BSC NURSING SEM1 APPLIED ANATOMY UNIT 2 The Respiratory system
Structure of the organs of respiration
Structure of the Organs of Respiration
The organs of respiration form the respiratory system, which facilitates the exchange of oxygen and carbon dioxide between the body and the environment. The respiratory system is divided into two main parts:
Upper Respiratory Tract: Includes the nasal cavity, pharynx, and larynx.
Lower Respiratory Tract: Includes the trachea, bronchi, bronchioles, and lungs.
1. Upper Respiratory Tract
Nasal Cavity
Nasal Cavity
The nasal cavity is a hollow space within the nose and skull that serves as the primary entry point for air into the respiratory system. It plays a crucial role in filtering, warming, humidifying incoming air, and detecting smells.
Structure of the Nasal Cavity
External Openings:
Nostrils (External Nares):
Openings that allow air to enter the nasal cavity.
Supported by cartilage and skin.
Divisions:
Nasal Septum:
A vertical partition dividing the nasal cavity into left and right halves.
Composed of:
Cartilage (anteriorly).
Bone (posteriorly, formed by the vomer and perpendicular plate of the ethmoid bone).
Boundaries:
Roof:
Formed by the ethmoid bone and sphenoid bone.
Floor:
Formed by the hard palate (maxilla and palatine bones).
Lateral Walls:
Contain nasal conchae (superior, middle, and inferior) and meatuses.
Posterior:
Opens into the nasopharynx through the choanae (internal nares).
Lining:
Respiratory Mucosa:
Pseudostratified ciliated columnar epithelium with goblet cells.
Secretes mucus to trap dust and pathogens.
Olfactory Mucosa:
Found in the upper part of the nasal cavity.
Contains olfactory receptors for the sense of smell.
Nasal Conchae (Turbinates):
Three bony projections on the lateral walls:
Superior Concha: Part of the ethmoid bone.
Middle Concha: Part of the ethmoid bone.
Inferior Concha: A separate bone.
Function: Increase surface area and create turbulence to filter and humidify air.
Paranasal Sinuses:
Air-filled spaces connected to the nasal cavity.
Include:
Frontal Sinuses.
Maxillary Sinuses.
Ethmoidal Sinuses.
Sphenoidal Sinuses.
Function: Lighten the skull, produce mucus, and resonate the voice.
Blood Supply:
Richly supplied by branches of the internal carotid artery (e.g., anterior and posterior ethmoidal arteries) and external carotid artery (e.g., sphenopalatine artery).
The Kiesselbach’s plexus in the anterior septum is a common site for nosebleeds (epistaxis).
Nerve Supply:
Olfactory Nerve (Cranial Nerve I):
Responsible for the sense of smell.
Trigeminal Nerve (Cranial Nerve V):
Provides sensory innervation to the nasal cavity.
Functions of the Nasal Cavity
Air Filtration:
Cilia and mucus trap dust, pathogens, and foreign particles.
Air Conditioning:
Warms and humidifies incoming air to protect the delicate respiratory tissues.
Olfaction:
Detects and processes smells via the olfactory receptors.
Resonance:
Enhances voice quality by acting as a resonating chamber.
Drainage:
Drains mucus and fluids from the paranasal sinuses and nasolacrimal ducts.
Pharynx
Pharynx
The pharynx is a muscular tube that serves as a shared passageway for both the respiratory and digestive systems. It connects the nasal cavity and mouth to the larynx and esophagus. The pharynx plays a critical role in breathing, swallowing, and vocalization.
Anatomical Divisions of the Pharynx
The pharynx is divided into three regions based on location and function:
Nasopharynx:
Location:
Lies posterior to the nasal cavity and above the soft palate.
Structure:
Lined with pseudostratified ciliated columnar epithelium.
Contains the pharyngeal tonsil (adenoids) on the posterior wall.
Openings of the Eustachian tubes (auditory tubes) are located on the lateral walls.
Function:
Serves as an air passageway only.
Equalizes air pressure between the middle ear and the atmosphere via the Eustachian tubes.
