Respiratory System Anatomy

The respiratory system anatomy focuses on the path from the nose to the lungs, emphasizing key structures and terminology.

Upper vs. Lower Respiratory Tract

Defining the upper and lower respiratory tracts is crucial for understanding the location of infections.

Respiratory System Structures

Nose: The entry point for air.
Pharynx: A tube connecting the nose to the larynx.
Larynx (Voice Box): Located at the front, leading to the trachea. It's essential for voice production.
Trachea: Extends from the larynx and divides into the right and left bronchi leading to each lung.
Bronchi: The trachea splits into two main bronchi, one for each lung.

Bronchial Tree

Main/Primary Bronchi: The initial branches from the trachea.
Secondary (Lobar) Bronchi: The primary bronchi divide into secondary bronchi, each serving a lobe of the lung.
Tertiary Bronchi: Secondary bronchi branch into tertiary bronchi.
Bronchioles: Smaller branches resulting from the division of tertiary bronchi; analogous to arterioles in the circulatory system.
Terminal Bronchioles: Bronchioles branch further into terminal bronchioles.
Respiratory Bronchioles: Terminal bronchioles transition into respiratory bronchioles where gas exchange begins.
Alveolar Ducts: Respiratory bronchioles lead to alveolar ducts.
Alveoli: Sac-like structures attached to alveolar ducts, surrounded by capillaries, where oxygen and carbon dioxide exchange occurs.

Gas Exchange

Air enters the alveoli, where oxygen diffuses into capillaries and carbon dioxide diffuses out.

Lung Structure

Right Lung: Three lobes divided by two fissures.
Left Lung: Two lobes divided by one fissure.
Bronchopulmonary Segments: Each lobe is further divided into bronchopulmonary segments, numbering 8-10 in total across both lungs.

Bronchi Divisions and Lung Lobes

The trachea divides into two branches because there are two lungs.
The number of secondary bronchi corresponds to the number of lobes in each lung (three on the right, two on the left).
Tertiary bronchi supply bronchopulmonary segments; they are also called segmental bronchi.

Bronchioles and Asthma

Bronchioles lack cartilage, making them susceptible to collapse during asthma.
Asthma primarily affects the bronchioles due to the absence of supportive cartilage.

Terminology: Upper vs. Lower Respiratory Tract

Upper Respiratory Tract: From the nose to the larynx; infections are typically less severe.
Lower Respiratory Tract: From the trachea downwards; infections such as pneumonia are more dangerous.

Conducting vs. Respiratory Portions

The division between terminal and respiratory bronchioles marks the switch from air conduction to respiration.

Terminal vs. Respiratory Bronchioles

Terminal Bronchioles: End of the conducting zone, where air transport occurs without gas exchange.
Respiratory Bronchioles: Beginning of the respiratory zone, where gas exchange (respiration) starts.
Gas exchange primarily occurs in the alveoli but can also happen in the alveolar ducts and respiratory bronchioles.

Pleura

The lungs are covered by pleura, which has two layers: parietal (outer) and visceral (inner).
The parietal layer attaches to the rib cage and diaphragm, facilitating breathing movements.
The movement of the diaphragm pulls the parietal pleura influencing air flow.

Pleural Space

A space between the parietal and visceral pleura contains a small amount of fluid.
The pressure in the pleural space is slightly negative (around $756$ mm Hg) compared to atmospheric pressure (760 mm Hg), which is crucial for lung function.

Respiratory System Functions

Ventilation: Exchange of air between the outside environment and the respiratory system.
Respiration: Exchange of gas between the respiratory system and the blood; occurs in the respiratory zone.
The respiratory system also produces sound, aids olfaction, and provides defense mechanisms.

Defense Mechanisms

Mucosa-Associated Lymphoid Tissue (MALT): Provides defense against pathogens in the respiratory tract.

Nasal Anatomy

Conchae: Superior and middle conchae belong to the ethmoid bone, while the inferior concha is a separate bone.
The upper part of the nose is bony (nasal bone), while the rest is cartilage.

