Chapter 51: Endocrine System

51-1 Hormones

51-2 Endocrine Glands

51-3 Feedback Mechanisms

I. Types of Glands (2 TYPES in our body)• A GLAND secretes materials into BLOODSTREAM.

51-1 Hormones

(1) Exocrine Glands (e.g., sweat glands, mucous glands, salivary glands)• Secrete NON-hormonal substances into DUCTS transport these inside AND outside body.

(2) Endocrine Glands (e.g., pituitary gland, thyroid gland, adrenal gland)• Ductless glands dump HORMONES directly into bloodstream.

II. Types of Hormones (TWO classes)• Chemicals that in SMALL amounts INFLUENCE activity of DISTANT cells (using our bloodstream as the MEDIUM).

(1) Amino Acid (Peptide) Hormones (e.g., epinephrine, adrenaline)

• PROTEIN hormones that attach directly to cell membrane.

(2) Steroid Hormones (e.g., estrogen, testosterone)

• LIPID hormones derived from cholesterol (diffuse through cell membrane).

III. Hormone Action• When a hormone BINDS to a receptor on (or INSIDE) its TARGET CELL, it triggers a SERIES of events leading to CELL CHANGES.

(1) Target Cells (e.g., testosterone works on SKELETAL muscle cells)• Cells that have receptors SPECIFIC to a SPECIFIC type of HORMONE.

(2) Receptors• Proteins BOTH INSIDE cytoplasm and ON SURFACE of a target cell.

(A) Amino Acid Hormones (CANNOT diffuse needs a MESSENGER)• ID target cells by SURFACE RECEPTORS embedded in cell membrane.

(1) First Messenger (i.e, the HORMONE)• HORMONE 1ST messenger by BINDING to target cell receptor.

(2) Hormone-Receptor Complex (HRC)• Complex formed BETWEEN hormone and RECEPTOR protein—the HRC activates a 2nd messenger INSIDE target cell.

(3) Second Messenger (i.e., cyclic AMP or simply cAMP—gets ACTIVATED)• cAMP initiates a SERIES of events that LEADS to CHANGES within target cell (NOTE: Different ORGANS may respond differently to cAMP).

(B) Steroid Hormones (fat soluble, easily PASS THROUGH cell membrane)• Diffuse THROUGH membrane, bind to a receptor INSIDE cell—the HRC then ENTERS nucleus and CHANGES cell activity.

IV. Prostaglandins (stimulate LABOR contractions & blood CLOTTING)• A group of LIPIDS (i.e., NOT hormones, NO glands) produced by cells ALL OVER the body, AND only act LOCALLY.

I. Pituitary Gland (i.e., “MASTER gland,” links nervous WITH endocrine)• Releases hormones that AFFECT other glands and organs

(BUT is regulated by HYPOTHALAMUS).

51-2 Endocrine Glands

(1) Why might damage to the PITUITARY gland be considered far MORE SERIOUS that damage to one of the other endocrine glands?

Critical Thinking

(1) Neurosecretory Cells (located in HYPOTHALAMUS)• Makes hormones that REGULATE pituitary’s activity.

(releasing OR inhibiting hormones)

(A) Posterior Pituitary (back of pituitary)• Secretes OXYTOCIN and ADH.

(1) Oxytocin (TARGETS mammary glands AND uterine muscles)• Initiates uterine CONTRACTIONS during childbirth; stimulates SECRETION of breast milk.

(2) Antidiuretic Hormone (ADH—TARGETS kidney nephrons)• Stimulates REABSORPTION of WATER by kidneys, concentrates urine.

(B) Anterior Pituitary (TOP of pituitary, regulated by hypothalamus)• Secretes GH, PROLACTIN, TSH, LH and ACTH.

(1) Releasing Hormones (TARGET anterior pituitary)• STIMULATES secretion of AP hormones.

(2) Release-Inhibiting Hormones (TARGET anterior pituitary)• INHIBITS secretion of AP hormones.

