xvi. endocrine system

adrenal cortex

outer section (cortex) of each adrenal gland; secretes cortisol, aldosterone, and sex hormones

adrenal medulla

inner section (medulla) of each adrenal gland; secretes epinephrine and norepinephrine

ovaries

located in the lower abdomen of a female; responsible for egg production and estrogen and progesterone secretion

pancreas

located behind the stomach; Islet (alpha and beta) cells (islets of Langerhans) secrete hormones from this; also contains cells that are exocrine in function that secrete enzymes, via a duct, into the small intestine to aid digestion

parathyroid glands

four small glands on the posterior of the thyroid gland; some people may have three or five

pituitary glands (hypophysis)

located at the base of the brain in the sella turcica; composed of an anterior lobe (adenohypophysis; composed of glandular epithelial tissue) and a posterior lobe (neurohypophysis; composed of nervous tissue); it weighs only 1⁄16 of an ounce and is a half-inch across

testes

two glands enclosed in the scrotal sac of a male; responsible for sperm production and testosterone secretion

thyroid gland

located in the neck on either side of the trachea; secretes thyroxine, triiodothyronine, and calcitonin

adrenaline (epinephrine)

secreted by the adrenal medulla; increases heart rate and blood pressure, and dilates airways

adrenocorticotropic hormone (ACTH; adrenocorticotropin)

secreted by the anterior lobe of the pituitary gland; stimulates the adrenal cortex

aldosterone

secreted by the adrenal cortex; increases salt (sodium) reabsorption

androgen

male hormone secreted by the testes and to a lesser extent by the adrenal cortex; testosterone is an example

antidiuretic hormone (ADH; vasopressin)

secreted by the posterior lobe of the pituitary glan; increases reabsorption of water by the kidney and raises blood pressure

calcitonin

secreted by the thyroid gland; decreases blood calcium levels; also increased calcium storage in bone and strengthens weakened bone tissue, preventing spontaneous bone fractures (ex. osteoporosis)

cortisol

secreted by the adrenal cortex; increases blood sugar; it is secreted in times of stress and has an anti-inflammatory effect

epinephrine (adrenaline)

secreted by the adrenal medulla; increases heart rate and blood pressure and dilates airways (sympathomimetic); it is part of the body’s “fight or flight” reaction

estradiol

estrogen (female hormone) secreted by the ovaries

estrogen

female hormone secreted by the ovaries and to a lesser extent by the adrenal cortex; examples are estradiol and estrone

follicle-stimulating hormone (FSH)

secreted by the anterior lobe of the pituitary gland; stimulates hormone secretion and egg production by the ovaries and sperm production by the testes

glucagon

secreted by alpha islet cells of the pancreas; increases blood sugar by conversion of glycogen (starch) to glucose

growth hormone (GH); somatotropin

secreted by the anterior lobe of the pituitary gland; stimulates growth of bones and soft tissues

insulin

secreted by beta islet cells of the pancreas; helps glucose (sugar) to pass into cells, and it promotes the conversion of glucose to glycogen

luteinizing hormone (LH)

secreted by the anterior lobe of the pituitary gland; stimulates ovulation in females and testosterone secretion in males

norepinephrine (noradrenaline)

secreted by the adrenal medulla; increases heart rate and blood pressure (sympathomimetic)

oxytocin (OT, OXT)

secreted by the posterior lobe of the pituitary gland; stimulates contraction of the uterus during childbirth

parathormone (PTH; parathyroid hormone)

secreted by the parathyroid glands; increases blood calcium

progesterone

secreted by the ovaries; prepares the uterus for pregnancy

prolactin (PRL)

secreted by the anterior lobe of the pituitary gland; stimulates breast development during pregnancy and promotes milk secretion after birth

testosterone

male hormone secreted by the testes

thyroid-stimulating hormone (TSH); thyrotropin

secreted by the anterior lobe of the pituitary gland; acts on the thyroid gland to promote its functioning

