BSC2086 Chapter 17: The Endocrine System

Developed for the Broward College course BSC2086/L Anatomy and Physiology II.

nervous system

• One of the body systems

• Utilizes both electrical and chemical messages.

• Reacts and adapts quickly to stimuli.

• Targeted and specific effects.

endocrine system

• One of the body systems.

• Utilizes chemical messages only.

• Reacts and adapts slowly to stimuli.

• General and widespread effects.

exocrine gland

• A type of gland.

• Secretes onto a surface or organ cavity by ducts.

• Extracellular effects (e.g., digestion).

endocrine gland

• A type of gland.

• Secretes directly into the bloodstream by fenestrated capillaries.

• Intracellular effects (e.g., cell metabolism).

hormone

• A chemical messenger that stimulates cell response.

• Secreted by an endocrine gland into the bloodstream.

• Can reach distant targets.

paracrine hormone

• A chemical messenger that stimulates cell response.

• Secreted by an endocrine gland and diffuses.

• Targets nearby cells.

axis

• The pathway by which a hormone reaches its target cell or organ.

• Describes the interactions of endocrine glands.

hypothalamus

• An endocrine organ.

• Forms the floor and walls of the third ventricle of the brain.

• Regulates primitive functions and homeostasis.

• Secretes releasing and inhibiting hormones.

• Closely associated with the hypophysis.

hypophysis

• An endocrine organ.

• Located in the sella turcica of the sphenoid bone and suspended from the hypothalamus by a stalk.

• Composed of anterior and posterior portions.

• Also known as the pituitary gland.

infundibulum

The stalk suspending the hypophysis from the hypothalamus.

adenohypophysis

• The anterior lobe of the hypophysis.

• Connected to the hypothalamus by the hypothalamo–hypophyseal portal system.

• Regulated by hypothalamic hormones.

• Secretes tropic hormones, PRL, and GH.

neurohypophysis

• The posterior lobe of the hypophysis.

• Connected to the hypothalamus by the hypothalamo–hypophyseal tract.

• Regulated by neuroendocrine reflexes.

• Stores and secretes hormones produced by the hypothalamus.

tropic hormone

A type of hormone that targets other endocrine glands.

gonadotropins

• Class of hormones.

• Targets the gonads.

• Includes FSH and LH.

follicle-stimulating hormone

• Hormone secreted by gonadotrope cells of the adenohypophysis.

• Classified as a gonadotropin.

• Stimulates the production of egg or sperm cells.

• Targets the gonads.

• Abbreviated FSH.

luteinizing hormone

• Hormone secreted by gonadotrope cells of the adenohypophysis.

• Classified as a gonadotropin.

• Stimulates androgen hormone production (e.g., estrogen, progesterone, testosterone).

• Targets the gonads.

• Abbreviated LH.

thyroid-stimulating hormone

• Hormone secreted by thyrotropes of the adenohypophysis.

• Stimulates the growth of the thyroid gland and the secretion of TH.

• Targets the thyroid gland.

• Abbreviated TSH.

adrenocorticotropic hormone

• Hormone secreted by corticotropes of the adenohypophysis.

• Regulates the response to stress and stimulates adrenal cortex secretion.

• Abbreviated ACTH.

• Also known as corticotropin.

prolactin

• Hormone secreted by lactotropes of the adenohypophysis.

• Stimulates milk synthesis after delivery in females; increases sensitivity to LH and secretion of testosterone in males.

• Abbreviated PRL.

growth hormone

• Hormone secreted by somatotropes of the adenohypophysis.

• Promotes tissue growth and the secretion of insulin-like growth factors in the liver.

• Abbreviated GH.

• Also known as somatotropin.

antidiuretic hormone

• Hormone secreted by the neurohypophysis.

• Promotes water retention and reabsorption by the kidneys.

• Abbreviated ADH.

oxytocin

• Hormone secreted by the neurohypophysis.

• Promotes labor contractions and lactation in females.

• Abbreviated OT.

pineal gland

• An endocrine organ.

• Located at the posterior end of the hypothalamus.

