Bio Test 2: Endocrine System

Endocrine system

Collection of endocrine glands and other tissues that secrete hormones into the bloodstream to alter body physiology and help maintain homeostasis.

Hormone (classic definition)

An organic molecule made by living cells, secreted into the bloodstream, and transported to distant target cells with specific receptors to change their functioning.

Endocrine vs. exocrine secretion

Endocrine glands release hormones into the blood; exocrine glands release secretions through ducts.

Target cell

A cell that has specific receptors for a particular hormone and can respond to it.

Endocrine gland

An organ or group of cells that secretes hormones into the bloodstream.

Pineal gland hormone

Melatonin.

Melatonin hormone class

Amine derived from tryptophan.

Melatonin function

Regulates internal daily and annual body rhythms and influences hormones such as gonadotropins associated with these cycles.

Anterior pituitary (adenohypophysis)

Separate gland that secretes TSH, FSH, LH, ACTH, GH, prolactin, and other substances with possible hormonal activity.

Growth hormone (GH)

Anterior pituitary hormone that stimulates body growth and cell mitosis.

Prolactin (PRL)

Anterior pituitary hormone that stimulates milk production in mammary glands.

Adrenocorticotropic hormone (ACTH)

Anterior pituitary hormone that stimulates the adrenal cortex to produce and secrete steroid hormones related to stress and water balance.

Thyroid-stimulating hormone (TSH)

Anterior pituitary hormone that stimulates thyroid growth and the synthesis and secretion of thyroid hormones, including T3 and T4.

Follicle-stimulating hormone (FSH)

Anterior pituitary gonadotropin that contributes to development of the ovaries and testes, egg and sperm production, and gonadal sex hormone production.

Luteinizing hormone (LH)

Anterior pituitary gonadotropin that contributes to gonadal development and function, ovulation, and gonadal sex hormone production.

Gonadotropins

FSH and LH; anterior pituitary hormones that regulate gonadal development and reproductive functions.

β-Endorphin

POMC-derived pituitary hormone that suppresses pain and may act as an endogenous opioid.

β-Lipotropin (β-LPH)

POMC-derived pituitary hormone that affects lipid metabolism, primarily through lipolysis.

Melanocyte-stimulating hormone (MSH)

In animals, stimulates melanocytes to produce melanin; the study guide states it is not actually secreted in humans, may be produced through ACTH cleavage, and has unknown functional importance in humans.

Posterior pituitary (neurohypophysis)

Part of the hypothalamic-pituitary system that releases oxytocin and vasopressin made by hypothalamic neurosecretory neurons.

Oxytocin (OT/OXY)

Peptide released from the posterior pituitary that stimulates uterine contractions during labor and milk let-down from mammary glands.

Vasopressin (AVP/ADH)

Antidiuretic hormone that promotes water retention, reduces urine volume, concentrates urine, and can increase blood pressure through vasoconstriction.

Oxytocin regulation

Controlled by neuroendocrine reflexes involving stimulation from the nipples and uterus.

Vasopressin regulation

Stimulated by low blood pressure detected by baroreceptors and increased blood tonicity detected by osmoreceptors.

Thyroid hormones

Triiodothyronine (T3) and thyroxine (T4); iodinated amino acid hormones that stimulate metabolism, nervous system activity, and growth.

Triiodothyronine (T3)

Thyroid hormone containing three iodine atoms.

Thyroxine (T4)

Thyroid hormone containing four iodine atoms; also called tetraiodothyronine.

Calcitonin (CT)

Thyroid C-cell hormone that inhibits osteoclast-mediated bone breakdown and increases calcium and phosphate excretion by the kidneys, lowering their blood concentrations.

Parafollicular cells (C cells)

Cells located between thyroid follicles that secrete calcitonin.

Parathyroid hormone (PTH)

Parathyroid hormone that raises blood calcium by stimulating bone breakdown, increasing calcium absorption from the gut, and decreasing calcium excretion by the kidneys.

Thymosin and thymopoietin

Thymus peptides that stimulate the production and activation of certain white blood cells.

Atrial natriuretic hormone (ANH)

Heart-derived peptide that promotes sodium excretion and, according to the study guide, inhibits potassium excretion; increased water loss helps lower blood pressure.

