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Endocrine system


Adrenal gland disorders
Thyroid gland disorders
Parathyroid gland disorders
Pancreatic disorders
Pituitary gland disorders
Gonadal dysfunction
Polyglandular syndromes
Endocrine tumors
Endocrine system pathology review



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High Yield Notes
13 pages


12 flashcards

USMLE® Step 1 style questions USMLE

3 questions

A 15-month-old boy is brought to the clinic after his parents noticed frequent falls and abnormal twitching of his limbs over the past month. Prior to the onset of these symptoms, the patient had been walking without assistance and developing normally. Vital signs are within normal limits. Physical examination shows bilateral jerking eye movements and sporadic muscle contractions of the trunk and limbs. The patient has difficulty walking in a straight line and stumbles several times. A left-sided abdominal mass is palpated. Biopsy of the mass reveals small, round, blue cells arranged concentrically around a central neuropil. Staining with neuron-specific enolase is positive. Based on these findings, which of the following is most likely to be elevated?  


Neuroblastoma is a type of tumor composed of “neuroblasts,” specifically neural crest cells, which are cells involved in the development of the sympathetic nervous system.

Neuroblastoma is the most common cancer in infants, and it’s only rarely seen in children over five years old.

When a fetus is in its 5th week of development, special cells called neural crest cells start migrating along the spine.

In the thoracic region of the spine, neural crest cells differentiate into the neurons of the sympathetic chain, lying on either side of the entire spinal cord.

In the lumbar region, neural crest cells differentiate into the cells of the adrenal medulla, the inner part of the adrenal gland that sits atop the kidneys.

Together, the sympathetic chain and adrenal medulla form the sympathetic nervous system, connecting the brain and central nervous system to various organs including the heart and blood vessels.

So, when you’re under some sort of stress, like playing a competitive sport like badminton, the sympathetic nervous system kicks into action.

The sympathetic neurons releases norepinephrine, also called noradrenaline, and the cells of the adrenal medulla release norepinephrine and epinephrine, also called adrenaline.

These hormones bind to receptors in various tissues like the blood vessels, the heart, and the lungs, redirecting blood flow to your muscles, make your heart pump faster, and expanding the airways in your lungs, all of which can help you make the winning hit.

After the game is over, and the hormones are no longer needed, epinephrine and norepinephrine break down into metabolites like homovanillic acid or HMA, and vanillylmandelic acid, or VMA.

In neuroblastoma, some neural crest cells in the sympathetic chain or adrenal medulla don’t differentiate properly during fetal development, and these cells ultimately go on to form a tumor, which most often form in the adrenal medulla, but can also develop in other areas of the sympathetic chain.

While no one knows exactly how it happens, this abnormal cell differentiation has been associated with mutations in the MYCN oncogene, Anaplastic lymphoma kinase ALK fusion oncogenes, and mutations in tumor suppressor genes, like the Paired-like homeobox 2b or PHOX2B, and other tumor suppressor genes on chromosome 1 and 11.

Oncogenes help cells grow and proliferate, while tumor suppressor genes slow down cell growth and proliferation.

So both an MYCN amplification or ALK gene fusion, where the oncogene is “turned on,” or a PHOX2B and chromosome 1 and 11 deletions, where tumor suppressor genes are “turned off,” can potentially cause uncontrolled cell growth.

There are three types of neuroblastomas, and they’re categorized based on the size and shape of the tumor cells: undifferentiated, poorly differentiated, and differentiating neuroblastoma.

An undifferentiated neuroblastoma is mostly comprised of neural crest cells, which are sometimes called small round blue cells, due to a lack of cytoplasm, and a large blue nuclei.

A poorly differentiated neuroblastoma is composed of slightly more differentiated cells, with smaller nuclei and a bit more cytoplasm.

In addition, the cells of a poorly differentiated neuroblastoma may be surrounded by a substance called neuropil, which is a dense network of interwoven nerve fibers, like axon and dendrite branches.

Finally, a differentiating neuroblastoma is composed of cells with lots of cytoplasm, and is often surrounded by a substance called Schwannian stroma.

Schwannian stroma is a connective tissue from non-neuronal cells that forms myelin, which insulates the axons of the mature neurons.

When any type of neuroblastoma forms, cells in the surrounding tissue release chemokines called CXCL12 and that stimulates nearby immune cells.

CXCL12 is normally produced by some organs like the lymph nodes, liver, bones, and especially the bone marrow, but gets produced in higher amounts when tissue is damaged.


Neuroblastoma is a type of tumor composed of neural crest cells, which are cells involved in the development of the sympathetic nervous system. It is most commonly found in the adrenal gland, but it can also occur in other parts of the body along the sympathetic chain, such as the neck, chest, or pelvis. Neuroblastoma most often affects children, and it is more common in males than in females.

Symptoms of neuroblastoma can vary depending on the location and size of the tumor. They may include abdominal pain, a lump in the abdomen, difficulty breathing, bone pain, weight loss, sweating, fatigue, and changes in bowel or bladder function. Treatment for neuroblastoma may include surgery to remove the tumor, chemotherapy, radiation therapy, and immunotherapy.

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