Question

Define endocrine, paracrine, and autocrine and give example of each.

Answer 1

1)Endocrine signaling - The signaling molecules are secreted by some specialized ( endocrine cells ) and these molecules are transported by the blood stream to act upon distantly located target cell. The target cell possess intracellular or extracellular receptors for the signaling molecule.

For eg- Action of hormones on their particular target cell.

Estrogen hormone, synthesized and secreted by ovary in female is responsible for development and maintenance of female reproductive system and many secondary sexual characters also.

2) paracrine signaling - the target cell of these signaling molecule is located in proximity to the cells secreting them. The signaling molecule diffuses in the extracellular matrix and acts on the neighboring cells.

For eg- neurotransmitters carry the signal between the neurons at synapse. Neurotransmitters transmit the signal from axons of a neuron to the dendrites of another neuron.

3)Autocrine signaling - the signaling molecule affects the same cell by which it is produced.

For example - when and foreign antigen attacks the body, some T lymphocytes give response to this antigenic stimulation by synthesizing growth factors which drive their proliferation and causes increase in their number.