The circulatory system, also known as the cardiovascular system, is comprised of the heart, blood vessels (arteries, veins, and capillaries), and blood. The heart pumps oxygenated blood received from the lungs through the arteries to nourish tissues throughout the body and pumps deoxygenated blood back to the lungs through veins to be reoxygenated. Arteries carry oxygenated blood away from the heart while veins carry deoxygenated blood back to the heart. Capillaries connect arteries and veins and facilitate the exchange of oxygen, nutrients, waste and more between blood and tissues.

1. CARDIOVASCULAR
SYSTEM

2. CIRCULATORY SYSTEM
The Circulatory System is made up of blood vessels
that carry blood away from and towards the
Heart. Arteries carry blood away from the heart
and veins carry blood back to the heart. The
circulatory system carries Oxygen, Nutrients,
and Hormones to cells, and removes waste products,
like carbon dioxide. These roadways travel in one
direction only, to keep things going where they
should. It is also known as Cardiovascular System.

3. COMPONENTS
The Circulatory System is mainly composed of the following :-
• Heart: Heart is a muscular organ; which is composed of cardiac muscles. The heart is a pumping organ
which pumps the blood.
• Arteries: These are thick-walled blood vessels which carry oxygenated blood from the heart to different
organs. Pulmonary arteries carry deoxygenated blood from the heart to lungs; where oxygenation of
blood takes place.
• Veins: These are thin-walled blood vessels which carry deoxygenated blood from different organs to the
heart. Pulmonary veins carry oxygenated blood from lungs to the heart.
• Capillaries: These are the blood vessels which have single-celled walls.
• Blood: Blood is a connective tissue which plays the role of the carrier for various substances in the body.

4. THE HEART
The Heart is a Muscular Organ in most animals, which
pumps blood through the blood vessels of the circulatory
system. The pumped blood carries Oxygen and nutrients to
the body, while carrying metabolic waste such as Carbon
Dioxide to the lungs. The heart is sort of like a pump. The
right side of the heart receives blood from the body and
pumps it to the lungs. The left side of the heart does the
exact opposite: It receives blood from the lungs and pumps it
out to the body. It is located between the lungs, in the middle
compartment of the chest.

5. FUNCTIONS OF THE HEART
The four main functions of the heart are:
• Pumping oxygenated blood to the other body parts.
• Pumping hormones and other vital substances to
different parts of the body.
• Receiving deoxygenated blood and carrying metabolic
waste products from the body and pumping it to the
lungs for oxygenation.
• Maintaining Blood Pressure.

7. ARTERIES
Arteries are the Blood Vessels that takes blood away from
the heart to one or more parts of the body. Most arteries carry
Oxygenated Blood; the two exceptions are the Pulmonary
and the Umbilical Arteries, which carry Deoxygenated Blood
to the organs that oxygenate it. The effective arterial blood
volume is that extracellular fluid which fills the Arterial
System. These are responsible for the delivery of oxygen and
nutrients to all cells, as well as the removal of carbon dioxide
and waste products, the maintenance of Optimum Blood pH,
and the circulation of proteins and cells of the human immune
system.

8. STRUCTURE OF AN ARTERY
The wall of an Artery consists of three layers. The Innermost
Layer, the Tunica Intima, is Simple Squamous Epithelium
surrounded by a connective tissue basement membrane with
Elastic Fibers. The Middle Layer, the Tunica Media, is
primarily Smooth Muscle and is usually the Thickest Layer, it
provides support for the vessel and changes vessel diameter
to regulate blood flow and blood pressure. The Outermost
Layer, which attaches the vessel to the surrounding tissue, is
the Tunica Externa (Tunica Adventitia). This layer is
Connective Tissue with varying amounts of Elastic and
Collagenous Fibers.

9. VEINS
Veins are a type of blood vessel that return Deoxygenated
Blood from your organs back to your heart. Deoxygenated
Blood that flows into your veins is collected within tiny blood
vessels called Capillaries. Oxygen passes through the walls
of your capillaries to your tissues. Carbon dioxide can also
move into your capillaries from the tissue before entering
your veins. The Venous System refers to the network of
Veins that work to deliver deoxygenated blood back to the
Heart.

10. STRUCTURE OF A VEIN
The walls of your veins are made up of three different
layers:
• Tunica Externa: This is the Outer Layer, and it’s also
the Thickest. It’s mostly made up of Connective
Tissue. It also contains tiny blood vessels called Vasa
Vasorum that supply blood to the walls of your veins.
• Tunica Media: This is the Middle Layer. It’s Thin and
contains a large amount of Collagen.
• Tunica Intima: This is the Innermost Layer. It’s a Single
Layer of Endothelium Cells and some connective
tissue.

11. CAPILLARIES
Capillaries are very tiny blood vessels — so small that a
single red blood cell can barely fit through them. They help
to connect your arteries and veins in addition to facilitating
the exchange of certain elements between your blood and
tissues. This is why tissues that are very Active, in Muscles,
Liver, and Kidneys, have an abundance of capillaries. Less
metabolically active tissues, such as certain types of
connective tissue, don’t have as many.

12. THE BLOOD
Blood is a body fluid in humans and other animals that
delivers necessary substances such as nutrients and
oxygen to the cells and transports metabolic waste products
away from those same cells. In Vertebrates, it is composed
of blood cells suspended in blood plasma. Plasma, which
constitutes 55% of Blood Fluid, is mostly water and contains
proteins, glucose, mineral ions, hormones, carbon dioxide
and blood cells themselves. The blood cells are mainly Red
Blood Cells (RBCs or Erythrocytes), White Blood Cells
(WBCs or Leukocytes) and Platelets (Thrombocytes). It
contain Hemoglobin, an iron-containing protein, which
facilitates oxygen transport..

14. FUNCTIONS OF BLOOD
The main functions of the blood are :-
• Transporting oxygen and nutrients to the lungs and tissues.
• Forming blood clots to prevent excess blood loss.
• Carrying cells and antibodies that fight infection.
• Bringing waste products to the kidneys and liver, which filter and clean the
blood.
• Regulating body temperature.