The Endocrine System

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1

Endocrine System

Interacts with the nervous system to coordinate and integrate the activity of body cells

2

Endocrinology

The scientific study of hormones and the endocrine organs

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Endocrine Glands

Also called ductless glands that produce hormones and lack ducts. They release their hormones into the surrounding tissue fluid (endo =within; crine = to secrete), and they typically have a rich vascular and lymphatic drainage that receives their hormones.

4

Neuroendocrine Organ

Hypothalamus, along with its neural functions, produces and releases hormones.

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Autocrines

Chemicals that exert their effects on the same cells that secrete them. For example, certain prostaglandins released by smooth muscle cells cause those smooth muscle cells to contract.

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Paracrines

Act locally (within the same tissue) but affect cell types other than those releasing the paracrine chemicals. For example, somatostatin released by one population of pancreatic cells inhibits the release of insulin by a different population of pancreatic cells.

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Amino Acid Based

Most hormones are ______________. Molecular size varies widely in this group-from simple amino acid derivatives (which include thyroxine constructed from the amino acid tyrosine and amines), to peptides (short chains of amino acids), to proteins (long polymers of amino acids).

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Steroids

___________ hormones are synthesized from cholesterol. Of the hormones produced by the major endocrine organs, only gonadal and adrenocortical hormones are __________.

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Eicosanoids

Some researchers add this third class of hormones, which include leukotrienes and prostaglandins. Effects are typically highly localized, affecting only nearby cells, they generally act as paracrines and autocrines and do not fit the definition of true hormones.

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Target Cells

All major hormones circulate to virtually all tissues, but a hormone influences the activity of only those tissue cells that have receptors for it. These cells are called ___________.

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Second Messengers

With the exception of thyroid hormone, amino acid-based hormones exert their signaling effects through intracellular _____________ generated when a hormone binds to a receptor in the plasma membrane. Ex: Cyclic AMP (cAMP)

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Cyclic AMP (cAMP)

Second messenger which is used by neurotransmitters and olfactory receptors

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First Messenger

The hormone that binds to its receptor in the plasma membrane

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G Protein

Protein that relays signals between extracellular first messengers (hormones or neurotransmitters) and intracellular second messengers (such as cyclic AMP) via an effector enzyme.

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Adenylate Cyclase

The effector enzyme that converts ATP to cAMP (2nd messenger)

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Protein Kinases

Enzymes that phosphorylate (add a phosphate group to) various proteins, many of which are other enzymes.

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Phosphodiesterase

The action of cAMP persists only briefly because the molecule is rapidly degraded by the intracellular enzyme ____________.

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Phospholipase C

An enzyme that splits a plasma membrane phospholipid called PIP2 into two second messengers.

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PIP2 (Phosphatidyl Inositol Bisphosphate)

Plasma membrane phospholipid

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Diacylglycerol (DAG)

(Like cAMP) activates a protein kinase enzyme, which triggers responses within the target cell.

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Inositol Trisphosphate (IP3)

Releases Calcium from intracellular storage sites

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Calmodulin

Intracellular regulatory protein. Once Calcium binds to ________, it activates enzymes that amplify the cellular response.

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Up-Regulation

Persistantly low levels of a hormone can cause its target cells to form additional receptors for that hormone

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Down-Regulation

Prolonged exposure to high hormone concentrations can decrease the number of receptors for that hormone.

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Negative Feedback Mechanism

The synthesis and release of most hormones are regulated by some type of ______________.

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Humoral Stimuli

Some endocrine glands secrete their hormones in direct response to changing blood levels of certain critical ions and nutrients. These are the simplest endocrine controls.

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Neural Stimuli

In a few cases, nerve fibers stimulate hormone release.
Ex: Response to stress, in which the sympathetic nervous system stimulates the adrenal medulla to release norepinephrine and epinephrine

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Hormonal Stimuli

Many endocrine glands release their hormones in response to hormones produced by other endocrine organs.
Ex: Releasing and inhibiting hormones produced by the hypothalamus regulate the secretion of most anterior pituitary hormones, and many anterior pituitary hormones in turn stimulate other endocrine organs to release their hormones.

