Kaplan MCAT Biology Chapter 5: The Endocrine System

Gland

an organ that produces and releases hormones

Hormones

chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues

Peptide hormone

a hormone made up of amino acids that is charged and can't pass through the plasma membrane which binds to an extracellular receptor; effects are usually rapid but short-lived; most names end in -in

Signaling cascade

the series of events, starting with the binding of a peptide hormone to a surface receptor (first messenger), which ultimately results in a change in cellular behavior via the transmission of a second messenger

Amplification

characteristic of a signaling cascade, in which the binding of a single peptide hormone to a membrane-bound receptor results in a signal that increases in strength through the signaling cascade

Steroid hormone

a hormone derived from cholesterol and produced primarily by the gonads and adrenal cortex; can easily cross the cell membrane, receptors are generally intracellular; most names end in -one, -ol, or -oid

Amino acid-derivative hormone

a hormone derived from one or two amino acids; examples include epinephrine, norepinephrine, triiodothyronine, and thyroxine

Direct hormone

a substance secreted into the bloodstream that causes a change in the physiological activity of cells without requiring an intermediary

Tropic hormone

a hormone which travels to a target cell or organ, where it triggers release of another hormone, which causes changes in the physiological activity of target cells

Hypothalamus

the region of the forebrain that controls the autonomic nervous system and is the control center for hunger, thirst, body temp, and other visceral functions; also secretes factors that regulate pituitary secretions (controls anterior pituitary)

Hypophyseal portal system

a blood vessel system that directly connects the hypothalamus with the anterior pituitary

Gonadotropin-releasing hormone (GnRH)

a hormone released from the hypothalamus that triggers the anterior pituitary to secrete FSH and LH

Growth hormone-releasing hormone (GHRH)

a hormone released from the hypothalamus that triggers the anterior pituitary to secrete growth hormone (GH)

Thyroid-releasing hormone

a hormone released from the hypothalamus that triggers the anterior pituitary to secrete thyroid-stimulating hormone (TSH)

Corticotropin-releasing hormone (CRH)

a hormone released from the hypothalamus that triggers the anterior pituitary to secrete adrenocorticotropic hormone (ACTH)

Anterior pituitary gland

an endocrine gland whose secretions are controlled by the hypothalamus; secretes seven peptide hormones, four tropic (FLAT) and three direct (PEG)

Posterior pituitary gland

an endocrine gland which contains the nerve terminals of neurons with cell bodies in the hypothalamus; receives and stores two hormones produced by the hypothalamus, ADH and oxytocin, but does not produce any hormones itself

Thyroid gland

an endocrine gland located in the neck that synthesizes triiodothyronine, thyroxine, and calcitonin

Adrenal glands

a pair of endocrine glands that sit just above the kidneys and secrete epinephrine, norepinephrine, and several corticosteroids

Adrenal cortex

the outer section of each adrenal gland; secretes corticosteroids

Corticosteroids

a group of steroid hormones produced in the adrenal cortex, including glucocorticoids (cortisol + cortisone), mineralocorticoids (aldosterone), and cortical sex hormones; functions are the three S's: sugar, salt, and sex

Glucocorticoids

a group of steroid hormones released from the adrenal cortex which increase blood glucose levels; their release is under the control of ACTH

Mineralocorticoids

a group of steroid hormones produced by the adrenal cortex which regulate salt and water homeostasis; most notable example is aldosterone

Renin-angiotensin-aldosterone system

a hormone cascade pathway that helps regulate blood pressure and blood volume

Islets of Langerhans

small clusters of hormone-producing cells in the pancreas which make up the endocrine portion of the organ

Alpha cells

cells in the pancreatic islets of Langerhans which secrete glucagon

Beta cells

cells in the pancreatic islets of Langerhans which secrete insulin

Delta cells

cells in the pancreatic islets of Langerhans which secrete somatostatin

Diabetes mellitus

a group of metabolic disorders characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both

Pineal gland

a gland located deep within the brain which secretes melatonin

Follicle-stimulating hormone (FSH)

a tropic peptide hormone secreted by the anterior pituitary which stimulates follicle maturation in females and spermatogenesis in males

Luteinizing hormone (LH)

a tropic peptide hormone secreted by the anterior pituitary which stimulates ovulation in females and testosterone synthesis in males

Adrenocorticotropic hormone (ACTH)

a tropic peptide hormone secreted by the anterior pituitary which stimulates the adrenal cortex to synthesize and secrete glucocorticoids

Thyroid-stimulating hormone (TSH)

a tropic peptide hormone secreted by the anterior pituitary which stimulates the thyroid to produce thyroid hormones

Prolactin

a direct peptide hormone secreted by the anterior pituitary which stimulates milk production and secretion

Endorphins

direct peptide hormones secreted by the anterior pituitary which decrease the sensation of pain and can promote euphoria

Growth hormone (GH)

a direct peptide hormone secreted by the anterior pituitary which stimulates bone and muscle growth and raises blood glucose levels

Antidiuretic hormone (ADH)

a peptide hormone produced by the hypothalamus and secreted by the posterior pituitary which stimulates water reabsorption in the kidneys by increasing the permeability of the collecting duct

Oxytocin

a peptide hormone produced by the hypothalamus and secreted by the posterior pituitary which stimulates uterine contractions during labor and milk secretion during lactation and may promote bonding behavior

Triiodothyronine (T3) and Thyroxine (T4)

amino-acid derivative hormones secreted by the follicular cells of the thyroid which stimulate metabolic activity

Calcitonin

a peptide hormone secreted by the parafollicular cells of the thyroid which decreases blood calcium concentrations

Parathyroid hormone (PTH)

a peptide hormone secreted by the parathyroid glands that increases blood calcium concentrations

Cortisol and cortisone

steroid hormones secreted by the adrenal cortex which increase blood glucose concentrations and decrease protein synthesis

Aldosterone

a steroid hormone secreted by the adrenal cortex which increases water reabsorption in the kidneys by increasing sodium reabsorption and also promotes potassium and hydrogen ion excretion

Epinephrine and norepinephrine

amino-acid derivative hormones secreted by the adrenal medulla which increase blood glucose concentrations, increase HR, dilate bronchi, and alter blood flow patterns; effects centered on the "fight-or-flight" response

Glucagon

a peptide hormone secreted by pancreatic endocrine alpha cells that raises blood glucose levels; an antagonistic hormone to insulin

Insulin

a peptide hormone secreted by pancreatic endocrine beta cells that lowers blood glucose levels; an antagonistic hormone to glucagon

Somatostatin

a peptide hormone secreted by pancreatic endocrine delta cells that inhibits both insulin and glucagon secretion

Melatonin

a peptide hormone secreted by the pineal gland which is involved in circadian rhythms

Erythropoietin

a peptide hormone secreted by the kidney which stimulates bone marrow to produce erythrocytes

Atrial natriuretic peptide (ANP)

a peptide hormone secreted by cells of the atria of the heart in response to high blood pressure which promotes excretion of sodium, increasing urine volume; functionally antagonistic to aldosterone

Thymosin

a peptide hormone secreted by the thymus which stimulates T-cell development