Blood Circulatory System of Frog | Diagram

Blood Circulatory System of Frog

• The blood circulatory system of frog is closed.
• The whole blood circulatory system of frog consists of blood, heart, arterial system, venous system. 

Blood of Frog

• It is the chief circulatory fluid of the body.
• It contains blood plasma and blood corpuscles.
• It is a liquid connective tisse.

1. Blood Plasma

• • • It forms the two third part of the blood.
    • Almost 90% of the blood plasma is water.
    • It contains mineral salts, absorbed food (sugars, proteins), excretory wastes, hormones and other soluble substances.

2. Blood Corpuscles

• • • There are three types of blood corpuscles and they are erythrocytes, leukocytes and thrombocytes.
    • Erythrocytes or red blood corpuscles are oval, nucleated and flattened.
    • Erythrocytes bear the respiratory pigment haemoglobin which carry oxygen to the tissues.
    • Leukocytes or white blood corpuscles are colorless, nucleated and amoeboid cells.
    • Leukocytes are phagocytic, ingesting bacteria and other foreign particles that arrive in blood.
    • Thrombocytes or blood platelets play an important role in blood coagulation.

Heart of Frog

Fig : Heart of frog; A – Dorsal view; B – Ventral view.

External Features

• It lies mid-ventrally inside the anterior trunk region.
• It is protected by the pectoral girdle.
• It is reddish in color.
• It is somewhat conical or triangular in shape.
• Its broad base is directed anteriorly and the narrow apex is directed posteriorly.

a) Pericardium

• • • The heart is enclosed by a sac, called the pericardium.
    • It is a thin, transparent, and two-layered sac.
    • The outer wall of the pericardium is called the parietal pericardium and the inner wall is called the visceral pericardium.
    • Between the two pericardial layers, there is a narrow cavity that contains a fluid called the Pericardial fluid.
    • The pericardial fluid protects the heart from friction or mechanical shocks.

b) Chambers of Heart

• • • Frog’s heart is three chambered; two auricles and a ventricle.
    • The two auricles are externally demarcated by the inter-auricular groove.
    • The two auricles are clearly marked off from the ventricle by the auriculo-ventricular groove.
    • The heart of frog has two additional chambers and they are sinus venosus and truncus arteriosus.
    • Sinus venosus is formed by the union of three large caval veins; two anterior precavals and one posterior postcaval.
    • The truncus arteriosus bifurcates into two branches and each branch further divides into three arches and they are carotid, systematic and pulmocutaneous.

Internal Features

a) Auricles

• • • The two auricles are thin-walled.
    • They are completely separated from each other by the inter-auricular septum.
    • The right auricle is larger than the left.
    • The sinus venosus opens into right auricle through the sinu-auricular aperture.
    • Both auricles open into the ventricle through the auriculo-ventricular aperture which is guarded by the auriculo-ventricular valves.

b) Ventricle

• • • The ventricle has thick muscular and spongy wall.
    • The cavity of ventricle is greatly reduced.
    • The flaps of auriculo-ventricular valves are connected to the wall of ventricle by thread-like chordae tendineae.

c) Truncus Arteriosus

• • • The opening of ventricle into truncus arteriosus is guarded by three semilunar valves.
    • The valves prevent the backflow of blood.
    • The truncus arteriosus bifurcates into two branches and each branch further divides into three arches and they are carotid, systematic and pulmocutaneous.

Working of Heart

• Contraction of the heart is called systole and the relaxation of the heart is called diastole.
• Sinus venosus receives the deoxygenated blood from the venous system.
• Then the sinus venosus contracts. The deoxygenated blood from sinus venosus is forced to the right auricle.
• Meanwhile the oxygenated blood from the lungs is poured into the left auricle.
• Then the two auricles contract to force their blood into the ventricle.

Arterial System of Frog

• Arteries carry blood away from the heart.
• The arterial system of frog begins with the truncus arteriosus.
• The truncus arteriosus divides into right and left branches. Both branches later subdivides into three major aortic arches and they are common carotid arch, systemic arch and pulmocutaneous arch.
• The common carotid arch divides into two branches and they are external carotid and internal carotid.
• The common carotid arch supplies blood to the head.
• The systemic arch is the longest of the three arches.
• The two systemic arches gives off three arteries and they are oesophageal, occipito-vertebral and subclavian arteries.
• The both systemic arches later join with each other behind the heart to form the dorsal aorta.
• The dorsal aorta gives off five types arteries and they are coeliaco-mesenteric, gonadial, renal, posterior mesenteric and common iliac arteries.
• The pulmocutaneous arches divide into two arteries and they are pulmonary and cutaneos artery.
• The pulmonary artery supplies blood to the lungs and the cutaneous artery supplies blood to the skin.

Venous System of Frog

• The venous system collects blood and returns to the heart.
• The venous system has four parts and they are pulmonary veins, caval veins, renal portal veins, and hepatic portal veins.
• Oxygenated blood from the lungs are collected by the two pulmonary veins.
• There are three caval veins. Of them two are anterior vena cava or precavals and one is posterior vena cava or postcaval.
• All the caval veins open into the sinus venosus.
• Each precaval is formed by the union of three veins and they are external jugular, innominate and subclavian veins.
• The postcaval receives renal veins, genital veins and hepatic veins before opening into the sinus venosus.
• Frog has two well-developed portal systems. They are the renal portal system and the hepatic portal system.
• The veins which carry blood to a capillary system in the kidneys constitute the renal portal system.
• A large hepatic portal vein is formed by the union of several branches from stomach, intestine, pancreas and spleen.

 

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Reference:

• Rana (genus) – Wikipedia