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Permissiveness

The situation in which one hormone cannot exert its full effects without another hormone being present.
Ex: Reproductive system hormones largely regulate the development of the reproductive system.

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Synergism

_______________ occurs when more than one hormone produces the same effects at the target cell and their combined effects are amplified.
Ex: Both glucagon and epinephrine cause the liver to release glucose to the blood.

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Antagonim

_____________ occurs when one hormone opposes the action of another hormone.
Ex: Insulin, which lowers blood glucose levels, is antagonized by glucagon, which raises blood glucose levels.

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Pituitary Gland or Hypophysis

Secretes at least 8 hormones. Usually said to be the size and shape of a pea. Seated in the sella turcica of the sphenoid bone.

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Infundibulum

Funnel-shaped stalk that connects the pituitary gland to the hypothalamus.

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Posterior pituitary (lobe)

Composed largely of neural tissue such as pituicytes and nerve fibers. Releases neurohormones (hormones secreted by neurons) received ready-made from the hypothalamus. Hormone-storage area and not a true endocrine gland. (Part of the brain)

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Neurohypophysis

The posterior lobe of the pituitary gland plus the infundibulum make up the region called _____________.

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Anterior Pituitary (lobe) or Adenohypophysis

composed of glandular tissue (adeno = gland). Manufactures and releases a number of hormones.

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Hypothalamic-hypophyseal tract

Nerve bundle that runs through the infundibulum to connect the hypothalamus to the posterior lobe.

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Paraventricular & Supraoptic Nuclei

The hypothalamic-hypophyseal tract arises from neurons in the ___________ & __________ of the hypothalamus.

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Primary and Secondary Capillary Plexuses

There is no direct neural connection between the anterior lobe and hypothalamus, but there is a vascular connection. ___________ & __________ and the intervening hypophyseal portal veins make up the hypophyseal portal system.

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Hypophyseal portal veins

The Primary Capillary Plexus in the infundibulum communicates inferiorly via the small _______________ with a secondary capillary plexus in the anterior lobe.

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Releasing and Inhibiting Hormones

Via the hypophyseal portal system ______________________ secreted by neurons in the ventral hypothalamus circulate to the anterior pituitary, where they regulate secretion of its hormones.

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Oxytocin

Produced by: Hypothalamus
Target: Uterine & Breast
Function: Strong stimulant of uterine contraction & Hormonal trigger for milk ejection (the "letdown" reflex) in lactating women

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Antidiuretic hormone (ADH)

Produced by: Hypothalamic neurons
Target: Kidneys
Function: prevents wide swings in water balance, helping the body avoid dehydration and water overload

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Vasopressin

At high blood concentrations, ADH causes vasoconstriction, primarily of visceral blood vessels, raising blood pressure. This response targets different ADH receptors found on vascular smooth muscle. For this reason, ADH is also called ___________.

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Diabetes Insipidus

One result of ADH deficiency, a syndrome marked by intense thirst and huge urine output.

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Tropic hormones or Tropins

Four of the six anterior pituitary hormones - thyroid stimulating hormone, adrenocorticotropic hormone, follicle stimulating hormone, and luteinizing hormone. Regulate the secretory action of other endocrine glands.

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Somatotropic Cells

____________ of the anterior lobe produce growth hormone.

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Growth Hormone (GH)

Produced by: Somatotropic cells of the anterior lobe
Target: Liver, muscle, bone, cartilage, and other tissues
Function:Anabolic (tissue building) hormone that has both metabolic and growth-promoting actions

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Insulin-like Growth Factors (IGFs)

A family of growth-promoting proteins

50

Growth Hormone-Releasing Hormone (GHRH)

Hypothalamic hormone that stimulates GH release

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Growth Hormone-Inhibiting Hormone (GHIH)
also called Somatostatin

Hypothalamic hormone that inhibits GH release

52

Gigantism

Hypersecretion in children results in __________ because GH targets the still-active epiphyseal (growth) plates. The person becomes abnormally tall, but has relatively normal body proportions.

