Endocrine System Hormones  2007-2008

Regulation Why are hormones needed? chemical messages from one body part to another communication needed to coordinate whole body daily homeostasis & regulation of large scale changes solute levels in blood glucose, Ca++, salts, etc. metabolism growth development maturation reproduction growth hormones

Regulation & Communication Animals rely on 2 systems for regulation endocrine system system of ductless glands secrete chemical signals directly into blood chemical travels to target tissue target cells have receptor proteins slow, long-lasting response nervous system system of neurons transmits “electrical” signal & release neurotransmitters to target tissue fast, short-lasting response Hormones coordinate slower but longer–acting responses to stimuli such as stress, dehydration, and low blood glucose levels. Hormones also regulate long–term developmental processes by informing different parts of the body how fast to grow or when to develop the characteristics that distinguish male from female or juvenile from adult. Hormone–secreting organs, called endocrine glands, are referred to as ductless glands because they secrete their chemical messengers directly into extracellular fluid. From there, the chemicals diffuse into the circulation.

Regulation by chemical messengers Neurotransmitters released by neurons Hormones released by endocrine glands endocrine gland neurotransmitter axon hormone carried by blood receptor proteins receptor proteins Lock & Key system target cell

Classes of Hormones Protein-based hormones Lipid-based hormones polypeptides small proteins: insulin, ADH glycoproteins large proteins + carbohydrate: FSH, LH amines modified amino acids: epinephrine, melatonin Lipid-based hormones steroids modified cholesterol: sex hormones, aldosterone insulin

How do hormones act on target cells Lipid-based hormones hydrophobic & lipid-soluble diffuse across cell membrane & enter cells bind to receptor proteins in cytoplasm & nucleus bind to DNA as transcription factors turn on genes Protein-based hormones hydrophilic & not lipid soluble can’t diffuse across cell membrane bind to receptor proteins in cell membrane trigger secondary messenger pathway activate internal cellular response enzyme action, uptake or secretion of molecules…

Action of lipid (steroid) hormones target cell blood S 1 S cross cell membrane protein carrier S 2 cytoplasm binds to receptor protein becomes transcription factor 5 mRNA read by ribosome 3 S plasma membrane 4 DNA mRNA 6 7 nucleus protein protein secreted ex: secreted protein = growth factor (hair, bone, muscle, gametes)

Action of protein hormones signal-transduction pathway Action of protein hormones 1 signal protein hormone P plasma membrane binds to receptor protein activates G-protein activates enzyme cAMP receptor protein acts as 2° messenger ATP transduction GTP transduction: the action or process of converting something and especially energy or a message into another form activates cytoplasmic signal ATP activates enzyme 2 secondary messenger system cytoplasm activates enzyme 3 response target cell produces an action

Benefits of a 2° messenger system 1 signal Activated adenylyl cyclase receptor protein 2 Not yet activated amplification 4 amplification 3 cAMP amplification 5 GTP G protein protein kinase 6 amplification Amplification! enzyme Cascade multiplier! 7 amplification FAST response! product

Maintaining homeostasis hormone 1 gland lowers body condition high specific body condition low raises body condition gland Negative Feedback Model hormone 2

Controlling Body Temperature Nervous System Control Feedback Controlling Body Temperature nerve signals hypothalamus sweat dilates surface blood vessels high body temperature (37°C) low hypothalamus constricts surface blood vessels shiver nerve signals

Regulation of Blood Sugar Endocrine System Control Feedback Regulation of Blood Sugar islets of Langerhans beta islet cells insulin body cells take up sugar from blood liver stores glycogen reduces appetite pancreas liver high blood sugar level (90mg/100ml) low liver releases glucose triggers hunger pancreas liver islets of Langerhans alpha islet cells glucagon

osmoreceptors in hypothalamus Endocrine System Control Feedback Blood Osmolarity increase thirst osmoreceptors in hypothalamus ADH increased water reabsorption nephron pituitary high nephron blood osmolarity blood pressure JuxtaGlomerular Apparatus low nephron (JGA) increased water & salt reabsorption adrenal gland renin aldosterone angiotensinogen angiotensin

Nervous & Endocrine systems linked Hypothalamus = “master nerve control center” nervous system receives information from nerves around body about internal conditions releasing hormones: regulates release of hormones from pituitary Pituitary gland = “master gland” endocrine system secretes broad range of “tropic” hormones regulating other glands in body hypothalamus posterior pituitary anterior

QUIZ – 1st Period Describe the movement of hormones throughout the body. Why do hormones initiate a response in only some cells as opposed to all body cells? Briefly describe what occurs during synaptic signaling. How can one hormone elicit several different responses in the body? What is negative feedback?

QUIZ – 7th Period What are target cells? Describe what occurs during endocrine signaling. How can one hormone elicit several different responses in the body? What is negative feedback? How is homeostasis maintained by insulin and glucagon?