Chapter 17: Introduction to the Endocrine System

Activated G protein "turns on" adenylate cyclase

1. Activated G protein binds to and causes activation of the plasma membrane enzyme adenylate cyclase. 2. Adenylate cylase converts ATP molecules to cAMP molecules. 3. cAMP serves as the "second messenger" by activating protein kinase A, a phosphorylating enzyme that adds phosphate to other molecules; these molecules may be activated or inhibited as a result.

Activated G protein "turns on" phopholipase C

1. Activated G protein binds to and causes activation of the plasma membrane enzyme phospholipase C. 2. Phospholipase C splits PIP2 into two second messengers: DAG, diaclyglycerol, and IP3, inositol triphosphate. 3. DAG activates protein kinase C, a phosphorylating enzyme. 3a. IP3 increases CA2 in cytosol, by stimulating Ca2 release from the endoplasmic reticulum and entry across the plasma membrane from the interstitial fluid. 3b. Ca2 acts as a third messenger to activate protein kinase enzymes, Ca2 does this directly or by first binding to calmodulin. Ca2 may also alter activity of ion channel within the plasma membrane.

Liver and muscle tissue

1. Glycogenesis 2. Glycogenolysis 3. Gluconeogenesis.

Activation of G proteins

1. Hormone, first messenger, binds to receptor and induces shape change to activate the receptor. 2. G protein binds to activated receptor. 3. GDP is "bumped off" and GTP binds to G protein, G protein is then activated. 4. Activated G protein, with GTP, is released from the receptor and moves along the inside of the plasma membrane, which results in formation or availability of second messenger.

Thyroid hormone: synthesis, storage and release

1. I- uptake: Iodide ion, I-, is moved by active transport into follicular cells. 2a. I2 formation: Two I- join to form molecular iodine, I2. 2b. Thyroglobulin synthesis: Thyrogobulin protein, containing tyrosine amino acids, is synthesized in follicular cells. 3. Transport to colloid: Both I2 and thyrogobulin are transported into the colloid. 4. MIT and DIT formation: One I2 binds to tryosine within thryoglobulin to form MIT, two I2 bind to tryosine to form DIT. 5. Pre-T3, pre-T4 formation: Within thyroglobulin molecules, one DIT and one MIT join to form pre-T3, or, two DIT join to form pre-T4. 6. Endocytosis into follicular cell: The modified protein strand containing pre-T3 and pre-T4 is endocytosed into follicular cell and taken to a lysosome. 7. T3, T4 release: T3 and T4 are excised from molecule and released into the blood.

Adipose connective tissue

1. Lipogenesis 2, Lipolysis

4 major functions of the Endocrine system

1. Maintaining homeostasis of blood composition and volume: regulate substances dissolved in blood (glucose, ions) regulate blood volume, cellular concentration, and platelet number 2. Controlling reproductive activities: development and function & expression of sexual behaviors 3. Regulating development, growth, and metabolism:cell division and differentiation; nutrient catabolism & anabolism. 4. Controlling digestive processes: secretion & movement through digestive tract

All cells, especially muscles

1. Protein anabolism 2. Protein catabolism

Regulation and action of glucagon

1. Stimulus: Decrease in blood glucose. 2. Receptor: Alpha cells within the pancreas detect a decrease in blood glucose levels. 3. Control center: Alpha cells within the pancreas release glucagon. 4. Gucagon stimulates target cells, effectors. Effectors: Liver- increased glycogenolysis and gluconeogenesis, decreased glycogenesis. Adipose connective tissue- increased lipolysis and decreased lipogenesis. 5. Net effect: increased blood glucose and fatty acid levels, note no change in amino acids or proteins. Negative feedback: Glucagon release is inhibited as blood glucose levels increase to normal.