(2) Severe structural abnormalities result from gigantism, a condition of extremely rapid growth, and from pituitary dwarfism, a condition of slowed growth. Based on your understanding of the endocrine system, suggest what causes these inherited disorders.

Critical Thinking

(3) Growth Hormone (GH, targets growth tissue)• Regulates GROWTH of muscle AND bone tissue.

(4) Prolactin (TARGETS mammary glands)• Stimulates and sustains MILK PRODUCTION in breasts before AND during lactation.

II. Thyroid Gland (TWO lobes, near larynx)• Regulated by TSH; secretes thyroxine, triiodothyronine, and calcitonin.

(1) Thyroid-Stimulating Hormone (TSH, TARGETS thyroid gland)• Secreted by AP, REGULATES thyroid gland.

(2) Thyroxine and Triiodothyronine (TARGETS various tissues)

• MAINTAIN heart rate, blood pressure, temperature, and metabolism.

(3) Calcitonin (TARGETS osteoblasts of BONE tissue)• Stimulates DEPOSIT of CALCIUM IONS (Ca ++) from BLOOD TO BONE.

(4) Hyperthyroidism (OVER-production of thyroid hormones)• OVER-activity, weight LOSS, HIGH blood pressure, an ELEVATED heart rate and temp. (treated w/medicine)

(5) Hypothyroidism (UNDER-production of thyroid hormones)• SLOWED-growth, lethargy, weight GAIN, DECREASED heart rate AND temp. (treated with thyroxine)

(6) Cretinism (can result from a HYPOthyroidism, a DEFICIENCY)• A form of mental IMPAIRMENT during fetal and childhood development.

(7) Goiter (if there is an IODINE deficiency, a NUTRIENT for thyroid)• A SWELLING of thyroid gland treated with IODINE and THYROXINE.

III. Adrenal Glands (above EACH kidney, two regions—medulla & cortex)• Medulla (controlled by NS) and cortex (controlled by AP) function as TWO separate glands.

(A) Adrenal Medulla (e.g., work with SYMPATHETIC nervous system)• Produce EPINEPHRINE (adrenaline) and NOREPINEPHRINE.

(1) Epinephrine and Norepinephrine (released under STRESS or danger)• Blood-glucose levels are RAISED (liver), bronchi ENLARGE, pupils/blood vessels DILATE, and heart rate INCREASES.

(B) Adrenal Cortex (CENTER region of adrenal gland)• Responds to adrenocorticotropic hormone (ACTH) in order to secrete 2 hormones: (1) Cortisone, (2) Aldosterone

(1) Adrenocorticotropic Hormone (ACTH, TARGETS adrenal cortex)• Secreted by AP under STRESS, forces secretion of STEROID hormones cortisol and aldosterone.

(2) Cortisol (Cortisone) (e.g., the STRESS hormone)

• Regulates METABOLISM of carbs and proteins.

(3) Aldosterone (TARGETS the kidneys)• Helps to regulate your SALT-AND-WATER balance in blood.

IV. Gonads• ALSO supply steroid SEX HORMONES.

(1) Sex Hormones and Puberty

• Changes in body PREPARE for reproductive behaviors.

(2) Luteinizing Hormone (LH, TARGETS ovaries AND testes)• Stimulates P AND E; initiates OVULATION (females); stimulates TESTOSTERONE (males) (made by AP).

(3) Follicle-Stimulating Hormone (FSH, TARGETS ovaries and testes)• Stimulates oogenesis AND spermatogenesis (made by AP).

(4) Estrogen (stimulated by LH in females)• Female SEX hormone, prepares for features NEEDED for reproduction (made in ovaries).

(5) Progesterone (stimulated by LH in females)• Works with E to maintain OR shed UTERINE LINING during ovulation

(also made in ovaries).

(6) Androgens (stimulated by LH in males)• SEX hormones; testosterone driving agent in BOTH sexes.

(7) Testosterone• Responsible for sex drive, and muscle-building features.