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Acromegaly

If excessive GH is secreted after the epiphyseal plates have closed, ___________ results. This condition is characterized by overgrowth of bony areas still responsive to GH.

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Pituitary Dwarfism

GH deficiency in children slows long bone growth, a condition called ___________. Such individuals attain a maximum height of 4 feet, but usually have fairly normal body proportions.

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Thyroid-Stimulating Hormone (TSH)
or Thyrotropin

Produced by: Thyrotropic cells of the anterior pituitary lobe (TRH)
Target: Thyroid gland
Function: Stimulates normal development and secretory activity of thyroid gland.

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Thyrotropin-Releasing Hormone (TRH)

A hypothalamic peptide that triggers the release of TSH from thyrotropic cells of the anterior pituitary.

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Thyrotropic Cells

Cell of the anterior pituitary which release TSH

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Adrenocorticotropic Hormone (ACTH)
or Corticotropin

Produced by: Corticotropic cells of the anterior pituitary (CRH)
Target: Adrenal Cortex
Function: Stimulates the adrenal cortex to release corticosteroid hormones, most importantly glucocorticoids that help the body resist stressors.

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Corticotropic Cells

Cells of the anterior pituitary which secrete ACTH

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Pro-Opiomelanocortin (POMC)

ACTH is split from a prohormone (a large precursor molecule) ______________.

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Corticotropin-Releasing Hormone (CRH)

ACTH release, elicited by hypothalamic ______________ has a daily rhythm, with levels peaking in the morning, shortly before awakening.

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Follicle-Stimulating Hormone (FSH)

Produced by: Hypothalamus GnRH
Target: Ovaries and Testes
Function: In females, stimulates ovarian follicle maturation and estrogen production
In males, promotes testosterone production

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Luteinizing Hormone (LH)

Produced by: Hypothalamus GnRH
Target: Ovaries and Testes
Function: In females, triggers ovulation and stimulates ovarian production of estrogen and progesterone
In males, promotes testosterone production

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Gonadotropins

FSH and LH are referred collectively as _______________.

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Gonadotropic cells

During puberty, the _______________ of the anterior pituitary are activated and gonadotropin levels rise, causing the gonads to mature.

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Gonadotropin-Releasing Hormone (GnRH)

In both sexes, the ______________ produced by the hypothalamus prompts gonadotropin (FSH and LH) release.

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Prolactin (PRL)

Produced by: Prolactin Cells
Target: Breasts
Function: Stimulate milk production by the breasts

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Prolactin-Inhibiting Hormone (PIH)
AKA Dopamine

Prevents prolactin secretion

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Thyroid gland

Butterfly shaped gland located in the anterior neck, on the trachea just inferior to the larynx. The largest pure endocrine gland in the body. Internally, this gland is composed of hollow, spherical follicles.

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Thyroglobulin

Follicular cells in side the thyroid gland produce the glycoprotein ___________.

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Colloid

The central cavity, or lumen, of the thyroid gland follicles stores _________, an amber-colored, sticky material consisting of thyroglobulin molecules with attached iodine atoms. Thyroid hormone is derived from this iodinated thyroglobulin.

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Thyroid Hormone (TH)

Two iodine-containing amine hormones, thyroxine, or T4, and triiodothyronine, or T3.

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Thyroxine (T4)

Produced by: Thyroid follicles
Target: Every cell in the body
Function: Increasing basal metabolic rate and body heat production, regulating tissue growth and development, and maintaining blood pressure.

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Triiodothyronine (T3)

Produced by: Thyroid follicles
Target: Every cell in the body
Function: Increasing basal metabolic rate and body heat production, regulating tissue growth and development, and maintaining blood pressure.

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Calorigenic Effect

A result of the increased metabolic rate and increased oxygen consumption by cells. When the metabolic rate increases, more heat is generated and body temperature rises.

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Monoiodotyrosine (MIT)

Attachment of one iodine to a tyrosine produces _______________.

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Diiodotyrosine (DIT)

Attachment of two iodines produces _______________.

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Myxedema

In adults, the full-blown hypothyroid syndrome is called ____________. Symptoms include a low metabolic rate; felling chilled; constipation; thick, dry skin and puffy eyes; edema; lethargy; and mental sluggishness.

