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What do the endocrine system/hormones control and integrate?
-Growth and development
-Maintenance of electrolytes, water, and nutrient balance of blood
-Regulation of cellular metabolism and energy
-Mobilization of body defenses
The Endocrine system works with the Nervous system to?
Coordinate and integrate activity of body cells
What are exocrine glands and what do they produce?
Have ducts that carry substances to a membrane surface. They produce non-hormonal substances (sweat & saliva)
What are some other tissues and organs that produce hormones?
-Cells in walls of small intestine, stomach, kidneys, and heart
What chemical messengers are no considered part of the endocrine system?
Autocrines and paracrines because they are local chemical messengers.
Amino acid-based hormones are what?
-Amino acid derivatives (thyroxine, tyrosine, & amines)
-Peptides (short chains of amino acids)
-Proteins (long polymers of amino acids)
These are water-soluble
Hormones typically produce one or more of the following changes
-Alter plasma membrane permeability and/or membrane potential by opening or closing ion channels.
-Stimulate synthesis of enzymes or other proteins.
-Activate or deactivate enzymes.
-Induce secretory activity
Hormones act at receptors in one of two ways, depending on their chemical nature and receptor location.
-Water-soluble: (In plasma membrane)
* Act on plasma membrane receptors
* Act via G protein second messengers
* Cannot enter cell
-Lipid-soluble hormones: (Inside the cell)
* Act on intracellular receptors that directly activate genes
* Can enter cell
What are the steps of the cAMP signaling mechanism?
1. Hormone (1st messenger) binds to receptor
2. Receptor activates G protein
3. G protein activates adenylate cyclase
4. Adenylate cyclase converts ATP to cAMP (second messenger)
5. cAMP activates protein kinases that phosphorylate proteins
What is the process of the PIP2-calcium signaling mechanism?
Involves the G protein and membrane-bound effector phosopholipase C
1. Phospholipase C splits PIP2 into two second messengers-diacylglycerol (DAG) and inositol trisphosphate (IP3)
2. DAG activates protein kinase; IP3 causes Ca2+ release
3. Calcium ions act as second messenger
Steroid and thyroid hormones direct gene activation process.
1. Diffuse into target cells and bind with intracellular receptors.
2. Receptor-hormone complex enters nucleus; binds to specific region of DNA.
3. Prompts DNA transcription to produce mRNA.
4. mRNA directs protein synthesis.
5. Promote metabolic activities, or promote synthesis of structural proteins or proteins for export from cell.
What does target cell activation depend on?
1. Blood levels of hormone.
2. Relative number of receptors on or in target cell.
3. Affinity of binding between receptor and hormone.
Endocrine gland stimulated to synthesize and release hormones in response to what?
Humoral (body fluids), neural, and hormonal stimuli.
What is an example of humoral stimuli?
Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH.
What is an example of neural stimuli?
Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines. Epinephrine/norepinephrine
What is an example of hormonal stimuli?
Hypothalamic hormone stimulate release of most anterior pituitary hormones.
What is the hypothalamic-pituitary-target endocrine organ feedback loop?
Hormones from final target organs inhibit release of anterior pituitary hormones.
What is nervous system modulation?
Nervous system modifies stimulation of endocrine glands and their negative feedback mechanisms.
What is an example of nervous system modulation?
Under severe stress, hypothalamus and sympathetic nervous system activated, body glucose levels rise. Nervous system can override endocrine.
How do steroids and thyroid hormones circulate?
Attached to plasma proteins because they are hydrophobic, carrier proteins. All others circulate without carriers.
What does the concentration of circulation hormones reflect?
1. Rater of release
2. Speed of inactivation and removal from the body.
What is a half-life?
Time required for hormone's blood level to decrease by half. Sometimes minutes to a week.
What is the onset of hormone activity?
-Some, especially steroid, hours to days
-Some must be activated in target cells
What is the duration of hormone activity?
-Ranges from 10 seconds to several hours.
-Effects may disappear as blood levels drop
-Some persist at low blood levels
What are the two major lobes of the pituitary gland or hypophysis?
1. Posterior pituitary (neural tissue)
2. Anterior pituitary (glandular tissue)
The hypophyseal portal system carries what to the anterior pituitary to regulate hormone secretion?
Releasing and inhibiting hormones.
What are the anterior pituitary hormones?