Regulation and action of thyroid hormone

1. Stimulus: Hypothalamus is stimulated by one or more of the following- decreased thyroid hormone, other stimuli including cold weather, pregnancy, high altitude and hypoglycemia. 2. Receptor: the hypothalamus responds to various stimuli. 3. Control center: The hypothalamus releases thyrotropin-releasing hormone, TRH, into the hypothalamo-hypophyseal portal system. 4. In response to TRH, the anterior pituitary releases thyroid-stimulating hormone, TSH. 5. TSH stimulates the thyroid gland to release thyroid hormone, TH, into the blood. 6. TH then acts on target cells, effectors. Effectors: all cells, especially neurons- increased metabolic rate, increased glucose uptake. Liver tissue- increased glycogenolysis and glucogenesis. Adipose connective tissue- increased lipolysis, decreased lipogenesis. Lungs and heart- increased breathing rate, increased heart rate, increased force of contraction, these response help meet increased O2 demand for aerobic cellular respiration. 7. Net effect: increased metabolic rate, which is supported by increased release of stored fuel molecules, and increased delivery O2. 8. TH levels increase, inhibiting release of TRH and TSH.

Regulation and action of cortisol hormone

1. Stimulus: Variables that act on the hypothalamus: negative feedback by cortisol, time of day, stress. 2. Receptor: Hypothalamus responds to various stimuli. 3. Control center: The hypothalamus releases corticotropin-releasing hormone, CRH, into the hypothalamo-hypophyseal portal system. 4. In response to CRH, the anterior pituitary release adrenocorticotropic hormone, ACTH. 5. ACTH stimulates the adrenal cortex to release glucocorticoids into the blood. 6. Cortisol stimulates target cells, effectors. Effectors: Liver- Stimulation of gluconeogenesis, use amino acids and fatty acids. Adipose connective tissue- Stimulation of lipolysis, inhibition of lipogenesis. All cells- Stimulation of protein catabolism, occurs in all cells except hepatocytes. High doses of cortisol- increase retention of Na, H2O, decrease inflammation, suppress the immune system, inhibit connective tissue repair. 7. Net effect: Increase of all nutrients in the blood. 8. Cortisol levels increase inhibiting release of CRH and ACTH.

Growth hormone

1. Stimulus: Variables that influence the release of GHRH from the hypothalamus; age, time of day, nutrient levels in the blood, stress and exercise. 2. Receptor: The hypothalamus responds to various stimuli. 3. Control center: The hypothalamus releases growth hormone, GHRH, into the hypothalam0-hypohyseal portal system. 4. In response to GHRH, the anterior pituitary releases growth hormone, GH. 5. GH stimulates hepatocytes to release insulin-like growth factor, IGF, into the blood. 6. Both GH and IGF stimulate target cells, effectors. -effectors: responds to GH and/or IGF in the following way; bone, muscles, all cells- increase growth, increased amino acid uptake which result in protein synthesis, stimulated mitosis, cell differentiation. Liver tissue- increased glycogenolysis and gluconeogenesis, decreased glycogenesis. Adipose connective tissue- increased lipolysis, decreased lipogenesis. 7. Net effect: Increased protein synthesis, mitosis, and cell differentiation-especially in cartilage, bone and muscle, release of stored nutrients into the blood. 8. Increased levels of both GH and IGF inhibit the release of GHRH from the hypothalamus, increased levels of GH also inhibits the release of GH from the anterior pituitary.

Regulation and action of insulin

1. Stimulus: increase in blood glucose. 2. Receptor: Beta cells within the pancreas detect an increase in blood glucose levels. 3. Control center: Beta cells within pancreas release insulin. 4. Insulin stimulates target cells, effectors. Effectors: Liver tissue- increased glycogenesis, decreased glycogenolysis and gluconeogenesis. Adipose connective tissue- increase lipogenesis, and decreased lipolysis. All cells, especially muscle- increase uptake of amino acids, which stimulates protein anabolism. Most cells- increased uptake of glucose by increasing glucose transport proteins in the plasma membrane. 5. Net effect: Decreased blood glucose, fatty acids and amino acids are also decreased in the blood. 6. Negative feedback: Insulin release is inhibited as blood glucose levels decrease to normal.

