Endocrine

• Endocrine system

  A system that continuously interacts with our nervous system in order to control activity within the cell in the body

  
• Endocrine system

  • Composed of glands that secrete particular compounds called hormones
  • Hormones act as messengers that travel throughout the blood stream and deliver messages to the cells over the body
• • Nerve impulses are produced by the nervous system
  • Regulation of hormones is particular to the endocrine system

  
• Classes of chemical messengers

  • Lipid-soluble hormones
  • Water-soluble hormones

  
• Lipid-soluble hormones

  Non-polar, attached to binding proteins, degraded slowly, not rapidly eliminated, can only dissolve in lipid environment

  
• Water-soluble hormones

  Polar, most can be dissolved in blood, have short half-lives, can dissolve in polar solvent or environment
• Functions of endocrine system

  • Metabolism
  • Control of food intake and digestion
  • Tissue development
  • Ion regulation
  • Water balance
  • Heart rate and blood pressure regulation
  • Control of blood glucose and other nutrients
  • Control of reproductive functions
  • Uterine contraction and milk release
  • Immune system regulation
• Characteristics of endocrine system

  • Comprises of ductless glands and special cells
  • Secretion of hormones directly into the bloodstream
  • Specific receptors for specific hormones
  • Secretes hormones within the blood stream

  
• Hormone

  • Derived from Greek word "hormao" meaning "to set in motion"
  • Used to regulate almost every physiological process in the body

  
• Types of hormones

  • Lipid-soluble hormones (e.g. steroid hormones, thyroid hormones)
  • Water-soluble hormones (e.g. amines, peptides, eicosanoids)

  
• Processes that control hormone secretion

  • Hormonal stimulus
  • Humoral stimulus
  • Neural stimulus

  
• Hormonal stimulus

  Hypothalamus secretes hormones that act on pituitary gland to secrete hormones in particular endocrine glands

  
• Humoral stimulus

  Changes in concentration of certain blood components like ions and nutrients stimulate secretion of hormones
• Neural stimulus

  Nerve fibers, such as sympathetic preganglionic fibers, stimulate endocrine glands to secrete hormones

  
• Inhibition of hormone release

  • Humoral stimuli
  • Neural stimuli
  • Hormonal stimuli

  
• Negative feedback

  Process that maintains hormonal levels within a relatively narrow range

  
• Positive feedback

  Often thought to have a destabilizing effect, as the target endocrine system acts on itself to stimulate or inhibit further hormone secretion

  
• Negative feedback is important for maintaining homeostasis in the body
• Positive feedback is very rare to happen
• Positive feedback


  Often thought to have a destabilizing effect, but the target endocrine system can both inhibit or stimulate actions of the anterior pituitary

  
• Negative feedback


  One way for the endocrine system to keep homeostasis, it senses when a hormone needs to decrease production to maintain homeostasis
• Positive feedback is considered to be an additive effect, releasing a hormone that initiates actions that could lead to an additional release of that hormone
• Protein hormones


  Don't need to bind to plasma protein because they cannot enter a cell
• Lipid-soluble hormones


  Diffuse through the cell membrane and bind to cytoplasmic or nuclear receptors

  
• Water-soluble hormones


  Bind to membrane-bound receptors

  
• Action of nuclear receptors

  Lipid-soluble hormone diffuses into cell, binds to nuclear receptor, hormone-receptor complex binds to DNA to stimulate protein synthesis

  
• Action of membrane-bound receptors


  Water-soluble hormone binds to receptor, activates G protein, leads to production of second messengers that cause cellular response

  
• Signal amplification


  One hormone action can activate multiple pathways, making the effect more effective

  
• Pituitary gland (hypophysis)


  Small sac-like structure inferior to the hypothalamus, comprises anterior and posterior lobes, secretes many hormones

  
• Hypothalamus


  Regulates the pituitary gland and the endocrine system

  
• Anterior pituitary


  Derives from embryonic oral cavity, manufactures and secretes hormones that regulate other endocrine glands

  
• Posterior pituitary


  Extends from the brain, secretes hormones produced in the hypothalamus

  
• Growth hormone (somatotropin)


  Promotes tissue growth, has many metabolic actions, secretion follows a diurnal rhythm

  
• Thyroid gland


  Butterfly-shaped structure on the anterior trachea, produces thyroid hormones
• Thyroxine (T4) and triiodothyronine (T3)


  Thyroid hormones, T4 is synthesized by the thyroid gland and converted to the more potent T3 in target tissues