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132 terms

Chapter 16: The Endocrine System

Taken directly from power point presentation from class.
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What do the endocrine system/hormones control and integrate?
-Reproduction
-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
How is the response of the Endocrine system versus the Nervous system?
Slower but longer lasting
What is Endocrinology?
The study of hormones and endocrine organs
What does the endocrine system influence?
Metabolic activities via hormones transported in blood
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 endocrine glands?
Ductless glands that produce hormones
What are the endocrine glands?
-Pituitary
-Thyroid
-Parathyroid
-Adrenal
-Pineal
They hypothalamus is what type of organ?
Neuroendocrine organ
Which organs have exocrine and endocrine functions?
-Pancreas
-Gonads
-Placenta
What are some other tissues and organs that produce hormones?
-Adipose cells
-Thymus
-Cells in walls of small intestine, stomach, kidneys, and heart
What are hormones?
Long-distance chemical signals; travel in blood or lymph
What are autocrines?
Chemicals that exert effects on the same cells that secrete them
What are paracrines?
Locally acting chemicals that affect cells other than those that secrete them
What chemical messengers are no considered part of the endocrine system?
Autocrines and paracrines because they are local chemical messengers.
What are the two main classes of hormones?
Amino acid-based hormones and steroids.
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
Steroid hormones are what?
-Gonadal
-Adrenocortical
Lipid-soluble
Steroids are synthesized from what?
Cholesterol.
What are target cells?
Tissues with receptors for a specific hormone.
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
-Stimulate mitosis
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
What is target cell specificity?
Target cells must have specific receptor to which hormone binds.
What causes smooth muscle to contract?
Calmodulin
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.
ACTH receptors are found only on
certain cells of the adrenal cortex.
Thyroxin receptors are found on
nearly all cells of the body.
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.
What is up-regulation?
More receptors in response to low hormone levels.
What is down-regulation?
lose receptors in response to high hormone levels.
Blood levels of hormones are controlled by what?
Negative feedback systems.
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 hormones circulate?
In blood either free or bound.
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.
How are hormones removed from blood?
-Degrading enzymes
-Kidneys
-Liver
-Half-life
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 responses~immediate
-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 is permissiveness?
One hormone cannot exert its effects without another hormone being present.
What is synergism?
More than one hormone produces same effects on target cell (amplification)
What is antagonism?
One or more hormones opposes action of another hormone.
What are the two major lobes of the pituitary gland or hypophysis?
1. Posterior pituitary (neural tissue)
2. Anterior pituitary (glandular tissue)
What type of connection does the posterior pituitary have to the hypothalamus?
Neural
What is the hypothalamic-hypophyseal tract?
Neural connection to hypothalamus
Nuclei of hypothalamus synthesize neurohormones call what?
Oxytocin and ADH
What are tracts made from?
Nerves
What are portal made from?
Blood vessels
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)
Calmodulin
Causes smooth muscle to contract.
Activated kinases phosphorylate various proteins which
Activate some and inactivate others.
Calcium ions act as
A second messenger.
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.
ACTH receptors found only on certain cells of
Adrenal cortex
Tyroxin receptors are found on
Nearly all cells of body and affects metabolism
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
Blood levels of hormones are controlled by
Negative feedback systems
Diabetes insipidus
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 major targets
Bone and skeletal muscle
Growth hormone release chiefly regulated b hypothalamic hormones
Ghrelin (hunger hormone) also stimulates release.
Hypersecretion of GH
Children-gigantism
Adults-acromegaly
Hyposecretion of GH
Pituitary dwarfism
Internal and external factors that alter the normal ACTH rhythm
Fever, hypoglycemia, and stressors can alter release of CRH (corticotropin-releasing hormone)
Prolactin
Stimulates milk production and role in males is not yet understood.
