physiology

• Endocrine system


  A control system of ductless glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant cells within specific organs
• Major endocrine glands

  • Pineal gland
  • Pituitary gland
  • Thyroid gland
  • Thymus
  • Adrenal gland
  • Pancreas
  • Ovary
  • Testis

  
• Endocrine glands


  • Secrete their products immediately into the blood or interstitial fluid, without storage of the chemical
  • Hormones act as "messengers," and are carried by the bloodstream to different cells in the body, which interpret these messages and act on them
• Ability to maintain homeostasis and respond to stimuli

  • Largely due to hormones secreted within the body
  • Without hormones, you could not grow, maintain a constant temperature, produce offspring, or perform the basic actions and functions that are essential for life
• Endocrinology


  The field of medicine that deals with disorders of the endocrine glands
• Endocrinologist


  The specialist in endocrinology
• How endocrine system works

  1. Provides an electrochemical connection from the hypothalamus of the brain to all the organs that control the body metabolism, growth and development, and reproduction

  2. Hormones bind to receptors on target cells

  3. Receptors bind a specific hormone and the result is a specific physiologic response
• Types of hormones


  • Steroidal
  • Nonsteroidal (protein-based)
• Steroidal hormones


  Triggered by on-off switch's mechanism within the cell nucleus, controlling development, differentiation, and regulation of tissues
• Nonsteroidal hormones


  Bind to receptor sites on the external surface of the cell membrane and use a second messenger methods of altering internal cell functions
• Endocrine system regulation


  • Regulated through negative feedback - increases in hormone activity decrease the production of that hormone
  • The immune system and other factors contribute as control factors also, altogether maintaining constant levels of hormones
• Exocrine glands


  Release their cellular secretions through a duct which empties to the outside or into the lumen (empty internal space) of an organ
• Endocrine glands


  Have no duct and release their secretions directly into the intercellular fluid or into the blood
• Main endocrine glands

  • Pituitary (anterior and posterior lobes)
  • Thyroid
  • Parathyroids
  • Adrenal (cortex and medulla)
  • Pancreas
  • Gonads
• Pituitary gland

  Attached to the hypothalamus of the lower forebrain

  
• Thyroid gland


  Two lateral masses, connected by a crossbridge, attached to the trachea, slightly inferior to the larynx
• Parathyroids


  Four masses of tissue, two embedded posteriorly in each lateral mass of the thyroid gland
• Adrenal gland


  One located on top of each kidney, with a cortex (outer layer) and medulla (inner core)
• Pancreas


  Along the lower curvature of the stomach, close to where it meets the duodenum
• Gonads


  Found in the pelvic cavity
• Hormone


  A specific chemical substance produced by certain cells that control, or help to control, cellular processes elsewhere in an organism
• Chemical classifications of hormones

  • Amino acid-derived
  • Polypeptide and proteins
  • Steroids
  • Eicosanoids
• Lipid-soluble hormones

  Diffuse through the cell membranes of target cells and bind to a receptor
• Water-soluble hormones


  Bind to a receptor protein on the plasma membrane of the cell
• Stimuli for endocrine gland hormone release


  • Hormones from other endocrine glands
  • Chemical characteristics of the blood (other than hormones)
  • Neural stimulation
• Hormone production management


  • Most is managed by a negative feedback system
  • Some is controlled by positive feedback, which is uncommon but occurs during childbirth and lactation
• Antagonistic hormones


  Hormones that act to return body conditions to within acceptable limits from opposite extremes
• Regulation of blood glucose concentration

  Illustrates how the endocrine system maintains homeostasis by the action of antagonistic hormones (insulin and glucagon)
• Maintenance of Ca2+ concentration in the blood

  Parathyroid hormone (PTH) increases Ca2+, calcitonin (CT) decreases Ca2+
• Hypothalamus


  Controls many internal body conditions, receives nervous stimuli and monitors blood characteristics, communicates to other glands via releasing hormones and inhibiting hormones

  
• Hypothalamus-released hormones


  • TRH (thyrotropin-releasing hormone)
  • CRH (corticotropin-releasing hormone)
  • DA (dopamine, "prolactin inhibiting factor"/PIF)
  • GnRH (gonadotropin-releasing hormone)
  • GHRH (growth hormone releasing hormone)
• Anterior pituitary secreted hormones

  • Growth hormone
  • Prolactin
  • Follicle-stimulating hormone
  • Luteinizing hormone
  • Thyroid-stimulating hormone
  • Adrenocorticotropic hormone
  • Endorphins
  • Other hormones
• Thyroid gland

  Produces T3 (triiodothyronine) and T4 (thyroxine) hormones that increase metabolic activity, and calcitonin which regulates blood calcium levels
• Thyroid-stimulating hormone (TSH)


  Produced by the pituitary gland, stimulates thyroxine secretion by the thyroid gland
• Iodine deficiency

  Leads to enlargement of the thyroid gland (goiter)
• Hypothyroidism


  Results in puffy skin, sluggishness, lowered vitality, and in children can cause mental retardation, dwarfism, and sexual immaturity (cretinism)
• Hyperthyroidism

  Produces high body temperature, profuse sweating, high blood pressure, weight loss, irritability, muscular weakness, and exophthalmia (protruding eyeballs)
• Parathyroid glands

  Regulate the body's calcium and phosphorus levels
• Parathyroid hormone (PTH)

  Secreted by the parathyroid glands, increases calcium in the blood
• Calcitonin (CT)


  Secreted by the thyroid gland, decreases calcium in the blood