THE RESPIRATORY SYSTEM

THE RESPIRATORY SYSTEM 

 ( BY USAMA MUSTAFA )




 

THE RESPIRATORY SYSTEM

  The respiratory system consists of the nose, nasal cavity, pharynx (throat), larynx (voice box), trachea (windpipe), bronchi, and lungs 

Structurally, the respiratory system consists of two parts:

 (1) the upper respiratory system includes the nose, nasal cavity, pharynx, and associated structures;

    (2) the lower respiratory system includes the larynx, trachea, bronchi, and lungs.

Zones of Respiratory System

 1) The conducting zone consists of a series of interconnecting cavities and tubes both outside and within the lungs.

These passageways include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles; their function is to filter, warm, and moisten air and conduct it into the lungs.

  (2) The respiratory zone consists of tubes and tissues within the lungs where gas exchange occurs.

These tubes and tissues include the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli, and are the main sites of gas exchange between air and blood.

UPPER RESPIRATORY SYSTEM ANATOMY

Nose

   The head has two openings through which substances such as air and food can enter the body—the nose and the mouth.

    The nose is a special organ at the entrance to the respiratory system that is divided into a visible external portion and an internal portion inside the skull called the nasal cavity.

   The openings into the external nose are the external nares or nostrils, which lead into cavities about the size of a fingertip called the nasal vestibules.

Nasal cavity

•Deeper into the skull, beyond the region of the nasal vestibules, is the nasal cavity, also called the internal nose.

•Anteriorly, the nasal cavity merges with the external nose, and posteriorly the internal nose communicates with the pharynx through two openings called the internal nares or choanae.

Functions

•     The interior structures of the nose have three functions:

•     (1) warming, moistening, and filtering incoming air;

•     (2) detecting olfactory (smell) stimuli; and

•     (3) modifying speech vibrations as they pass through the large, hollow resonating chambers.

•     Resonance refers to prolonging, amplifying, or modifying a sound by vibration.

Pharynx

•     The pharynx (FAR-inks), or throat, is a funnel-shaped tube about 13 cm (5 in.) long that starts at the internal nares and extends to the level of the cricoid cartilage, the most inferior cartilage of the larynx (voice box).

•     The branch of medicine that deals with the diagnosis and treatment of disease of the ears, nose, and throat (ENT) is called otorhinolaryngology

Parts of pharynx

•     The pharynx can be divided into three anatomical regions:

•     Nasopharynx The superior portion of the pharynx, called the nasopharynx

•     Oropharynx The intermediate portion of the pharynx, the oropharynx, lies posterior to the oral cavity and extends from the soft palate inferiorly to the level of the hyoid bone.

•     Laryngopharynx. The inferior portion of the pharynx, the laryngopharynx or hypopharynx, begins at the level of the hyoid bone.

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•     Two pairs of tonsils, the palatine tonsils and lingual tonsils, are found in the oropharynx.

•     The posterior wall also contains the pharyngeal tonsil

•     At its inferior end, it opens into the esophagus (food tube) posteriorly and the larynx (voice box) anteriorly.

•     Like the oropharynx, the laryngopharynx is both a respiratory and a digestive pathway and is lined by nonkeratinized stratified squamous epithelium.

LOWER RESPIRATORY SYSTEM ANATOMY

•     The larynx or voice box, is a short passageway that connects the laryngopharynx with the trachea.

•     It lies in the midline of the neck anterior to the fourth through sixth cervical vertebrae (C4–C6).

•     The wall of the larynx is composed of nine pieces of cartilage

•     Three occur singly (thyroid cartilage, epiglottis, and cricoid cartilage), and three occur in pairs (arytenoid, cuneiform, and corniculate cartilages).

The thyroid cartilage,

•     The thyroid cartilage, the largest cartilage of the larynx, consists of two fused plates of hyaline cartilage that form the upper  anterior and lateral walls of the larynx and give it a triangular shape.

•     The anterior junction of the two plates forms the laryngeal prominence (Adam’s apple).

•     It is usually larger in males than in females due to the influence of male sex hormones on its growth during puberty.

•     The epiglottis is a large, leaf shaped piece of elastic cartilage that is covered with epithelium.

•     The broad superior “leaf” portion of the epiglottis is unattached and is free to move up and down like a trap door.

•     During swallowing, the pharynx and larynx rise.

•     Elevation of the pharynx widens it to receive food or drink; elevation of the larynx causes the epiglottis to move down and form a lid over the opening into the larynx, closing it off.