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Goiter

An enlarged protruding thyroid gland. Occurs if myxedema results from lack of iodine.

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Cretinism

Severe hypothyroidism in infants. The child is mentally retarded and has a short, disproportionately sized body and a thick tongue and neck.

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Graves' Disease

The most common hyperthyroid pathology. Autoimmune condition where a person makes abnormal antibodies directed against thyroid follicular cells. Typical symptoms include elevated metabolic rate; sweating; rapid, irregular heartbeat; nervousness; and weight loss despite adequate food.

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Calcitonin

A polypeptide hormone released by the parafollicular, or C, cells of the thyroid gland in response to a rise in blood Calcium levels, does not have a known physiological role in humans.

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Parafollicular or C, Cells

Releases calcitonin

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Parathyroid Glands

Tiny, yellow-brown glands that are nearly hidden from view in the posterior aspect of the thyroid gland. There are usually four of these glands.

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Parathyroid cells

Secrete parathyroid hormone (PTH)

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Parathyroid Hormone (PTH)

Produced by: Parathyroid cells in parathyroid glands
Target: Bones, kidneys, and intestine
Function: Simulates osteoclasts (bone-resorbing cells), enhances reabsorption of Calcium by the kidneys, and promotes activation of vitamin D, thereby increasing absorption of Calcium by intestinal mucosal cells. Kidneys must first convert Vit D to its active D3 form, calcitriol in order to absorb Calcium from food.

87

Adrenal Glands
or Suprarenal Glands

Pyramid-shaped organs perched atop the kidneys where they are enclosed in fibrous capsule and a cushion of fat. Each gland is structurally and functionally two endocrine glands. Each region produces its own set of hormones, but all adrenal hormones help us cope with stressful situations.

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Adrenal Medulla

Th inner ___________ of the adrenal glands, more like a knot of nervous tissue than a gland, is part of the sympathetic nervous system.

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Adrenal Cortex

The outer ___________ of the adrenal glands, encapsulating the medulla and forming the bulk of the gland, is glandular tissue derived from embryonic mesoderm. Synthesizes well over two dozen steroid hormones.

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Corticosteroids

The adrenal cortex synthesizes well over two dozen steroid hormones, collectively called ____________.

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Zona Glomerulosa

Outsize zone of the adrenal cortex. The cell clusters forming this superficial layer produce mineralocorticoids, hormones that help control the balance of minerals and water in the blood.

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Zona Fasciculata

Middle layer of the adrenal cortex. The cells of this middle layer, arranged in more or less linear cords, mainly produce the metabolic hormones called glucocorticoids.

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Zona Reticularis

The innermost layer of the adrenal cortex. These cells abutting the adrenal medulla have a netlike arrangement and mainly produce small amounts of adrenal sex hormones, or gonadocorticoids.

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Mineralocorticoids

Essential function is to regulate electrolyte (mineral salt) concentrations in extracellular fluids, particularly of Sodium and Potassium.

95

Aldosterone

Produced by: Adrenal Gland
Target: Kidneys
Function: Increase blood levels of Sodium and decrease blood levels of Potassium; since water reabsorption accompanies sodium retention, blood volume and blood pressure rise

96

The Renin-Angiotensin-Aldosterone Mechanism

Influences both blood volume and blood pressure by regulating the release of aldosterone and therefore Sodium and water reabsorption by the kidneys.

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Renin

_________ cleaves off part of the plasma protein angiotensinogen, triggering an enzymatic cascade that forms angiotensin II, which stimulates the glomerulosa cells to release aldosterone.

98

Angiotensinogen

A plasma protein part of the renin-angiotensin-aldosterone mechanism

99

Angiotensin II

Produced by: Liver and Lungs
Target: Kidneys
Function: Stimulates the glomerulosa cells to release aldosterone

100

Glucocorticoid

Influence the energy metabolism of most body cells and help us resist stressors.

