When iron cannot be properly incorporated into heme, or insufficient heme is produced, the iron will accumulate in mitochondria around the nucleus of the erythroblast.
The image shows Prussian blue staining of the mitochondrial iron.
This defect may be seen in a variety of disorders, such as congenital deficiency of heme production, exposure to mitochondrial toxins such as lead or alcohol, or in myelodysplastic syndromes—indeed an increase of ringed sideroblasts is one of the defining features for “MDS-refractory anemia with ringed sideroblasts.”
The resulting anemia is typically microcytic and hypochromic.
Metabolic pathway of heme synthesis.
Heme synthesis occurs partly in the mitochondria and partly in the cytoplasm. The process begins in the mitochondria because one of the precursors (Succinyl CoA) is found only there. Since this reaction is regulated in part by the concentration of heme, the final step (which produces the heme) is also mitochondrial.
VIBRIO CHOLERAE: The Bacterial Cause of the Disease Cholera
- When Vibrio cholerae bacteria reach the small intestine,
- they need to propel themselves through the thick mucus that lines the small intestine to get to the intestinal walls where they can thrive.
- So they start to produce the hollow cylindrical protein flagellin to make flagella, the cork-screw fibers they rotate to propel themselves through the mucus.
- However, once the cholera bacteria reach the intestinal wall they no longer need the flagella to move.
- In response to the changed chemical surroundings, they stop producing flagellin
- and start producing the toxic proteins
- that give rise to the watery diarrhea
- that carries new generations of V. cholerae bacteria out into the drinking water of the next host.
See Wikipedia for more …
In cholera, a secretion system facilitates the movement of complex proteins (such as the toxin described above) across bacterial membranes.
Using cryo-electron microscopy, [researchers identified] a structural basis for such a secretion mechanism, showing that the barrel-shaped channel appears to contain a gate in between the cholera bacterium’s two outer membranes.
CREDIT: Tamir Gonen (via Janelia Farm)
Goblet and Secretory Cells
Colored transmission electron micrograph of a section through a goblet cell and secretory cells of the duodenum, part of the small intestine.
- Goblet cells (pink & blue) secrete mucus which neutralizes stomach acid.
- Mucigen granules (circular objects, at upper center) combine with water to form the mucus.
- On either side of the goblet cell are the secretory cells whose secretions help in the digestive process.
- The microvilli (green hair- like structures, upper frame) serve to increase the secretory capacity of the secretory cells by increasing their surface area.
CREDIT: Science Photo
metastatic chordoma in a pulmonary artery (note normal lung tissue — alveoli — surrounding the large blue mass)
chordomas are exceedingly rare, indolent tumors arising from remnants of the embryonic notochord, typically along the neuraxis
responsible for absorbing shock and distributing compressive loads on the spinal column, the nucleus pulposus (a gel-like matrix in the core of intervertebral discs) is a remnant of the notochord
credit: Steffen Albrecht
Neurons colored with silver stain.
You’re beautiful on the inside!
skin under the microscope in my histology-class