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What Is Pernicious Anemia? - The Loss of Intrinsic Factor

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  • 0:35 What Is Intrinsic Factor?
  • 1:32 How is Vitamin B12 Absorbed?
  • 2:53 What Is Pernicious Anemia?
  • 4:32 Signs, Symptoms & Diagnostics
  • 6:09 Schilling Test & Treatment
  • 9:10 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will describe pernicious anemia. We'll first describe how vitamin B12 is normally absorbed and then what can go wrong, how it can be diagnosed, and treated.

Small Factors Causing a Big Problem

One little factor can sometimes make all the difference in life. If you're a fan of watching those police chase videos, you know how just one little wrong decision could truly spell disaster for drivers or pedestrians.

This lesson will go over one little factor so small that you can't even see it. Despite the factor's size, it is capable of causing big problems. In fact, the lack of this factor, as opposed to its presence, has killed others before due to a condition known as pernicious anemia.

What Is Intrinsic Factor?

Your stomach is obviously an important organ for digestion. You know that it helps to secrete acid that kills potentially deadly bacteria found in your food. The acid also helps to break down the food for better absorption.

The acid produced in the stomach is made by cells called parietal cells. Parietal cells are cells of the stomach that secrete gastric acid.

What's more important for this lesson is that parietal cells also secrete something known as intrinsic factor (IF). Intrinsic factor is a protein that binds vitamin B12 so that the terminal ileum can absorb it into the body. Vitamin B12 is also known as cobalamin, and the terminal ileum is the last segment of your small intestines.

An interesting side note that may help you remember the technical name for vitamin B12: the reason that vitamin B12 is called cobalamin is because it has the mineral cobalt in it.

How Is Vitamin B12 Absorbed?

Anyways, cobalamin is mainly obtained in our diets from animal products, such as meat and milk.

When you are chewing on your favorite piece of steak, your saliva releases all sorts of things that help to lubricate and digest the food in your mouth. One of the proteins released by your saliva is known as the R protein. This protein, along with your tasty piece of meat, travels into your stomach as you swallow your food.

Here, your stomach acid and enzymes (proteins that increase the speed of biochemical reactions) release cobalamin from its protein source. Once cobalamin is released in the stomach, the R protein binds it right there and then. This R protein-cobalamin combination then moves into the duodenum, the first part of the small intestines. Here, pancreatic enzymes secreted into the duodenum free cobalamin from the R protein. Thereafter, the IF originally produced in the stomach finally binds the cobalamin. This IF-cobalamin combination travels from the duodenum and into the ileum, where it is then absorbed into the body.

What Is Pernicious Anemia?

Any defect in this long sequence of events can lead to inadequate absorption of vitamin B12. The one I want to focus on in this lesson is a disease called pernicious anemia. Pernicious anemia is an autoimmune disease that attacks parietal cells and intrinsic factor, causing cobalamin malabsorption and subsequent anemia.

The problem in people with pernicious anemia is that your own body produces autoantibodies that target and destroy parietal cells.

Normal antibodies are fired, in a manner of speaking, by your immune system to kill off invading pathogens, such as bacteria. If they attack your own body's cells due to a malfunction, they are called autoantibodies.

Autoantibodies are proteins that attack their own master, so to speak. It's like a gun that fires a bullet but the bullet, like a boomerang, comes back to hurt the person who fired the gun.

In our case, these autoantibodies destroy, damage, or incapacitate the parietal cells of the stomach, just like a bullet would incapacitate someone. In any case, not enough IF is secreted in pernicious anemia. Logically, this means not enough cobalamin will be absorbed.

Another problem is that some autoantibodies simply bind and neutralize intrinsic factor instead - meaning these autoantibodies bind the IF, and this blocks intrinsic factor's ability to bind cobalamin. Imagine if someone glued your hands to a basketball. That sticky basketball is like an autoantibody. If this happens, your hands are stuck and unable to bind or catch anything else.

Signs, Symptoms, and Diagnostics

The problem is, cobalamin is important for many things, including proper red blood cell formation, DNA synthesis, and proper neurological function. Therefore, its deficiency can cause some serious issues.

In pernicious anemia, a CBC, or complete blood count, will reveal macrocytic anemia. Anemia is a condition where, as a result of decreased numbers of red blood cells or hemoglobin, oxygen carrying capacity of the blood is diminished, leading to inadequate oxygen delivery to body tissues, organs, and cells.

'Macrocytic' refers to the abnormally increased size of red blood cells in macrocytic anemias as a result of improper DNA synthesis. This impaired DNA synthesis also causes an abnormal decrease in white blood cells, called leukopenia, with odd-looking shapes in their nuclei.

On physical exam, a person with pernicious anemia may have paleness of the skin, weakness, and a red, thick, and sore tongue, as well as paresthesia, the sensation of pins and needles as a result of nerve dysfunction. Mood changes, memory loss, and depression can occur in serious cases as well.

An endoscopic examination with biopsy may reveal atrophic gastritis, the inflammation and destruction of the stomach due to an autoimmune disease. A biopsy is basically like a little bite or sample taken out of your stomach with some instruments. Just like you took a bite out of your favorite food in order to get some much-needed vitamin B12, we can take little bites of our own tissues to help diagnose disease.

Schilling Test and Treatment

Another important test to be aware of is called the Schilling test. In the first part of this test, non-radioactive vitamin B12 is injected into the patient in order to saturate the patient's receptors with vitamin B12. After this, a radioactive dose of cobalamin is given to the patient. It's radioactive so it can be easily tracked.

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