IT WILL BE HELPFUL FOR IRREGULAR STUDENTS LIKE ME. YOU MAY COPY AND PASTE IT. The circulatory system is an organ system that permits blood and lymph circulation to transport nutrients, oxygen, carbon dioxide, hormones, blood cells, etc. to and from cells in the body to nourish it and help to fight diseases, stabilize body temperature and pH, and to maintain homeostasis. This system may be seen strictly as a blood distribution network, but some consider the circulatory system as composed of the cardiovascular system, which distributes blood, and the lymphatic system, which returns excess filtered blood plasma from the interstitial fluid (between cells) as lymph. While humans, as well as other vertebrates, have a closed cardiovascular system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open cardiovascular system. The more primitive, diploblastic animal phyla lack circulatory systems. The lymphatic system, on the other hand, is an open system providing an accessory route for excess interstitial fluid to get returned to the blood.

1. Circulation of Blood

2. Content
Topic
Page
01
Circulatory System
04
02
Cardiovascular System
05
- Cardiovascular System Anatomy
- The Heart and Circulation
03
Blood Vessel
10
- Arteries and Arterioles
-Capillaries
-Veins and Venules
04
Coronary Circulation
13
05
Hepatic Portal Circulation
15
06
The Path of Blood through the Human Body
15
07
Pulmonary circulation
16
08
Systemic circulation
17
09
Capillary exchange
18
10
References
19
2

3. Circulatory system
The circulatory system is an organ system that permits blood and lymph circulation
to transport nutrients, oxygen, carbon dioxide, hormones, blood cells, etc. to and
from cells in the body to nourish it and help to fight diseases, stabilize body
temperature and pH, and to maintain homeostasis.
This system may be seen strictly as a blood distribution network, but some
consider the circulatory system as composed of the cardiovascular system, which
distributes blood, and the lymphatic system, which returns excess filtered blood
plasma from the interstitial fluid (between cells) as lymph. While humans, as well
as other vertebrates, have a closed cardiovascular system (meaning that the blood
never leaves the network of arteries, veins and capillaries), some invertebrate
groups have an open cardiovascular system. The more primitive, diploblastic
animal phyla lack circulatory systems. The lymphatic system, on the other hand, is
an open system providing an accessory route for excess interstitial fluid to get
returned to the blood.
Figure 1: Sectional view of Human heart
3

4. Two types of fluids move through the circulatory system: blood and lymph.
Lymph is essentially recycled blood plasma after it has been filtered from the
blood cells and returned to the lymphatic system. The blood, heart and blood
vessels form the cardiovascular system.
The essential components of the human cardiovascular system are the heart, blood,
and blood vessels. It includes: the pulmonary circulation, a "loop" through the
lungs where blood is oxygenated; and the systemic circulation, a "loop" through
the rest of the body to provide oxygenated blood. An average adult contains five to
six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of
their total body weight. Blood consists of plasma, red blood cells, white blood
cells, and platelets. Also, the digestive system works with the circulatory system to
provide the nutrients the system needs to keep the heart pumping.
Cardiovascular System
The cardiovascular system consists of the heart, blood vessels, and the
approximately 5 liters of blood that the blood vessels transport.
Figure 2: Cardiovascular System
4

5. Responsible for transporting oxygen, nutrients, hormones, and cellular waste
products throughout the body, the cardiovascular system is powered by the body’s
hardest-working organ — the heart, which is only about the size of a closed fist.
Even at rest, the average heart easily pumps over 5 liters of blood throughout the
body every minute.
Cardiovascular System Anatomy
The Heart and Circulation
The heart is a muscular pumping organ located medial to the lungs along the
body’s midline in the thoracic region. The bottom tip of the heart, known as its
apex, is turned to the left, so that about 2/3 of the heart is located on the body’s left
side with the other 1/3 on right. The top of the heart, known as the heart’s base,
connects to the great blood vessels of the body: the aorta, vena cava, pulmonary
trunk, and pulmonary veins.
Figure 3: Blood Circulation Through Heart
5