• Secretes serotonin and melatonin to regulate the circadian rhythm.

thymus

• An endocrine organ.

• Located in the mediastinum.

• Secretes thymosin and thymopoietin that regulate the development and activation of T lymphocytes.

thyroid gland

• An endocrine organ.

• Located on the anterolateral sides of the trachea.

• Composed of two large lobes connected by an isthmus.

• Composed of follicles.

• Secretes thyroid hormone and calcitonin.

thyroid follicle

• The basic structural unit composing the thyroid gland.

• Filled with colloid and lined with follicular cells.

thyroid hormone

• Hormone secreted by the follicular cells of a thyroid follicle.

• Has a calorigenic effect on the body by raising the metabolic rate and respiration rate.

• Abbreviated T₃ and T₄.

• Requires iodine to be synthesized.

calcitonin

• Hormone secreted by the parafollicular cells in the thyroid gland.

• Lowers blood calcium levels by promoting bone deposition and formation.

parathyroid gland

• An endocrine gland.

• Located on the surface of the thyroid gland.

• Secretes PTH.

parathyroid hormone

• Hormone secreted by the parathyroid glands.

• Raises blood calcium levels by promoting synthesis of calcitriol.

• Abbreviated PTH.

adrenal gland

• An endocrine gland.

• Located on the superior surfaces of the kidneys.

• Composed of an outer cortex and inner medulla.

adrenal medulla

• The inner layer of the adrenal gland.

• Composed of chromaffin cells.

• Secretes catecholamines that initiates the fight-or-flight response.

epinephrine

• Hormone secreted by the adrenal medulla.

• Classified as a catecholamine.

• Increases alertness, blood pressure, heart rate, air flow, and metabolism in response to stress.

• Abbreviated Epi.

norepinephrine

• Hormone secreted by the adrenal medulla.

• Classified as a catecholamine.

• Increases alertness, blood pressure, heart rate, air flow, and metabolism in response to stress.

• Abbreviated NE.

adrenal cortex

• The outer layer of the adrenal gland.

• Composed of an outer zona glomerulosa, middle zona fasciculata, and inner zona reticularis.

• Secretes corticosteroids.

zona glomerulosa

• The outer layer of the adrenal cortex.

• Secretes mineralocorticoids.

zona fasciculata

• The middle layer of the adrenal cortex.

• Secretes glucocorticoids.

zona reticularis

• The inner layer of the adrenal cortex.

• Secretes sex steroids.

mineralocorticoids

• Class of corticosteroids secreted by the zona glomerulosa.

• Controls electrolyte balance.

• For example, aldosterone.

glucocorticoids

• Class of corticosteroids secreted by the zona fasciculata.

• Stimulates catabolism of fat and protein into glucose and gluconeogenesis.

• For example, cortisol.

sex steroids

• Class of corticosteroids secreted by the zona reticularis.

• Includes androgen and estrogen.

pancreas

• An endocrine and exocrine gland.

• Located inferior and dorsal to the stomach.

• Composed of islets that produce hormones.

alpha cell

• One of the cells composing the pancreas.

• Secretes glucagon.

beta cell

• One of the cells composing the pancreas.

• Secretes insulin.

delta cell

• One of the cells composing the pancreas.

• Secretes somatostatin.

glucagon

• Hormone secreted by the alpha cells of the pancreas.

• Classified as a hyperglycemic hormone.

• Raises blood glucose levels by promoting glycogenolysis, gluconeogenesis, and fat catabolism.

• Antagonizes insulin.

insulin

• Hormone secreted by the beta cells of the pancreas.

• Classified as a hypoglycemic hormone.

• Lowers blood glucose levels by promoting glucose uptake and synthesis of fat, protein, and glycogen.

• Antagonizes glucagon.

somatostatin

• Hormone secreted by the delta cells of the pancreas.

• Inhibits secretion of glucagon and insulin and regulates the speed of digestion and nutrient absorption.

• Also known as growth hormone–inhibiting hormone.

ovary

• An endocrine gland.

• Composed of granulosa cells and a corpus luteum.

• Also the female reproductive gonad.

granulosa cell

• Composes the wall of an ovarian follicle.

