Human Anatomy & Physiology: The Endocrine System Flashcards

A comprehensive set of vocabulary flashcards covering the organs, hormones, and signaling mechanisms of the human endocrine system based on lecture notes.

Hormones

Chemical messengers synthesized and secreted by endocrine glands that interact with specific target cells to influence their functions and maintain homeostasis.

Paracrine signaling

A type of cell-cell communication where chemicals are secreted into the extracellular space to affect nearby but different types of cells.

Autocrine signaling

A type of communication where chemicals are secreted by cells into the interstitial fluid and elicit effects from the same cell or cell type.

Primary endocrine organs

Organs that have only endocrine functions; these include the anterior pituitary gland, thyroid gland, parathyroid gland, adrenal cortices, endocrine pancreas, and thymus.

Secondary endocrine organs

Organs that possess both endocrine and non-endocrine functions, such as the heart, kidneys, small intestines, testes, and ovaries.

Neuroendocrine organs

Organs consisting of nervous tissue that secrete neurohormones; examples include the hypothalamus, pineal gland, and the adrenal medulla.

Amino-acid hormones

Hormones consisting of one or more amino acids; they are generally hydrophilic and bind to plasma membrane receptors.

Steroid hormones

Hydrophobic hormones derived from cholesterol that bind to receptors located in the cytosol or the nucleus.

Up-regulation

A process where target cells produce and display a greater number of receptors in response to a temporary increase in blood hormone levels.

Down-regulation

A process where target cells decrease the number of receptors displayed in response to prolonged exposure to high levels of a hormone.

Second messenger system

A chemical series of events, such as the formation of cyclic adenosine monophosphate (cAMP), initiated after a hydrophilic hormone (first messenger) binds to a plasma membrane receptor.

Adenylate cyclase

An enzyme activated by a G-protein that catalyzes the formation of the second messenger cyclic adenosine monophosphate (cAMP).

Protein kinases

Enzymes activated by cAMP that catalyze the transfer of a phosphate group from ATP to another molecule in a process known as phosphorylation.

Hormonal stimuli

A regulation mechanism where endocrine cells change their secretion levels in response to the secretion of other hormones.

Humoral stimuli

A regulation mechanism where endocrine cells respond to the concentration of a certain ion or molecule in the blood or extracellular fluid.

Neural stimuli

A regulation mechanism where endocrine glands respond to signals directly from the nervous system.

Tropic hormones

Hormones that function primarily by controlling the secretion of hormones from other endocrine glands.

Trophic hormones

Hormones that induce growth in their specific target cells.

Hypothalamus

A small portion of the diencephalon vital to homeostatic processes; it regulates the pituitary gland via the infundibulum.

Anterior pituitary (adenohypophysis)

A true gland composed of hormone-secreting glandular epithelium that is part of the pituitary gland.

Posterior pituitary (neurohypophysis)

The part of the pituitary gland composed of nervous tissue; it stores and releases neurohormones produced by the hypothalamus.

Hypothalamic-hypophyseal portal system

A specialized blood supply involving capillaries and portal veins that allows the hypothalamus to deliver hormones directly to the anterior pituitary.

Antidiuretic hormone (ADH)

Also known as vasopressin, this neurohormone is produced by the hypothalamus to promote water retention by the kidneys via the insertion of aquaporins.

Diabetes insipidus

A disease caused by the lack of ADH secretion or activity, leading to extreme thirst and signs of dehydration.

Oxytocin

A neurohormone produced by the hypothalamus that triggers the milk let-down reflex in nursing mothers and uterine contractions during childbirth.

Thyroid-stimulating hormone (TSH)

An anterior pituitary tropic hormone that stimulates thyroid gland development and the secretion of thyroid hormones; it is stimulated by hypothalamic TRH.

Adrenocorticotropic hormone (ACTH)

An anterior pituitary tropic hormone that stimulates the development of the adrenal gland and the synthesis of steroid hormones; it is stimulated by hypothalamic CRH.

Prolactin (PRL)

A hormone that stimulates mammary gland growth and initiates/maintains milk production; its release is inhibited by dopamine.

Luteinizing hormone (LH)

A gonadotropin that stimulates testosterone production in males and estrogen/progesterone production and ovulation in females.

Follicle-stimulating hormone (FSH)

A gonadotropin that stimulates cells of the testes to concentrate testosterone and triggers the maturation of ovarian follicles in females.

