Introduction to Endocrine Principles

• Hormones bind to receptor molecules expressed by target cells
• Concentrations of hormones in the blood vary in response to varying conditions
• Most hormones fall into three chemical classes
• Hormone molecules exert their effects by producing biochemical changes in target cells
• Water-soluble carrier proteins in the blood transport lipid-soluble hormones and many water-soluble hormones

Synthesis, Storage, and Release of Hormones

• Peptide hormones are synthesized at ribosomes, stored in vesicles, and secreted on demand
• Steroid hormones are synthesized on demand prior to secretion, and are released into the blood by diffusion

Types of Endocrine Cells and Glands

Control of Endocrine Secretion: The Vertebrate Pituitary Gland

• The posterior pituitary illustrates neural control of neurosecretory cells
• The anterior pituitary illustrates neurosecretory control of endocrine cells
• Hormones and neural input modulate endocrine control pathways

The Mammalian Stress Response

• The autonomic nervous system and HPA axis coordinate the stress response to an acute threat
• The HPA axis modulates the immune system
• Chronic stress causes deleterious effects
• Plasma glucocorticoid concentrations show seasonal variations

Endocrine Control of Nutrient Metabolism in Mammals

• Insulin regulates short-term changes in nutrient availability
• Glucagon works together with insulin to ensure stable levels of glucose in the blood
• Other hormones contribute to the regulation of nutrient metabolism

Endocrine Control of Salt and Water Balance in Vertebrates

• Antidiuretic hormones conserve water
• The renin–angiotensin–aldosterone system conserves sodium and excretes potassium
• Atrial natriuretic peptide promotes excretion of sodium and water

Endocrine Control of Calcium Metabolism in Mammals

• Parathyroid hormone increases Ca²⁺ in the blood
• Active vitamin D increases Ca²⁺ and phosphate in the blood
• Calcitonin opposes bone resorption and decreases Ca²⁺ and phosphate in the blood

Endocrine Principles in Review

Chemical Signals along a Distance Continuum

• Paracrines are local chemical signals distributed by diffusion
• BOX 16.1 Hormones, Neurons, and Paracrine Neuromodulators Influence Behavior
• Pheromones and kairomones are used as chemical signals between animals

Insect Metamorphosis

• Insect metamorphosis may be gradual or dramatic
• BOX 16.2 Juvenile Hormone (JH) in the Laboratory, Silk Industry, and Environment
• BOX 16.3 Insects in Forensics and Medicine
• Hormones and neurohormones control insect metamorphosis

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