Endocrine System Lecture Flashcards

These flashcards provide definitions for key vocabulary terms related to the Endocrine System, including glands, hormones, action mechanisms, and associated disorders.

Endocrine system

A system of ductless glands that, along with the nervous system, regulates body functions to maintain homeostasis and coordinate communication.

Endocrine glands

Ductless cells, tissues, and organs that secrete hormones directly into the body fluids; "endocrine" means internal secretion.

Exocrine glands

Glands that secrete products into ducts or tubes that lead to a body surface for external delivery to a specific site.

Paracrine secretions

Chemical messengers that affect nearby cells, often referred to as local hormones.

Autocrine secretions

Chemical messengers that affect only the cells that actually secrete them.

Steroid hormones

Lipid-soluble organic compounds containing rings of carbon and hydrogen atoms, all produced from cholesterol.

Nonsteroid hormones

Hormones that include amines (derived from tyrosine), proteins (long amino acid chains), peptides (short amino acid chains), and glycoproteins (carbohydrates joined to proteins).

Upregulation

An increase in the number of receptors on a target cell in response to a decrease in hormone level.

Downregulation

A decrease in the number of receptors on a target cell due to an increase in hormone level.

Signal transduction

The entire process of chemical communication from outside a cell to inside, often involving first and second messengers.

Second messenger

A chemical, such as cyclic adenosine monophosphate ($cAMP$), that induces changes inside a cell leading to a hormone's effect.

Prostaglandins

Potent paracrine substances synthesized just before release that regulate cellular responses to hormones and are rapidly inactivated after use.

Negative feedback

A control mechanism where a rising level of a hormone leads to a decrease in its secretion to maintain stable concentrations.

Tropic hormones

Hormones that act on other glands to control their activity.

Pituitary gland

A gland at the base of the brain in the sella turcica of the sphenoid bone, consisting of an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis).

Growth hormone ($GH$)

An anterior pituitary hormone that stimulates cells to enlarge and divide, increases protein synthesis, and increases fat usage.

Thyroid-stimulating hormone ($TSH$)

An anterior pituitary hormone that stimulates the secretion of thyroid hormones ($T_3$ and $T_4$).

Adrenocorticotropic hormone ($ACTH$)

Hormone that stimulates the secretion of cortisol and other glucocorticoids from the adrenal cortex.

Antidiuretic hormone ($ADH$)

A posterior pituitary hormone that decreases urine production to reduce water excretion and causes vasoconstriction to increase blood pressure.

Oxytocin ($OT$)

A posterior pituitary hormone that causes muscle contraction in the uterine wall during childbirth and milk ejection during lactation.

Thyroxine ($T_4$)

A thyroid hormone produced by follicular cells that increases the rate of energy release and protein synthesis; contains 4 iodine atoms.

Triiodothyronine ($T_3$)

A potent thyroid hormone that increases the rate of energy release and protein synthesis; more potent than $T_4$.

Calcitonin

A thyroid hormone produced by extrafollicular cells that lowers blood calcium and phosphate ion concentrations.

Parathyroid hormone ($PTH$)

A hormone that increases blood calcium levels by acting on bones, kidneys, and intestines.

Adrenal cortex

The outer portion of the adrenal gland which secretes steroid hormones including aldosterone, cortisol, and sex hormones.

Adrenal medulla

The central portion of the adrenal gland which secretes amine hormones, approximately $80\%$ epinephrine and $20\%$ norepinephrine.

Aldosterone

A mineralocorticoid from the adrenal cortex that regulates electrolytes by conserving $Na^+$ and excreting $K^+$.

Cortisol

A glucocorticoid that decreases protein synthesis, increases fatty acid release, and stimulates glucose synthesis from noncarbohydrates.

Insulin

A hormone secreted by beta cells of the pancreatic islets that decreases blood glucose by promoting glycogen formation.

Glucagon

A hormone secreted by alpha cells of the pancreatic islets that increases blood glucose by stimulating the liver to break down glycogen.

Diabetes Mellitus

A metabolic disease resulting from a lack of insulin (Type 1) or the inability of cells to recognize insulin (Type 2).

Pineal gland

A gland in the brain that secretes melatonin, which regulates circadian rhythms.

Thymus gland

A gland in the mediastinum that secretes thymosins to promote the development of T-lymphocytes for immunity.

General Adaptation Syndrome ($GAS$)

The hypothalamus-controlled response to stress occurring in three stages: alarm, resistance, and exhaustion.