Endocrine System. Endocrine System. Hormone structures. Hormone effects. Hormone effects. How a hormone effects 4/2/2013

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1 Endocrine System A communication system Signals are chemical Message requires specific receptor Slower onset, longer duration than nervous system Endocrine System Endocrine vs exocrine Exocrine secretions are to external body services or routes to the outside (like the GI tract) Endocrine secretions are into the blood, lymph or interstitial spaces Hormone effects Turns on protein synthesis Specific protein: enzyme or surface protein Change the rate of synthesis Activate/inactivate an enzyme process Stimulate mitosis Hormone structures Amino acid based (pretty small molecules) Thyroid hormones Peptide (chains of amino acids) ADH, oxytocin Steroids (cholesterol based) Estrogen, testosterone aldosterone Prostaglandins and leukotrienes- from arachidonic acid- act locally Hormone effects Changes target cell membrane permeability Increase protein synthesis in a cell Turn on/off enzymes Induce secretion (more enzyme turn on?) Promote cell division How a hormone effects Depends on the type (chemical) of hormone Amino acid-based hormones (hydrophilic) bind to the receptors in the membrane This activates a 2 nd messenger on the inside of the membrane (607) 1

2 Hormone effects Hormones binding to the cell membrane are called the 1 st messenger and these trigger a 2 nd messenger which is activated inside the cell. 1 st messenger camp effect in cell See image on p 607 How a hormone effects- 2 nd Messenger system 1. Hormone binds to outside of membrane 2. Hormone binding outside, leads to G protein binding inside. 3. G protein is activated (has higher energy bond GTP vs GDP) 4. The activated G protein binds to adenylate cyclase (in the membrane) and stimulates or inhibits it How a hormone effects- 2 nd Messenger system (cont.) 5. If stimulated, Adenylate cyclase converts ATP to camp 6. camp activates protein kinase molecules (these add or remove phosphate groups from other molecules) 7. phosphorylation by the kinase activates or inactivates processes inside a cell 8. phosphodiesterase breaks down camp Steroid Hormone effectsdirect gene activation See 609 The steroid based hormone can pass directly through the cell membrane into the nucleus to have a direct effect on protein synthesis (no 2 nd messenger ) Thyroid hormone- a small, amino acid based hormone- is able to pass through the cell wall to have a direct effect Hormone effects (more!) 1. For a hormone to have an effect, the target cell must have a receptor for the hormone. 2. Hormone receptors are not static- the numbers change. 3. Receptor affinity for a hormone can vary Much hormone + many receptors of high affinity = more hormone effect. 2

3 Hormone effects ( still more!) Hormones travel in the blood free or bound to a carrier protein (generally, the lipid soluble). Most are removed from circulation by liver and/or kidney Hormone interactions Permissive- one hormone s presence is needed for full function of another Thyroid/repro Synergism- 2 hormones effects are increased by each others presence Gluc/epi Antagonism- the effect of one hormone diminishes the effect of another. Gluc/Ins Hormone controls 3 kinds of stimuli Humoral Hormones are released in response to blood levels of particular molecules/ions: glucose, Ca + Neural Hormones are released in response to stimulation by nerves, directly Hormonal One hormone stimulates (or inhibits) release of another Hormone controls Negative feedback Positive feedback A A B B Pituitary/hypothalamus some key points The pituitary connects to the hypothalamus by way of the infundibulum- containing nerves linking post. pit. and specific nuclei. Some hormones (made in the hypothalamus) travel down these linking neurons to be released from the post. pit. The hypophyseal portal system links (by blood vessels) the infundibulum to the anterior pituitary Releasing hormones Understand that when we talk about pituitary hormones, there is often a control higherup from the hypothalamus, commonly referred to as releasing hormones. For example, there is a hormone GHRH (growth hormone releasing hormone) from the hypothalamus. It causes release of GH from the pituitary. (see ) 3

