Chapter 23: Disorders of Red Blood Cells – Causes and Symptoms

Welcome to Last Minute Lecture.

This free chapter overview is designed to help students review and understand key concepts.

These summaries supplement not replaced the original textbook and may not be redistributed or resold.

For complete coverage, always consult the official text.

Welcome to the Deep Dive.

Today we're diving into, well, a really critical area, Chapter 23 from Porth's Essentials, focusing on disorders of red blood cells.

Our mission, to break down how these vital cells work, how they fail, and how the body reacts, making some dense stuff digestible.

Exactly.

We want to give you the core concepts without you needing the textbook right in front of you.

We'll cover the basics of red cells and hemoglobin, blood types, and why matching is so crucial for transfusions, and then the big disorders, anemia and polycythemia.

Plus a quick look at how things change with age.

Okay, let's hit the scene.

The main job, the absolute primary function.

Hemoglobin inside red blood cells transports oxygen, lungs to tissues.

Simple, but so vital.

And they also help carry CO2 back and manage acid -base balance.

So starting with the cell itself, the structure, it's this non -nucleated biconcave disc, like a little flattened donut.

Why that specific shape?

What's the advantage?

It's really about efficiency.

That shape massively increases the surface area relative to the volume, allows for super rapid oxygen diffusion in and out.

And because it's so thin, the oxygen doesn't fart travel, but it's not just about getting oxygen across.

Right.

It's also a durability, isn't it?

These cells have a tough journey, squeezing through tiny capillaries.

How do they manage that without just falling apart?

That comes down to the cell membrane and its internal support structure.

It's surprisingly flexible.

There's this complex network of fibrous proteins just underneath the membrane.

The main ones are a spectrum and anchoring.

Think of it like a microscopic scaffolding.

Spectrum is anchored by anchoring and this whole setup gives the cell elasticity.

It can bend and twist to get through tech spots and then snap back into shape.

Spectrum and anchoring.

Okay, got it.

That's the key to their resilience.

Yeah.

Now inside that flexible container is the actual oxygen carrier, hemoglobin or HDB, four polypeptide chains, each with a heme unit containing iron.

You mentioned two main types normally found, HbA and HbF.

Yes, adult hemoglobin HbA and fetal hemoglobin HbF.

The crucial difference is their affinity for oxygen.

HbF binds oxygen much more tightly than HbA.

This is absolutely essential during pregnancy.

It allows the fetus to effectively pull oxygen from the mother's blood across the placenta.

Ah, so it ensures the baby gets enough oxygen even when the mother's oxygen levels might be slightly lower.

Precisely.

After birth, though, you don't need that high affinity anymore, so the body switches over.

HbF is gradually replaced by HbA, usually completed by about six months of age.

And central to hemoglobin is iron.

You can't make a meme without it.

How does the body handle its iron supply?

It seems like something you wouldn't want too much or too little of.

It's tightly regulated.

Most iron we need actually comes from recycling.

Old red blood cells get broken down, mainly in the spleen, and the iron is recovered and reused.

But we do absorb some from our diet, mostly in the duodenum, the first part of the small intestine.

And how does it travel around?

Where is it stored?

Once absorbed, it binds to a transport protein called transferrin that carries it in the blood.

For storage, it's mainly kept inside cells bound to another protein, ferritin, mostly in the liver.

So if you measure serum ferritin levels in a blood test, you're getting an idea of the body's total iron reserves.

Okay, that makes sense.

Let's shift to

erythropoiesis.

Making new red cells.

Where does this happen and what kicks it off?

It happens in the red bone marrow.

In adults, that's mainly in the flat bones, like the pelvis, vertebrae, ribs, sternum.

Stem cells differentiate into erythroblasts, which mature into red blood cells.

The key trigger, the regulator, is a hormone called erythropoietin, or EPO.

And what stimulates EPO release?

Tissue hytoxia, low oxygen levels.

Specialized cells in the kidneys sense when oxygen delivery drops.

They then release APO, which travels to the bone marrow and tells it to ramp up red cell production.

About 90 % of EPO comes from the kidneys.

Okay, so that's the direct link.

Kiddie problems mean potential EPO problems.

Exactly.

It's why severe anemia is such a common complication of chronic kidney failure.

The damaged kidneys just can't produce enough EPO.

