Endocrine System Hormones Homeostasis Regents Biology 2009 2010
Endocrine System Hormones & Homeostasis Regents Biology 2009 -2010
Homeostasis u maintaining internal balance in the body organism must keep internal conditions stable even if environment changes also called “dynamic equilibrium” u example: body temperature humans: w too cold = shiver w too warm = sweat Regents Biology lizard: w too cold = bask in sun w too warm = hide in shade
Regulation How we maintain homeostasis u nervous system u nerve signals control body functions endocrine system hormones chemical signals control body functions Regents Biology
Nervous System Control Feedback Controlling Body Temperature nerve signals brain sweat high body temperature low brain constricts surface shiver blood vessels Regents Biology nerve signals dilates surface blood vessels
Hormones Why are hormones needed? chemical messages from one body part to cells in other parts of body u communication needed to coordinate whole body u maintaining homeostasis u Regents Biology growth hormones
Endocrine System Endocrine system releases hormones u glands which secrete (release) chemical signals into blood Regents Biology chemicals cause changes in other parts of body w growth hormones w sex hormones w response hormones w metabolism hormones w and more….
Responding to hormones Lock and key system u hormone fits receptor on “target” cell target cell secreting cell Regents Biology can’t read signal nontarget cells can’t read signal
Glands Pineal u Pituitary u insulin, glucagon Ovary u adrenaline Pancreas u thyroxine Adrenal u many hormones: master gland Thyroid u melatonin estrogen Testes u testosterone Regents Biology
Positive vs. Negative Feedback Positive- Causes the variable to accelerate the change in the same direction of the initial disturbance. or Negative- Causes the variable to change in a direction opposite to that of the initial change. or Regents Biology
Feedback Maintaining homeostasis hormone 1 lowers body condition gland high specific body condition low raises body condition Regents Biology gland hormone 2
Negative Feedback Response to changed body condition u if body is high or low from normal level u signal tells body to make changes that will bring body back to normal level once body is back to normal level, signal is turned off gland hormone 1 lowers body condition high Regents Biology specific body condition
Endocrine System Control Regulation of Blood Sugar Feedback insulin liver stores sugar body cells take up sugar from blood pancreas high liver blood sugar level (90 mg/100 ml) low triggers hunger Regents Biology liver releases sugar liver pancreas glucagon reduces appetite
Positive or Negative Feedback? Oxytocin Production during birth Baby pushes on the cervix Nervous system sends a signal to the hypothalamus Hypothalamus manufactures oxytocin Oxytocin is transported to the posterior pituitary gland released Oxytocin stimulates uterine contraction Loop stops when the baby leaves the birth Regents Biology canal
Positive or Negative Feedback? Thyroid Gland TRH production 1. 2. 3. 4. 5. Hypothalamus senses that the thyroxine level in the blood is low Hypothalamus secretes thyrotropinreleasing hormone (TRH) TRH stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH) TSH stimulates the release of thyroxine by the thryoid gland High levels of thyroxine in the blood inhibit the secretion of TRH and TSH (stops the release of additional thyroxine) *This loop keeps the level of thyroxine in the blood relatively constant. Regents Biology
Feedback Suppose the secretion of a certain hormone causes an increase in the concentration of substance X in the blood. A low concentration of X causes the hormone to be released. What is the effect on the rate of hormone secretion if an abnormal condition causes the level of X in the blood to remain very low? Regents Biology
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