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*The endocrine system helps to regulate body function like the metabolism by releasing certain hormones.

*The nervous system is what sends impulses to the brain to assist the endocrine system.

*“Both function to achieve and maintain stability of the internal environment” (2).

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*The endocrine system is much slower than the nervous system.

*Instead of shooting impulses straight to the brain through nerves, the hormones are released and move through the bloodstream to their target cells (2).

*The endocrine system controls more of the internal body than the nervous system.

*Hormones are chemical messengers and are produced by the ENDOCRINE SYSTEM. They are distributed throughout the body by diffusion into the bloodstream. They travel through the blood to whichever organ or muscle they are meant to effect which are called target organs or target cells. Only the specific target will be affected by the particular hormone that goes with it. Endocrine glands are ductless glands. The glands make the hormones but the hormones are not excreted through ducts but by diffusion.

*These are the major endocrine glands: The Hypothalamus, the Pituitary and the Pineal gland are located in the brain. The Thyroid and Parathyroid glands are each paired and are located in the neck. The Thymus gland is located right in the center of the chest (also called the mediastinum.) The Adrenal glands are a pair and they are located in the abdominal cavity. Also in the abdominal cavity are the Pancreatic Islets, near the pancreas. In a female, there are two ovaries located in the pelvic cavity. In a male, there are two Testes, located in the scrotum. Another Endocrine gland is the placenta in a pregnant female.

*There are many useful ways to classify the various hormones that these glands produce. One way is by function. Tropic hormones target other endocrine glands and stimulate their growth and secretions. Sex hormones, the kind we are most familiar with, relate to reproductive organs and their functions. Anabolic hormones stimulate anabolism in their target cells.

*Steroid hormone molecules are manufactured by endocrine cells from cholesterol, an important type of lipid in the human body.

*Nonsteriod hormones are synthesized primarily from amino acids rather than from cholesterol. Some nonsteroid hormones are protein hormones.

*Hormones signal a cell by binding to specific receptors on or in the cell.

*In a “lock-and-key” mechanism , hormones will bind only to receptor molecules that “fit” them exactly. Any cell with one or more receptors for a particular hormone is said to be a target of that hormone.

*A common type of combined action of hormones is seen in the phenomenon of antagonism. In antagonism, one hormone produces the opposite effect of another hormone.

Hormone Source Targets Principal Action

Growth hormone-releasing hormone GRH

Hypothalamus Adenohypophysis (somatotrophs)

Stimulates secretion of growth hormone

Growth hormone- inhibiting hormone GIH, or somatostatin

Hypothalamus Adenohypophysis (somatotrophs)

Inhibits secretion of growth hormone

Corticoptropin- releasing hormone CRH

Hypothalamus Adenohypophysis (corticotrophs)

Stimulates release of adrenocorticotrophic hormone ACTH

Thyrotropin-releasing hormone TRH

Hypothalamus Adenohypophysis (thyrotrophs)

Stimulates release of thyroid-stimulating TSH

Gonadotropin- releasing hormone GNRH

Hypothalamus Adenohypophysis (gonadotrophs)

Stimulates release of gonadotropins (FSH and LH)

Prolactin-releasing hormone PRH Hypothalamus Adenohypophysis (corticotrophs)

Stimulates secretion of prolactin

Prolactin- inhibiting hormone PIH Hypothalamus Adenohypophysis (corticotrophs)

Inhibits secretion of prolactin

Growth hormone GH (somatotrophs [STH])

Adenohypophysis (somatotrophs)

General Promotes growth by stimulating protein anabolism

Prolactin PRL (lactogenic hormone) Adenohypophysis (lactotrophs)

Mammary glands (alveolar secretory cells)

Promotes milk secretion

Thyroid-stimulating hormone TSH Adenohypophysis (thyrotrophs)

Thyroid gland Stimulates development and secretion in the thyroid gland

Adenocorticotrophic hormone ACTH

Adenohypophysis (corticotrophs)

Adrenal cortex Promotes development and secretion in the adrenal cortex

Follicle-stimulating hormone FSH Adenohypophysis (gonadotrophs)

Gonads (primary sex organs)

Female: promotes development of ovarian follicle; stimulates estrogen secretionMale: promotes development of testis; stimulates sperm production

Luteinizing hormone LH Adenohypophysis (gonadotrophs)

Gonads Female: triggers ovulation; promotes development of corpus luteumMale: simulates production of testosterone

Antidiuretic hormone ADH Neurohypophysis Kidney Promotes water retention by kidney tubules

Oxytocin OT Neurohypophysis Uterus and mammary gland

Stimulates uterine contractions; stimulates ejection of milk into mammary glands

Hormone Source Targets Principal Action

Triiodothyronine (T3) Thyroid gland (follicular cells) General Increase rate of metabolism

Tetaiodothyronine (T4) or thyroxine

Thyroid gland (follicular cells) General Increases rate of metabolism (usually converted to T3 first)

Calcitonin CT Thyroid gland (parafollicular cells)

