Description of all kind of blood vessel present in earthworm?
Description of all kind of blood vessel present in earthworm?
Blood Vessels:
The blood vessels are of two types collecting blood vessels and distributing blood vessels which are closed tubes with definite walls and they break up into capillaries to ramify in the different parts of the body. The arrangement of blood vessels in the anterior thirteen segments is somewhat different from that behind the thirteen segment, i.e., in the region of intestine.
Therefore, for convenience the blood vessels can be described under the following two heads:
A. Blood vessels and their arrangement in the segments behind 13th, i.e. intestinal region.
B. Blood vessels and their arrangement in the anterior thirteen segments.
A. Blood Vessels and their Arrangement in the Segments behind Intestinal Region:
The blood vessels of this region include:
1. Median longitudinal blood vessels;
2. The intestinal blood plexus;
3. The commissural vessel;
4. The integumentary vessel; and
5. The nephridial vessels.
1. Median Longitudinal Blood Vessels:
(i) Dorsal Vessel:
It runs mid-dorsally above the alimentary canal from the posterior to the anterior end of the body. It is the thickest vessel with contractile muscular walls visible from outside as a dark line through the thin and semi transparent body wall.
The direction of flow of blood in this vessel remains from behind to forward (from posterior to anterior). It is contractile and pulsates rhythmically to force the blood from posterior to anterior side. In each segment it has a pair of valves internally which check the backward flow of blood. It is the main collecting vessel behind the 14th segment, but in front it distributes the blood.
From the posterior segment up to the 14th segment it receives two pairs of dorsointestinal vessels from the intestine in each segment and a pair of commissural vessels from the sub-neural vessel.
The commissural vessels form a loop behind each septum and they receive blood from the body wall, nephridia and prostrate glands. The commissural vessels also give out blood in each segment through a septointestinal branch to the intestine.
(ii) Ventral Vessel:
It is also a long vessel and runs ventrally below the alimentary canal and above the ventral nerve cord from second segment up to the last segment of the body.
It is thin- walled without muscles and valves. The direction of flow of blood in this vessel remains from anterior to the posterior side or from in front to backwards. It is a distributing vessel. It gives out a pair of ventrotegumentary vessels, one on each side in front of the septum in all segments.
The ventrotegumentary vessels run upwards along the body wall and supply blood to the body wall, integumentary nephridia, septal nephridia, gonads, seminal vesicles and spermathecae.
The ventral vessel also gives out a ventrointestinal vessel in each segment behind the 13th segment, these take blood to the lower part of the intestine. The branches in intestine form blood plexuses consisting of two networks in the intestinal wall.
(iii) Sub-neural Vessel:
It is also a long but thin vessel extending from anterior 14th segment up to the last segment situated mid-ventrally below the ventral nerve cord. It is without muscular walls and internal valves. The direction of flow of blood in this vessel remains from anterior to posterior side and it is mainly a collecting vessel.
It receives a pair of slender branches in each segment which bring blood from the ventral body wall and the nerve cord. It gives a pair of commissural vessels in each segment which join the dorsal vessel, as already mentioned while describing the dorsal vessel. Thus, it collects blood from the ventral body wall and supplies some blood to the intestine.
2. Intestinal Blood Plexus:
The intestine of Pheretima is richly supplied with blood capillaries which form a close network. The intestinal blood plexus consists of a close network of capillaries in the wall of intestine.
In fact, there are two capillary networks in the intestine:
(i) The external and
(ii) The internal.
The capillary network which is present at the outer surface of intestine is known as external plexus which receives blood from the ventral vessel through ventrointestinal and passes it on to the internal plexus.
The capillary network which is present between the circular muscle layer of intestine and its internal epithelial lining is known as internal plexus which serves to absorb the nutrients from the gut and is connected with dorsal blood vessel through the dorsointestinals.
3. Commissural Vessels:
These vessels connect the dorsal and sub-neural vessels. These vessels receive blood from nephridia, body wall and reproductive organs through capillaries and then they send it to dorsal blood vessel.
4. Integumentary Vessels:
These vessels coming from ventral vessels supply the blood to integument for aeration and the aerated blood is collected by numerous capillaries of commissural vessel in each segment. Thus, there is a close parallelism between venous and arterial capillaries throughout the body wall.
5. Nephridial Vessels:
These vessels originate from the ventrotegumentary vessels of ventral vessel and supply the blood to the nephridia.
