The Endocrine System
37.1 Types of Hormones
The endocrine system plays a role in growth, metabolism, and other processes by releasing hormones into the blood.
Lipid-Derived, Amino Acid-Derived, and Peptide Hormones
All hormones in the human body can be divided into lipid-derived, amino acid-derived, and peptide hormones.
37.2 How Hormones Work
How Hormones Work
Hormones are chemical messengers that relay messages to cells that display specific receptors for each hormone and respond to the signal.
Intracellular Hormone Receptors
Lipid-soluble hormones diffuse across the plasma membrane of cells, binding to receptors inside the cells where they alter gene expression.
Plasma Membrane Hormone Receptors
Hormones that cannot diffuse through the plasma membrane instead bind to receptors on the cell surface, triggering intracellular events.
37.3 Regulation of Body Processes
Hormonal Regulation of the Excretory System
The contrasting actions of antidiruetic hormone and aldosterone work to regulate the level of water in the body.
Hormonal Regulation of the Reproductive System
Male and female gonads are regulated by FSH and LH from the pituitary; their production is stimulated by GnRH, secreted by the hypothalamus.
Hormonal Regulation of Metabolism
The levels of glucose in the blood are regulated by the hormones insulin and glucagon from the pancreas, and T3 and T4 from the thyroid.
Hormonal Control of Blood Calcium Levels
Blood levels of calcium are regulated by the parathyroid hormone, which acts on the bones, kidneys, and intestines to keep levels constant.
Hormonal Regulation of Growth
Body growth is controlled by growth hormone (GH), produced by the anterior pituitary, and IGF-1, whose production is stimulated by GH.
Hormonal Regulation of Stress
The adrenal glands respond to either short-term or long-term stressors by releasing different hormones that act differently on the body.
37.4 Regulation of Hormone Production
Humoral, Hormonal, and Neural Stimuli
The release of hormones can be triggered by changes in the blood ("humor"), by the actions of other hormones, or by neurological stimuli.
37.5 Endocrine Glands
The hypothalamus, an endocrine organ, regulates the anterior pituitary gland and transports hormones along the posterior pituitary gland.
The thyroid gland, the largest endocrine gland, is responsible for the production of the hormones T3, T4, and calcitonin.
Parathyroid glands produce parathyroid hormone, which is responsible for specific physiological responses in the body related to calcium.
Adrenal glands are composed of the adrenal cortex and medulla; both produce hormones that control essential body functions and responses.
The pancreas produces digestive enzymes and hormones, which are important in blood sugar regulation and other body functions.
Pineal Gland and Gonads
The pineal gland is responsible for melatonin production, while the gonads secrete hormones relating to sexual characteristic development.
Organs with Secondary Endocrine Functions
Several organs with specialized non-endocrine functions possess endocrine roles, such as hormone production and release.