A&P II: CHAPTER 18.3 Erythrocytes

What are erythrocytes?

Red blood cells (RBCs), the most abundant formed elements in blood

What is the primary function of erythrocytes?

To deliver oxygen from the lungs to body tissues and help transport carbon dioxide from tissues to the lungs.

About how many erythrocytes are found per microliter of blood in males?

Approximately 5.4 million RBCs per µL.

About how many erythrocytes are found per microliter of blood in females?

Approximately 4.8 million RBCs per µL.

What is the approximate diameter of an erythrocyte?

About 7 to 8 µm.

What is the shape of a mature erythrocyte?

A biconcave disc: thickest around the rim and thin in the center.

Why is the biconcave shape of an RBC important?

It increases surface area for gas exchange, decreases diffusion distance, and leaves more internal space for hemoglobin.

What is one advantage of erythrocyte flexibility?

It allows RBCs to bend or fold through very narrow capillaries and then return to their usual shape.

What structural protein helps give RBCs flexibility?

Spectrin.

What is a rouleaux?

A stack of red blood cells that resembles a roll of coins, often seen when RBCs are in wider blood vessels.

Do mature erythrocytes have a nucleus?

No. Mature RBCs eject their nucleus during development.

Do mature erythrocytes have mitochondria?

No. They lack mitochondria and therefore do not use the oxygen they carry for aerobic respiration.

Why is the lack of mitochondria advantageous for RBCs?

They rely on anaerobic metabolism and do not consume the oxygen they transport to tissues.

Can mature erythrocytes synthesize new proteins?

No. They lack a nucleus and endoplasmic reticulum, so they cannot make significant new proteins.

What percentage of carbon dioxide produced by tissues is carried by erythrocytes?

Approximately 23 to 24 percent binds to hemoglobin; most of the remaining carbon dioxide is transported in plasma as bicarbonate.

How long does a typical erythrocyte circulate?

Up to about 120 days.

Where are erythrocytes produced?

Primarily in red bone marrow.

Approximately how many erythrocytes are produced each second?

More than 2 million RBCs per second.

What is erythropoiesis?

The production of erythrocytes (red blood cells).

What is the lineage pathway for erythrocyte production?

Hematopoietic stem cell → myeloid stem cell → erythrocyte precursors → reticulocyte → mature erythrocyte.

What is a reticulocyte?

An immature erythrocyte recently released from bone marrow that still contains traces of ribosomal material and other organelles.

How long do reticulocytes usually remain immature after entering circulation?

Approximately 1 to 2 days.

What percentage of circulating RBCs are normally reticulocytes?

About 1 to 2 percent.

Why is reticulocyte count clinically useful?

It indicates the rate of RBC production by bone marrow.

What can a low reticulocyte count suggest?

Inadequate erythrocyte production by the bone marrow.

What can a high reticulocyte count suggest?

Increased marrow response, often after blood loss or increased RBC destruction.

What hormone primarily stimulates erythrocyte production?

Erythropoietin (EPO).

Where is erythropoietin produced?

Mainly by interstitial fibroblast cells in the kidneys.

What is the primary trigger for erythropoietin secretion?

Low blood oxygen levels.

Describe the EPO negative-feedback loop.

Low oxygen stimulates kidney EPO release; EPO increases RBC production; improved oxygen delivery reduces the stimulus for EPO release.

How does high altitude affect erythropoiesis?

Lower oxygen availability stimulates EPO release, increasing RBC production and hematocrit over time.

What symptoms may occur during early exposure to high altitude?

Fatigue, headache, shortness of breath, and reduced exercise tolerance.

What is hemoglobin?

A large iron-containing protein in erythrocytes that binds and transports oxygen and contributes to blood's red color.

How many globin chains are in one hemoglobin molecule?

Four globin chains.

What globin chains make up adult hemoglobin?

Two alpha globins and two beta globins.

How many heme groups are in one hemoglobin molecule?

Four heme groups.

What is found at the center of each heme group?

One iron ion in the ferrous state, Fe2+.

How many oxygen molecules can one hemoglobin molecule bind?

Up to four oxygen molecules, one per heme iron.

What is oxyhemoglobin?

Hemoglobin with oxygen bound to its heme iron groups.

What is deoxyhemoglobin?

Hemoglobin after it has released oxygen; it appears darker red than oxyhemoglobin.

Approximately how many hemoglobin molecules can one RBC contain?

Around 300 million hemoglobin molecules.

Approximately how many oxygen molecules could one RBC bind at maximum capacity?

About 1.2 billion oxygen molecules.

What is carbaminohemoglobin?

Hemoglobin with carbon dioxide bound to amino acids on the globin portion of the molecule.

Does carbon dioxide bind to the iron in heme?

No. Carbon dioxide binds to amino acids in the globin chains, not to heme iron.

What is the main form in which carbon dioxide is transported in blood?

