RESPIRATION:
Respiration is the transport of oxygen from the clean air to the tissue cells and the transport of carbon dioxide in the opposite direction.
RESPIRATORY SYSTEM:
In humans and other animals, the respiratory system can be conveniently subdivided into an upper respiratory track and lower respiratory track.
In humans and other animals, the respiratory system can be conveniently subdivided into an upper respiratory track and lower respiratory track.
Air moves through the body in the following order :
- Posterior
- Nasal cavity
- Pharynx (naso-, oro-, laryngo-)
- Larynx (voice box)
- Trachea (wind pipe)
- Thoracic cavity (chest)
- Bronchi (right and left)
- Alveoli (site of gas exchange)
UPPER RESPIRATORY SYSTEM
NASAL CAVITY:
The lateral wall of the nasal cavity is mainly made up by the maxilla, however there is a deficiency that is compensated by: the perpendicular plate of the palatine bone, the medial pterygoid plate, the labyrinth of the ethmoid and the inferior concha. The nasal cavity is enclosed by the nasal bone above. The floor of the nasal cavity, which forms the roof of the mouth, is made up by the bones of the hard palate: the horizontal plate of the palatine bone posteriorly and the palatine process of the maxilla anteriorly. To the front of the nasal cavity is the nose, while the back is continuous with the pharynx. The paranasal sinuses are connected to the nasal cavity through small orifices called ostia.
The nasal cavity is divided in two by a vertical fin called the nasal septum. On the sides of the nasal cavity are three horizontal outgrowths called turbinates or conchae (singular "concha"). These turbinates disrupt the airflow, directing air toward the olfactory epithelium on the surface of the turbinates and the septum. The vomeronasal organ is located at the back of the septum and has a role in pheromone detection.
Cilia and mucus along the inside wall of the nasal cavity trap and remove dust and pathogens from the air as it flows through the nasal cavity. The cilia move the mucus down the nasal cavity to the pharynx, where it can be swallowed.
The nasal cavity is divided in two by a vertical fin called the nasal septum. On the sides of the nasal cavity are three horizontal outgrowths called turbinates or conchae (singular "concha"). These turbinates disrupt the airflow, directing air toward the olfactory epithelium on the surface of the turbinates and the septum. The vomeronasal organ is located at the back of the septum and has a role in pheromone detection.
Cilia and mucus along the inside wall of the nasal cavity trap and remove dust and pathogens from the air as it flows through the nasal cavity. The cilia move the mucus down the nasal cavity to the pharynx, where it can be swallowed.
The nasal cavity is divided into two segments: the respiratory segment and the olfactory segment. The respiratory segment is lined with ciliated pseudostratified columnar epithelium (also called respiratory epithelium). The conchae are located in this region. The respiratory segment has a very vascularized lamina propria allowing the venous plexuses of the conchal mucosa to engorge with blood, restricting airflow and causing air to be directed to the other side of the nose. This cycle occurs approximately every 20-30 minutes. Nose bleeds in the inferior concha are common in this region. The olfactory segment is lined with a specialized type of pseudostratified columnar epithelium, known as olfactory epithelium, which contains receptors for the sense of the smell. This segment is located along the dorsal roof of the nasal cavity. Histological sections appear yellowish-brown due to the presence of lipofuscin pigments. Olfactory mucosal cell types include: bipolar neurons, supporting (sustentacular) cells, basal cells, and Bowman's glands. The axons of the bipolar neurons form the olfactory nerve (cranial nerve I) which enters the brain through the cribiform plate. Bowman's glands are serous glands in the lamina propria, whose secretions trap and dissolve oderiferous substances.the nasal cavity also can be called the nostrel.
PHARYNX:
The human pharynx is conventionally divided into three sections:
Oropharynx:
The oropharynx lies behind the oral cavity. The anterior wall consists of the base of the tongue and the vallecula; the lateral wall is made up of the tonsil, tonsillar fossa, and tonsillar (faucial) pillars; the superior wall consists of the inferior surface of the soft palate and the uvula.
Nasopharynx:
The nasopharynx lies behind the nasal cavity. Postero-superiorly this extends from the level of the junction of the hard and soft palates to the base of Skull, laterally to include the fossa of Rosenmuller. The inferior wall consists of the superior surface of the soft palate.
Hypopharynx:
The hypopharynx, laryngopharynx roughly corresponds to the levels between C3 to C6, it includes the pharyngo-esophageal junction (postcricoid area), the piriform sinus, and the posterior pharyngeal wall.
Like the oropharynx above it the hypopharynx serves as a passageway for food and air and is lined with a stratified squamous epithelium.
