Airway Anatomy

Innate Immunity: The body's initial defense against pathogens, which comprises physical barriers such as skin and mucous membranes, as well as immune cells like neutrophils and macrophages. This immune response is non-specific, meaning it responds to all pathogens in the same way and is present from birth. Notable components include the complement system, a group of proteins that enhance immune responses, and inflammatory responses that help limit infection spread.

Adaptive Immunity: A specific immune response that develops over time, involving antibodies produced by B cells and specific lymphocytes known as T cells. This system adapts to recognize specific pathogens that the body has encountered before, providing a more robust and quicker response upon subsequent exposures. Memory cells are also created, allowing for long-lasting immunity.

Respiration Overview

Breathing: Involves the movement of air into the lungs (inhalation) and out of the lungs (exhalation). The diaphragm and intercostal muscles play crucial roles in this process by changing thoracic cavity volume, facilitating air pressure changes that promote airflow.

Types of Respiration:

• External Respiration: Gas exchange occurs between the air in the alveoli and the blood in the pulmonary capillaries. This process is essential for oxygenating blood and removing carbon dioxide, a waste product of metabolism.

• Internal Respiration: Gas exchange occurs between the blood and tissue fluid. Oxygen diffuses from the blood into cells, while carbon dioxide moves from cells into the blood.

• Cellular Respiration: A biochemical process occurring in mitochondria that produces adenosine triphosphate (ATP), the energy currency of the cell. This process requires oxygen and involves various metabolic pathways, including glycolysis and the citric acid cycle, while releasing carbon dioxide as a byproduct.

Functions of the Respiratory System

• Gas Exchange: Critical for providing oxygen to the bloodstream and eliminating carbon dioxide, thereby maintaining homeostasis.

• Communication: Enables speech production and vocal sounds through the manipulation of airflow across the vocal folds within the larynx.

• Olfaction: The sense of smell provided by olfactory receptors located in the nasal cavity, which are crucial for taste and environmental awareness.

• Acid-Base Balance: Helps regulate the pH of body fluids through the elimination of carbon dioxide, thus affecting bicarbonate levels in the blood.

• Blood and Lymph Flow: Creates pressure gradients that aid in the circulation of blood and lymph throughout the body.

• Expulsion of Abdominal Contents: Assists in bodily functions such as urination, defecation, and childbirth, specifically through maneuvers like the Valsalva maneuver that increase abdominal pressure.

• Production of Substances: Such as histamine, a mediator in allergic responses, and angiotensin I, which plays a role in blood pressure regulation.

• Neurotransmitter Clearance: Involves the removal of catecholamines (e.g., epinephrine and norepinephrine) from the blood to regulate stress responses effectively.

Respiratory System: Gross Anatomy

Upper Respiratory Tract

• Nasal Cavity: Filters, warms, and moistens incoming air while containing mucus-secreting cells that trap pathogens and particles.

• Pharynx: Functions as a passageway for air and food; it divides into the nasopharynx (airway), oropharynx (passage for food), and laryngopharynx.

• Glottis and Larynx: Produce sound via vocal fold vibration while preventing food from entering the trachea during swallowing with the epiglottis acting as a flap.

• Trachea: A tubular structure that conducts air to the bronchi, lined with ciliated epithelium that traps debris and pathogens.

• Bronchi and Bronchioles: Conduct air to alveoli and distribute airflow to the areas of the lungs optimized for gas exchange.

Lower Respiratory Tract

• Lungs: House the alveoli, where extensive gas exchange occurs; the right lung has three lobes while the left has two to accommodate the heart.

• Diaphragm: A dome-shaped skeletal muscle that plays a vital role in ventilation by contracting and relaxing to facilitate airflow in and out of the lungs.

Conducting vs Respiratory Zones

• Conducting Zone: Comprises structures that facilitate airflow, such as the nose, pharynx, trachea, bronchi, and bronchioles. No gas exchange occurs here.

