Endocrine 1

• Endocrine glands characteristics

  • they are ductless
  • they secrete hormones into the blood
  • they are widely scattered throughout the body
• Endocrine glands are mostly made of glandular epithelium, some of them are made of neurosecretory tissue
• Endocrine glands

  • hypothalamus (cranial cavity)
  • pituitary gland (cranial cavity)
  • pineal gland (cranial cavity)
  • thyroid gland (neck)
  • parathyroid glands (neck)
  • thymus (mediastinum)
  • adrenal glands (abdominal cavity)
  • pancreatic islets (abdominal cavity)
  • ovaries (pelvic cavity)
  • testes (scrotum)
  • placenta (pregnant uterus)
• Hormone: chemical produced by endocrine glands or tissues, they are carried in the bloodstream
• Hormone functions

  • help maintain homeostasis
  • involved in growth and development
  • influence reproductive processes
  • participate in circadian rhythms
• Hormones act only on target cells that recognize the hormone by their shape
• Target cells

  • they have binding sites specific for that hormone
  • they have thousands of receptors specific for a particular hormone
  • they may have more than one type of receptor, meaning cells respond to more than one hormone
• Types of hormones: tropic hormones, sex hormones, anabolic hormones
• Tropic hormones are hormones that target other endocrine glands and stimulate their growth and secretion
• Sex hormones are hormones that target reproductive tissue
• Anabolic hormones are hormones that stimulate anabolism (growth) in their target cells
• Hormone classification by chemical structure

  • proteins
  • peptides (smaller than protein hormones)
  • glycoproteins (proteins with carbohydrates)
  • amino acid derivatives
  • steroids (fats)
• Hormones classified by structure are subdivided into lipophilic (steroid) hormones and hydrophilic (non-steroid) hormones
• Lipophilic hormone characteristics

  • lipid soluble
  • bind to intracellular receptors
  • permanent effect
  • eg: steroid hormones and thyroid hormones
• Hydrophilic hormone characteristics

  • water soluble
  • bind to extracellular receptors
  • temporary effect
  • all hormones except steroid and thyroid
• Steroid hormones are manufactured by endocrine cells from cholesterol

  They pass freely through the plasma membrane and nuclear membrane of the cell

  eg: aldosterone, cortisol, testosterone, estradiol, progesterone
• Types of nonsteroid hormones

  • primarily synthesized from amino acids
  • some are protein hormones (long chain of amino acids, eg: insulin and parathyroid hormones)
  • peptide hormones are made from short chains of amino acids (eg: oxytocin and ADH)
  • amino acid derivatives come from one amino acid
• Mechanism of steroid hormone action

  • travel through the blood using a carrier
  • detaches from carrier as it approaches target cells
  • passes freely through plasma membrane into cytoplasm
  • attaches to a receptor inside the nucleus and activates it
  • complex activates gene expression, proteins are produced inducing a change in the cell
• Mechanisms of nonsteroid hormone action

  • Hormone receptor binds to the extracellular receptor on plasma membrane
  • Second messenger forms inside the cell
  • Second messenger causes activation of several protein which causes physiological temporary responses