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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