CHP 17 ENDOCRINE SYSTEM I 1 1 Essay

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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 System Components
• endocrine system - glands, tissues, and cells that secrete hormones • endocrinology – the study of this system and the diagnosis and treatment of its disorders
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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

Endocrine cells Target cells

Hormone in bloodstream (b) Endocrine system

Figure 17.2b

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Endocrine Organs
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Pineal gland
Hypothalamus
Pituitary gland

Thyroid gland
Thymus

Adrenal gland
Pancreas
Parathyroid glands Posterior view Trachea

Gonads:
Ovary (female)
Testis (male)

Figure 17.1

• major organs of endocrine system

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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

• adaptation to long-term stimuli
– nervous - response declines (adapts quickly)
– endocrine - response persists (adapts slowly)

• area of effect
– nervous - targeted and specific (one organ)
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– endocrine - general, widespread effects (many organs)

Communication by the Nervous and Endocrine Systems
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Neurotransmitter

Nerve impulse

Neuron
Target cells
(a) Nervous system

Endocrine cells Target cells

Hormone in bloodstream (b) Endocrine system

Figure 17.2 a-b

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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

• both systems with overlapping