Intercellular Commication and
• Cells of body must communicate with one
• Coordinates organ systems
• Takes place directly:
– Physical contact between cells
• Gap junctions
• Direct linkage of surface markers
• Or indirectly
– Extracellular chemical messengers or signal
– Specific to target cell receptors
• Four types of chemical messengers
• Local chemical messengers
• Exert effect only on neighboring cells in immediate
environment of secretion site
• Short-range chemical messengers
• Diffuse across narrow space to act locally on
adjoining target cell (another neuron, a muscle, or
• Long-range messengers
• Secreted into blood by endocrine glands in
response to appropriate signal
• Exert effect on target cells some distance away
from release site
• Hormones released into blood by neurosecretory
• Distributed through blood to distant target cells
• Cell responses brought about primarily by signal
– Incoming signals conveyed to target cell’s interior
• Binding of extracellular messenger (first
messenger) to receptor brings about intracellular
response by either
– Opening or closing channels
• Chemically gated receptor channel
– Activating second-messenger systems
• Activated by first messenger
• Relays message to intracellular proteins that carry out
– G-protein coupled receptor
– Study of homeostatic activities accomplished
• Two distinct groups of hormones based on
their solubility properties
– Hydrophilic hormones
• Highly water soluble
• Low lipid solubility
– Lipophilic hormones
• High lipid solubility
• Poorly soluble in water
Mechanism of hydrophilic
hormones via cyclic AMP
second messenger pathway
Comparison of Nervous System and
Animation: Mechanism of action
of a peptide hormone
Animation: Mechanism of action
of a steroid hormone
1. There are 3 ways cells communicate. The 2 direct means of
communication is through ___________ and _______________.
Cells indirectly communicate through _______________.
2. Name and describe the 4 types of chemical messengers. Include
which fluid medium they travel through: blood, extracellular fluid,
3. Why is a neurotransmitter different than paracrine signalling?
4. What is a syncytium?
5. What is a ligand? What is a receptor?
6. How does a chemical messenger “know” which organ to affect?
7. Name 3 ways that an extracellular chemical messenger can bring
about an intracellular response.
8. Is the response between a chemical messenger and a particular
receptor always the same?
9. How can a chemical receptor elicit a different response inside a
10. In a second messenger system, where does the first messenger
bind? Where is the second messenger?
11. There are 2 major 2nd messengers: cyclic AMP and Ca2+ .
Describe the action of a hydrophilic hormone via activation of the
cyclic AMP 2nd messenger pathway. If you draw pictures, you must
label everything and explain what is happening.
12. How does using an 2nd messenger system amplify the response
inside the cell?
13. How do some chemical messengers affect gene activity (hence,
protein synthesis) within a cell?
14. Which type of hormone can affect gene activity, hydrophilic or