Metabolisme Zat Besi

Summary

In this video, Ima, a nutrition student from Universitas Gadjah Mada, explains the process of iron metabolism in the human body. She covers the key stages: absorption, transport, storage, and excretion. Iron is vital for hemoglobin synthesis, which transports oxygen in the blood. The video details the forms of iron (heme and non-heme), their food sources, and how they are absorbed differently. It also explains how iron is stored in organs like the liver and macrophages and highlights the body's limited ability to excrete iron, making regulation crucial.

Takeaways

• 🩸 Iron is an essential microelement necessary for the human body, especially for synthesizing hemoglobin, which is crucial for oxygen transport in red blood cells.
• 🍖 Iron exists in two main dietary forms: heme (found in animal products) and non-heme (found in plant-based sources). Heme iron is in the ferro form, while non-heme iron is typically in the ferric form.
• 🍽️ The digestion of iron begins in the stomach by denaturing iron-binding proteins, and its absorption mainly occurs in the duodenum and proximal jejunum.
• 🔄 Non-heme iron requires metabolic conversion from the ferric to the ferro form via duodenal cytochrome B and ascorbic acid before it can be absorbed.
• 🚪 The absorption of non-heme iron into cells is facilitated by divalent metal transporter 1 (DMT1), which moves ferro iron into enterocytes.
• 🛡️ Inside the cells, ferro iron is either oxidized and stored as ferritin or transferred out of the enterocytes via ferroportin into the bloodstream.
• 🧬 In the bloodstream, ferro iron is oxidized to the ferric form and binds to transferrin, which distributes it throughout the body, including the liver and bone marrow.
• 🩺 The liver stores iron using ferritin and hemosiderin, and it plays a key role in regulating the body’s iron reserves, storing up to 20-30% of the body’s total iron.
• 🔋 Macrophages recycle iron from degraded red blood cells, storing it as ferritin or hemosiderin for future use.
• 🚰 The body does not have a regulated mechanism for iron excretion. It is lost through urine, feces, skin shedding, and menstrual blood, but the amount remains relatively constant.

Q & A

What is the role of iron in the human body?

Iron is essential for the formation of hemoglobin, which is a key protein in red blood cells responsible for transporting oxygen throughout the body. One-third of hemoglobin's weight consists of iron.

What are the two main forms of iron in the body?

Iron exists in two main forms: ferrous (Fe2+) and ferric (Fe3+). Ferrous iron is involved in transmembrane transport, ferritin storage, and heme synthesis, while ferric iron is typically found when bound to hemoglobin at high oxygen concentrations.

What are the dietary sources of heme and non-heme iron?

Heme iron, found in animal products like fish, beef, eggs, and cheese, is usually in the ferrous form. Non-heme iron, found in plant-based sources like broccoli, beans, spinach, corn, and bananas, is often in the ferric form.

Where does the digestion and absorption of iron occur in the body?

Iron digestion begins in the stomach, where proteins binding iron are denatured. Its absorption primarily occurs in the duodenum and proximal jejunum, with 10% of iron from heme sources and 90% from non-heme sources.

How is non-heme iron absorbed in the body?

Non-heme iron is initially in its ferric form (Fe3+), which needs to be reduced to ferrous form (Fe2+) by duodenal cytochrome B and apical membrane ferric reductase. It is then transported into enterocytes via the divalent metal transporter 1 (DMT1).

How is iron transported from the enterocytes into the bloodstream?

Ferrous iron (Fe2+) is oxidized back to ferric iron (Fe3+) by the enzyme hephaestin and is either stored as ferritin or transferred to the bloodstream by ferroportin 1. Once in the blood, ferric iron binds to transferrin for transport throughout the body.

What happens to iron when it reaches the liver?

In the liver, transferrin-bound iron binds to transferrin receptors and is internalized. Inside the liver cells, transferrin is degraded by lysosomes, releasing iron that can be stored as ferritin or hemosiderin.

How is iron used in erythropoiesis (red blood cell formation)?

Iron transported by transferrin can be delivered to the bone marrow, where it plays a critical role in erythropoiesis by being incorporated into hemoglobin in red blood cells.

What are the two main storage forms of iron in the body?

Iron is stored in two main forms: ferritin, which is stored in the cytosol, and hemosiderin, which is the result of ferritin metabolism. These stores are found primarily in the liver and macrophages.

How does the body excrete iron?

Unlike other minerals, iron excretion is not highly regulated. Small amounts are lost through urine (0.1-0.3 mg per day), skin shedding (0.2-1.2 mg per day), feces (10-15 mg), and menstrual blood (up to 42 mg per cycle).