Bioenergetics: Circulation in Humans

Circulatory System: Overview

The circulatory system is responsible for transporting oxygen, nutrients, hormones and waste products around the body.
It comprises the heart, blood vessels (arteries, veins, and capillaries), and blood.

The heart is a muscular organ consisting of four chambers: two upper atria and two lower ventricles.
The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs, where it picks up oxygen. This is known as pulmonary circulation.
The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body, a process known as systemic circulation.
The heart is myogenic, meaning it can contract without receiving signals from the nervous system. However, the rate of heart contractions is regulated by the autonomic nervous system.

Arteries carry blood away from the heart. These vessels have thick, elastic walls to withstand high pressure.
Veins carry blood towards the heart. Veins have thinner walls and valves to prevent backflow of blood.
Capillaries are tiny blood vessels that connect arteries and veins. They provide a large surface area for the exchange of substances between blood and tissues.

Blood is a fluid tissue made up of plasma, red blood cells, white blood cells, and platelets.
Red blood cells contain haemoglobin, which binds with oxygen to transport it around the body. These cells are also involved in the removal of carbon dioxide from the body.
White blood cells are part of the immune system, helping to fight infections.
Platelets help in blood clotting, preventing excessive blood loss during injury.

The rate of circulation can be influenced by several factors, including physical activity, emotional state, and overall health.
During physical activity, heart rate increases to supply muscles with more oxygen and nutrients.
Stress or emotional state can cause the heart rate to increase as part of the body’s “fight or flight” response.
Chronic diseases such as hypertension or atherosclerosis can negatively affect circulation, leading to risks of heart disease or stroke.