1. Growth hormone (GH)
2. Thyroid-stimulation hormone (TSH)
3. Adrenocorticotropic hormone (ACTH)
4. Follicle-stimulation hormone (FSH)
5. Luteinizing hormone (LH)
6. Prolactin (PRL)
In direct gene activation, steroid and thyroid hormones
-Diffuse into target cells and bind with intracellular receptors
-Binds to specific region of DNA
-Prompts DNA transcription to produce mRNA
-mRNA directs protein synthesis
-Promotes metabolic activities or proteins.
Target cell activation depends on three factors
1. Blood levels of hormone
2. Relative number of receptors on or in target cell
3. Affinity of binding between receptor and hormone
ADH definiciency due to hypothalamus or posterior pituitary damage, must keep well-hydrated
Syndrome of inappropriate ADH secretion (SIADH)
Retention of fluid, headache, disorientation, fluid restriction, blood sodium level monitoring
Growth hormone or Somatotropin direct actions on metabolism
Glycogen breakdown and glucose release to blood.
Growth hormone release chiefly regulated b hypothalamic hormones
Ghrelin (hunger hormone) also stimulates release.
Internal and external factors that alter the normal ACTH rhythm
Fever, hypoglycemia, and stressors can alter release of CRH (corticotropin-releasing hormone)
Transport and regulation of TH
Both bind to target receptors, but T3 is ten times more active than T4
Negative feedback regulation of TH release
Rising TH levels provide negative feedback inhibition on release of TSH
Adrenal cortex has three layers
1. Zona glomerulosa (mineralocorticoids)
2. Zona fasciculata (glucocorticoids)
3. Zona reticularis (gonadocorticoids)
Aldosterone release triggered by
Decreasing blood volume and blood pressure, rising blood levels of K+
Cortisol (hydrocortisone) only one in significant amounts in humans, cortisone (decrease inflammation, corticosterone
Hypersecretion of glucocorticoids (lady with hump on back of neck)
-Depresses cartilage and bone formation, inhibits inflammation, depresses immune system, disrupts cardiovascular, neural, and gastrointestinal function
Hyposecretion of glucocorticoids
-Decrease in glucose and Na+ levels, weight loss, severe dehydration, and hypotension.
Gonadocorticoids (Sex hormones)
Most weak androgens (male sex hormones) converted to testosterone in tissue cells, some to estrogens
-May contribute to-puberty, secondary sex characteristics, sex drive in women, estrogens in premenopausal women
Hypersecretion in adrenal medulla
-Increased metabolic rate, rapid heartbeat/palpitations, hypertension, intense nervousness, sweating
Pancreatic islets (islets of Langerhans)
Contain alpha cells that produce glucagon and beta cells that produce insulin
Effects of insulin
Lowers blood glucose levels and inhibits glycogenolysis and gluconeogenesis.
-Not needed for glucose uptake in liver, kidney, or brain.
Insulin action on cells
-Cascade-increased glucose uptake
-Triggers enzymes to catalyze oxidation of glucose for ATP production (1st priority), polymerize glucose to form glycogen, convert glucose to fat.
Factors that influence insulin release
Elevated blood glucose levels and release of acetylcholine by parasympathetic nerve fibers
Diabetes mellitus causes
Glycosuria (glucose spilled into urine), ketonuria and ketoacidosis (fatty acid metabolites) ketone bodies begin to spill into the urine.
Three cardinal signs of diabetes mellitus
1. Polyuria-huge urine output
2. Polydipsia-excessive thirst
3. Polyphagia-excessive hunger and food consumption
Excessive insulin secretion, causes hypoglycemia (anxiety, nervousness, disorientation, unconsciousness, death), treated by sugar ingestion.
-initiates maturation of male reproductive organs
-male secondary sex characteristics
Adipose tissue releases
Leptin-appetite control, stimulates increased energy
Adiponectin-enhances sensitivity to insulin
Enteroendocrine cells secrete
-Secretin-stimulates liver and pancreas
-Cholecystokinin-stimulate pancreas, gallbladder, and hepatopancreatic sphincter
-Serotonin-acts as paracrine
Erythropoietin-production of RBCs
Renin- initiates the renin-agiotensin-aldosterone mechanism
Thymulin, thymopoietins, and thymosins. May be involved in normal development of T lymphocytes in immune response
What hormones are vulnerable to the effects of pollutants?
Sex hormones, thyroid hormone, and glucocorticoids.
As ovaries age they
Undergo significant changes and become unresponsive to gonadotropin; problems associated with estrogen deficiency occur.
As males age what hormone diminishes
Testosterone but effect is not usually seen until very old age.
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