevented from entering the air
tube by a thin structure, called epiglottis , that
closes the air tube. This is why we cannot breathe
while we are swallowing.
42. Larynx and Trachea
At the lower end of the pharynx is the larynx
which forms part of the air tube. It is made of
cartilage. One of its functions is production of
voice. It does this with the help of either one of
two pairs of vocal cords. When air from the lungs
passes over the stretched vocal cords, vibrations
are produced. The tongue palate and lips modify
the vibrations to produce speech. Another
function of the larynx is to prevent choking. The
elongated space between the vocal cords is called
glottis .
46. -
The epiglottis folds back over the glottis when we
swallow food, so the food cannot enter the trachea or
air tube. The trachea, or windpipe , begins just below
the larynx and ends behind the upper part of the
breastbone where it divides to form two tubes. The
trachea is made of elastic tissue and smooth muscle. It
also has rings of elastic cartilage that keep the trachea
open when the neck moves. It is lined with a mucous
membrane and hair like projections called cilia . Mucus
helps trap dust and bacteria in the incoming air. The
cilia move the mucus upward to clear the respiratory
tract.
47. The Lower Respiratory Tract
The lower respiratory tract includes the
following:
• airways (bronchi and bronchioles)
• air sacs (alveoli)
• lungs
50. Bronchi, Bronchioles and Alveoli
The trachea branches into two tubes-the
bronchi. Each bronchus (singular of bronchi)
enters the lung and branches into narrower
tubes called bronchioles . The walls of the
bronchi and larger bronchioles are supported
by cartilage. Their walls produce mucus which
is moved upward by the cilia to clear the air
passage. Each bronchiole ends in balloon like
air sacs called alveoli .
53. -
The alveoli have thin walls which are
surrounded by blood vessels. The bronchi and
bronchioles form the air passage into the
lungs. The exchange of oxygen and carbon
dioxide takes place in the alveoli. There are
about 300 million alveoli in the lungs. These
alveoli increase the surface area of the lungs
and allow many blood vessels to collect
oxygen.
54. Lungs
The lungs are a pair of conical organs present
in pleural cavities; both the lungs together
form an important part of the human
respiratory system. Left lung is divided into 2
lobes (superior and inferior) while the right
one in 3 (superior, inferior and middle). Each
lung has a median slit and hilus (or hilum).
