Lecture #19 - Homeostatic Regulation

Respiratory System Physiology

Ventilation Process

  • Definition of Ventilation: Moving air through the conducting portion into and out of the respiratory system.

  • Phases of Ventilation

    • Inhalation: Process of pulling air into the lungs.

    • Key Muscle Involved: Diaphragm (skeletal muscle, consciously controlled).

      • Functions by contracting downwards, increasing volume and lowering pressure within thoracic cavity, thereby creating a vacuum for air intake.

    • Accessory Muscles for Deep Breathing:

      • External Intercostals: Elevate and expand thoracic cavity by pulling ribs upward.

      • Sternocleidomastoid: Assists in inhalation by elevating the sternum.

    • Exhalation:

    • Primarily passive; involves relaxing the diaphragm and allowing it to return to the dome shape, forcing air out.

    • Active Exhalation:

      • Utilizes abdominal muscles (external obliques, rectus abdominis, and transverse abdominis) and internal intercostals to physically compress thoracic cavity and push air out forcefully.

      • Elastic fibers in the lungs assist in pushing air out.

Mechanisms of Breathing

  • Air movement is dependent on lung volume increase along with thoracic cavity expansion through the pleural membranes (serous membranes).

  • Pleural Cavity: Two pleural cavities (one for each lung) filled with serous fluid to allow lung expansion with thoracic cavity.

  • Pneumothorax: Condition arising when air enters the pleural space, reducing lung expansion capability (resulting in a collapsed lung).

Control of Ventilation

Neural Control Centers

  • Ventilation control is managed by the medulla oblongata and pons in the brainstem.

    • Medulla Oblongata: Basic respiratory rhythm regulation, stimulates inhalation.

    • Pons: Modifies respiratory rate/depth according to the body’s needs (e.g., exercise).

  • Cerebrum: Responsible for conscious control of breath (e.g., when speaking or singing).

Negative Feedback Loop for Oxygen Regulation

  • Components of Feedback Loop:

    1. Sensor: Detects changes in the body (e.g., chemoreceptors and baroreceptors).

    2. Integrator: Medulla oblongata processes data from sensors.

    3. Effector: Muscles (mainly diaphragm and external intercostals) that respond by adjusting respiration rate.

  • Importance of Homeostasis: Maintaining appropriate oxygen and carbon dioxide levels, with the nervous system detecting changes.

Urinary System Functions

Overview of the Urinary System

  • Key Organs: Two kidneys, two ureters, urinary bladder, urethra.

  • Primary Function of Kidneys: Filter blood to maintain homeostasis and balance various parameters.

  • Main Functions:

    1. Remove Wastes: Eliminate metabolic waste products (e.g., urea).

    2. Conserve Nutrients: Retain valuable compounds like glucose.

    3. Regulate Blood Volume and Pressure: Adjust water content.

    4. Electrolyte Regulation: Control levels of ions in plasma.

    5. Regulate Blood pH: Maintain normal pH levels for compatibility with life.

Feedback Loop for Water Regulation

  • Sensor: Osmoreceptors in the hypothalamus respond to changes in solute concentration (detects dehydration).

  • Integrator: Hypothalamus processes signals from osmoreceptors.

  • Effector: Hypothalamus and posterior pituitary gland secretes antidiuretic hormone (ADH) to conserve water.

  • Thirst Center: Triggers conscious thirst response to replenish lost fluids.

  • Goal: Maintain isotonic environment and adequate perfusion to organs.

Feedback Loop for Electrolyte Regulation

  • Definition of Electrolytes: Substances that dissociate into ions in solution (such as sodium and potassium).

  • Sodium & Potassium Regulation: Both contribute to peripheral and central nervous system function (e.g., generation of nerve impulses).

  • Both enter the body via the digestive system and are primarily excreted in urine.

  • Negative Feedback Loops:

    • Sodium Loop: Baroreceptors in kidneys detect blood pressure; low pressure triggers aldosterone release from adrenal glands to conserve sodium and therefore water.

    • Potassium Loop: Aldosterone promotes potassium secretion to prevent arrhythmia.

Feedback Loop for Calcium Regulation

  • Calcium Ions: Critical for signaling in muscle contraction and neuron function.

  • Stored in bone through osteoblast activity, released when needed using osteoclasts.

  • Triggered by Hormones:

    • Low calcium levels release parathyroid hormone to stimulate osteoclasts, increasing serum calcium.

    • High calcium levels release calcitonin to inhibit osteoclasts and promote urinary excretion of calcium to decrease serum calcium levels.

Acid-Base Regulation (pH)

  • pH Scale: Normal physiological range is between 7.35 and 7.45 (neutral is 7, less than 7 is acidic and more than 7 is basic).

  • Hydrogen Ions: The concentration of hydrogen ions defines acidity.

  • Carbon Dioxide Relation: Higher carbon dioxide levels lead to lower pH (more acidic environment). CO₂ combines with water to form carbonic acid (H₂CO₃), dissociating to release H⁺ ions.

  • Breathing Regulation: Organism must off-load CO₂ to maintain blood pH balance; impaired ventilation can result in acidosis (too high CO₂, too low pH).