"Organ" - what is it, definition of the term
The term denotes a discrete anatomical entity composed of multiple tissue types that cooperate to perform a specific physiological function; in laboratory rodents such as rats and mice, examples include the heart, which generates circulatory force, the liver, which processes nutrients and detoxifies chemicals, and the kidney, which regulates fluid and electrolyte balance, each exhibiting characteristic morphology, vascular supply, and innervation that together sustain the animal’s homeostasis.
Detailed information
Rats and mice share a compact vertebrate body plan in which each physiological unit performs specialized tasks essential for survival. The cardiovascular component consists of a four‑chambered heart, aortic arch, and extensive capillary network that supports high metabolic rates. Respiratory structures include a pair of lungs with a high surface‑area alveolar arrangement, facilitating efficient gas exchange during rapid activity. The digestive tract is divided into oral cavity, esophagus, stomach, small and large intestines, and accessory glands such as pancreas and liver, each contributing to nutrient breakdown, absorption, and detoxification.
The nervous system features a brain divided into cerebral cortex, hippocampus, cerebellum, and brainstem, complemented by a spinal cord that transmits motor and sensory signals. Peripheral nerves innervate skeletal muscles, enabling fine motor control and locomotion. Sensory organs—eyes, ears, and olfactory epithelium—provide visual, auditory, and chemical detection capabilities adapted to nocturnal and burrowing lifestyles.
Reproductive anatomy differs between sexes. Males possess paired testes, epididymides, and a prostate gland that produce and mature sperm. Females contain ovaries, oviducts, a uterus, and mammary glands, supporting oogenesis, implantation, and lactation. Both sexes exhibit endocrine glands—thyroid, adrenal, and pituitary—that regulate metabolism, stress response, and growth through hormone secretion.
Key physiological parameters for laboratory rodents include:
- Body mass: 20–30 g (mouse), 250–350 g (rat)
- Heart rate: 300–500 beats min⁻¹ (mouse), 350–450 beats min⁻¹ (rat)
- Respiratory rate: 80–150 breaths min⁻¹ (mouse), 70–110 breaths min⁻¹ (rat)
- Lifespan: 2–3 years (mouse), 2–4 years (rat)
Developmental stages progress from embryonic formation of primary germ layers to organogenesis, where each functional unit attains structural maturity. Postnatal growth involves rapid expansion of skeletal muscle mass, adipose depots, and immune tissue, reflecting the species’ high reproductive output.
In biomedical research, these internal structures serve as models for human disease. Cardiac physiology mirrors human electrophysiology, enabling arrhythmia studies. Pulmonary mechanics aid investigations of asthma and fibrosis. Gastrointestinal architecture supports microbiome and metabolic disorder research. Neurological regions provide platforms for neurodegeneration, learning, and memory experiments. Reproductive and endocrine systems facilitate endocrine disruption and fertility assessments.
Understanding the detailed composition and function of each physiological unit in rats and mice underpins experimental design, data interpretation, and translational relevance across biomedical fields.