The rat heart, a muscular organ circulating blood throughout the body, supports the rat’s physiology. Understanding its structure is key to comprehending how it functions to support the animal’s metabolic demands. Its anatomical study provides insights into its efficiency within the circulatory system.
Gross Anatomy of the Rat Heart
The rat heart is located within the thoracic cavity and is encased in a two-layered sac called the pericardium. It has a quadrangular pyramidal shape, with its apex pointing towards the anterior thoracic wall. Approximately 21 mm in length and 13 mm wide, it is comparable in size to a human thumbnail.
Internally, the rat heart is divided into four chambers: the right atrium, right ventricle, left atrium, and left ventricle. The right and left atria are dark, ear-shaped structures positioned on each side of the anterior portion of the heart. These receiving chambers collect blood before it moves into the more muscular ventricles. The ventricles, responsible for pumping blood out of the heart, are not easily distinguished externally.
Blood flow between these chambers and into the major vessels is regulated by a series of valves. The tricuspid valve separates the right atrium from the right ventricle, while the bicuspid (or mitral) valve lies between the left atrium and left ventricle. Exiting the ventricles, the pulmonary semilunar valve controls blood flow from the right ventricle into the pulmonary trunk, and the aortic semilunar valve regulates flow from the left ventricle into the aorta. These valves ensure unidirectional blood movement, preventing backflow within the heart.
Functional Overview of Rat Heart Circulation
The circulatory system of a rat is a closed system, meaning blood circulates continuously within a network of vessels. Deoxygenated blood from the body returns to the heart through three main veins: the right superior vena cava, left superior vena cava, and the inferior vena cava, all emptying into the right atrium. The vena cavae return blood from the body, with the superior vena cavae bringing blood from the head and neck.
From the right atrium, blood passes through the tricuspid valve into the right ventricle. The right ventricle then pumps this deoxygenated blood through the pulmonary semilunar valve into the pulmonary trunk, which subsequently divides into the right and left pulmonary arteries, carrying blood to the lungs for oxygenation. In the lungs, carbon dioxide is released and oxygen is absorbed by the blood.
Oxygenated blood returns from the lungs to the left atrium via the right and left pulmonary veins. From the left atrium, the blood moves through the bicuspid (mitral) valve into the large, muscular left ventricle. The left ventricle, having the thickest walls, then contracts, pushing the oxygenated blood through the aortic semilunar valve into the aorta, the body’s largest artery, which distributes blood to the rest of the body. This continuous pumping action, involving the contraction (systole) and relaxation (diastole) of the heart chambers, maintains blood flow throughout the rat’s circulatory system.
Similarities and Differences with the Human Heart
The rat heart and the human heart share structural and functional similarities. Both species possess a four-chambered heart, consisting of two atria and two ventricles, designed for efficient double circulation. The general pathway of blood flow, involving pulmonary circulation to the lungs and systemic circulation to the body, is conserved between rats and humans. Both hearts utilize a similar set of valves—tricuspid, mitral, pulmonary, and aortic—to ensure unidirectional blood flow and prevent backflow within the chambers.
Despite these similarities, differences exist in size and physiological parameters. A rat heart is smaller, approximately the size of a marble, whereas a human heart is roughly the size of a clenched fist. This difference contributes to a difference in heart rate; a rat’s heart beats around 300 to 480 times per minute, while a human’s resting heart rate averages 60 to 100 beats per minute. The walls of the human heart are thicker due to the greater pressure required to pump blood throughout a larger body.
Beyond these differences, variations exist, such as the absence of epicardial adipose tissue (fat around the heart) in rats, which is present in human hearts. While both species exhibit similar rates of ATP synthesis in cardiac tissue, the energy transferred per beat is nearly three times greater in humans, reflecting the differing demands of their respective body sizes. These distinctions highlight adaptations to their varying sizes and metabolic needs.
Significance in Biomedical Research
The rat heart serves as a widely used model in biomedical research. Its physiological, anatomical, and genetic similarities to humans make it a tool for understanding various cardiovascular conditions and testing new therapies. The rat’s short life cycle, ease of handling, and lower maintenance costs compared to larger animals also contribute to its widespread use in laboratory settings.
Researchers employ rat models to study human cardiovascular diseases, such as myocardial infarction (heart attack) and hypertension. Specific inbred rat strains, like the spontaneous hypertensive rats (SHR) or Dahl salt-sensitive rats (DSS), are useful for investigating the mechanisms of hypertension and heart failure progression. The ability to induce and study these pathologies in a controlled environment allows for an understanding of disease mechanisms.
Rat hearts are used for drug testing and physiological studies, including investigations into cardiac arrhythmias and the effects of ischemia-reperfusion injury. The larger myocardial mass and blood volume of rats, compared to mice, enable a higher number of biological and ex-vivo histological analyses, which can reduce the number of animals needed per study. The development of genetic manipulation techniques, such as CRISP/Cas-9, has enhanced the utility of rat models by allowing for the creation of genetically modified rats, similar to knockout mice, for targeted research.