Review Sheet #1 B Test 3         Biology 1108                                 Dr. Adams

Hormonal Control - Endocrine System; one of two control systems in animals


  1. Hormones typically released from one place (a gland) into bloodstream and affect organs elsewhere in the body; there are plenty of exceptions, however. This also means that in order for a given hormone to affect specific target cells, it is the receptors at the target cells that determine whether or not a cell will respond to a given hormone.
  2. Frequently, in order to maintain balance of levels of certain molecules in the body, there are two hormones whose affects antagonize one another.
  3. Hormone release is typically controlled by one of three factors:
    a.  other hormones stimulate release of hormones from target gland (tropic hormones)
    b. nerve cells stimulate release of hormones
    c. hormones release is directly stimulated by levels of compounds around the glands (in the        

Hormone Classes: your book talks about four types, but I will simplify this to two.

  1. Steroid (Lipid-based) hormones (includes fatty acid derivatives and steroids from book) --  can typically diffuse through cell membranes (WHY?) and so the receptors must be inside the cell.
  2. Protein-based hormones (includes amino acid derivatives and peptides from book) -- typically can=t diffuse into cells, so receptors must be on the cell membrane. This means that these hormones affect target cells through secondary messengers.

Mechanism of Action B you will learn that the mechanism of action is quite different for lipid versus protein-based hormones (know what the different mechanisms are), but the end result is the same B active proteins in cells that did not have this activity previously.

Hormonal control in other organisms B an example

    Control of growth/molting/metamorphosis in insects.
        Involves the release of two series of semi-antagonistic (neuro)hormones:
                 1.  Juvenile hormone released from corpus allatum that stimulates maintenance of juvenile
                     characteristics (maintains larval state)
                2.    Brain hormone
(released from brain!) that stimulates release of ecdysone (molting 
                      hormone) from prothoracic glands B stimulates molting.

Stretch receptors respond to growth by stimulating brain to release brain hormone periodically. As larva gets bigger, proportionally less and less juvenile hormone is released, so eventually a molt occurs into the pupal, and then adult stages.

Human Endocrine Organs     SEE BOOK and HANDOUT
     Actually includes a number of different organs in the body, including such organs as the heart, stomach, intestines, etc. Covered here are the Aclassic@ endocrine organs.

I. Pancreas B Islets of Langerhans
        two types of cells: α cells - glucagon; β cells - insulin - glucose metabolism

II. Adrenal (Aat kidney@) glands B compound gland
A. Medulla: epinephrine/norepinephrine B many stimulatory effects
B. Cortex: around 2 dozen hormones; 3 types of corticosteroids
        1. glucocorticoids B glucose metabolism
        2. mineral corticoids B regulation of ion (Na+/K+) balance
        3. gonadocorticoids B androgens (supplementary sexual hormones)

III. Thyroid gland
    A. thyroid hormones B stimulates increase in metabolism (increases temperature); growth (protein
    B. calcitonin B Ca+2 excretion and uptake by bones

IV. Parathyroid glands - PT hormone - Ca+2 retention from kidneys, absorption from digestive tract
         (through activation of vitamin D), and release from bones

V. Pineal Gland - melatonin - metabolic depressant, whose release is inhibited by light.  Therefore,
        involved in circadian rhythms/moods; also inhibits release of GnRH from Hypothalamus

VI. The Pituitary Gland and the Hypothalamus
    A. The Pituitary - compound gland
     1. Posterior (Neurohypophysis)  --  hormones released from here are produced in the hypothalamus
            a. oxytocin - uterine contraction/ejection of milk from breasts
            b. ADH (antidiuretic) - water resorption in kidney
     2. Anterior (adenohypophysis): 6 major hormones; most are tropic hormones
            a. Growth hormone (GH)
            b. Prolactin - milk production
            c. Thyroid stimulating hormone (TSH)
            d. Adrenocorticotropic hormone (ACTH)
            e. Gonadotropic hormones - stimulates ovaries/testes
                    i. follicle stimulating hormone (FSH)
                    ii. luteinizing hormone (LH)
    B. The Hypothalamus (a neuroendocrine organ): the true Amaster@ gland; produces 
                                releasing/inhibiting hormones
        1. Growth hormone releasing hormone (GHRH) and GH inhibiting hormone (GHIH)
        2. Prolactin RH (PRH) and PIH
        3. Thyroid RH (TRH)                                         all control precise timing and
        4. Corticotropic RH (CRH)                                release of (stimulating) hormones
        5. Gonadotropic RH (GnRH)                              from the anterior pituitary

VII. Gonads:  
    A. Ovaries - estrogen and progesterone
    B. Testes - testosterone