• Respiratory Zone: Includes respiratory bronchioles and alveoli, the primary sites of gas exchange due to their thin walls and large surface area.

Anatomy of the Nose

Function

• Serves as an airway, filters and cleans inhaled air, enhances sound resonance for vocalization, and houses olfactory receptors for the sense of smell.

External Structures

• Nasal Cavity: Located posterior to the external nose, divided by the nasal septum into two nostrils.

• Paranasal Sinuses: Cavities in the skull that produce mucus to moisten and filter air while reducing the overall weight of the skull and enhancing sound resonance.

Internal Structures

• Conchae: Turbinate bones that increase surface area within the nasal cavity, aiding in effective air treatment by stirring the air for better filtration and conditioning.

• Vestibule & Olfactory Mucosa: Contain sensory receptors and facilitate smell; the olfactory mucosa specifically contains receptor neurons for the detection of odorants.

The Pharynx

Location: Extends from the base of the skull to the level of C6, serving as a crucial pathway for both the respiratory and digestive systems.

Functions: Acts as a resonator for sound and serves as a conduit for both air to the larynx and food to the esophagus.

Parts: Divided into three sections—nasopharynx (air), oropharynx (food and air), and laryngopharynx (food and air)—each structured to fulfill specific functions in air and food passage.

The Larynx

Position: Connects the pharynx to the trachea while playing a fundamental role in the respiratory and vocal systems.

Functions: Keeps airways open by providing rigidity, directs airflow and food with the help of the epiglottis, and facilitates sound production via vibrating vocal folds.

Structure: Composed of nine cartilages that support its form and include pairs of vocal folds for sound generation, controlled by various intrinsic and extrinsic laryngeal muscles.

Sound Production and Control

• Volume: Controlled by regulating air pressure and the vibration of vocal folds, which can be modulated by both tension and airflow.

• Pitch: Influenced by the tension and length of true vocal cords as well as the size and shape of the larynx and resonating cavities.

Trachea

Structure: Extends from cervical vertebrae C6 to thoracic vertebrae T4/T5; supported by C-shaped cartilage rings that anchor and maintain the airway's openness.

Functions: Maintains an open airway, filters and moisturizes air, and initiates a cough reflex via embedded sensory receptors that respond to irritants.

The Bronchial Tree

Structure: Comprises primary bronchi that branch into secondary (lobar) bronchi and tertiary (segmental) bronchi, progressively narrowing into smaller bronchi and bronchioles.

Function: Conducts air deep into the lungs where gas exchange occurs, with diminishing cartilage and increasing smooth muscle in the airway walls to facilitate air control.

Histology: Epithelium transitions from a pseudostratified ciliated columnar in bronchi to cuboidal in smaller bronchioles, with mucus-producing cells that aid in air filtration.

Alveoli and Gas Exchange

Types of Cells:

• Type I Cells: Primary site for gas exchange, consist of simple squamous epithelium that facilitates rapid gas diffusion due to their thin walls.

• Type II Cells: Secretes pulmonary surfactant that reduces surface tension in the alveoli, preventing their collapse during exhalation.

• Macrophages: Immune defenders that reside in the alveoli, ingesting pathogens, debris, and particulates to protect lung health.

Lung Anatomy

• Right Lung: Comprised of three lobes (upper, middle, lower), accommodating greater air volume due to its broader structure.

• Left Lung: Comprised of two lobes (upper, lower), with a cardiac notch to accommodate the heart's position.

• Features: Includes anatomical landmarks such as the apex (top), hilus (entry/exit point for bronchi and blood vessels), and various surfaces in contact with thoracic wall structures.

Thoracic Cavity

Structure: Encloses the lungs and is lined with pleura, comprising visceral pleura (covering the lungs) and parietal pleura (lining the thoracic wall), allowing for frictionless movement during respiration.

Components: The rib cage, sternum, intercostal muscles, and diaphragm constitute the thoracic wall, which assists in breathing mechanics and protects the thoracic organs.