Respiratory System Function and Anatomy

Respiratory System Structures and Function

• The trachea leads to the bronchi in the lungs.
• The tiny air sacs in the lungs are called alveoli.
• The epiglottis prevents food from entering the trachea.
• Approximately 300 million alveoli are found in human lungs.

Gas Exchange in the Lungs

• During gas exchange, oxygen passes into the blood and carbon dioxide passes out of the blood.

Respiratory Pathway

• Air travels through the nose, pharynx, trachea, and lungs.

Pressure Changes During Respiration

• When inhaling (breathing in), the pressure in the thorax increases.

Regulation of Pulmonary Blood Flow

• Pulmonary blood flow is proportional to cardiac output.
• Pulmonary blood flow is inversely proportional to vascular resistance.
• During inspiration, pulmonary blood vessels are distended due to decreased intrathoracic pressure.
• During exercise, vascular resistance decreases, and pulmonary blood flow increases.

Factors Affecting Pulmonary Blood Vessels

• Sympathetic nervous system causes vasoconstriction (b2).
• Excess carbon dioxide and lack of oxygen cause vasoconstriction.

Gravity and Hydrostatic Pressure

• In a standing position, blood pressure is high in the lower extremities and low in parts above the heart.
• Blood flow distribution in the lung varies across different zones (apex, zone 2, zone 3, base).

Zones of Blood Flow in the Lungs

• Zone 1: Pulmonary capillary pressure is similar to alveolar pressure; zero blood flow.
• Zone 2: Alveolar pressure is below pulmonary systolic pressure and above diastolic pressure; intermittent blood flow.
• Zone 3: Pulmonary arterial pressure is higher than alveolar pressure; continuous blood flow.

Respiratory Movements

• Respiratory muscles include inspiratory muscles (diaphragm and external intercostals) and expiratory muscles (internal intercostals and abdominal muscles).

Mechanisms of Respiration

• During inspiration, the diaphragm moves down and the ribs move out, expanding the thoracic cavity.
• During expiration, the diaphragm moves up and the ribs move in, compressing the thoracic cavity.

Lung Movement and Pressure

• During inspiration, the negative pressure in the thoracic cavity causes lung expansion.
• During expiration, the thoracic cavity decreases in size, compressing the lungs and expelling air.

Collapsing Tendency of the Lungs

• Factors causing collapse include: elastic lung tissue properties and surface tension of alveolar fluid.
• Factors preventing collapse include: negative intrapleural pressure and surfactant.

Surfactant

• Surfactant is a lipoprotein complex secreted by type II alveolar epithelial cells.
• It lowers surface tension in the alveoli, preventing collapse.

Respiratory Pressures

• Two types of pressures are exerted: intrapleural (intrathoracic) and intra-alveolar (intrapulmonary).
• Transpulmonary pressure is the difference between alveolar and intrapleural pressures.
• Transthoracic pressure is the difference between pleural and atmospheric pressures.
• Transthoraco-pulmonary pressure is the difference between alveolar and atmospheric pressures.
• Driving pressure is calculated as plateau pressure—PEEP.

Intrapleural Pressure

• The pressure within the pleural cavity, normally negative, keeps the lungs inflated.

Intra-alveolar Pressure

• The pressure within the alveoli, fluctuating with breathing. It's equal to atmospheric pressure at the end of inspiration and expiration.

Lung Function Tests

• Types of lung function tests: static (volume-based) and dynamic (flow-based).
• Static tests measure volumes and capacities (e.g., tidal volume, inspiratory reserve volume, expiratory reserve volume, residual volume).

Lung Volumes

• Tidal volume: Volume of air inhaled and exhaled during a normal breath.
• Inspiratory reserve volume: Maximum volume of air that can be inhaled after a normal breath.
• Expiratory reserve volume: Maximum volume of air that can be exhaled after a normal breath.
• Residual volume: Volume of air remaining in the lungs after a maximum exhalation.

Other Key Terms

• Spirometer: A device used to measure respiratory volumes.

Test your knowledge on the structures and functions of the respiratory system, including gas exchange, airflow, and regulation of pulmonary blood flow. This quiz covers essential concepts like alveoli, trachea, and pressure changes during breathing.