101

Cortisol (Hydrocortisone)
Cortisone, and Corticosterone (Not secreted in significant amounts)

Produced by: ACTH
Target: Body Cells
Function:Promote gluconeogenesis and hyperglycemia; mobilize fats for energy metabolism; stimulate protein catabolism; assist body to resist stressors; depress inflammatory and immune responses.

102

Cushing's Syndrome

The pathology of glucocorticoid excess. Persistent elevated blood glucose levels (steroid diabetes), dramatic losses in muscle and bone protein, and water and salt retention, leading to hypertension and edema. Swollen face, redistribution of fat to the abdomen and the posterior neck, easy bruising and poor wound healing. Eventually muscles weaken and spontaneous fractures force the person to become bedridden.

103

Cushing's Disease

The Pathology of glucocorticoid excess caused by an ACTH-releasing pituitary tumor

104

Addison's Disease

The major hyposecretory disorder of the adrenal cortex, usually involves deficits in both glucocorticoids and mineralocorticoids. Weight loss; plasma glucose and sodium levels drop, and potassium levels rise. Severe dehydration and hypotension are common.

105

Gonadocorticoids

Adrenal Sex Hormones

106

Androgens

Produced by: ACTH
Target: Many
Function: Insignificant effects in males
Females, contributes to libido; development of pubic and axillary hair; source of estrogen after menopause

107

Medullary Chromaffin Cells

Modified postganglionic sympathetic neurons that synthesize epinephrine and norepinephrine (NE) via a molecular sequence from tyrosine to dopamine to NE to epinephrine

108

Epinephrine

Produced by: Preganglionic fibers of the sympathetic nervous system
Target: Sympathetic nervous system target organs
Function: Effects mimic sympathetic nervous system activation; increased heart rate and metabolic rate; increase blood pressure by promoting vasoconstriction

109

Norepinephrine (NE)

Produced by: Preganglionic fibers of the sympathetic nervous system
Target: Sympathetic nervous system target organs
Function: Effects mimic sympathetic nervous system activation; increased heart rate and metabolic rate; increase blood pressure by promoting vasoconstriction

110

Hyperglycemia

Symptoms of uncontrolled sympathetic nervous system activity. Elevated blood glucose, increased metabolic rate, rapid heartbeat and palpitations, hypertension, intense nervousness, and sweating.

111

Pineal Gland

Tine, pine cone-shaped gland that hangs from the roof of the third ventricle in the diencephalon. The endocrine function is still somewhat of a mystery. Major secretory product is melatonin.

112

Pinealocytes

Secretory cells of the Pineal Gland, arranged in compact cords and clusters.

113

Melatonin

An amine hormone derived from serotonin. Concentrations in the blood rise and fall in a daily cycle. Peak levels occur during the night and make us drowsy, and lowest levels occur around noon. May also control the production of protective antioxidant and detoxification molecules within cells.

114

Pancreas

Located partially behind the stomach in the abdomen, the soft, tadpole-shaped ___________ is a mixed gland composed of both endocrine and exocrine gland cells.

115

Pancreatic Islets (Islets of Langerhans)

Tiny cell clusters that produce pancreatic hormones. Contain glucagon-synthesizing, alpha cells and insulin-synthesizing beta cells. These cells act as tiny fuel sensors, secreting glucagon and insulin appropriately during the fasting and fed states.

116

Alpha Cells

Glucagon-synthesizing

117

Beta Cells

Insulin-synthesizing

118

Glucagon

Produced by: Pancreas
Target: Liver
Function: Breakdown of glycogen to glucose, synthesis of glucose from lactic acid and from noncarbohydrate molecules, and release of glucose to the blood by liver cells causing blood glucose levels to rise.

119

Insulin

Produced by: Pancreas
Target: Liver and tissue cells
Function: Lower blood glucose levels, influences protein and fat metabolism. 3 ways it lowers blood glucose levels: Enhances membrane transport of glucose into most body cells, especially muscle and fat cells. Inhibits the breakdown of glycogen to glucose. Inhibits the conversion of amino acids or fats to glucose.

120

Diabetes Mellitus (DM)

Results from either hyposecretion or hypoactivity of insulin. When insulin is absent, the result is type 1 diabetes mellitus. If insulin is present, but its effects are deficient, the result is type 2 diabetes mellitus. In either case, blood glucose levels remain high after a meal because glucose is unable to enter most tissue cells.

