Anatomy and Physiology of the Respiratory System: Structured Study Notes

The Respiratory System

Introduction

The respiratory system is essential for gas exchange, supplying oxygen to the body and removing carbon dioxide. Its structure is closely related to its function, with specialized organs and tissues facilitating efficient respiration.

Major Organs of the Respiratory System

• Nose

• Pharynx

• Larynx

• Trachea

• Bronchi

• Lungs—Alveoli

Functional Anatomy of the Respiratory System

Overview of Gas Exchange

• Gas exchanges between the blood and external environment occur only in the alveoli of the lungs.

• The upper respiratory tract includes passageways from the nose to the pharynx.

• The lower respiratory tract includes passageways from the trachea to the alveoli.

• Passageways to the lungs purify, humidify, and warm the incoming air.

Anatomy of the Nose

Structure and Function

• Nose: The only externally visible part of the respiratory system.

• Nostrils (nares): The route through which air enters the nose.

  • Air is filtered, moistened, and warmed before entering the lungs.

• Nasal cavity: The interior of the nose.

  • Helps filter, warm, and humidify incoming air.

  • Houses sensory receptors for the sense of smell.

• Nasal septum: Divides the nasal cavity.

  • Ensures air is evenly distributed between both sides, aiding efficient breathing and airflow.

Upper and Lower Respiratory Tract

Classification and Functions

• Upper respiratory tract: Nose, nasal cavity, pharynx.

  • Functions: Air filtration, humidification, warming, and olfaction.

• Lower respiratory tract: Larynx, trachea, bronchi, lungs, alveoli.

  • Functions: Conducting air to the lungs, gas exchange, and protection against pathogens.

Relationship Between Structure and Function

Key Anatomical Features

• Nasal cavity: Large surface area and mucosa for air filtration and humidification.

• Pharynx: Muscular tube for passage of air and food; divided into nasopharynx, oropharynx, and laryngopharynx.

• Larynx: Contains vocal cords for sound production; routes air and food into proper channels.

• Trachea: Reinforced with cartilage rings to maintain airway patency.

• Bronchi: Branch into smaller bronchioles, distributing air throughout the lungs.

• Lungs and alveoli: Site of gas exchange; alveoli have thin walls and large surface area for efficient diffusion.

Physiology of Respiration

Mechanics of Breathing

• Inspiration (inhalation): Diaphragm and external intercostal muscles contract, increasing thoracic volume and decreasing pressure, allowing air to flow in.

• Expiration (exhalation): Muscles relax, thoracic volume decreases, pressure increases, and air flows out.

Respiratory Volumes and Capacities

• Tidal Volume (TV): Amount of air inhaled or exhaled during normal breathing (about 500 mL).

• Inspiratory Reserve Volume (IRV): Additional air that can be inhaled after a normal inspiration (about 3,100 mL).

• Expiratory Reserve Volume (ERV): Additional air that can be exhaled after a normal expiration (about 1,200 mL).

• Residual Volume: Air remaining in lungs after expiration (about 1,200 mL).

• Vital Capacity (VC): Total amount of exchangeable air. $VC = TV + IRV + ERV$ (About 4,800 mL in men; 3,100 mL in women)

• Dead Space Volume: Air in conducting zone not involved in gas exchange (about 150 mL).

• Functional Volume: Air that actually reaches the respiratory zone (about 350 mL).

Control of Breathing

Neural Regulation

• Respiratory centers in the medulla and pons regulate rate and depth of breathing.

• Medulla sets basic rhythm; pons smoothes out breathing patterns.

• Normal respiratory rate (eupnea): 12–15 respirations per minute.

Non-Neural and Chemical Factors

• Physical factors: Temperature, exercise, talking, coughing.

• Volition: Conscious control of breathing.

• Emotional factors: Fear, anger, excitement.

• Chemical factors:

  • CO2 levels: Increased CO2 (acidosis) increases rate and depth of breathing.

  • O2 levels: Detected by chemoreceptors in the aorta and carotid arteries.

Gas Exchange and Transport

External Respiration

• Exchange of gases between alveoli and pulmonary blood.

• Oxygen diffuses into blood; carbon dioxide diffuses into alveoli.

Internal Respiration

• Exchange of gases between blood and tissue cells.

• Oxygen diffuses into tissues; carbon dioxide diffuses into blood.

Transport in the Blood

• Oxygen:

  • 98% bound to hemoglobin as oxyhemoglobin.

  • 2% dissolved in plasma.

• Carbon Dioxide:

  • 70% transported as bicarbonate ion (HCO3-).

  • 20% bound to hemoglobin (carbaminohemoglobin).

  • 10% dissolved in plasma.

Bicarbonate Buffer System

• CO2 is converted to bicarbonate for transport: $CO_2 + H_2O ightleftharpoons H_2CO_3 ightleftharpoons H^+ + HCO_3^-$

• In the lungs, bicarbonate is converted back to CO2 for exhalation.

Homeostasis in the Respiratory System

Physiological and Biochemical Mechanisms

• Maintains blood pH via regulation of CO2 levels.

• Ensures adequate oxygen delivery and carbon dioxide removal.

• Surfactant production prevents alveolar collapse and maintains lung elasticity.

Summary Table: Respiratory Volumes and Capacities

Volume/Capacity	Definition	Average Value
Tidal Volume (TV)	Air inhaled/exhaled in normal breath	500 mL
Inspiratory Reserve Volume (IRV)	Extra air inhaled after normal inspiration	3,100 mL
Expiratory Reserve Volume (ERV)	Extra air exhaled after normal expiration	1,200 mL
Residual Volume	Air remaining after forced expiration	1,200 mL
Vital Capacity (VC)	Total exchangeable air (TV + IRV + ERV)	4,800 mL (men)
Dead Space Volume	Air not involved in gas exchange	150 mL
Functional Volume	Air reaching respiratory zone	350 mL

Example Application

During exercise, increased CO2 production stimulates the medulla to increase breathing rate and depth, ensuring efficient removal of CO2 and delivery of O2 to tissues.

Additional info: These notes expand on the provided slides with definitions, physiological mechanisms, and a summary table for clarity and completeness.