Endocrinology

• The hypothalamus is a major control center for the endocrine system, regulating the release of hormones from the pituitary gland.
• Endocrine Glands (type, function, anatomy)


  Ductless, secrete hormones into the blood, mostly made of glandular epithelium
• Some of the endocrine glands are made of neurosecretory tissue, widely scattered throughout the body
• Hormone


  Molecule produced by endocrine glands or tissues carried into the bloodstream to target tissue
• Hormones help maintain homeostasis on a daily basis. Involved in growth, development, reproductive processes and participate in the circadian cycle
• Hormones act only on targets that recognize the hormone who have binding sites (receptors) specific for that hormone
• Target cells have thousands of receptors specific for certain hormones, may have more than one type of receptors
• Tropic Hormones


  Hormones targeting other endocrine glands and stimulate their growth or secretion of other hormones
• Sex hormones


  Hormones that target reproductive tissues
• Anabolic Hormones


  Hormones that stimulate anabolism in their target cells
• Anabolism


  Growth, Development
• Hormones can be classified by their chemical structure which changes how they work. They can be made of proteins, peptides, amino acids derivatives, glycoproteins or steroids (lipids)
• Lipophilic Steroid Hormones


  Bind to intracellular receptors due to their ability to enter cells at will (fat-soluble). Gives a permanent effect. Examples are steroid and thyroid hormones.
• Hydrophilic (nonsteroid) Hormones


  Bind to extracellular receptors, unable to enter cell (water-soluble). Gives a temporary effect. Example of hormones are all except steroid and thyroid hormones.
• Steroid hormones are manufactured by endocrine cells from cholesterol. Lipid Soluble. Able to pass freely through plasma membrane and nuclear membrane of target cells
• Nonsteroid Hormones are primarily synthesized from amino acids. Can be protein, chains of amino acids (peptides).
• Protein or long chain of amino acids examples


  Insulin and Parathyroid hormones
• Peptide hormones (short chain of amino acids)


  Oxytocin and Antidiuretic Hormones
• Steroid Hormone Action Mechanisms

  1. Travel through the blood using a carrier
  2. Detaches from carrier as it approaches target cells
  3. Passes freely through plasma membrane into cytoplasm
  4. Attaches to a receptor inside the nucleus forming a hormone-receptor complex
  5. Complex activates gene expression, proteins are produced inducing a change in the cell. (Modifying phenotypic expression from existing genotype)
• Nonsteroid Hormone Action Mechanisms

  1. A hormone-receptor complex forms as the hormone binds to the extracellular receptor.
  2. The G protein (coupled to hormone receptor) is activated and this, in turn, activates an adenyl cyclase enzyme.
  3. The adenyl cyclase converts ATP into cAMP (the second messenger - intracellular)
  4. Protein Kinases are activated causing changes in the cell (phosphorylation)
• Phosphorylation


  Changes substrates and adds a phosphorus group covalently, product has different function and form
• Steroid Hormones Characteristics


  Lipid, not stored in vesicles, diffuses through membrane to mobile receptor in nucleus, regulates gene activity, takes one hour to several days to act
• Nonsteroid Hormones Characteristics


  Protein associated molecules, stored in vesicles before release, binds to specific embedded plasma membrane receptors, triggers signal cascade producing internal messengers with rapid effects in target cell. Takes several seconds to few minutes to act.
• Pituitary Glands (Hypophysis)


  About 1.5cm and 0.5g (almond sized), also called Master Gland.
• The pituitary gland consists of two separate glands : the anterior and posterior pituitaries
• Hypothalamus


  Master regulator of the pituitary gland
• The pituitary gland is attached to the hypothalamus by a bridge-like apparatus called the infundibulum
• The anterior pituitary produces 6 different hormones:

  1. Growth Hormone (GH)
  2. Adrenocorticotrophic hormone (ACTH)
  3. Thyroid Stimulating Hormone (TSH)
  4. Prolactin (PRL)
  5. Leutinizing Hormone (LH)
  6. Follicle Stimulating Hormone (FSH)
• The hypothalamus and anterior pituitary gland are partially controlled by the very hormones whose secretion they stimulate because of the negative feedback or feedback inhibition system
• Positive feedback is uncommon because it causes deviations from homeostasis
• Growth Hormone


  Most abundant anterior pituitary hormone that promotes body growth by stimulating production of insulin-like growth factor, stimulating protein anabolism and fat metabolism
• GH target cells :

  1. Liver - Use of sugar for build and reparation
  2. Skeletal Muscle - Development
  3. Bones - Growth and development
• GH induces cells to use lipids as an energy source, increasing the amount of carbohydrate in the blood. Increases growth of bones, muscles and other tissues
• Prolactin


  Also called the lactogenic hormone. It's target cell is the mammary glands and initiates milk production and secretion (into duct to store). During pregnancy, high level of PRL promotes development of breasts in anticipation of milk secretion. At birth of infant, PRL in the mother stimulates mammary glands to begin milk secretion.
• Tropic - to go (bossy)
• Other tropic hormones of anterior pituitary

  • Thyroid Stimulating Hormone: promoting growth and development of thyroid, also causes it to secrete it's hormones
  • Adrenocorticotropic Hormone: Promotes growth and development of the adrenal gland cortex and stimulates the gland to synthetize and secrete some of it's hormones
• Sex/Tropic Hormones of anterior pituitary

  • Follicle Stimulating Hormone : In females, stimulates primary follicles to grow towards maturity and in males, stimulates sperm production. (Overall, production of sex cells)
  • Luteinizing Hormone : In females, stimulates ovulation to create the corpus luteum that secretes progesterone (Stimulation of another hormone production) and in males, stimulates interstitial cells to secrete testosterone (Overall, secretion of other hormones)
• Through negative feedback mechanisms, the hypothalamus adjusts the secretions of the anterior pituitary gland. The anterior pituitary adjusts the secretion of hormones in its target glands, which in turn adjusts the activity of their target tissues.
• The posterior pituitary gland (also called neurohypophysis) is the smaller of the two lobes. It does not produce hormones, only stores and releases hormones produced by the hypothalamus' neurons
• Hormones stored in the posterior pituitary gland:

  1. Antidiuretic Hormone (ADH)
  2. Oxytocin (OT)