Konrad Michael W
Sausalito , CA , United States.
PeerJ. 2016 Dec 14;4:e2771. doi: 10.7717/peerj.2771. eCollection 2016.
The body of the ascidian tunicate is relatively transparent. Thus, the circulatory system can be visualized by injecting high molecular weight fluorescein labeled dextran into the heart or the large vessels at the ends of the heart without surgery to remove the body wall. In addition, after staining with neutral red, the movement of blood cells can be easily followed to further characterize the circulatory system. The heart is two gently curved concentric tubes extending across the width of the animal. The inner myocardial tube has a partial constriction approximately in the middle. As in other tunicates, the heart is peristaltic and periodically reverses direction. During the branchial phase blood leaves the anterior end of the heart by two asymmetric vessels that connect to the two sides of the branchial basket. Blood then flows in both transverse directions through a complex system of ducts in the basket into large ventral and dorsal vessels which carry blood back to the visceral organs in the posterior of the animal. During the visceral phase blood leaves the posterior end of the heart in two vessels that repeatedly bifurcate and fan into the stomach and gonads. Blood velocity, determined by following individual cells in video frames, is high and pulsatory near the heart. A double peak in velocity at the maximum may be due to the constriction in the middle of the heart tube. Blood velocity progressively decreases with distance from the heart. In peripheral regions with vessels of small diameter blood cells frequently collide with vessel walls and cell motion is erratic. The estimated volume of blood flow during each directional phase is greater than the total volume of the animal. Circulating blood cells are confined to vessels or ducts in the visible parts of the animal and retention of high molecular weight dextran in the vessels is comparable to that seen in vertebrates. These are characteristics of a closed circulatory system.
海鞘的身体相对透明。因此，无需手术切除体壁，通过将高分子量荧光素标记的葡聚糖注入心脏或心脏末端的大血管，就可以观察到循环系统。此外，用中性红染色后，可以很容易地追踪血细胞的运动，以进一步表征循环系统。心脏是两根轻轻弯曲的同心管，横跨动物的宽度延伸。内部的心肌管在大约中间位置有部分收缩。与其他海鞘一样，心脏是蠕动的，并且会周期性地反转方向。在鳃阶段，血液通过两条不对称的血管离开心脏前端，这两条血管连接到鳃篮的两侧。然后血液通过鳃篮中复杂的管道系统在两个横向方向流动，进入大的腹侧和背侧血管，这些血管将血液带回动物后部的内脏器官。在内脏阶段，血液通过两条血管离开心脏后端，这两条血管反复分支并呈扇形分布到胃和性腺。通过在视频帧中跟踪单个细胞确定的血流速度在心脏附近很高且呈脉动性。速度最大值处的双峰可能是由于心脏管中间的收缩。血流速度随着与心脏距离的增加而逐渐降低。在小直径血管的周边区域，血细胞经常与血管壁碰撞，细胞运动不稳定。每个定向阶段估计的血流量大于动物的总体积。循环血细胞局限于动物可见部分的血管或管道中，血管中高分子量葡聚糖的保留情况与脊椎动物相似。这些是封闭循环系统的特征。
