Respiratory System Anatomy & Physiology

Respiratory System Anatomy & Physiology

Introduction

• Learning Changes Everything®
• Title: Chapter 23 Part 1 of 2: Respiratory System Anatomy & Physiology
• Authors: Michael P. McKinley, Valerie Dean O’Loughlin, Theresa Stouter Bidle
• © McGraw Hill LLC. All rights reserved. No reproduction or distribution without prior written consent of McGraw Hill LLC.

1. The Respiratory System

• Definition of Respiration: Gas exchange involving O2 and CO2 between the atmosphere and body cells.
  • O2 Function: Required for aerobic ATP production.
  • CO2 Function: Byproduct that must be disposed of during cellular respiration.
• Role of the Respiratory System: Provides pathways and structures for gas exchange.
  • Organization: Composed of respiratory passageways located in the head, neck, trunk, and the lungs.

2. General Functions of the Respiratory System

2.1 Passageway for Air

• Air movement occurs between the atmosphere and alveoli during breathing.

2.2 Site for Gas Exchange

• Oxygen diffuses from alveoli into the blood.
• Carbon dioxide diffuses from the blood into the alveoli.

2.3 Olfaction (Sense of Smell)

• Olfactory receptors are located in the superior nasal cavity.

2.4 Sound Production

• Air moves across vocal cords in the larynx (voice box).
• Vocal cords vibrate to produce sound.

3. General Organization of the Respiratory System

3.1 Structural Organization

• Upper Respiratory Tract: nose, nasal cavity, pharynx, larynx.
• Lower Respiratory Tract: trachea, bronchi, bronchioles, alveolar ducts, alveoli.

3.2 Functional Organization

• Conducting Zone: Structures that transport air (from nose to terminal bronchioles).
• Respiratory Zone: Structures involved in gas exchange (respiratory bronchioles, alveolar ducts, alveoli).

4. Respiratory Mucosa

• Definition: The respiratory tract is lined by a mucous membrane (respiratory mucosa).
• Components:
  • Epithelium with cilia.
  • Underlying lamina propria of areolar connective tissue.
  • Mucosa-associated lymphoid tissue (MALT).
• The mucosa becomes thinner from the nasal cavity to the alveoli:
  • Starts as pseudostratified ciliated columnar and transitions to simple ciliated columnar, simple cuboidal, and finally simple squamous.
  • Exceptions: Stratified squamous epithelium found in areas of high abrasion (oropharynx, laryngopharynx, vocal cords, superior larynx).

5. Mucous Secretions

• Produced by:
  • Goblet cells in the epithelial lining.
  • Mucous and serous glands of the lamina propria.
• Composition: Contains mucin protein, increasing viscosity to trap dust and microbes.
  • Defense Mechanisms: Includes lysozyme (antibacterial enzyme), defensins (antibacterial proteins), and immunoglobulin A (antibody).
  • Sputum: Refers to the mixture of coughed-up saliva and trapped substances.

6. Clinical View: Cystic Fibrosis

• Pathophysiology: Defective chloride channels lead to thick mucus in the respiratory tract.
  • Lack of water hydration on cell surfaces results in obstructed mucus, causing respiratory problems.
• Frequent pulmonary infections due to mucus build-up.
• Can also block pancreatic and salivary gland ducts, causing potential damage.

7. Nose and Nasal Cavity

7.1 Nose

• First conducting structure for inhaled air composed of bone, hyaline cartilage, dense irregular connective tissue, and skin.
• Structure Components:
  • Bridge formed by paired nasal bones.
  • Lateral cartilages and alar cartilages shape nostrils (nares).

7.2 Nasal Cavity

• Extends from nostrils to choanae (posterior nasal apertures leading to the pharynx).
• Floor formed by the palate; roof consists of nasal, frontal, ethmoid, and sphenoid bones.
• Nasal Septum: Divides left and right nasal cavities; composed of septal nasal cartilage and bony structures (perpendicular plate of the ethmoid and vomer bone).

7.3 Nasal Conchae and Meatuses

• Three paired bony projections (superior, middle, inferior nasal conchae) create air passages called meatuses beneath each concha.

