Human Respiratory System Anatomy and Physiology

1. *

2. *
*When most people think of the respiratory system,
they naturally focus on the lungs and breathing.
Indeed, breathing is a necessary function of a
healthy body. Without the lungs taking in air, the
cells of the body could not operate properly.
However, the lungs are only one part of the
respiratory system. The respiratory system also
includes the nose, mouth, pharynx, larynx (voice
box), trachea (windpipe), bronchi, alveoli, and
diaphragm.

3. The airways of the body are commonly
divided into two sections:
a)The upper respiratory tract and
b) The lower respiratory tract.
The nose, pharynx, and larynx are considered
the upper respiratory tract.
The trachea, bronchial tree, and the lungs make
up the lower respiratory tract.

4. *
*In order to breathe, the body must take in air through the nose. Air
is made up of many different gases. About 78 percent of it is
nitrogen, 21 percent is oxygen, and argon, carbon dioxide, methane,
and other more rare gases make up the last 1 percent.
*Of all the gases that make up the air we breathe, however, oxygen
is the only one that the body can use.

5. The nose has external and internal parts
*External Nose: This is the triangular projection in front of
the face. It is composed of a small nasal bone, a lot of
cartilage and covered with skin.
*Internal Nose: It is lined with mucus membrane containing
olfactory cells and divided into two chambers (fossa) by the
nasal septum. The lateral wall of each chamber is formed by
three “scroll-shaped” nasal conchae or turbinate, below each
is the corresponding meatus (groove-like passage). The
paranasal sinuses open into these meatuses.

7. Paranasal Sinuses
These are air-filled spaces, lined with mucus membrane within some of
the bones of the skull. They open into the nasal cavity via the meatuses, and are
named according to the bone in which they are situated. They include the Frontal
sinuses (2), Maxillary sinuses(2), Sphenoid sinuses(2), and the Ethmoid sinuses
(consisting of many spaces inside the ethmoid bone
Their proposed functions are
increasing resonance of voice
and humidifying and heating of
inhaled air because of slow air
turnover in the region.
*Openings of the sinuses into
the nasal cavity are visible
following removal of the
conchae.

8. FUNCTIONS OF THE NOSE
*The Hair prevents large air borne foreign objects like insects from
entering the nose
*The Sticky mucus prevents smaller particles like pollen and dust
*The Mucus Membrane
It is a delicate layer of cell constantly moistened by secreted
watery serous fluid (this moisture is transferred to the air as it passes the
nasal cavity).
Deep in mucus membrane is an extensive network of vessels in
septum, which bring warm blood to the surface and
a) Allow mucus to warm the inhaled air as it passes
b)Keep mucus supplied with nutrients

9. *Kiesselbach’s plexus/area
This is the area where about 5 arteries of nasal septum confluence.
This area is prone to drying in trauma, leading to epistaxis.
In Summary, the nose functions are to filter, warm, and moisten
inhaled air before it reaches the lungs. It anatomically achieves them by its
large surface area and well vascularized mucosa.

10. *
*Breathing through the mouth is common when a stuffy nose is
present. When we breathe through our mouths, the air is not
moistened and not filtered; this can lead to respiratory infections
(bacteria or virus) or lung damage (dust, insects, and foreign bodies)
*This is why we have a cough reflex (body tries to protect us from
inhaling foreign objects).

11. *
The nose and mouth lead to a passageway
called the pharynx. The pharynx is the scientific name
for what most people call the throat. This
passageway is shared by the respiratory and the
digestive systems. The pharynx receives air from the
nose and mouth to allow the respiratory system to
do its work. It also accepts food and water from the
mouth for the digestive system. Just below the oral
cavity, the pharynx splits into two passages—the
esophagus and the trachea.

12. *The esophagus takes food from the mouth into the stomach. The trachea, or
windpipe, diverts air from the nose and mouth to the lungs. To prevent food from
going down the trachea, a flap of tissue, called the epiglottis, covers the opening of
the trachea during swallowing.
The pharynx has 3 portions; the Nasophaynx, Oropharynx, and the
Laryngopharynx.
*The Nasopharynx
It extends from the Internal naries (the meatuses) to the tip of the soft
palate. There is also the opening of the auditory tube; the Eustachian tube (connects
to the middle ear). In the posterior wall, there is the Pharyngeal tonsil or Adenoid (a
collection of lymphoid tissue). Enlargement of the adenoids can cause obstruction to
breathing through the nose and block the Eustachian tube (glue ear).

