"Liver" - what is it, definition of the term
The hepatic organ in rats and mice is a large, reddish‑brown gland situated beneath the diaphragm, composed of lobules formed by hepatocytes surrounding central veins; it conducts nutrient metabolism, detoxifies xenobiotics, synthesizes plasma proteins, and stores glycogen and essential micronutrients.
Detailed information
The hepatic organ of rodents constitutes a lobulated mass situated in the right dorsal cavity, extending from the diaphragm to the caudal pole. In both species, the right lobe dominates the volume, while left and median lobes contribute to overall mass distribution. Blood supply derives from the portal vein (approximately 70 % of inflow) and the hepatic artery (about 30 %). Venous drainage proceeds through the hepatic veins into the inferior vena cava. Biliary excretion follows a network of intra‑hepatic ducts converging into the common bile duct.
Functionally, the organ performs gluconeogenesis, glycogen storage, lipid synthesis, and detoxification of xenobiotics. Enzymatic activity includes cytochrome P450 isoforms, glutathione‑S‑transferases, and UDP‑glucuronosyltransferases, which metabolize endogenous compounds and administered drugs. Protein synthesis occurs primarily for plasma albumin, clotting factors, and acute‑phase reactants. Ammonia conversion to urea proceeds via the urea cycle, maintaining nitrogen balance.
In experimental settings, the hepatic tissue of rats and mice serves as a model for:
- Metabolic disease research (e.g., non‑alcoholic fatty liver disease, insulin resistance).
- Toxicology assessments (dose‑response to hepatotoxic agents, evaluation of protective compounds).
- Genetic manipulation studies (knock‑out or transgenic lines targeting metabolic pathways).
- Regeneration investigations (partial hepatectomy, stem‑cell engraftment).
Histologically, the organ exhibits a hexagonal lobular architecture with central veins at the core and portal triads at the periphery. Hepatocytes arrange in one‑cell‑thick plates radiating outward, interspersed with sinusoidal endothelial cells and Kupffer cells. In mice, lobular diameter averages 200 µm; in rats, it approaches 300 µm, reflecting size differences.
Physiological parameters differ between the two species. Basal hepatic blood flow rates are approximately 55 ml min⁻¹ kg⁻¹ in rats and 45 ml min⁻¹ kg⁻¹ in mice. Enzyme expression profiles show higher cytochrome P450 2E1 activity in rats, whereas mice exhibit greater CYP2C29 levels. These variations influence drug metabolism and toxicological outcomes.
When sampling tissue, standard practice involves rapid perfusion with cold saline to clear blood, followed by snap‑freezing in liquid nitrogen for molecular analyses or fixation in formalin for histopathology. Precautions include minimizing ischemia time to preserve enzymatic activity and prevent post‑mortem alterations.
Overall, the hepatic organ of rodents provides a robust platform for investigating metabolic regulation, disease mechanisms, and therapeutic interventions, with species‑specific characteristics informing experimental design and data interpretation.