So cells are made, they circulate for about 120 days,

then what?

Destruction time.

Right.

They get old, less flexible, and are eventually removed by phagocytic cells, mostly in the spleen and liver.

When the red cell is broken down, the hemoglobin is disassembled, the iron is recycled, as we said, the globin chains are broken down into amino acids, and the heme part that gets converted into bilirubin.

Bilirubin.

That's the stuff that can make you yell at, right?

Jaundice?

Yes, but there's a process.

Initially, the bilirubin is unconjugated.

It's not water soluble, it has to bind to albumin to travel in the plasma.

The liver picks it up, attaches glucuronic acid to it, that's conjugation, making it water soluble.

This conjugated bilirubin is then excreted into the bile and eliminated.

So, John, this happens when...

Either when there's excessive red cell breakdown overwhelming the liver's capacity to conjugate, or when the liver itself isn't working properly, or if the bile ducts are blocked.

It's the buildup of unconjugated bilirubin in the blood that causes the yellow discoloration of the skin and eyes.

Okay, before we move into disorders, let's quickly touch on the lab test.

The sort of quick reference guy, what are the key ones?

Well, first you want to know if the factory is working.

That's the reticulocyte count.

Reticulocytes are immature red cells just released from the marrow.

Normally, they make up about 1 to 1 .5 % of total red cells.

A high count means the marrow is churning out cells.

A low count suggests a production problem.

Got it.

Production rate.

What else?

Hematocrit, or HCT,

that's the percentage of blood volume occupied by red blood cells.

So if your HCT is 45%, it means 45 milliliters out of every 100 milliliters of blood are red cells.

One key thing to remember here, dehydration can artificially raise the hematocrit because the plasma volume decreases, concentrating the cells.

Good point.

So HCT reflects concentration.

And the last piece, the indices.

Yes, the red cell indices.

These tell you about the characteristics of the average red cell.

I mean corpuscular volume, or MCV, measures the average size.

Are the cells too small, microcytic, too large, macrocytic, or normal, normacytic?

And the other one.

Mean corpuscular hemoglobin concentration, or MCHC.

This measures the concentration of hemoglobin within the cell, basically its color.

Are the cells pale, hypochromic, because they don't have enough hemoglobin, or are they normal, normachromic?

These indices, MCV and MCHC, are crucial for classifying different types of anemia.

Okay, that's a solid foundation on the cell itself.

Now let's talk about putting cells into someone.

Transfusion therapy.

This feels like high stakes territory.

Compatibility is everything.

Absolutely critical.

Mistakes here can be fatal.

The two main blood group systems you have to match are ABO and RH.

The ABO system depends on whether you have A antigens, B antigens, both, or neither, typo, on your red cells.

And the really important thing about ABO is the antibodies, right?

Yes.

Unlike many other antibody systems, the ABO antibodies develop spontaneously.

If you don't have the A antigen, your body naturally produces anti -A antibodies a few months after birth.

Same for B.

So, typo people have both anti -A and anti -B antibodies.

Type AB people have neither.

This is why careful matching is essential.

Okay, so ABO antibodies are natural.

What about RH?

That's the positive negative part.

Right.

RH status depends mainly on the presence or absence of the D antigen.

If you have it, you're RH positive.

If not, you're RH negative.

But here's the key difference from ABO.

RH antibodies, specifically anti -D, only develop after exposure.

Exposure meaning?

Usually through pregnancy if an RH negative mother carries an RH positive fetus or through an incompatible blood transfusion.

So, a first time exposure might sensitize the person, but a second exposure could cause a major reaction.

And if you do get incompatible blood, especially an ABO mismatch, what happens?

That leads to an acute hemolytic transfusion reaction, or AHTR.

It's a medical emergency.

The recipient's antibodies rapidly attack and destroy the donor red cells right in the blood stream.

What's the most immediate life -threatening consequence of that massive sudden hemolysis?

Renal failure.

Kidney damage.

All the hemoglobin released from the destroyed cells floods the kidneys.

It can block the tubules and cause acute kidney injury, sometimes leading to complete shutdown or oliguria.

It's incredibly serious.

Beyond AHTR, what are other major transfusion risks?

I know fluid overload is one.

Yes, transfusion -associated circulatory overload, or TACO.

