CHAPTER 17
ENDOCRINE
PART I
OVERVIEW/PHYSIOLOGY
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Chapter 16 Objectives: Endocrine System
Endocrine System
• Overview
• Hypothalamus and Pituitary Gland
• Other Endocrine Glands
• Hormones and Their Actions
• Stress and Adaptation
• Eicosanoids and Paracrine Signaling
• Endocrine Disorders
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Overview of Cell Communications
• internal communication is necessary for coordination of cell activities • four principal mechanisms of communication between cells
– gap junctions
• pores in cell membrane allow signaling molecules, nutrients, and electrolytes to move from cell to cell
– neurotransmitters
• released from neurons to travel across synaptic cleft to second cell – paracrine (local) hormones
• secreted into tissue fluids to affect nearby cells
– hormones
• chemical messengers that travel in the bloodstream to other tissues and organs
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• endocrine glands – organs that are traditional sources of hormones
• hormones - chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells of another tissue or organ, often a considerable distance away
Comparison of Endocrine and
Exocrine Glands
• exocrine glands
– have ducts carry secretion to an epithelial surface or the mucosa of the digestive tract – ‘external secretions’
– extracellular effects (food digestion)
• endocrine glands
– no ducts
– contain dense, fenestrated capillary networks which allows easy uptake of hormones into bloodstream
– ‘internal secretions’
– intracellular effects such as altering target cell metabolism
• liver cells defy rigid classification – releases hormones, releases bile into ducts, releases albumin and bloodclotting factors into blood (not hormones)
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Comparison of Nervous and Endocrine
Systems (Differences)
• both serve for internal communication
– nervous - both electrical and chemical
– endocrine - only chemical
• speed and persistence of response
– nervous - reacts quickly (1 - 10 msec), stops quickly
– endocrine - reacts slowly (hormone release in seconds or days), effect may continue for weeks
Nervous and Endocrine Systems
(Similarities)
• several chemicals function as both hormones and neurotransmitters – norepinephrine, cholecystokinin, thyrotropin-releasing hormone, dopamine and antidiuretic hormone
• some hormones secreted by neuroendocrine cells
(neurons) that release their secretion into the bloodstream
– oxytocin and catecholamines