Oropharynx:
Location:
Lies posterior to the oral cavity, extending from the soft palate to the epiglottis.
Structure:
Lined with non-keratinized stratified squamous epithelium to protect against mechanical stress.
Contains the palatine tonsils (on the lateral walls) and lingual tonsil (at the base of the tongue).
Function:
Serves as a passageway for both air and food.
Plays a role in swallowing and immune defense.
Laryngopharynx (Hypopharynx):
Location:
Extends from the epiglottis to the cricoid cartilage, where it continues as the esophagus posteriorly and the larynx anteriorly.
Structure:
Lined with non-keratinized stratified squamous epithelium.
Function:
Serves as a passageway for both air and food.
Directs food and liquids into the esophagus and air into the larynx.
Structure of the Pharynx
Walls:
Composed of skeletal muscle layers:
Outer Circular Muscles:
Includes the superior, middle, and inferior pharyngeal constrictor muscles.
Function: Constrict the pharynx during swallowing.
Inner Longitudinal Muscles:
Includes the stylopharyngeus, salpingopharyngeus, and palatopharyngeus muscles.
Function: Elevate the pharynx during swallowing and speech.
Oropharynx and Laryngopharynx: Non-keratinized stratified squamous epithelium.
Openings:
Nasal Cavity (anterior).
Oral Cavity (anterior).
Larynx (inferiorly).
Esophagus (posteriorly).
Functions of the Pharynx
Respiratory Role:
Conducts air from the nasal cavity to the larynx.
Digestive Role:
Directs food and liquids from the oral cavity to the esophagus.
Swallowing (Deglutition):
The pharyngeal muscles contract to move food from the oropharynx into the esophagus.
Vocalization:
Resonates sound during speech.
Immunological Defense:
Houses lymphoid tissues (e.g., tonsils) that protect against pathogens.
Larynx (Voice Box)
Larynx (Voice Box)
The larynx, also known as the voice box, is a cartilaginous structure located in the neck. It plays a crucial role in respiration, protection of the lower respiratory tract, and sound production (phonation). The larynx connects the pharynx to the trachea and is an essential component of the respiratory system.
Anatomy of the Larynx
Location:
Found in the anterior part of the neck.
Lies at the level of the C3-C6 vertebrae.
Structure:
Composed of cartilage, ligaments, muscles, and a mucosal lining.
Divided into three regions:
Supraglottis: Area above the vocal cords.
Glottis: Includes the vocal cords and the rima glottidis (opening between the cords).
Subglottis: Area below the vocal cords leading to the trachea.
Cartilages:
Framework formed by nine cartilages:
Unpaired Cartilages:
Thyroid Cartilage:
The largest cartilage, forming the Adam’s apple (prominent in males).
Cricoid Cartilage:
Ring-shaped, located below the thyroid cartilage.
Epiglottis:
Leaf-shaped elastic cartilage that folds to cover the laryngeal inlet during swallowing.
Paired Cartilages:
Arytenoid Cartilages:
Pyramid-shaped; pivotal in vocal cord movement.
Corniculate Cartilages:
Small cartilages on top of the arytenoids.
Cuneiform Cartilages:
Embedded in the aryepiglottic folds for structural support.
Muscles:
Intrinsic Muscles:
Control vocal cord tension and shape the glottis.
Examples: Cricothyroid, thyroarytenoid, and posterior cricoarytenoid (the only muscle that abducts the vocal cords).
Extrinsic Muscles:
Move the larynx as a whole during swallowing and speaking.
Examples: Sternothyroid, thyrohyoid.
Vocal Cords (Folds):
True Vocal Cords:
Contain the vocal ligament and vocalis muscle.
Vibrate to produce sound.
False Vocal Cords (Vestibular Folds):
Do not participate in sound production; help close the larynx during swallowing.
Epithelium:
Lined by:
Stratified Squamous Epithelium: Over the vocal cords for protection.
Pseudostratified Ciliated Columnar Epithelium: Elsewhere for mucus production and debris removal.
Functions of the Larynx
Airway Protection:
Prevents food and liquids from entering the trachea during swallowing, with the help of the epiglottis and vocal cords.