Insulin-like growth factors (IGF-I and IGF-II)

Liver-derived peptides that stimulate mitosis, body growth, and protein anabolism.

Gastrin

Gastrointestinal hormone that stimulates stomach acid secretion and increases gut activity.

Cholecystokinin (CCK)

Gastrointestinal hormone that stimulates pancreatic digestive enzyme secretion and gallbladder bile release while inhibiting stomach activity and acid secretion.

Glucose-dependent insulinotropic hormone (GIP)

Also called gastric inhibitory peptide; stimulates insulin secretion and inhibits gastrin secretion.

Motilin

Gastrointestinal hormone that stimulates intestinal smooth muscle contraction.

Secretin

Gastrointestinal hormone that stimulates alkaline pancreatic secretions to neutralize stomach acid entering the intestine.

Insulin

Pancreatic hormone that promotes glucose uptake into cells, glycogenesis, lipogenesis, and protein anabolism; lowers blood glucose.

Insulin and glucose metabolism

Insulin promotes storage and use of nutrients and inhibits conversion of amino acids and fatty acids into glucose.

Glucagon

Pancreatic hormone that stimulates gluconeogenesis and glycogenolysis, increasing blood glucose.

Somatostatin (SS)

Pancreatic hormone that inhibits insulin and glucagon secretion; also acts as growth hormone release-inhibiting hormone in the hypothalamic-pituitary system.

Epinephrine and norepinephrine

Adrenal medulla amines that increase heart rate, blood pressure, breathing rate, and blood flow to skeletal muscles while reducing gut activity and gut blood flow.

Aldosterone

Adrenal cortex steroid that promotes potassium excretion and sodium retention by the kidneys; water retention helps increase blood volume and pressure.

Cortisol

Adrenal cortex steroid that supports glucose availability between meals by increasing the use of amino acids and fatty acids for energy and inhibiting protein production.

Adrenal cortex sex hormones

Supplemental source of androgens such as DHEA and androstenedione, as well as estrogens and progesterone.

Erythropoietin (EPO)

Kidney-derived hormone that stimulates red blood cell production.

Calcitriol

Active form of vitamin D, 1,25-(OH)2-vitamin D3; stimulates calcium absorption from the gut and calcium retention by the kidneys.

Androgens

Testicular and other steroid hormones, including testosterone and dihydrotestosterone, that promote male secondary sex characteristics, sexual activity, and sperm production.

Testosterone (T)

Androgen that supports male secondary sex characteristics, sexual activity, and sperm production.

Dihydrotestosterone (DHT)

Androgen formed from testosterone that has greater potency at certain target cells.

Estrogens

Include estradiol; promote female secondary sex characteristics and contribute to egg development and ovulation.

Estradiol (E2)

A major estrogen involved in female reproductive functions and secondary sex characteristics.

Progestins

Include progesterone; influence reproductive functions and help maintain pregnancy.

Progesterone (P)

Steroid hormone involved in reproductive functions and maintenance of pregnancy; also produced by the placenta.

Placental progestins and estrogens

Placental steroid hormones that support pregnancy.

Human chorionic gonadotropin (hCG)

Placental glycoprotein hormone that supports the placenta during pregnancy and stimulates placental steroid synthesis.

Growth hormone family

Includes growth hormone (GH), prolactin (PRL), and human placental lactogen (hPL).

Glycoprotein hormone family

Includes LH, FSH, TSH, and human chorionic gonadotropin (hCG).

Gastrin hormone family

Includes gastrin and cholecystokinin (CCK).

Secretin hormone family

Includes secretin, vasoactive intestinal peptide (VIP), glucagon and glicentin, and gastric inhibitory peptide (GIP), as listed in the study guide.

Insulin hormone family

Includes insulin, IGF-I, IGF-II, and relaxin.

POMC (proopiomelanocorticotropin)

Precursor protein produced by some anterior pituitary cells that can be cleaved into ACTH, MSH variants, β-endorphin, met-enkephalin, and β-lipotropin.

Hypothalamus

Brain region that contains neurosecretory neurons and regulates pituitary hormone release.

Neurosecretory neuron

Neuron with axon terminals positioned near capillary blood vessels so it can release hormones into the blood.

Paraventricular and supraoptic nuclei

Hypothalamic nuclei containing neurosecretory neurons whose axons travel to the posterior pituitary.

