Teri Goes To See Her PCP After Feeling Depressed Last Couple ✓ Solved

Teri Goes To See Her Pcp After Feeling Depressed Last Couple Of Months

Teri visits her primary care provider after experiencing depression for the past few months and having an episode of seizure earlier in the week. The physician orders laboratory tests, which reveal low hematocrit levels, decreased vitamin B12, low oxygen saturation, presence of autoantibodies against parietal cells, and abnormal red blood cells (large and pale). Based on these findings, Teri is diagnosed with pernicious anemia, a condition characterized by autoantibodies destroying parietal cells within the stomach lining.

Since parietal cells are destroyed in pernicious anemia, Teri is lacking in intrinsic factor, a glycoprotein critical for vitamin B12 absorption. Parietal cells produce both hydrochloric acid (HCl) and intrinsic factor; thus, their destruction impairs the secretion of intrinsic factor, leading to decreased vitamin B12 uptake in the ileum. Vitamin B12 is essential for DNA synthesis in developing red blood cells (RBCs); deficiency results in ineffective erythropoiesis and the formation of large, immature, and dysfunctional RBCs, known as megaloblasts.

The destruction of parietal cells directly causes vitamin B12 deficiency because without intrinsic factor, vitamin B12 cannot be properly absorbed from the gastrointestinal tract. Consequently, the hallmark features include macrocytic anemia with large, pale RBCs and neurological symptoms in advanced cases. A healthy individual’s RBCs are generally small and biconcave, optimized for efficient oxygen transport. Hematocrit reflects the proportion of blood volume occupied by RBCs, an important marker of erythropoietic health.

Low oxygen levels stimulate erythropoiesis—the production of new RBCs—by activating the hormone erythropoietin (EPO). When tissues experience hypoxia, the kidneys release increased EPO, which promotes the proliferation and differentiation of erythroid progenitor cells in the bone marrow into mature RBCs. This process involves several stages, including erythroid burst-forming unit (BFU-E) proliferation, subsequent erythroblast maturation, and enucleation of reticulocytes into functional erythrocytes capable of efficient oxygen transport.

Hemoglobin (Hb) is the primary protein responsible for oxygen transport in the human body. It is a tetrameric protein composed of four polypeptide chains—two alpha and two beta chains—each bound to a heme group. The heme contains an iron atom in the ferrous (Fe2+) state, which reversibly binds oxygen molecules. This structure allows hemoglobin to pick up oxygen in the lungs and release it in tissues, facilitating efficient oxygen delivery.

Antibodies, or immunoglobulins, are glycoproteins secreted predominantly by plasma cells, a type of differentiated B lymphocyte. They play essential roles in immune defense by identifying and neutralizing pathogens such as bacteria and viruses. Antibodies bind specifically to antigens, marking them for destruction or directly inactivating them. Functions include opsonization, complement activation, and antibody-dependent cellular cytotoxicity.

There are five main classes of immunoglobulins: IgG, IgA, IgM, IgE, and IgD, each with unique characteristics. IgG is the most abundant antibody in circulation, providing long-term immunity; it can cross the placenta to confer passive immunity to the fetus. IgA is predominant in mucosal areas, protecting mucous membranes; it exists as a dimer and prevents pathogen adherence. IgM is the largest antibody in size, primarily involved in initial immune responses; it is pentameric, allowing for avid antigen binding. IgE plays a crucial role in allergic reactions and defense against parasitic infections; it binds to mast cells and basophils, triggering histamine release. IgD functions mainly as a receptor on naive B cells and has a less well-understood role.

Structurally, immunoglobulins are Y-shaped glycoproteins composed of two identical heavy chains and two identical light chains linked by disulfide bonds. Each chain has a variable region, responsible for antigen recognition, and a constant region, defining the antibody's class and effector functions. The antigen-binding sites are formed by the variable regions of the heavy and light chains, giving each immunoglobulin its specificity.

Conclusion

Teri’s case illustrates the critical interplay between the digestive, immune, and cardiovascular systems. The destruction of parietal cells leads to intrinsic factor deficiency, impairing vitamin B12 absorption and resulting in macrocytic anemia characterized by abnormal large RBCs with reduced oxygen-carrying capacity. This deficiency also affects neurological functions due to demyelination of nerves. The body responds to hypoxia by stimulating erythropoiesis via erythropoietin production, ensuring oxygen delivery. Hemoglobin’s structure—a heme group bound to iron within a globular protein—enables efficient oxygen transport. Furthermore, the immune response, mediated by antibodies produced by plasma cells, involves diverse immunoglobulin classes tailored to specific defensive roles. Understanding these mechanisms reveals the profound interconnectedness of human physiological systems in health and disease management.

References

• Edmunds, M. (2020). Human Physiology: An Integrated Approach. Pearson.
• Kumar, V., Abbas, A. K., & Aster, J. C. (2018). Robbins Basic Pathology (10th ed.). Elsevier.
• Janeway, C. A., et al. (2017). Immunobiology (9th ed.). Garland Science.
• Kliegman, R. M., et al. (2020). Nelson Textbook of Pediatrics (21st ed.). Elsevier.
• Guyton, A. C., & Hall, J. E. (2016). Textbook of Medical Physiology (13th ed.). Elsevier.