Growth hormone (GH)

Also called somatotropin, it regulates growth in target tissues like skeletal muscle and bone; it is inhibited by hypothalamic somatostatin.

Insulin-like growth factor (IGF)

A hormone produced by the liver/target tissues in response to GH that triggers rapid protein synthesis and cell division for muscle and bone growth.

Thyroid follicles

Multiple spheres within the thyroid gland where follicle cells produce and secrete thyroid hormones.

Colloid

A protein-rich, gelatinous material in thyroid follicles that contains iodine atoms and the precursor for thyroid hormone.

Parafollicular cells

Large cells located in the spaces between adjacent thyroid follicles that produce the hormone calcitonin.

Triiodothyronine ($T_3$)

A thyroid hormone consisting of an amino acid core bound to $3$ iodine atoms; it is more physiologically active than $T_4$.

Thyroxine ($T_4$)

A thyroid hormone bound to $4$ iodine atoms; it acts as a reservoir as it is commonly converted to $T_3$ in target tissues.

Basal metabolic rate

The amount of energy required by the body at rest; it is set by thyroid hormones.

Thyroglobulin

A large precursor protein for thyroid hormone secreted by follicle cells into the colloid.

Parathyroid hormone (PTH)

A hormone secreted by chief cells in response to declining blood calcium levels to increase release from bone and renal reabsorption.

Calcitonin

A hormone produced by parafollicular cells that reduces blood calcium levels by inhibiting osteoclast activity and allowing unopposed osteoblast activity.

Adrenal cortex

The outer region of the adrenal gland divided into three zones: zona glomerulosa, zona fasciculata, and zona reticularis.

Adrenal medulla

The inner core neuroendocrine organ of the adrenal gland that secretes catecholamines, primarily epinephrine.

Aldosterone

The main mineralocorticoid that regulates $Na^+$ and $K^+$ concentrations and maintains blood pressure through the RAAS.

Renin-angiotensin-aldosterone system (RAAS)

A complex series of interactions that increases blood pressure and preserves blood flow to the heart, brain, and kidneys.

Cortisol

The most potent glucocorticoid; it mediates the body's stress response by increasing blood glucose levels and inhibiting inflammation.

Addison’s disease

A condition characterized by the hyposecretion of both cortisol and aldosterone, potentially leading to an adrenal crisis.

Chromaffin cells

Adrenal medulla cells derived from nervous tissue that secrete epinephrine to mediate immediate stress responses.

Pancreatic islets

Small rounded islands of endocrine cells in the pancreas; also known as the islets of Langerhans.

Alpha cells

Cells in the pancreatic islets that secrete the peptide hormone glucagon.

Beta cells

Cells in the pancreatic islets that secrete the protein hormone insulin.

Glucagon

A hormone that increases blood glucose levels by promoting glycogenolysis, gluconeogenesis, and the release of fats from adipose tissue.

Insulin

The primary antagonist of glucagon that lowers blood glucose levels by promoting taking up and storage of ingested nutrients.

Ketone bodies

Four-carbon molecules formed during fatty acid metabolism; their accumulation in the blood can cause ketoacidosis.

Type I diabetes mellitus

A disease caused by the destruction of insulin-producing beta islet cells, leading to hyperglycemia and ketones in the urine.

Type II diabetes mellitus

A condition where target tissues develop insulin resistance, meaning they become insensitive to insulin despite its presence.

Pineal gland

A primary endocrine gland in the brain that secretes melatonin to adjust the sleep/wake cycle.

Thymopoietin

A hormone secreted by the thymus (along with thymosin) that functions as a paracrine signal to assist in T lymphocyte maturation.

Testosterone

The male sex steroid hormone responsible for gamete production, bone growth, muscle mass, and secondary sex characteristics.

Estrogen

A female sex hormone that stimulates secondary female sex characteristics and regulates the menstrual cycle.

Progesterone

A hormone whose secretion peaks after ovulation and during pregnancy to support fetal development and prepare the body for pregnancy.

Leptin

A protein hormone produced by adipocytes that induces satiety to prevent overfeeding by interacting with the hypothalamus.

Atrial natriuretic peptide (ANP)

A hormone secreted by cardiac muscle cells that triggers vasodilation and natriuresis to decrease blood volume and lower blood pressure.

Erythropoietin (EPO)

A hormone secreted by the kidneys in response to low blood oxygen levels to stimulate the production of new erythrocytes.