This happens more often in patients who already have heart or kidney problems and can't handle the extra fluid volume from the transfusion.

They basically go into heart failure, showing signs like respiratory distress.

And there's another lung -related one that's even more dangerous.

That's transfusion -related acute lung injury, or TRALI.

This is actually the leading cause of transfusion -related death.

It's thought to be an immune reaction, possibly involving antibodies in the donor plasma reacting with the recipient's white blood cells.

It causes sudden severe lung inflammation, pulmonary edema, and profound hypoxemia, usually within six hours of the transfusion.

It's fatal in maybe 10 to 20 percent of cases.

Wow.

Okay, so transfusion safety is paramount.

Let's move to the core disorders now.

Starting with the most common issue, anemia.

Right.

And the first thing to stress is that anemia isn't really a disease itself.

It's a sign, a manifestation, that something else is wrong.

The basic definition is a low level of either red blood cells or hemoglobin, which results in diminished oxygen -carrying capacity.

And the symptoms generally reflect that lack of oxygen, don't they?

Exactly.

You see fatigue, weakness.

People get short of breath easily, dyspnea.

They might look pale, pallor, because there's less hemoglobin and blood gets shunted away from the skin.

And the heart often tries to compensate by beating faster, leading to tachycardia.

Okay.

Let's break down the causes.

First, blood loss anemia.

How does acute loss differ from chronic loss in terms of the anemia itself?

Acute blood loss, like from trauma, is primarily a problem of volume loss leading to shock.

The red cells that remain are initially normal in size and color, normacytic, normochromic, because the bone marrow hasn't had time to change production.

But chronic loss is different.

Yes.

Slow, persistent bleeding, maybe from a GI ulcer or heavy menstruation, gradually depletes the body's iron stores.

Without enough iron, the bone marrow can't make enough hemoglobin.

So it starts producing smaller cells with less hemoglobin.

That gives you the classic microcytic, hypochromic anemia characteristic of iron deficiency.

Okay.

What about anemias caused by destruction?

Hemolytic anemias.

The cells are being destroyed too early.

Right.

The hallmark is premature disruption of red cells.

Because they're breaking down, iron is actually retained in the body and the bone marrow cranks up production.

You see increased erythropoiesis, lots of reticulocytes.

A classic inherited example is sickle cell disease.

Sickle cell.

What's the fundamental problem there?

It's an inherited disorder caused by a single mutation in the gene for the beta globin chain hemoglobin.

This results in hemoglobin S or HBS.

The key issue is that when HBS gives up its oxygen, it changes shape and tends to polymerize, forming long rigid rods inside the red cell.

This forces the cell into that characteristic crescent or sickle shape.

And what are the consequences of that sickling?

Two major things.

First, the sickled cells are fragile and easily destroyed, leading to chronic hemolytic anemia.

Second, and often more devastating, these rigid cells can't squeeze through capillaries, they get stuck blocking blood flow.

This causes vaso -occlusive crises, episodes of severe pain, organ damage due to lack of oxygen, and potentially life -threatening events like acute chest syndrome.

Another inherited type is thalassemia.

How is that different from sickle cell?

Thalassemias are also inherited defects in hemoglobin, but instead of a structural change like in HBS, they involve deficient production of either the alpha or beta globin chains.

So it's a quantitative problem.

What happens when you don't make enough of one chain?

You get an imbalance.

The red cells are small and pale, microcytic, hypochromic, because there isn't enough normal hemoglobin being made.

Plus, the globin chain that is being produced normally accumulates in excess.

These excess chains are unstable, they precipitate within the cell, damage the membrane, and lead to premature destruction in the bone marrow or spleen.

Are some forms worse than others?

Oh yes.

It ranges from mild asymptomatic forms to severe transfusion -dependent types like beta thalassemia major, also known as Cooley anemia.

These individuals have severe anemia,

massive bone marrow expansion trying to compensate, which can cause bone deformities, and a huge problem with iron overload from all the necessary transfusions.

Okay, let's shift from destruction back to problems with production.

Anemias of deficient red cell production, the most common one worldwide.

Iron deficiency anemia, or IDA, we mentioned it stems from chronic blood loss, especially in Western adults, or inadequate dietary intake, which is more common globally.

The cells are microcytic, hypochromic.