•     The narrowed passageway through the larynx is called the glottis.

Trachea

•     The trachea or windpipe, is a tubular passageway for air that is about 12 cm (5 in.) long and 2.5 cm (1 in.) in diameter.

•     It is located anterior to the esophagus and extends from the larynx to the superior border of the fifth thoracic vertebra (T5), where it divides into the right and left main bronchi.

•     The layers of the tracheal wall, from deep to superficial, are

•     (1) the mucosa,

•     (2) the submucosa,

•     (3) the fibromusculocartilaginous layer, and

•     (4) the adventitia.

•     In the fibromusculocartilaginous layer, the 16–20 incomplete horizontal rings of hyaline cartilage resemble the letter C.

•     The rings are stacked one above another and are joined together by dense connective tissue.

•     They may be felt through the skin inferior to the larynx.

•     The open part of each C-shaped cartilage ring faces posteriorly toward the esophagus and is spanned by a fibromuscular membrane.

•     Within this membrane are transverse smooth muscle fibers, called the trachealis muscle

Bronchi

•     In the thorax, the trachea ends below at the carina by dividing into right and left principal (main) bronchi.

•     The right principal (main) bronchus is wider, shorter, and more vertical than the left and is about 1 in. (2.5 cm) long.

•     Before entering the hilum of the right lung, the principal bronchus gives off the superior lobar bronchus.

•     On entering the hilum, it divides into a middle and an inferior lobar bronchus.

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•     The left principal (main) bronchus is narrower, longer, and more horizontal than the right and is about 2 in. (5 cm) long.

•     It passes to the left below the arch of the aorta and in front of the esophagus.

•     On entering the hilum of the left lung, the principal bronchus divides into a superior and an inferior lobar bronchus

•     The lobar bronchi continue to branch, forming still smaller bronchi, called segmental (tertiary) bronchi

•     The segmental bronchi then divide into bronchioles.

•     Bronchioles in turn branch repeatedly, and the smallest ones branch into even smaller tubes called terminal bronchioles.

•     Terminal bronchioles resembles an inverted tree, it is commonly referred to collectively as the bronchial tree.

•     Beyond the terminal bronchioles of the bronchial tree, the branches become microscopic.

•     These branches are called the respiratory bronchioles and alveolar ducts,

Lungs

•     The lungs are paired cone-shaped organs in the thoracic cavity.

•     A pulmonologist is a specialist in the diagnosis and treatment of diseases of the lungs.

•     Each lung is surrounded by a protective, double-layered serous membrane called the pleural membrane.

•     The superficial layer of the pleural membrane lining the wall of the thoracic cavity is called the parietal pleura.

•     The deep layer, the visceral pleura, adheres to the lungs

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•     Between the visceral and parietal pleurae is a small space, the pleural cavity which contains a small amount of lubricating fluid secreted by the two layers.

•     This fluid reduces friction between the membranes, allowing them to slide easily over one another during breathing.

•     The mediastinal (medial ) surface of each lung contains a region, the hilum

•     Due to the space occupied by the heart, the left lung is about 10 percent smaller than the right lung.

Surface anatomy

Lobes, Fissures, and Lobules

•    Right Lung is divided by the oblique and horizontal fissures into three lobes: the upper, middle, and lower lobes

•    The horizontal fissure divides right lung into upper and middle lobe.

•    The oblique fissure runs from the inferior border upward and backward and separates the middle and inferior lobe

•    The left lung is divided by a similar oblique fissure into two lobes: the upper and lower lobes  There is no horizontal fissure in the left lung.

Broncho pulmonary segment

•     The portion of lung tissue that each segmental bronchus supplies is called a broncho pulmonary segment

•     Each bronchopulmonary segment of the lungs has many small compartments called lobules.

•     Terminal bronchioles in a lobule subdivide into microscopic branches called respiratory bronchioles

•     Respiratory bronchioles in turn subdivide into several (2–11) alveolar ducts which consist of simple squamous epithelium.

Alveolar Sacs and Alveoli

•     The terminal dilation of an alveolar duct is called an alveolar sac and is analogous to a cluster of grapes.

•     Each alveolar sac is composed of outpouchings called alveoli analogous to individual grapes

•     The wall of an alveolus (singular) consists of two types of alveolar epithelial cells.

•     Type I alveolar cells, the predominant cells, are simple squamous epithelial cells that form a nearly continuous lining of the alveolar wall.

•     Type II alveolar cells, also called septal cells, are fewer in number and are found between type I alveolar cells.