thyroxine (T4; tetraiodothyronine)

secreted by the thyroid gland; increases metabolism in cells

triiodothyronine (T3)

secreted by the thyroid gland; increases metabolism in cells

catecholamines

hormones derived from an amino acid and secreted by the adrenal medulla; epinephrine is an example

corticosteroids

hormones (steroids) produced by the adrenal cortex; examples are cortisol (raises sugar levels), aldosterone (raises salt reabsorption by kidneys), and androgens and estrogens (sex hormones)

electrolyte

mineral salt found in the blood and tissues and necessary for proper functioning of cells; potassium, sodium, and calcium

glucocorticoid

steroid hormone secreted by the adrenal cortex; regulates glucose, fat, and protein metabolism; cortisol raises blood sugar and is part of the stress response

homeostasis

thendency of an organism to maintain a constant internal environment

hormone

chemical, secreted by an endocrine gland, that travels through the blood to a distant organ or gland where it influences the structure or function of that organ or gland

hypothalamus

region of the brain lying below the thalamus and above the pituitary gland; it secretes releasing factors and hormones that affect the pituitary gland

mineralocorticoid

streroid hormone secreted by the adrenal cortex to regulate mineral salts (electrolytes) and water balance in the body; aldosterone is an example

receptor

cellular or nuclear protein that binds to a hormone so that a response can be elicited

sella turcica

cavity at the base of the skull; contains the pituitary gland

sex hormones

steroids (androgens and estrogens) produced by the adrenal cortex to influence male and female sexual characteristics

steroid

complex substance related to fats (derived from a sterol, such as cholesterol), and of which many hormones are made; examples are estrogens, androgens, glucocorticoids, and mineralocorticoids

sympathomimetic

pertaining to mimicking or copying the effect of the sympathetic nervous system

target tissue

cells of an organ that are affected or stimulated by specific hormones

endocrine glands

glands that secrete hormones directly into the bloodstream

exocrine glands

glands that send chemical substances (tears, sweat, milk, saliva) via ducts to the outside of the body; ex. sweat, mammary, mammary, mucous, salivary, and lacrimal (tear) glands

pineal gland

gland in the central portion of the brain, secretes melatonin and may be linked to body’s “biological clock” (thought to induce sleep); linked to a mental condition, seasonal affective disorder (SAD), in which a person suffers from depression in winter months (melatonin secretion increases with deprivation of light, inhibited by sunlight)

erythropoietin

secreted by the kidney; stimulates erythrocyte production

human chorionic gonadotropin (hCG or HCG)

secreted by the placenta; sustains pregnancy

cholecystokinin

secreted by the gallbladder; contracts the gallbaldder

prostaglandins

hormone-like substances that affect the body in many ways; secreted by cells throughout the body; have roles in many body processes including inflammation, clot formation, and muscles contraction (in uterus during labour)

gastrin

secreted by the GI tract; stimulates gastric acid secretion

secretin

secreted by the GI tract; stimulates secretion of pancreatic enzymes

activated vitamin D

secreted by the skin; increases absorption of calcium

thyroid cartilage

large piece of cartilage that covers the larynx and produces a prominence on the neck (”Adam’s apple” in men)

isthmus

narrow strip of glandular tissue that connects the two lobes of the thyroid gland on the ventral (anterior) surface of the trachea

gonadotropic hormones

hormones that influence growth and hormone secretion of the ovaries in females and testes in males

goiter

enlargement of the thyroid gland

endemic goiter

a type of goiter that occurs in certain regions where low iodine levels lead to low T3 and T4 levels; causes feedback to the hypothalamus and adenohypophysis, stimualting them to secrete releasing factors and TSH; TSH promotes the thyroid gland to secrete T3 and T4 but since there is no iodine, the only effect is an increase in size of the thyroid gland

nodular/adenomatous goiter

a type of goiter in which hyperplasia occurs, and there is formation of nodules and adenomas; some develop hyperthyroidism

