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Respiratory System - PPT/PDF

Download notes (PPT/PDF) on the Respiratory System, covering its functions, anatomy, and physiology. These notes provide detailed explanations of the roles of the respiratory system, the structures of the nose, pharynx, larynx, trachea, bronchi, lungs, and respiratory membrane, as well as the processes of respiration, mechanics of breathing, respiratory volumes and capacities, respiratory sounds, gas exchange, gas transport, and control of respiration. Suitable for B.Pharm and related health science programs.

Keywords: Respiratory System, Functions, Anatomy, Physiology, Nose, Pharynx, Larynx, Trachea, Bronchi, Lungs, Respiratory Membrane, Respiration, Breathing, Lung Volumes, Respiratory Sounds, Gas Exchange, Gas Transport, Control of Respiration, Human Anatomy and Physiology, B.Pharm, PPT, PDF, Download.

Respiratory System - Detailed Explanation

1. Functions of the Respiratory System

The respiratory system's primary function is to facilitate gas exchange between the body and the environment. Key functions include:

• Gas Exchange: Taking in oxygen (O2) from the air and releasing carbon dioxide (CO2) from the body. Oxygen is needed for cellular respiration (energy production), and carbon dioxide is a waste product of this process.
• Regulation of Blood pH: The respiratory system helps regulate blood pH by controlling the levels of carbon dioxide in the blood. CO2 combines with water to form carbonic acid, so increased CO2 levels make the blood more acidic.
• Voice Production: Air passing over the vocal cords in the larynx produces sound.
• Olfaction (Smell): Olfactory receptors in the nasal cavity detect airborne chemicals.
• Protection: The respiratory system provides some protection against airborne pathogens and irritants through mechanisms like the mucociliary escalator (mucus traps particles, and cilia sweep them out) and alveolar macrophages (immune cells in the alveoli).

2. Anatomy of the Respiratory System

The respiratory system can be divided into the upper respiratory tract (nose, nasal cavity, pharynx) and the lower respiratory tract (larynx, trachea, bronchi, lungs).

• The Nose:
  • The external portion of the respiratory system.
  • Functions:
    • Provides an airway for respiration.
    • Warms, humidifies, and filters incoming air.
    • Serves as a resonating chamber for speech.
    • Houses olfactory receptors.
  • External Nares (Nostrils): The openings to the nasal cavity.
  • Nasal Cavity: Divided by the nasal septum. Lined with a mucous membrane. Contains nasal conchae (turbinates), which increase surface area and create turbulence to improve air filtration.
• Pharynx (Throat):
  • A common passageway for air and food.
  • Divided into three regions:
    • Nasopharynx: Posterior to the nasal cavity; primarily an air passageway. Contains the pharyngeal tonsil (adenoid).
    • Oropharynx: Posterior to the oral cavity; passageway for both air and food. Contains the palatine tonsils and lingual tonsil.
    • Laryngopharynx: Inferior to the oropharynx; passageway for both air and food. Connects to the larynx and esophagus.
• Larynx (Voice Box):
  • Connects the pharynx to the trachea.
  • Contains the vocal cords (vocal folds), which vibrate to produce sound.
  • Composed of several cartilages, including:
    • Thyroid Cartilage: The largest cartilage; forms the "Adam's apple."
    • Cricoid Cartilage: A complete ring of cartilage inferior to the thyroid cartilage.
    • Epiglottis: A flap of cartilage that covers the opening of the larynx (glottis) during swallowing, preventing food from entering the trachea.
    • Arytenoid Cartilages, Corniculate Cartilages, Cuneiform Cartilages: Smaller paired cartilages that are involved in voice production.
• Trachea (Windpipe):
  • Extends from the larynx to the primary bronchi.
  • Lined with pseudostratified ciliated columnar epithelium with goblet cells (produce mucus). The cilia sweep mucus and trapped particles upward towards the pharynx (mucociliary escalator).
  • Supported by C-shaped rings of hyaline cartilage, which keep the trachea open. The open part of the "C" faces posteriorly, allowing the esophagus to expand during swallowing.
• Main Bronchi (Primary Bronchi):
  • The trachea divides into a right main bronchus and a left main bronchus, one for each lung.
  • The right main bronchus is wider, shorter, and more vertical than the left main bronchus, making it more likely for foreign objects to become lodged there.
  • The main bronchi branch into smaller and smaller bronchi (secondary bronchi, tertiary bronchi, etc.) and eventually into bronchioles.
  • The walls of the bronchi contain cartilage and smooth muscle. The amount of cartilage decreases and the amount of smooth muscle increases as the bronchi become smaller.
• Lungs:
  • Paired, cone-shaped organs located in the thoracic cavity.
  • Surrounded by the pleural membranes:
    • Visceral Pleura: Covers the surface of the lungs.
    • Parietal Pleura: Lines the thoracic cavity.
  • The pleural cavity, the space between the visceral and parietal pleura, contains a small amount of pleural fluid, which reduces friction during breathing.
  • The right lung has three lobes (superior, middle, inferior); the left lung has two lobes (superior, inferior) and a cardiac notch to accommodate the heart.
  • Each lobe is further divided into bronchopulmonary segments.
  • The *bronchial tree* refers to the branching system of airways within the lungs (trachea → main bronchi → lobar bronchi → segmental bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli).
• The Respiratory Membrane:
  • The very thin barrier where gas exchange occurs between the air in the alveoli and the blood in the pulmonary capillaries.
  • Composed of:
    • Alveolar Wall: Made up primarily of simple squamous epithelium (Type I alveolar cells). Also contains Type II alveolar cells, which secrete pulmonary surfactant.
    • Capillary Wall: Made up of simple squamous epithelium (endothelium).
    • Fused Basement Membranes: A thin layer between the alveolar and capillary walls.
  • The respiratory membrane is extremely thin (about 0.5 micrometers), facilitating rapid diffusion of gases.