(3) A number of different hormones secreted by various endocrine glands help regulate the blood glucose concentration. Based on your knowledge of the importance of glucose, hypothesize why glucose should be controlled by several hormones rather than just one hormone.

Critical Thinking

V. Pancreas (digestive AND endocrine organ)• Contains endocrine cells known as “Islets of Langerhans”.

(1) Islets of Langerhans (REGULATE BLOOD SUGAR)• Secretes 2 hormones, insulin AND glucagon.

(2) Insulin (i.e., LOWERS blood sugar)• Brings glucose FROM bloodstream INTO cells for glycolysis.

(3) Glucagon (i.e., ELEVATES blood sugar)• Stimulates CONVERSION of glycogen (from LIVER) into blood glucose.

(4) Diabetes Mellitus (results from insulin deficiency, Types I and II)• Condition of abnormally HIGH blood glucose concentration—

NOTE: In diabetics, excess glucose INHIBITS water reabsorption by kidneys, producing DILUTE urine—possibly dehydration, kidney damage, rapid breathing, or even DIABETIC COMA.

(4) Suppose a friend tells you that he or she has recently experienced some of the warning signs of diabetes mellitus. What other conditions could cause symptoms that are similar to those of diabetes?

Critical Thinking

(5) Hypoglycemia (results from EXCESSIVE insulin in bloodstream)• Glucose is rapidly STORED, leaving starving cells LOOKING for glucose

Leads to LOWER blood-glucose levels and release of glucagon and epinephrine (symptoms may include LETHARGY or DISORIENTATION).

VI. Other Endocrine Glands• Thymus gland, pineal gland, parathyroid glands, and endocrine cells within walls of digestive organs (e.g., stomach and small intestine).

(1) Thymus Gland• Between lungs, holds T-cells; as a gland—secretes THYMOSIN.

(2) Thymosin• PEPTIDE hormone stimulates development of T-cells (in thymus gland).

(3) Pineal Gland (sunlight influenced)• Base of brain secretes MELATONIN into blood during NIGHTFALL.

(4) Melatonin• Cyclic RELEASE helps to regulate SLEEP patterns.

(5) Parathyroid Glands• 4 glands in back of thyroid gland, secrete PARATHYROID hormone.

(6) Parathyroid Hormone (works with OSTEOCLASTS of bone tissue)• INCREASES Ca ++ in BLOOD bone growth, muscle and nerve impulses.

(5) Why might OVERACTIVE parathyroid glands cause BONE problems?

Critical Thinking

(7) Gastrin (secreted by endocrine cells of STOMACH after a meal)• Stimulates stomach cells (in gastric pits) to release DIGESTIVE ENZYMES (pepsin) and HCl.

(8) Secretin (secreted by endocrine cells of SMALL INTESTINE)• Stimulates release of enzymes from PANCREAS and bile from LIVER.

I. Homeostasis (requires a COORDINATION of cells—tissues—organs)

• FEEDBACK mechanisms regulate [HORMONE] within a SAFE RANGE.

51-3 Feedback Mechanisms

(2) Why might it be important to CAREFULLY control the dose of supplemental THYROXINE administered to a person with hypothyroidism?

Critical Thinking

(1) Antagonistic Hormones (e.g., Insulin & Glucagon)• Exert OPPOSITE effects in body (a tightly regulated SYSTEM)

(2) Feedback Mechanisms (i.e., positive OR negative)• A series of EVENTS in which the LAST step controls the FIRST.

(3) Negative Feedback (LAST step INHIBITS FIRST step)• Release of X stimulates production of Y that subsequently INHIBITS FURTHER release of X.

(4) Positive Feedback (LAST step STIMULATES FIRST step)• Release of X stimulates production of OTHER hormones which INCREASE FURTHER RELEASE of X.

II. Negative Feedback Mechanisms (inhibits signal ~ products build up)• Original signal is INHIBITED as PRODUCTS begin to BUILD UP.