Respiratory System: Anatomy and Function

Introduction to the Respiratory System

• The respiratory system includes the nose, nasal cavity, sinuses, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli.

Overview of the Respiratory System and Tract

• The upper respiratory system consists of the nose, nasal cavity, sinuses, and pharynx.
• The lower respiratory system consists of the larynx, trachea, bronchi, bronchioles, and alveoli.
• The respiratory system allows for gas exchange between the air and blood.
• It also protects respiratory surfaces from dehydration and pathogens.
• Verbal communication is enabled through sound production.
• The respiratory system assists in regulating blood volume, blood pressure, and body fluid pH.

The Respiratory Epithelium

• It consists of pseudostratified, ciliated, columnar cells, except in the pharynx, smaller bronchi, and alveoli.
• Stratified squamous cells are found in the pharynx.
• Mucus-producing cells are present in the nasal cavity and lower respiratory tract.
• Ciliated columnar cells move mucus upward to cough out debris.
• Stratified squamous cells provide protection against abrasion.
• Mucous cells produce mucus that traps inhaled debris, preventing it from entering the lungs.

Protection of the Respiratory System

• Nose hairs, known as vibrissae, block some inhaled debris.
• The nasal cavity produces mucus to trap inhaled debris, which can be removed by sneezing.
• The respiratory epithelium mucus traps inhaled debris, which can be removed by coughing.

The Upper Respiratory System - Air Pathway

• Air enters through the external nares and passes by the nasal vestibule.
• The nasal vestibule area is surrounded by two pairs of alar cartilage.
• The air then enters the nasal cavity.
• Air flows in and around the nasal conchae (inferior, middle, and superior), where debris gets stuck in the mucus.
• As air swirls around the conchae, it warms before entering the trachea.
• Air enters the internal nares, followed by entering the nasopharynx area.

The Nose and Nasal Cavity

• The nose consists of nasal bones, the nasal septum, cartilage, external nares, alar cartilage, the dorsum and apex and the nasal conchae.
• The nasal septum includes the vomer and perpendicular plate of the ethmoid.

The Pharynx

• The pharynx connects the nose to the mouth to the throat.
• The nasopharynx is located at the back of the nose area.
• The oropharynx is located at the back of the moth area and consists of the pharyngeal arch and uvula.
• The laryngopharynx is the area that has the entrance to the trachea and esophagus.

The Larynx

• The larynx is a cylindrically shaped organ.
• Its cartilaginous walls are stabilized by ligaments or skeletal muscles.
• It begins at vertebra C3 or C4 and ends at vertebra C7.
• The larynx has unpaired cartilages including the thyroid cartilage, cricoid cartilage, and epiglottis.
• The thyroid cartilage contains the laryngeal prominence.
• The cricoid and epiglottis are unpaired cartilage.
• The epiglottis closes over the glottis during swallowing of food.
• Paired laryngeal cartilages play a role in opening and closing the glottis.
• These cartilages are the arytenoid, corniculate, and cuneiform cartilages.

Laryngeal Ligaments

• Intrinsic ligaments bind the laryngeal cartilages together.
• Extrinsic ligaments bind the thyroid cartilage to the hyoid bone and cricoid cartilage.
• Vestibular and local ligaments extend between the thyroid cartilage and the arytenoids.

Sound Production and Laryngeal Musculature

• Air passing between the vocal cords creates sound.
• Pitch depends on the vocal cords' diameter, length, and tension.
• Children have slender, short vocal folds, creating a high-pitched sound.
• At puberty, males' vocal cords thicken and lengthen, creating a deeper voice than females.
• Sound amplification occurs in the sinus cavities.
• Production of sounds depends on the movement of the lips, tongue, and cheeks.
• Intrinsic muscles regulate tension of the vocal cords and the opening/closing of the glottis.
• Extrinsic muscles position and stabilize the larynx.

The Trachea

• The trachea is 11 cm long and 2.5 cm in diameter.
• It bifurcates at the carina into the right and left bronchi at T5.
• The trachea contains 15-20 C-shaped tracheal cartilages.
• Annular ligaments connect one cartilage ring to another.
• The lining consists of respiratory epithelia, lamina propria, and submucosa.
• The posterior side of the cartilage ring is the trachealis muscle.
• This allows constriction and dilation of the trachea.

The Primary Bronchi

• The trachea branches at the carina forming the left and right primary bronchi.
• Primary bronchi enter each lung at the hilum.
• The hilum is the point of entrance and exit of the pulmonary blood vessels.
• The right primary bronchus is steeper and larger in diameter than the left.
• A person can aspirate foreign objects into the right lung easier than the left lung because of this.
• The combination of the bronchus, artery, and vein is referred to as the root.