7.4 Nasal Vestibule

• Located just inside the nostrils, lined by skin and vibrissae (hair).

7.5 Nasal Regions

• Olfactory Region: Contains olfactory epithelium for detecting odors.
• Respiratory Region: Lined by pseudostratified ciliated columnar epithelium, vascular network for warming, cleansing, and humidifying air.
• Nosebleeds (epistaxis) are common due to high vascularization.

8. Clinical View: Runny Nose (Rhinorrhea)

• Causes: Increased mucus production from allergies or viruses, crying, or cold exposure.

9. Paranasal Sinuses

• Definition: Spaces within skull bones named for their housing bone.
• Connect to nasal cavity through ducts.
• Include:
  • Frontal sinuses
  • Ethmoidal sinuses
  • Sphenoidal sinuses
  • Maxillary sinuses

9.1 Mucus Drainage

• Lined by pseudostratified ciliated columnar epithelium;
• Mucus is swept into the pharynx and swallowed.

9.2 Clinical View: Sinus Infections

• Inflammation from infection or allergies can block drainage, leading to mucus accumulation and further infections.

10. Pharynx

• Definition: Funnel-shaped passageway located posterior to the nasal cavity, oral cavity, and larynx.
• Muscular structure above larynx, divided into:
  • Nasopharynx: Most superior, connects to middle ear (house tubal tonsils); air passage only.
  • Oropharynx: Passage for both air and food; contains palatine and lingual tonsils.
  • Laryngopharynx: Inferior portion, also a passage for both air and food.

11. Larynx

• Definition: Pyramid-shaped airway structure between laryngopharynx and trachea.
• Functions:
  • Produces sound through vocal folds.
  • Ensures airflow passage, preventing ingestion into the respiratory tract (epiglottis covers during swallowing).
  • Assists in increasing abdominal pressure during actions such as urination, defecation, and childbirth (Valsalva maneuver).
  • Participates in cough and sneeze reflexes for clearing irritants.

11.1 Laryngeal Anatomy

• Supported by nine pieces of cartilage:
  • Unpaired: thyroid (large, shield-shaped), cricoid (ring-shaped), epiglottis (spoon-shaped).
  • Paired: arytenoid, corniculate, cuneiform.
• Cartilages are stabilized by ligaments and muscles.

11.2 Vocal Production

• Vocal ligaments between thyroid and arytenoid cartilages create vocal folds that produce sound.
• Rima Glottidis: The opening between vocal folds;
  • Glottis: Comprised of rima glottidis and vocal folds.
  • Pitch: Determined by tension on vocal cords; loudness is determined by air pressure from lungs.
  • Differences in vocal cord length and thickness are observed between genders, impacting voice depth.

11.3 Clinical View: Laryngitis

• Inflammation of the larynx leading to hoarse voice and sore throat; can result from infections or overuse.

12. Lower Respiratory Tract

• Comprises conducting pathways from trachea to terminal bronchioles and gas exchange structures (respiratory bronchioles, alveolar ducts, alveoli).

13. Trachea

13.1 Structure

• Definition: The windpipe connecting the larynx to the bronchi.
• Gross anatomy: About 13 cm long and 2.5 cm in diameter with C-shaped cartilaginous rings for support.
• Trachealis Muscle: Contracts during coughing to control airflow.
• Carina: An internal ridge at the tracheal bifurcation containing sensory receptors that initiate cough reflex upon irritant detection.

13.2 Clinical View: Tracheotomy and Cricothyrotomy

• Tracheotomy: Incision into the trachea for obstructed airflow.
• Cricothyrotomy: Incision made between the cricoid and thyroid cartilages for urgent airway access.

13.3 Histology of the Trachea

• Composed of mucosa (pseudostratified ciliated columnar epithelium), submucosa (areolar connective tissue, glands), cartilage, and adventitia.

14. Bronchial Tree

14.1 Structure and Function

• Highly branched air passage system arising from the main bronchi, leading to smaller bronchi and bronchioles.
• Right main bronchus: shorter, wider, more vertical, making it more prone to obstruction than the left.