Lipid-soluble hormones and intracellular receptors

1. The unbound lipid-soluble hormone diffuses readily through the plasma membrane and binds with an intracellular receptor, either within the cytosol or the nucleus to form a hormone-receptor complex. 2. The hormone-receptor complex then binds with a specific DNA sequence called a hormone-response element. 3. This binding stimulates mRNA synthesis. 4. mRNA exits the nucleus and is translated by a ribosome in the cytosol. A new protein is synthesized.

Cortisol level is increased by stress

Both emotional stress, anxiety, anger, fear, and physical stress, fever, trauma, or intense exercise the release of cortisol.

Glycogenolysis

Breakdown of glycogen to glucose.

Protein catabolism

Breakdown of protein to amino acids.

Lipolysis

Breakdown of triglycerides to glycerol and fatty acids.

Down-regulation

Cells may decrease the number of receptors and reduce the cell's sensitivity to a hormone.

Up-regulation

Cells may increase the number of receptors, thereby increasing cell sensitivity to a hormone.

Target Cells

Cells with specific receptors for a hormone.

Cortisol release fluctuates based on the time of day

Cortisol levels fluctuate throughout the day. This rhythm of release is regulated by light and dark cycles detected by the retina as nerve signals are relayed to the hypothalamus.

GH release is altered by stress

Emotional, physical and chemical stress, including surgery, trauma, exercise or electroshock therapy increase GH release.

acromegaly

Excessive growth hormone production in an adult.

Adrengenital syndrome, androgen insensitivity syndrome or congenital adrenal hyperplasia

First manifests in the embryo and fetus. It is characterized by the inability to synthesize corticosteroids.

Gluconeogenesis

Formation of glucose from noncarbohydrate source.

Glycogenesis

Formation of glycogen from glucose.

Lipogenesis

Formation of triglycerides from glycerol and fatty acids.

GH release changes in response to nutrient blood levels.

GH release is regulated by the level of nutrient molecules in the blood. GH levels increase in response to an increase in amino acid levels and to a decrease in glucose levels or fatty acids levels.

Pineal gland

Hormone produced: Melatonin Function: Helps regulate the body's cicadian rhythem, sleep patterns.

Adrenal glands, medulla

Hormone- Catecholamines, epinephrine and norepinephrine Function- prolong fight or flight response.

Adrenal glands, cortex

Hormone- Mineralocorticoids, aldosterone Glucocorticoids, cortisol Gonadocorticoids, androgens Function- Mineralocorticoids- regulate blood sodium and potassium levels. Glucocorticoids- participate in stress response Gonadocorticoids- stimulates maturation and functioning of reproductive system.

Parathyroid gland

Hormone- Parathyroid hormone, PTH Function- PTH- increases blood calcium levels

Thyroid gland

Hormone- Thyroid hormone, TH Calcitonin, Function- TH- increases metabolism Calcitonin- decreases blood calcium levels

Pituitary gland, posterior gland

Hormone: Oxytocin, OT Antidiuretic hormone, ADH Function: OT- Uterine contractions, breast milk release. ADH- Fluid balance.

Pituitary gland, anterior gland

Hormone: Thyroid-stimulating hormone, TSH Prolactin, PRL Follicle-stimulating hormone, FSH Luteinizing hormone, LH Adrenocorticotropic hormone, ACTH Growth hormone, GH Function: TSH- Stimulates thyroid gland to release thyroid hormone. PRL- breast milk production FSH- Development of gametes LH- Development of gametes ACTH- stimulates adrenal cortex to release corticosteroids. GH- Stimulates cell growth and division.

Liver

Hormones- Angiotensinogen, Erythropoietin (EPO) Function- regulates blood volume and blood pressure, increases production of erythrocytes.

Heart

Hormones- Atrial natriuretic peptide, ANP Function- regulates blood sodium levels and blood volume.