• signs and symptoms: rapid pulse, tremors, nervousness, excessive sweating

hyperthyroidism

overactivity of the thyroid gland; thyrotoxicosis

Graves disease

most common form of hyperthyroidism; resulting from autoimmune processes in which the metabolism is faster

• marked by: increased heart rate (with irregular beats), higher body temperature, hyperactivity, weight loss, increased peristalsis (diarrhea occurs), exophthalmos

hypothyroidism

underactivity of the thyroid gland

• can be produced by: thyroidectomy, thyroiditis, endemic goiter, destruction of the gland by irradiation

• physiologic effects: fatigue, muscular and mental sluggishness, weight gain, fluid retention, slow heart rate, low body temperature, constipation

myxedema

advanced hypothyroidism in adulthood; atrophy of the thyroid gland occurs, and no hormone is produced; skin becomes dry and puffy (edema) because of collection of mucus-like material under the skin; many develop atherosclerosis because the lack of thyroid hormone increases blood lipids

cretinism

extreme hypothyroidism during infancy and childhood, leads to the lack of normal physical and mental growth; skeletal growth is more inhibited than soft tissue, so an affected person has the appearance of obese, short, stocky child

thyroid carcinoma

cancer of the thyroid gland; less than half are slow-growing papillary carcinomas, and about a third are rapidly growing anaplastic (widely metastatic) tumors; radioactive iodine scans can distinguish hyperfunctioning areas (“hot”, benign) from hypofunctioning areas (“cold”, benign or malignant)

hypoparathyroidism

excessive production of parathormone; hypercalcemia occurs as calcium leaves bones and enters the bloodstream; bones become decalcified with general loss of bone density (osteoporosis) and susceptible to fractures and formation of cysts; caused by parathyroid hyperplasia or tumor

hypoparathyroidism

deficient production of parathyroid hormone; hypocalcemia results as calcium remain in bones and unable to enter the bloodstream; leads to muscle and nerve weakness with spasm of muscles (tetany)

adrenal virilism

excessive secretion of adrenal androgens; caused by adrenal hyperplasia, or more commonly adrenal adenomas or carcinomas (in adult women)

• signs and symptoms: amenorrhea, hirsutism (excessive hair on the face and body), acne, deepening of voice

Crushing syndrome

group of signs and symptoms produced by excess cortisol from adrenal cortex; can also be caused by tumor of adrenal cortex; most cases result from chronic use of cortisone-like drugs (ex. steroids)

• includes: obesity, moon-like fullness of the face, excess deposition of fat in the thoracic region of the back (buffalo hump), diabetes, hypernatremia, hypokelmia, osteoporosis, virilization, hypertension

Crushing disease

benign tumor of the pituitary gland (adenoma) that increases ACTH secretion, stimulating the adrenal cortex to produce excess cortisol

Addison disease

hypofunction of the adrenal cortex; aldosterone and cortisol blood levels are low (1); insufficient supply of cortisol signals the pituitary gland to secrete more ACTH (2); primary insufficiency due to autoimmune adrenalitis

1. general malaise, weakness, muscle atrophy, severe loss of fluids and electrolytes (with hypoglycemia, low blood pressure, hyponatremia)

2. increased pigmentation of the skin, scars, and breast nipples (hyperpigmentation)

pheochromocytoma

benign tumor of the adrenal medulla (hypersecretion); tumor cells produce excess epinephrine and norepinephrine

• hypertension, tachycardia, palpitations, severe headaches, sweating, flushing of the face, muscle spasms

hyperinsulisnism

excess secretion of insulin causing hypoglycemia; caused by an overdose of insulin; hypoglycemia occurs as insulin draws sugar out of the bloodstream