• Secretes estradiol during the first half of the menstrual cycle and inhibin.

corpus luteum

• The remnants of a follicle after ovulation.

• Secretes estradiol, progesterone, and inhibin; secretes estradiol and progesterone for an extended time during pregnancy.

estradiol

• Hormone secreted by granulosa cells and the corpus luteum.

• Regulates development of the female reproductive system, secondary female sex characteristics, the menstrual cycle, pregnancy, and lactation of the mammary glands.

progesterone

• Hormone secreted by corpus luteum.

• Regulates development of the female reproductive system, secondary female sex characteristics, the menstrual cycle, pregnancy, and lactation of the mammary glands.

inhibin

• Hormone secreted by the granulosa cells and the corpus luteum.

• Inhibits secretion of FSH and stabilizes sperm production rates in males.

testis

• An endocrine gland.

• Composed of interstitial cells, sustentacular sertoli cells, and seminiferous tubules.

• Also the male reproductive gonad.

interstitial cell

• Located between the seminiferous tubules of the testes.

• Secretes testosterone and estrogen.

sustentacular sertoli cell

• One of the cells composing the testes.

• Secretes inhibin.

seminiferous tubule

• One of the structures composing the testes.

• Sustains sperm production and sex drive.

natriuretic peptides

• Class of hormones.

• Secreted by the heart.

• Lowers blood volume and blood pressure by increasing sodium retention by the kidneys.

erythropoietin

• Hormone secreted by mostly the kidneys and, in lesser amounts, by the liver.

• Stimulates the production of red blood cells in the bone marrow.

angiotensinogen

• Hormone secreted by the liver.

• A precursor hormone of angiotensin II.

insulin-like growth factor I

• Hormone secreted by the liver in response to GH.

• Raises the metabolic rate and rate of protein synthesis.

• Abbreviated IGF-I.

calcidiol

• Hormone secreted by the liver by conversion of vitamin D3.

• A precursor hormone of calcitriol.

hepcidin

• Hormone secreted by the liver.

• Promotes intestinal absorption of iron.

angiotensin I

• Hormone secreted by the kidneys by conversion of angiotensinogen.

• A precursor hormone of angiotensin II.

calcitriol

• Hormone secreted by the kidneys by conversion of calcidiol.

• Raises blood calcium levels by promoting intestinal absorption of calcium and decreasing loss by urine.

enteric hormones

• Class of hormones.

• Secreted by the stomach.

• Coordinates digestive motility and secretion.

steroids

• Class of hormones.

• Hydrophobic.

• Derived from cholesterol.

• Examples include sex steroids and corticosteroids.

peptides

• Class of hormones.

• Consists of chains of amino acids.

• Hydrophilic.

• Synthesized by the rough endoplasmic reticulum and Golgi complex in a similar process to protein synthesis.

• Examples include glucagon and insulin.

glycoproteins

• Class of hormones.

• Consists of chains of amino acids conjugated with short carbohydrate chains.

• Subcategory of peptides.

monoamines

• Class of hormones.

• Hydrophilic (except for thyroid hormone).

• Derived from amino acids that retain an amino group. Most are synthesized from tyrosine; melatonin is synthesized from tryptophan.

• Examples include catecholamines and thyroid hormone.

• Also known as biogenic amines.

hydrophilic hormone

• Type of hormone that mixes easily with blood plasma.

• Transport proteins are not needed for transport.

• Requires surface cell receptors and a second-messenger system for activation.

• Includes peptides and monoamines.

hydrophobic hormone

• Type of hormone that does not mix easily with blood plasma.

• Transport proteins are needed for transport.

• Can pass directly through the cell membrane and into the nucleus.

• Includes steroids and thyroid hormone.

bound hormone

• A hormone that is attached to a transport protein.

• The half-life of the hormone is extended and the hormone is protected from degradation.

unbound hormone

• A hormone that is not attached to a transport protein.

• Leaves capillaries to reach the target cell.

specificity

• A property of hormone receptors.

• Receptors will bind to exactly one hormone and not any other.

saturation

• A property of hormone receptors.

