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Hormones
substances secreted into bloodstream which stimulate a response in another cell, tissue, or organ; chemical mediators that regulate tissue/organ growth and development, metabolism and energy balance, blood, ECF, and internal envir.’s chemical composition and volume, cause contraction of cardiac and smooth muscle
Endocrine glands
secrete hormones in low amounts into interstitial fluid and capillaries; pituitary, thyroid, parathyroid, adrenal, pineal
Exocrine glands
secrete substances into ducts going to external environment (cavities, lumen, surfaces) e.g. sweat and oil glands, mucous glands (saliva), digestive glands (enzymes into GI tract)
Secreting cells
found in hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, placenta; some of these organs/tissue aren’t part of the endocrine system or classified as endocrine glands but secrete hormones
Synergistic effect
hormones work more effectively when a second is present to assist; act together so the sum of their individual effects is greater e.g. glucagon and epinephrine
Antagonistic effect
hormones oppose the action of others; one causes the opposite cellular response to the other or reduces the number of receptors e.g. insulin and glucagon
Hormone receptors
continually synthesized and broken down; down-regulated (less sensitive=less effect) in the presence of high concentrations of hormones (i.e. insulin and T2D) or up-regulated (more sensitive=more effect) in the presence of low concentrations of hormone (i.e. testosterone with age)
Local hormones
hormones that act close by; don’t enter the bloodstream or circulate
Paracrines
local hormones that act on nearby cells; Interleukin-2 is produced by T cells which helps activate other immune cells
Autocrines
local hormones that act on the same cell that secretes them; -Interleukin-2 can stimulate the T cell to produce more T cell
Water-soluble hormones
amine hormones, peptide/protein hormones; circulate freely in blood plasma; bind to cell surface receptors on plasma membrane and need help of messengers because they can’t diffuse through PM
Lipid-soluble hormones
steroid hormones, thyroid hormones, nitric oxide, eicosanoids; require transport protein (made in liver) to travel through blood; receptors inside target cell; 10% are free in the blood and penetrate plasma membrane to enter nucleus and cause reaction
Steroid hormones
lipid-soluble hormone; derived from cholesterol; each is unique due to the presence of different chemical groups attached at various sites on the four rings at the core of its structure
Nitric oxide
lipid-soluble hormone; vasodilator; hormone and neurotransmitter; secreted from endothelial cells lining blood vessels
Eicosanoid hormones
lipid-soluble local hormone; derived from a 20-carbon fatty acid –> arachidonic acid; produce prostaglandins and leukotrienes (mediate/promote inflammatory response); appear in the blood in small quantities; inactivated quickly; bind to receptors on target cells to stimulate or inhibit synthesis of second messengers
Amine hormones
water-soluble hormone; synthesized by decarboxylating and modifying amino acids; e.g. catecholamines: epinephrine, norepinephrine and dopamine (from tyrosine), histamines (from histidine) and serotonin and melatonin (from tryptophan)
Peptide and protein hormones
water-soluble hormone; amino acid polymers (small and large chain); ADH and oxytocin; hGH and insulin; TSH (glycoprotein hormones)
Secretion regulation
signals from the nervous system, chemical changes in the blood, other hormones; mostly by negative and a few positive feedback
Hypothalamus
links nervous and endocrine systems; produce 5 releasing and 2 inhibiting hormones via the hypophyseal portal system; control the release of hormones by the pituitary gland
Neurosecretory cells (hypothalamus)
secrete hypothalamic hormones in response to stimulation; axons form the hypothalamohypophyseal tract
Pituitary gland
connected to the hypothalamus by the infundibulum; composed of the anterior and posterior lobes
Anterior lobe (adenohypophysis)
75% of the pituitary’s weight; secretes 7 hormones (hGH, TSH, FSH, LH, PRL, ACTH, MSH) that circulate and target other endocrine glands (tropic hormones) from 5 types of cells (somatotrophs [-], thyrotrophs [-], gonadotrophs, lactotrophs, corticotrophs [-])
Posterior lobe (neurohypophysis)
made of hypothalamic neural axon tissue; stores/secretes 2 hormones (ADH, OT) from axon terminals made by neurosecretory cells
Releasing hormones (hypothalamus)
1. Growth hormone-releasing hormone 2. Thyrotropin releasing hormone 3. Corticotropin-releasing hormone 4. Prolactin-releasing hormone 5. Gonadotropin-releasing hormone
Inhibiting hormones (hypothalamus)
1. Growth hormone-inhibiting hormone (somatostatin) 2. Prolactin-inhibiting hormone (dopamine)
Human growth hormone
most plentiful; controlled by GHRH and GHIH; exerts its growth-promoting effect indirectly through IGFs; increases growth of bone and soft tissues (by increasing amino acid uptake and protein synthesis)
Insulin-like growth factors
small protein hormones
Antidiuretic hormone (ADH)
secretion varies with blood osmotic pressure; increase in blood volume = decrease in ADH secretion; decrease in blood volume = increase in ADH secretion
Osmoreceptors
in the hypothalamus; monitor blood osmotic pressure
Pineal gland