• signs and symptoms: fainting spells, convulsions, and loss of consciousness

diabetes mellitus (DM)

lack of insulin secretion or resistance of insulin in promoting sugar, starch, and fat metabolism in cells; insulin insufficiency or ineffectiveness prevents sugar from leaving the blood and entering body cells (used to produce energy)

(1) type 1 (T1D) — autoimmune disease; autoantibodies are against normal pancreatic islet cells present

• onset is usually in early childhood, can occur in adulthood

• destruction of beta islet cells leads to complete deficiency of insulin in the body

(2) type 2 (T2D)

• patients are often older, can also be adolescents

• usually have family history

• obesity is very common

• islet cells are not initially destroyed; there is relative deficiency of insulin secretion with resistance by target tissues to insulin

continuous glucose monitor (CGM)

a device that tracks glucose levels throughout the day and night, and communicates with an insulin pump to deliver insulin as needed

hypoglycemic agents

drugs that stimulate the release of insulin from the pancreas and improve the body’s sensitivity to insulin

ketoacidosis

accumulation of ketones and acids in the body due to fats being improperly burned

insulin shock

severe hypoglycemia caused by an overdose of insulin, decreased intake of food, or excessive exercise

• signs and symptoms: sweating, hunger, confusion, trembling, nervousness, numbness

diabetic retinopathy

destruction of retinal blood vessels, causing visual loss and blindness

diabetic nephropathy

destruction of the kidneys, causing renal insufficiency; often requires hemodialysis or renal transplantation

atherosclerosis

destruction of blood vessels; leading to stroke, heart disease, and peripherovascular ischemia (gangrene, infection, loss of limbs)

diabetic neuropathy

destruction of nerves, involving pain or loss of sensation (most commonly in extremities)

gastroparesis

loss of gastric motility

gestational diabetes

diabetes as a result of hormonal changes during pregnancy; occur in women with predisposition to diabetes during the second or third trimester of pregnancy

acromegaly

hypersecretion of growth hormone from the anterior pituitary after puberty, leading to enlargement of extremities; excess of GH is produced by adenomas of the pituitary gland during adulthood; bones in the hands, feet, face and jaw grow abnormally large, producing the characteristic “coarsened” facial appearance

somatomedin C or insulin-like growth factor (IGF)

hormone secreted by the liver that causes clinical manifestations of acromegaly

gigantism

hypersecretion of growth hormone from the anterior pituitary before puberty, leading to abnormal overgrowth of body tissues; benign adenomas of the pituitary gland before puberty produce excess of GH

hypopituitary dwarfism

congenital hyposecretion of growth hormone; children affected are normal mentally, but their bones remain small

achondroplastic dwarfism

genetic defect in cartilage formation that limits the growth of long bones

panhypopituitarism

deficiency of all pituitary hormones; caused by tumors of the sella turcica or arterial aneurysms

syndrome of inappropriate ADH (SIADH)

excessive secretion of antidiuretic hormone; produces excess water retention in body; possible causes include tumor, drug reactions, or head injury

diabetes insipidus (DI)

insufficient secretion of antidiuretic hormone (vasopressin); causes kidney tubules to fail to hold back (reabsorb) needed water and salts

fasting plasma glucose (FPG; fasting blood sugar test)

measures circulating glucose level in a patient who has fasted for at least eight hours; can diagnose diabetes and prediabetes (when blood glucose is higher than normal but not high enough for a diagnosis of diabetes)

oral glucose tolerance test

test used to diagnose prediabetes and gestational diabetes

glycosylated hemoglobin (HbA1C) test (A1c)

test performed by measuring the precentage of RBCs with glucose attached to them, monitors long-term glucose control; high level indicates poor glucose control in diabetic patients

serum and urine tests

measurement of hormones, electrolytes, glucose, and other substances in serum (blood) and urine as indicators of endocrine function

serum studies

assays for GH, somatomedin C (insulin-like growth factor or IGF-1), prolactin level, gonadotropin levels, PTH, calcium, and cortisol