Chapter 5 Chemical Messengers
I. Mechanisms of Intercellular Communication
•
Direct Communication Through
Gap Junctions
•
Indirect Communication Through Chemical Messengers
–
CAP JUNCTIONS
–
Channels formed between 2 cells
–
Direct electrical and metabolic coupling
–
THERE IS NO RECEPTOR INVOLVED
–
Common in smooth and cardiac muscle
–
ALSO IN THE BRAIN
Indirect Communication Through Chemical Messengers
– fig 5.1ab
All about the receptor; chemical messenger carries from the secretory cell into the receptor
II. Chemical Messengers
–
Functional Classification of Chemical Messengers
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Chemical Classification of Messengers
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Synthesis and Release of Chemical Messengers
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Transport of Messengers
Functional Classification of Chemical Messengers
–
Paracrines
: released by cell, moves to target cell by diffusion (limited distance)
–
Act on neighboring cells (fig 5.2a)
–
Recpetor on the outside of cell membrane means that the messenger cannot
go into the cell; the receptor will trigger the response of the cell
–
Examples:
–
Histamines: release with tissue damage and causes dilation of local
blood vessels
–
Clotting factors
–
Testosterones: Moves from the Leydig cells into the seminiferous
tubules (sperm is made)
–
Prostaglandins
–
Paracrine substance; ACT LOCALLY; very potent in small
amounts
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Regulate celluar response to hormones
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Can activate or inhibi adenylate cyclase
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Controls cAMP production
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**ALTERS CELL’S RESPONSE TO HORMONES**
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Wide variety of functions
–
Autocrines
–
Act on cell that release it; the cell releases the messenger and also holds the
receptor for reaction to take place (fig 5.2b)
–
Secretory & Target cell
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–
Neurotransmitters
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Messengers of nervous system (fig 5.2c)
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Released from neuron by exocytosis
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Diffuse to very close target cell across a synapse
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Hormones
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Messenger of endocrine system
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Released from endocrine gland into blood
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Transported in blood to target
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Target cell = cells in body with receptors specific to the hormone
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Neurohormones
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Hormones released from the axons of neurons in the hypothalamus
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ADH & Oxytocin in posterior pituitary
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Inhibiting & releasing hormones into the portal system going to the
anterior pituitary
CYTOKINES
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Cytokines = peptides or proteins
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Can be transported in blood
–
Released by most cell types
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Involved in cell development, differentiation, and immune response
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Often act on a wide range of targets
CHEMICAL CLASSIFICATION OF MESSENGERS
–
Chemical class determines mechanism of transport and mechanism of action on
target cell
•
Lipophilic/ Hydrophobic
- can cross plasma membrane;
recpetors are
going to found inside the cell
•
Lipophobic/ Hydrophilic

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- Fall '08
- KT
- Physiology, MESSENGER, RECEPTOR PROPERTIES
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