Endocrine system

• Endocrine system


  Includes all the endocrine cells and tissues of the body that produce hormones
• Endocrine cells


  Glandular secretory cells that release hormones directly into the interstitial fluids, lymphatic system, or blood
• Hormones


  Chemical messengers that stimulate specific cells or tissues in the body
• Types of hormones


  • Amino acid-based molecules (including proteins, peptides, and amines)
  • Steroids (made from cholesterol, include sex hormones and hormones produced by the adrenal cortex)
  • Prostaglandins
• Amino acid derivatives


  Small molecules that are structurally similar to amino acids
• Amino acid derivatives


  • Thyroid hormones
  • Catecholamines (epinephrine, norepinephrine, dopamine)
  • Melatonin
• Peptide hormones


  Chains of amino acids, largest group of hormones
• Eicosanoids


  Small molecules with a five-carbon ring at one end, coordinate cellular activities and affect enzymatic processes
• Steroid hormones


  Lipids that are structurally similar to cholesterol, released by reproductive organs and adrenal cortex
• Hormone action


  • Hormones bind and exert influence in target cells/organs only
  • Target cell must express specific protein receptors to which hormone binds
  • Receptor must be present on the cell's plasma membrane or in its interior
• Hormone action


  1. Change plasma membrane permeability or membrane potential

  2. Activate or inactivate enzymes

  3. Stimulate or inhibit cell division

  4. Promote or inhibit secretion of a product

  5. Turn on or turn off transcription of certain genes
• Direct gene activation


  Steroid hormones can diffuse through plasma membranes, enter nucleus, bind to hormone receptor, and activate transcription of certain genes
• Second-messenger system


  Hormones that can't enter target cells directly bind to membrane receptors, triggering enzyme cascades that produce second messenger molecules like cAMP to promote intracellular changes
• Stimuli for control of hormone release

  • Hormonal
  • Humoral
  • Neural
• Hormonal stimuli


  Endocrine organs are stimulated into action by other hormones, creating a hormonal "feedback" to inhibit/regulate their own release
• Humoral stimuli


  Changing blood levels of certain ions and nutrients may stimulate hormone release
• Neural stimuli


  Nerve fibers can stimulate hormone release from endocrine cells
• Major endocrine organs


  • Pituitary, pineal, thyroid, parathyroid, thymus, adrenal glands, pancreas, gonads (ovaries and testes), hypothalamus
• Posterior pituitary


  Does not make peptide hormones, acts as a storage area for hormones made by hypothalamic neurons
• Oxytocin


  Stimulates powerful contractions of the uterine muscle, causes milk ejection (let-down reflex) in nursing women
• Antidiuretic hormone (ADH) or Vasopressin


  Inhibits or prevents urine production, causes kidneys to reabsorb more water from forming urine
• Anterior pituitary


  Contains a variety of endocrine cells that produce hormones like TSH, ACTH, GH, PRL, FSH, LH, and MSH
• Anterior pituitary hormones


  Are proteins/peptides, act through second-messenger systems, and are regulated by hormonal stimuli and negative feedback
• Melanocyte-stimulating hormone (MSH)


  Increases the rate of melanin production and distribution in skin melanocytes
• Growth hormone (GH)


  Causes growth of skeletal muscles and long bones, is protein-sparing and anabolic, helps maintain blood sugar homeostasis
• Prolactin (PRL)


  Stimulates and maintains milk production in the mother's breasts after childbirth
• Gonadotropic hormones


  Regulate the hormonal activity of the gonads (FSH and LH)
• Thyrotropic hormone (TSH)


  Influences the growth and activity of the thyroid gland
• Adrenocorticotropic hormone (ACTH)


  Regulates the endocrine function of the adrenal glands
• Tropes


  • Its only known target in humans is the breast
  • After childbirth, it stimulates and maintain milk production by the mother's breasts
  • Its function in men is not known
• Gonadotropic hormones


  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)


  • In women, it stimulates follicle development in the ovaries
  • In men, it stimulates sperm development by the testes
• Luteinizing hormone (LH)


  • In women, it triggers ovulation of an egg from the ovary and causes the ruptured follicle to produce progesterone and some estrogen
  • In men, it stimulates testosterone production by the interstitial cells of the testes
• Pituitary hormones


  • Thyrotropic hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
• Thyrotropic hormone (TSH)


  • Influences the growth and activity of the thyroid gland
  • Secreted by cells of the pars distalis called thyrotropes
• Adrenocorticotropic hormone (ACTH)


  • Regulates the endocrine activity of the cortex portion of the adrenal gland
  • The cells secreting ACTH are called corticotropes
• Thyroid gland


  • Located at the base of the throat, just inferior to the Adam's apple
  • Consists of two lobes joined by a central mass, or isthmus
  • Makes two hormones: thyroid hormone and calcitonin
• Thyroid hormones


  • Thyroxine (T4)
  • Triiodothyronine (T3)
• Thyroid hormone


  • The body's major metabolic hormone
  • Controls the rate at which glucose is "burned," or oxidized, and converted to body heat and chemical energy (ATP)
  • Important for normal tissue growth and development, especially in the reproductive and nervous systems
• Without iodine, functional thyroid hormones cannot be made