Thyroid gland has two lateral lobes connected by median mass called
Isthmus
Thyroid gland is composed of
Follicles that produce glycoprotein thyroglobulin
The parafollicular cells in the thyroid produce
Calcitonin
Thyroid hormone is a major
Metabolic hormone and increases metabolic rate and heat production
Transport and regulation of TH
Both bind to target receptors, but T3 is ten times more active than T4
Osteoclasts
Hormone that releases calcium
Negative feedback regulation of TH release
Rising TH levels provide negative feedback inhibition on release of TSH
Cretinism
Hyposecretion of TH in infants
Graves' disease
Hypersecretion of TH
Myxedema
Hyposecretion of TH in adults; goiter if due to lack of iodine
Negative feedback control of PTH
Rising Ca2+ in blood inhibits PTH release
Adrenal medulla
Inside, part of the sympathetic nervous system
Adrenal cortex
Outside, synthesize and secrete corticosteroids
Adrenal cortex has three layers
1. Zona glomerulosa (mineralocorticoids)
2. Zona fasciculata (glucocorticoids)
3. Zona reticularis (gonadocorticoids)
Most potent mineralocorticoid that stimulates Na+ reabsorption
Aldosterone
Aldosterone release triggered by
Decreasing blood volume and blood pressure, rising blood levels of K+
Causes small increases of aldosterone during stress
ACTH
Blocks renin and aldosterone secretion to decrease blood pressure
Atrial natriuretic peptid (ANP)
Keep blood glucose levels relatively constant
Glucocorticoids
Glucocorticoids secrete
Cortisol (hydrocortisone) only one in significant amounts in humans, cortisone (decrease inflammation, corticosterone
Cushing's syndrome/disease
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
Addison's disease
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
Hyperglycemia
Hypersecretion in adrenal medulla
-Increased metabolic rate, rapid heartbeat/palpitations, hypertension, intense nervousness, sweating
Hyposecretion of adrenal medulla
Not problematic, adrenal catecholamines not essential to life
Major secretory product of the pineal gland
Melatonin
Melatonin may affect
Day/night cycles, body temperature, sleep, appetite.
Pancreas is located
Partially behind the stomach and is triangular shaped
The pancreas has both ___________ and __________ cells.
Exocrine and endocrine
Acinar cells in the pancreas produce
Enzyme-rich juice for digestion
Pancreatic islets (islets of Langerhans)
Contain alpha cells that produce glucagon and beta cells that produce insulin
Glucagon major target
Liver and increased blood glucose levels
Glycogenolysis
Breakdown of glycogen to glucose
Gluconeogenesis
Synthesis of glucose from lactic acid and noncarbohydrates
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
Hyperinsulinism
Excessive insulin secretion, causes hypoglycemia (anxiety, nervousness, disorientation, unconsciousness, death), treated by sugar ingestion.
Ovaries produce
Estrogens and progesterone
Progesterone causes
Breast development and cyclic changes in uterine mucosa
Placenta secretes
Estrogens, progesterone, and human chorionic gonadotropin (hCG)
Testes produce
Testosterone
-initiates maturation of male reproductive organs
-male secondary sex characteristics
Adipose tissue releases
Leptin-appetite control, stimulates increased energy
Resistin-insulin antagonist
Adiponectin-enhances sensitivity to insulin
Enteroendocrine cells secrete
-Secretin-stimulates liver and pancreas
-Cholecystokinin-stimulate pancreas, gallbladder, and hepatopancreatic sphincter
-Serotonin-acts as paracrine
Heart secretes
Atrial natriuretic peptide (ANP) decreases blood Na+
Kidneys secrete
Erythropoietin-production of RBCs
Renin- initiates the renin-agiotensin-aldosterone mechanism
Skeleton secretes
Osteocalcin-more insulin, improves glucose handling, reduces body fat
Skin secretes
Cholecalciferol-precursor of vitamin D
Thymus secretes
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.
GH levels decline with age and accounts for
Muscle atropy
TH declines with age contributing to
Lower basal metabolic rates
PTH levels remain fairly constant, but lack of
Estrogen in older women makes them more vulnerable to bone-demineralizing effects of PTH