The endocrine system consists of the glands in the body that produce hormones, which are chemical messengers that travel through the blood to the target cells upon which they act. Hormones regulate the body's metabolism, development, sexual function, and mood among other things. The endocrine system is one of the body's main communication systems along with the nervous system.

For the MCAT, the endocrine system presents one of the biggest memory challenges from within physiology for the exam. Endocrine function is a long-standing favorite of MCAT writers. Ideally, a person should to begin studying the endocrine glands and hormones as early as possible in MCAT review (Several Knowledge Mapping tasks begin this work in earlier modules.) Don't let the final phase of review turn into one big physiology cram session. Start earlier than Module 12 to review the factual material within the endocrine system and the other topics of physiology.

WikiPremed Resources

The Endocrine System Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for The Endocrine System
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Be able to distinguish categories of hormones based on chemical structure.

Know which glands secrete steroid hormones, their basic structure, and the generic mode of action within the target cell.

Be able to distinguish which hormones are peptides and which are the tyrosine derived amine hormones.

Be familiar with how the endocrine system employs cycles and negative feedback to regulate the secretion of most hormones.

Understand the difference in signaling mechanism when a nonsteroid hormone reaches the target cell membrane in contrast to a steroid hormone.

Recognize the most common second messenger systems and be able to narrate the events of the classic examples, especially the G-protein coupled receptor system.

Be prepared to name the hormones, their functions and their mechanisms of the endocrine glands including pineal, hypothalamus, posterior pituitary, anterior pituitary, thyroid, parathyroid, adrenals, heart, kidneys, pancreas, stomach, small intestine, ovary, and testes.

Gain a thorough understanding of the anatomical distinction between the anterior and posterior pituitary glands and their different mechanisms of hormone production and release.

Understand the structure of the adrenal gland and how that relates to the different hormones it produces.

Be ready to construct the endocrine narratives for regulation of blood glucose levels, calcium levels, and blood pressure.

Suggested Assignments

Review the terminology for the endocrine system using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Complete the advanced crossword puzzle for the endocrine system. Here is the solution to the puzzle.

Read pp. 73-82 and pp. 84-92 in ExamKrackers Biology II. Perform practice items 49-56 on pg. 83 and practice items 57-64 on pg. 93.

Review the web resources for the endocrine system.

