BIO_313_Respiratory_System_S24

RESPIRATORY SYSTEM

Overview

The respiratory system plays a crucial role in maintaining homeostasis by facilitating gas exchange necessary for cellular respiration, which is vital for sustaining life. Oxygen (O₂) is not only essential for oxidizing nutrients to generate adenosine triphosphate (ATP), the energy currency of cells, but also plays a critical role in various biochemical pathways. As cells metabolize nutrients, carbon dioxide (CO₂) is produced as a by-product, which must be expelled from the body to maintain an optimal internal environment and prevent acidosis.

Key Processes

• Breathing: This process involves two primary phases: inhalation (the intake of air) and exhalation (the expulsion of air). Inhalation allows O₂ to enter the lungs, where it diffuses into the bloodstream, while exhalation removes CO₂ from the body.

• Cellular Respiration: A biochemical process where glucose (C₆H₁₂O₆) reacts with oxygen to produce energy. The overall chemical reaction can be represented as:

  [ C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + 36 ATP ]

  This process occurs in the mitochondria of cells and is critical for cellular function.

Acidity and the Bicarbonate Buffer System

The body carefully regulates pH levels through the bicarbonate buffer system, which involves:

• Carbonic Acid (H₂CO₃): Acts as a weak acid that can dissociate into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺), thus helping to moderate changes in pH.

• This system includes renal excretion of H⁺ ions and the ventilation of HCO₃⁻, coordinating closely with respiratory activity to maintain acid-base balance in the body.

Types of Respiration

• External Respiration: Refers to the gas exchange that takes place in the lungs. O₂ diffuses from the alveoli into the blood, while CO₂ diffuses from the blood into the alveoli.

• Internal Respiration: This occurs at the tissue level and involves the exchange of gases between blood and tissue cells. O₂ is utilized by tissues for metabolic processes, while CO₂ is produced as a waste product.

• Key Driving Mechanism: Gas exchange occurs through diffusion down a pressure/concentration gradient, where gases move from areas of higher concentration to lower concentration.

Respiratory Mechanics

• Breathing vs. Ventilation: While breathing specifically refers to the act of inhaling and exhaling, ventilation encompasses the total movement of air into and out of the lungs and is measured in liters per minute.

Functions of the Respiratory System

1. Gaseous Exchange: Facilitating O₂ intake and CO₂ expulsion.

2. Acid–base Balance: Maintaining the body's pH through regulation of gases.

3. Vocalization/Phonation: Allowing for sound production through the larynx.

4. Humidification of Air: Moisten incoming air to protect lung tissue.

5. Aiding in Olfaction: Assisting in the sense of smell.

6. Defense Against Pathogens: Acts as a barrier and filtering system.

7. Regulation of Blood and Lymph Flow: Assists in the circulation of these fluids.

Functional Classification of Respiratory Structures

• Conducting Zone: Responsible for filtering, warming, moistening, and delivering air to the lungs. Structures include the nose, pharynx, larynx, trachea, and bronchi. This zone also includes anatomical dead space, areas where no gas exchange occurs.

• Respiratory Zone: The site of gas exchange, which includes respiratory bronchioles, alveolar ducts, and alveoli.

Anatomy of the Upper Respiratory Tract

• Nasal Cavity: Contains sinuses that filter and warm incoming air. It is lined with mucous membranes and cilia that trap particles.

• Pharynx: Divided into three sections:

  • Nasopharynx: Serves as an air passage.

  • Oropharynx: Allows passage of air, food, and liquids.

  • Laryngopharynx: A common pathway for air and food before entering the larynx or esophagus.

• Larynx: Functions as a voice box, composed of cartilage; its roles include directing food to the esophagus and producing sound through the vocal cords.

The Trachea and Airways

• Trachea: Contains C-shaped cartilage rings that prevent collapse, lined with ciliated pseudostratified columnar epithelium that traps and moves debris out of the airways.

• Bronchi: Divides into primary, secondary, and tertiary bronchi to lead into the lungs. Each bronchus is surrounded by elastic connective tissue that allows for recoil during exhalation.

