ch. 16 - endocrine

• Endocrine system


  One of the body's two major control systems
• Endocrine system acts with nervous system


  To coordinate and integrate activity of body cells
• Endocrine system


  • Influences metabolic activities via hormones transported in blood
  • Responses slower but longer lasting than nervous system responses
• Functions controlled and integrated by endocrine system

  • Reproduction
  • Growth and development
  • Maintenance of electrolyte, water, and nutrient balance of blood
  • Regulation of cellular metabolism and energy balance
  • Mobilization of body defenses
• Exocrine glands


  • Produce nonhormonal substances (examples: sweat, saliva)
  • Have ducts to carry secretion to membrane surface
• Endocrine glands


  • Produce hormones
  • Lack ducts

  
• Examples of endocrine glands

  • Pituitary
  • Thyroid
  • Parathyroid
  • Adrenal
  • Pineal

  
• Hypothalamus


  Neuroendocrine organ
• Organs/tissues that produce hormones

  • Pancreas
  • Gonads
  • Placenta
  • Stomach
  • Cells in walls of small intestine
  • Thymus
  • Heart
  • Kidneys
  • Adipose cells

  
• Hormones


  Long-distance chemical signals; travel in blood or lymph
• Autocrines


  Chemicals that exert effects on same cells that secrete them
• Paracrines


  Locally acting chemicals that affect cells other than those that secrete them
• Two main classes of hormones

  • Amino acid-based hormones (amino acid derivatives, peptides, and proteins)
  • Steroids (synthesized from cholesterol, gonadal and adrenocortical hormones)
• Water-soluble hormones


  • Act on plasma membrane receptors
  • Act via G protein second messengers
  • Cannot enter cell
• Lipid-soluble hormones


  • Act on intracellular receptors that directly activate genes
  • Can enter cell
• Cyclic AMP (cAMP) signaling mechanism

  1. Hormone (first messenger) binds to receptor

  2. Receptor activates a G protein

  3. G protein activates or inhibits effector enzyme adenylate cyclase

  4. Adenylate cyclase converts ATP to cAMP (second messenger)

  5. cAMP activates protein kinases that phosphorylate other proteins
• PIP2-calcium signaling mechanism


  1. Hormone-activated G protein activates phospholipase C

  2. Activated phospholipase C splits membrane protein, PIP2, into two second messengers: Diacylglycerol (DAG) activates protein kinases, Inositol trisphosphate (IP3) causes Ca2+ release from intracellular storage sites

  3. Calcium ions act as another second messenger
• Insulin receptor


  • A tyrosine kinase enzyme
  • Autophosphorylates upon insulin binding
  • Activated tyrosine kinases provide docking sites for relay proteins that trigger cell responses
• Intracellular Receptors and Direct Gene Activation

  1. Lipid-soluble steroid hormones and thyroid hormone diffuse into target cells and bind with intracellular receptors

  2. Receptor-hormone complex enters nucleus

  3. Binds to specific region of DNA

  4. Helps initiate DNA transcription to produce mRNA

  5. mRNA is then translated into specific protein

  
• Blood levels of hormones

  • Controlled by negative feedback systems
  • Levels vary only within narrow, desirable range
• Stimuli that cause hormone release

  • Endocrine gland stimuli
  • Nervous system modulation
  • Hormonal stimuli

  
• Humoral stimuli


  Changing blood levels of ions and nutrients directly stimulate secretion of hormones
• Neural stimuli


  Nerve fibers stimulate hormone release

  
• Hormonal stimuli

  Hormones stimulate other endocrine organs to release their hormones

  
• Nervous System can make adjustments to hormone levels when needed

  
• Nervous system can override normal endocrine controls
• Target cells


  Tissues with receptors for a specific hormone
• Up-regulation


  Target cells form more receptors in response to low hormone levels
• Down-regulation


  Target cells lose receptors in response to high hormone levels
• Half-life


  Time required for level of hormone in blood level to decrease by half
• Permissiveness

  One hormone cannot exert its effects without another hormone being present
• Synergism


  More than one hormone produces same effects on target cell, causing amplification
• Antagonism


  One or more hormones oppose(s) action of another hormone
• Posterior pituitary


  Composed of neural tissue that secretes neurohormones

  
• Anterior pituitary

  Consists of glandular tissue
• Oxytocin


  • Strong stimulant of uterine contractions released during childbirth
  • Acts as hormonal trigger for milk ejection
  • Acts as neurotransmitter in brain

  
• Antidiuretic hormone (ADH)


  • Targets kidney tubules to reabsorb more water to inhibit or prevent urine formation
  • Release also triggered by pain, low blood pressure, and drugs
  • Inhibited by alcohol, diuretics
  • High concentrations cause vasoconstriction
• Anterior pituitary hormones


  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
  • Thyroid-stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Growth hormone (GH)
  • Prolactin

  
• Oxytocin


  Strong stimulant of uterine contractions released during childbirth
• Oxytocin


  Acts as hormonal trigger for milk ejection