Phonation (Sound Production):
The vibration of the true vocal cords produces sound.
Pitch is controlled by tension in the vocal cords, adjusted by the intrinsic muscles.
Respiration:
Regulates airflow to the lower respiratory tract through the glottis.
Cough Reflex:
Helps expel foreign particles by closing the vocal cords momentarily and then forcefully opening them.
Blood Supply and Innervation
Blood Supply:
Arteries:
Superior laryngeal artery (branch of the superior thyroid artery).
Inferior laryngeal artery (branch of the inferior thyroid artery).
Veins:
Drain into the superior and inferior thyroid veins.
Nerve Supply:
Vagus Nerve (Cranial Nerve X):
Superior Laryngeal Nerve:
External branch: Controls cricothyroid muscle.
Internal branch: Provides sensory innervation to the larynx above the vocal cords.
Recurrent Laryngeal Nerve:
Controls all intrinsic muscles except the cricothyroid.
Provides sensory innervation below the vocal cords.
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2. Lower Respiratory Tract
Trachea (Windpipe)
Trachea (Windpipe)
The trachea, commonly known as the windpipe, is a vital part of the respiratory system. It serves as the main airway, connecting the larynx to the bronchi, allowing air to flow into and out of the lungs.
Anatomy of the Trachea
Location:
Extends from the cricoid cartilage of the larynx (C6 vertebra) to the level of the T4-T5 vertebra, where it bifurcates into the right and left bronchi (at the carina).
Located anterior to the esophagus and posterior to the sternum.
Structure:
Length: Approximately 10–12 cm (4–5 inches).
Diameter: About 2–2.5 cm in adults.
Layers:
Mucosa:
Inner lining composed of pseudostratified ciliated columnar epithelium with goblet cells.
Goblet cells produce mucus, which traps dust and debris.
Cilia move mucus upward toward the pharynx for removal (mucociliary escalator).
Submucosa:
Contains connective tissue, blood vessels, and seromucous glands.
Cartilage:
16–20 C-shaped rings of hyaline cartilage provide structural support and keep the trachea open.
The open ends of the rings face the esophagus and are connected by the trachealis muscle and elastic connective tissue.
Adventitia:
Outermost layer of connective tissue that anchors the trachea to surrounding structures.
Carina:
A ridge of cartilage located at the bifurcation of the trachea into the right and left main bronchi.
Highly sensitive; stimulation can trigger the cough reflex.
Functions of the Trachea
Air Passageway:
Conducts air between the larynx and bronchi.
Air Filtration:
Mucus traps dust, debris, and microorganisms, which are then expelled by the ciliary action of the mucosa.
Cough Reflex:
Protects the lower respiratory tract by expelling irritants and foreign particles.
Structural Integrity:
The cartilage rings prevent the trachea from collapsing during breathing.
Blood Supply and Innervation
Blood Supply:
Arteries:
Branches from the inferior thyroid artery and bronchial arteries.
Veins:
Drain into the inferior thyroid veins and brachiocephalic veins.
Nerve Supply:
Vagus Nerve (Cranial Nerve X):
Provides parasympathetic innervation.
Sympathetic Nerves:
Regulate smooth muscle tone in the trachea.
Bronchi
Bronchi
The bronchi are major airways that branch from the trachea to deliver air into the lungs. They serve as the primary passage for air to move into smaller airways, ultimately leading to the alveoli where gas exchange occurs. The bronchi are an essential component of the lower respiratory tract.
Anatomy of the Bronchi
Division:
The trachea divides at the carina (T4-T5 vertebral level) into:
Right Main (Primary) Bronchus:
Wider, shorter (2.5 cm), and more vertical than the left.
More prone to foreign body aspiration.
Left Main (Primary) Bronchus:
Narrower, longer (5 cm), and more horizontal.
Further Branching:
Lobar (Secondary) Bronchi:
Branch from the main bronchi.
Correspond to the lung lobes:
Right lung: 3 lobar bronchi (superior, middle, inferior).
Left lung: 2 lobar bronchi (superior, inferior).
