Anatomy of finfish and shellfish

Unit 5 - Circulatory System

5.1.2. Heart
The heart is modified blood vessel exhibiting the three layers characteristic of arteries an inner lining (endocardium) of endothelium and elastic tissue on muscular layer (myocardium) that is very thick, especially in the ventricular region and an outer fibrous tunic (epicardium) on the surface of which is the visceral pericardium. The heart pulsates as a result of the response of the muscle cells to the electrolytes (Blood electrolytes) that infuse it. The rhythmicity of the pulsations is regulated by flexly by the autonomic nervous system except in hag fishes, in which no nerve fibers supply the muscle. The heart occupies the pericardial cavity (a sub division of the coelom anterior to the septum transversem). The heart of all vertebrates is built in accordance with a basic architectural pattern. It is demonstrated in its simplest form in hag fishes where its exhibits a series of four chambers sinus venous, atrium, ventricle and conus arterious through which flood flow in that sequences.



Chondrychthyes has contractile, muscular and valved base the conus arteriosus to the ventral aorta where it leaves the ventricle. In higher bony fishes the plan is like that of the shark and its relatives, but the first section of the ventral aorta is typically thin-walled and valved bulbus arteriosus and not contractile but elastic, alternately enlarging and shrinking in response to changes in blood pressure from alternate ventricular contraction, systole (contraction) and dia stole (relaxation)
The ventral aorta in a fish is median in position, beneath the gills from its branch the afferent bronchial arteries to each gill pouch or arch. With in the gills, afferent bronchial break down into capillaries and collect again in to efferent vessel that form the dorsal aorta main vessel for distribution of blood to the body.