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The Circulatory System – Anatomy, Functions and Diseases


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The human body can be said to be the structure of a human being. It constitutes different types of cells that come together to form tissues and then organ systems, which ensure homeostasis and the sustainability of the human body.


The circulatory system consists of all organs entrusted with the responsibility of carrying blood, nutrients, and waste around the body with the cardiovascular system.

The circulatory system helps to defend the body against germs and diseases and also helps the body maintain the normal body temperature, and provides the right hormonal balance that provides the body’s homeostasis or state of equilibrium among all its systems.

This system consists of blood, the heart (which is sometimes referred to as the blood pumping organ ) and blood vessels. This network supplies tissues in the body with respiratory gases, nutrients and transports hormones and also removes metabolic waste.

The circulatory system comprises of three independent systems that function together to achieve circulation: the heart (cardiovascular) lungs (pulmonary), and arteries, veins, coronary and portal vessels (systemic).

The circulatory system is in control of the flow of blood, oxygen and other gases, nutrients and also responsible for supplying hormones to the cell compartments.

The system also includes the lymphatic system, which circulates lymph. The flow of lymph takes much duration than that of blood.

The blood is a fluid that disseminates the red blood cells (which helps in transporting oxygen to the cells), White blood cells (which resist infections) and Platelets (tinier cells that help the blood to clot) that is circulated by the heart through animal’s vascular system, carrying oxygen and nutrients inside and waste materials from all body tissues.

Lymph is basically recycled excess blood plasma that has been filtered from the extracellular fluid and deposited back to the lymphatic system.

Arteries usually carry oxygenated blood and veins usually carry deoxygenated blood ( blood which can also be referred to haemoglobin).


However, the pulmonary arteries and pulmonary veins are an exception to this rule because the pulmonary veins transport oxygenated haemoglobin(blood) to the heart and the pulmonary arteries transport unoxygenated haemoglobin away from the heart.

Blood (Haemoglobin) is always red. But sometimes the vein can come across as blue, as it can sometimes be seen through the skin, which makes people think deoxygenated blood is blue, which studies have proven to be erroneous, as blood only appears blue as a result of the way tissues absorb light and our eyes see colour.

Albeit oxygen, does have an impact on the brightness of the blood ( the higher the amount of oxygen, the brighter the shade of red will become) which reiterates that blood can never be blue.

The cardiovascular system comprises of the blood, heart, and blood vessels while the lymph, lymph vessels, and the lymph nodes are from the lymphatic system, which returns purified blood plasma from the extracellular fluid as lymph.

The circulatory system of the blood has two major components, a systemic circulation and a pulmonary circulation.

Systemic circulation

The systemic circulation is the fraction of the cardiovascular system which transfers oxygenated blood from the blood pumping organ (the heart) to the body and returns deoxygenated blood to the heart.

The cardiovascular system moves blood away from the heart through the aorta from the left ventricle where the blood has been deposited formerly from pulmonary circulation to the rest of the body and returns oxygen-depleted blood back to the heart.

The circuit vessels responsible for supplying oxygenated blood to the heart and returning deoxygenated blood from the tissues of the body is the systemic circulation.

Here, blood is moved from the left ventricle of the heart through the aorta and arterial branches to the arterioles and moves through the capillaries, where it then reaches a conformity with the tissue fluid, and then empties through the venules into the veins and re-deposits, via the venae cavae, to the right atrium of the heart.

Pressure in the arterial system, resulting from the hearts activities and expansion by the blood, maintains systemic blood flow.


The systemic route, however, consists of many circuits in symmetry, all of which has its own arteriolar defence that allows blood flow independently of the overall flow and pressure and without necessarily disrupting. Hence why blood flow through the digestive tract increases after meals, during fitness activities

Pulmonary circulation

The pulmonary circulation is a design of the circulatory system which carries deoxygenated blood from the right ventricle to the lungs, and then returns oxygenated blood to the left atrium and ventricle of the heart; it only transfers blood through the heart and lungs, distinctive from the systemic circulation that moves blood between the heart and the rest of the body.

This type of circulation conveys deoxygenated blood to the lungs to absorbs oxygen and emits carbon dioxide while the oxygenated blood then streams back to the heart.

Humans, as well as other vertebrates, have a closed cardiovascular system, which means that the blood never exits the intricate network of arteries, veins and capillaries, An average adult contains 4.7 to 5.7 litre of blood, which accounts for approximately 7% of the body’s total weight.

The circulatory system can not function on its own, so the digestive system aids the circulatory system, to provide the nutrients the system needs to keep the heart running. Unlike the vertebrates, invertebrate animals have an open cardiovascular system.

Invertebrate animals have a great assortment of fluids, cells, and modes of circulation, in which fluid passes freely around the tissues or particular areas of tissue.

All vertebrates, however, have a closed system as earlier mentioned, this system contains two fluids, blood and lymph, and functions by means of two interacting modes of circulation, the cardiovascular system and the lymphatic system and operates by means of those two interacting channels and both fluid and the vessels through which they flow to have reached the greatest development and specialization in the mammalian systems.

Anatomy of the Circulatory System

The circulatory system consists of three independent systems that work jointly: the heart (cardiovascular), lungs (pulmonary), and arteries, veins and portal vessels (systemic).

The system is responsible for the flow of blood, nutrients, oxygen and other gases, and as well as hormones to and from cells.

There has been a debate over the years on whether the heart is an organ or a muscle. The heart is a muscular organ, that’s four-chambered and located just behind and breastbone, it pumps blood through the web of arteries and veins called the cardiovascular system.


The network of veins, arteries and blood vessels conveys oxygenated blood from the heart, delivers oxygen and nutrients to the body’s cells and then returns deoxygenated blood to the heart.