Are there any unique signs that might point specifically to iron deficiency beyond just general anemia symptoms?

Sometimes, yes.

Too classic, though not always present, signs are pica, this unusual craving to eat non -food substances like ice, clay, or dirt in koala anechia, where the fingernails become thin, brittle, and spoon -shaped.

Interesting.

Okay, next category.

Megaloblastic anemias.

What defines these?

Megalo means large.

These anemias are characterized by abnormally large red blood cells, a high MCV.

The underlying problem is impaired DNA synthesis, which affects rapidly dividing cells, including those in the bone marrow.

The cells grow large, but division is delayed.

This usually points to a deficiency in either vitamin B12 or folic acid.

Right, B12 and folic acid.

They often get grouped together, but there's a critical difference in the consequences of deficiency, isn't there?

Let's start with B12.

Yes.

This distinction is super important clinically.

Vitamin B12 absorption is complex.

It needs something called intrinsic factor, or IF, which is secreted by parietal cells in the stomach lining.

EF binds to B12 and allows it to be absorbed later in the small intestine.

If the stomach fails to produce IF, often due to autoimmune attack on those parietal cells, you get pernicious anemia.

And the absolutely key differentiator for B12 deficiency, especially pernicious anemia.

The neurologic complications.

This is unique to B12 deficiency.

Lack of B12 affects myelin maintenance in the nervous system.

So patients can develop symptoms like numbness and tingling in the extremities, paresthesias, difficulty with balance, loss of position sense, things you do not see with folate deficiency.

So if you see megaloblastic anemia plus neurological symptoms, you have to think B12 deficiency.

Absolutely.

Folic acid deficiency causes the exact same large red cells, the same megaloblastic changes in the bone marrow, but no neurologic problems.

Folic acid deficiency is common in situations of increased need, like pregnancy, which is why supplementation is routine to prevent neural tube defects or with poor diet or certain medications.

Okay, what about when the whole factory shuts down?

A plastic anemia.

A plastic anemia is scary.

It's a failure of the pluripotent stem cells in the bone marrow, the ones that give rise to all blood cell lines.

So you end up with pancetopenia, low red cells, anemia, low white cells, leukopenia, specifically neutropenia, increasing infection risk, and low platelets, thrombocytopenia, leading to bleeding, bruising, petechia.

What causes that kind of complete marrow failure?

It can be caused by exposure to toxins, radiation, certain drugs, viral infections like hepatitis, or sometimes it's an autoimmune attack where the body's own immune system destroys the stem cells.

Treatment often involves bone marrow transplant or immunosuppressive therapy.

And one last production related category, anemia is linked to other ongoing health issues.

Right, anemia of chronic disease.

This is very common in people with chronic infections, inflammation, like rheumatoid arthritis, or cancer.

The mechanisms are complex, involving inflammatory cytokines that suppress red cell production and interfere with iron metabolism.

But a particularly important subtype is the anemia seen in chronic renal failure.

And that brings us back full circle, doesn't it?

It does.

As we said, the kidneys make most of the EPO.

In chronic kidney disease, EPO production falls off dramatically, leading directly to insufficient red cell production and often severe anemia.

Okay, we've covered too few pretty thoroughly.

Let's flip to the other side.

Cholecythemia, too many red blood cells.

What's the main danger here?

The main problem is increased blood viscosity.

The blood becomes too thick, too sludgy.

This increases the workload on the heart and raises the risk of circulatory problems like hypertension and blood clots.

Generally, we define it as a hematocrit consistently above 54 % in men or 49 % in women.

Is it always a disease process?

Not necessarily.

You can have relative polycythemia.

This isn't actually an increase in red cells.

It's a decrease in plasma volume, usually due to dehydration.

The wet cells become more concentrated so the HCT goes up, rehydrate the person, and the HCT returns to normal.

Okay, so that's relative.

What about a true increase in red cell mass?

Absolute polycythemia.

There are two main types here.

Primary polycythemia, also called polycythemia vira, is a neoplastic disease.

It's essentially a cancer of the bone marrow stem cells.

These cells overproduce red blood cells uncontrollably, often along with increased white cells and platelets, too.

And what does that look like clinically?

Symptoms are related to the increased blood volume and viscosity.

Headaches, dizziness, high blood pressure.

