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Chemical Signals in Animals � Chapter 45 � The Endocrine System

Hormone � is a chemical signal that is secreted into body fluids (blood) and communicates regulatory messages within the body

Target cells � respond to hormones

Two systems of internal communication and regulation nervous system and endocrine system




Nervous high speed signals along neurons … movement in response to env changes

Endocrine all of an animal’s hormone secreting cells … endocrine glands hormone secreting organs (ductless glands � directly into body fluids)

Endo and nerv are structurally, chemically, and functionally related

-endo organs contain nerve cells called NEUROSECRETORY CELLS … secrete hormones … many chemicals = signals in nervous system, hormones in endocrine sys …

-each system affects the output of the other .. release of milk suckling = sensory cells - nervous signals - hypothalamus - oxytocin from pituitary - secrete milk

Invertebrates hormones = reproduction and development … nerve and hormne interaction …

-Arthropods crustaceans growth and repro, water balance, movement of pigments, reg of meta … aquire adult characteristics in single, terminal molt .. molting is triggered by ECDYSONE … also favors development of adult characteristics (cater - butter) … ecdysone production is controlled by nd hormone brain hormone (bh) … stimulates prothoracic glands to secrete ecdysone

-balanced by juvenile hormone (JH) . secreted by corpora allata … propotes retention of larval characteristics … high JH = molting but just larger larva … low JH = pupa - metamorphosis …

local regulators � act between cells on a localized scale … upon release taken up by target cells, broken up by enzymes, or hend by extracellular matrix � thus, can only affect local targets .. Pheromones � carry messages between different individuals of a species … ie mate attraction …

local regulators neurotransmitters one neuron to another, or one neuron to muscle, gland …

Nitric oxide (NO) � multiple functions … highly reactive/toxic … affects targets in few seconds and breaks down … secreted by neurons …. Funct as a neurotransmitter .. secreted by white blood cells � kills cancer cells and bacteria in bf … sec by endothelial cells in blood vessels � makes smooth muscle relax, dilating vessel walls

-Growth Factors � peptides and proteins that fuction as local reg … each can affect several types of cells and have variety of functions … Nerve growth factor NGF � speeds rate of developing white blood cells

-epidermal GF � accelerates epid development … Insulinlike GF � skeletal development (produced by liver) … transforming GF � enhance the strength of synapses between neurons in brain of mature animal

-Prostaglandins PGs - modified fatty acids derived from lipids of pm … in semen promote contractions of uterus …

-released by cells into interstital fluid � func as local regulators … sec by placenta = changes in chem. Of uterus = induce labor (positive feedback) …

-defense mech induce fever and inflammation … intensify pain … ^Aspirin inhibits enzymes to synthesize prostagladins

-PGE and PGF � similar structures but different effects on smooth muscle cells of blood vessels serving lungs … PGE = relax (dilate blood vells, promote oxygenation) … PGF = contract (reduce blood flow) … thus antagonistic …

chem. Signal can affect different tcells diff or diff species diff … ie thyroxine vertebrates metabolic reg … and development … ie frog from tadpole …

-modes of action of all chem. Sig are similar … each sig has specific shape to be recog by tcells … binds to receptor receptor in pm or inside tcell … signal molecules are ligands small molecule that bind specifically to larger ones (proteins) … triggers chem. Events .. result in change in behavior of cell … diversity of responses depends on nature of tcells and # and affinity of receptor proteins on/in cells …

bind to pm � signal trasnduction pathways … melanocyte-stimulating hormone MSH (peptide hormone secrted by pituitary) … melaoncytes specialized skin cells containing dark brown pigment melanin in cyto organelle called melanosomes … skin appears light when melano are clustered tightly around nucleus … darker when spread … MSH secreted = disperse … direct injection into cells does nothing

-most chem. Signals ( neurot, gf, hormones) unable to pass through pm … instead are components of signal transduction pathways …. Convert extracellular chem. Sig into specific response … changing behavior of cell …. Stp trigger enzyme cascades that amplify the hormonal signal

most steroid receptors and receptors of thyroid hormones and some local receptors (NO) are specialized proteins within target cells … enter target cells … bind with receptors … activate receptor … response