Pharynx

The pharynx connects the nose and mouth to the larynx and esophagus.
Choana: The opening from the nasal cavity to the nasopharynx.
The pharynx is divided into three parts: nasopharynx, oropharynx, and laryngopharynx.
Nasopharynx: Connected to the nose.
Oropharynx: Connected to the mouth.
Laryngopharynx: Connected to the larynx and esophagus.
Fauces: The opening from the mouth to the oropharynx.

Epithelial Tissue Types in the Pharynx

Nasopharynx: Ciliated pseudostratified epithelium, similar to the nose.
Oropharynx: Stratified squamous epithelium to protect against friction.
Laryngopharynx: Nonkeratinized stratified squamous epithelium, also for protection against friction.

Oropharynx Anatomy

The mouth opens into the oropharynx.
Palatine Tonsils: Located between two arches in the oropharynx.
Palatoglossal Arch: The arch closest to the tongue.
Palatopharyngeal Arch: The arch closer to the pharynx.

Paranasal Sinuses

Cavities surrounding the nose can become inflamed, leading to sinusitis.

Larynx Functions

A passage for air.
Prevents food from entering the respiratory tract.
Produces sound.
Helps increase pressure inside the abdominal cavity (Valsalva maneuver).
Involved in cough/sneeze reflex.

Larynx Cartilages

The larynx is composed of nine cartilages.

Key Cartilages:

Hyoid Bone: The only bone in the body that doesn't articulate with any other bone.
Thyroid Cartilage: Forms the Adam's apple. (palpable through the skin)
Cricoid Cartilage: Located below the thyroid cartilage. (palpable through the skin)
Cricothyroid Ligament: Connects the thyroid and cricoid cartilages, an important landmark for emergency procedures.
Arytenoid Cartilages: Two cartilages sitting on the cricoid cartilage.
Corniculate Cartilages: Two cartilages on top of the arytenoid cartilages.
Epiglottis: A flap-like cartilage that prevents food from entering the trachea.
Cuneiform Cartilages: Embedded in the aryepiglottic folds.

Vocal Cords

Vocal Cords (True Vocal Cords): Connect the arytenoid cartilages to the thyroid cartilage; responsible for sound production.
False Vocal Cords (Vestibular Folds): Located above the true vocal cords, but are not involved in sound production.
Rima Glottidis: The space between the true vocal cords.

Valsalva Maneuver

Closing the 'rima glottidis' to increase abdominal pressure, used during activities like defecation.
Can also slow down heart rate.

Larynx Anatomy (Cont.)

Muscles control the arytenoid cartilages, influencing vocal cord movement and pitch.

Trachea

Also known as the windpipe, 12-15 cm in length.
Composed of tracheal cartilages (C-shaped) and trachealis muscle.
Carina: The division point where the trachea splits into the left and right primary bronchi.
Annular Ligaments: Connect the tracheal cartilages.
The C-shape of the tracheal cartilages allows the esophagus to expand during swallowing because it does not fully encircle

Epithelial Tissue in Lower Respiratory Tract

The wall of the trachea is lined with pseudostratified ciliated columnar epithelium.
The trachea branches into primary, secondary, and tertiary bronchi, eventually leading to terminal and respiratory bronchioles.
Alveoli are the primary sites of gas exchange but it can occur higher up in the respiratory bronchioles

Lungs (Cont.)

The right lung has two fissures (horizontal and oblique), while the left lung has only one (oblique).
Each lobe contains bronchopulmonary segments. No memorization of them is needed for the class
The left lung is slightly smaller due to the cardiac notch, which accommodates the heart.
Lingula: A structure in the left lung, below the cardiac notch. Thought of as a way to discriminate between the lobes.

Pressure Dynamics

Air flows from areas of high pressure to low pressure.
During swallowing and breathing, air flows always towards the lungs due to its lower pressure than other vessels such as the espohagus
Epiglottis helps to close to prevent air from getting to the stomach
All the mechanisms described allow us to swallow and breathe without getting water on the vessels