Circulatory System of Rabbit

The circulatory system of a rabbit, much like in other mammals, plays a vital role in sustaining its overall health and functionality.

This intricate network of blood vessels and organs ensures the efficient transport of oxygen, nutrients, hormones, and other essential substances throughout the rabbit's body.

By understanding the key components and functions of the rabbit's circulatory system, we can gain valuable insights into the remarkable ways in which nature has adapted these creatures to thrive in their environments.

• The circulatory system in animals is the primary transport system.
• In lower animals like Protozoa, Porifera, and cnidaria the transportation of oxygen and nutrients to different organs of the body and expulsion of carbon dioxide and nitrogenous wastes occur by means of diffusion through the body surface.
• However, in higher animals, the diffusion of substances does not occur more efficiently due to the complexity of the body organization.
• A special transport system is essential for the transportation of various substances to each and every corner of the body. Consequently, the circulatory system evolved in the animals.
• In Arthropoda and Mollusca other than Cephalopoda, an open type of circulatory system is present.
• In the open type of circulatory system, definite blood vessels are absent and the flow of blood is confined to sinuses or spaces present in the body.
• In Cephalopoda (Mollusca), Annelida, and Chordata, a closed type of circulatory system is developed.
• In the closed type of circulatory system, the blood flows always in definite blood vessels and capillaries. In this system, the various nutrients, gases, hormones and wastes are directly supplied to the tissues or mediated by tissue fluids.
• The circulation is maintained by a pumping center called the heart and blood vessels like arteries and veins.
• The circulatory system of higher animals is most efficient because of a closed circulation.
• The circulatory system of rabbits is closed type i.e., the blood flows through blood vessels only. The circulatory system constitutes;
  1. Heart
  2. Arterial System
  3. Venous System
  4. Blood

External Structure of Heart

1. The heart of a rabbit is conical, and muscular and lies in the thoracic cavity between the two lungs.
2. The broader end of the heart is towards the upper side while the conical end is directed downwards.
3. The heart is slightly towards the left side and enclosed by a double-walled pericardium.
4. The inner pericardial layer is called the visceral layer while the outer pericardial layer is called the parietal layer.
5. A narrow space is left between the two pericardial layers, called the pericardial cavity that is filled by pericardial fluid.
6. The pericardial fluid helps in the protection of the heart from external shocks and injuries.
7. The pericardium is applied to the diaphragm to maintain the position of the heart in the thoracic cavity from the lungs through pulmonary veins.
8. Two aortic arches originate from the ventricles.
9. A carotid-systemic aorta originates from the left ventricle while a pulmonary aorta arises from the right ventricle.

Internal Structure of Heart

1. The two auricles are internally separated by the inter-auricular septum.
2. Similarly, the two ventricles are internally separated by the interventricular septum.
3. The two auricles are communicated with the ventricles by openings called auriculo-ventricular apertures.
4. The two pre-cavals and one post-caval open into the right auricle.
5. The opening of the posterior vena cava is guarded by a membranous fold called Eustachian valve.
6. The right auriculo-ventricular aperture is guarded by three membranous flaps which constitute the tricuspid valve.
7. The tricuspid valve allows the flow of blood from the right auricle into the right ventricle but prevents the backward flow of blood from the ventricle into the auricle.
8. The inner surface of the walls of the ventricle is provided with a number of ridges called columnar carneae and a few conical elevations called the papillary muscles.
9. The free edges of the tricuspid valves are connected to the papillary muscles by white fibers called chordae tendinae.
10. From the left anterior angle of the right ventricle, a large blood vessel called the pulmonary aorta arises that carries blood to the lungs.
11. The base of the pulmonary aorta is guarded by three semilunar valves which prevent the backward flow of blood from the pulmonary aorta into the ventricle.
12. The left auriculo-ventricular aperture is guarded by two membranous flaps called the bicuspid valve or Mitral valve.
13. The free edges of these flaps are continued into chordae tendinae attached to the papillary muscles of the ventricle.
14. At the right angle of the left ventricle arises a large aortic trunk called the carotid-systemic aorta.
15. The base of the carotid-systemic aorta is guarded by three semilunar valves which allow the flow of blood from the left ventricle into the aorta but prevent the downward flow.

Working of the Heart

1. The heart of a rabbit exhibits rhythmic contractions and relaxations.
2. The contraction is called Systole while the relaxation is called Diastole.
3. The systole and diastole are together referred to as Heartbeat.
4. The heartbeat is initiated by a particular node of muscular tissue called sinu - the auricular node present on the inner wall of the right auricle.
5. The sinuauricular node acts as a pacemaker and generates certain power in the form of electric impulses.
6. The frequencies of the impulses are governed by nerve fibers.
7. Such impulses are conveyed to the muscles of the heart to exhibit rhythmic contractions and relaxations.
8. The impulses are also picked up by another node called the auriculo-ventricular node lying on the inter-auricular septum.
9. The impulses are conveyed to the Bundle of His and Purkinje fibers running through the interventricular septum to carry to the wall of ventricles.
10. The right auricle receives impure or de-oxygenated blood from different regions of the body by two superior venae cavae and one inferior vena cava.
11. The left auricle receives pure or oxygenated blood from the lungs by means of pulmonary veins.
12. When the auricles are filled by blood they contract to force the blood into the two ventricles through auriculo- ventricular apertures.
13. When the ventricles are filled with blood, they contract to force the blood into aortic trunks.
14. The backward flow of blood from the ventricles into the auricles is prevented by the closure of the bicuspid and tricuspid valves. The closure of the bicuspid and tricuspid valves produces the first heartbeat.
15. When the ventricles contract the semilunar valves situated at the base of the carotid - systemic trunk and pulmonary aorta are opened.
16. As a result, the deoxygenated blood from the right ventricle is forced into the pulmonary aorta while the pure blood from the left ventricle is forced into the Aortic arch.
17. Now the semilunar valves close to prevent the downward flow of blood from the aortic trunks into the ventricles.
18. The closure of semilunar valves produces the second heartbeat.
19. The pulmonary aorta carries deoxygenated blood to the lungs for aeration.
20. The aortic trunk supplies pure blood to different organs of the body.
21. In different parts of the body, the blood gets deoxygenated due to the release of CO₂.
22. The aerated blood from the lungs and deoxygenated blood from the tissues enter the heart to repeat the circulation once again.