Question

Cells signalling between distant cells mediated by hormones released from specific cells that travel to target cells, producing a slower, long-lasting response is known as

• A. Paracrine signalling
• B. Endocrine signalling
• C. Autocrine signalling
• D. Direct signalling

Hint:

• Endocrine Long distance, via bloodstream, hormones, slow, long-lasting (e.g., insulin, growth hormone).
• Paracrine Local, acts on nearby cells, short diffusion (e.g., growth factors, some neurotransmitters outside synapse).
• Autocrine Acts on the same cell that secreted it.
• Synaptic Neuronal, fast, precise, across synapse via neurotransmitters.
• Contact-Dependent (Juxtacrine) Requires direct cell-cell contact.

Answer 1

The Correct Option is B

Cell signaling can occur over different distances and via different mechanisms:

• (a) Paracrine Signalling: Cells release signaling molecules (local mediators) that act on nearby target cells. The signals diffuse over short distances through the extracellular fluid. Example: Growth factors acting on neighboring cells.
• (b) Endocrine Signalling: Specialized endocrine cells secrete signaling molecules called hormones into the bloodstream. These hormones travel throughout the body via the circulatory system and act on distant target cells that possess specific receptors for them. Endocrine signaling is typically slower to initiate but can produce widespread and long-lasting responses. This matches the description in the question.
• (c) Autocrine Signalling: Cells release signals that bind to receptors on the same cell that secreted them, or on nearby cells of the same type. The cell signals itself. Example: Some growth factors.
• (d) Direct Signalling (Contact-Dependent or Juxtacrine Signalling): Requires direct physical contact between the signaling cell and the target cell. Signaling molecules on the surface of one cell bind to receptors on the surface of the other (e.g., Notch signaling), or signals pass through gap junctions connecting adjacent cells.
• Synaptic Signalling (Neuronal Signalling): Neurons transmit signals electrically along their axons and release chemical signals (neurotransmitters) at synapses, which act on specific target cells (neurons, muscle cells, gland cells) over a very short distance across the synaptic cleft. This is fast and precise.

The description "signalling between distant cells mediated by hormones released ... that travel to target cells, producing a slower, long-lasting response" clearly defines endocrine signalling. \[ \boxed{\text{Endocrine signalling}} \]