Structure and Function of Red Blood Cells

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List the factors that maintain red cell size:

RBC count is maintained by negative feedback factors Ė receptors in kidneys detect low RBC count and release erythropoietin.

Describe the primary function of the RBC. What other functions does the RBC have?

Primary function is to transport oxygen to the body cells. Other functions include regulation and protection.

Describe the hemoglobin molecule:

It carries four heme molecules that carry an oxygen molecule.

Why is hemoglobin carried in RBCs and not dissolved in the plasma?

RBCs donít use oxygen because they donít have a nucleus. Their power themselves anaerobically.

Describe the role of iron in the red blood cell?

Iron is found at the center of each hemoglobin molecule and this ion combines with oxygen and sticks to it.

Oxygen is poorly dissolved in plasma. Describe how hemoglobin carries oxygen to the tissues:

A hemoglobin molecule contains four hemes that contain iron in their centers. Oxygen reversibly binds to these centers and is transported within the body.

Erythrocytes are bi-concave discs. What is a biconcave disc? What is the advantage of this?

It has the greatest surface area for its volume.

The RBC contains no mitochondria. What is the advantage of this?

They donít use up any of the oxygen.

What are the stages of a developing RBC? At what stage does the developing RBC acquire hemoglobin?

Pluripotent stem cell > Myeloid stem cell > CFU-E > Proerythroblast > Reticulocyte > RBC (erythrocyte)

Hemoglobin is acquired at proerythroblast stage.

Describe what a reticulocyte is:

Proerythroblast ejects its nucleus and synthesizes hemoglobin, and this results in the formation of a reticulocyte.

State the percentage of the total number of RBCs that is destroyed daily. How are they replaced?

Less than 1%. They are replaced by newly formed erythrocytes leaving the bone marrow.

List the organs where reticuloendothelial (RE) cells are found:

Lymph nodes, spleen and bone marrow.

List the functions of the RE cells:

Immune, cleaning up of dead tissues/blood and removal of foreign materials. Reticuloendothelial system is also called a macrophage system of a mononuclear phagocyte system.

Where can a bone marrow sample be obtained in a 20yr old man being investigated for anemia?

Femur.

Describe the role of erythropoietin. Explain the homeostatic mechanism which controls the level of erythropoietin:

It promotes the synthesis of RBCs. Here is the mechanism:

• RBC count in blood goes low.

• A negative feedback system kicks in.

• Hypoxia develops due to low oxygen in blood.

• Kidneys release erythropoietin.

• Erythropoietin goes the red bone marrow, then speeds up the development of proerythroblasts into reticulocytes.

• Number of circulating RBCs increases.

Important substances involved in RBC production. What are the origins of these substances?

Erythropoietin, haptoglobin, ferritin and iron. They are made in kidneys, and liver.

Where are RBCs destroyed? What happens to the components of the RBC upon destruction?

Spleen. This process takes place:

• RBCs are ruptured.

• Heme and globin portions separated.

• Globin > amino acids.

• Iron transferred in transferrin into the blood > into bone marrow for reuse.

• Heme > Biliverdin > Bilirubin > small intestine.

Aspiration:

Breathing in food.

Trephination:

Removal of a circular piece of bone from the skull using a trephine.

Pluripotent / totipotent cells:

Have the ability to develop into several types of body cells.

CFU:

Colony forming unit / Proginator cells -> destined to become certain types of cells.

More Red Blood Cell Facts:

• Life span of a RBC: 120 days.

• RBC formation site for a 20 year old: femur.

• RBC formation site for a 40 year old: vertebrae.

• The average biological half life of antibodies in the adult is about: 13 days.

Additional Reading:

Basic Pathology

1. Cell Injury
2. Inflammation and Repair
3. Immunopathology
4. Water, Electrolyte, Acid-Base, Hemodynamic Disorders
5. Genetic and Developmental Disorders
6. Environmental Pathology
7. Nutritional Disorders
8. Neoplasia
9. Vascular Disorders
10. Heart Disorders
11. Red Blood Cell Disorders
12. White Blood Cell Disorders
13. Lymphoid Tissue Disorders
14. Hemostasis Disorders
15. Blood Banking and Transfusion Disorders
16. Upper and Lower Respiratory Disorders
17. Gastrointestinal Disorders
18. Hepatobiliary and Pancreatic Disorders
19. Kidney Disorders
20. Lower Urinary Tract and Male Reproductive Disorders
21. Female Reproductive and Breast Disorders
22. Endocrine Disorders
23. Musculoskeletal Disorders
24. Skin Disorders
25. Nervous System Disorders
26. Notes on Tissue Regeneration
27. A Table of Bleeding Disorders
28. FAQ on Structure and Function of Red Blood Cells
29. FAQ on Components of Blood
30. Notes on Hemostatic Mechanisms
31. What is Fever?
32. What is Edema?
33. FAQ on Blood Pressure
34. FAQ on principles of fluid and flow dynamics of Blood
35. Causes of Thrombocytopenia
36. Squamous cell carcinoma of head and neck mucosa
37. Four tumors which never metastasize to the brain
38. What is caustic injury?
39. What causes Peripheral Edema?

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