Kidneys

Hormones- Erythopoietin, EPO Function- increases production of erythrocytes

Ovaries, gonads

Hormones- Estrogen, progesterone, inhibin Function- stimulate maturation and function of female reproductive system.

Stomach

Hormones- Gastrin Function- increases secretions and motility of the stomach

Pancreas

Hormones- Insulin, glucagon Function- decreases blood glucose, increases blood glucose

Skin

Hormones- Vitamin D Function- promotes absorption of calcium from gastrointestinal GI tract into blood

Testes, gonads

Hormones- androgens (testosterone), inhibin Function- stimulate maturation and function of male reproductive system

Small intestine

Hormones- secretion, cholecystokinin Function- regulates digestive processes of the small intestine.

Thymus

Hormones- thymosin, thymulin, thymopoietin Function- stimulates maturation of T-lymphocytes

Graves disease

Includes all the symptoms of hyperthyroidism plus a peculiar change in the eyes known as exopthalmos, protuding and bulging eyeballs.

Synergistic

Interaction occurs when the activity of one hormone reinforces the activity of another hormone.

Antagonistic

Interaction occurs when the effects of one hormone oppose the effects of another hormone.

Permissive

Interaction takes place when the activity of one hormone requires a second hormone- as if one hormone "gives permission" for a different hormone to function.

Pituitary dwarfism

Is a condition that exists at birth as a result of inadequate growth hormone production due to a hypothalamic or pituitary problem.

Addison disease

Is a form of adrenal insufficiency that develops when the adrenal glands fail, resulting in a chronic shortage of glucocorticoids and sometimes mineralocorticoids.

Diabetes mellitus

Is a metabolic condition marked by inadequate uptake of glucose from the blood.

Gestational diabetes

Is seen in some pregnant women, typically in the latter half of the pregnancy.

Type 1 diabetes

It is characterized by absent or diminished production and release of insulin by the pancreatic islet cells. Occur in childern.

Steroid hormone

Lipid-soluble, formed from cholesterol, produced by gonads and adrenal cortex.

Hypoglycemia

Occurs when blood glucose levels drop below 60mg/dL. Is not a disease, however, it may by a nonspecific indicator of some underlying homeostatic balance.

Goiter

Refers to enlargement of the thyroid, typically due to an insufficient amount of dietary iodine.

Hormonal stimulation

Release of a hormone in response to another hormone

Nervous system stimulation

Release of a hormone in response to stimulation by the nervous system.

Hypothyroidism

Results from decreased production of TH. Its characterized by low metabolic rate, lethargy, a feeling of being cold, weight gain and photophobia.

Type 2 diabetes

Results from either decreased insulin release from the pancreatic beta cells or decreased insulin effectiveness at peripheral tissues. Adult on set diabetes.

Hyperthyroidism

Results from excessive production of TH and is characterized by increased metabolic rate, weight loss, hyperactivity, and heat intolerance.

Cushing syndrome

Results from the chronic exposure of the body's tissues to excessive levels of glucocorticoid hormones.

Protein anabolism

Synthesis of protein from amino acids.

Endocrine System

Synthesize and secrete molecules called hormones. hormones released into the blood and transported throughout the body to target cells.

Hypophysectomy

The surgical removal of the pituitary gland. To treat advanced breast and prostate cancer.

GH release fluctuates based on the time of day.

There are daily fluctuations in the release of GH. Most growth occur while we are sleeping. Nocturnal peaks account for the majority of the GH release daily.

Pituitary gigantism

Too much growth hormone causes excessive growth and leads to increased levels of blood sugar.

Biogenic amine

Water-soluble (expect thyroid hormone), Derived from amino acid that is modified

Protein hormone

Water-soluble, consists of amino acids chains, 3 sub groups: polypeptides, oligopeptides, glycoproteins.

GH release changes with age

levels fluctuate with age. GH starts to decrease as we age.

Hypothalamus

regulates hormone release from pituitary gland.

Humoral stimulation

release of a hormone in response to changes in level of nutrient or ion in the blood.