Most carbon dioxide is transported in plasma after conversion to bicarbonate ions.

What is percent saturation or SpO2?

The percentage of hemoglobin oxygen-binding sites that are occupied by oxygen.

What is a typical normal pulse oximeter reading?

Approximately 95 to 100 percent oxygen saturation.

What is hypoxemia?

Abnormally low oxygen in the blood.

What is hypoxia?

Insufficient oxygen availability at the tissue level; it is a broader term than hypoxemia.

What does PO2 measure?

The partial pressure of oxygen, reflecting free oxygen dissolved in plasma.

How is PO2 commonly measured?

With an arterial blood sample, such as in an arterial blood gas test.

How does a pulse oximeter estimate oxygen saturation?

It measures differences in red and infrared light absorption by oxygenated and deoxygenated hemoglobin.

What basic nutrients are needed for erythropoiesis?

Glucose, lipids, amino acids, iron, copper, zinc, folate, and vitamin B12.

Why is iron essential for erythropoiesis?

Iron is required to make the heme groups of hemoglobin.

What type of dietary iron is generally absorbed more efficiently?

Heme iron from meat, poultry, and fish.

What is non-heme iron?

Iron found mainly in plant foods, which is generally less readily absorbed than heme iron.

About what percentage of ingested iron is typically absorbed?

Less than 20 percent.

What proteins store iron in the body?

Ferritin and hemosiderin.

Where is iron commonly stored?

Especially in the liver, spleen, and bone marrow.

What is ferroportin?

A protein that transports iron out of intestinal cells and storage cells into circulation.

What is transferrin?

A plasma protein that transports iron in the bloodstream, including to red bone marrow for erythropoiesis.

What role does copper have in iron metabolism?

Copper supports proteins that oxidize iron so it can bind transferrin and be transported effectively.

What are hephaestin and ceruloplasmin?

Copper-containing proteins that help convert Fe2+ to Fe3+, enabling iron to bind transferrin.

What may result from copper deficiency?

Impaired iron transport and heme synthesis, with possible iron accumulation in tissues.

Why are folate and vitamin B12 important in RBC production?

They are required for DNA synthesis in developing erythrocyte precursors.

Where are aged or damaged erythrocytes mainly removed?

By macrophages in the spleen, liver, and bone marrow.

What happens to globin when hemoglobin is broken down?

Globin proteins are broken into amino acids and reused in protein synthesis.

What happens to iron from heme after RBC breakdown?

It is recycled, stored as ferritin or hemosiderin, or transported by transferrin to bone marrow for reuse.

What happens to the non-iron portion of heme after RBC breakdown?

It is converted to biliverdin, then bilirubin, and is ultimately eliminated mainly through bile and feces.

What is biliverdin?

A green pigment produced during heme breakdown.

What accounts for the greenish color of a healing bruise?

Biliverdin produced during breakdown of hemoglobin.

What is bilirubin?

A yellow pigment produced from biliverdin during heme breakdown.

How is bilirubin transported to the liver?

It travels in the bloodstream bound to albumin.

What happens to bilirubin in the liver?

It is incorporated into bile and released into the intestine.

What pigment gives feces its typical brown color?

Stercobilin, produced from bilirubin derivatives in the intestine.

What pigment contributes to the yellow color of urine?

Urobilins, which are related to bilirubin breakdown products.

What is jaundice?

Yellow discoloration of the skin and tissues caused by accumulation of bilirubin.

What can cause jaundice?

Impaired bilirubin processing or excretion, often involving liver dysfunction or excessive RBC breakdown.

What is anemia?

A condition in which RBC number and/or hemoglobin amount is insufficient to provide normal oxygen delivery to tissues.

What are common symptoms of anemia?

Fatigue, lethargy, shortness of breath, headache, irritability, impaired thinking, and reduced tissue oxygen delivery.

What are the two broad approaches to classifying anemia?

Kinetic classification and morphological classification.

What does the kinetic approach to anemia evaluate?

RBC production, destruction, and removal.

What does the morphological approach to anemia evaluate?

The size and physical characteristics of erythrocytes.

What does mean corpuscular volume (MCV) measure?

Average erythrocyte size.

What does normocytic mean?

Red blood cells are normal in size.

What does microcytic mean?

Red blood cells are smaller than normal.

What does macrocytic mean?

Red blood cells are larger than normal.

What are the three broad mechanisms that can cause anemia?

Blood loss, decreased/impaired RBC production, and excessive RBC destruction.

What are examples of blood-loss anemia causes?

Wounds, ulcers, hemorrhoids, gastritis, gastrointestinal cancers, heavy menstruation, and childbirth.

What is iron-deficiency anemia?

Anemia caused by inadequate iron for heme and hemoglobin production.

What is the most common form of anemia?

Iron-deficiency anemia.

What can cause iron-deficiency an