Circulatory System of Rat

Anatomy of Earthworm,Cockroach & Frog of Class 11

Circulatory System

The heart of the rat consists of four chambers. There is a right ventricle, and a left ventricle, which are not easy to distinguish externally. Right atrium and left atrium are dark ear-shaped structures on each side of the anterior portion of the heart.

Three main blood vessel enter the right atrium which bring the deoxygenated blood back to the heart from all regions of the body. These blood vessels are the right superior vena cava, the left superior vena cava and the inferior vena cava.

The inferior vena cava is a large vein running from the diaphragm to the right atrium. The left superior vena cava run across the ‘dorsal surface of the thoracic cavity to enter the right atrium close to the point of entry of the inferior vena cava and the right superior vena cava.

The right and left superior venae cavae return deoxygenated blood to the heart from the right and left side of the head and neck. The thoracic cavity is drained by the azygous vein which empties into the left superior vena cava near its entry into the right atrium.

The deoxygenated blood in the right atrium is pumped to the right ventricle through an opening guarded by the tricuspid valve. The blood is pumped from the right ventricle through the pulmonary semilunar valve into the pulmonary trunk (usually colourless) which divides into right and left pulmonary arteries going to the lungs. The oxygenated blood returns from the lungs to the left atrium via the right and left pulmonary veins. From the left atrium the blood enters the large muscular left ventricle through the bicuspid valve.

Arterial System

Arterial System

Fig. Arterial System in Rat

The arterial system in rat shows the following main arteries and their branches :

Anterior Region

A. A pulmonary aorta arises from the right ventricle and divides into right left pulmonary arteries that supply blood to the lungs.

B. An aortic arch arises from the left ventricle and supplies blood to all the parts of the body. It divides into three main branches :

1. Innominate artery : It arises from the aorta on the right side and divides into two arteries.

(a) Right common carotid : It runs upwards on the side of trachea and divides into external and internal carotids that supply blood to the right side of head and face.

(b) Right subclavian : It further divides into following arteries :

(i) Right cervical supplies blood to the muscles of neck.

(ii) Right subscapular supplies blood to the scapular region.

(iii) Right brachial supplies blood to the arm.

(iv) Right internal mammary supplies blood to the muscles of the back

2. Left common carotid : It arises directly from aortic arch and runs upwards along the side of trachea. It divides into external and internal carotids that supply blood to the left side of head and face.

3. Left subclavian : It also arises from the aortic and divides in the same way as right subclavian branch of innominate.

Posterior Region

The aortic arch curves down as dorsal aorta and gives the following arteries :

1. Intercostal arteries : Several pairs of intercostal arteries arise from dorsal aorta in the thoracic region supplying blood to the chest wall.

2. Coeliac artery : gives off two branches :

(a) Hepatic artery supplying blood to the liver.

(b) Gastric artery supplying blood to the stomach.

3. Anterior mesenteric artery : supplies blood to various parts of intestine and forms a network of vessels.

4. Renal arteries : A pair of renal arteries supply blood to the kidneys. From each renal artery, an adrenal artery arise that supplies blood to the adrenal gland.

5. Gonadial arteries : A pair of arteries supplies blood to ovaries and uterus (in females); and to testis and epididymis (in males).

6. Ilio-lumbar arteries : A pair of these arteries supply blood to the wall of the abdominal cavity.

7. Postero-mesenteric artery : supplies blood to the rectum.

8. Common iliac artery : A pair of common iliac arteries arise from dorsal aorta at the level of hindlimbs. Each divides into an external iliac and an internal iliac that supply blood to the hind limbs. It also divides into vesicle arteries that supply blood to the urinary bladder and reproductive organs; and pudendal arteries that supply blood to the pelvis.

9. Caudal artery : The dorsal aorta continues into all tail region as caudal artery.

Venous System

Venous system in rat cosists of the following veins :

Fig. Venous System in Rat

Anterior Region

1. A pair of pulmonary veins collect oxygenated blood from lungs and open into left atrium.

2. A pair of precavals or anterior vena cava collect the deoxygenated blood from the anterior region of the body and open into the right atrium. Each precaval is formed by the union of following veins :

(a) Jugular vein : Is formed by the union of :

(i) External jugular collects blood from lower jaw.

(ii) Internal jugular collects blood from forelimbs.

(b) Subclavian vein : collects blood from forelimbs.

(c) Internal mammary vein : collects blood from the inner surface of ventral thoracic wall.

(d) Anterior intercostal vein : collects blood from intercostal space.

(e) Phrenic vein : collects blood from diaphragm.

(f) Azygous vein : present only to the left side, so it opens into left precaval. It collects blood from the region of vertebral column.

Posterior Region

1. A postcaval vein collects blood from the posterior region of the body and is formed by the union of following veins:

(a) Caudal vein : Collects blood from tail region and opens into postcaval where iliac veins join it.

(b) Iliac veins : Each iliac vein is formed by the union of :

(i) Femoral vein - collects blood from the outer side of leg.

(ii) Sciatic vein - collects blood from the inner side of leg.

(c) Posterior mesenteric vein: collects blood from various parts of large intestine.

(d) Ilio-lumbar veins : A pair of them collect blood from the lumbar region of the body.

(e) Gonadial veins : A pair of them collect blood from the gonads. Note that the right gonadial opens into postcaval, while left gonadial opens into renal vein of that side.

(f) Renal veins : pair of them collect blood from kidneys.

(g) Hepatic veins : pair of them collect blood from the liver.

2. A hepatic portal vein collects blood from various parts of alimentary canal and opens into liver (instead of heart). It is formed by the union of following veins:

(a) Gastric vein collects blood from stomach.

(b) Splenic vein collects blood from spleen.

(c) Anterior mesenteric vein collects blood from ileum

(d) Posterior mesenteric vein collects blood from large intestine.

Note : There is no renal portal system in rats.

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