Question

autocrine signaling examples
which is not an example of autocrine signaling?
fibroblasts producing platelet - derived growth factor (pdgf)
pancreatic cells releasing insulin to regulate blood sugar
immune cells releasing cytokines to modulate their own activity
tumor cells secreting growth factors for self - stimulation

Explanation:

Autocrine signaling is when a cell secretes a signal (like a growth factor or cytokine) that acts on itself. Let's analyze each option:

• Fibroblasts producing PDGF: PDGF can act on the fibroblasts themselves, so this is autocrine.
• Pancreatic cells releasing insulin: Insulin acts on target cells like liver, muscle, fat cells (not the pancreatic cells that release it), so this is endocrine (or paracrine/other, not autocrine).
• Immune cells releasing cytokines: Cytokines modulate the immune cells that release them, so autocrine.
• Tumor cells secreting growth factors: The growth factors stimulate the tumor cells themselves, autocrine.

So the one not autocrine is pancreatic cells releasing insulin.

Answer:

B. Pancreatic cells releasing insulin to regulate blood sugar (assuming the options are labeled A, B, C, D with A as Fibroblasts..., B as Pancreatic..., C as Immune..., D as Tumor...; if labels differ, adjust to the option text for pancreatic cells releasing insulin).