Endocrine 1

• 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 cells over the body
• Nervous system and Endocrine system


  The two main regulatory systems that contribute to homeostasis
• Nervous system


  Coordinates rapid, precise responses such as muscle contractions using electrical impulses, with effects of short duration (milliseconds)
• Endocrine system


  Regulates metabolic activity within cells of organs and tissues, coordinates activities that require longer duration (hours or days), such as growth, plasma volume/blood pressure regulation, menstrual cycles
• Classes of chemical messengers


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

  
• Functions of endocrine system


  • Metabolism (e.g. insulin, glucagon, thyroid hormone)
  • Control of food intake and digestion (e.g. ghrelin, leptin, sciatic hormones)
  • Tissue development (e.g. growth hormone, thyroid hormones)
  • Ion regulation (e.g. aldosterone)
  • Water balance (e.g. aldosterone)
  • Heart rate and blood pressure regulation (e.g. epinephrine)
  • Control of blood glucose and other nutrients (e.g. insulin, glucagon)
  • Control of reproductive functions (e.g. sex hormones)
  • Uterine contraction and milk release (e.g. oxytocin, somatostatin)
  • Immune system regulation (e.g. insulin)
• Endocrine system


  • Composed of ductless glands and special cells throughout the body
  • Secretes hormones directly into the bloodstream
  • Hormones have specific receptors to act on target tissues/organs
  • Derived from the Greek words "within" and "to secrete"

  
• Hormones


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

  
• Types of hormones


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

  
• Lipid-soluble hormones


  • Non-polar
  • Attached to binding proteins
  • Degraded slowly and not rapidly eliminated
  • Can only dissolve in lipid environments or non-polar solvents
  • Have longer half-lives (days to weeks). includes our steroid hormone, our thyroid hormone.

  
• Water-soluble hormones

  • Polar
  • Most can dissolve in blood
  • Have short half-lives
  • Can dissolve in polar solvents/environments
  • Larger ones use fenestrated capillaries to move from blood to tissues
  • Smaller ones need binding proteins to enter cells, includes eicosanoids (classification)
• Processes controlling hormone secretion


  • Hormonal stimulus
  • Humoral stimulus
  • Neural stimulus

  
• Hormonal stimulus


  Hypothalamus secretes hormones that act on pituitary gland to stimulate secretion of hormones from endocrine glands (e.g. thyroid, adrenal, gonads)

  
• Humoral stimulus


  Changes in concentration of blood components (e.g. ions, nutrients) that stimulate endocrine gland secretion (e.g. parathyroid hormone)

  
• Neural stimulus


  Nerve fibres (e.g. sympathetic preganglionic fibres) that stimulate endocrine gland secretion (e.g. adrenal medulla)

  
• Mechanisms of hormone release inhibition


  • Humoral stimuli (e.g. aldosterone, ANP)
  • Neural stimuli (e.g. inhibitory targets)
  • Hormonal stimuli (e.g. thyroid hormones inhibiting anterior pituitary)

  
• Negative feedback


  The main process by which the endocrine system regulates hormone levels within a relatively narrow range to maintain homeostasis

  
• Positive feedback


  A less common process that can have a destabilizing effect, where a hormone initiates actions that lead to additional release of that hormone

  
• 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 will act on specific target and then if their work is done or the situation that is needed to fix could be controlled it can both inhibit or stimulate actions of the anterior pituitary

  
• In some diseases the negative feedback is imbalanced
• Positive feedback


  Considered to be an additive effect, as it releases a hormone that initiates actions that could lead to an additional release of that hormone
• Positive feedback is very rare to happen
• Negative feedback


  One way for the endocrine system to keep homeostasis, as it senses when an endocrine gland initiates the decrease production of a hormone to maintain homeostasis
• Protein hormones


  Don't need to bind to plasma proteins because they cannot enter a cell
• Liver-made proteins


  Used to bind to some hormones in the blood
• Up-regulation


  Adds up or increases the number of receptors for one hormone, to increase cell activity and the effect of the hormone
• Down-regulation


  Decreases the number of receptors for one hormone, decreasing the cell's sensitivity and the effect of the hormone
• Lipid-soluble hormones


  Diffuse through the cell membrane and bind to cytoplasmic or nuclear receptors, stimulating a response in the DNA

  
• Water-soluble hormones


  Bind to membrane-bound receptors, activating G proteins and the production of second messengers that elicit a cellular response

  
• Signal amplification


  The action of a hormone activates more G proteins, which further activate enzymes like adenylate cyclase, releasing more second messengers and making the hormone's action more effective
• Pituitary gland (hypophysis)


  • Located inferior to the thalamus, comprises an anterior lobe and a posterior lobe, secretes many hormones that regulate other endocrine glands

  
• Hypothalamic-hypophysial track


  Neural connection between the pituitary gland and the hypothalamus
• Growth hormone


  • Promotes tissue growth and metabolism, secretion follows a diurnal rhythm, can be stimulated by exercise, stress, trauma, and hypoglycemia, and inhibited by aging and hyperglycemia

  
• Thyroid gland


  • Butterfly-shaped structure over the trachea, produces thyroid hormones derived from the amino acid thyroxine
• Thyroxine (T4)


  Synthesized by the thyroid gland, converted to the more potent triiodothyronine (T3) in target tissues
• Diabetic ketoacidosis (DKA) occurs when there are high levels of glucose and fatty acids but low levels of insulin
• Thyroid hormones are involved in the regulation of basal metabolism, growth and development, body temperature, heart rate, blood pressure, and cholesterol synthesis.
• Cortisol, released by the adrenal glands, helps the body respond to stress and regulates metabolism.