Segmental (Tertiary) Bronchi:
Branch from the lobar bronchi.
Correspond to the bronchopulmonary segments (10 segments in the right lung, 8-10 in the left lung).
Smaller bronchi continue branching into bronchioles.
Structure:
Cartilage:
Main and lobar bronchi have cartilage rings, while segmental bronchi have irregular cartilage plates.
Cartilage decreases as the airways branch.
Smooth Muscle:
Increases as cartilage decreases, allowing for regulation of airway diameter.
Epithelium:
Lined with pseudostratified ciliated columnar epithelium.
Goblet cells secrete mucus to trap particles, and cilia move mucus toward the throat (mucociliary escalator).
Functions of the Bronchi
Air Conduction:
Transport air from the trachea to the bronchioles and lungs.
Airway Clearance:
Cilia and mucus in the bronchial epithelium trap and expel dust, pathogens, and foreign particles.
Regulation of Airflow:
Smooth muscle controls the diameter of the bronchi to regulate airflow during respiration.
Differences Between the Right and Left Main Bronchi
Feature
Right Main Bronchus
Left Main Bronchus
Length
Shorter (2.5 cm)
Longer (5 cm)
Width
Wider
Narrower
Angle
More vertical
More horizontal
Aspiration Risk
Higher (foreign objects more likely)
Lower
Blood Supply and Innervation
Blood Supply:
Arteries:
Bronchial arteries (branches of the thoracic aorta) supply oxygenated blood to the bronchi.
Veins:
Bronchial veins drain into the azygos and pulmonary veins.
Sympathetic nerves cause bronchodilation and reduce mucus secretion.
Bronchioles
Bronchioles
Bronchioles are small, tubular airways in the respiratory system that branch off from the segmental (tertiary) bronchi and lead to the alveoli. They are the first airways in the respiratory tract that lack cartilage, relying on smooth muscle for structure and function.
Anatomy of Bronchioles
Location:
Found within the lungs, branching from the tertiary bronchi.
Structure:
Diameter:
Less than 1 mm.
Wall Composition:
Epithelium:
Changes from pseudostratified ciliated columnar epithelium (larger bronchioles) to simple cuboidal epithelium (terminal bronchioles).
Contains goblet cells in larger bronchioles for mucus secretion, but these are absent in smaller bronchioles.
Smooth Muscle:
Regulates airway diameter through bronchoconstriction and bronchodilation.
Connective Tissue:
Provides flexibility and support.
Cartilage:
Absent, differentiating bronchioles from larger bronchi.
Types of Bronchioles:
Primary Bronchioles:
Branch from the tertiary bronchi.
Terminal Bronchioles:
The smallest conducting bronchioles.
Lead to the respiratory bronchioles.
Respiratory Bronchioles:
Contain some alveoli along their walls.
Mark the transition from the conducting to the respiratory zone.
Functions of Bronchioles
Air Conduction:
Transport air from the bronchi to the alveoli.
Regulation of Airflow:
Smooth muscle controls the diameter of bronchioles, regulating airflow resistance and distribution in the lungs.
Transition to Gas Exchange:
Respiratory bronchioles are involved in the initial stages of gas exchange due to the presence of alveoli.
Blood Supply and Innervation
Blood Supply:
Bronchial Arteries:
Supply oxygenated blood to the bronchioles.
Pulmonary Circulation:
Facilitates gas exchange in the respiratory bronchioles.
Innervation:
Parasympathetic:
Mediated by the vagus nerve, causing bronchoconstriction.
Sympathetic:
Mediated by sympathetic nerves, causing bronchodilation.
Alveoli
Alveoli
The alveoli are the tiny air sacs in the lungs where gas exchange occurs between the air and the blood. They are the terminal structures of the respiratory tract and are critical for oxygenating blood and removing carbon dioxide.
Structure of Alveoli
Shape and Size:
Small, balloon-like sacs.
Approximately 300–500 million alveoli in the human lungs.
Diameter: About 200–300 micrometers.
Alveolar Wall (Respiratory Membrane):
Type I Alveolar Cells:
Composed of simple squamous epithelial cells.