6. Circulatory Loops
There are 2 primary circulatory loops in the human body: the pulmonary
circulation loop and the systemic circulation loop.
Pulmonary circulation transports deoxygenated blood from the right side of
the heart to the lungs, where the blood picks up oxygen and returns to the
left side of the heart. The pumping chambers of the heart that support the
pulmonary circulation loop are the right atrium and right ventricle.
Systemic circulation carries highly oxygenated blood from the left side of
the heart to all of the tissues of the body (with the exception of the heart and
lungs). Systemic circulation removes wastes from body tissues and returns
deoxygenated blood to the right side of the heart. The left atrium and left
ventricle of the heart are the pumping chambers for the systemic circulation
loop.
Figure 4: Represents The circulation
6

7. The primary function of the heart is to pump blood through blood vessels to the
body's cells. Imagine a simple machine like a water pump working for perhaps 70
or more years without attention and without stopping. Impossible? Yet this is
exactly what the heart can do in our bodies. The heart is really a muscular bag
surrounding four hollow compartments, with a thin wall of muscle separating the
left hand side from the right hand side. The muscles in the heart are very strong
because they have to work harder than any of the other muscles in our body,
pushing the blood to our head and feet continuously.
The blood flow around our body is called our circulation. The heart connects the
two major portions of the circulation's continuous circuit, the systemic circulation
and the pulmonary circulation. The blood vessels in the pulmonary circulation
carry the blood through the lungs to pick up oxygen and get rid of carbon dioxide,
while the blood vessels in the systemic circulation carry the blood throughout the
rest of our body.
The heart actually has two separate sides, one designed to pump deoxygenated
blood into the pulmonary circulation where the blood becomes oxygenated, and
one designed to pump the oxygenated blood into the systemic circulation where the
blood flows throughout the body. Each side of the heart has two chambers or
compartments. The top chamber on each side is called the atrium. The right atrium
receives incoming deoxygenated blood from the body and the left atrium receives
incoming oxygenated blood from the lungs. The thin-walled atrium on each side
bulges as it fills with blood, and as the lower heart muscle relaxes, the atrium
contracts and squeezes the blood into a second chamber, the thick muscular
ventricle. The ventricle is the pumping chamber that, with each muscular
contraction, pushes the blood forcefully out and into the lungs (right ventricle) and
the rest of the body (left ventricle).
The atrium and ventricle on each side of the heart are separated by tissue flaps
called valves. The structure of these valves prevents blood from flowing backward
into the atrium as the ventricle squeezes blood out. The valve on the right side,
between the atrium and the ventricle, is called the tricuspid valve. The valve on the
left side, between the atrium and the ventricle, is called the bicuspid or mitral
valve. There are two other important valves that help to keep the blood Rowing in
the proper direction. These two valves are located at the two points where blood
7

8. exits the heart. The pulmonary valve is located between the right ventricle and the
pulmonary artery that carries the deoxygenated blood from the heart to the lungs,
and the aortic valve is located between the left ventricle and the aorta, the major
artery that carries the oxygenated blood from the heart to the rest of the body.
The arteries are the blood vessels that transport blood out of the heart under high
pressure to the tissues. The arterioles are the last small branch of the arterial system
through which blood is released into the capillaries. The capillaries are very small,
thin-walled blood vessels where the exchange of gases, nutrients, and waste takes
place between the cells and the blood. Blood flows with almost no resistance in the
larger blood vessels, but in the arterioles and capillaries, considerable resistance to
flow does occur because these vessels are so small in diameter that the blood must
squeeze all its contents through them. The venules collect blood from the
capillaries and gradually feed into progressively larger veins. The veins transport
the blood from the tissues back to the heart. The walls of the veins are thin and
very elastic and can fold or expand to act as a reservoir for extra blood, if required
by the needs of the body.
Figure 5: The path of a typical RBC through the heart.
8

