Physiology of Finfish and Shellfish (2+1)

2.2.27. Morphology of the circulatory system

1. Heart

The heart is a single, muscular chamber making up 0.1 – 0.15% of total body weight. A thin pericardium composed of spongy and fibrous connective tissues, surrounds the bulk of the heart, which is composed of striated muscle arranged into a complex series of trabecular strands. Cardiac muscle fibres are composed of multinucleate, cross-striated cells connected by intercalated disks. Thick and thin filaments as well as two separate membrane systems have been found in cardiac muscle.

Satellite cells, reverse inclusion (R1) cells, and phagocytes are also present in the heart. Satellite cells may function in regeneration of cardioc cells. RI cells (Cyanocytes) both produce and store hemocyanin and have been observed with in the myocardium of lobster. RI cells reportedly possess some phagocytic capabilities; it is unclear whether the cardiac phagocytes are hemocytes or RI cells.

The heart is suspended within a pericardial cavity by three pairs of alary ligments. Although, the alary ligaments themselves contain little or no muscle, their attachment to the body wall contains elastic material, muscle and neural innervation.

2. Vessels

The crustaceans have an extensive set of vessels conducting hemolymph, away from the heart. Although the distribution of these vessels has been described, a statisfactory functional classification of the vessels is still lacking. Now at present only three categories of vessels are commonly identified. They are arteries, large vessels (thick walls), arterioles small vessels with thinner walls that open into sinuses or capillaries, small vessels with thin walls that are morphologically similar to arterioles, but appear to be involved in gas and nutrient exchange between hemolymph and tissue because they do not give rise to sinuses. However, the layers of all vessels walls include the following, progressing outward from the lumen.

They are,

1. Intima – an cellular layer
2. Endothelium – a cellular layer
3. a loss connective tissue layer
4. External laminar – thin a cellular layer

In these four layers “intima” is one of the most important layer. It is called as basal lamina or basement membrane.

• It’s not separated from the plasma by an endothelial layer.
• It is not divided into zones like dense and rara.

3. Sinuses

Several sinus gland hormones may be related crustacean hyperglycemic hormones (CHH). They are

• Molting – inhibiting hormone (MIH) 
• Vitellogenesis inhibiting hormore (VIH) 
• Peptide G, hormone

These are all related to each other structurally and to some degree, functionally. They are appear have be four CHH activities. They are 2 peptide G activities, one MIH activities, two VIH isoforms of these one of the CHH molecules, MIH and peptide G, appear to have identical sequences. VIH has also a high degree of structural similarity of these molecular.