Chapter_5_Chemical_Messengers - Chapter 5 Chemical Messengers I Mechanisms of Intercellular Communication Direct Communication Through Gap Junctions

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 – Chemical Classification of Messengers – Synthesis and Release of Chemical Messengers – 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 – Regulate celluar response to hormones – Can activate or inhibi adenylate cyclase – Controls cAMP production – **ALTERS CELL’S RESPONSE TO HORMONES** – 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 – Messengers of nervous system (fig 5.2c) – Released from neuron by exocytosis – Diffuse to very close target cell across a synapse – Hormones – Messenger of endocrine system – Released from endocrine gland into blood – Transported in blood to target – Target cell = cells in body with receptors specific to the hormone – Neurohormones – Hormones released from the axons of neurons in the hypothalamus – ADH & Oxytocin in posterior pituitary – Inhibiting & releasing hormones into the portal system going to the anterior pituitary CYTOKINES – Cytokines = peptides or proteins – Can be transported in blood – Released by most cell types – Involved in cell development, differentiation, and immune response – 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