9. Let us follow a single red blood cell (RBC) through one full cycle along the
circulatory pathway. Remember that RBCs carry oxygen throughout the body.
Since the blood travels endlessly, an arbitrary choice must be made of a starting
point to describe the RBC's route. We will begin at the point where the RBC has
delivered its oxygen to a cell in need and is on its return back to the heart.
1. Once the deoxygenated red blood cell (RBC) returns to the heart, it enters
either through the superior vana cava or the inferior vena cava. The superior
vena cava returns deoxygenated blood from the upper part of the body to the
heart. The inferior vena cava returns deoxygenated blood from the lower
part of the body to the heart. These large veins lead into the right atrium.
2. The RBC passes through the tricuspid valve into the right ventricle.
3. The RBC is then pumped through the pulmonary valve into the pulmonary
artery and on to the lungs. There the RBC gives off carbon dioxide and picks
up oxygen.
4. The RBC returns to the heart through a pulmonary vein, enters the left
atrium, passes through the mitral valve, and flows into the left ventricle.
5. The left ventricle pumps the fully oxygenated RBC through the aortic valve,
into the aorta, the body's main artery, and out to the body.
6. From the aorta, the RBC flows into one of the many arteries of the body,
through the arterioles, and then to the capillaries, where the RBC will deliver
oxygen and nutrients to the cells and remove wastes and carbon dioxide.
Next it moves through the venules, veins, and on to the vena cava in a
deoxygenated state, and returns to the heart, only to begin its repetitive
journey once again. This whole process has taken approximately 20 seconds!
That single RBC will travel about 950 miles (more than 1500 kilometers) in its
brief 4-month lifetime!
Blood Vessels
Blood vessels are the body’s highways that allow blood to flow quickly and
efficiently from the heart to every region of the body and back again. The size of
blood vessels corresponds with the amount of blood that passes through the vessel.
All blood vessels contain a hollow area called the lumen through which blood is
9

10. able to flow. Around the lumen is the wall of the vessel, which may be thin in the
case of capillaries or very thick in the case of arteries.
All blood vessels are lined with a thin layer of simple squamous epithelium known
as the endothelium that keeps blood cells inside of the blood vessels and prevents
clots from forming. The endothelium lines the entire circulatory system, all the
way to the interior of the heart, where it is called the endocardium.
Figure 6: Three types of blood vessels
There are three major types of blood vessels: arteries, capillaries and veins.
Blood vessels are often named after either the region of the body through which
they carry blood or for nearby structures. For example, the brachiocephalic artery
10

11. carries blood into the brachial (arm) and cephalic (head) regions. One of its
branches, the subclavian artery, runs under the clavicle; hence the name
subclavian. The subclavian artery runs into the axillary region where it becomes
known as the axillary artery.
Arteries and Arterioles: Arteries are blood vessels that carry blood away from the
heart. Blood carried by arteries is usually highly oxygenated, having just left the
lungs on its way to the body’s tissues. The pulmonary trunk and arteries of the
pulmonary circulation loop provide an exception to this rule – these arteries carry
deoxygenated blood from the heart to the lungs to be oxygenated.
Arteries face high levels of blood pressure as they carry blood being pushed from
the heart under great force. To withstand this pressure, the walls of the arteries are
thicker, more elastic, and more muscular than those of other vessels. The largest
arteries of the body contain a high percentage of elastic tissue that allows them to
stretch and accommodate the pressure of the heart.
Smaller arteries are more muscular in the structure of their walls. The smooth
muscles of the arterial walls of these smaller arteries contract or expand to regulate
the flow of blood through their lumen. In this way, the body controls how much
blood flows to different parts of the body under varying circumstances. The
regulation of blood flow also affects blood pressure, as smaller arteries give blood
less area to flow through and therefore increases the pressure of the blood on
arterial walls.
Arterioles are narrower arteries that branch off from the ends of arteries and carry
blood to capillaries. They face much lower blood pressures than arteries due to
their greater number, decreased blood volume, and distance from the direct
pressure of the heart. Thus arteriole walls are much thinner than those of arteries.
Arterioles, like arteries, are able to use smooth muscle to control their aperture and
regulate blood flow and blood pressure.
Capillaries: Capillaries are the smallest and thinnest of the blood vessels in the
body and also the most common. They can be found running throughout almost
every tissue of the body and border the edges of the body’s avascular tissues.
Capillaries connect to arterioles on one end and venules on the other.
11

