lec8 anatomy

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Anatomy Dr.Israa H. Mohsen
Lecture 8
Respiratory System
The respiratory and cardiovascular systems work closely together to provide the body
with oxygen and to remove carbon dioxide. The respiratory system assumes other
roles as well: it influences sound production and speech; it makes the sense of smell it
helps the body maintain homeostasis through the regulation of acid-base balance. The
respiratory system is divided into two tracts:
1.The upper respiratory tract consists of structures located outside the thoracic
cavity.
2.The lower respiratory tract consists of structures located inside the thoracic
cavity.
Upper respiratory tract
Functionally, the respiratory system also includes the:
? Oral cavity
? Rib cage
? Respiratory muscles (including the diaphragm)
upper
respiratory
tract
lower
respirato
ry tract
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The structures of the upper respiratory tract—consisting of the nose, nasopharynx,
oropharynx, laryngopharynx, and larynx—warm and humidify inspired air. They’re
also responsible for the senses of smell and taste as well as chewing and swallowing
food.
Nose and Nasal Cavities
Air enters and leaves the respiratory system through the nose. Just inside the nostrils
are small hairs called cilia that filter out dust and large foreign particles.
The nasal cavity lies just over the mouth, separated from that orifice by a bony
structure called the palate. A vertical plate of bone and cartilage—called the
septum—separates the cavity into two halves. The cavity is lined with epithelium rich
in goblet cells that produce mucus.
Pharynx
Just behind the nasal and oral cavities is a muscular tube called the pharynx.
Commonly called the throat, the pharynx can be divided into three regions:
Projecting from the
lateral wall of each
cavity are three bones
called conchae.
These bones create
narrow passages,
ensuring that most air
contacts the mucous
membrane on the way
through.
As it does, the air picks
up moisture and heat
from the mucosa. At
the same time, dust
sticks to the mucus,
which is then
swallowed.
Branches of the olfactory
nerve (responsible for the
sense of smell) penetrate the
upper nasal cavity and lead
to the brain.
The sphenoid sinus
(shown here), as well
as the other
paranasal sinuses
(including the frontal,
maxillary, and
ethmoidal sinuses),
drain mucus into the
nasal cavity
1.The nasopharynx extends from the
posterior nares to the soft palate. It contains
openings for the right and left auditory
(eustachian) tubes.
2.The oropharynx is a space between the soft
palate and the base of the tongue. It contains the
palatine tonsils (the ones most commonly
removed by tonsillectomy) as well as the lingual
tonsils, found at the base of the tongue.
3.The laryngopharynx passes dorsal to the
larynx and connects to the esophagus.
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Only air passes through the nasopharynx, while both food and air pass through the
oropharynx and laryngopharynx.
Larynx
Lying between the root of the tongue and the upper end of the trachea, the larynx is a
chamber formed by walls of cartilage and muscle. Because it contains the vocal cords,
it’s often called the voice box; however, it actually has three functions:
1. It prevents food and liquids from entering the trachea.
2. It acts as an air passageway between the pharynx and trachea.
3. It produces sound.
• The epiglottis—which
closes over the top of the
larynx during swallowing
to direct food and liquids
into the esophagus—is
the uppermost cartilage
• The largest piece of
cartilage is the thyroid
cartilage, which is also
known as the Adam’s
apple.
• The mucous
membrane lining the
larynx forms two pairs
of folds. The superior
pair—called
vestibular folds, or,
occasionally, false
vocal cords—play no
role in speech. They
close the glottis (the
opening between the
vocal cords) during
swallowing to keep
food and liquids out of
the airway.
• The inferior pair, the
vocal cords,
produces sound when
air passes over them
during exhalation.
• The opening
between the cords is
called the glottis.
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Lower respiratory tract
The lower respiratory tract consists of the trachea, bronchi, and lungs. The trachea and the bronchi distribute air to the interior of the lungs; deep within the lungs is where gas exchange occurs.
Trachea
Lying just in front of the esophagus, the trachea is a rigid tube about 4.5 inches (11 cm) long and 1 inch (2.5 cm) wide. C-shaped rings of cartilage encircle the trachea to reinforce it and keep it from collapsing during inhalation. The open part of the “C” faces posteriorly, giving the esophagus room to expand during swallowing.