B. Blood Vessels and their Arrangement in the Anterior 13 Segments:
The blood vascular system in the first thirteen segments is modified considerably and differs markedly from that of the intestinal region.
It consists of the following:
1. Median longitudinal vessels;
2. Hearts and anterior loops;
3. Blood vessels of the gut.
The function of collecting blood from the anterior region of the gut is taken over by a new vessel supra-oesophageal, while the blood from the peripheral structures is collected by the right and left lateral oesophageal.
1. Median Longitudinal Blood Vessels:
(i) Dorsal vessel:
This blood vessel becomes the distributing vessel in these segments instead of collecting vessel. Structurally, it retains its original identity as it was in the posterior segments. But is has neither dorsointestinals nor commissural vessels opening into it.
It sends out all the collected blood from the posterior region of the body into hearts and the anterior region of the gut where it divides into three branches distributed over the pharyngeal bulb and the roof of the buccal chamber. However, it supplies to stomach, gizzard, oesophagus, pharynx and other related parts.
(ii) Ventral vessel:
This blood vessel remains distributing in these segments also but extends only up to the second segment. The ventrointestinals are absent, hence, it does not supply to the alimentary canal in this region. However, the ventrotegumentary vessels, a pair in each segment, supply blood to the integument, nephridia, septa and reproductive organs.
(iii) Supra-oesophageal vessel:
It is the shortest longitudinal vessel extending from 9th to 13th segment situated above the stomach. It receives blood from the lateral oesophageals by two pairs of anterior loops that encircle the stomach in the 10th and 11th segments. It sends its collected blood by the latero-oesophageal hearts in segments 12th and 13th to the ventral vessel.
(iv) Lateral oesophageals:
In fact, the sub-neural vessel bifurcates in the 14th segment to form two lateral oesophageals. These vessels are considerably thick and situated along the ventrolateral margins of alimentary canal in the anterior thirteen segments. These vessels are closely attached to the wall of the stomach from 10th to 13th segments and communicate with the ring vessels.
But in the region of gizzard and further forwards, they remain free from the wall of the alimentary canal even though they receive branches from it in each segment.
These vessels receive a pair of branches in each segment bringing blood from the body wall and the septum. They also collect blood from the reproductive organs and nephridia, thus, functioning like the sub-neural and commissural vessels of the posterior region, i.e., these are collecting vessels.
Blood Vessels:
The blood vessels are of two types collecting blood vessels and distributing blood vessels which are closed tubes with definite walls and they break up into capillaries to ramify in the different parts of the body. The arrangement of blood vessels in the anterior thirteen segments is somewhat different from that behind the thirteen segment, i.e., in the region of intestine.
Therefore, for convenience the blood vessels can be described under the following two heads:
A. Blood vessels and their arrangement in the segments behind 13th, i.e. intestinal region.
B. Blood vessels and their arrangement in the anterior thirteen segments.
A. Blood Vessels and their Arrangement in the Segments behind Intestinal Region:
The blood vessels of this region include:
1. Median longitudinal blood vessels;
2. The intestinal blood plexus;
3. The commissural vessel;
4. The integumentary vessel; and
5. The nephridial vessels.
1. Median Longitudinal Blood Vessels:
(i) Dorsal Vessel:
It runs mid-dorsally above the alimentary canal from the posterior to the anterior end of the body. It is the thickest vessel with contractile muscular walls visible from outside as a dark line through the thin and semi transparent body wall.
The direction of flow of blood in this vessel remains from behind to forward (from posterior to anterior). It is contractile and pulsates rhythmically to force the blood from posterior to anterior side. In each segment it has a pair of valves internally which check the backward flow of blood. It is the main collecting vessel behind the 14th segment, but in front it distributes the blood.
From the posterior segment up to the 14th segment it receives two pairs of dorsointestinal vessels from the intestine in each segment and a pair of commissural vessels from the sub-neural vessel.
The commissural vessels form a loop behind each septum and they receive blood from the body wall, nephridia and prostrate glands. The commissural vessels also give out blood in each segment through a septointestinal branch to the intestine.
(ii) Ventral Vessel:
It is also a long vessel and runs ventrally below the alimentary canal and above the ventral nerve cord from second segment up to the last segment of the body.
It is thin- walled without muscles and valves. The direction of flow of blood in this vessel remains from anterior to the posterior side or from in front to backwards. It is a distributing vessel. It gives out a pair of ventrotegumentary vessels, one on each side in front of the septum in all segments.