The system of blood vessels in the human body are believed to measure about 60,000 miles. Arteries carry oxygen-enriched blood from the heart through the body. Veins carry oxygen-depleted blood back to the heart.

The circulatory system contains four major constituents

  • Heart: The Heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system. The Blood provides the body with oxygen and nutrients needed, as well as assists the removal of metabolic wastes. In humans, the heart is located between the lungs, in the middle cavity of the chest and the heart keeps the circulatory system working at all times.
  • Arteries: Arteries carry oxygen-rich blood away from the heart.
  • Veins: Veins carry deoxygenated blood to the lungs where they receive oxygen.
  • Blood: Blood is the transport channel of nearly everything within the body. It transports hormones, nutrients, antibodies, oxygen, and other gases needed to keep the body in a state of equilibrium.

Functions of the circulatory system

Circulatory System
Circulatory System

The functions of the tissues, organs and systems in the body cannot be overemphasised as without out them the body would lack vitality and sustenance and hence be a haven for diseases and germs.

The circulatory system is one of the transport system of the human body that comprises of the heart, the blood, and the blood vessels. It functions includes:

  • The circulatory system delivers nutrients and oxygen to different cells of the body.
  • It carries body metabolic waste away
  • It protects the body from diseases as it serves as the body’s defence system
  • It circulates blood from one part of the body to the other and transports nutrients such aa amino acid and electrolytes, Gases such as Oxygen, carbon dioxide, hormones and blood cells to and from the cells in the body to transport nutrient.
  • It stabilises body temperature and PH and maintains homeostasis.
  • The circulatory system permits every cell whether present on the surface of the animal or ingrained deep within to derive nourishment and to be protected from pathogens, to communicate and coexist with other cells in a consistent microenvironment.

Diseases of the circulatory system

Some of the diseases of the circulatory system are highlighted below:

Coronary Artery disease

Coronary artery disease develops when the major blood vessels that provide the heart with blood, oxygen and nutrients (coronary arteries) become deteriorated or damaged by Cholesterol-containing deposits (plaque) in the arteries which leads to inflammation.

When plaque builds up, it narrows the coronary arteries, reducing blood flow to the heart. Eventually, the reduced blood flow may cause chest pain, shortness of breath, or other coronary artery disease signs and symptoms.

A complete blockage can cause a heart attack. Because coronary artery disease often develops over decades, and might not be noticeable until one has a significant blockage or a heart attack.

Some of the symptoms of this disease can be Chest pain, Shortness of breath, Heart attack which can be caused by unhealthy life choices like smoking and sedentary lifestyle, High blood pressure, diabetes or insulin resistance.


So once the inner wall of an artery is damaged, fatty deposits called plaques made of cholesterol and other cellular waste products tend to amass at the site of injury in a process called atherosclerosis.

If the surface of the plaque breaks or ruptures, blood cells called platelets will clump at the site to try to repair the artery, this clump can block the artery, leading to a heart attack.
This can be prevented and controlled by healthier life choices such as exercises and dieting.

Atherosclerosis, arteriosclerosis, and arteriosclerosis

Arteriosclerosis happens when the blood vessels that transport oxygen and nutrients from the heart to the rest of the body (arteries) become thick and stiff — sometimes restricting blood flow to the organs and tissues.

Healthy arteries are flexible and elastic, but over time, the walls of the arteries can stiffen, a condition commonly called hardening of the arteries which can be caused by High blood pressure, High cholesterol, High triglycerides, a type of lipid in the blood, Smoking and other sources of tobacco, insulin resistance, obesity or diabetes, Inflammation from diseases, such as arthritis, lupus or infections etc.


A stroke occurs when the blood supply to part of the brain is interrupted or reduced, preventing brain tissue from getting oxygen and nutrients which leads to the death of the brain cells in minutes.

Some of the signs and symptoms of the disease are Numbness of the face and some other parts of the body, problem seeing in one or both eyes, headaches etc. There are two main causes of stroke which ischemic stroke) or hemorrhagic stroke.

High blood pressure (Hypertension)

High blood pressure is a common condition in which the long-term force of the blood against your artery walls is high enough that it may eventually cause health problems, such as heart disease.

Blood pressure is determined both by the amount of blood your heart pumps and the amount of resistance to blood flow in the arteries i.e The more blood the heart pumps and the narrower the arteries become and the higher the blood pressure.

One can have high blood pressure (hypertension) for years without any symptoms. Even without symptoms, damage to blood vessels and the heart continues and can be detected. Uncontrolled high blood pressure increases the risk of serious health problems, including heart attack and stroke.


Cardiomyopathy is a disease of the heart muscle that makes it harder for the heart to pump blood to the rest of the body.


Cardiomyopathy can lead to heart failure. The main types of cardiomyopathy include dilated hypertrophic and restrictive cardiomyopathy.

Treatment — which might include medications, surgery or, in severe cases, a heart transplant — depends on which type cardiomyopathy one has and how serious it is.

Some of the symptoms can be; Breathlessness even at rest, Swelling of the legs, ankles, Cough while lying down, Fatigue, Heartbeats that feel rapid, pounding or fluttering, Chest discomfort or pressure, dizziness, lightheadedness and even fainting.

Heart valve disease

Heart valve disease is one of the diseases that can affect the circulatory system. In heart valve disease, one or more of the heart valves is not working properly.

The heart has four valves that keep blood flowing in the correct direction. In some cases, one or more of the valves don’t open or close properly. This can cause the blood flow through the heart to your body to be disrupted.

Some of the symptoms are fatigue, irregular heartbeat, dizziness and swelling of the feet and ankles amongst others.

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