3. Physiology of the Respiratory System

• Respiration
  • Pulmonary ventilation- movement of air in and out.
  • External respiration- Exchange of gases between lungs and blood.
  • Internal respiration- Exchange of gases between blood and tissue.
  • Cellular respiration- Use of oxygen for ATP production.

4. Mechanics of Breathing (Pulmonary Ventilation)

Breathing involves two phases: inspiration (inhalation) and expiration (exhalation). These are driven by pressure changes within the thoracic cavity.

• Inspiration:
  • An active process (requires muscle contraction).
  • The diaphragm contracts and flattens, increasing the vertical dimension of the thoracic cavity.
  • The external intercostal muscles contract, lifting the rib cage and increasing the anteroposterior and lateral dimensions of the thoracic cavity.
  • The volume of the thoracic cavity increases, causing the intrapulmonary pressure (pressure inside the lungs) to decrease below atmospheric pressure.
  • Air flows from the higher pressure atmosphere into the lower pressure lungs.
• Expiration:
  • Normally a passive process at rest (due to elastic recoil of the lungs and chest wall).
  • The diaphragm and external intercostal muscles relax.
  • The elastic recoil of the lungs and chest wall decreases the volume of the thoracic cavity, increasing the intrapulmonary pressure above atmospheric pressure.
  • Air flows from the higher pressure lungs to the lower pressure atmosphere.
  • Forced expiration (e.g., during exercise or coughing) is an active process involving contraction of the internal intercostal muscles and abdominal muscles.
• Respiratory Volumes and Capacities: These are measurements of lung function.
  • Tidal Volume (TV): The amount of air inhaled or exhaled during normal breathing (around 500 mL).
  • Inspiratory Reserve Volume (IRV): The additional amount of air that can be inhaled after a normal inspiration.
  • Expiratory Reserve Volume (ERV): The additional amount of air that can be exhaled after a normal expiration.
  • Residual Volume (RV): The amount of air remaining in the lungs after a maximal exhalation. Keeps the alveoli partially inflated.
  • Inspiratory Capacity (IC): TV + IRV
  • Functional Residual Capacity (FRC): ERV + RV
  • Vital Capacity (VC): TV + IRV + ERV (the maximum amount of air that can be exhaled after a maximal inhalation).
  • Total Lung Capacity (TLC): VC + RV (the total amount of air the lungs can hold).
• Respiratory Sounds:
  • Bronchial Sounds: Produced by air rushing through the trachea and bronchi. Louder and higher-pitched.
  • Vesicular Breathing Sounds: Produced by air filling the alveoli. Softer, rustling sounds.
  • Abnormal lung sounds (e.g., crackles, wheezes) can indicate respiratory disorders.

