Respiration phys plus patho

Anatomy of the Respiratory System

• Respiratory System Overview

  • Organ system that takes in air and expels it from the body.

  • Respiration: refers to ventilation of the lungs (breathing).

  • Functions:

    • Gas Exchange: O2 and CO2 exchanged between blood and air.

    • Communication: speech and other vocalizations.

    • Olfaction: sense of smell.

    • Acid-Base Balance: eliminates CO2, influencing pH of body fluids.

    • Blood Pressure Regulation: assists synthesis of angiotensin II.

Organization of Respiratory Organs

• Conducting Zone:

  • Passages for airflow (no gas exchange).

  • Includes nostrils through major bronchioles.

• Respiratory Zone:

  • Regions participating in gas exchange.

  • Includes alveoli and nearby structures.

The Lungs and Bronchial Tree

• Respiratory Membrane:

  • Thin barrier between alveolar air and blood.

  • Each alveolus surrounded by capillaries from pulmonary artery.

  • Gases exchanged across membrane:

    • Layers:

      • Squamous alveolar cells.

      • Endothelial cells of blood capillary.

      • Shared basement membrane.

Pulmonary Circulation

• Lung Blood Supply:

  • Pulmonary Circuit:

    • Pulmonary trunk → pulmonary arteries → capillaries around alveoli → pulmonary veins.

    • Unloads CO2 from blood, picks up O2 from inhaled air.

  • Systemic Blood Supply:

    • Bronchial arteries arise from aorta, supplying lung tissue with blood.

    • Bronchial veins drain into the azygos vein.

  • Right-to-Left Shunt: some bronchial blood mixes with pulmonary venous blood, diluting oxygen content.

Gas Exchange and Circulation Efficiency

• Diffusion is slow in liquid, necessitating low blood pressure in capillaries.

• Capillary Blood Pressure:

  • Mean pressure: 10 mm Hg (compared to 30 mm Hg elsewhere).

  • This low pressure prevents rupture of respiratory membrane and keeps alveoli dry.

  • Extensive lymphatic drainage is vital for maintaining fluid balance.

Neural Control of Breathing

• Skeletal Muscle Activation:

  • Breathing is dependent on repetitive stimulation from the brain

  • Brain Levels:

    • Cerebral: voluntary control.

    • Unconscious: automatic functions.

Breathing Control Centers

• Brainstem Centers:

  • Automatic control via reticular formation in medulla and pons.

• Ventral Respiratory Group (VRG):

  • Primary generator of respiratory rhythm (12 breaths/min).

• Dorsal Respiratory Group (DRG):

  • Modifies breathing rate and depth as needed.

• Pontine Respiratory Group (PRG):

  • Adapts breathing for special circumstances (sleep, exercise, etc.).

Respiratory Pressure Dynamics

• Airflow Regulation:

  • Governed by Boyle’s law: air pressure inversely proportional to volume.

  • Changes in thoracic cage alter intrapulmonary pressure, facilitating airflow in/out of lungs.

Inspiration Mechanics

• Thoracic Expansion:

  • Lungs expand with thoracic cage due to negative intrapleural pressure.

  • Rib and Pleura Dynamics:

    • Ribs elevate, expanding thoracic cavity and decreasing pressure to draw in air.

• Additional Factors Enhancing Expansion:

  • Warming of inhaled air increases volume due to Charles’s law.

Alveolar Ventilation Rate (AVR)

• Amount of air ventilating alveoli per minute (critical for oxygen delivery and CO2 disposal).

• Example Calculation:

  • If 500 mL inhaled, 150 mL stays in dead space = 350 mL reaches alveoli.

  • AVR = 350 mL × 12 bpm = 4,200 mL/min.

Measurement of Pulmonary Volumes

• Tidal Volume (TV): air volume in one cycle (~500 mL).

• Inspiratory Reserve Volume (IRV): maximum inhalation capacity above TV (~3,000 mL).

• Expiratory Reserve Volume (ERV): maximum exhalation above TV (1,200 mL).

• Residual Volume (RV): air left post-max expiration (1,300 mL), crucial for gas exchange.

Respiratory Capacities

• Vital Capacity (VC): total maximum air inhaled and exhaled (4,700 mL).

• Inspiratory Capacity (IC): maximum air inhaled after normal exhalation (3,500 mL).

• Functional Residual Capacity (FRC): air remaining post-normal expiration (2,500 mL).

• Total Lung Capacity (TLC): maximum lung volume (6,000 mL).

Variations in Respiratory Rhythm

• Eupnea: relaxed breathing.

• Hyperventilation: excess ventilation; occurs under stress/exercise.

• Apnea: temporary cease of breathing.

• Dyspnea: labored breathing.

Gas Transport and Exchange

• Oxygen Transport:

  • O2 is primarily carried bound to hemoglobin (98.5%); remainder dissolved in plasma.

  • Cooperative binding phenomenon illustrated by oxyhemoglobin dissociation curve.

• Carbon Dioxide Transport:

  • 90% as bicarbonate; 5% in carbamino compounds; 5% dissolved.

• Carbon Monoxide Poisoning: prevents O2 delivery by competing with hemoglobin.

Systemic Gas Exchange Dynamics

• Unloading O2 and loading CO2 at systemic capillaries involves carbonic anhydrase facilitating reactions.

• Blood pH Regulation:

  • Acidosis (<7.35) or alkalosis (>7.45) influenced by CO2 levels.

Oxygen Imbalances & COPD

• Hypoxia Types:

  • Hypoxemic, ischemic, anemic, and histotoxic.

• Chronic Obstructive Pulmonary Diseases (COPDs): include chronic bronchitis and emphysema, often due to smoking.

Lung Cancer

• Lung cancer is the leading cause of cancer deaths.

• Major forms include squamous-cell carcinoma, adenocarcinoma, and small-cell carcinoma, the latter being the most aggressive.