Question

MSH of pars intermedia of pituitary causes in lower vertebrates
(a)Darkening of the skin
(b)Light coloration of the skin
(c)Both A and B
(d)None of the above

Answer 1

Hint: The boundary between the anterior and posterior pituitary lobes is Pars intermedia. It comprises three cell types: basophils, chromophobes, and cysts packed with colloids. The cysts are the remainder of the pouch from Rathke.

Complete answer:
Collectively known as MSH, also known as melanotropins or intermedins, melanocyte-stimulating hormones are a family of peptide hormones and neuropeptides consisting of alpha-melanocyte-stimulating hormone (alpha-MSH), beta-melanocyte-stimulating hormone (beta-MSH), and gamma-melanocyte-stimulating hormone (gamma-MSH) formed by cells in the anterior lobe of the pituitary gland.
MSH development is increased in some animals (such as the claw-toed Xenopus laevis frog) when the animal is in a dark spot. In the pigment cells in the skin of the toad, this allows the pigment to be spread, making it darker and harder for predators to detect. The pigment cells are called melanophores, so the hormone is also referred to as the melanophore-stimulating hormone in amphibians.
A rise in MSH would also cause human skin to be darker. In humans, during pregnancy, MSH rises. This induces increased pigmentation in pregnant women, along with increased oestrogen. Hyperpigmentation, such as acanthosis nigricans in the axilla, can also result from Cushing's disease due to excess adrenocorticotropic hormone (ACTH). Most people with primary Addison's disease have darkening (hyperpigmentation) of the skin, including areas not exposed to the sun; skin creases (e.g. of the hands), nipples, and the inside of the cheek (buccal mucosa) are typical sites; recent scars are hyperpigmented, while older ones are not darkened. This happens because the same precursor molecule, proopiomelanocortin, shares MSH, and ACTH (POMC).

So, the correct answer is ‘darkening of the skin’.

Note: Different levels of MSH are not the primary cause of skin color variation. However, there are differences in their hormone receptors in certain red-headed individuals, and other individuals who do not tan well, causing them to not respond to MSH in the blood.