PSL201 – Feb 14 – Endocrine 1 Introduction to Hormones.docx

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11 Apr 2012
PSL201 Feb 14 Endocrine 1: Introduction to Hormones
Mechanisms of Intercellular Communication
- all body functions require communication between cells
- there are only a few mechanisms in the body for cells to communicate with
one another
- few instances: linked by gap junctions
- most instances: communicate through chemical messengers
Direct Communication Through Gap Junction
- gap junctions link adjacent cells
o formed by connexins (plasma membrane proteins)
o form channels that allow molecules to pass through
- metabolically couples cells so that one cell can provide for another
Indirect Communication Through Chemical Messengers
- chemical messenger = ligand (molecules that bind to proteins reversibly)
- hundreds of chemical messengers with different functions
- one cell releases a chemical into the interstitial fluid (secretion)
- another cell (target cell) responds to the chemical messenger b/c of its
receptors, which specifically recognize the ligand
o this binding produces a response in the target cell through signal
- Strength of response increases as the number of bound receptors increases
o Bound receptors increases as [messenger] in ISF increases
Chemical Messengers
- classified on basis of structure and function
Functional Classification of Messengers
- 3 main categories:
o paracrines
o neurotransmitters
o hormones
- when released into ISF transmit signal by binding to receptor
- Paracrines: chemicals that communicate with neighboring cells
o Released into ECF and must reach target by simple diffusion
o Include growth factors, clotting factors and cytokines
o Growth Factors: proteins that stimulate proliferation and
differentiation of cells
o Clotting Factors: stimulate the formation of blood clots
o Cytokines: peptides usually released from immune cells
coordinate the bodies immune response
can also sometimes travel in the blood stream
o histamine is a paracrine messenger
important in allergic reactions (secreated by mast cells)
responsible for runny nose, red eyes
part of inflammation
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