Make up 90-95% of the alveolar surface area.
Thin to facilitate efficient gas exchange.
Type II Alveolar Cells:
Cuboidal cells that secrete surfactant, which reduces surface tension and prevents alveolar collapse.
Alveolar Macrophages (Dust Cells):
Immune cells that remove debris, pathogens, and particles.
Basement Membrane:
Thin connective tissue layer supporting the epithelial cells.
Capillary Network:
Dense network of pulmonary capillaries surrounding each alveolus.
Facilitates gas exchange between the alveoli and blood.
Pores of Kohn:
Small openings between adjacent alveoli.
Allow collateral air movement and equalize pressure.
Surrounding Structures:
Supported by elastic fibers, which help the alveoli expand during inhalation and recoil during exhalation.
Function of Alveoli
Gas Exchange:
Oxygen diffuses from the alveoli into the capillaries and enters the bloodstream.
Carbon dioxide diffuses from the blood into the alveoli to be exhaled.
Surfactant Production:
Type II alveolar cells produce surfactant, which reduces surface tension, making it easier for alveoli to expand during inhalation.
Immune Defense:
Alveolar macrophages protect the lungs from infection by engulfing foreign particles and pathogens.
Respiratory Membrane
The respiratory membrane is the barrier through which gas exchange occurs. It is extremely thin (approximately 0.5 micrometers) to facilitate rapid diffusion.
Layers:
Type I alveolar cells.
Fused basement membranes of alveolar and capillary walls.
Endothelial cells of the capillaries.
Gas Exchange Process
Oxygen:
Diffuses from alveolar air (higher partial pressure) into the blood (lower partial pressure).
Carbon Dioxide:
Diffuses from the blood (higher partial pressure) into the alveolar air (lower partial pressure) for exhalation.
Clinical Relevance
Pneumonia:
Inflammation of the alveoli due to infection.
Alveoli fill with fluid, impairing gas exchange.
Chronic Obstructive Pulmonary Disease (COPD):
Includes emphysema, where alveoli lose elasticity and their walls are destroyed, reducing surface area for gas exchange.
Acute Respiratory Distress Syndrome (ARDS):
Severe inflammation and fluid accumulation in the alveoli.
Results in impaired oxygenation.
Pulmonary Fibrosis:
Thickening of the alveolar walls due to scar tissue, reducing the efficiency of gas exchange.
Surfactant Deficiency:
Common in premature infants, leading to respiratory distress syndrome (RDS).
Alveolar Collapse (Atelectasis):
Collapse of alveoli due to blockage or surfactant deficiency.
Comparison of Alveoli with Other Respiratory Structures
Feature
Trachea/Bronchi
Bronchioles
Alveoli
Function
Conduct air
Regulate airflow
Gas exchange
Cartilage
Present
Absent
Absent
Epithelium
Pseudostratified columnar
Simple cuboidal
Simple squamous
Smooth Muscle
Present
Prominent
Absent
Lungs
Comprehensive Details of the Lungs
The lungs are vital organs in the respiratory system, responsible for facilitating the exchange of oxygen and carbon dioxide. Below is a detailed breakdown of their anatomy, physiology, functions, and related clinical aspects.
1. Anatomy of the Lungs
Location and General Structure
Location:
The lungs are located in the thoracic cavity on either side of the mediastinum.
Enclosed by the rib cage, separated by the diaphragm below, and the heart lies between them.
Shape:
Conical, with a broad base resting on the diaphragm and a narrow apex extending above the first rib.
Right and Left Lungs
Right Lung:
Larger and heavier but shorter due to the liver’s position.
Divided into three lobes: Superior, middle, and inferior.
Separated by two fissures: Horizontal and oblique fissures.
Left Lung:
Smaller and narrower due to the heart’s position.
Divided into two lobes: Superior and inferior.
Separated by one fissure: Oblique fissure.
Features the cardiac notch and lingula (small tongue-like projection).
Microscopic Structure
Trachea and Bronchial Tree:
The trachea bifurcates into two primary bronchi:
Right bronchus: Wider, shorter, and more vertical.
