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Chapter 16

Endocrine System

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The Endocrine System

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Mechanisms ofHormone Action

Endocrine glands secrete chemicals (hormones) into the blood Hormones perform general functions of communication and control, but a slower, longer-lasting type of control than that provided by nerve impulsesCells acted on by hormones are called target organ cells

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Regulation of Hormone Secretion

Hormone secretion is controlled by homeostatic feedback

Negative feedback—mechanisms that reverse the direction of a change in a physiological system

Positive feedback—(uncommon) mechanisms that amplify physiological changes

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Mechanisms of Endocrine Disease

Hypersecretion—secretion of excess hormoneHyposecretion—insufficient hormone secretionPolyendocrine disorders—hyper- or hyposecretion of more than one hormone Target cell insensitivity produces results similar to hyposecretionEndocrinologists have developed many different strategies for treatment (e.g., surgery and hormone therapy)

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Pituitary Gland

Anterior pituitary gland Names of major hormones

Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Growth hormone (GH) Prolactin (lactogenic hormone)

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Pituitary Gland

Functions of major hormones TSH—stimulates growth of the thyroid gland; also

stimulates it to secrete thyroid hormone ACTH—stimulates growth of the adrenal cortex and

stimulates it to secrete glucocorticoids (mainly cortisol) FSH—initiates growth of ovarian follicles each month

in the ovary and stimulates one or more follicles to develop to the stage of maturity and ovulation; FSH also stimulates estrogen secretion by developing follicles; stimulates sperm production in the male

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Pituitary Gland

Functions of major hormones LH—acts with FSH to stimulate estrogen

secretion and follicle growth to maturity; causes ovulation; causes luteinization of the ruptured follicle and stimulates progesterone secretion by corpus luteum; causes interstitial cells in the testes to secrete testosterone in the male

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Pituitary Gland

GH—stimulates growth by accelerating protein anabolism; also accelerates fat catabolism and slows glucose catabolism; by slowing glucose catabolism, tends to increase blood glucose to higher than normal level (hyperglycemia)

Hypersecretion during childhood results in gigantism and during adulthood results in acromegaly

Hyposecretion during childhood results in pituitary dwarfism

Prolactin or lactogenic hormone—stimulates breast development during pregnancy and secretion of milk after the delivery of the baby

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Pituitary Gland

Posterior pituitary gland Names of hormones

Antidiuretic hormone (ADH) Hyposecretion causes diabetes insipidus,

characterized by excessive volume of urine

Oxytocin (OT)

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Pituitary Gland

Functions of hormones ADH—accelerates water reabsorption from

urine in the kidney tubules into the blood, thereby decreasing urine secretion

Oxytocin—stimulates the pregnant uterus to contract; may initiate labor; causes glandular cells of the breast to release milk into ducts

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Hypothalamus

Actual production of ADH and oxytocin occurs in the hypothalamusAfter production in the hypothalamus, hormones pass along axons into the pituitary glandThe secretion and release of posterior pituitary hormones is controlled by nervous stimulationThe hypothalamus controls many body functions related to homeostasis (temperature, appetite, and thirst)

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Thyroid Gland

Names of hormones Thyroid hormone—thyroxine (T4) and

triiodothyronine (T3) Calcitonin (CT)

Functions of hormones Thyroid hormones—accelerate catabolism

(increase the body’s metabolic rate) Calcitonin—decreases the blood calcium

concentration by inhibiting breakdown of bone, which would release calcium into the blood

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Thyroid Gland

Hyperthyroidism (hypersecretion of thyroid hormones) increases metabolic rate Characterized by restlessness and

exophthalmos (protruding eyes)

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Thyroid Gland

Hypothyroidism (hyposecretion of thyroid hormones) May result from different conditions Simple goiter—painless enlargement of

thyroid caused by dietary deficiency of iodine Hyposecretion during early development may

result in cretinism (retardation) and during adulthood in myxedema (characterized by edema and sluggishness)

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Parathyroid Glands

Name of hormone—parathyroid hormone (PTH)

Function of hormone—increases blood calcium concentration by increasing the breakdown of bone with the release of calcium into the blood