Infundibulum

Structure through which hypothalamic neuron axons travel to reach the posterior pituitary.

Hypophysiotropic hormones

Hypothalamic releasing hormones and release-inhibiting hormones that regulate the anterior pituitary.

Median eminence

Hypothalamic region where neurosecretory neurons release hypophysiotropic hormones into the blood supply controlling the anterior pituitary.

Thyrotropin-releasing hormone (TRH)

Hypothalamic releasing hormone that stimulates anterior pituitary TSH secretion.

Corticotropin-releasing hormone (CRH)

Hypothalamic releasing hormone that stimulates anterior pituitary ACTH secretion.

Growth hormone-releasing hormone (GHRH)

Hypothalamic releasing hormone that stimulates anterior pituitary GH secretion.

Gonadotropin-releasing hormone (GnRH)

Hypothalamic releasing hormone that stimulates anterior pituitary gonadotropin secretion, including FSH and LH.

Somatostatin / GHRIH

Hypothalamic peptide that inhibits growth hormone release; also called growth hormone release-inhibiting hormone.

Dopamine (DA)

Hypothalamic catecholamine that acts as a release-inhibiting hormone, especially inhibiting prolactin secretion.

Hypothalamic releasing hormone chemical classes

All the releasing and release-inhibiting hormones listed in the study guide are peptides except dopamine, which is a catecholamine.

Posterior vs. anterior pituitary

The posterior pituitary releases hypothalamic hormones oxytocin and vasopressin; the anterior pituitary synthesizes and secretes its own hormones in response to hypothalamic regulation.

Anterior pituitary hormone families

TSH, FSH, and LH are glycoproteins; GH and prolactin belong to the growth hormone family.

POMC-derived hormones

ACTH, α-, β-, and γ-MSH, β-endorphin, met-enkephalin, and β-lipotropin can be produced by cleavage of POMC.

Hormone family formation

Similar hormone genes are thought to have arisen through gene duplication, producing related hormones with similar structures or functions.

Peptide, polypeptide, and protein hormones

Water-soluble hormones that vary in size and amino acid sequence.

Peptide hormone synthesis

Peptide hormones are synthesized in the rough ER as prohormones, then cleaved or modified in the smooth ER and Golgi and stored in secretory vesicles.

Prohormone

Precursor molecule that must be processed or cleaved to produce an active hormone or hormone products.

Biogenic amines

Hormones derived from amino acids by modification, including removal of the carboxyl group; examples include histamine, serotonin, melatonin, dopamine, epinephrine, and norepinephrine.

Histamine

Biogenic amine derived from histidine.

Serotonin

Biogenic amine derived from tryptophan.

Melatonin precursor

Melatonin is derived from tryptophan.

Catecholamine precursors

Dopamine, epinephrine, and norepinephrine are derived from tyrosine.

Steroid hormones

Hydrophobic hormones derived from cholesterol that are not very water-soluble.

Steroid hormone storage

Steroid hormones are generally synthesized as needed rather than stored in secretory vesicles.

Iodinated amino acid hormones

T3 and T4 are made only in the thyroid gland from thyronine derived from tyrosine; they are hydrophobic and not very water-soluble.

Eicosanoids

Hydrophobic signaling molecules derived from membrane phospholipids; synthesized as needed rather than stored.

Eicosanoid examples

Prostaglandins, prostacyclins, thromboxanes, leukotrienes, and HETEs.

Eicosanoid actions

Can act at many levels in the body; the study guide identifies them as signaling molecules derived from membrane phospholipids.

Growth factors (GFs)

Molecules that influence cell growth and division; they can function as hormones, cytokines, or paracrines and often influence cell-cycle checkpoints.

Oncogenes

Genes associated with growth-factor-related genes that can contribute to abnormal cell growth when altered or activated.

Oncogene products

Can include altered versions of growth factors or proteins associated with growth-factor signaling, as introduced in the lecture.

APUD

Amine precursor uptake and decarboxylation; the term describes a group of cells associated with uptake and processing of amine precursors.

APUDomas

Tumors associated with APUD cells that can cause ectopic hormone secretion.

Ectopic secretion

Hormone secretion from an inappropriate source or at an inappropriate time.