Patients often have a characteristic ruddy, reddish -purple complexion, especially on the face, hands, feet, called a plethoric appearance.

Because platelet counts can also be high and function abnormally, they might have issues with both clotting and bleeding.

Treatment usually involves periodic therapeutic phlebotomy,

basically, removing blood to reduce the cell mass and viscosity.

Okay, that's primary.

The marrow itself is the problem.

What's secondary absolute polycythemia?

Secondary polycythemia is different.

It's not a marrow disease.

It's an appropriate compensatory response by the body to chronic hypoxia or low oxygen levels.

So the body's trying to fix a problem.

Exactly.

If the tissues aren't getting enough oxygen over a long period, maybe because someone lives at high altitude, has chronic lung disease like COPD, severe heart disease, or even smokes heavily, carbon monoxide reduces oxygen carriage,

the kidneys sense this hypoxia.

They respond by producing more erythropoietin.

The increased EPO then stimulates the bone marrow to make more red cells to try and improve oxygen delivery.

It's the body doing what it's supposed to do in response to low oxygen.

That makes sense.

All right, to wrap up our journey through red cells, let's briefly touch on age -related changes.

Neonates first.

Newborns have quite high hemoglobin levels at birth, largely composed of that high affinity HbF we talked about.

As HbF gets replaced by HbA and red cell turnover is high, their HgB levels normally drop, reaching a low point around two months of age, sometimes called physiologic anemia of infancy.

Also, their liver's ability to conjugate bilirubin isn't fully mature yet.

And that ties into jaundice, right?

Yes.

The combination of increased red cell breakdown, switching from HbF to HbA, and the immature liver conjugation system means many newborns develop physiologic jaundice, usually mild and resolves on its own.

But the danger is if the unconjugated bilirubin level gets too high.

Why is unconjugated bilirubin the dangerous one in babies?

Because it's lipid soluble.

In infants, the blood -brain barrier is not fully developed yet.

High levels of unconjugated bilirubin can cross this barrier and deposit in the brain tissue, particularly the basal ganglia.

This causes permanent neurological damage known as cornectoris.

It's a devastating outcome.

Which is why monitoring bilirubin levels and using phototherapy is so important.

Exactly.

Phototherapy uses specific wavelengths of light that penetrate the skin and convert the unconjugated bilirubin into water -soluble isomers that the baby can excrete without needing liver conjugation.

It's a simple but effective way to prevent cornectoris.

In severe cases, an exchange transfusion might be needed.

Okay, and shifting to the other end of the spectrum.

Older adults.

What are the key considerations there?

Anemia becomes much more common with aging.

While baseline HGB levels might be maintained reasonably well in healthy older adults, their reserve capacity diminishes.

The bone marrow just doesn't respond as robustly or quickly to stimuli like blood loss or inflammation compared to a younger person.

So they're more vulnerable when things go wrong.

Precisely.

An older adult facing a stressor like surgery, infection, or chronic illness is much more likely to develop significant anemia, and it might take them longer to recover simply because their red cell replacement machinery isn't as efficient as it used to be.

So we've really covered the whole life cycle, haven't we?

From the incredible design of the red cell itself, the constant balancing act of production and destruction, the absolute necessity of getting transfusions right, and then the consequences when things go wrong, either too few cells in anemia or too many in polycythemia.

It's quite a journey.

And thinking about that final provocative thought,

you mentioned the spectrum anchoring network earlier, the scaffolding giving the red cell its flexibility.

Would you consider inherited disorders where that network is defective, like hereditary spherocytosis, where cells become rigid spheres?

Yeah, they get trapped and destroyed in the spleen simply because they can't deform properly.

It really highlights how something so microscopic, that loss of simple mechanical flexibility in a single cell type, has such profound consequences for the entire organism's ability to get oxygen.

The link between basic cell structure and systemic health is just unavoidable, isn't it?

Absolutely.

It's a perfect example of how cellular pathophysiology impacts the whole person.

Well, hopefully this deep dive has helped clarify some of these complex processes for you.

Thanks for joining us.

Yes, we hope this breakdown of Chapter 23 makes things clearer and maybe even a bit less daunting for your studies.

Thanks for listening and we'll catch you on the next deep dive from the Last Minute Lecture Team.