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Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in controlling hemorrhage and reducing acute blood loss.
In a healthy heart all activities and rests during each individual cardiac cycle, or heartbeat, are initiated and orchestrated by signals of the heart's electrical conduction system, which is the "wiring" of the heart that carries electrical impulses throughout the body of cardiomyocytes, the specialized muscle cells of the heart.
The tubular heart or primitive heart tube is the earliest stage of heart development. [1] The heart is the first organ to develop during human embryonic development. [2]From the inflow to the outflow, the tubular heart consists of sinus venosus, primitive atrium, the primitive ventricle, the bulbus cordis, and truncus arteriosus. [3]
These are known as transverse-tubules (t-tubules); which are also found in skeletal muscle cells and allow for the action potential to travel into the centre of the cell. [7] Special proteins called L-type calcium channels (also known as dihydropyridine receptors (DHPR)) are located on the t-tubule membrane , and are activated by the action ...
In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. [1] [2] It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek kardia meaning heart, and Latin vascula meaning vessels).
T-tubules (transverse tubules) are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells.With membranes that contain large concentrations of ion channels, transporters, and pumps, T-tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration.
They conduct cardiac action potentials more quickly and efficiently than any of the other cells in the heart's electrical conduction system. [4] Purkinje fibers allow the heart's conduction system to create synchronized contractions of its ventricles, and are essential for maintaining a consistent heart rhythm. [5]
The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. [1] The system is composed of canals connecting numerous tube feet. Echinoderms move by alternately contracting muscles that force water into the tube feet, causing them to ...