Conceptual Vocabulary for The Endocrine System

Endocrine system
The endocrine system is an integrated system of small organs which involve the release of extracellular signaling molecules known as hormones.
A hormone is a chemical messenger that carries a signal from one cell, or group of cells, to another.
Endocrine glands
Endocrine glands are glands that secrete their product directly into the blood rather than through a duct.
Located just below the thalamus, the hypothalamus links the nervous system to the endocrine system via the pituitary gland.
Posterior pituitary
The posterior pituitary gland and is part of the endocrine system, secreting the hormones oxytocin and vasopressin, which are produced in the hypothalamus.
Anterior pituitary
Under the influence of the hypothalamus, the anterior pituitary produces and secretes several peptide hormones which regulate many physiological processes including stress, growth, and reproduction.
Arginine vasopressin, also known as antidiuretic hormone, plays a major role in regulating the body's retention of water, being released when the body is dehydrated.
Pituitary gland
The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea that sits in a small, bony cavity covered by a dural fold at the base of the brain.
Growth hormone
Growth hormone or somatotropin is a protein hormone which stimulates growth and cell reproduction.
Prolactin is a peptide hormone on the anterior pituitary gland primarily associated with lactation.
Oxytocin is a hormone that also acts as a neurotransmitter in the brain. In females, it is released in large amounts during labor and it is also released during breastfeeding. It is released in both sexes during orgasm.
One of the largest endocrine glands in the body, the thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones.
Thyroxine, often abbreviated as T4, is the major hormone secreted by the follicular cells of the thyroid gland.
Triiodothyronine (T3) is a thyroid hormone similar to thyroxine but with one less iodine atom per molecule. T3 exhibits greater activity than thyroxine but is produced in smaller quantity.
Calcitonin is a polypeptide hormone produced by the parafollicular cells of the thyroid which participates in calcium and phosphorus metabolism, lowering blood calcium, countering the effects of parathyroid hormone.
Parathyroid gland
The parathyroid glands are small endocrine glands in the neck, usually located behind the thyroid gland.
Parathyroid hormone
Parathyroid hormone is secreted by the parathyroid glands, acting to increase the concentration of calcium in the blood, opposite the effect of the thyroid hormone calcitonin.
Angiotensin is an oligopeptide in the blood that causes vasoconstriction, increased blood pressure, and release of aldosterone from the adrenal cortex.
Islets of Langerhans
The endocrine cells of the pancreas are grouped in the islets of Langerhans.
Insulin is an animal hormone which causes liver and muscle cells to take in glucose and store it in the form of glycogen and causes fat cells to take in blood lipids and turn them into triglycerides.
Glucagon is released by the pancreas when the glucose level in the blood is low, causing the liver to convert stored glycogen into glucose and release it into the bloodstream.
Angiotensin is an oligopeptide in the blood that causes vasoconstriction, increased blood pressure, and release of aldosterone from the adrenal cortex.
Aldosterone is a steroid hormone produced by the outer-section of the adrenal cortex in the adrenal gland which regulates sodium and potassium balance in the blood.
Adrenal medulla
The adrenal medulla is the part of the adrenal gland located in the center of the gland, being surrounded by the adrenal cortex.
Signal transduction
Signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another.
Second messenger system
A secondary messenger system is a method of cellular signalling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change.
Peptide hormone
Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.
Adrenocorticotropic hormone
Adrenocorticotropic hormone or corticotropin is a polypeptide hormone produced and secreted by the pituitary gland. It is an important player in the hypothalamic-pituitary-adrenal axis.
Atrial natriuretic peptide
Atrial natriuretic peptide is a polypeptide hormone involved in the homeostatic control of body water, sodium, and adiposity.
Beta cell
Beta cells are a type of cell in the pancreas in areas called the islets of Langerhans which make and release insulin.
Alpha cell
Alpha cells are endocrine cells in the islets of Langerhans of the pancreas which are responsible for synthesizing and secreting the peptide hormone glucagon.
Erythropoietin, also called hematopoietin, is a glycoprotein hormone that acts as a cytokine for erythrocyte precursors in the bone marrow.
Renin is released by the juxtaglomerular apparatus of the kidneys in response to low blood volume or decreased serum NaCl concentration.
Adrenal gland
The adrenal glands are triangle-shaped endocrine glands that sit on top of the kidneys which regulate the stress response through the synthesis of corticosteroids and catecholamines.
Adrenal cortex
The adrenal cortex, situated along the perimeter of the adrenal gland, mediates the stress response through the production of mineralocorticoids and glucocorticoids.
Mineralocorticoids are a class of steroid hormones that include aldosterone which influence salt and water balance.
Glucocorticoids are a class of steroid hormones characterised by an ability to bind with cortisol receptors and trigger events which increase and maintain normal concentrations of glucose in blood.
