Chapter 41 – Chemical Signals in Animals
The Endocrine System
Hormones – regulatory function, internal communication
-different from nervous system, high speed conducting
-communication, organ to organ, also, individual to individual – pheromones
-also neurotransmitters
-chemical signal, secreted into body fluids by endocrine or neurosecretory cells
-goes to target cells, equipped to effect a response
-effective in minute amounts
-glands – ductless
-pancreas – exo and endocrine –
-lipid or steroid hormones – i.e. sex, made from cholesterol
-can bind with DNA to effect changes in DNA expression (pic, pg. 916) by expression of specific genes – birds, same hormone, induces production of egg white, and produce certain proteins in liver
-amine hormone
-changing of skin color in chameleon, in response to light stimulation of pituitary
-because they are proteins, and big, don’t usually travel into a target cell
-usually just change how target cell responds by electrical changes
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-all have specific shapes that are recognizable by target
-often, have antagonistic, opposing hormones, regulated by feedback
Pheromones
-between animals of same species
-mate attractants, territorial markers, alarms
-i.e. – gypsy moth
-synchronous menstrual cycles
-smelling underarm odor, sexual attractant
Local regulators
-neurotransmitters
-release into local fluid – affect local cells – histamines, swelling after mosquito or other bite
-NO – dilates blood vessels, such as in erectile tissue of penis, then breaks down
-Growth factors
-Several different kinds – linked to particular types of cells – bone, nerve
-Prostaglandins
-What causes uterus to contract – birth, labor, cramping
-Induce fever and inflammation, pain, lots of analgesics (aspirin) act to suppress production of prostaglandins
Examples of different effects
-thyroxin – regulates metabolism and changes in growth (tadpole to frog)
The Domino Effect of Hormones
-Sutherland, Vanderbilt, Nobel – 1971 –
-Discovered effects of epinephrine
-Mobilization of glycogen fuel reserves in liver for quick action
-But, needed a second messenger in order to do this
-Cyclic AMP
-Also G proteins, both act as relays
The Response – both size and specificity
-there’s a whole series of steps
-enzyme cascade – amplifies response to hormone – a few released epinephrine moles can trigger mobilization of millions of glycogen molecules to glucose at one
-this explains the fairly rapid response one has to a scare – the “fight or flight” reaction
-specificity results from particular target cell which is activated – steps in enzyme cascade are different depending on which cell is activated first
Calcium ion concentration in cytoplasm
-another way to regulate, besides cAMP
-messages either uptake Ca from extracellular fluid or release from probably the ER
Review
-steroid hormones enter cell, bind with DNA, affects synthesis of proteins, generally a slower response, but responses last longer
-peptide hormones, signal conduction pathway, affects activity of protein enzymes, quicker response, shorter duration of response
Invertebrate Hormone regulation
-regulate water balance
-more complex, mollusks, I’m thinking oysters, don’t generally harvest them in months without R’s – because hormonal control causing them to put all their energy into reproduction, gamete making – little of the viscera dedicated to production of the stuff you like to eat
-Arthropods – 3 hormones
-Insect molting hormone, stimulates production of adult characteristics
-Hormone to stimulate production of the above
-Both controlled by a third hormone
Regulatory Hormones – pituitary and hypothalamus
-called tropic hormones, regulate other endocrine glands
-hypothalamus
-integrates nervous and endocrine
-receives sensory stimulation about seasons, amt. of light
-hypo then triggers release of hormones in reproductive glands to produce gametes
-also, it regulates pituitary gland, by secreting either “releasing” or “inhibiting” hormones
-multiple endocrine functions
-called the “master gland”
-posterior – hormones that affect uterus and kidney directly
-oxytocin – contracts uterus and releases milk from mammary glands
-ADH – increases retention of water in kidney, dec. urine output
-regulates osmolarity of blood – negative feedback system – when osmolarity of blood increases, cells shrink, send message, ADH released, causes water to be resorbed into general circulation, thus decreasing osmolarity, etc., etc., etc.
-also stimulates thirst, drink, inc. conc. of water in blood
-anterior hormones
-TSH – regulates release of thyroxin in thyroid gland – high TSH, low release, not great , sluggish, cold
-ACTH
-Stress hormones and endorphins – natural “opiates” – inhibit perception of pain – heroin mimics this
-LH and FSH – stimulate ovaries to mature and release eggs
-GH – stimulate release of insulin-like factors – results in growth of bone and cartilage
-Gigantism, in adulthood – giant hands and feet, low GH – dwarfism – big success in biotech is production of GH by bacteria by recombinant DNA, GH can be used as a steroid in athletes
-Prolactin – milk synthesis, delays growth in metamorphosis, regulates salt and water balance
Thyroid gland
-produces 2 hormones – both with iodine in them
-early lack of = cretinism – retarded skeletal growth and brain function
-hyper = sweating, rapid pulse, weight loss (I wish), high bp
-hypo – lethargy, weight gain, cold, and goiter, if diet has no iodine, but addition of iodine to salt in the 1930’s helped that – found naturally in seafood
-also, secret calcitonin – lowers Ca in blood (I had trouble with that, initially)
Parathyroids – embedded in thyroids
-raises levels of calcium, opposite to calcitonin
-if too little, Ca level in blood drops, muscles spasm = tetany
Pancreas
-Islets of Langerhans – insulin and glucagon, antagonistic
-Both regulate levels of blood glucose
-If too much glucose in blood, not enough insulin, is secreted by kidneys, and body metabolizes fats for energy – results in lots of “fat” molecules in blood – results in stopped up capillaries in eyes and kidney (glomeruli) where capillaries are so small – basically blows the capillaries
Type I – insulin dependent – autoimmune – islets cells attacked and destroyed
Type II – adult onset, non insulin dependent – reduced response by target cells
Adrenal glands
-cortex and medulla
-from medulla, epinephrine and norepinephrine – both catecholamines
-function to regulate heart rate, etc., in extreme stress – cold, fear, pleasure
-glucose metabolism, heartrate, urination, respiration rate
-a lot of asthma inhalants are epinephrine based – why you shake and heartrate is faster when you inhale
-these are very connected to nervous system stimulation
-from cortex
-responds to endocrine signals more
-mobilize glucose too, breakdown muscle proteins which are converted to glucose
-prednisone – suppress inflammatory response
-used in asthma, arthritis, but…..lowers immunity and because of its action, deteriorates joints (precisely what you don’t want it to do, especially in arthritis)
-other hormones regulate level of salt and water in blood
-both gluco and mineral steroids – regulate body in long term stress situations – today, can be interpreted as high power jobs and lifestyle – some say it’s this continuous release of these hormones that gradually “break down” body – expresses in terms of heart disease, etc
Ovaries and Testes
-Corticosteroids – sex hormones – testosterone and estrogen and progesterone
-Androgens (one is testosterone) affect development of male reproductive system
-Estrogens – same with female reproductive systems
-Progestins – maintain uterus for pregnancy
Pineal gland
-in the brain, secretes melatonin, sleep, biological clocks, also stimulates chickens to lay eggs with light – henhouses – keep lights on all the time to induce continuous egg production – kind of wears the chicken out, so then we eat them
Thymus – atrophies during puberty
-makes T cells, HIV cocktails induce thymus to greater production
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