Lung Structure

• The lungs have an apex which points superiorly and the base points inferiorly.
• The right lung has superior, middle, and inferior lobes, divided by the horizontal and oblique fissures.
• The left lung has superior and inferior lobes, separated by the oblique fissure and a cardiac notch.
• Lungs have costal, mediastinal, and diaphragmatic surfaces.
• The primary bronchi branch numerous times into extrapulmonary bronchi (outside lungs) and intrapulmonary bronchi (inside lungs).
• Primary bronchus divides to form secondary and tertiary bronchi.
• Each tertiary bronchus serves a specific area called a bronchopulmonary segment.
• The right primary bronchus divides into the superior lobar, middle lobar, and inferior lobar secondary bronchi.
• The left primary bronchus divides into the superior lubar and inferior lobar secondary bronchi.
• The right lung has 10 tertiary bronchi and therefore 10 bronchopulmonary segments.
• The left lung has 9 tertiary bronchi and therefore 9 bronchopulmonary segments.

The Bronchioles

• The tertiary bronchi give rise to the bronchioles.
• Bronchioles have a diameter of 0.3–0.5 mm are self-supporting, thus not requiring cartilage plates.
• Smooth muscle enables bronchodilation (sympathetic stimulation) and bronchoconstriction (parasympathetic stimulation).
• Bronchioles terminate with clusters of alveolar sacs.

Alveolar Ducts and Alveoli

• Each lung has about 150 million alveoli, surrounded by an extensive capillary network.
• These capillaries drop off carbon dioxide and pick up oxygen.
• Elastic tissue surrounds each alveolus, maintaining its shape and position during breathing.
• The alveoli are lined with a single layer of squamous cells.
• These linings are called Type I pneumocytes.
• Type II pneumocytes secrete surfactant, which prevents alveolar collapse, as well as scattered among the Type 1 pneumocytes.
• Alveolar macrophages wander around phagocytizing particulate matter.
• Pulmonary arteries transport carbon dioxide to alveolar capillaries.
• Carbon dioxide leaves the capillaries and enters the alveolar sacs.
• Oxygen leaves the alveolar sacs and enters the lung capillaries.
• Oxygen enters the pulmonary veins which returns to the heart to be pumped to all body parts.

Pleural Cavities and Membranes

• The plural cavities are located between the visceral and parietal membranes and is filled with pleural fluid.
• The right and left pleural cavities are separated by the mediastinum.
• Visceral pleura covers the lung's outer surface, while the parietal pleura lines the thoracic wall.
• The space between the visceral and parietal pleura is the pleural cavity.
• Pleural fluid reduces friction during breathing.
• Pleurisy occurs when the membranes produce too much pleural fluid or adhere to the thoracic wall resulting in pain upon breathing.

Respiratory Muscles and Pulmonary Ventilation

• The muscles involved in pulmonary ventilation (breathing) are the diaphragm, external intercostals, and internal intercostals.
• The diaphragm contracts (lowers) to cause inhalation and relaxes (raises) to cause exhalation.
• External intercostals elevate the ribs aiding in inhalation.
• Internal intercostals depress the ribs aiding in exhalation.
• Respiratory movements can be eupnea or hyperpnea.
• Eupnea is quiet breathing, which can be diaphragmatic or costal breathing.
• Women typically use costal breathing due to pregnancy pushing upward on the diaphragm.
• Hyperpnea is forced breathing and generally requires the use of accessory breathing muscles.

Respiratory Changes at Birth

• Pulmonary arterial resistance is high and vessels are collapsed.
• The rib cage is compressed and passages contain no air, just fluid.
• At birth, air enters, forcing fluid out, which triggers the closure of Foramen ovale and ductus arteriosus.

Respiratory Centers of the Brain

• There are three pairs of nuclei in the pons and medulla oblongata that regulate the respiratory muscles.
• The respiratory rhythmicity center sets the base respiratory pace, it is located in the medulla oblongata.
• The apneustic center adjusts the respiratory pace, and is located in the pons.
• The pneumotaxic center adjusts the respiratory pace, and it is located in the pons.
• There are three different reflexes involved in respiration:
• Mechanoreceptor reflexes respond to changes in lung volume or changes in blood pressure.
• Chemoreceptor reflexes respond to changes in partial pressures of carbon dioxide and oxygen, and also changes in pH.
• Protective reflexes respond to physical injury or irritation.

Aging and the Respiratory System

• The respiratory system becomes less efficient as we age.
• Noteworthy changes include elastic tissue deterioration and restricted rib movements due to arthritis.
• Some degree of emphysema hinders breathing.
• 1 square foot of respiratory membrane is lost annually after age 30.