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Pancreatic Islets

Names of hormones Glucagon—secreted by alpha cells Insulin—secreted by beta cells

Functions of hormones Glucagon increases the blood glucose

level by accelerating liver glycogenolysis (conversion of glycogen to glucose)

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Pancreatic Islets

Functions of hormones Insulin decreases the blood glucose by

accelerating the movement of glucose out of the blood into cells, which increases glucose metabolism by cells

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Pancreatic Islets

Diabetes mellitus Type 1 results from hyposecretion of

insulin Type 2 results from target cell insensitivity

to insulin Glucose cannot enter cells and thus blood

glucose levels rise, producing glycosuria (glucose in the urine)

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Female Sex Glands

The ovaries contain two structures that secrete hormones—the ovarian follicles and the corpus luteum

Effects of estrogen (feminizing hormone) Development and maturation of breasts and

external genitals Development of adult female body contours Initiation of menstrual cycle

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Male Sex Glands

The interstitial cells of testes secrete the male hormone testosterone

Effects of testosterone (masculinizing hormone) Maturation of external genitals Beard growth

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Male Sex Glands

Effects of testosterone Voice changes at puberty Development of musculature and body

contours typical of the male

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Thymus

Name of hormone—thymosin

Function of hormone—plays an important role in the development and function of the body’s immune system

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Other Endocrine Structures

Many organs (e.g., the stomach, intestines, and kidney) produce endocrine hormones

The atrial wall of the heart secretes atrial natriuretic hormone (ANH), which stimulates sodium loss from the kidneys

Fat-storing cells secrete leptin, which controls how full or hungry we feel

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Endocrine Glands (cont’d)

pituitary (cont’d) anterior lobe produces hormones (cont’d)

antidiuretic hormone (ADH) oxytocin

hypothalamus: located near the pituitary gland in the brain; which secretes “releasing” hormone that functions to stimulate or inhibit the release of pituitary gland hormones

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Endocrine Glands (cont’d)

thyroid: largest endocrine gland located in the neck below the larynx produces hormones

triiodothyronine (T3)

thyroxine (T4)

parathyroid: four small bodies lying directly behind the thyroid produces hormone

parathormone (PTH)

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Endocrine Glands (cont’d)

islets of Langerhans: clusters of endocrine tissue found throughout the pancreas produces hormones

insulin glucagon

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Endocrine Glands (cont’d)

adrenal glands: paired glands, one above each kidney. The outer portion is called the cortex, and the inner portion is called the medulla. produces hormones

cortisol (hydrocortisone) Aldosterone epinephrine (adrenaline)

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Combining Forms for the Endocrine System

aden/o

adren/o, adrenal/o

cortic/o

endocrin/o

parathyroid/o

thyroid/o, thyr/o

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Combining Forms Commonly for the Endocrine System (cont’d)

acr/o

calc/i

dips/o

kal/i

natr/o

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Suffix

-drome

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Disease and Disorder Terms Built from Word Parts

acromegaly adenomalacia adenomegaly adrenalitis adrenomegaly

calcipenia

hypercalcemia

hyperglycemia

hyperkalemia

hypocalcemia

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Helpful Information

hypocalcemia and calcipenia both mean a deficiency of calcium

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Disease and Disorder Terms Not Built from Word Parts

acidosis Addison’s disease cretinism Cushing’s syndrome diabetes insipidus (DI) diabetes mellitus (DM) gigantism goiter Graves’ disease

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Cushing Syndrome

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Goiter

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Surgical Terms Built from Word Parts

adenectomy

adrenalectomy

parathyroidectomy

thyroidectomy

thyroidotomy

thyroparathyroidectomy

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Diagnostic Not Built from Word Parts

Diagnostic imaging radioactive iodine uptake test (RAIU) thyroid scan

Laboratory fasting blood sugar (FBS) thyroxine level (T4) thyroid-stimulating hormone level (TSH)

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Complementary Terms Built from Word Parts

adrenopathy calcipenia cortical endocrinologist endocrinology endocrinopathy polydipsia syndrome

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Complementary Terms Not Built from Word Parts

exophthalmos

hormone

metabolism

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Abbreviations

DI

DM

FBS

RAIU

T4