The trachea extends from the larynx to a cartilaginous ridge called the carina.
Bronchial Tree
At the carina, the trachea branches into two primary bronchi. Like the trachea, the primary bronchi are supported by C-shaped rings of cartilage. (All of the divisions of the bronchial tree also consist of elastic connective tissue.)
The right bronchus is slightly wider and more vertical than the left, making this the most likely location for aspirated (inhaled) food particles and small objects to lodge.
Immediately after entering the lungs, the primary bronchi branch into secondary bronchi: one for each of the lung’s lobes. Since the left lung consists of two lobes, it has two secondary bronchi; the right lung has three lobes, so it has three bronchi. Secondary bronchi branch into smaller tertiary bronchi. The cartilaginous rings around the bronchi become irregular and disappear entirely in the smaller bronchioles. Tertiary bronchi continue to branch, resulting in very small airways called bronchioles. Less than 1 mm wide and lacking any supportive cartilage, bronchioles divide further to form thin walled passages called alveolar ducts Alveolar ducts throughout the lungs terminate in clusters of alveoli called alveolar sacs, the primary structures for gas exchange.
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Alveoli
The lung passages all exist to serve the alveoli because it’s within the alveoli that gas
exchange occurs. It’s estimated that the lungs contain 300 million alveoli. The alveoli
are wrapped in a fine mesh of capillaries. The extremely thin walls of the alveoli, and
the closeness of the capillaries, allow for efficient gas exchange.
For gas to enter or leave a cell, it must be dissolved in a liquid. Therefore, the inside
of each alveolus is coated with a thin layer of fluid. This fluid contains surfactant, a
substance that helps reduce surface tension (the force of attraction between water
molecules) to keep the alveolus from collapsing as air moves in and out during
respiration.
Infants born before 28 weeks’ gestation commonly lack surfactant. Without
surfactant, surface tension restricts alveolar expansion during inspiration and causes
alveolar collapse during expiration. That’s why neonates often develop respiratory
distress syndrome and require the administration of artificial surfactant.
Trachea
carina.
Primary
bronchi
.
secondary
bronchi
tertiary
bronchi
bronchioles
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The alveoli are
wrapped in a fine
mesh of
capillaries
The exchange of air occurs through what’s called
the respiratory membrane, which consists of
the alveolar epithelium, the capillary endothelium, and
their joined basement membranes.
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Lungs
The lungs fill the pleural cavity: they extend from just above the clavicles to the
diaphragm and lie against the anterior and posterior ribs. The medial portion of each
lung is concave to allow room for the heart and great vessels. The primary bronchi
and pulmonary blood vessels enter each lung through an opening on the lung’s medial
surface called the hilum.
Pleurae
There are two membranes cover the lungs called Pleurae
1. visceral pleura : serous membrane covers the surface of the lungs, extending
into the fissures.
2. parietal pleura: The parietal pleura lines the entire thoracic cavity.
The space between the visceral and parietal pleurae is called the pleural cavity. The
pleural cavity is only a potential space; the two membranes are normally separated
only by a film of slippery pleural fluid. The fluid in the pleural cavity serves two
purposes:
The top, or apex, of each lung
extends about 1/2” (1.3 cm)
above the first rib.
The right lung is shorter,
broader, and larger than
the left. It has three
lobes—the superior,
middle, and inferior—
and handles 55% of the
gas exchange. The right
lung contains two
fissures:
• Horizontal fissure
• Oblique fissure
The base of each
lung rests on the
diaphragm.
Because the heart extends toward
the left, the left lung has only two
lobes: the superior and inferior.
It contains one fissure:
• Oblique fissure
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• It lubricates the pleural surfaces, allowing the two surfaces to glide painlessly
against each other as the lungs expand and contract.
• Because the pressure in the pleural cavity is lower than atmospheric pressure, it
creates a pressure gradient that assists in lung inflation.
visceral pleura
Parietal pleura
Pleural cavity.