Blood-Vascular of Pila. An Apple Snail.

Blood Vascular System of Pila: An Apple Snail.

Blood Vascular System of An Apple Snail has attained a great complicity due to its double mode of respiration. It is open type involving both gills as well as lung. It consists of following parts.

(i) Pericardium.

It is a thin-walled, roughly ovoid chamber lying dorsally on the left side of the body whorl behind the mantle cavity.It extends anteriorly up to the stomach and digestive gland. The pericardium corresponds to the true coelom,I,e coelom of Annelida and the vertebrates. It encloses the two chambers of the heart, the main aortic arches and the aortic ampulla. It is the fairly deep cavity which communicates with that of the posterior renal chamber through a reno-pericardial aperture. It also communicates the kidney, and in the embryo, reproductive cells from the develop from its wall.

(ii) Heart.

The heart of An Apple Snail lying enclosed within the pericardium. It consists of two chambers and single auricle and one ventricle.

(a) Auricle.

The auricle is a thin-walled, highly contractile, roughly triangular shape, situated in the dorsal part of the pericardium.The auricle lies in the dorsal part of the pericardium, while the ventricle is situated just below it on the same vertical axis. The dorsal apex of the auricle receive blood from the three main veins, I,e the efferent ctenidia vein from the gill, efferent renal vein from the posterior renal chamber, and the pulmonary vein from the pulmonary sac.Ventrally, the auricle communicates with the ventricle by an aperture auriculo-ventricular opening having two semi-lunar valves, so arrange as to allow the blood from the auricle to flow into the ventricle but not in the reverse direction.

(b) Ventricle.

Lt is an ovoid sac lying below the auricle. It has thick spongy wall formed of a large number of muscular strands forming a meshwork which greatly reduces the cavity of the ventricle. The aorta trunk arises from the-the lower end of the ventricle and divides immediately into two branches, the cephalic aorta and visceral aorta.The opening between the ventricle and the aortic trunk is guarded by two-semi lunar valves which prevent the flow of blood from back into the ventricle.

(iii) Arteries.

From the ventricles arises an aorta or aortic-trunk which divided into two chambers, a cephalic aorta and-and visceral aorta.Each aorta breaking up into numerous arteries.

(a) Cephalic aorta.

The base of the cephalic aorta bears a bulb-like, thick-walled and highly contractile structure, called the aortic ampulla. These are characteristic of the members of the family Picidae. Rhythmic contraction of the ampulla helps in the circulation of blood. The opening of the ampulla into the aorta is without a valve.The cephalic aorta sends arteries to the head and buccal mass, the visceral aorta forms arteries going to the visceral mass.

Immediately beyond the ampulla, the cephalic aorta gives out three arteries; first supplies to the fine cutaneous artery of the skin, second supplying to the oesophagus and the oesophagus artery and third supplies to the left side of the mantle, the left pallial artery.On its inner side, the cephalic aorta gives out and supplying to the pericardium, renal chamber and to a portion of the genital organs, the pericardial artery.The main trunk of cephalic aorta then runs ahead and crosses over the oesophagus so as to reach to its right side. It no gives off numerous small branches to the oesophageal area and a large branch. On the right, it gives off a large branch which further divides into three arteries.A right pallial artery to the right part of the mantle, (ii) a right siphonal artery to the right, nuchal lobe, (iii) a penal artery to the copulatory organ.

The main trunk further sends

-(i) a radula sac artery to the radula sac,

(ii) optic arteries to the eyes and eyes-stalks,

(iii) tentacular arteries to the tentacles, and finally

(iv) pedal arteries to the foot of which they form an irregular network.

(b) Visceral aorta.

Visceral aorta runs posteriorly into the visceral mass and supplies the visceral organ through a series of numerous branches.These branches are .

(i) A small pericardial artery to the pericardium, skin and digestive gland,

(ii) a large gastric artery to stomach,

(iii) several intestinal arteries to the intestine,

(iv) renal arteries to the roof of the posterior renal chamber,Blood and the course of circulation of

(v) a large artery to the digestive gland and gonad,

(vi) a second set of several intestinal arteries to the intestine,

(vii) several renal arteries to the roof of the anterior renal chamber, and

(viii) several arteries to the terminal part of the genital duct and then finally the visceral aorta terminates in the rectal wall.