14. *The Oropharynx
It is immediately behind the oral cavity. It
extends from the tip of the soft palate to the tip
of the epiglottis. Within the oropharynx, we can
find palatine tonsils. At the root of the tongue,
the lingual tonsil is present.
*The Laryngopharynx
It is behind the epiglottis and extends to the
opening of the esophagus.

15. *
*Sitting below the pharynx
and on top of the trachea is
a structure called the larynx,
or the voice box. It has the
following functions;
a) Production of sound via
the vocal cords (When
people speak, parts of the
larynx, called the vocal
cords, vibrate as air is
expelled from the lungs and
rushes over them. This
produces sound. The vocal
cords are two bands of
elastic, smooth muscle
tissue that are attached at
the front and back of the
throat.

16. When we breathe in or out without making any sounds, the vocal cords
are open and do not touch. This allows air to move through the gap between the
cords. This gap is called the glottis. To produce sound, the vocal cords must close.
When the vocal cords are closed, they provide resistance to the air being exhaled
from the lungs).
b) Prevents food and foreign substances from entering the airway via the epiglottis
(cartilage that flaps down and covers larynx to keep food and foreign bodies from
entering the lungs).
c) Passage for air during
respiration.
GLOTTIS: the hole or space between
the vocal cords
EPIGLOTTIS: covers the glottis

17. *
* Below the larynx is the trachea, or the windpipe. The trachea is the major
airway for the body and it is made up and held open by hard C-shaped rings
of cartilage. The cartilages are open at the back (connected by trachealis
muscle). The cartilage stiffens the trachea and prevents the pipe from
collapsing in on itself. This hard cartilage can be felt in the front of the neck.
The esophagus is behind the trachea. It is made of soft tissue and cannot be
felt through the skin.

18. * Like the nose, the trachea is lined with mucous
membranes. The mucus in the trachea traps any foreign
particles that get past the mucus and hairs in the nose.
This mucus, or phlegm, is moved up into the throat
where it is either expelled out of the body by coughing
or swallowed. Any foreign particles swallowed with the
phlegm are usually destroyed by stomach acids.
* At the bifurcation of the trachea, there is the
presence of a sensitive carina (carina; keel). Anything
that touches the carina (e.g. suction catheter) causes a
cough reflex (for protection, because it’s one step away
from each lung).

19. *
* Partway down the chest, the trachea splits into two
branches—the left and the right main-stem bronchi. The Right
main bronchus is wider, shorter, higher and more vertical than
the left and has more tendency to foreign bodies. These two
branches feed air into the left and the right lung. The bronchial
tubes are also lined with mucous membranes and with
microscopic hair-like structures called cilia. The cilia move in tiny
wavelike motions that move mucus up and out of the bronchi
before it can get into the lungs.

20. Primary segments – to
each lung
Secondary – to each
lobe
Tertiary – to each
segment
There are 2 primary
bronchi (for R and L), 5
secondary (3 for right,
2 for left) and
numerous tertiary
bronchi (to the
segments).

21. *
* The left and the right bronchi branch into smaller
airways called the bronchioles. They contain no
cartilage or mucus glands in their walls. They are
wrapped in smooth muscle. They extend for up to 20
generations before reaching the terminal bronchioles.
Each Terminal bronchiole divides into a number of
Respiratory bronchioles, from which the Alveoli open.

22. *
*This is the only place where gas exchange takes place. It is a cluster of air
sacs; tiny spongy sacs. Surrounding each alveolus is a pulmonary capillary bed
(blood vessels). Alveoli are very thin walled, they have a single layer of
pneumocytes; this is for rapid diffusion of gases. Average adult has more than
300 million alveoli in each lung; children have about 20million in each.