5. External Respiration, Gas Transport, and Internal Respiration

• External Respiration:
  • Gas exchange between the air in the alveoli and the blood in the pulmonary capillaries.
  • Oxygen (O2) diffuses from the alveoli (high PO2) into the blood (low PO2).
  • Carbon dioxide (CO2) diffuses from the blood (high PCO2) into the alveoli (low PCO2).
  • Driven by partial pressure gradients.
• Gas Transport in the Blood:
  • Oxygen Transport:
    • Most oxygen (about 98.5%) is transported bound to hemoglobin in red blood cells. Each hemoglobin molecule can bind up to four oxygen molecules.
    • A small amount of oxygen (about 1.5%) is dissolved in the plasma.
  • Carbon Dioxide Transport:
    • About 7% is dissolved in the plasma.
    • About 23% is bound to hemoglobin (carbaminohemoglobin). CO2 binds to the globin portion of hemoglobin, not the heme.
    • About 70% is transported as bicarbonate ions (HCO3-) in the plasma. CO2 reacts with water in red blood cells (catalyzed by carbonic anhydrase) to form carbonic acid (H2CO3), which dissociates into H+ and HCO3-. The HCO3- diffuses out of the red blood cells into the plasma (in exchange for chloride ions - the "chloride shift").
• Internal Respiration:
  • Gas exchange between the blood in the systemic capillaries and the tissue cells.
  • Oxygen (O2) diffuses from the blood (high PO2) into the tissue cells (low PO2).
  • Carbon dioxide (CO2) diffuses from the tissue cells (high PCO2) into the blood (low PCO2).
  • Driven by partial pressure gradients.
• Control of Respiration:
  • Breathing is primarily controlled by respiratory centers in the brainstem (medulla oblongata and pons).
  • Medullary Respiratory Center:
    • Dorsal Respiratory Group (DRG): Primarily involved in inspiration. Contains inspiratory neurons that send signals to the diaphragm and external intercostal muscles.
    • Ventral Respiratory Group (VRG): Involved in both inspiration and expiration, especially during forceful breathing. Contains both inspiratory and expiratory neurons.
  • Pontine Respiratory Centers: Influence the activity of the medullary centers, helping to smooth the transition between inspiration and expiration.
  • Factors Influencing Breathing Rate and Depth:
    • Chemical Factors:
      • PCO2: The most important chemical factor. Increased arterial PCO2 (hypercapnia) stimulates increased ventilation (both rate and depth). Detected by central chemoreceptors in the medulla and peripheral chemoreceptors in the carotid and aortic bodies.
      • PO2: Decreased arterial PO2 (hypoxia) stimulates increased ventilation, but it's a less potent stimulus than increased PCO2. Detected by peripheral chemoreceptors.
      • pH: Decreased arterial pH (increased acidity) stimulates increased ventilation. Can be caused by increased PCO2 or by other metabolic factors.
    • Higher Brain Centers: Voluntary control (e.g., holding your breath), emotional influences (e.g., fear, anxiety).
    • Proprioceptors: In muscles and joints; provide information about body movement, stimulating increased ventilation during exercise.
    • Pulmonary Irritant Reflexes: Irritants in the airways can cause coughing or sneezing.
    • Inflation Reflex (Hering-Breuer Reflex): Stretch receptors in the lungs inhibit inspiration when the lungs are overinflated, preventing damage.

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