## Core Concept
Somatomedins, also known as insulin-like growth factors (IGFs), are proteins that play a crucial role in mediating the effects of growth hormone (GH) on growth and development. They are produced mainly in the liver in response to GH stimulation. Somatomedins have insulin-like effects on various tissues.

## Why the Correct Answer is Right
The correct answer, **C. Growth promoting actions of growth hormone**, is right because somatomedins are known to mediate the growth-promoting actions of growth hormone. Growth hormone stimulates the production of somatomedins (IGF-1 and IGF-2), which in turn promote the growth of bones and other tissues by stimulating cell proliferation and inhibiting cell death.

## Why Each Wrong Option is Incorrect
- **Option A:** Inhibition of glucose uptake in muscles - This is incorrect because somatomedins actually have insulin-like effects, which would facilitate glucose uptake in muscles rather than inhibit it.
- **Option B:** Stimulation of lipolysis - This is incorrect because the primary role of somatomedins is not related to lipolysis; growth hormone itself is more directly associated with stimulating lipolysis.
- **Option D:** Increased secretion of thyroid hormones - This is incorrect because somatomedins do not directly influence the secretion of thyroid hormones; their primary role is related to growth promotion.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **IGF-1 (somatomedin C)** levels are used as an indicator of growth hormone activity. Low levels of IGF-1 can indicate growth hormone deficiency, and high levels can be associated with growth hormone excess (as in acromegaly).

## Correct Answer: C. Growth promoting actions of growth hormone