Tip
- In the adrenal medulla, norepinephrine is rapidly converted to epinephrine by phenylethanolamine-N-methyltransferase (PNMT).
- Expression of PNMT in the adrenal medulla is upregulated by cortisol. Because the venous drainage of the adrenal cortex passes through the adrenal medulla, cortisol concentrations in the medulla can be very high, and PNMT is expressed at a high level. However, following pituitary resection, the loss of ACTH leads to decreased synthesis of cortisol in the adrenal cortex. The result is decreased PNMT activity and reduced conversion of norepinephrine to epinephrine.
- It’s named methyltransferase because it transfer a methyl group from SAM to norEpi, forming Epi.
Alkaptonuria
- Dark urine
- Arthralgia
- Discolored face
Albinism
- Translucent, hypopigmented blue, grey, or green irides
- Normal NUMBER of Melanocytes
- Decreased PRODUCTION of Melanin
Differential diagnostics
- Albinism in Chédiak-Higashi syndrome: due to defect in uptake of melanin by keratinocytes
- Vitiligo: CD8+ lymphocyte–mediated melanocyte apoptosis
Phenylketonuria
Mnemonic
Musty → having a stale, moldy, or damp smell → MOLD-E