121

Ketones
or Ketone bodies

Organic fatty acid metabolites

122

Ketoacidosis

When ketones accumulate in the blood, the blood pH drops, resulting in ___________________, and ketone bodies begin to spill into the urine. Can be severe = life threatening

123

Polyuria

Excessive glucose in the blood leads to excessive glucose in the kidney filtrate where it acts as an osmotic diuretic (this is, it inhibits water reabsorption by the kidney tubules), resulting in ___________, a huge urine output that decreases blood volume and causes dehydration.

124

Polydipsia

Dehydration stimulates hypothalamic thirst centers, causing ________, or excessive thirst.

125

Polyphagia

Excessive hunger and food consumption, a sign that the person is "starving in the land of plenty."

126

Hypoglycemia

Excessive insulin secretion, results in low blood glucose levels, or ______________. This condition triggers the release of hyperglycemic hormones, which cause anxiety, nervousness, tremors, and weakness.

127

Gonads

These produce steroid sex hormones, identical to those produced by adrenal cortical cells. The major distinction is the source and relative amounts produced.

128

Estrogens

Produced by: Gonads = Ovaries
Target: Uterus
Function: Maturation of the reproductive organs and the appearance of the secondary sex characteristics of females at puberty. With Progesterone they promote breast development and cyclic changes in the uterine mucosa (the menstrual cycle)

129

Progesterone

Produced by: Gonads = Ovaries
Target: Uterus
Function: Acting with estrogens it promotes breast development and cyclic changes in the uterine mucosa (the menstrual cycle)

130

Testosterone

Produced by: Gonads = Scrotum
Target:
Function: During puberty, testosterone initiates the maturation of the male reproductive organs and the appearance of secondary sex characteristics and sex drive. Is also necessary for normal sperm production and maintains the reproductive organs in their mature functional state adult males.

131

Leptin

Adipose cells release ____________, which serves to tell your body how much stored energy (as fat) you have. The more fat you have the more _________ there will be in your blood.

132

Resistin

Produced by: Adipose cells
Target: Fat, muscle and liver
Function:Antagonizes insulin's action

133

Atrial Natriuretic Peptide (ANP)

Produced by: Response to rising blood pressure (heart)
Target: Kidneys and adrenal cortex
Function: Inhibits sodium ion reabsorption and renin release (kidney)
Inhibits secretion of aldosterone; decreases blood pressure (Adrenal cortex)

134

Erythropoietin (EPO)

Produced by: Response to hypoxia (kidneys)
Target: Red bone marrow
Function: Stimulates production of red blood cells

135

Cholecalciferol

The skin produces _________________, an inactive form of vitamin D3, when modified cholesterol molecules in epidermal cells are exposed to ultraviolet radiation. This compound then enters the blood via the dermal capillaries, is modified in the liver, and becomes fully activated in the kidneys.

136

Calcitriol

The active form of vitamin D3. It is an essential regulator of the carrier system that intestinal cells use to absorb calcium from food.

137

Thymus

Located deep to the sternum in the thorax. Large and conspicuous in infants and children, but shrinks throughout adulthood. By old age, it is composed largely of adipose and fibrous connective tissue. It's cells secrete several different families of peptide hormones.

138

Tshymulin
Thymopoietins
Thymosins

Three hormones secreted by thymic epithelial cells that are thought to be involved in the normal development of T lymphocytes and immune response, but their roles are not well understood. They mainly act locally as paracrines.

139

Gastrin

Produced by: Secreted in response to food (Stomach)
Target: Stomach
Function: Stimulates glands to release hydrochloric acid (HCl)

140

Cholecystokinin (CCK)

Produced by: Secreted in response to food (Duodenum)
Target: Pancreas, gallbladder and hepatopancreatic sphincter
Function: Stimulates release of enzyme-rich juice (pancreas)
Stimulates expulsion of stored bile (gallbladder)
Causes sphincter to relax, allowing bile and pancreatic juice to enter duodenum (hepatopancreatic sphincter)