• No additional hormone produces an effect when all receptors are occupied.

inositol triphosphate

• A second messenger.

• The smaller part of a membrane phospholipid split by phospholipase.

• Induces changes in the cellular calcium concentration to activate effects.

• Abbreviated IP₃.

diacylglycerol

• A second messenger.

• The larger part of a membrane phospholipid split by phospholipase.

• Activates other enzymes in a similar process to cAMP.

• Abbreviated DAG.

metabolic clearance rate

• The rate of hormone removal from the body.

• Inversely proportional to the half-life of the hormone.

• Abbreviated MCR.

synergistic effect

• Type of hormone interactive effect.

• Multiple hormones act together to strengthen a response.

permissive effect

• Type of hormone interactive effect.

• One hormone enhances the effect of a later hormone.

antagonistic effect

• Type of hormone interactive effect.

• One hormone opposes the effect of another hormone.

stress

Caused by any situation that upsets homeostasis and threatens physical or emotional well-being.

general adaptation syndrome

• The bodily reaction to stress.

• Composed of three stages: alarm reaction, stage of resistance, and stage of exhaustion.

alarm reaction

• The first stage of general adaptation syndrome.

• Secretion of epinephrine and norepinephrine increases blood pressure, heart rate, and blood glucose levels.

• Secretion of aldosterone increases sodium and water retention.

stage of resistance

• The second stage of general adaptation syndrome.

• Depletion of glycogen; breakdown of fat and protein.

• Secretion of adrenocorticotropic hormone and cortisol.

• Decreased immune function and increased susceptibility to infection.

stage of exhaustion

• The third stage of general adaptation syndrome.

• Depletion of fat; breakdown of protein and wasting of muscle.

• Loss of glucose homeostasis, imbalance of electrolytes, and hypertension.

• Hypokalemia and alkalosis leads to death.

eicosanoids

• Class of paracrine hormones.

• Composed of 20-carbon backbones.

• Derived from the conversion of arachidonic acid by lipoxygenase or cyclooxygenase.

• Includes leukotrienes, prostacyclin, thromboxanes, and prostaglandins.

leukotrienes

• Class of eicosanoids.

• Converted from arachidonic acid by lipoxygenase.

• Mediates allergic and inflammatory reactions.

prostacyclin

• An eicosanoid.

• Converted from arachidonic acid by cyclooxygenase.

• Inhibits blood clotting and vasoconstriction.

thromboxanes

• Class of eicosanoids.

• Converted from arachidonic acid by cyclooxygenase.

• Secreted by platelets after injury.

• Stimulates blood clotting and vasoconstriction.

prostaglandins

• Class of eicosanoids.

• Converted from arachidonic acid by cyclooxygenase.

• PGE relaxes smooth muscle in the bladder, intestines, and bronchioles; stimulates contraction of blood vessels.

• PGF induces the opposite effects of PGE.

hyposecretion

• Class of endocrine disorders.

• Marked by inadequate hormone release.

• Typically caused by a tumor or lesion that destroys gland tissue.

hypersecretion

• Class of endocrine disorders.

• Marked by excessive hormone relase.

• Typically caused by a tumor or autoimmune disorder.

dwarfism

• Disorder of the pituitary gland.

• Caused by pituitary hyposecretion of GH in childhood or adolescence.

gigantism

• Disorder of the pituitary gland.

• Caused by pituitary hypersecretion of GH in childhood or adolescence.

acromegaly

• Disorder of the pituitary gland.

• Caused by pituitary hypersecretion of GH in adulthood.

• Marked by thickening of the bones and soft tissues.

congenital hypothyroidism

• Disorder of the thyroid gland.

• Caused by thyroid hyposecretion at birth.

• Marked by abnormal bone development, thickened facial features, hypothermia, lethargy, and brain damage.

myxedema

• Disorder of the thyroid gland.

• Caused by thyroid hyposecretion in adulthood.

• Marked by low metabolic rate, lethargy, weight gain, dry skin and hair, cold sensitivity, hypertension, and edema.

• Also known as adult hypothyroidism.