-hormone-receptor complex binds to specific sites on DNA .. transported into nucleus, attaches to reg sites along genome … transcrp of gene into mra … trans into protein … hr complex binding to these sites can induce or suppress expression of spe genes … ECDYSONE � steroid … triggers synthesis of enzymes that catalyze new exoskel … estrogen induces female bird repro cells to syn ovalbumin (storage protein in egg white)

Vertebrate Endocrine system

Tropic hormones target other endocrine glands … chem. Coordination …

Figure 45.6

-many organs with nonendo functions also secrete hormones … digestive gastrin/secretin … liver gf … thymus gland immune sys … replaced by adiposefibrous tissue by adulthood … secretes thymosin (T-lympho development) …. Pineal gland � mid brain … hypthalmus �b base … pituatiry- under hypo … thyroid … butterfly in neck … thymus … upside down tooth in chest … adrenal above kidneys … pancreas snail crossing middle til left kidney .. ovary ball … testis … lower ball ..

Table 45.1

Hypothalamus makes hormones released by posterior pit and hormones that reg anterior pit

Pituary gland Posterior

a. oxytocin … ya right!

HYPOTHALAMUS lower brain .. receives info from nerves … initates endocrine signals .. in response to env changes …

-hormone releasing cells in hypo neurosecretory cells whose secretions are stored in or regulate activity of pituitary gland (small organ w/ endo fuctions) ..

-pit located at base of hypo … two parts from diff parts of embryo and diff functions .. anterior pituatiary ( adenohypophysis) � develops from fold on roof of mouth … consists of cells that secrte/synth hormones into blood … hyp controls AP by two hormones … releasing hormones � tell it to secrete … inhibiting hormones � stop secretion

--these two hormones are released into capillaries - portal vessels - second cap bed in AP .. each AP hormone controlled by at least one rel hormone

---posterior pit (neurohypophysis) extension of the brain… remains attached to hypo … stores and secretes two hormones made by hypo

Posterior P Hormones

Oxytocin and antidiuretic hormone ADH

-made my hypothalamus … oxy acts on uterus and ADH on kidneys … do not effect other endo glands … oxy induces contraction/mammary glands eject milk … ADH increases water retention and dec water volume

--ADH regulates osmolarity of blood … blood osmo is regulated by nerve cells in hypo … osmo increases cells shrink (due to osmosis) and transmit nerve impulses to neurosec cells in hypo … release ADH …. Post p stores ADH and releases it into circulation … ADH reaches kidneys … binds to receptors on surface of cells lining collecting ducts … stp .. increases water permeability … also brains stimulates thirst drive … hormonal reaction augmented by behavioral reponse … more dilute blood = reduction in release of adh … stop thirst … negative feedback

Anterior P Hormones

Thyroid SF � release of thyroid hormones … adrenocorticotropic hormone ACTH � controls adrenal cortex … Follice SH Luteinizing H � reproduction (act on gonads) … [all are tropic] …. Other hormones GH, prolactin PRL, melanocyte SH … endorphins

--GH � protein … direct/tropic effects … stimulates production of growth factors or affects growth directly … ie bone and cartilage signals liver to produce IGF = growth … absence of GH � skeletal growth stops …

--disorders abnormal GH production … too much during development = giantism … during adulthood abnormal bone growth in hands, feet, head (acromegaly) … too little childhood pituitary drawfism … treatable with cadaver GH … or bacteria produced GH

-Prolactin (PRL) � similar to GH VERY MUCH SO … diff role … diversity of effets on diff veretebrates … mammals mammary gland growth, milk synthesis … birds fat metab/reproduction … amphibians delays metam … fresh fish reg salt/water balance … ancient hormone

--FSH, LH, TSH � related chemically … all glycoprotins … (proteins w/ carbohydrate attached) … FSH/LH � gonadotropins … TSH � production of hormones by thyroid gland

-remaining hormones come form PRO-OPIOMLANOCORTIN � cleaved into fragments … ACTH � production/secrtion of steroid hormones by adrenal corte … MSH � pigment in skin … mammals fat metabolism … endorphins … = also produced by neurons in brain … inhibit pain…

Pineal Gland � biorhythms

-small mass of tissue near center of brain … secretes melatonin (aa) … contains light sensitive cells or has nervous connections from the eyes… regulates func related to light/seasons (by changes in day length) … skin pigmenation … bio rhythems (reproduction) … melatonin secreted at night (winter = more) … target suprachiamastic nucleus (SCN) .

