Endocrine System

• Endocrine System


  The system composed of endocrine glands and specialized endocrine cells located throughout the body that secrete hormones into the bloodstream
• Types of glands in the human body

  • Central endocrine glands
  • Peripheral endocrine glands
• Central endocrine glands


  • Hypothalamus
  • Pituitary gland (anterior and posterior)
• Peripheral endocrine glands


  • Pancreas
  • Ovaries
  • Testes
  • Thyroid gland
  • Adrenal gland
• Chemical messenger


  Any compound that serves to transmit a "message" to allow cells to communicate with each other and regulate body activities
• Classes of chemical messengers

  • Autocrine
  • Paracrine
  • Neurotransmitter
  • Endocrine
• Autocrine chemical messenger


  Stimulates the cell that originally secreted it
• Autocrine chemical messenger


  • Eicosanoids released by white blood cells
• Paracrine chemical messenger


  Acts locally on nearby cells
• Paracrine chemical messenger


  • Histamines released by white blood cells acting on endothelial cells
• Neurotransmitter


  Chemical messengers secreted by neurons to activate an adjacent neuron or muscle
• Endocrine chemical messenger


  Also known as "hormones", secreted into the bloodstream by certain glands and cells to affect distant target cells/organs

  
• Endocrine system


  • Glands and cells secrete hormones into the bloodstream
  • Hormones reach and bind to target organs/cells
• Hormone


  Greek word meaning "to set in motion", regulates almost every physiological process in the body, can be lipid-soluble or water-soluble
• Regulation of hormone levels in the blood

  1. Central (hypothalamus and pituitary gland)

  2. Peripheral (target organs)
• Negative feedback


  Most common mechanism for regulation of hormone secretion, the secretion of hormones is inhibited once blood levels reach a certain level
• Positive feedback


  The release of a hormone will trigger more release of the hormone, the original stimulus is promoted rather than negated
• Hormones of the anterior pituitary gland

  • Growth hormone
  • Adrenocorticotropic hormone
  • Thyroid-stimulating hormone
  • Gonadotropic hormones
  • Melanocyte-stimulating hormone
  • Prolactin
• Hormones of the posterior pituitary gland

  • Antidiuretic hormone (ADH)
  • Oxytocin
• Pituitary gland


  Also called the hypophysis, a small gland about the size of a pea located in the sella turcica of the sphenoid bone, connected to the hypothalamus by the infundibulum
• Growth hormone


  Stimulates the growth of bones, muscles, and other organs by increasing gene expression, favors lipid breakdown, resists protein breakdown, and increases blood sugar level
• Pituitary dwarfism


  • Deficiency of growth hormone, can be treated with growth hormone supplementation
• Gigantism


  • Excess of growth hormone before the bones finish growing in length, results in excessive growth in length of bones and abnormally tall stature
• Acromegaly


  • Excess of growth hormones after bone growth is complete, results in excessive growth in diameter of bones and abnormally large facial features and hands
• Thyroid-stimulating hormone (TSH)


  Binds to receptors in the thyroid gland and causes it to release thyroid hormones
• Adrenocorticotropic hormone (ACTH)


  Binds to cells in the adrenal cortex and increases secretion of the hormone cortisol, also binds to melanocytes and increases skin pigmentation
• Gonadotropins


  Hormones that bind to receptors on the gonads (ovaries or testes) and regulate their growth, development, and functions

  
• Prolactin


  Binds to receptors in breast cells and helps promote development of the breast during pregnancy and stimulate milk production after pregnancy
• Melanocyte-stimulating hormone


  Binds to receptors on melanocytes and causes them to synthesize melanin, over-secretion causes skin darkening
• Antidiuretic hormone (ADH)


  Binds to receptors and increases water reabsorption by kidney tubules, decreasing water volume in urine, can also cause vasoconstriction
• Diabetes insipidus


  • Lack of ADH secretion, leading to production of large amounts of dilute urine

  
• Oxytocin


  Binds to receptors and causes contraction of the smooth muscle cells of the uterus, as well as milk letdown from the breasts in lactating women
• Thyroid gland


  • Made up of two lobes connected by an isthmus, located on each side of the trachea just inferior to the larynx, highly vascular, main function is to secrete thyroid hormones
• How ACTH is released

  1. Low blood sugar level detected by hypothalamus

  2. Hypothalamus secretes ACTH-releasing hormone

  3. ACTH-releasing hormone acts on pituitary to release ACTH

  4. ACTH acts on adrenal cortex to release cortisol
• Childbirth


  1. Uterus contracts

  2. Baby is expelled
• Thyroid gland


  Made up of two lobes connected by a narrow band called the ISTHMUS ("constriction")
• Parts of thyroid gland

  • Left Lobe
  • Right Lobe
  • Isthmus
• Thyroid gland


  • Located on each side of the trachea, just inferior to the larynx
  • Appears more red than the surrounding tissues because it is highly vascular
• Function of thyroid gland

  To secrete the THYROID HORMONES
• ACTH release


  1. Low blood sugar level detected by hypothalamus

  2. Hypothalamus secrete ACTH-Releasing hormone

  3. ACTH-Releasing hormone acts on pituitary gland to release ACTH

  4. ACTH acts on adrenal cortex to release cortisol