Bone tissue Increases calcium storage in bone; lowering blood Ca++ levels

Parathyroid hormone PTH or parathromone

Parathyroid glands Bone tissue and kidney

Increases removal from storage in bone and produces the active form of vitamin D in the kidneys, increasing absorption of calcium by intestines and increasing blood Ca++ levels

Aldosterone Adrenal cortex (zona glomerlulosa)

Kidney Stimulates kidney tubules to conserve sodium, which, in turn, triggers, the release of ADH and the resulting conservation of water by the kidney

Cortisol (hydrocortisone)

Adrenal cortex (zona fasciculata) General Influences metabolism of food molecules; in large amounts, it has an anti-inflammatory effect

Adrenal androgens Adrenal cortex (zona reticularis) Sex organs, other effectors

Exact role uncertain, but may support sexual function

Adrenal estrogens Adrenal cortex (zona reticularis) Sex organs Thought to be physiologically insignificant

Epinephrine (adrenaline)

Adrenal medulla Sympathetic effectors

Enhances and prolongs the effects of the sympathetic division of the autonomic nervous system

Norepinephrine Adrenal medulla Sympathetic effectors

Enhances and prolongs the effects of the sympathetic division of the autonomic nervous system

Glucagon Pancreatic islets (alpha [a] cells or A cells)

General Promotes movement of glucose from storage and into the blood

Insulin Pancreatic islets (beta [b] cells or B cells)

General Promotes movement of glucose out of the blood and into cells

Somatostatin Pancreatic islets (delta [d] cells or D cells)

Pancreatic cells and other effectors

Can have general effects in the body, but primary role seems to be regulation of secretion of other pancreatic hormones

Pancreatic polypeptide

Pancreatic islets (pancreatic polypeptide [PP] of F cells)

Intestinal cells and other effectors

Exact function uncertain, but seems to influence absorption in the digestive tract

Growth hormone-releasing hormone

Hypothalamus Adenohypophysis Stimulates secretion of growth hormone

Growth hormone-inhibiting hormone

Hypothalamus Adenohypophysis Inhibits secretion of growth hormone

Corticotropin- releasing hormone

Hypothalamus Adenohypophysis Stimulates release of adrenocorticotropic hormone

Thyrotropin- releasing hormone

Hypothalamus Adenohypophysis Stimulates release of thyroid-stimulating hormone

Gonadotropin- releasing hormone

Hypothalamus Adenohypophysis Stimulates release of gonadotropins

Prolactin- releasing hormone

Hypothalamus Adenohypophysis Stimulates secretion of prolactin

Prolactin- inhibiting hormone

Hypothalamus Adenohypophysis Inhibits secretion of prolactin

Growth Hormone Adenohypophysis General Promotes growth by stimulating protein anabolism and fat

Prolactin Adenohypophysis Mammary glands Promotes milk secretion

Thyroid-stimulating hormone

Adenohypophysis Thyroid Glad Stimulates development and secretion in the thyroid gland

Adrenocorticotropic Adenohypophysis Adrenal Cortex Promotes development and secretion in the adrenal cortex

Follicle-stimulating hormone

Adenohypophysis Gonads Female: Promotes development of ovarian follicle; simulates estrogen secretionMale: development of testies; sperm productions

Luteinizing hormone Adenohypophysis Gonads Female: triggers ovulation; promotes corpus luteumMale: stimulates production of testosterone

Antidiurectic hormone Adenohypophysis Kidney Promotes water retention by kidney tubules

Oxytocin Uterus and mammary

Stimulates uterine contractions; stimulates ejection in mammary

Triiodothyronine Thyroid gland General Increases rate of metabolism

Tetraiodothyronine Thyroid Gland General Increases, rate of metabolism

Calcitonin Thyroid Gland Bone Tissue Increases calcium storage in bone, lowering blood Ca level

Parathyroidhormone

Parathyroid Gland Bone Tissue and Kidney

Increases calcium removal from storage in bone and produces the active form of vitamin D in the kidneys, increasing absorption of calcium by intestines and increasing blood

Aldosterone Adrenal Cortex Kidney Stimulates kidney tubules to conserve sodium, which in turn, triggers the release of ADH and the resulting conservation of water by the kidney

Cortisol Adrenal Cortex General Influences metabolism of food molecules

Adrenal Androgens

Adrenal Cortex Sex organs other effectors

Exact role uncertain, but may support sexual function

Adrenal Estrogens

Adrenal Cortex Sex organs Though to be physiologically insignificant

Epinephrine Adrenal Medulla Sympathetic effectors

Enhances and prolongs effects of sympathetic division of nervous system

Norenpine-phrine

Adrenal Medulla Sympathetic effectors

Enhances and prolongs effects of sympathetic division of nervous system

Glucagon Pancreatic Islets General Movement of glucose to blood

Insulin Pancreatic Islets General Movement of glucose out of blood into cells

Somatostatin Pancreatic Islets Pancreatic cells and other effectors

Secretion of pancreatic hormones

Pancreatic Polypeptide Pancreatic Islets Intestinal Cells and other effectors

Influence absorption in digestive tract