뒤로Endocrine System - Anatomy & Physiology
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The endocrine system regulates body functions by releasing hormones that control metabolism, growth, reproduction, and homeostasis.
A hormone is a chemical messenger secreted by endocrine glands that travels through the blood to target cells to regulate physiology and behavior.
An endocrine gland is a discrete organ that secretes hormones, while endocrine tissue refers to hormone-producing cells within organs not primarily endocrine.
A target cell is a cell that has specific receptors for a hormone and responds to its signal.
The nervous system uses electrical impulses for rapid, short-term control; the endocrine system uses hormones for slower, long-lasting regulation.
Hormones are classified as amino acid derivatives, peptides/proteins, and steroids.
Amino acid and peptide hormones are water-soluble and travel freely; steroid hormones are lipid-soluble and travel bound to carrier proteins.
Water-soluble hormones bind to cell membrane receptors; lipid-soluble hormones bind to intracellular receptors in the cytoplasm or nucleus.
Water-soluble hormones activate second messenger systems; lipid-soluble hormones directly affect gene transcription.
Hormone release is controlled by humoral (blood chemistry), neural, and hormonal stimuli.
Negative feedback decreases hormone secretion when levels reach a set point to maintain homeostasis.
Positive feedback amplifies hormone secretion to rapidly increase a physiological response.
The hypothalamus connects to the anterior and posterior pituitary glands, regulating their hormone secretion.
A releasing hormone from the hypothalamus stimulates the anterior pituitary to secrete specific hormones.
An inhibiting hormone from the hypothalamus suppresses anterior pituitary hormone secretion.
A tropic hormone is secreted by the anterior pituitary and stimulates another endocrine gland to release hormones.
The hypothalamus secretes releasing and inhibiting hormones into the hypophyseal portal system to regulate anterior pituitary secretion.
The hypothalamus produces hormones stored in the posterior pituitary, which releases them into the blood upon neural signals.
The anterior pituitary contains cells that produce hormones like GH, TSH, and ACTH; the posterior pituitary stores ADH and oxytocin.
The adrenal cortex produces mineralocorticoids, glucocorticoids, and androgens; the medulla produces epinephrine and norepinephrine.
Insulin is secreted by pancreatic beta cells in response to high blood glucose; it lowers blood glucose by promoting cellular uptake.
PTH is secreted by parathyroid glands in response to low blood calcium; it raises calcium levels by stimulating bone resorption.
Thyroid hormone is produced by follicular cells of the thyroid gland; it regulates metabolism and growth.
Oxytocin is produced by the hypothalamus and released by the posterior pituitary; it stimulates uterine contractions and milk ejection.
ADH is produced by the hypothalamus and released by the posterior pituitary; it promotes water reabsorption in kidneys to conserve water.
Tropic hormones from the anterior pituitary regulate other endocrine glands, controlling hormone secretion and maintaining homeostasis.