Bio 133 Exam 1

• Homeostasis


  Organisms use homeostasis to maintain a "steady state" or internal balance regardless of external environment
• Thermostat


  Regulation of room temperature by a thermostat is analogous to homeostasis
• Thermoregulation in mammals


  1. Sensor/control center: Thermostat in hypothalamus

  2. Stimulus: Increased/decreased body temperature

  3. Response: Blood vessels dilate/constrict, Sweat, Shivering
• Endocrine system


  Organs and tissues that produce hormones
• Hormones


  Regulatory chemicals secreted into extracellular fluid and carried by the blood, Can act at a distance from source, Only targets with correct receptor can respond

  
• Classes of hormones


  • Peptides and proteins
  • Amino acid derivatives (Catecholamines, Thyroid hormones, Melatonin)
  • Steroids (Sex steroids, Corticosteroids)
• Lipophilic hormones


  Steroid hormones and thyroid hormones, Travel on transport proteins in blood, Bind to intracellular receptors, Tend to act over brief time period

  
• Hydrophilic hormones


  All other hormones (example: protein hormones), Freely soluble in blood, Bind to extracellular receptors, Tend to have much longer active period
• Major endocrine glands and their hormones

  • Pancreas: Insulin, Glucagon
  • Testes: Androgens
  • Parathyroid glands: Parathyroid hormone (PTH)
  • Ovaries: Estrogens, Progestins
  • Thyroid gland: Thyroid hormone (T3 and T4), Calcitonin
  • Pineal gland: Melatonin
  • Hypothalamus and Pituitary gland: Oxytocin, Vasopressin (antidiuretic hormone, ADH)
  • Adrenal glands: Epinephrine, Norepinephrine, Glucocorticoids, Mineralocorticoids

  
• Anterior pituitary


  Epithelial tissue in origin (true endocrine)
• Posterior pituitary


  Nervous tissue in origin
• Anterior pituitary regulation


  1. Hypothalamus secretes releasing hormones and inhibiting hormones, which diffuse into blood capillaries at the hypothalamus' base

  2. Each hormone delivered by the hypothalamohypophyseal portal system regulates a specific anterior pituitary hormone

  
• Tropic hormones


  Hormones from the anterior pituitary that stimulate other endocrine glands

  
• Negative feedback or feedback inhibition

  Acts to maintain proper levels of the target cell hormone
• Posterior pituitary


  1. Contains axons that originate in cell bodies within the hypothalamus and that extend along the stalk of the pituitary as a tract of fibers

  2. Stores and releases two hormones: Antidiuretic hormone (ADH), Oxytocin

  
• Coordination of pH control in the duodenum

  1. Low pH in duodenum stimulates S cells of duodenum to secrete the hormone secretin

  2. Secretin causes target cells in the pancreas to raise the pH in the duodenum

  
• The pancreas can act as an exocrine gland, secreting substances through a duct, or as an endocrine gland, secreting hormones directly into interstitial fluid