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Circulatory System

Materials / Reagents Required :

            10 % Neutral Buffered Formalin (NBF), Normal saline (10 litre), 70 % Ethanol (1 litre), different sizes of scissors, forceps, scalpel, spatula, bone cutter, cardboard paper, etc.

Safety Precautions :

            Protective equipments including laboratory coats, gloves, apron, etc., should be worn during euthanasia, necropsy as well as during the preparation of the solutions.

Procedure :

  • The heart is a four-chambered muscular pump that lies within the pericardium in the thoracic cavity. The arterial supply to the heart is met by the left and right coronary arteries, which arise from the aorta.
  • Observe that the rats have small hearts (approximately 0.3 % of body weight). Heart is located in the space between the left and right lungs. Right and left atria are seen as dark reddish flaps on top of the heart.
  • Heart has the shape of a pyramidal triangle with its greater axis oriented obliquely to the left. The septum divides it into left and right halves with no communication  between them. An atrium and a ventricle form each half of the heart.
  • The blood from the atrium passes into the ipsilateral ventricle and then into the circulation. The vessels that enter the right atrium are the vena cavae that return deoxygenated blood to the heart.
  • Pulmonary veins from each lung enter the left atrium. Pulmonary artery exits the right ventricle and passes under the aorta. Observe the pericardium that appears as a tough fibrous sack surrounding the heart for protection.
  • Aorta exits the top of the heart and forms an arch that bends to the left. It empties the left ventricle and supplies oxygenated blood to the entire body. The first artery to branch off from the aorta is the brachiocephalic artery and it supplies blood to the head and right arm.
  • This artery branches to form the right subclavian artery that supplies the right arm and the right carotid artery that supplies the head. The second artery to branch off is the left common carotid artery which also supplies the head.
  • The third artery to branch off is the left subclavian artery which supplies the left arm. The fourth artery to branch off is the common iliac artery. The common iliac artery branches to form the internal iliac artery (supplying organs in the pelvic area) and the external iliac artery (passing to the leg).
  • External iliac artery gives a branch at the medial surface of the thigh called as the femoral artery. Subclavian Vein drains the arm and connects with the lateral thoracic vein, external iliac vein and internal iliac vein to form the anterior vena cava.
  • Anterior Vena Cava - enters the right atrium on the dorsal side of the heart. The external iliac vein is found parallel to the External Iliac Artery. The internal iliac vein is parallel to the internal iliac artery.
  • Posterior vena cava is formed by the right and left common iliac veins and it drains into the right atrium. The hepatic portal vein carries blood from the digestive organs to the liver. The vena cava carries blood from the body to the right atrium.
  • Pulmonary vein enters the left atrium with blood from the lungs. The internal and external jugular veins are found in the neck region and carry blood from the head region back to the heart.


Collection of stomach, intestine, liver and pancreas

  • After induction of anaesthesia/euthanasia, the fur of the animal shall be moistened with alcohol to prevent the fur from getting adhered into the tissue samples.
  • Normal saline shall be kept ready during the necropsy to keep the lungs moist. The thoracic and abdominal cavities shall be opened with a median incision starting from the just above the penis in male rat and just above the urethral orifice in the female rat up to the neck region.
  • In the centre of the thorax, the heart is located within the pericardial sac. Examine the major arteries / veins surrounding the rat heart.


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