Left bronchus: Narrower, longer, and more horizontal.
Develop from the foregut endoderm in the 4th week of gestation.
Progress through stages:
Embryonic (4–7 weeks): Formation of primary bronchial buds.
Pseudoglandular (5–17 weeks): Branching of bronchi and bronchioles.
Canalicular (16–25 weeks): Formation of respiratory bronchioles.
Saccular (24 weeks–birth): Development of alveolar sacs.
Alveolar (Birth–8 years): Growth and maturation of alveoli.
Accessory Structures
Diaphragm:
A dome-shaped muscle separating the thoracic and abdominal cavities.
Contracts to expand the thoracic cavity during inspiration.
Intercostal Muscles:
Found between the ribs.
Assist in expanding and compressing the thoracic cavity during breathing.
Pathway of Airflow
Nasal cavity →
Pharynx →
Larynx →
Trachea →
Primary bronchi →
Secondary bronchi →
Tertiary bronchi →
Bronchioles →
Alveoli.
Muscles of respiration
Muscles of Respiration
The muscles of respiration are responsible for facilitating breathing by altering the volume of the thoracic cavity. These muscles are categorized into primary muscles (used during normal breathing) and accessory muscles (activated during deep or labored breathing).
1. Primary Muscles of Respiration
The primary muscles are essential for quiet or relaxed breathing (eupnea).
a. Diaphragm
Location:
Dome-shaped muscle separating the thoracic and abdominal cavities.
Function:
The primary muscle for inspiration.
Contraction flattens the diaphragm, increasing thoracic volume and decreasing intrathoracic pressure, drawing air into the lungs.
Innervation:
Phrenic nerve (C3, C4, C5 keep the diaphragm alive).
Significance:
Responsible for about 75% of inspiratory effort during quiet breathing.
b. External Intercostal Muscles
Location:
Found between the ribs, oriented obliquely downward and forward.
Function:
Elevate the ribs during inspiration, increasing the anterior-posterior and lateral dimensions of the thoracic cavity.
Innervation:
Intercostal nerves (T1–T11).
2. Accessory Muscles of Respiration
These muscles are engaged during forced inspiration or expiration (e.g., during exercise, respiratory distress, or chronic obstructive pulmonary diseases).
a. Accessory Muscles for Inspiration
Sternocleidomastoid (SCM):
Location: Neck.
Function: Elevates the sternum.
Innervation: Accessory nerve (CN XI) and cervical nerves.
Scalene Muscles:
Location: Lateral neck.
Function: Elevate the first and second ribs.
Innervation: Cervical spinal nerves (C3–C8).
Pectoralis Major and Minor:
Location: Chest.
Function: Elevate the ribs when the arms are fixed.
Innervation: Medial and lateral pectoral nerves.
Serratus Anterior:
Location: Lateral thorax.
Function: Elevates the ribs when the scapula is fixed.
Innervation: Long thoracic nerve (C5–C7).
Latissimus Dorsi:
Function: Assists in rib elevation during deep breathing.
Innervation: Thoracodorsal nerve.
b. Accessory Muscles for Expiration
Expiration is generally passive during quiet breathing due to the elastic recoil of the lungs and thoracic structures. However, forced expiration involves the following muscles:
Internal Intercostal Muscles:
Location: Deep to the external intercostal muscles, oriented obliquely downward and backward.
Function: Depress the ribs, reducing thoracic volume.
Innervation: Intercostal nerves (T1–T11).
Abdominal Muscles:
Rectus Abdominis:
Compresses the abdominal contents and pushes the diaphragm upward.
External and Internal Obliques:
Assist in rib depression and increase intra-abdominal pressure.
Transversus Abdominis:
Compresses the abdominal contents, aiding in forced expiration.
Innervation: Thoracoabdominal nerves (T7–T12) and subcostal nerve.
3. Respiratory Mechanics
Inspiration:
Active process involving diaphragm contraction and external intercostal muscles.
Accessory muscles help in deep or labored breathing.
Expiration:
Passive during quiet breathing due to lung recoil.
Active during forced breathing using abdominal and internal intercostal muscles.