The human circulatory system is a closed system that circulates blood throughout

the body through a network of blood vessels. It is composed of the heart, blood vessels,
blood, and lymphatic system.

1. Heart: The heart is a muscular organ that pumps blood to all parts of the body. It is a
muscular organ located slightly on the left side of the body. It sits between the right
and left of the lungs. The left lung is slightly smaller to make room for the heart in the
left chest.

- Four chambers of heart: the left atrium, the left ventricle, the right atrium,
and the right ventricle. The right atrium receives deoxygenated blood from the
body and pumps it into the right ventricle. The right ventricle then pumps the
blood into the lungs where it is oxygenated. The oxygenated blood then
returns to the left atrium, which pumps it into the left ventricle. The left
ventricle then pumps the oxygenated blood into the body to supply oxygen
and nutrients to all the organs and tissues.
- Heart walls: the muscles that squeeze and relax to send blood throughout
the body. A layer of muscular tissue called the septum divides the heart walls
into the left and right sides.Heart walls have three layers: Endocardium: inner
layer. Myocardium: muscular middle layer. Epicardium: protective outer layer.
The epicardium is one layer of your pericardium. The pericardium is a
protective sac that covers your entire heart. It produces fluid to lubricate your
heart and keep it from rubbing against other organs.
- Heart valves: control the flow of blood through the chambers and out of the
heart. They are designed to open and close in a specific order and direction,
ensuring that blood flows in the correct direction and doesn't flow back into
the chambers it just left. There are four main valves in the heart: the tricuspid
valve, the mitral valve, the aortic valve, and the pulmonary valve. Each valve
has specific functions and can become diseased or damaged, leading to
heart valve problems such as stenosis (narrowing) or regurgitation (leakage).
Treatment options for heart valve problems include medication, surgery, or
replacement of the damaged valve.
- Electrical conduction system: a network of specialized cells in the heart
that generate and transmit electrical impulses, causing the heart to contract
and pump blood throughout the body. It includes the sinoatrial (SA) node, the
atrioventricular (AV) node, the bundle of His, and the Purkinje fibers. The SA
node, located in the right atrium, is the natural pacemaker of the heart and
generates the first electrical impulse. The impulse then travels through the
atria, causing them to contract and pump blood into the ventricles. The AV
node, located between the atria and ventricles, slows down the electrical
impulse before it reaches the ventricles, allowing the atria to complete their
contraction before the ventricles begin to contract. The bundle of His, located
in the interventricular septum, carries the electrical impulse from the AV node
to the ventricles, causing them to contract and pump blood out of the heart.
The Purkinje fibers, located in the ventricular walls, help to distribute the
electrical impulse throughout the ventricles, ensuring that they contract in a
coordinated manner.
 2. Blood vessels: the channels through which the blood flows. In a system, the body
contains blood vessels about 60,000 miles long. They are divided into three main:
the arteries, veins, and capillaries. Arteries carry oxygenated blood away from the
heart and have thick walls to withstand the high pressure of the blood flow. Veins
carry deoxygenated blood back to the heart and have thinner walls. Capillaries are
the smallest blood vessels and connect the arteries and veins. They are responsible
for the exchange of oxygen, nutrients, and waste products between the blood and the
body's cells. Another 2 secondary types: Arterioles and Venules. Arterioles:
Arteries branch into smaller vessels called arterioles. Both arteries and arterioles are
very flexible. They get bigger or smaller to help maintain your body’s blood pressure.
Venules: Veins begin as tiny vessels called venules and get gradually larger as they
near your heart. Venules receive blood from capillaries.

3. Blood: blood is a fluid that carries oxygen, nutrients, hormones, and waste products
throughout the body. It is composed of plasma, red blood cells, white blood cells, and
platelets. Plasma is the liquid part of the blood and is mostly composed of water. Red
blood cells carry oxygen and are responsible for the red color of the blood. White
blood cells are responsible for the immune system and fight off infections. Platelets
are responsible for blood clotting.

4. Lymphatic system: network of vessels, organs, and tissues that help to remove
excess fluid, waste, and toxins from the body. It is an important part of the immune
system and plays a crucial role in protecting the body against infection and
disease.The lymphatic system is made up of three main components:

- Lymph vessels: These are a network of small, thin-walled vessels that

transport lymph (a clear fluid that contains immune cells) throughout the body.
Lymph vessels are found in all parts of the body, but are most concentrated in
the head, neck, and upper limbs.
- Lymph nodes: These are small, bean-shaped structures that are found along
the lymph vessels. Lymph nodes act as filters for the lymph fluid, trapping and
removing any harmful substances such as bacteria, viruses, or cancer cells.
- Lymphoid organs: These include the spleen, thymus, and tonsils, which play a
key role in producing and storing immune cells that help to fight off infection
and disease.

The circulatory system plays a vital role in maintaining the body's overall health, well-being,
and helping to fight off infections and diseases.

Overall, the human circulatory system is a complex and essential system that keeps the
body alive by supplying oxygen and nutrients to all the organs and tissues and removing
waste products.