Iron deficiency anemia

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Introduction0:00–0:20

Anemia is a condition where there’s a decrease in the number of healthy red blood cells, or RBCs, in the body. So, iron deficiency anemia means anemia caused by a deficiency in iron.
Iron deficiency anemia is also the most common type of anemia worldwide. If we take a close look at our red blood cells, we’ll notice that they’re loaded with millions of copies of the same exact protein called hemoglobin, which binds to oxygen and turns our blood cells into little oxygen transporters, and basically allow us to move oxygen to all the tissues in our body.

Physiology0:20–1:41

If we take an even closer look at those hemoglobin proteins, we’ll find that they’re made of four heme molecules, which have, right in the middle, iron.
This iron molecule is what binds to oxygen, so each hemoglobin molecule can bind four molecules of oxygen. In addition, iron is also an important part of proteins like myoglobin, which delivers and stores oxygen in muscles; and mitochondrial enzymes like cytochrome oxidase, which help generate ATP.
Normally, when a red blood cell dies, some iron is recycled from it. But, we also lose about 1 milligram of iron every day - some through the sweat, some in shedded skin cells, and some in shedded cells in the gastrointestinal tract, which get out of the body through feces.
But most of us take in 10-20 mg of dietary iron every day, and absorb about 10% of it, or about 1 or 2 milligrams - so it all evens out at the end of the day!

Iron Metabolism1:41–3:12

Now, our diet contains two forms of iron. The first is heme iron, or iron bound to hemoglobin or myoglobin, which comes from animal products like meat.
Heme iron is in the ferrous, or Fe2+, state. The other form is non-heme iron, which is free iron molecules in the ferric, or Fe3+, state.
Non-heme iron comes from plant based foods like spinach and beans. Now, when food is broken down in the stomach, iron is released.
Heme iron is absorbed directly into the duodenal cells, where it is broken down to release Fe2+ molecules. Non-heme iron, however, needs to be reduced to heme iron first.
So the stomach’s hydrochloric acid activates a group of enzymes in the duodenal cells, collectively called ferri-reductase, which live up to their name by reducing non-heme iron to Fe2+ molecules.
Fe2+ molecules then bind to a protein in the duodenal cells called ferritin, which temporarily stores the iron. And when iron is needed in the body, some Fe2+ molecules are released from ferritin and transported into the blood, where the enzyme hephaestin converts them back to the Fe3+ state.
Fe3+ molecules then bind to an iron transport protein called transferrin that carries iron to various target tissues and releases them there.
Fe3+ enters these various tissue cells, where there’s some more ferritin that can store them for future use. Iron deficiency anemia can develop as a result of four main causes: decreased intake, decreased absorption, increased demand, and increased loss.

Causes3:12–5:14

Decreased intake is the most common cause of iron deficiency anemia worldwide, and it occurs in infants, because breast milk is surprisingly low in iron; and vegetarians, whose iron intake is mostly nonheme iron, which is harder to absorb.
Decreased absorption can also occur when there’s a decrease in stomach acid production, like after a gastrectomy, where a part of the stomach is surgically removed.
Finally, decreased absorption may occur with inflammatory bowel disease or celiac disease, both of which cause inflammation and destruction of duodenal cells.
Next up, increased demand can occur in children and adolescents due to rapid growth and increase in blood volume, which requires them to make more hemoglobin.
Alternatively, it may occur during pregnancy, due to increased iron requirements for fetal development. Finally, increased iron loss generally occurs in people with chronic slow bleeding, because iron is lost along red blood cells.
This includes females with frequent or heavy menstruation or people with bleeding gastric ulcers, and, most importantly, elderly males with colon cancer, because the tumor can bleed and cause anemia.
In fact, the first symptom of colon cancer is often iron deficiency anemia. Another cause of iron deficiency is a Helicobacter pylori infection, which classically causes gastric ulcers and gastrointestinal bleeding.
This bacteria also traps dietary iron for itself, preventing it from even reaching the duodenum. Finally, in developing countries, a common cause of blood loss is hookworms.
These worms latch on to the intestines and suck out the blood. Yikes!

Pathology5:14–6:25

Now, regardless of the cause, iron deficiency leads to impaired hemoglobin production. Since there’s not enough hemoglobin for a normal sized RBC, the bone marrow starts pumping out microcytic, or smaller, RBCs.
These cells containing less hemoglobin are called hypochromic, since they appear pale. Therefore, iron deficiency anemia is also called microcytic hypochromic anemia.
Okay, so besides being puny, these microcytic RBCs can’t carry enough oxygen to the tissues, and this is called hypoxia.
Hypoxia signals the bone marrow to increase RBC production. And when even that increase doesn’t help, the bone marrow kinda goes into overdrive and pumps out incompletely formed RBCs.
As a result, red blood cells of various shapes, called poikilocytosis, and sizes, called anisocytosis, enter the circulation.
In addition to anemia, iron deficiency also results in defective production of mitochondrial enzymes that generate necessary ATP for growth and development, and this affects fast growing tissues, like hair and nails, the most.

Signs and Symptoms6:25–7:08

Iron deficiency anemia presents with typical signs and symptoms of anemia like pallor, palpitations, shortness of breath, and easy fatigability.
Specific symptoms for iron deficiency include koilonychia, or spooning of nails; hair loss; and pica, which is consumption of non-food substances like clay or dirt.
Sometimes iron deficiency anemia may occur in the context of Plummer-Vinson syndrome, along with glossitis, meaning inflammation of the tongue, and esophageal webs, which are membranes made up of damaged esophageal epithelium and mucosa.

Diagnosis7:08–7:58

Anemia is diagnosed using a couple of parameters in the blood. First, there are decreased hemoglobin levels, typically below 13.5 g/dL in males and below 12.0 g/dL in females.
But those numbers can differ based on which guidelines you’re using. Next, the mean corpuscular volume or MCV, is decreased - this reflects the volume of an RBC.
There’s also low serum iron, low ferritin, and a high TIBC, or total iron binding capacity. TIBC indicates the amount of unbound transferrin in the blood.
There’s also a high red blood cell distribution width, or RDW, which indicates that RBCs come in a lot of different sizes, and a peripheral blood smear shows microcytic and hypochromic RBCs.

Treatment7:58–8:30

Treatment for iron deficiency anemia includes addressing the cause and giving oral iron supplements, like ferrous sulfate.
They can be taken with orange juice, which is slightly acidic and can help absorption. Common side effects of oral iron include nausea, diarrhea, and constipation.
If oral iron isn’t effective, or the side effects can’t be tolerated, intravenous iron can be used instead. Severe cases may also require a blood transfusion.

Summary8:30–9:14

All right, as a quick recap… Iron deficiency anemia is a type of microcytic hypochromic anemia caused due to a decrease in the body’s iron stores.
It can be caused by decreased intake, which is seen in infants and vegetarians, by decreased absorption due to decreased hydrochloric acid production or a duodenal disorder, by increased demand which is seen in children, adolescents, and pregnant females; and increased loss in case of females with frequent or heavy menstruation, bleeding gastric ulcers, and colon cancer.
Treatment involves oral or intravenous iron supplements, or blood transfusion in severe cases.