The ventrotegumentary vessels run upwards along the body wall and supply blood to the body wall, integumentary nephridia, septal nephridia, gonads, seminal vesicles and spermathecae.
The ventral vessel also gives out a ventrointestinal vessel in each segment behind the 13th segment, these take blood to the lower part of the intestine. The branches in intestine form blood plexuses consisting of two networks in the intestinal wall.
(iii) Sub-neural Vessel:
It is also a long but thin vessel extending from anterior 14th segment up to the last segment situated mid-ventrally below the ventral nerve cord. It is without muscular walls and internal valves. The direction of flow of blood in this vessel remains from anterior to posterior side and it is mainly a collecting vessel.
It receives a pair of slender branches in each segment which bring blood from the ventral body wall and the nerve cord. It gives a pair of commissural vessels in each segment which join the dorsal vessel, as already mentioned while describing the dorsal vessel. Thus, it collects blood from the ventral body wall and supplies some blood to the intestine.
2. Intestinal Blood Plexus:
The intestine of Pheretima is richly supplied with blood capillaries which form a close network. The intestinal blood plexus consists of a close network of capillaries in the wall of intestine.
In fact, there are two capillary networks in the intestine:
(i) The external and
(ii) The internal.
The capillary network which is present at the outer surface of intestine is known as external plexus which receives blood from the ventral vessel through ventrointestinal and passes it on to the internal plexus.
The capillary network which is present between the circular muscle layer of intestine and its internal epithelial lining is known as internal plexus which serves to absorb the nutrients from the gut and is connected with dorsal blood vessel through the dorsointestinals.
3. Commissural Vessels:
These vessels connect the dorsal and sub-neural vessels. These vessels receive blood from nephridia, body wall and reproductive organs through capillaries and then they send it to dorsal blood vessel.
4. Integumentary Vessels:
These vessels coming from ventral vessels supply the blood to integument for aeration and the aerated blood is collected by numerous capillaries of commissural vessel in each segment. Thus, there is a close parallelism between venous and arterial capillaries throughout the body wall.
5. Nephridial Vessels:
These vessels originate from the ventrotegumentary vessels of ventral vessel and supply the blood to the nephridia.
B. Blood Vessels and their Arrangement in the Anterior 13 Segments:
The blood vascular system in the first thirteen segments is modified considerably and differs markedly from that of the intestinal region.
It consists of the following:
1. Median longitudinal vessels;
2. Hearts and anterior loops;
3. Blood vessels of the gut.
The function of collecting blood from the anterior region of the gut is taken over by a new vessel supra-oesophageal, while the blood from the peripheral structures is collected by the right and left lateral oesophageal.
1. Median Longitudinal Blood Vessels:
(i) Dorsal vessel:
This blood vessel becomes the distributing vessel in these segments instead of collecting vessel. Structurally, it retains its original identity as it was in the posterior segments. But is has neither dorsointestinals nor commissural vessels opening into it.
It sends out all the collected blood from the posterior region of the body into hearts and the anterior region of the gut where it divides into three branches distributed over the pharyngeal bulb and the roof of the buccal chamber. However, it supplies to stomach, gizzard, oesophagus, pharynx and other related parts.
(ii) Ventral vessel:
This blood vessel remains distributing in these segments also but extends only up to the second segment. The ventrointestinals are absent, hence, it does not supply to the alimentary canal in this region. However, the ventrotegumentary vessels, a pair in each segment, supply blood to the integument, nephridia, septa and reproductive organs.
(iii) Supra-oesophageal vessel:
It is the shortest longitudinal vessel extending from 9th to 13th segment situated above the stomach. It receives blood from the lateral oesophageals by two pairs of anterior loops that encircle the stomach in the 10th and 11th segments. It sends its collected blood by the latero-oesophageal hearts in segments 12th and 13th to the ventral vessel.
(iv) Lateral oesophageals:
In fact, the sub-neural vessel bifurcates in the 14th segment to form two lateral oesophageals. These vessels are considerably thick and situated along the ventrolateral margins of alimentary canal in the anterior thirteen segments. These vessels are closely attached to the wall of the stomach from 10th to 13th segments and communicate with the ring vessels.
But in the region of gizzard and further forwards, they remain free from the wall of the alimentary canal even though they receive branches from it in each segment.
These vessels receive a pair of branches in each segment bringing blood from the body wall and the septum. They also collect blood from the reproductive organs and nephridia, thus, functioning like the sub-neural and commissural vessels of the posterior region, i.e., these are collecting vessels.