23. *Gas Exchange:
When a person inhales air, the oxygen in the air
can move through the thin walls of the alveoli into the
capillaries. Blood vessels then distribute the oxygen to
the body. Carbon dioxide, a waste product that is carried
from other parts of the body through the blood vessels,
can move through the capillary walls into the alveoli so
that it can be exhaled.

24. Ventilation/Perfusion ratio – It is defined as the ratio of
amount of air reaching the alveoli to the amount of
blood reaching the alveoli.
*V – Ventilation – amount of air reaching alveoli
*Q – Perfusion – amount of blood reaching alveoli
*V/Q ratio is measured by V/Q scan. Ideal ratio is 0.95.

25. *
These are 2 spongy shaped organs in the chest. Right lung is shorter
and wider (larger) than the left and can hold higher volume of air. It has 3
lobes and 10 segments (3, 2, and 5). The Left lung is longer, skinnier and has
an indentation called the cardiac notch. It has 2 lobes and 8 segments (4, 4).
The lungs are both encased in a double serous membrane called the
pleura; the 2 layers are separated by small amounts of fluid. Function of pleura
is to cushion the lungs. Pleural cavity is the space in the chest that encases the
lungs.

26. *The lungs are expanded and compressed by the
movements of the rib cage during breathing.
*THE MEDIASTINUM
It is located in the center of the thoracic cavity
between the right and left lungs. It contains the trachea,
heart, great vessels, portions of esophagus, thymus
gland and lymph nodes.

27. *The lungs rest on the diaphragm. It is a sheet or layer of dome-shaped
strong muscle and tendon that lies at the bottom of the pleural cavity. It has
two muscles (right and left hemidiaphragms). The diaphragm separates the
chest cavity from the abdominal cavity. It gets its shape from the organs that
surround it. It is attached to the lower ribs at each side and to the sternum
and backbone at the front and back. It bulges upwards against the heart and
lungs. It arches over the stomach, liver and spleen.

28. *During Inspiration, It contracts, becomes flattened downwards and
increases the volume of thoracic cavity thus allowing air flow in to the
lungs.
*With each Expiration, it relaxes and restores its dome shape; it
moves upwards, ribs move in downward forcing air (CO2), out of the
lungs.
One full cycle of inhalation and exhalation is one breath. (RR).
*Average adult has 12-18 breaths per minute
*Newborns – 40-60 breaths per minute.
*Breathing slows down as people age.

29. *
*Respiration is involuntary. It is controlled by a part of
the brain called the medulla. The medulla signals
nerves cells in the diaphragm and tells it when to
contract or relax, causing breathing. The movement of
air from the environment into the body through the
lungs is called ventilation. Together, ventilation and the
exchange of gases between the lungs and the blood
are called External respiration.

30. *The body also goes through a process called Internal
respiration. Internal respiration is the exchange of gases
between red blood cells in the circulatory system and the
body’s tissues. This process starts when oxygen comes
into the body through the nose and mouth and ends up
in the alveoli of the lungs. Oxygen from inhaled air
passes through the walls of the alveoli into the
capillaries. Red blood cells flow through the capillaries
and special proteins in the blood, called hemoglobin,
pick up the oxygen.

31. * Each hemoglobin molecule can carry four oxygen
molecules. When oxygen binds to the hemoglobin in the red
blood cells, the blood becomes oxygenated. Oxygenated
blood flows from the capillaries into larger blood vessels
called arteries. Arteries carry the oxygen-rich blood to the
heart where it is pumped to other parts of the body.
* When the oxygenated blood reaches tissue in other parts
of the body, the red blood cells once again enter capillaries
that surround tissues and organs. The hemoglobin releases
the oxygen it is carrying and the gas moves through capillary
walls into the surrounding tissue. Here the oxygen can be
picked up and used by the body’s cells.

32. * Cells release carbon dioxide gas as a waste product.
Carbon dioxide and the deoxygenated blood move
through veins back to the heart. The heart pumps this
oxygen-depleted, carbon dioxide-rich blood into the
capillaries surrounding the alveoli in the lungs. Carbon
dioxide moves through the capillary walls and into the
alveoli and is removed from the body by exhalation. The
red blood cells pick up more oxygen and the cycle starts
over again.