12. Capillaries carry blood very close to the cells of the tissues of the body in order to
exchange gases, nutrients, and waste products. The walls of capillaries consist of
only a thin layer of endothelium so that there is the minimum amount of structure
possible between the blood and the tissues. The endothelium acts as a filter to keep
blood cells inside of the vessels while allowing liquids, dissolved gases, and other
chemicals to diffuse along their concentration gradients into or out of tissues.
Precapillary sphincters are bands of smooth muscle found at the arteriole ends of
capillaries. These sphincters regulate blood flow into the capillaries. Since there is
a limited supply of blood, and not all tissues have the same energy and oxygen
requirements, the precapillary sphincters reduce blood flow to inactive tissues and
allow free flow into active tissues.
Veins and Venules: Veins are the large return vessels of the body and act as the
blood return counterparts of arteries. Because the arteries, arterioles, and capillaries
absorb most of the force of the heart’s contractions, veins and venules are
subjected to very low blood pressures. This lack of pressure allows the walls of
veins to be much thinner, less elastic, and less muscular than the walls of arteries.
Veins rely on gravity, inertia, and the force of skeletal muscle contractions to help
push blood back to the heart. To facilitate the movement of blood, some veins
contain many one-way valves that prevent blood from flowing away from the
heart. As skeletal muscles in the body contract, they squeeze nearby veins and push
blood through valves closer to the heart.
When the muscle relaxes, the valve traps the blood until another contraction pushes
the blood closer to the heart. Venules are similar to arterioles as they are small
vessels that connect capillaries, but unlike arterioles, venules connect to veins
instead of arteries. Venules pick up blood from many capillaries and deposit it into
larger veins for transport back to the heart.
Coronary Circulation
The heart has its own set of blood vessels that provide the myocardium with the
oxygen and nutrients necessary to pump blood throughout the body. The left and
right coronary arteries branch off from the aorta and provide blood to the left and
12

13. right sides of the heart. The coronary sinus is a vein on the posterior side of the
heart that returns deoxygenated blood from the myocardium to the vena cava.
Figure 7: Coronary Circulation
Figure 8: Hepatic Circulation
13

14. Hepatic Portal Circulation
The veins of the stomach and intestines perform a unique function: instead of
carrying blood directly back to the heart, they carry blood to the liver through the
hepatic portal vein. Blood leaving the digestive organs is rich in nutrients and other
chemicals absorbed from food. The liver removes toxins, stores sugars, and
processes the products of digestion before they reach the other body tissues. Blood
from the liver then returns to the heart through the inferior vena cava.
The Path of Blood through the Human Body:
When a heart contracts and forces blood into the blood vessels, there is a certain
path that the blood follows through the body.
Figure 9: Blood circulation through human body
14

