revised endocrine.ppt
TRANSCRIPT
The Endocrine System
Hormones are secreted into the blood byendocrine glands
See table 1- some endocrine organs arespecialized for hormone secretion
Some (e.g., skin, stomach, liver,etc.) haveadditional functions
(specialized)
What is a hormone?
Small molecule that affects metabolism of targetorgan
Amines- from tyrosine and tryptophanadrenal medulla, thyroid, pineal glands
Polypeptides and proteinsmore than 100 amino acidsexample: growth hormone
Glycoproteinslarge chain of amino acids with carbohydratesattached (FSH and LH)
Steroidsderived from cholesterolprogesterone, cortisol, testosterone(only by adrenal gland and gonads)
Some are synthesized as a precursor and lateractivated
Some are polar, some lipid-soluble- these can passthrough cell membranes if small enough
Endocrine vs neural control
A lot of overlapsome polypeptides are hormones ANDneurotransmitters
Neurotransmitters do not travel in the blood,but across a synaptic cleft
Neural control generally considered faster-acting
Common requirementstarget cells must have specific receptorsfor the hormone/neurotransmitter
binding to receptor must trigger specificchanges in the target cell
mechanism for quickly switching offthe activity (removal or inactivationof the hormone/neurotransmitter)
Effects of hormones
One tissue can respond to many hormones
Synergistic effect- hormones work together toproduce a result
Example: epinephrine and norepinephrine havean additive effect to increase heart rate
FSH and testosterone have complementaryeffect on sperm production
Permissive effect- one hormone enhances theeffect of another
Glucocorticoids enhance effectiveness ofcatecholamines (epinephrine andnorepinephrine)
Antagonist effect- one hormone opposes theeffect of another
insulin promotes fat formationglucagon promotes fat breakdown
Modulation of hormone effect
Hormones do not usually accumulate in bloodhalf-life usually several hours; usuallydeactivated in liver
Concentration is important
Physiological range- normal activityPharmacological (high) range
may affect other cellsmay affect other hormone levels
Priminghormone bindsmore receptors synthesized
more hormone can bind cell
Downregulation- prolonged exposure to highhormone levels can reduce receptorexpression. Cells are therefore desensitized
Some hormones are therefore secreted in spurts
Mechanisms of hormone action
Lipophilic (steroids and thyroxine) pass throughmembranebind receptors inside target cells
in cytoplasm or nucleus
Water-soluble hormones can’t pass throughmembranebond to receptors on cell (membrane)surface
“Second messenger” activation requiredadenylate cyclase-cAMPphospholipase C- calcium
Some important endocrine glands
Pituitary glandanterior lobe secretes its own hormones
regulated by hypothalamusfeedback control
posterior lobe- neural tissuestores and releases products ofhypothalamus
Adrenal glands- paired organs that sit “on top”of the kidneys
Outer cortex and inner medulla have different functions
Medulla- catecholamines (epinephrine,norepinephrine)stimulated by sympathetic nerves
Cortex- controlled by ACTH from anteriorpituitary
Cortex secretes steroid hormones(corticosteroids)
Mineralocorticoids- regulate Na and K balancealdosterone
Glucocorticoids- regulate glucose metabolismcortisol
Androgens, supplement sex steroids secretedby gonads
Adrenal medulla- innervated by sympatheticnervous system
“Fight or flight”rise in blood glucoserise in blood fatty acids
Sustained stress- general adaptation syndrome1. Alarm2. Resistance3. Exhaustion
Thyroid and parathyroid glands
Thyroglobulin+ iodine = thyroxine (T4) and triiodothyronine (T3)
Released from precursor (thyroxine) throughaction of TSH
Protein synthesisMaturation of nervous systemIncrease rate of cell respiration
Calcitoninreleased by parafollicular cellsworks with parathyroid hormone
inhibits dissolution of bonestimulates excretion of calcium in urine
(lowers blood calcium levels)
Thyroid diseases
Iodine deficiency goitercan’t make enough T3 and T4no inhibition of TSHstimulates abnormal thyroid growth
Hypothyroidlow metabolic rate; inability to adapt tocoldmyxedema (swelling) in adults
Lots of possible causes for hypothyroidism
Lack of:thyrotropin-releasing hormone from hypothalamusinsufficient TSH from pituitaryiodine deficiency (goiter)
HyperthyroidGraves’ disease; tumorsmetabolic rate is too highirritability; intolerance of heathigh blood pressure
See Table 11.8 for comparison
Children with thyroxine deficiencieswill lack normal gowth and nervous systemdevelopment (cretinism)
(lack of growth hormone does not affectintelligence)
Immediate treatment with thyroxine willrestore intelligence
Children are now routinely tested at birthfor thyroid function
Review other hormones for:where produced and what are targetorgans/tissues
how regulated (feedback, pituitary, etc.)
disorders associated with overproductionor underproduction