Thyroid hormones � development, bioenergetics, homeostatis

-two lobes on ventral side of trachea … produces two similar hormones from aa tyrosine … triodothyronine T ( iodine atoms, tetraio) … or thyroxine t4 (4 iod) … T more active form … both have same affects … controlled by hypo/pit … neg feedback

--development/maturation metamorphosis in frog … thyroid deficiency (inherited) � cretinism � retarded skeletal growth and poor mental development … thy hormones required for development of bone forming cells/nerve cells during embroynoi develop

-homeostatis normal blood pressure, heart rate, muscle tone, digestion, reprod … bioengetics increase rate of oxy consumption/cellular metabolism … too much hyperthyroism high body temp, sweating, weight loss, irritiabilty, high blood p … hypothy … cretinism (infants) … weight gain, lethargy, intol to cold in adults … shortage of thy hormones enlargement of thyroid (goiter) [defi of iodine]

-calcitonin … lowers calcium levels …

Parathyroid glands 4 embedded in thyroid surface … homeo of calcium ions .. screte parathyroid hormone PTH … raises blood levels of Ca … stimulates Ca+ reapsorbtion in kidneys and induces osteoclasts to decompose matrix of bone and releae ca to blood … calcitonin … opp affects on kid/bone … Vitamen D ( syn in skin ) …. Essential for PTH function … lack of PTH low calcium … convulsive contractions … tetany … fatal … antagonistic hormones … [V D enables pth to increase ca uptake in intestines]

Pancreas insulin/glucagons … antagonisci … reg blood gluc

-endo/exo fuctions … bicarbonate/digestive enzymes carried to small intest via pancreatic duct (exocrine stuff) … scattered among exo tissue islets of Lanerhans (secrete two hormones into circ sys) … alpha cells (peptide hormone glucagons) … beta cells (insulin) .. glucose fuel for cellular respiration/carbon skeletons … set point 0mg/100ml … exceeds level insulin released to lower … drops glucagons increases … neg feedback

-insulin lowers by stimulating body cells (except brain) to take up glucose from blood … slowing glycogen breakdown in liver and inhibiting conversion of aa and fa to sugar

-liver, skeletal musc, adipose tissue � store fuel mole … liver/mus store sugar as glycogen … adipose fat … only liver cells are sensitive to glucagons … glucagons has affect before glucose levels drop below set point … signals liver cells to increase glycogen hydrolysis, convert aa and fa to glucose, and slowly release gluco back into circ …

-manages fuel storage and fuel use … livers ability rests on its metabolic versatitly of its cells and access to absorbed nutrients via hepatic portal vessel (blood coming directly from small intestine) …

-mech of glu homeo go crazy diabetes mellitus … deficiency of insulin or loss of response to inslulin in target tissues … = high blood glucose … kidneys begin to excrete glucose (=sugar in urine… and more water excreted with it = lots of peeing and lots of thirst ) … glucose unavaible to body cells as major fuel source … fat serves as substrate for cell resp … acidic metabolides formed during fat breakdown accumulate in blood � lower blood pH, uh oh…

-two forms Type I � insulin dependent … autoimmune disorder (immune sys mounts attack on cells of pancreas) … during childhood … destroys ability to produce insulin .. insulin injections … bacteria … Type II � non insulin dependent … defi of insulin or reduced responsiveness in target cells (due to change in insulin receptors) … occurs after age 40 … more common … manageable by exercise and dietary control … type II � heredity

Adrenal medulla/cortex � stress

-adjacent to kidneys … each is actually two glands w/ diff cell types, functions, origins … adrenal cortex (outer) … adrenal medulla (central) … secretory cells of medulla are derived from cells of neural crest … neural crest cells in abdominal region of vertebrate embryo may diff into either endo cells of med or neurons … dpending on chem. Signals and immediate surroundings … glucocorticoids vs NGF

-fight or flight response of ad medulla hormones epinephrine (adrenaline) and norepineprine (noradrenaline) … members of class of compounds that are syn from aa tyrosne (catecholamines) … secreted in resp to pos or neg stress … gives body rapid bioeng boost (increasing basal meta rate … ) … increase rate of glyco breakdown in liver and skeletal muscles … and glucose

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