15. The blood moves through pulmonary circulation and then continues on through
systemic circulation. Pulmonary and systemic are the two circuits in the two-circuit
system of higher animals with closed circulatory systems.
Humans and other mammals have two-circuit circulatory systems: one circuit is
for pulmonary circulation (circulation to the lungs; pulmo = lungs), and the other
circuit is for systemic circulation (the rest of the body). As each atrium and
ventricle contract, blood is pumped into certain major blood vessels, and from
there, continues through the circulatory system.
Pulmonary circulation
Blood that is lacking oxygen is said to be deoxygenated. This blood has just
exchanged oxygen for carbon dioxide across cell membranes, and now contains
mostly carbon dioxide. Deoxygenated blood enters the right atrium through the
superior vena cava and the inferior vena cava. Superior means higher, and inferior
means lower, so the superior vena cava is at the top of the right atrium, and the
inferior vena cava enters the bottom of the right atrium.
From the right atrium, the deoxygenated blood drains into the right ventricle
through the right atrioventricular (AV) valve, which is so named because it is
between the atrium and the ventricle. This valve is also referred to as the tricuspid
valve because it has three flaps in its structure. When the ventricles contract, the
AV valve closes off the opening between the ventricle and the atrium so that blood
does not flow back up into the atrium.
As the right ventricle contracts, it forces the deoxygenated blood through the
pulmonary semilunar valve and into the pulmonary artery. Semilunar means halfmoon and refers to the shape of the valve. Note that this is the only artery in the
body that contains deoxygenated blood; all other arteries contain oxygenated
blood. The semilunar valve keeps blood from flowing back into the right ventricle
once it is in the pulmonary artery. The pulmonary artery carries the blood that is
very low in oxygen to the lungs, where it becomes oxygenated.
15

16. Systemic circulation
Freshly oxygenated blood returns to the heart via the pulmonary veins. Note that
these are the only veins in the body that contain oxygenated blood; all other veins
contain deoxygenated blood.
The pulmonary veins enter the left atrium. When the left atrium relaxes, the
oxygenated blood drains into the left ventricle through the left AV valve. This
valve is also called the bicuspid valve because it has only two flaps in its structure.
Now the heart really squeezes. As the left ventricle contracts, the oxygenated blood
is pumped into the main artery of the body — the aorta. To get to the aorta, blood
passes through the aortic semilunar valve, which serves to keep blood flowing
from the aorta back into the left ventricle. The aorta branches into other arteries,
which then branch into smaller arterioles. The arterioles meet up with capillaries,
which are the blood vessels where oxygen is exchanged for carbon dioxide.
Figure 10: Pulmonary and Systemic Circulation
16

17. Capillary exchange
Capillaries bridge the smallest of the arteries and the smallest of the veins. Near the
arterial end, the capillaries allow materials essential for maintaining the health of
cells to diffuse out (water, glucose, oxygen, and amino acids).
To maintain the health of cells, it is also necessary for the capillaries to transport
wastes and carbon dioxide to places in the body that can dispose of them. The
waste products enter near the venous end of the capillary. Water diffuses in and out
of capillaries to maintain blood volume, which adjusts to achieve homeostasis.
Capillaries are only as thick as one cell, so the contents within the cells of the
capillaries can easily pass out of the capillary by diffusing through the capillary
membrane. And, because the capillary membrane abuts the membrane of other
cells all over the body, the capillary’s contents can easily continue through the
abutting cell’s membrane and get inside the adjoining cell.
The process of capillary exchange is how oxygen leaves red blood cells in the
bloodstream and gets into all the other cells of the body. Capillary exchange also
allows nutrients to diffuse out of the bloodstream and into other cells. At the same
time, the other cells expel waste products that then enter the capillaries, and carbon
dioxide diffuses out of the body’s cells and into the capillaries.
17

18. References:
Kent. G.C’.Jr (1954). Comparative anatomy of the Vertebrates.
Kotpal, R.L. (2000). Modern Textbook of Zoology, Vertebrates.
http://en.wikipedia.org/wiki/Circulatory_system
http://www.innerbody.com/anatomy/cardiovascular-male
http://www.nsbri.org/humanphysspace/focus2/heartcirculation.html
6. http://www.dummies.com/how-to/content/the-path-of-bloodthrough-the-human-body.html
1.
2.
3.
4.
5.
18