The cardiovascular system is sometimes
called the blood-vascular or simply the circulatory
system. It consists of the heart, which is a muscular
pumping device, and a closed system of vessels called
arteries, veins, and capillaries. As the name implies,
blood contained in the circulatory system is pumped
by the heart around a closed circle or circuit of vessels
as it passes again and again through the various "circulations"
of the body.
|
|
As in the adult, survival of the developing embryo depends
on the circulation of blood to maintain homeostasis and a
favorable cellular environment. In response to this need,
the cardiovascular system makes its appearance early in development
and reaches a functional state long before any other major
organ system. Incredible as it seems, the primitive heart
begins to beat regularly early in the fourth week following
fertilization.
The vital role of the cardiovascular system in maintaining
homeostasis depends on the continuous and controlled movement
of blood through the thousands of miles of capillaries that
permeate every tissue and reach every cell in the body. It
is in the microscopic capillaries that blood performs its
ultimate transport function. Nutrients and other essential
materials pass from capillary blood into fluids surrounding
the cells as waste products are removed.
Numerous control mechanisms help to regulate and integrate
the diverse functions and component parts of the cardiovascular
system in order to supply blood to specific body areas according
to need. These mechanisms ensure a constant internal environment
surrounding each body cell regardless of differing demands
for nutrients or production of waste products.
|