14.2 Branching and Division

• Main bronchi divide into lobar bronchi (serving specific lung lobes) and further into segmental bronchi; continues to smaller bronchi and terminal bronchioles.

15. Clinical View: Bronchitis

• Acute Bronchitis: Temporary inflammation post-infection; resolves in 10-14 days.
• Chronic Bronchitis: Due to long-term irritant exposure, marked by excessive mucus secretion and prolonged cough.

16. Respiratory Zone: Respiratory Bronchioles, Alveolar Ducts, and Alveoli

16.1 Structures

• Microscopic structures involved in gas exchange; respiratory bronchioles lead to alveolar ducts and sacs.
• Alveolus: Sack-like structure vital for gas exchange (diameter 0.25–0.5 mm).

16.2 Histology

• Epithelium:
  • Respiratory bronchioles: Simple cuboidal epithelium.
  • Alveolar ducts and sacs: Simple squamous epithelium.
• The thinness of alveolar epithelium supports efficient gas exchange.

17. Alveoli

17.1 Structure

• Each lung contains 300 to 400 million alveoli, surrounded by pulmonary capillaries.
• Alveolar Pores: Allow for collateral ventilation, connecting adjacent alveoli.

17.2 Cell Types within Alveoli

• Alveolar Type I Cells: Squamous alveolar cells covering 95% of surface area; facilitates gas exchange.
• Alveolar Type II Cells: Secrete surfactant to lower surface tension and prevent collapse.
• Alveolar Macrophages: Engulf microorganisms; can be fixed or free in alveolar spaces.

18. Respiratory Membrane

• Definition: The barrier (0.5 microns thick) between alveoli and pulmonary capillaries.
  • Composed of the plasma membrane of type I cells, endothelial cells of capillaries, and their fused basement membranes.
  • Gas Exchange Process: O2 diffuses from alveoli into capillaries; CO2 diffuses from blood into alveoli for expiration.

19. Clinical View: Pneumonia

• Infection causing alveoli to fill with fluid, leading to symptoms such as cough, fever, and difficulty breathing; can be mild (walking pneumonia) or severe.

20. Circulation to and from the Lungs

20.1 Pulmonary Circulation

• Supplies deoxygenated blood via pulmonary arteries to alveolar capillaries for gas exchange.
• Returns oxygenated blood through pulmonary veins to the left atrium.

20.2 Bronchial Circulation

• Supplies oxygenated blood directly to lung tissue through bronchial arteries.
• Bronchial veins collect venous blood, some draining into pulmonary veins.

21. Lymphatic Drainage

• Importance: Filters out excess fluid from lungs, collecting particles not removed by upper respiratory defenses.
• Located in lung connective tissue, around bronchi, and in pleura.

22. Pleural Membranes and Cavity

22.1 Structure

• Pleura: Serous membrane lining lung surfaces and thoracic walls composed of simple squamous epithelium and areolar connective tissue.
• Visceral Pleura: Adheres to the lung surface.
• Parietal Pleura: Lines thoracic walls, mediastinum, and diaphragm.
• Each lung is enclosed within a separate visceral pleura to limit infection spread.

22.2 Pleural Cavity

• Located between visceral and parietal pleura, filled with serous fluid for smooth movement during breathing.

22.3 Clinical View: Pleurisy and Pleural Effusion

• Pleurisy: Inflammation leading to sharp pain and friction between pleural surfaces.
• Pleural Effusion: Excess fluid in pleural cavity, can result from heart failure or infections, leading to dyspnea.

23. How Lungs Remain Inflated

• Mechanism involves the expanding chest wall, lung recoiling properties, and pleural cavity arrangement.
• Intrapleural Pressure: Maintained at a lower pressure than intrapulmonary pressure to keep lungs inflated.

23.1 Clinical Views: Pneumothorax and Atelectasis

• Pneumothorax: Air enters pleural cavity, potentially leading to lung collapse.
• Atelectasis: Lung collapse due to pressure equalization.

24. Review Questions

• Section 23.2: Learn about respiratory gases, upper respiratory structures, epithelial differences, larynx functions, vocal folds differences.
• Section 23.3: Inquire about C-shaped tracheal cartilage functions, differences between bronchi and bronchioles.