When food is digested, it is absorbed into the blood from the small intestine walls. From there the blood is drained into the hepatic portal vein. The hepatic portal vein then goes to the liver. The blood in this vein is very rich in nutrients. If it was allowed to drain into the main blood stream directly, these large amounts of nutrients would disrupt the osmotic and chemical balance of the blood and tissues.
In the liver, excess substances are removed and stored for further use. Toxic compounds like alcohol and drugs are also metabolized and converted into harmless compounds that can then be excreted from the body.
After the liver is done, the nutrients, in a correct amount, enter the main blood stream. From here they flow in the blood to the heart. The heart oxygenates this blood and returns it to the circulatory system. Blood flows into arteries and from these into capillaries in the tissues. This brings the blood in contact with the cells.
Now, the cells can take up the nutrients. The manner in which cells take up a nutrient depends on the nature of the nutrient. Some may flow into the cell down their concentration gradient, others might need to use carrier proteins. Some substances like glucose require active transport to be taken up (by the action of insulin on gated protein channels).
So the route of food to the cells is:
Stomach ---> Small intestines ---> Hepatic portal vein ---> Liver ---> Blood stream (vein) ---> vena cava ---> heart ---> aorta ---> arteries ---> capillaries ---> tissue ---> cells
In the liver, excess substances are removed and stored for further use. Toxic compounds like alcohol and drugs are also metabolized and converted into harmless compounds that can then be excreted from the body.
After the liver is done, the nutrients, in a correct amount, enter the main blood stream. From here they flow in the blood to the heart. The heart oxygenates this blood and returns it to the circulatory system. Blood flows into arteries and from these into capillaries in the tissues. This brings the blood in contact with the cells.
Now, the cells can take up the nutrients. The manner in which cells take up a nutrient depends on the nature of the nutrient. Some may flow into the cell down their concentration gradient, others might need to use carrier proteins. Some substances like glucose require active transport to be taken up (by the action of insulin on gated protein channels).
So the route of food to the cells is:
Stomach ---> Small intestines ---> Hepatic portal vein ---> Liver ---> Blood stream (vein) ---> vena cava ---> heart ---> aorta ---> arteries ---> capillaries ---> tissue ---> cells
