Circulatory System- Earthworm, Cockroach, and Frog

The circulatory system of a frog is comparable to humans as it includes a heart, a few blood vessels and a lymphatic system; it’s a closed circulatory system and well-developed. 

The circulatory system in earthworm species is of closed type because there are blood vessels in an earthworm facilitating the blood flow. Repetitive contractions force the blood in one direction. One cannot find haemoglobin in the blood cells of an earthworm. The pigments are in a dissolved state in the blood plasma.

Cockroaches have an open blood vascular system, unlike the circulatory system in earthworms and frogs. It has an elongated tube that serves the function of the heart. It regulates the blood, which we know as haemolymph containing haemocytes and a colourless plasma.

Let us dig deeper to know more about the circulatory system in earthworms, cockroaches and frogs.

The circulatory system in earthworm

The circulatory system in earthworms is a closed vascular system. An earthworm possesses a well-developed circulatory system with transverse and longitudinal blood vessels. The circulatory system in earthworms involves continuous blood flow in an intricate arrangement of blood vessels.

The blood circulates exclusively via the following blood vessels:

• Aortic arches
• Dorsal blood vessels
• Ventral blood vessels

Following are the major longitudinal vessels in the circulatory system in earthworm:

•  Lateral esophageal vessels – these are paired vessels
• Dorsal blood vessel– Carry blood to the front portion of the earthworm
• Ventral blood vessel– Carry blood to the back of the earthworm’s body
•  Supraoesophageal- It is the smallest blood vessel in the circulatory system of an earthworm 

The five pairs of aortic arches perform the cardiac function by pumping blood into ventral and dorsal blood vessels. The blood glands on the 4th, 5th, and 6th segments produce haemoglobin and blood cells. Haemoglobin is not part of blood cells as it is present in blood plasma.

The dorsal blood vessel performs the heart’s function in earthworms. It distributes blood from the first to the 13th segment and collects blood from the 14th segment onwards. 

Following are the details of blood circulation in the circulatory system in earthworms:

•  Ventral vessels– the location of these vessels is below the alimentary canal. These blood vessels help the blood flow to the posterior from the anterior direction. The segmental organs receive blood from the paired vessels emerging from the ventral vessels
• Lateral oesophageal vessels – these begin from the segment 1st to 13th.These vessels collect blood from seminal vesicles in the 11th and 12th segment
•  Lateral oesophageal hearts- A pair each from the 12th and 13th segments send blood to the ventral vessel from 
• Lateral Hearts– One pair each from the 7th and 9th pair sends blood to ventral vessels from the dorsal vessel
• Anterior loops – these loops send blood to the supraesophageal vessel from the lateral oesophageal vessel. The location of anterior loops is a pair each in the 10th and 11th segments

The circulatory system in earthworm includes the heart, blood vessels and capillaries that carry blood from the glands on the 4th, 5th and 6th segments.

The circulatory system in cockroach

In contrast to the open circulatory system in earthworm, a cockroach shows an open blood vascular system. Poor development of blood vessels is an attribute of the circulatory system in cockroaches. The cockroach has hemolymph as its blood. It surrounds the visceral organs in the open space, known as hemocoel. Let us learn about different parts of the circulatory system in a cockroach.

Heart

The heart is a vital organ of the circulatory system in a cockroach. It is located right beneath the terga and in the mid-dorsal line of the thorax. The cockroach’s heart resembles a long tube and consists of thirteen different chambers. There is a deep constriction between the two chambers. A valve allows blood flow only in one direction.

Sinuses

Haemocoel is a large cavity with separate horizontal partitions of a membrane that divide the cavity into three flat sinuses as follows:

• Dorsal pericardial sinus– This is the heart of cockroach
• The dorsal diaphragm- It separates pericardial and perivisceral sinuses
•  Perivisceral sinus– This sinus lies in the middle and contains gut
• The ventral diaphragm- It separates the perivisceral and perineural sinuses
• Perineural sinus– It consists of the nerve cord

Alary muscles support the dorsal diaphragm and are on the floor of the pericardial sinus.

Circulation of blood 

Haemolymph pushes forward because of the pulsating heart of the cockroach. The tubular structure of the heart receives respiratory movements of the abdomen and force of contraction from the alary muscles. The following are steps involved in the circulation of haemolymph in the cockroach:

1. In the systole phase, haemolymph enters the heart to cause a contraction. 
2. The diastole phase makes the heart return to its normal position. 
3. The cycle continues at the rate of fifty pulses a minute. 
4. The closing of the Ostia inhibits haemolymph from entering into the pericardial tissue. 
5. The haemolymph pours through the anterior aorta into the head sinus. 
6. A portion of haemolymph also enters segmental vessels. 
7. Haemolymph flows back into the abdomen and thorax from the head sinus
8. In the next stage, haemolymph flows through pores of the dorsal diaphragm into the perivisceral sinus.
9. In the final stage, haemolymph enters the pericardial sinus and fills the heart via Ostia during the diastole phase.

The circulatory system in the frog

Similar to the circulatory system in the earthworm, the blood vascular system of the frog is a closed system. It has a lymphatic system similar to humans. The blood vascular system of frogs consists of the heart, blood vessels and lymph nodes.

The heart is located in the upper part and has three separate chambers with muscle tissues. The pericardium covers the heart. The three chambers of the heart consist of two atria and a single ventricle. The arterial system carries the blood to all organs and parts of the frog’s body. The blood is red and opaque consisting of haemoglobin, blood cells, and plasma. The venous system is responsible for carrying the blood back to the heart.

Conclusion

The circulatory system in earthworms and frogs are  closed circulation. The circulation system in a cockroach is an open circulation system. These are the primary differences between the two circulatory systems. The closed circulatory system includes blood vessels to carry blood to various organs and systems. The circulatory system in earthworms is complex because of the intricate arrangement of blood vessels across the segments. 

The circulatory system in cockroaches is of open type. The heart of a cockroach is an elongated tube that runs across its length. Since there are no blood vessels, the cockroach has ill-defined spaces and sinuses. Because of the three chambers and pericardium, a frog’s heart is very similar to the human heart. The blood vascular system of a frog is also identical to humans in several aspects.