The blood after being distributed to the various parts of the body through the arteries and their branches passes to the small lacunae, which in turn unite to form large sinuses.There are four chief sinuses in the body. These are (i) Peri-visceral sinus. (ii) Peri-intestinal sinus.(iii) Branch-renal sinus and (iv) pulmonary sinus.

(a) Peri-visceral sinus.

It lies on the floor of the mantle cavity and above the foot surrounding the anterior part of the alimentary canal. It collects blood supplied by the cephalic aorta, except pericardial artery, and some branches of the visceral aorta.

(b) Peri-intestinal sinus.

It lies on the columellar axis next to the intestinal and the terminal part of the genital duct and runs along the coils of the intestine up to the junction of the anterior and posterior renal chambers. It collects blood from visceral mainly distributed by visceral aorta.

(iii) Branch-renal sinus.

It lies along the right side of the anterior renal chamber. It collects blood from renal chambers.

(d) Pulmonary sinus.

It lies in the walls of the pulmonary sac. It collects blood from the pulmonary sac.

(e) Veins.

The veins carry venous blood from different parts of the body to the auricle directly or through the gill, mantle and kidney.The chief veins are as follows.

(i) Afferent ctenidial vein,

(ii) Efferent ctenidial vein,

(iii) Afferent renal vein,

(iv) Efferent renal vein,

(v) pulmonary vein.

(a) Afferent ctenidial vein.

It lies above the rectum and receives branches from the rectum, terminal part of the genital duct, perivisceral sinus and branch-renal sinus. It sends blood through numerous branches, to the gill lamellae for purification.

(b) Efferent ctenidial vein.

It lies along the roof of the anterior renal chamber and carries blood from ctenidial leaflets, mantle and conveys to the auricle.

(c) Afferent renal vein.

It is situated on the roof of the posterior renal chamber and originates from the peri-intestinal sinus. It pours its blood into the posterior renal chamber.

(d) Efferent renal vein.

It carries blood from the walls of the pulmonary sac and opens into the auricle.

Blood .

The blood serves as to transport nutrients, oxygen and waste products from one part of the blood to the other.It contains some colourless stellate amoeboid cells, and a respiratory pigment called haemocyanin. Amoeboid cells are phagocytic in nature. It is a compound of copper and proteins, dissolve in the plasma and gives a faintly blue colour to the blood.But in few gastropods, such as Planorbis, haemoglobin is found in place of haemocyanin. Amoeboids which are phagocytic, remove waste substance and some of them carry on intercellular digestion.

The course of circulation.

All parts of the body are supplied with blood from the ventricle through the cephalic and visceral aortae. The cephalic aorta carries blood to the head and its associated structures, a part of the mantle, the buccal mass, the oesophagus, the copulatory organ and the columellar muscle. The visceral aorta supplies the whole of the visceral mass. The blood is collected from the various parts of the body into to main sinuses the perivisceral and peri-intestinal. From these sinuses, the blood passes either into the ctenidium, pulmonary sac or into the renal organ.During the aquatic respiration the blood from the perivisceral sinus goes to the ctenidium and is purified; an efferent ctenidial vein then takes this blood into the auricle. During aerial-respiration the blood from the perivisceral sinus goes to the lung and is purified, a pulmonary vein takes this blood into the auricle. The blood from the peri- intestinal sinus takes two courses, it either goes from this sinus to the anterior renal chamber and from there to the ctenidium and is purified, then through the efferent ctenidial vein it goes to the auricle.The blood from the peri-intestinal sinus goes to the anterior renal chamber, then to the posterior renal chamber (blood from the peri-intestinal sinus can also go directly to the posterior renal chamber without going to the anterior renal chamber); in any case of the blood from the posterior renal chamber goes through an efferent renal vein into the auricle. Thus, the auricle receives pure blood from the ctenidium or the lung and impure blood from the posterior renal chamber, this mixed blood enters the ventricle and is distributed to the arteries. The renal chambers, however, remove waste substances from the blood.

Reference.

Aggrawal Sarita. A Text Book of Biology,New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L.,Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

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