Student Performance Objectives - for the lecture Show 1. Ductless glands produce hormones- While exocrine glands have a duct through which the gland's
product reaches its destination (e.g., the parotid salivary gland secretes saliva through Stensen's duct into the mouth; the lacrimal gland secretes tears through the lacrimal duct onto the eye's surface), endocrine glands have no ducts - they are ductless glands. They secrete their products, called hormones, into the interstitial fluid surrounding the
gland. From there the hormone diffuses into the blood and is carried throughout the body. 3. Hormonal transport - some hormones can travel freely in the blood because they are water soluble (hydrophilic). The steroid hormones, being fat soluble (hydrophobic), must be bound to and carried around by transport proteins (like albumin and globulins which are blood proteins produced by the liver). Free (unbound) hormones are able to enter target organs. Bound hormones must be released from the transport proteins to get into their target organs. 4. Hormonal breakdown - hormones are broken down in target cells, in the liver and in the kidneys. The hormonal breakdown products are excreted from the body in urine and feces. Hormones that are freely dissolved in blood and other body fluids are broken down rapidly - they are said to have a short half-life. Examples are epinephrine and norepinephrine that have half-lives measured in minutes. Hormones that are bound to transport proteins can circulate longer and break down only after they disassociate from their transport proteins and are free in the body fluids. Hormonal breakdown is important in that at any given moment, the hormones circulating within us are mostly freshly made in response to recent environmental conditions. We are adapted hormonally to current conditions. The hormones from yesterday or several hours ago are mostly gone. B. Hormonal Classification 1. Polypeptides (small proteins: 14 - 199 amino acids)- a. Growth hormone - stimulates growth of epiphyseal plates in the long bones. b. Insulin - lowers the blood sugar after a meal. c. Glucagon - raises the blood sugar if it falls when you are not eating. 2. Oligopeptides (very small proteins: 3 - 10 amino acids) a. Anti-diuretic hormone - ADH - helps the body hold on to its water preventing dehydration. b. Oxytocin - helps the uterus to contract during childbirth and causes the breasts to pump out milk. c.Angiotensin II - a vasoconstrictor that raises blood pressure. 3. Modified amino acids a. Thyroxine - regulates the basal metabolic rate. Thyroxine consists of two attached amino acids (both are tyrosine) with attached iodine atoms. b. Epinephrine - a "fight or flight" hormone affecting heart and breathing rate. c. Norepinephrine - works much like epinephrine but as a "local" neurotransmitter. Both epinephrine and nor epinephrine are modifications of a single amino acid, tyrosine, and are in a class frequently called monoamines. 4. Steroids (derivatives of cholesterol) a. Androgens, like testosterone, that stimulate male sexual characteristics. b. Estrogens, like estradiol, that stimulate female sexual characteristics. c. Aldosterone (an adrenal steroid) regulates blood sodium and potassium levels. 5. Glycoproteins (combinations of protein and carbohydrate) a. Follicle stimulating hormone - FSH - stimulates egg and sperm development. b. Luteinizing hormone - LH - causes ovulation. c. Thyroid stimulating hormone - TSH - stimulates the thyroid gland to release its hormone, thyroxine. 6. Paracrines - There are other substances that act as hormones, but more locally. These are called paracrines: e.g., neurotransmitters like acetylcholine, histamine (a mediator of inflammation), and the eicosanoids, which are fatty acid derivatives influencing metabolism (e.g., blood pressure, blood clotting, and inflammation). The neurotransmitters are discussed in the nervous system area. Eicosanoids are generally considered as a group in courses in nutrition, and also, often, in the cardiovascular system area with regard to their influence on cardiovascular health and inflammatory processes. C. Hormonal-Cell interactions1. Hydrophilic (water soluble) hormones like epinephrine, norepinephrine, dopamine, glucagon, and ADH, attach to receptors on the cell surface. These water soluble hormones cannot easily penetrate through the cell membrane which is mostly hydrophobic. Attachment of hydrophilic hormones to surface receptors activates second messenger systems on the cytoplasmic side of the cell membrane. http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/moaction/surface.html There are several different 2nd messenger systems, but they operate in the same general way. The second messenger system eventually produces the hormone's effects. It is an intracellular enzyme amplification system in that 5 or 6 sequential chemical