Epinephrine and norepinephrine are a fight or flight hormones released from the adrenal glands, and they are also neurotransmitters within the central and sympathetic nervous systems.
Thrombopoietin is a glycoprotein hormone produced mainly by the liver and the kidney that regulates the production of platelets by the bone marrow.
Thyrotropin-releasing hormone
Thyrotropin-releasing hormone is a tripeptide hormone that stimulates the release of thyroid-stimulating hormone and prolactin by the anterior pituitary.
Gonadotropin-releasing hormone
Gonadotropin-releasing hormone is a peptide hormone responsible for the release of FSH and LH from the anterior pituitary.
Growth hormone releasing hormone
Growth hormone releasing hormone is carried by the hypothalamo-hypophysial portal circulation to the anterior pituitary gland where it stimulates somatotropin secretion.
Corticotropin-releasing hormone
Corticotropin-releasing hormone stimulates corticotropes in the anterior pituitary to secrete adrenocorticotropic hormone and other biologically active substances such as beta endorphin.
Somatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation.
Tropic hormone
Tropic hormones describes as a class the anterior pituitary-secreted hormones which regulate the activity of various endocrine glands.
Thyroid-stimulating hormone
Thyroid-stimulating hormone or thyrotropin is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland.
Melanocyte-stimulating hormone
The melanocyte-stimulating hormones are a class of peptide hormones produced by cells in the intermediate lobe of the pituitary gland which stimulate the production and release of melanin by melanocytes in skin and hair.
Hyperthyroidism is the clinical syndrome caused by an excess of circulating free thyroxine or free triiodothyronine.
Brain natriuretic peptide
Brain natriuretic peptide is a polypeptide secreted by the ventricles of the heart in response to excessive stretching of myocytes in the ventricles.
Renin-angiotensin-aldosterone system
The renin-angiotensin system is a hormone system that helps regulate long-term blood pressure and extracellular volume in the body.
Hypothalamic-pituitary-adrenal axis
The hypothalamic-pituitary-adrenal axis is a complex set of direct influences and feedback interactions between the hypothalamus, the pituitary gland, and the adrenal gland.
Hypothyroidism is the disease state in humans and animals caused by insufficient production of thyroid hormone by the thyroid gland.
Melatonin is a hormone found in all living creatures from algae to humans, at levels that vary in a diurnal cycle.
Lipotropin is a hormone produced by the cleavage of pro-opiomelanocortin, which also produces adrenocorticotropin in the cleavage.
Endothelin is a vasoconstricting peptide that plays a key part in vascular homeostasis. It is one of the strongest vasoconstrictors yet studied.
Pancreatic polypeptide
Pancreatic polypeptide is secreted by PP cells in the endocrine pancreas. It is a cholecystokinin antagonist, suppressing pancreatic secretion and stimulating gastric secretion.
Advanced terms that may appear in context in MCAT passages
Juxtaglomerular cell
The juxtaglomerular cells are cells in the kidney that synthesize, store, and secrete the enzyme renin.
Paraventricular nucleus of hypothalamus
The paraventricular nucleus (PVN) is an aggregation of neurons in the hypothalamus, which produces many hormones.
Hypophyseal portal system
The hypophyseal portal system is the system of blood vessels that links the hypothalamus and the anterior pituitary.
A preprohormone is the precursor protein to one or more prohormones, which are in turn precursors to peptide hormones.
Insulin-like growth factor
The insulin-like growth factors are polypeptides with high sequence similarity to insulin. They are part of a complex system that cells use to communicate with their physiologic environment.
Amylin is a peptide hormone secreted by pancreatic beta-cells at the same time as insulin
Zona glomerulosa
The zona glomerulosa of the adrenal gland is the most superficial layer of the adrenal cortex, lying directly beneath the adrenal gland's capsule.
Zona fasciculata
The cells of the zona fasciculata sit directly beneath the zona glomerulosa within the adrenal cortex, chiefly producing glucocorticoids.
Corticotropes are cells in the anterior pituitary which produce adrenocorticotrophic hormone and melanocyte stimulating hormone.
Somatotropes are cells in the anterior pituitary which produce growth hormone.
Pituitary stalk
The pituitary stalk (infundibulum) is the connection between the hypothalamus and the posterior pituitary.
Thyroid peroxidase
Thyroid peroxidase is an enzyme mainly expressed in the thyroid that liberates iodine for addition onto tyrosine residues on thyroglobulin for the production of thyroid hormones.
Deoxycorticosterone is a steroid hormone produced by the adrenal gland that possess mineralocorticoid activity and acts as a precursor to aldosterone.
Magnocellular neurosecretory cell
Magnocellular neurosecretory cells are large cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus which produce oxytocin and/or vasopressin.
Supraoptic nucleus
The supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain.
Herring bodies
Herring bodies are structures found in the posterior pituitary representing the terminal end of the axons from the hypothalamus, where hormones are temporarily stored.
Pars intermedia
Pars intermedia is the boundary between the anterior and posterior lobes of the pituitary.