"Lung" - what is it, definition of the term
The pulmonary organ in rodents is a paired, highly vascularized structure occupying the thoracic cavity, composed of branching bronchi that terminate in alveolar sacs where oxygen diffuses into the bloodstream and carbon dioxide is expelled; its delicate membrane, supported by connective tissue, provides a large surface area relative to body size, enabling efficient respiration essential for metabolic demands of species such as rats and mice.
Detailed information
The pulmonary organ of rodents serves as the primary site for gas exchange, supplying oxygen to the bloodstream and removing carbon dioxide. In both rats and mice, the organ is divided into distinct lobes: rats typically possess five lobes (right cranial, right middle, right caudal, left cranial, left caudal), whereas mice have four (right cranial, right middle, left, and right accessory). The structural arrangement influences ventilation distribution and susceptibility to injury.
Alveolar architecture is similar across species, with thin epithelial walls, a rich capillary network, and surfactant-producing type II cells that reduce surface tension. Differences emerge in alveolar size and density: rats exhibit larger alveolar sacs and lower surface‑area‑to‑volume ratios, while mice display higher alveolar density, providing greater diffusion capacity per unit lung mass.
Key physiological parameters include tidal volume, respiratory rate, and minute ventilation. Typical values are:
- Rat: tidal volume ~2 ml kg⁻¹, respiratory rate 80–120 breaths min⁻¹, minute ventilation 150–200 ml min⁻¹ kg⁻¹.
- Mouse: tidal volume ~1 ml kg⁻¹, respiratory rate 150–200 breaths min⁻¹, minute ventilation 200–250 ml min⁻¹ kg⁻¹.
Blood–gas exchange efficiency is reflected in arterial oxygen tension (PaO₂) and carbon dioxide tension (PaCO₂). Rats maintain PaO₂ around 90–100 mmHg and PaCO₂ near 35 mmHg under normoxic conditions; mice show slightly lower PaO₂ (80–90 mmHg) and comparable PaCO₂ values.
Developmental timelines differ. In rats, alveolarization accelerates between postnatal days 4 and 14, reaching functional maturity by day 21. Mice complete alveolar development earlier, with rapid expansion from day 3 to 10 and functional maturity by day 14. These periods are critical for experimental models of neonatal lung injury.
Pathological responses to insults such as hyperoxia, endotoxin exposure, or mechanical ventilation are species‑specific. Rats tend to develop more pronounced edema and inflammatory infiltrates, whereas mice exhibit higher susceptibility to fibrosis and altered cytokine profiles. Genetic manipulation is more readily performed in mice, enabling precise investigation of molecular pathways governing pulmonary development and disease.
In experimental design, selection between the two species should consider anatomical size, ventilation parameters, developmental stage, and genetic tractability. Rats provide larger tissue samples for physiological recordings and surgical interventions; mice offer extensive transgenic resources and accelerated developmental timelines.