Metamyelocyte Information and Courses from MediaLab, Inc.

A 23-year old man had complained of right lower quadrant abdomonal pain for approximately one week. Initially the pain was sharp and localized to a small area just above the right iliac crest.The pain subsided for approximately two days, but then recurred more diffusely over the lower abdomen, accompanied by cramping and mild diarrhea.The onset of fever and vomiting promted a visit to the emergency room. His temperature was 101 F, pulse was 90/minute, and palpation of the right lower abdomen elicited severe pain.The white blood count was 23,000/mm with a distinct left shift, including 5% metamyelocytes.Emergency surgery was performed for a large peri-appendiceal abscess. During surgery, multiple abscesses were noted in the spleen, which was removed (see photograph).Recovery was uneventful following 5 days of adjuvant clindamycin therapy.

Within the hematopoietic cords each cell line has a specific location for development. Erythroid precursors are located near a venous sinusoid and cluster around a macrophage. This is referred to as an erythroblastic island. Developing red cells obtain iron needed for hemoglobin production from macrophages. Megakaryocytes are also located close to a venous sinus. They extend their cytoplasm in fingerlike projections through the sinus wall in order to release their platelets directly into the blood in the sinus. Immature granulocytes lie within the hematopoietic cords. The metamyelocyte stage is the first stage of the granulocyte series that is motile and able to move toward the sinus area. Mature neutrophils, eosinophils and basophils enter the sinusoidal blood through the basement membrane. As maturing erythrocytes also move toward the sinus wall any remaining nuclei are lost as the red cells move through small openings in the cells lining the sinus wall.