Lungs Anatomy

• Right Lung: Composed of three lobes (superior, middle, inferior) and is larger in volume to accommodate additional bronchial passageways.

• Left Lung: Consists of two lobes and has a cardiac impression for the heart; its anatomy is adapted to provide space for the heart’s location.

• Lung Surfaces: Includes the base (rests on the diaphragm), apex (extending above the clavicle), costal surface (pressed against the rib cage), and mediastinal surface (facing the heart).

Alveoli and Gas Exchange

• Alveoli: Microscopic sacs where the critical exchange of gases takes place. They comprise two types of cells:

  • Type I Pneumocytes: Form the thin barrier facilitating gas diffusion.

  • Type II Pneumocytes: Secrete surfactant, reducing surface tension and preventing alveolar collapse.

• Respiratory Membrane: This thin membrane is made up of alveolar and capillary endothelium, enabling rapid gas diffusion required for efficient respiratory function.

Control of Breathing

• Involuntary Control: Centers located in the brain stem monitor levels of CO₂ and pH in the blood, adjusting respiratory rates based on the body’s needs.

• Chemoreceptors:

  • Peripheral: Located in the carotid and aortic bodies, they respond to changes in blood chemistry, notably elevated CO₂ and reduced O₂ levels.

  • Central: Located in the medulla, they primarily respond to acidic changes (H⁺ concentration) in the cerebrospinal fluid, thus influencing breathing rates.

Transport of Gases

• Oxygen Transport: Approximately 1.5% of the O₂ is dissolved in plasma, while 98.5% is bound to hemoglobin within red blood cells, which drastically increases the blood's O₂ carrying capacity.

• Carbon Dioxide Transport: CO₂ is transported in three ways: 7% is dissolved in plasma, 23% binds to hemoglobin, and approximately 70% travels as bicarbonate ions in plasma.

Pathologies and Physiology

• Hypoxia: A condition characterized by insufficient supply of O₂ to tissues, which can occur due to various physiological conditions including respiratory diseases, high altitudes, or anemia.

• Carbon Monoxide Poisoning: Hemoglobin has a higher affinity for carbon monoxide than for O₂, meaning that CO can bind preferentially to hemoglobin and inhibit O₂ delivery to tissues, potentially leading to severe hypoxia.

Summary of Breathing Mechanisms

• Inhalation: Involves the flattening of the diaphragm and contraction of intercostal muscles, leading to a decrease in pressure in the thoracic cavity, which draws air into the lungs.

• Exhalation: Typically a passive process where the diaphragm and intercostals relax, aided by the elastic recoil of lung tissue, thus expelling air from the lungs.

Important Definitions and Terms

• Tidal Volume: The volume of air exchanged during a typical, unforced breath.

• Vital Capacity: The maximum volume of air that can be expelled from the lungs after the maximum inhalation effort.

• Dead Space: Areas of the respiratory system where gas exchange does not take place, such as the trachea and bronchi.

• Alveolar Ventilation Rate: The frequency of breaths multiplied by the effective tidal volume, indicating the volume of fresh air entering the alveoli.

Factors Affecting Ventilation

• Surface Tension: The alveolar fluid creates surface tension that resists lung expansion. Surfactant reduces this tension, facilitating easier lung inflation.

• Compliance: Refers to the ability of the lungs to stretch and expand; this can be affected by lung tissue conditions such as fibrosis or emphysema.

• Airway Resistance: Influenced by the diameter of airways, which can be obstructed by conditions like asthma or bronchitis, leading to increased resistance to airflow.

External Influences on Breathing

Several external conditions such as environmental temperature, humidity, and acidity of the blood can modify ventilation rates, allowing for effective oxygen unloading in tissues that are metabolically active and producing more CO₂.

Study Guide Overview

To effectively study the respiratory system, review physiological parameters, mechanisms of respiration, lung capacities, and the various methods of respiratory control. Additionally, grasp the specific roles of different anatomical features in enhancing breathing efficiency and gas exchange functionality.