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Chapter 13Endocrine System
• Endocrine glands are ductless• Exocrine glands have ducts
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Endocrine Glands
Endocrine glands• release hormones• hormones travel through blood to target cells
Paracrine secretions• act locally• affect only neighboring cells
Autocrine secretions• affect only the secreting cell
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Comparison of Nervous System and Endocrine System
• Neurons release neurotransmitters into a synapse, affecting postsynaptic cells• Glands release hormones into the bloodstream • Only target cells of hormone responds
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Comparison of Nervous System and Endocrine System
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Major Endocrine Glands
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Chemistry of Hormones
Steroid or Steroid-Like Hormones• sex hormones• adrenal cortex hormones
Nonsteroid Hormones• amines• proteins• peptides• glycoproteins• most hormones
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Types of Hormones
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Structural Formulas of Hormones
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Actions of Steroid Hormones
• hormone crosses membranes
• hormone combines with receptor in nucleus
• synthesis of mRNA activated
• mRNA enters cytoplasm to direct synthesis of protein
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Actions of Steroid Hormones
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Actions of Nonsteroid Hormones
• adenylate cyclase activated
• hormone binds to receptor on cell membrane
• ATP converted to cAMP
• cAMP promotes a series of reactions leading to cellular changes
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Actions of Nonsteroid Hormones
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Prostaglandins
• paracrine substances
• act locally
• very potent in small amounts
• regulate cellular responses to hormones
• can activate or inhibit adenylate cyclase• controls cAMP production• alters cell’s response to hormones
• wide variety of functions
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Control of Hormonal Secretions
• primarily controlled by negative feedback mechanism
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Negative Feedback
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Major Endocrine Glands
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Pituitary Gland
Two distinct portions• anterior pituitary (adenohypophysis)• posterior pituitary (neurohypophysis)
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Pituitary Gland Control• Hypothalamic releasing hormones stimulate cells of anterior pituitary to release hormones
• Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary gland to release hormones
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Hypothalamic Hormones
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Hormones of the Pituitary Gland
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Thyroid Gland
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Thyroid Gland Hormones
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Disorders of the Thyroid Gland
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Disorders of the Thyroid Gland
Cretinism• Infantile hypothyroidism
Graves Disease • Hyperthyroidism
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Parathyroid Glands
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Parathyroid Hormone
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Parathyroid Hormone
Mechanism by which PTH promotes calcium absorption in the intestine
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Disorders of the Parathyroid Glands
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Adrenal Glands
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Hormones of the Adrenal Medulla
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Hormones of the Adrenal Cortex
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Hormones of the Adrenal Cortex
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Hormones of the Adrenal Cortex
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Pancreas
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Hormones of the Pancreatic Islets
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Insulin and Glucagon
Insulin and glucagon function together to stabilize blood glucose concentrations
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Other Endocrine Glands
Pineal Gland• secretes melatonin• regulates circadian rhythms
Thymus Gland• secretes thymosins• promotes development of certain lymphocytes• important in role of immunity
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Other Endocrine Glands
Reproductive• ovaries produce estrogens and progesterone• testes produce testosterone• placenta produces estrogens, progesterone, and gonadotropins
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Stress
Types of Stress• physical stress• psychological stress
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Responses to Stress
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Life-Span Changes
• endocrine glands decrease in size
• muscular strength decreases as GH levels decrease
• ADH levels increase due to slower break down in liver and kidneys
• calcitonin levels decrease; increase risk of osteoporosis
• PTH level changes contribute to risk of osteoporosis
• insulin resistance may develop
• changes in melatonin secretion affect the body clock
• thymosin production declines increasing risk of infections
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Clinical Application
Growth Hormone Ups and Downs
• Gigantism - hypersecretion of GH in children • Acromegaly – hypersecretion of GH in adults• Dwarfism – hyposecretion of GH in children
Figure shows oversecretion of GH in adulthood as changes occur in the same person at ages (a) nine, (b) sixteen, (c) thirty-three, and (4) fifty-two
