Chemical Signals in Animals

• 2 communication systems in body.

• 1Nervous system, 2endocrine system.

• Endocrine system - glands and tissues that secrete hormones, chemical messengers produced by cells to act on other cells.

http://scienceblogs.com/clock/upload/2006/06/endocrine%20system.jpg

• Some hormones act on nearby cells (paracrine signals) others on same cells that made them (autocrine signal).

• Signals in endocrine system take longer to reach destination (carried by blood), longer lasting than nervous impulses.

http://home.earthlink.net/~dayvdanls/paracrine.gif

• Endocrine glands secrete hormones directly into bloodstream.

• Exocrine secretions do not contain hormones; released through ducts into body compartment.

• Example - pancreas in digestion.

http://www.daviddarling.info/images/exocrine_gland_types.gif

• Hormones classified into 2 groups: steroid hormones, peptide hormones.

• Both must bind to protein receptor on target cell, peptide hormones must bind to receptors on cell surface since they cannot cross membrane.

• Causes signal to be transmitted to inside of cell.

http://web.indstate.edu/thcme/mwking/epinephrinephosphorylase.gif

• Signal can activate 2nd messengers, which amplify signal and alter cell activities - called signal transduction cascade because process amplified as it continues down path.

• Steroid hormones usually smaller and can pass through membrane.

• Most come from cholesterol and usually enter nucleus of cell, altering protein synthesis (transcription).

• Steroid hormones not stored, unlike protein hormones - need to be regulated in order to be secreted.

http://fig.cox.miami.edu/~cmallery/150/memb/c11x10hormone-receptors2.jpg

Endocrine glands

• Regulation of production and secretion of hormones done through feedback loop.

• Some hormones regulate release of other hormones.

• 1Hypothalamus and pituitary – found in forebrain, located above pituitary gland.

• Pituitary has 2 parts: anterior pituitary, posterior pituitary.

• Posterior - vasopressin (antidiuretic hormone or ADH) - acts on kidney to conserve water; oxytocin - aids in childbirth.

http://www.becomehealthynow.com/images/organs/nervous/glakgar_pit_hypothalamus.jpg

• Hormones made in hypothalamus, pass through posterior pituitary - secreted.

• Anterior pituitary regulated by hypothalamus through portal blood circulation - carries blood directly from hypothalamus to pituitary.

http://www.brainexplorer.org/brain-images/hypothalamus.jpg

• Hypothalamus stimulated - releasing factors into portal blood circulation carried to pituitary - cause release of hormone from anterior pituitary.

• Growth hormone promotes growth in body tissues.

http://www.3dscience.com/img/Products/Images/clip_art/endocrine_hypothalamus_pituitary_web.jpg

• Thyroid stimulating hormone (TSH) stimulates thyroid to secrete thyroxin.

• Adrenocorticotrophic hormone (ACTH) stimulates adrenal cortex to secrete corticosteroids in response to stress.

http://media.allrefer.com/s1/l/t0200300-thyroid-gland.jpg

• Prolactin - responsible for milk production.

• Follicle-stimulating hormone (FSH) promotes maturation of seminiferous tubules in males, ovaries in females.

• Luteinizing hormone (LH) - promotes testes to secrete testosterone in males; causes ovulation of egg in females.

http://www.discount-herbal-nutritional-supplements.com/weight_loss_supplements/images/brain2.gif

• Endorphins act on central nervous system to block pain signaling (like opiates).

• 2Thyroid gland – thyroxine accelerates metabolism.

• Person deficient can develop goiter, lethargy, obesity.

• Hyperthyroidism causes profuse sweating, weight loss, increased BMR.

http://www.hoslink.com/encocrineimages/hyperthyroid1.jpg

• Thyroxine secretion stimulated by hypothalamus in response to environment (like cold), acts on thyroid gland.

• Thyroid gland also produces calcitonin - regulates calcium concentration in blood.

http://www.cvm.okstate.edu/instruction/mm_curr/histology/HistologyReference/hrendo7.jpg

• Calcitonin increases stimulates bone formation, decreases bone destruction.

• Calcitonin opposed by parathyroid hormone.

• 3Parathyroid glands – located on backside of thyroid gland, secretes parathyroid hormone - regulates calcium, phosphate balance between blood, other tissue.

http://cyber.law.harvard.edu/blogs/static/heydan/parathyroid.jpg

• Increased parathyroid hormone increase bone resorption, elevates plasma calcium.

• Decreased calcium in blood causes secretion of parathyroid hormone which increases activity of osteoclasts (bone breaking cells) - remodels bones to release calcium.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• 4Pancreas – performs both exocrine, endocrine functions.

• Endocrine function occurs in islets of Langerhans which contain alpha and beta cells that secrete glucagon and insulin.

• Insulin stimulates muscles and other cells to release glucose from blood.

http://images.medicinenet.com/images/illustrations/pancreas.jpg

• Causes muscles and liver to convert glucose to glycogen (storage form of glucose).

• Glucagon responds to low levels of blood glucose - stimulates breakdown of glycogen to glucose.

• Diabetics cannot control levels of insulin.

• 5Adrenal glands – found on top of kidneys, consist of adrenal cortex on exterior + adrenal medulla on inside of gland.

• Medulla responsible for epinephrine and norepinephrine in response to stress.

http://training.seer.cancer.gov/module_anatomy/images/quiz_dd_adrenal_gland.jpg

• Epinephrine responsible for adrenaline release as well as causing blood to shunt away from skin, digestive organs, kidneys; increases blood flow to heart, brain, skeletal muscle.

• Also increases metabolic activity.

http://services.epnet.com/GetImage.aspx/getImage.aspx?ImageIID=4680

• Cortex responsible for secretion of corticosteroids - regulated by nervous system in response to stress, 3 types.

• AGlucocorticoids help to raise blood glucose levels.

• High doses help in inflammation response.

http://www.stanford.edu/group/hopes/treatmts/lifestyleandhd/f_an1hpaaxis.jpg

• BMineral corticoids - promote reabsorption of Na+, excretion of K by kidneys.

• CSex hormones – androgens responsible in part for female sex drive.

• 6Ovaries, Testes - testes produce testosterone in males, estrogen and progesterone in females.

• 7th week of development, information on Y chromosome (if present) starts to produce testosterone.

• Absent - female hormones are produced.

• ATestes – releases androgens (like testosterone) responsible for production of sperm and secondary male sex characteristics.

• BOvaries – secrete estrogen and progesterone.

http://www.redhotflush.co.uk/images/cartoons/hormones.jpg

• 1Estrogen responsible for stimulating lining of uterus to grow and secondary sex characteristics of females.

• 2Progesterone responsible for promoting lining of uterus to grow.

http://www.lef.org/magazine/mag2006/images/apr2006_report_prog_02_big.jpg

• 7Pineal gland - small mass of tissue near center mammalian brain.

• Secretes melatonin - aids in reproduction and cycle of light and dark.

http://www.rickrichards.com/chakras/pituitary_brain2a.jpg