Overarching Function

The circulatory system transports are blood cells, nutrients, and waste. Blood vessels carry those substances from the body to the heart, then back to the body.

Basic structures and functions

Macroscopic structures

  1. Heart

    The heart is a muscular organ located at the center of your chest. It pumps oxygenated blood to the body and deoxygenated blood to the heart.

  2. Blood Vessels

    1. Arteries — Arteries are blood vessels that carries nutrients such as oxygen away from the heart to other tissues. They are thick-walled vessels with three layers: an outer layer of connective tissue, a middle layer of smooth muscle, and an inner layer of endothelium. These layers make arteries capable of withstanding high blood pressures since it is pumped by the heart.
    2. Veins — Veins are blood vessels that carry nutrients and waste products like carbon dioxide to the heart. They contain oxygen-poor blood since oxygen is already delivered to other organs. The endothelial walls of veins are thinner than the wall of arteries because they do not need to withstand such high blood pressures. The contraction of muscles enables blood to keep moving. Some larger veins contain valves, which prevent blood from flowing backwards. Breathing movement forces blood back to the heart.

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Microscopic structures

  1. Plasma

    Plasma is the clear, yellowish fluid in the blood. 50% of the blood is made up of plasma, and 90% of the plasma is made up of water. Plasma carries broken down products such as glucose and lipids. It also transports vitamins, minerals, and chemical messengers.

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  1. Blood Cells

    Our blood contain two types of blood cells — red blood cell and white blood cell. Red blood cells contain hemoglobin, which binds to oxygen, and carries oxygen to the rest of the body. Red blood cells also carries carbon dioxide away from the cells to the lungs.

    Unlike red blood cells, there are fewer white blood cells. However, white blood cells are important for our immune system. Some white blood cells recognize invaders such as bacteria and alert the body. Some produce chemicals to fight the invaders. Others surround and kill the invaders.

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  1. Blood Vessel — Capillaries

    Unlike arteries and veins, capillaries are microscopic blood vessels that connect arteries to veins. They are extremely thin, which makes the exchange of important substances and waste products easier. The diameter of capillaries do not stay constant. When the body is in need for more nutrients or wastes to be removed, the capillaries dilate.

Connection to other systems

The circulatory system directly connects to all other systems of the body. It transports blood cells, nutrients, and waste through blood vessels and capillaries. It helps blood unload the nutrients picked up in the digestive system, pick up waste, and head back to the heart.

Differences between a frog and human

Both frogs and humans have a circulatory system to pump blood throughout the body. The largest difference between the two organisms is that frogs have a three-chambered heart, with two atria and one ventricle compared to human’s two atria and two ventricles.