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Lungs and Pleural Cavity

• Lungs are enclosed by the diaphragm and thoracic cage.

  • Each lung occupies most of the thoracic space.

  • Lungs are suspended in the cavity by a bronchus and blood vessels.

• Visceral pleura is attached to the lung's surface, folding back at the hilum to become parietal pleura.

  • Pleural cavity between them contains serous fluid for lubrication.

• Right lung is larger and has three lobes, while the left lung has two lobes.

• Each lobe of the lung is supplied by a lobar bronchus and connected to blood and lymphatic vessels.

Breathing Mechanism

• Breathing involves inspiration (inhalation) and expiration (exhalation).

• Atmospheric pressure moves air into the lungs during inspiration.

• Pressure and volume in the lungs are inversely related (Boyle's law).

• Diaphragm plays a crucial role in changing thoracic cavity volume for breathing.

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Parts of the Respiratory System

• Nose, nasal cavity, sinuses, pharynx, larynx, trachea, bronchial tree, and lungs are key parts.

• Functions include conducting air, filtering, warming, moistening air, and housing vocal cords.

Air Pressure and Breathing

• Inside surfaces of the lungs are subjected to pressure due to breathing.

• Pressure and volume in the lungs follow Boyle's law.

• Diaphragm muscle movement changes thoracic cavity volume for air movement.

• Air moves into and out of the lungs based on pressure changes.

By understanding the anatomy of the lungs, the pleural cavity, and the mechanics of breathing, one can appreciate the intricate processes involved in respiration and the vital role the respiratory system plays in sustaining life.

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Major Events in Inspiration

• Impulses conducted on phrenic nerves to muscle fibers in diaphragm and intercostal muscles

  • Elevates ribs and sternum, increasing thoracic cavity size

• External intercostal muscles contract, raising ribs and expanding thoracic cavity

• Pleural membranes movements aid lung expansion

• Surfactant production reduces alveolar collapse risk

• Additional muscles can aid in expanding thoracic cage

• Ventilator and synthetic surfactant used in respiratory distress syndrome

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Maximal Inspiration and Expiration

• Compliance of lungs decreases as volume increases

• Pneumothorax can decrease lung compliance

• Normal expiration aided by elastic recoil and surface tension

• Exhalation can be increased by contracting internal intercostal muscles and abdominal wall muscles

• Recoil of elastic fibers in lung tissues reduces pleural cavity pressure

• Pressure between pleural membranes is typically lower than atmospheric pressure

Treatment for Pneumothorax

• Covering chest wound with bandage

• Inserting chest tube to reestablish negative pressure

• Applying suction to expand collapsed lung

Steps in Expiration

• Exhalation occurs passively without muscle contraction

• Internal intercostal muscles and abdominal wall muscles aid in increasing air pressure in lungs

• Elastic fibers recoil to reduce pleural cavity pressure

• Pressure between pleural membranes is typically lower than atmospheric pressure

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Expiration

• Normal resting expiration is due to elastic recoil of lung tissues and abdominal organs.

  • Elasticity of lungs recoils inward.

• Contraction of abdominal wall muscles and posterior internal intercostal muscles aids maximal expiration.

  • Abdominal wall muscles contract and compress abdominal organs.

• Major events in expiration:

  1. The diaphragm and external respiratory muscles relax.

  2. Elastic tissues of the lungs suddenly recoil.

  3. Tissues recoiling around the lungs increase intra-alveolar pressure.

  4. Air is forced out of the lungs.

Respiratory Air Volumes and Capacities

• Different volumes of air can be moved in or out of the lungs.

• Three distinct respiratory volumes can be measured using spirometry.

  • Tidal volume, inspiratory reserve volume, and expiratory reserve volume.

• Residual volume remains in the lungs after forceful expiration.

• Total lung capacity varies with age, sex, and body size.

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Residual Volume and Capacities

• After forceful expiration, about 1,200 mL of air remains in the lungs as residual volume.

• Vital capacity plus residual volume equals total lung capacity.

• Mixing of newly inhaled air with existing air in the lungs prevents concentration fluctuations.

• Respiratory capacities can be calculated by combining respiratory volumes.

• Anatomic dead space contains air that does not reach the alveoli.

• Physiologic dead space is the sum of anatomic and alveolar dead spaces.

Respiratory Air Volumes and Capacities

• Various respiratory volumes and capacities:

  • Tidal volume, inspiratory reserve volume, expiratory reserve volume, residual volume, inspiratory capacity, functional residual capacity, vital capacity, total