reactions are triggered inside the cell by the initial attachment of a hormone to the surface receptor: the hormone's attachment stimulates thousands of molecules of GTP (a high energy molecule) to break down which causes thousands of cyclic AMP molecules to be produced from ATP; each cyclic AMP molecule stimulates production of thousands of enzymes called protein kinases; each protein kinase molecule stimulates formation of thousands of other enzymes, and so on. Taken as a whole, an initial stimulus from one molecule of hormone attaching to a receptor, results in thousands, times thousands, times thousands (at least 6 times) of "downstream" molecules being produced that carry out the hormone's work. So hormones are very potent chemicals and only tiny amounts are necessary to create powerful effects on cells and the body as a whole. 2. Hydrophobic (fat soluble) hormones like the steroid hormones do not attach to surface receptors. They break off from their blood transport proteins and then pass right through the cell and nuclear membranes attaching to receptors near or on specific regions of DNA (genes). DNA is then stimulated to transcribe messenger RNA resulting in new cytoplasmic protein synthesis that redirects cell metabolism. The thyroid hormones, also lipid soluble, enter the cytoplasm and attach to receptors on mitochondria and ribosomes as well as in the nucleus. The effect of thyroid hormones is to increase mitochondrial oxidations, increase protein synthesis, and to increase production of membrane ionic (sodium and potassium) transporters, all of which result in increases in the body's metabolic rate and overall heat production. D. Feedback, negative and positive - When the body receives a signal (input signal), there is a response - the output signal. We call any activity of the body a parameter. If we are measuring body temperature, then body temperature is the
parameter. If we are measuring blood sodium concentration (level), then blood sodium level is the parameter. All body parameters have a normal range of values (e.g., body temperature is 37 1 C). We will utilize this terminology to explain negative and positive feedback in the endocrine system. F. Endocrine glands in the neck and their secretions F. Endocrine glands in the thoracic cavity and their
secretions Biomedical Terminology: Define each term: ACTH 1. Choose one of the problems described below. Problem #1: A nineteen year old college student regularly experiences anxiety, abdominal bloating, craving for sugary foods, and mild depression during the 2 weeks prior to menstruation. She also regularly experiences cramping during the first 2 days of menstruation.
Her doctor recommends hormone pills to relieve the pre-menstrual symptoms as well as pain medication for the menstrual cramping. Utilize the Internet to research the pros and cons of hormonal therapy for PMS (pre-menstrual syndrome) and alternatives for such hormonal therapy. Problem #2: A 45 year old female, 5'4" and 220 lbs., experiencing low energy
levels, periods of dizziness, and knee pain, decides to see her doctor. Examination reveals hypertension, elevated blood sugar, elevated total cholesterol levels, elevated triglycerides, and elevated blood insulin levels. Her doctor's diagnosis is diabetes mellitus Type II and she is initially placed on "oral insulin" and after a year with marginal sign and symptom relief, she begins injecting insulin. She receives some benefit but indicates she does not feel a sense of well-being. Utilize the
Internet to answer the following questions: Is thyroid hormone a steroid or protein?Depending on the molecule, amino acid hormones can act as either a steroid or peptide hormone; for example, thyroid hormone is an amino acid hormone which acts like a steroid, while epinephrine, which is also an amino acid hormone, acts as a peptide hormone.
What are the two factors that affect the concentration of a circulating hormone?Describe the two primary factors that affect the concentration level of a circulating hormone. The two primary factors that influence hormone concentration are hormone synthesis by endocrine glands and hormone elimination by the liver, kidneys, and target cells.
How are hydrophobic hormones transported through the body?The steroid hormones, being fat soluble (hydrophobic), must be bound to and carried around by transport proteins (like albumin and globulins which are blood proteins produced by the liver). Free (unbound) hormones are able to enter target organs.
Are thyroid hormones lipid soluble?Thyroid hormones are lipid soluble and readily cross cell membranes. Once inside the nucleus, T3 binds to its receptor. This dimerizes with another T3 receptor (to form a homodimer) or with a different receptor, notably the retinoic acid receptor, to form a heterodimer (Box 3.9).
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