Respiratory System Anatomy

• GENERAL FEATURES OF THE RESPIRATORY SYSTEM

• The respiratory system is divided into two main subcategories: upper respiratory system and lower respiratory system.

LEARNING OBJECTIVES

• Upon completion of this lecture, students should be able to:

  • Describe the general features of the respiratory system.

  • Explain the structural and functional classifications of the respiratory system.

  • Detail the structure, function, and role of each organ that constitutes the respiratory system.

INTRODUCTION

• The respiratory system has three principal purposes in the human body:

  1. Gaseous Exchange: The process by which oxygen is taken in and carbon dioxide is expelled.

  2. Sound Production: The generation of sound for communication.

• The respiratory system can be categorized into:

  • Structural Divisions: Upper and lower respiratory systems.

  • Functional Divisions: Conducting and respiratory divisions.

RESPIRATION FUNCTIONS

• Respiration involves three interconnected functions:

  • Ventilation (Breathing): The delivery of oxygen in air to the alveoli of the lungs.

  • Gaseous Exchange: The exchange of gases that occurs between the alveoli and blood.

  • Oxygen Utilization: The exchange of gases between the blood and tissues, commonly referred to as cellular respiration.

TYPES OF RESPIRATION

• External Respiration: Includes ventilation and gaseous exchange at the air-blood interface.

• Internal Respiration: Refers to gaseous exchanges between the blood and tissues (oxygen utilization).

STRUCTURE OF THE RESPIRATORY SYSTEM

• The respiratory system comprises the following structures:

  • Nasal Cavity: A cavity located within the nose, involved in filtering and humidifying air.

  • Pharynx: The throat area used for both respiratory and digestive systems.

  • Larynx: The voice box that houses the vocal cords.

  • Trachea: The windpipe that connects the larynx to the bronchi.

  • Bronchi: The major air passages that branch from the trachea into the lungs.

  • Bronchioles: Smaller passages that branch from the bronchi.

  • Pulmonary Alveoli: Tiny air sacs where gas exchange occurs in the lungs.

STRUCTURAL CLASSIFICATION

• Upper Respiratory System:

  • The nose

  • The pharynx

  • The larynx

• Lower Respiratory System:

  • The trachea

  • The bronchial tree

  • The alveoli and lungs.

FUNCTIONAL CLASSIFICATION

• Conducting Division: This part transports gases to the alveoli. It includes:

  • Nasal cavities

  • Pharynx

  • Larynx

  • Trachea

  • Bronchi and terminal bronchioles

• Respiratory Division: This part is involved in gaseous exchange between the atmosphere and blood. It includes:

  • Respiratory bronchioles

  • Alveolar ducts

  • Alveolar sacs

  • Pulmonary atria and alveoli.

VESTIBULE OF THE NOSE

• The vestibule is the most anterior and dilated part of the nasal cavity.

  • Contains thick, short hairs (vibrissae) that filter out larger particles from inspired air.

  • The inner surface of the nares includes sebaceous and sweat glands.

  • Associated with sinuses including the frontal and sphenoid sinuses.

PHARYNX

• The pharynx consists of:

  • Nasopharynx: The upper part behind the nasal cavity.

  • Oropharynx: The middle part behind the oral cavity.

  • Lined with respiratory epithelium.

LARYNGEAL EPITHELIUM

• The lining epithelium of the larynx varies:

  • Stratified Epithelium: Covers the laryngeal inlet, most of the epiglottis, and true vocal cords.

  • Pseudostratified Columnar Ciliated Epithelium: Covers the remaining portions of the larynx, featuring goblet cells.

THE LARYNX

• Features notable structures:

  • Cricothyroid Ligament: Provides connection and support.

  • True Vocal Cords: Responsible for sound production.

  • Epiglottis: Prevents food from entering the airway during swallowing.

TRACHEA

• The trachea measures approximately 10 cm in length, extending from the base of the larynx to the sternal angle (2nd costal cartilage or T4 vertebra).

  • Bifurcates into two primary bronchi at the sternal angle.

  • Lined by respiratory epithelium containing goblet cells.

  • Lamina Propria has 16-20 C-shaped rings of hyaline cartilage.

  • The gaps between the posterior ends of each cartilage are bridged by fibroelastic ligaments and smooth muscle known as the trachealis.

BRONCHI

• Extra-pulmonary or Primary Bronchi:

  • Similar in structure to the trachea but smaller in diameter and D-shaped.

• Intra-pulmonary or Secondary Bronchi:

  • Differ from the extra-pulmonary bronchi in four ways:

  1. Smaller diameter.

  2. Round contour.

  3. Complete rings of smooth muscle.

  4. Irregular cartilaginous plates instead of complete cartilage.

BRONCHIOLES

• Measure 1 mm or less in diameter.

  • Exhibit gradual changes in epithelium transitioning from simple columnar to simple cuboidal ciliated epithelium.

  • Distinct features from bronchi:

  1. Lack of cartilage in their walls.

  2. Absence of glands.

TERMINAL BRONCHIOLES

• Measure 0.5 mm in diameter.

  • Lined by simple cuboidal epithelium with no goblet cells present.

  • Contain scattered non-ciliated, dome-shaped Clara cells.

RESPIRATORY BRONCHIOLES

• Act as a transitional zone between the conducting and respiratory divisions.

  • Distinguished by the presence of saccular out-pocketing (alveoli) on its walls.

PULMONARY ALVEOLI

• Structure:

  • Sac-like evaginations measuring approximately 200 µm in diameter.

  • Located at the terminal portion of the bronchial tree.

  • Lined by two types of epithelial cells:

  1. Squamous Alveolar Cells or Type I cells: Facilitate gas exchange.

  2. Great Alveolar Cells or Type II cells: Produce surfactant and maintain alveolar stability.

• Function: Main sites for the exchange of oxygen and carbon dioxide between inspired air and blood.

RESPIRATORY DIVISION

• Comprises:

  • Alveoli

  • Respiratory bronchioles

  • Terminal bronchioles

IDENTIFICATION SECTION

• Content left ambiguous for identification purposes.