4 Releasing hormones For example, there is a hormone GHRH (growth hormone releasing hormone) from the hypothalamus. It causes release of GH from the pituitary. Other examples: TRH (thyrotropin releasing hormone) GnRH (gonadotropin releasing hormone) PRH/PIH (prolactin releasing/inhibiting) others Anterior Pituitary Hormones Please read text 1. Growth hormone (p ) 2. TSH (616) 3. Gonadotrophs (= gonadotropin) (616) 4. Prolactin (616) 5. ACTH (616) Growth Hormone Stimulates growth- esp. of bone and muscle Inc. use of fats for fuel, sparing glucose Causes release of somatomedins (IGFs) from liver, skeletal muscle, bone inc. uptake of AA s to cells, sulfur to cartilage Anti-insulin raises blood sugar Growth Hormone Regulated by releasing hormones/inhibiting hormones Highest levels released during sleep Interesting note- GHIH inhibits TSH, GI and pancreas secretions. TSH Aka thyrotropin Release stimulated by TRH Inhibited by inc. blood levels of T3/T4, also by GHIH (which inc. w/ thyroid) ACTH Promotes release of adrenal cortical hormones, esp. glucocorticoids Promoted by CRH Daily cycle highest before waking Inc. by fever, hypoglycemia, stress 4

5 Gonadotrophs FSH and LH FSH promotes gamete production (sperm, egg) LH promotes gonadal hormones, ovulation GNRH promotes Feedback inhibition by FSH, LH Prolactin Promotes milk production Dec. PIH (dopamine) increases PRL Inc. by estrogen Posterior Pituitary Hormones ADH- P. 617 Oxytocin- p. 617 ADH In the hypothalamus are osmoreceptors - tracking concentration of blood- inc. concentration leads to ADH release Other triggers= pain, dec. BP, alcohol, nicotine, others AKA vasopressin- in high amounts, can cause vasoconstriction to raise BP Oxytocin Receptors on uterine tissue increase near end of pregnancy. Also stim by uterine stretch In breast tissue, causes release of milk w/ + feedback by nursing baby is thought to promote nurturing and affectionate behavior, that is, it acts as a cuddle hormone. p.617 The thyroid gland is situated in the neck, lateral on both sides to the thyroid cartilage, a little inferior. There are two lobes (one on either side) connected by the isthmus, with an occasional 3 rd lobe that runs superiorly from the isthmus in the midline. The blood supply is from the superior and inferior thyroid arteries 5

6 Thyroid Within the thyroid, follicles are formed- spheres lined by a cuboid epithelium. Filling the follicle is colloid. Within the colloid, is the protein thyroglobulin which is formed and secreted by the follicle cells Thyroid TSH promotes this process by : 1. increasing iodide into the follicle cells 2. increasing thyroglobulin production -TSH also directly stimulates release of formed hormone The thyroid concentrates iodine. The iodine (one or two ions) is bound to the amino acid tyrosine, then 2 of these (iodine+tyrosine) complexes are bound, forming T 4 (tetraiodothryronine=thyroxine) or T 3 ((triiodothyronine). These thyroid hormones are bound up in the thyroglobulin. Thyroid: C cells c for clear - they don t stain well Cells around the follicles (parafollicular cells) called C cells secrete the hormone Calcitonin The effect of calcitonin is to stimulate osteoblast activity, causing increases in calcium deposit to bone and bone growth. It also tells the kidneys to not conserve calcium ions Parathyroid Located on the posterior surface of the thyroid, contained in the capsule that wraps the thyroid Parathyroid Hormone(PTH): raises blood calcium by stimulating osteoclasts, intestinal absorption and urinary retention of calcium. (see p. 625) Hormone is secreted from chief cells in the parathyroid glands. PTH stimulates the release of calcitriol from the kidneys (tells the GI tract to absorb more Ca) Adrenals Sit on top of the kidneys Have a cortex (outer part) and a medulla (inner part) 3 zones: glomerulosa, fasciculata and reticularis 3 hormone classes from the cortex 1 hormone class from the medulla Adrenal cortex- source of corticosteroids Mineralocorticoids: Aldosterone (627) Conserves sodium at the cost of potassium Targets kidney tubules, sweat glands, saliva, pancreas Retaining sodium retention of water Why? - Comes from the zona glomerulosa - Increases sensitivity of salt receptive taste buds - Secreted in response to Na, BV, BP, inc. K 6

