Know and eat more delicious nutrients. [영양소 탐험]provides an easy-to-understand explanation of how essential nutrients essential for our body work through which processes in the human body, along with nutritionist Yoon Seong-won, a nutrition consultant at Hidak.
The food we eat is digested in the stomach and mostly absorbed in the small intestine. No matter how much you eat, nutrients must be well absorbed in the small intestine to function properly. The same goes for calcium. In particular, calcium ingested from food is easily absorbed in an acidic state, so absorption occurs well in the duodenum and jejunum with high acidity. There are two methods of absorption of calcium, ‘passive diffusion’ and ‘active transport’, and which method is selected depends on the calcium content in the diet. Let’s follow the process through which calcium is absorbed in our body.
What is the absorption process by which nutrients move, passive diffusion & active transport?
It is a natural phenomenon that substances move from a place of high concentration to a place of low concentration. Passive diffusion is the spontaneous diffusion of matter without any effort to move. It passes through the cell membrane from a high concentration to a low concentration through the cell membrane. Passive diffusion does not require energy because it occurs spontaneously according to concentration differences.
Conversely, energy is required to move from a low concentration to a high concentration. It’s like we have to work hard to climb a steep incline. Active transport is to reverse the flow according to the concentration difference of the aforementioned passive diffusion and to allow a substance with a low concentration to pass through the cell membrane using energy (ATP). Active transport plays an important role in nutrient absorption in the stomach and maintenance of ion concentration in the cytoplasm.
When the calcium content in the meal is high enough, calcium is absorbed from the small intestine by passive diffusion. On the other hand, when calcium content is low, it is transported through active transport. At this time, it is affected by calcitriol, an active vitamin D, and VDR, a vitamin D receptor. Therefore, vitamin D deficiency results in inhibition of calcium absorption.
‘Passive diffusion’ when the calcium content in the meal is high
When the amount of calcium ingested is large, calcium, which was present in the form of insoluble salts in food, meets gastric acid in gastric juice, is liberated as an ionic state (Ca2+), and goes down to the small intestine. Passive diffusion absorption of calcium is the process of passing between the cells of the small intestine in the jejunum and the ileum and being absorbed into the blood.
‘Active transport’ when calcium content is low in a meal
Calcium intake is low when calcium intake is less than 400 mg per day. At this time, calcium is absorbed by active transport. Active transport takes place in the duodenum and upper jejunum and, unlike passive diffusion, requires energy, where calcium binding proein carrier (CaBP) is involved.
First, calcium that has passed through the cell membrane by binding to a receptor in the chorionic cell membrane of the small intestine binds to calbindin-D, a protein that transports calcium, and moves toward the serous membrane within the cell. At this time, calbindin-D is a calcium transport protein produced by binding calcitriol (active vitamin D) to VDR and moving to the nucleus. Calcium that has passed through the cytoplasm of the small intestine cells is delivered to the calcium pump, and following passing through the serous membrane using energy, it is absorbed into the blood.
It is known that the absorption rate of calcium increases when the intake is low, but the amount is not enough to offset the insufficient intake and there is a certain level limit. Therefore, it is dangerous to think that a small amount of calcium will be okay.
Help = Hydak Nutrition Counseling Seongwon Yoon (nutritionist)