endocrine system

• Major glands of the endocrine system

  • Pituitary gland
  • Thyroid gland
  • Parathyroid glands
  • Adrenal glands
  • Pancreas
  • Pineal gland
  • Thymus
  • Reproductive glands (testes and ovaries)
• endocrine glands

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• Endocrine


  Internal secretion
• Endocrine system

  • Cells, tissues, and organs that compose it, collectively called endocrine glands, secrete chemical substances called hormones into the internal environment
  • Hormones diffuse from the interstitial fluid into the bloodstream where they act on target cells, some distance away
  • Target cells have specific receptors that are not found on other cells
  • Receptors are composed of proteins or glycoproteins and have binding sites for a specific hormone
• Exocrine glands

  Secrete chemical substances that enter tubes or ducts that lead to body surfaces
• Exocrine secretions

  • Stomach (gastric) acid reaching the lumen of the digestive tract
  • Sweat released at the skin's surface
• Nervous system

  Communicates using chemical messengers called neurotransmitters
• Neurotransmitter release and binding

  1. Released into the synaptic cleft

  2. Bind to receptor molecules on postsynaptic target cells a short distance away
• Endocrine system


  Releases hormones into the bloodstream that circulate everywhere in the body
• Neurotransmitters of the nervous system

  More fast-acting and short-lived
• Hormones of the endocrine system

  Have longer-lasting effects
• Nervous System

  • Cells: Neurons
  • Chemical signal: Neurotransmitter
  • Specificity of action: Receptors on postsynaptic cell
  • Speed of onset: <1 second
  • Duration of action: Very brief unless neuronal activity continues
• Endocrine System

  • Cells: Glandular epithelium
  • Chemical signal: Hormone
  • Specificity of action: Receptors on target cell
  • Speed of onset: Seconds to hours
  • Duration of action: May be brief or may last for days even if secretion ceases
• Hormones

  Organic compounds
• Types of hormones

  • Steroids (or steroidlike substances)
  • Nonsteroids
• Steroids

  • Synthesized from cholesterol
• Nonsteroids

  • Synthesized from amino acids
  • Include amines, peptides, proteins, and glycoproteins
• Steroids

  Lipids derived from cholesterol that include complex rings of carbon and hydrogen atoms and some oxygen atoms
• Steroids

  • They differ by the types and numbers of atoms attached to these rings and the ways they are joined
  • They include sex hormones, such as testosterone and the estrogens
• Steroids are lipids derived from cholesterol that include complex rings of carbon and hydrogen atoms and some oxygen atoms
• Hormones called amines (monoamines; biogenic amines)


  Derived from the amino acid tyrosine
• Hormones

  Norepinephrine and epinephrine
• Hormone synthesis

  Synthesized in the adrenal medulla (the inner portion of the adrenal gland)
• Prostaglandins

  Produced from a fatty acid called arachidonic acid, which is found in cell membranes
• Steroid hormone action

  1. Endocrine gland secretes steroid hormone

  2. Blood carries hormone molecules (often weakly bound to transport protein) throughout the body

  3. Unbound steroid hormone diffuses through target cell membrane and enters cytoplasm or nucleus

  4. Hormone combines with a receptor molecule in the cytoplasm or nucleus

  5. Steroid hormone-receptor complex binds to DNA in the nucleus and promotes transcription of messenger RNA

  6. Messenger RNA enters the cytoplasm and directs protein synthesis

  7. Newly synthesized proteins produce the steroid hormone's specific effects
• Cyclic adenosine monophosphate (cyclic AMP, or cAMP)

  Second messenger
• Hormone signaling mechanism

  1. Hormone binds to receptor

  2. Hormone-receptor complex activates G protein

  3. G protein is an enzyme complex joined to intracellular side of hormone receptor

  4. G protein is the link between first and second messenger
• Many hormones use cyclic AMP as a second messenger
• Sequence of Actions of Nonsteroid Hormone Using Cyclic AMP

  1. Endocrine gland secretes nonsteroid hormone

  2. Blood carries hormone molecules throughout the body

  3. Hormone combines with receptor site on membrane of its target cell, activating G protein

  4. Adenylate cyclase molecules are activated in target cell's membrane

  5. Adenylate cyclase converts ATP into cyclic AMP

  6. Cyclic AMP activates protein kinases

  7. Protein kinases activate protein substrates in the cell that change metabolic processes

  8. Cellular changes produce the hormone's effects
• How a steroid hormone acts on its target cells

  1. Steroid hormone penetrates cell membrane

  2. Binds to receptor protein inside cell

  3. Hormone-receptor complex binds to specific region of DNA molecule

  4. Activates gene transcription in nucleus

  5. Produces certain protein
• Second messenger

  A chemical that stimulates cellular changes in response to the binding of a nonsteroid hormone to its receptor
• Second messengers are necessary because nonsteroid hormones cannot penetrate the cell membrane
• Second messengers carry out the effects of the hormone
• Prostaglandins

  A group of lipids produced from a fatty acid, called arachidonic acid, found in cell membranes
• Prostaglandins

  • Potent
  • Produced in small quantities
  • Used in local areas (which makes them paracrine substances)
  • Quickly inactivated
• Prostaglandins are produced by many types of cells
• Prostaglandins regulate cellular responses to hormones

  1. Activating or inactivating adenylate cyclase in cell membranes

  2. Regulating the production of cAMP
• Effects of various prostaglandins

  • Relaxation of airway and blood vessel smooth muscle
  • Contraction of uterine smooth muscle
  • Secretion of hormones from the adrenal cortex
  • Inhibition of hydrochloric acid secretion in the stomach
  • Affecting blood pressure
  • Affecting sodium and water movement in the kidneys
  • Affecting male and female reproductive processes
  • Affecting inflammation
• Mechanisms of hormone control

  1. Hypothalamus controls anterior pituitary gland's release of hormones

  2. Nervous system directly stimulates some glands

  3. Glands respond directly to changes in internal environment
• Tropic hormones

  Hormones that act on other glands