Endocrine System Chapter 16 Part II PDF

11 Endocrine System Chapter 16 - Part II Topics: Blood levels (transport, duration, removal) Target cell interactions Release control Pituitary gland anatomy Anterior pituitary hormones  Blood Hormone Levels...

11 Endocrine System Chapter 16 - Part II Topics: Blood levels (transport, duration, removal) Target cell interactions Release control Pituitary gland anatomy Anterior pituitary hormones  Blood Hormone Levels 10  Hormones circulate in one of two forms: 1. bound - steroid hormones attach to blood carrier proteins 2. free (unbound) - most peptide hormones lack carrier proteins Except thyroid hormone, carried by thyroxine-binding globulin (TBG)  Blood concentrations reflect hormone rate of release & speed of inactivation/body removal - hormone 1/2 life - length of time required for a hormone level to decrease in blood by 50% H2O-soluble (seconds) vs. lipid-soluble (hours to days) - hormones can be removed by target cell enzyme degradation or kidney/liver action - very low concentrations (μg(urine toexcretion) ng/mL) needed makes for a narrow desirable range (10 to 10 ) -6 -9 TBG carrier protein http://www.obfocus.com/images/TFT1.gif  Target Cell Interaction 9  Hormones interact w/ each other in a variety of ways at target tissues (different receptors) 1. permissiveness - one hormone cannot exert full effects without another hormone being present reproductive hormones + thyroid hormone = timely sexual development 2. synergism - one hormone’s effects are multiplied by presence of another hormone (effects on a target cell are additive) glucagon + epinephrine + cortisol =  blood glucose, long-acting 3. antagonism - one or more hormone(s) oppose action of another hormone glucagon  blood glucose level while insulin  it http://faculty.weber.edu/rokazaki/Zoology4220/Lecture5PDF.pdf Hormone synergy Hormone Release Control 8  Several stimuli trigger hormone secretion (release)  Stimulus types: 1. humoral - secreted in response to changing ion/nutrient blood levels (concentration effect) Low blood Ca2+ levels causes parathyroid hormone (PTH) release 2. neural - direct nerve fiber innervation stimulates release Sympathetic fibers stimulate adrenal medulla to releases epinephrine (adrenaline) 3. hormonal - hormone released by 1st gland causes 2nd gland to produce/release different hormone TRH TSH thyroid hormone (TH) (hypothalamus) (pituitary) (thyroid)  Most synthesis/release is controlled by a negative feedback system - very few by positive feedback Pituitary (Hypophysis) 7  Pituitary - unusual bi-lobed gland composed of two different tissues, secretes 8 major peptide hormones - connected to hypothalamus by a stalk-like infudibulum  Lobes: 1. neurohypophysis (posterior lobe) - composed of neural tissue originating in hypothalamus stores/releases hypothalamic-produced peptide hormones Does not synthesize any hormones… stores hypothalamic hormones/secretes them 2. adenohypophysis (anterior lobe) - composed of glandular tissue not originating in hypothalamus produces/secretes several peptide hormones Pituitary-Hypothalamic Relationships: Posterior 6  Neurohypophysis (posterior pituitary) - downward growth of brain hypothalamic neural tissue - stores/releases two hypothalamic peptide neurohormones Oxytocin, antidiuretic hormone (ADH) - hypothalamic-hypophyseal tract - neural transport pathway fo delivery of oxytocin/ADH to posterior pituitary hypothalamic nuclei fibers extend downward through infundibulum into posterior pituitary hypothalamic nuclei directly cause release of stored ADH & oxytocin hormones Pituitary-Hypothalamic Relationships: Anterior 5  Adenohypophysis (anterior pituitary) - upward growth of oral mucosa w/ no direct hypothalamic contact - 6 different cell types synthesize/release 6 peptide hormones Growth hormone (GH), Thyroid stimulating hormone (TSH), Adrenocorticotrophic hormone (ACTH), Follicle stimulating hormone (FSH), Luteinizing hormone (LH), Prolactin (PRL) - hypophyseal portal system - local blood capillary system linking hypothalamus w/ anterior pituitary hypothalamic hormones use capillaries to reach/stimulate anterior pituitary cells hypothalamic hormones - indirectly cause production/release of anterior pituitary hormones Anterior Pituitary: Hormonal Regulation 4  Hypothalamus sends its peptide “signaling” hormones to anterior pituitary via hypophyseal portal system 1. releasing hormones stimulates hormone synthesis/release Example: growth hormone releasing hormone (GHRH) 2. inhibiting hormones* - shuts off hormone synthesis/release Example: growth hormone inhibiting hormone (GHIH)  Several anterior pituitary hormones regulate activity of other endocrine glands Releasing or Inhibiting Hormones Thyroid stimulating hormone (TSH) will cause the thyroid gland to produce and release thyroid hormone (TH) * Hypothalamic releasing hormones do not always have a corresponding hypothalamic  Anterior Pituitary: Stimulation of Other Glands 3  Anterior pituitary releases tropic hormones that stimulate (hormonal stimulus) other endocrine glands to produce their own hormone(s) - thyroid-stimulating hormone (TSH) thyroid thyroid hormone - adrenocorticotropic hormone (ACTH) adrenal cortex corticosteroids - follicle-stimulating hormone (FSH), luteinizing hormone (LH) gonads estrogen/testosterone  All anterior pituitary hormones are (gonadotrophins) Stimulation Pathway amino-acid based peptides 1 Releasing hormone Tropic means “turning towards” so anterior pituitary 2 Tropic hormone hormone TSH “turns towards” the thyroid gland 3 Target hormone http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/hypopit/tsh.gif  Growth Hormone (GH, Somatotropin) 2  Characteristics: - anabolic hormone produced by anterior pituitary somatotropic cells, mobilizes stored fat while conserving glucose - feedback is regulated by antagonistic hypothalamic hormones Hypothalamic GHRH causes anterior pituitary GH production/release Hypothalamic GHIH (somatostatin) shuts off pituitary GH production  Functions: 1. increases body size/cell division (most cells) 2. promotes bone/skeletal muscle (major targets) protein synthesis 3. ↑ synthesis of growth-promoting insulin-like growth factors (IGF) or somatomedins (IGF promotes skeletal muscle hypertrophy) Baby fat http://1.bp.blogspot.com/_V3zFQ1SSqLw/TGr5_yDRgMI/AAAAAAAAAp0/leSQ_nfz7MM/s1600/fat+baby+3.jpg Thyroid Stimulating Hormone (Thyrotropin) 1  Characteristics: - TSH is produced by anterior pituitary thyrotrope cells, stimulates normal thyroid development/secretory activity - hypothalamic thyrotropin-releasing hormone (TRH) triggers TSH release by anterior pituitary - two negative feedback mechanisms (no inhibiting hormone) 1o - excess thyroid hormone (TH) in blood acts on both pituitary & hypothalamus glands blocking further TSH & TRH release, respectively 2o - GHIH reinforces inhibition of TRH release  Function: GHIH - causes thyroid gland to produce/release thyroid hormones (TH)