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CIRCULATORY (BLOOD VASCULAR) SYSTEM OF
FROG
Circulatory system of frog is closed type containing Heart, Blood vessels and Blood. HEART The heart of frog is dark red colored, hollow, conical or somewhat triangular muscular organ situated ventrally in anterior region of body cavity along mid ventral line at the level of forelimbs. It is
enclosed within the double layered Pericardium.
The narrow cavity found in between pericardial
layers is called Pericardial cavity, which is filled
with Pericardial fluid. The functions of pericardial
fluid are I)Keeps the heart always moist. II)Protects the heart from mechanical injuries. III)Reduces friction allowing free movement. EXTERNAL STRUCTURE OF FROG’S HEART Externally the heart of frog is triangular with
broader anterior end ie Auricle/Atrium and narrow
posterior end ie Ventricle.
Auricle seems to be single from outside but internally it is divided into two chambers. The auricles are clearly marked off from the ventricle
externally by a narrow transverse auriculo-
ventricular groove or Coronary sulcus. Ventricle is
the prominent conical part of heart. In addition , two additional chambers can be observed from outside ie 1.Sinus venosus: Thin-walled, triangular, dark colored chamber attached dorsally to the heart, formed by the fusion of two pre cavals and one post caval. 2.Truncus arteriosus: Tubular chamber arises from right ventral side of ventricle, runs obliquely towards right auricle and divides into two branches. INTERNAL STRUCTURE OF FROG’S HEART
ventricle in order to prevent the flow of blood into auricles again. 2.Ventricle: The ventricle is a single chamber, prominent conical structure of frog’s heart with thick, muscular and spongy wall. Inner wall of ventricle has irregular strands or ridges called
Columnae carneae with depression between them
called Fissure which prevent the mixing of two
types of together 3.Truncus arteriosus: It is a tubular chamber arises from right ventral side of ventricle. It’s opening
towards ventricle is guarded by three Semi-lunar
valves which prevent the backflow of blood from
truncus arteriosus to ventricle again. Internally Truncus arteriosus is divided into 2 parts;ie
I) Long, basal, thick-walled Conus arteriosus or
Pylangium
II) Short, distal, thin- walled Bulbous arteriosus or
Synangium
The junction of pylangium and synangium is
guarded by two pairs of semi-lunar valves. The
Spiral valve divides pylangium into right Cavum
aorticum and left Cavum pulmocutaneum
incompletely. Anteriorly truncus arteriosus is
divided into two branches called Aortic trunks.
Each aortic trunk is further divided into 3 branches
ie Carotid, Systemic and Pulmocutaneous arches.
The common opening of pulmocutaneous arches lies at cavum pulmocutaneum where as separate openings of carotid and systemic arches lie at synangium.
WORKING MECHANISM OF FROG’S HEART
The heart of frog is Myogenic ie heart beat is
conducted by heart muscles itself. Regarding working mechanism of frog’s heart ,there are 2 views ie 1.Old view: The impure blood from right auricle remains at right side and pure blood from left auricle remains at left side of ventricle. These two types of blood willnot mix with each other in single chamber ventricle due to presence of columnae carneae and viscous nature of blood. In some extend, mixed blood is found at the middle of ventricle. The impure blood from cavum pulmocutaneum is transported into lungs and skin through pulmocutaneous arches. After purification, the pure is distributed into different parts of the body from cavum aorticum through carotid and systemic arches. The spiral valve controls the flow of blood from ventricle to truncus arteriosus.
Carotid labyrinth allows the flow of oxygenated
blood only.