regulates biological clock/sleep-wake cycle; produces serotonin by day, converts it to melatonin at night (promotes sleeps); darkness stimulates serotonin secretion, lightness inhibits secretion; back roof of 3rd ventricle
Pancreas
acini cells are exocrine, islet cells are endocrine: 1) alpha cells increase blood glucose (secrete glucagon); 2) beta cells decrease blood glucose (secrete insulin) 3) delta (D) cells secrete somatostatin 4) F cells secrete pancreatic polypeptides; scattered islets of Langerhans contain secretin cells
Somatostatin
acts as a paracrine and inhibits insulin and glucagon release; also inhibits secretion of hGH
Pancreatic polypeptide
inhibits somatostatin secretion, gall bladder contraction and release of digestive enzymes
Parathyroid glands
parathyroid hormone increases blood Ca2+; decreases urinary excretion; promotes synthesis of calcitriol (active vit D) which increases absorption of Ca²+ from foods and bone
Chief/principal cells
parathyroid gland cell; produce PTH/parathormone
Oxiphil cells
parathyroid gland cell; function not known in normal parathyroid glands but secrete excess PTH in cases of parathyroid cancer
Thyroid glands
calcitonin decreases blood Ca++; TSH stimulates thyroid hormones (T4 and T3); increase BMR; help maintain temp; stimulate protein synthesis; increase use of glucose and fatty acids for ATP production; upregulate β receptors that attach to epinephrine and norepinephrine; accelerate growth with GH and insulin
Adrenal glands
suprarenal cortex (80-90%) secretes steroid hormones: weak sex-specific androgens, glucocorticoids (cortisol), mineralocorticoids (aldosterone); suprarenal medulla stimulated by sympathetic preganglionic neurons of ANS secretes 3 catecholamines (epinephrine, norepinephrine, dopamine); covered by capsule; vascularized
Zona glomerulosa
secretes mineralocorticoids used to regulate mineral homeostasis (aldosterone)
Zona fasciculata
secretes glucocorticoids that affect glucose homeostasis (primarily cortisol [hydrocortisone]- the most produced, cortisone and corticosterone)
Zona reticularis
secretes weak androgens (hormones with masculinizing effects)
Renin-angiotensin-aldosterone (RAA) pathway
controls secretion of aldosterone; stimulated by dehydration, Na+ deficiency or hemorrhage (all decrease blood volume) → BP decreases stimulating secretion of renin (from juxtaglomerular cells) → renin converts angiotensin I to angiotensin II → adrenal cortex secretes aldosterone
Chromaffin cells
adrenal medulla; 80% secrete epinephrine and 20% norepinephrine (still controlled by hypothalamus); fight-or-flight response; increase heart rate, cardiac output, BP, blood flow to liver, respiration, dilation of airways, blood glucose, breakdown of glycogen, fat to fatty acids, proteins (nutrient delivery to muscles)
Gonads
ovaries and testes; produce oocytes and sperm (gametes); in conjunction with anterior pituitary secretion of FSH and LH (stimulated by GnRH); ovaries produce estrogens (estradiol and estrone), progesterone, relaxin, and inhibin; testes produce testosterone
Thymus
secretes thymic factor, thymic humoral factor, thymopoietin, and thymosin which regulate development, maturation, and later activation of T-lymphocytes (WBC that destroys microbes and foreign substances)
Growth factors
hormones that stimulate cell growth and division (from G0 to G1); newly discovered; involved in tissue development, growth, and repair
Eustress
helpful, everyday stress that prepares us to meet challenges
Distress
any type of harmful stress that may be damaging; body works to maintain homeostasis to counteract
Two-stage stress response
controlled by hypothalamus; 1. fight-or-flight response stimulates resources to prepare for immediate activity 2. resistance reaction lasts longer and can result in exhaustion if it lasts too long
Stress Response 1: Stressor
something threatening or exhilarating happens
Stress Response 2: Alarm
body initially responds to stressor by lowering resistance
Stress Response 3: resistance
stressor continues and the body mobilizes to withstand the stress and return to homeostasis
Stress Response 4a: Exhaustion
ongoing, extreme stressor eventually deplete the body’s resources so we function less than normal before finally returning to normal
Stress Response 4b: Illness/Death
body’s resources are not replenished and/or additional stressors occur so the the body suffers breakdowns
Pituitary gigantism/acromegaly
pituitary gland disorder caused by excess secretion of GH during adulthood
Dwarfism
pituitary gland disorder caused by low GH production
Goiter
pituitary gland disorder caused by reduced production of thyroid hormone (TSH); causes enlarged thyroid gland
Diabetes insipidus
pituitary gland disorder caused by defects in ADH which leads to excess urine production and dehydration
Graves disease
pituitary gland disorder that develops due to excess thyroid hormone
Cushing’s syndrome
hypersecretion of cortisol from adrenal cortex; characterized by loss of muscle mass, body weight, immune system gets tired
Addison’s disease
hyposecretion of glucocorticoids and aldosterone from adrenal gland; characterized by weakness, weak immune system, low blood volume and pressure
Diabetes mellitus
pancreatic islet disorders; most common endocrine disorder, caused by the inability to produce insulin; type I: autoimmune disease where beta cells are destroyed; type II (insulin resistance): more common, linked to lifestyle (obesity, inactivity), tissue don’t respond to normal-high blood sugar
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