It lies directly anterior to the upright epiglottis and extends to the larynx, where the respiratory and digestive pathways diverge.
At that point the laryngopharynx is continuous with the esophagus posteriorly. The esophagus conducts food and fluids to the stomach; air enters the larynx anteriorly. During swallowing, food has the "right of way", and air passage temporarily stops.
Oropharynx:
The oropharynx lies behind the oral cavity. The anterior wall consists of the base of the tongue and the vallecula; the lateral wall is made up of the tonsil, tonsillar fossa, and tonsillar (faucial) pillars; the superior wall consists of the inferior surface of the soft palate and the uvula.
Nasopharynx:
The nasopharynx lies behind the nasal cavity. Postero-superiorly this extends from the level of the junction of the hard and soft palates to the base of Skull, laterally to include the fossa of Rosenmuller. The inferior wall consists of the superior surface of the soft palate.
Hypopharynx:
The hypopharynx, laryngopharynx roughly corresponds to the levels between C3 to C6, it includes the pharyngo-esophageal junction (postcricoid area), the piriform sinus, and the posterior pharyngeal wall.
Like the oropharynx above it the hypopharynx serves as a passageway for food and air and is lined with a stratified squamous epithelium.
It lies directly anterior to the upright epiglottis and extends to the larynx, where the respiratory and digestive pathways diverge.
At that point the laryngopharynx is continuous with the esophagus posteriorly. The esophagus conducts food and fluids to the stomach; air enters the larynx anteriorly. During swallowing, food has the "right of way", and air passage temporarily stops.
LARYNX:
The larynx (plural larynges), colloquially known as the voicebox, is an organ in the neck of mammals involved in protection of the trachea and sound production. The larynx houses the vocal folds, and is situated just below where the tract of the pharynx splits into the trachea and the esophagus.
Muscles associated with the larynx:
Cricothyroid muscle lengthens and stretches the vocal cords.
Posterior cricoarytenoid muscle abducts the vocal cords.
Lateral cricoarytenoid muscle adducts the vocal cords.
Thyroarytenoid muscle (also called vocalis muscle) shortens vocal cords.
Transverse arytenoid muscle adducts the vocal folds.
Cricothyroid muscle lengthens and stretches the vocal cords.
Posterior cricoarytenoid muscle abducts the vocal cords.
Lateral cricoarytenoid muscle adducts the vocal cords.
Thyroarytenoid muscle (also called vocalis muscle) shortens vocal cords.
Transverse arytenoid muscle adducts the vocal folds.
Cartilages:
The cartilages of the larynx are the thyroid, cricoid, arytenoids, corniculates, and the cuneiforms.
The cartilages of the larynx are the thyroid, cricoid, arytenoids, corniculates, and the cuneiforms.
LOWER RESPIRATORY SYSTEM
TRACHEA:
The trachea, or windpipe, is a tube that has an inner diameter of about 20-25 mm and a length of about 10-16cm. It commences at the larynx at the level vertebral level of C6 and bifurcates into the primary main bronchi at the vertebral level of T4/T5, and from the pharynx, allowing the passage of air to the lungs. It is lined with pseudostratified ciliated columnar epithelium cells with mucosae goblet cells which produce mucus. This lines the cells of the trachea to trap inhaled foreign particles which the cilia then waft upwards towards their larynx and then the pharynx where it can then be swallowed into the stomach.
In humans there are about 15 – 20 incomplete C-shaped cartilaginous rings which reinforces the anterior and lateral sides of the trachea to protect and maintain the airway open. There is a piece of smooth muscle connecting the ends off the incomplete cartilaginous rings called the Trachealis muscle. This contracts reducing the size of the lumen of the trachea to increase the air flow rate during coughing. The esophagus lies posteriorly to the trachea. The cartilaginous rings are incomplete because this allows the trachea to collapse slightly to allow food to pass down the esophagus. The epiglottis is the flap that closes the trachea during swallowing to prevent swallowed matter from entering the trachea.
In humans there are about 15 – 20 incomplete C-shaped cartilaginous rings which reinforces the anterior and lateral sides of the trachea to protect and maintain the airway open. There is a piece of smooth muscle connecting the ends off the incomplete cartilaginous rings called the Trachealis muscle. This contracts reducing the size of the lumen of the trachea to increase the air flow rate during coughing. The esophagus lies posteriorly to the trachea. The cartilaginous rings are incomplete because this allows the trachea to collapse slightly to allow food to pass down the esophagus. The epiglottis is the flap that closes the trachea during swallowing to prevent swallowed matter from entering the trachea.
