Download Circulatory System The Human Heart Words to Know

Circulatory System
Words to Know
The circulatory system is responsible for delivering food,
oxygen, and other needed substances to all cells in all parts
of the body while taking away waste products. The basic
components of the circulatory system are the heart,
the blood vessels, and the blood. As blood circulates
around the body, it picks up oxygen from the lungs, nutrients
from the small intestine, and hormones from the endocrine
glands, and delivers these to the cells. Blood then picks up
carbon dioxide and cellular wastes from cells and delivers
these to the lungs and kidneys, where they are excreted.
The circulatory system is also known as the cardiovascular
system, from the Greek word kardia, meaning “heart,” and
the Latin vasculum, meaning “small vessel.”
The Human Heart
In humans, the adult heart is a hollow cone-shaped muscular organ located in the
center of the chest cavity. The heart is about the size of a clenched fist and weighs
approximately 10 ounces (300 grams). A heart beats more than 100,000 times a day
and close to 2.5 billion times in an average lifetime. The pericardium—a triple-layered
sac—surrounds, protects, and anchors the heart.
The heart is divided into four chambers (see figure 2). A septum, or partition, divides it
into a left and right side. Each side is further divided into an upper and lower chamber.
The upper chambers, the atria (singular atrium), are thin-walled. They receive blood
entering the heart and pump it to the ventricles, the lower heart chambers. The walls
of the ventricles are thicker and contain more cardiac muscle than the walls of the
atria. These muscles enable the ventricles to pump blood out to the lungs and the rest
of the body.
Artery
A blood vessel that
transports
oxygenated blood
away from the heart
to bodily tissues.
Atrium
Receiving chamber
of the heart.
Capillary
A microscopic blood
vessel that
transports blood to
and from tissues.
Hormone
A chemical
produced by a cell
or tissue that sends
a message to
another part of the
body, directing it to
act a certain way.
Vein
A blood vessel that
transports deoxygenated blood
away from bodily
tissues back to the
heart.
Ventricle
Pumping chamber of
the heart.
Figure 2
Figure 1
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The left and right sides of the heart function as two separate pumps. The right atrium receives blood carrying
carbon dioxide from the body through a major vein, the vena cava, and delivers it to the right ventricle. The right
ventricle, in turn, pumps the blood to the lungs via the pulmonary artery. The left atrium receives the oxygen-rich
blood from the lungs through the pulmonary veins, and delivers it to the left ventricle. The left ventricle then
pumps it into the aorta, the major artery that leads to all parts of the body. The wall of the left ventricle is thicker
than the wall of the right ventricle, making it a more powerful pump able to push blood through its longer trip
around the body.One-way valves in the heart keep blood flowing in the right direction and prevent backflow. The
valves open and close in response to pressure changes in the heart. In the heart, the two atria contract while the
two ventricles relax. Then, the two ventricles contract while the two atria relax.
Blood Vessels
The blood vessels of the body (arteries, capillaries, and veins) make up a
closed system of tubes that carry blood from the heart to tissues all over the
body and then back to the heart. Arteries carry blood away from the heart,
while veins carry blood toward the heart. Large arteries leave the heart and
branch into smaller ones that reach out to various parts of the body. These
divide still further into smaller vessels called arterioles that penetrate the body
tissues. Within the tissues, the arterioles branch into a network of microscopic
capillaries. Substances move in and out of the capillary walls as the blood
exchanges materials with the cells. Before leaving the tissues, capillaries unite
into venules, which are small veins. The venules merge to form larger and
larger veins that eventually return blood to the heart.
The walls of arteries, veins, and capillaries differ in structure. In all three, the
vessel wall surrounds a hollow center through which the blood flows. The walls
of both arteries and veins are composed of three coats, but they differ in
thickness. One-way valves in the walls of veins keep blood flowing in one
direction. The walls of capillaries are only one cell thick. Of all the blood
vessels, only capillaries have walls thin enough to allow the exchange of
materials between cells and the blood.
Blood
Blood is liquid connective tissue. It transports oxygen from the lungs and delivers it to cells. It picks up carbon
dioxide from the cells and brings it to the lungs. It carries nutrients from the digestive system and hormones
from the endocrine glands to the cells. It takes heat and waste products away from cells. It protects the body
by clotting and by fighting disease through the immune system.
Blood is composed of plasma (liquid portion) and blood cells. Plasma, which is about 91.5 percent water, carries
blood cells and helps conduct heat. The three types of cells in blood are red blood cells (erythrocytes), white
blood cells (leukocytes) and platelets (thrombocytes). More than 99 percent of all the blood cells are red blood
cells. They contain hemoglobin, a red pigment that carries oxygen, and each red cell has about 280 million
hemoglobin molecules. White blood cells fight disease organisms by destroying them or by producing antibodies
that disable or kill them. Platelets bring about clotting of the blood.
"Circulatory System." UXL Encyclopedia of Science, edited by Amy Hackney Blackwell and Elizabeth Manar, 3rd ed., UXL, 2015. Research in
Context, go.galegroup.com/ps/i.do?p=MSIC&sw=w&u=pioneer&v=2.1&id=GALE%7CCV2644300256&it=r&asid=09a3fc4eede9348d0ed11730175ed617.
Accessed 24 Feb. 2017.
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