Circulation/circulatory system

CIRCULATION / CIRCULATORY SYSTEM

• The circulatory system of mammals (vascular system or cardiovascular system) is a large network of organs and blood vessels that move blood throughout the body. The blood transports nutrients from the digestive system, oxygen from the lungs, waste products from cells and hormones around the body. The circulatory system is made up of the heart, arteries, veins, capillaries and blood.

The <3

• The heart is a large, muscular organism that pumps blood around the body through arteries and veins. Mammalian hearts have two sides.
• The left side pumps oxygen rich blood it has received from the lungs around the body.
• The right side of the heart pumps oxygen poor blood to the lungs, where it picks up oxygen and returns to the left side of the heart.
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<3

• Arteries are blood vessels that carry oxygen rich blood away from the heart and around the body while veins are blood vessels which carry oxygen poor blood back to the heart. Arteries carry Away ('a' to remember). Tiny blood vessels called capillaries connect the veins and the arteries, forming a large loop of blood vessels.
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Arteries

• Arteries have very thick, muscular walls which allows them to carry high pressure blood without bursting.
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Veins

• Veins do not have thick walls. However, they have special valves that prevent blood from flowing backwards.
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Capillaries

• Capillaries enable oxygen and nutrients in the blood to move into the cells of the body. As the blood flows through the capillaries, these molecules are transported out of the capillary walls and into the nearest cells. Waste products are also removed from cells, transported through the wall of the capillaries and into the bloodstream. The wall of the capillaries are only one cell thick, allowing small molecules to easily pass in and out of them.
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Blood

• Blood that is pumped around the body is made up of red blood cells, white blood cells, platelets and plasma.
• Red blood cells carry oxygen from the lungs to the rest of the body. They have a very large surface area, allowing them to absorb many oxygen molecules.
• White blood cells defend the body against diseases.
• Platelets are tiny cell fragments that release substances that help blood clot.
• These are all produced by bone marrow.
• Plasma is a liquid that is mainly made up of water absorbed by the large intestine. It also contains important nutrients, waste products, hormones and other solutes.

Villi

• Villi have a network of capillaries very close to their surface. This allows for the quick absorption of glucose and amino acids into the bloodstream, as the distance they have to travel between the digestive system and the blood vessels is very short.
• The capillaries in the villi come together to form the hepatic portal vein. This is a blood vessel that carries blood from the small intestine to the liver.
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Glucose in the circulatory system

• Glucose is absorbed into the bloodstream through the capillaries which leads into the hepatic portal veins and into the liver.
• Most of the glucose molecules from the digestive system are only briefly stored in the liver before they leave this organ through a series of blood vessels called hepatic veins.
• Glucose molecules are then carried throughout the body via the circulatory system. They move into capillaries where they are transported to cells and used to produce energy.
• Any glucose molecules that remain in the liver are built up into complex molecules called glycogen. Glycogen is a form of glucose that can be stored by the liver. The body always needs a constant supply of glucose, but it can only be supplied by the small intestine once food has been consumed. To supply cells with the necessary glucose between meals, the liver converts stored glycogen back into glucose when it is needed. It is then transported out of the liver by hepatic veins to cells throughout the body.

Amino acids in the circulatory system

• The liver builds up amino acids from the digestive system into proteins that are used for processes such as immune and cell repair. These proteins are then transported to the cells that require them by the circulatory system. Any excess amino acids are destroyed by the liver, as they are unable to be stored.

Lacteal

• Villi also have a lacteal (lymph capillary) running down their center. This capillary absorbs glycerol molecules and fatty acids into the lymphatic system. The lymphatic system eventually empties into the circulatory system, where these molecules are taken to the liver by blood vessels.
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Fatty acids + glycerol in circulatory system

• In the liver, fatty acids and glycerol molecules are built up into complex fat molecules. They are then transported out of the liver to the body fat deposits by the circulatory system. These fat deposits are important, as they can be broken down and used for energy by the body if the body runs out of available glucose.

Circulation

• Without circulation, nutrients from the digestive system would not be able to be transported between the small intestine, the liver and the cells of the body. If the flow of blood through the body is too low, vital organs such as the brain and the liver may not get enough oxygen and nutrients. This may cause them to become permanently damaged. This is why a healthy circulatory system is so important.