A real heart is not present in cephalochordates, like Branchiostoma. Blood is propelled by contractile waves in the walls of large arteries. Blood bathes tissues in open spaces and contains amoeboid cells.
Compared to most other chordates, cephalochordates have a smaller coelom. It only occurs in canals close to the gonads, endostyle, and gill bars. Excretory tubules are modified coelomic cells that are closely linked to blood arteries. This configuration points to active material transfer inside the blood. Here, let us discuss the blood vascular system of amphioxus, or Branchiostoma (Cephalochordate), in detail.
Table of Contents
- Branchiostoma – Blood Vascular System
- Branchiostoma Circulation – Major Vessels
- Frequently Asked Questions
Branchiostoma – Blood Vascular System
Branchiostoma has a well-developed, closed-type circulatory system. Due to the lack of respiratory pigment and corpuscles, its blood is colourless. The blood in Branchiostoma aids in the transfer of food and excretory products solely. All of the blood arteries in Branchiostoma are muscular and contractile in nature since they lack a heart.
There are not many anatomical differences between the veins and arteries. Despite these primitive characteristics, Branchiostoma‘s circulatory system has the following characteristics of a typical vertebrate system.
- Blood vessels are arranged similarly to those of vertebrates.
- Blood flows in a similar direction in the blood vessels.
Branchiostoma Circulation – Major Vessels
In amphioxus, the direction of blood flow is dorsally backwards and ventrally forward. In a connective tissue matrix, the Brachiostoma‘s circulatory system is made up of well-defined contractile vessels and vascular spaces or sinuses.
The contractile arteries are surrounded by a thin layer of contractile myoepithelial cells and have a discontinuous endothelial lining that rests on a basal lamina. The major and minor afferent and efferent arteries, as well as the blood sinuses, all have discontinuous endothelial linings.
The major blood vessels and their branches that make up the Branchiostoma circulation are:
- Sinus venous – Blood from various parts of Branchiostoma is collected into a thin-walled, large sac-like structure called sinus venous.
- Dorsal aorta – Blood is collected from the gill bars by the paired left and right lateral dorsal aorta.
- Ventral aorta – It is a large median artery extending from the sinus venous. It runs mid-ventrally.
- Cardinal vein – The blood flowing from the ventro lateral region is collected by a posterior cardinal vein and an anterior cardinal vein.
- Parietal vein – The blood flowing from the dorsal body wall is collected by a pair of parietal veins.
- Sub intestinal vein – Intestinal vein and mid ventral caudal vein combine to make this vein. Blood is drawn from the tail region by the caudal vein and the gut via the intestinal vein.
- Hepatic portal system – The sub intestinal vein continues as the hepatic portal vein.
Blood flows posteriorly through the median and lateral dorsal aortae and anterior cardinal vein, while it flows anteriorly inside the sub intestinal, parietal and posterior cardinal veins and the ventral aorta.
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