7 Aldosterone -regulation From kidney: cells in the juxtaglomerular apparatus release renin. This activates angiotensin 1, leading to angiotensin 2, leading to aldosterone release. (see 1003, 1010) In the blood, levels of K and Na directly stimulate/inhibit ACTH, under stress ANP- blocks renin, aldosterone secretion Adrenal cortical hormones Glucocorticoids- cortisol, corticosterone (629) - from fasciculata (and reticularis) - (-) feedback relationship with CRH - inc. rate of glucose and glycogen synth. - tissues use relatively more fat for fuel, sparing glucose for brain. (adipocytes release more FAs) - stored protein break-down encouraged -inc BP -inhibition of WBC function Adrenal cortical hormones Gonadocorticoids-Androgens (androstenedione, DHEA) - androgens, similar to those from the teste - some estrogens made - excess hormones here can result in masculanizing female or more rapid 2ary sex characteristics in males. Adrenal Medulla (catecholamine hormones) - epinephrine (adrenaline):norepinephrine - inc. glucose availability, fat mobilization, inc heart force and rate Adrenal Medulla (catecholamine hormones) (SEE 631) - blood directed to heart and skeletal muscle, away from GI tract Pancreas -located behind stomach, has a head about midline to the body, tail on the left. - developed as an outgrowth of the digestive tract - two functions discussed: endocrine and exocrine: exocrine related to digestive functions, will be covered later. 7

8 Pancreas (endocrine) Regions within the pancreas called the islets of Langerhans have the alpha and beta cells which make up the endocrine secretions of the pancreas α cells produce glucagon Β cells produce insulin Glucagon - Targets liver to release glucose from glycogen stores (glycogenolysis) - Targets liver to synthesize glucose (gluconeogenesis - Turned on by lowered blood glucose levels, symp. Stim. - Inhibited by inc. blood glucose, insulin, somatostatin (GHIH) Insulin - Targets liver to store glucose as glycogen (glycogenesis) - Targets adipose to synthesize fat from glucose - Targets body cells to take-up insulin (not liver, kidney, brain) - Promotes protein synthesis - Turned on by elevated blood glucose levels - somatostatin (GHIH) Pancreas endocrine function Insulin lowers blood sugar by opening the door to sugar for many body cells (brain and kidney have no receptors- can take in glucose as needed). It stimulates storage of sugar as glycogen, more energy storage in fat cells. Glucagon raises blood sugar by stimulating glycogen release from the liver, utilization of triglycerides, breakdown of protein to form new sugar. (See p. 633) Gonads (testes) Interstitial cells- testosterone 2ary sex characteristics, growth, Sustentacular cells Support sperm development (-) control with hormone inhibin and FSH and GnRH Gonads (ovaries) Follicle cells produce estrogens Estrogen stims development of uterus lining and oocyte growth (-) control with FSH and GnRH Corpus luteum produces progestins (progesterone) Affects uterus, enlarges mammary glands 8

9 Pineal gland (635) Makes melatonin from serotonin Melatonin high at night, low at daytime Functions (unclear) inhibit reproductive fxs--- plays a role in sexual maturity (by dec. GnRH?) Antioxidant Role in setting circadian rhythms Levels highest at night, lowest at mid-day Thymus- Thymopoietins, thymosins Located behind sternum. Reaches max size before puberty, then diminishes with age. Hormones apparently help develop and maintain immune functioning (in T cells, the T is for thymus) Kidneys Calcitriol : stims uptake of calcium in GI tract, kidneys, bone resorption. Turned on by PTH Erythropoietin: stims RBC production in marrow Renin: increased BP Heart Atrial Natriuretic Peptide (ANP) Secreted from cardiac tissue in response to excessive stretch of chambers Effect is to inc loss of Na and water Adipose Leptin: suppresses appetite, increases energy use, Missing ob gene results in leptin not being produced role in GnRH control, maturation of bone marrow cells, angiogenesis Resistin: decreases sensitivity of body cells to insulin GI tract- enteroendocrine hormones Many. See 638, 906 Stomach- Ghrelin (+others for GI control)* Stimulates appetite Levels relate inversely with body weight and nutritional status (resists weight loss) Target is hypothalamus *Whitney, Rolfes Understanding Nutrition 10 th edition Wadsworth Publisher,