Physiology of Finfish and Shellfish (2+1)

2.2.24. Heart Circulation

It is important to note that the circulatory system is at least partially closed. There is not only a richly – branched arterial, but a richly – branched venous system, the vessels of which have walls of their own. These two systems pass into one another in certain parts of the body. e.g. the integument muscle layers, through a system of capillary vessels. In other parts, however, the arterial branches conduct the blood into a lacunar system, when it has become venous; the blood collects out of this into sinuses (especially into a peripharyngeal cephalic sinus) and flows to the gills through veins with walls of their own. Two aorta rise from the ventricle

1. The aorta cephalica, which run downwards to the head and
2. The aorta abdominalis, which runs up towards the apex of the visceral dome.

The former is much stronger than the latter. The aorta cephalica first gives off branches to the mantle and to the anterior wall of the body and then provides the stomach, the pancreas, the digestive gland, the oesophagus, the salivary glands, and the funnel with arteries. After accompanying the oesophagus, it divides int eh head into two banches, which run to the bases of the arms, and there break up into as many arteriae branchiales as there are arms. The aorta abdominalis supplies with arteries. The hind-gut, the ink-bag, the genital organs, the dorsal part of the body wall and the fins, when these latter are present. Only in the Oegopsidae are the aorta, limited to the two, above described, springing from the heart.

In the octopoda and the myopsidoe, there are other arteries rising out of the ventricle and running to the same part of the body as the aorta, abdominalis in the Oegopsidoe; among these are the arteria genitalis, which runs to the genital glands and in the Myopsidoe, a fine vessel called the arteria anterior. At certain places, the arteries may swell out to form small muscular and contractile widening, called Peripheral arterial hearts. in the venous system of Sepia. The venous blood in each arm collects (Partly through capillaries and partly through lacunae) into a vein running down the inner side of the arm.

All the branchial veins convey their blood to a circular cephalica, which runs up along the posterior side of the oesophagus and the liver into the visceral dome, collecting on the way venous blood from the liver, the funnel etc. A little below the stomach it farks, forming the two venae cavae, which open into the two contractile venous hearts at the bases of the gills. From the upper part of the visceral dome, the blood collects into several abdominal veins, the most important of which are an unpaired vena abdominals, opening into the vena cephalica exactly at the point where it divides into the venae cavae, and two lateral abdominal veins, which open into the latter near their point of entrance into the branchial hearts. In the region of the heart, all these veins carry acinose or lobale appendages (venous appendages), which are hollow and communicate at many points with the veins, so that they are richly supplied with blood.

The cavity into which these appendages project is that of the renal sacs and the epithdium which covers them belongs to the epithelial wall of the kidneys. The blood flowing back from the body has abundant opportunity of giving off its excretory constituents to the kidneys; these are the pericardial glands, which will be further described later. The two branchial hearts, by their contraction, drive the venous blood into the afferent branchial vessel.

The blood, which has become arterial in the gills flows through the efferent branchial vessel into the auricles of the heart and then into the ventricle. In the cephalopoda, the whole of the blood, in returning from the body, flows through the gills, so that the heart contains only arterial blood. By far, the greater part of the blood, before entering the gills, comes into contact with the kidneys in the venous appendages. In the octopoda, the venous system shows some modifications. In octopus, two veins connected with one another by anastomoses, run along the outer side of each arm and collect the venous blood. At the bases of the arm, these veins become connected in pairs and unite later in such a way as to form on each side a lateral cephalic vein.

These two veins unite to form the large vena cephalica which runs up in front of the funnel and behind the oesophages. The branchial veins do not here, as in Sepia, convey their blood first to the venous cephalic circular sinus, but are directly connected with the cephalic vein. A cephalic sinus nevertheless exist in octopus; it is not, however, connected with the vena cephalica, but with a large sinus which fills the whole visceral dome, and it is in fact the primary body cavity, in which the viscera lie bathed by the venous blood. The later flows out of this large venous sinus through two wide veins, the so called peritoneal tubes, into the upper part of the vena cephalica, near the point where this divides into the two venae cavae. Nautilus is chiefly distinguished by the absence of the branchial heart. Further, each of the two venae cavae divides into two branches, which run as afferent vessels to the gills.