BRONCHUS:
A bronchus (plural bronchi, adjective bronchial) is a caliber of airway in the respiratory tract that conducts air into the lungs. No gas exchange takes place in this part of the lungs.
The trachea (windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the sternal angle. The right main bronchus is wider, shorter, and more vertical than the left main bronchus. The right main bronchus subdivides into three segmental bronchi while the left main bronchus divides into two. The lobar bronchi divide into tertiary bronchi. Each of the segmental bronchi supplies a bronchopulmonary segmen. A bronchopulmonary segment is a division of a lung that is separated from the rest of the lung by a connective tissue septum. This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. There are ten segments per lung, but due to anatomic development, several segmental bronchi in the left lung fuse, giving rise to eight. The segmental bronchi divide into many primary bronchioles which divide into terminal bronchioles, each of which then gives rise to several [respiratory bronchiole]]s, which go on to divide into 2 to 11 alveolar ducts. There are 5 or 6 alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.
There is hyaline cartilage present in the bronchi, present as irregular rings in the larger bronchi (and not as regular as in the trachea), and as small plates and islands in the smaller bronchi. Smooth muscle is present continuously around the bronchi.
In the mediastinum, at the level of the fifth thoracic vertebra, the trachea divides into the right and left primary bronchi. The bronchi branch into smaller and smaller passageways until they terminate in tiny air sacs called alveoli.
The cartilage and mucous membrane of the primary bronchi are similar to that in the trachea. As the branching continues through the bronchial tree, the amount of hyaline cartilage in the walls decreases until it is absent in the smallest bronchioles. As the cartilage decreases, the amount of smooth uscle increases. The mucus membrane also undergoes a transition from ciliated pseudostratified columnar epithelium to simple cuboidal epithelium to simple squamous epithelium.
The alveolar ducts and alveoli consist primarily of simple squamous epithelium, which permits rapid diffusion of oxygen and carbon dioxide. Exchange of gases between the air in the lungs and the blood in the capillaries occurs across the walls of the alveolar ducts and alveoli.
There is hyaline cartilage present in the bronchi, present as irregular rings in the larger bronchi (and not as regular as in the trachea), and as small plates and islands in the smaller bronchi. Smooth muscle is present continuously around the bronchi.
In the mediastinum, at the level of the fifth thoracic vertebra, the trachea divides into the right and left primary bronchi. The bronchi branch into smaller and smaller passageways until they terminate in tiny air sacs called alveoli.
The cartilage and mucous membrane of the primary bronchi are similar to that in the trachea. As the branching continues through the bronchial tree, the amount of hyaline cartilage in the walls decreases until it is absent in the smallest bronchioles. As the cartilage decreases, the amount of smooth uscle increases. The mucus membrane also undergoes a transition from ciliated pseudostratified columnar epithelium to simple cuboidal epithelium to simple squamous epithelium.
The alveolar ducts and alveoli consist primarily of simple squamous epithelium, which permits rapid diffusion of oxygen and carbon dioxide. Exchange of gases between the air in the lungs and the blood in the capillaries occurs across the walls of the alveolar ducts and alveoli.
ALVEOLUS:
An alveolus (plural: alveoli, from Latin alveolus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. Mainly found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates.
The lungs contain about 300 million alveoli, representing a total surface area of approx. 70-90 square meters (m2). Each alveolus is wrapped in a fine mesh of capillaries covering about 70% of its area.
The alveoli have radii of about 0.05 mm but increase to around 0.1 mm during inhalation.
The alveoli consist of an epithelial layer and extracellular matrix surrounded by capillaries. In some alveolar walls there are pores between alveoli.
The alveoli have radii of about 0.05 mm but increase to around 0.1 mm during inhalation.
The alveoli consist of an epithelial layer and extracellular matrix surrounded by capillaries. In some alveolar walls there are pores between alveoli.
There are three major alveolar cell types in the alveolar wall (pneumocytes):
Type I cells that form the structure of an alveolar wall
Type II cells that secrete surfactant to lower the surface tension of water and allows the membrane to separate thereby increasing the capability to exchange gases. Surfactant is continuously released by exocytosis. It forms an underlying aqueous protein-containing hypophase and an overlying phospholipid film composed primarily of dipalmitoyl phosphatidylcholine.
Macrophages that destroy foreign material, such as bacteria.
The alveoli have an innate tendency to collapse (atelectasis) because of their spherical shape, small size, and surface tension due to water vapor. Phospholipids, which are called surfactants, and pores help to equalize pressures and prevent collapse.
