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The Endocrine System
Hormones coordinate slow, long-lasting changes across the body. You will learn hormone classes and how they signal, the hypothalamic-pituitary axes, feedback loops, and the control of thyroid, calcium, stress, and blood glucose.
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What this chapter covers
- Hormone Classes & Mechanisms of Action. Whether a hormone is water- or lipid-soluble decides its receptor, its speed, and its second messenger.
- The Hypothalamus & Pituitary. The pituitary takes orders from the hypothalamus. Knowing the hormone chains lets you locate a defect from a lab panel.
- Feedback Loops & the Gonadal Axis. Negative feedback keeps hormones in range. A few positive loops drive one-time events, and the MCAT expects you to name them.
- Thyroid, Parathyroid & Calcium Balance. Thyroid disease and calcium control are frequent passage topics, and PTH versus calcitonin direction is a classic trap.
- Adrenal Glands, Pancreas & Glucose Control. Cortisol, aldosterone, insulin, and glucagon appear in almost every metabolism and physiology passage.
Key points to know
- Peptides: water-soluble, surface receptors, second messengers, fast
- Steroids: lipid-soluble, intracellular receptors, gene expression, slow
- Anterior pituitary is controlled by hypothalamic hormones via the portal system
- ADH and oxytocin are made in the hypothalamus, released by the posterior pituitary
- Negative feedback: end product inhibits upstream release
- Positive feedback examples: oxytocin in labor, pre-ovulatory LH surge
- PTH raises Ca²⁺ and lowers phosphate; calcitonin lowers Ca²⁺
- Thyroid hormone raises BMR; hypothyroid gives cold intolerance and high TSH
Try a practice question
Which hormone binds a receptor inside its target cell?
- Insulin
- Glucagon
- Cortisol
- Epinephrine
Show the answer
C. Cortisol is a lipid-soluble steroid that crosses the membrane and binds an intracellular receptor. Insulin, glucagon, and epinephrine are water-soluble and use surface receptors.
Common questions
What does this chapter cover?
The Endocrine System covers Hormone Classes & Mechanisms of Action, The Hypothalamus & Pituitary, Feedback Loops & the Gonadal Axis, Thyroid, Parathyroid & Calcium Balance, Adrenal Glands, Pancreas & Glucose Control.
What should I know first?
Peptides: water-soluble, surface receptors, second messengers, fast Steroids: lipid-soluble, intracellular receptors, gene expression, slow Anterior pituitary is controlled by hypothalamic hormones via the portal system
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.