Physiological processes controlled by hormones?

Transcription

1 : the study of hormones, their receptors, the intracellular signaling pathways they invoke, and the diseases and conditions associated with them. What are hormones? Major endocrine glands? Fig 7-2 Physiological processes controlled by hormones?

2 Hormones Known since ancient times Secreted by cells into the blood Transported to distant targets Effective at very low concentration Bind to receptors Hormone action must be of limited duration

3 Classification of Hormones 3 main types: Peptides and proteins Steroids Amines Differ on basis of synthesis, storage, release, transport and cellular mechanism of action (review Table 7-1)

4 Peptide (Protein) Hormones Synthesis as preprohormone posttranslational modification to prohormone then hormone Fig 7-4 Storage release? Short half-life (mins.) Most common type Fig 7-3

5 Cellular Mechanism of Action for Peptide Hormones Lipophobic how does message get into cell? Usually rapid cellular response because existing proteins are modified camp 2 nd messenger system most common

6 Steroid Hormones All derived from cholesterol Where synthesized? Fig 7-6 Storage release? Transport in blood? Longer half-life Mechanism of action Fig 7-7

7 Amine Hormones Derived from one or two amino acids 3 groups Tryptophan Melatonin Tyrosine Catecholamines behave like peptide hormones Tyrosine Thyroid hormones behave like steroid hormones Fig 7-8

8 Control of Hormone Release All endocrine reflex pathways have similar components Stimulus / input signal Integration (where?) Output signal (hormone / neurohormone) Physiological action Negative feedback turns off reflex One Hormone may follow > 1 reflex pathway pattern Fig 7-9

9 Simple Endocrine Reflex Endocrine cell acts as sensor AND integrating center no afferent pathway responds by secreting hormone Example: PTH increases [Ca 2+ ] in plasma Fig 7-10 Fig 6-31/➅

10 Fig 6-31/2 Neurohormone Reflex NH release by modified neurons upon NS signal 3 major groups of Neurohormones: Catecholamines from adrenal medulla Hypothalamic neurohormones from posterior pituitary Hypothalamic neurohormones acting on anterior pituitary

11 Neurohormones of Posterior Pituitary Other name of gland? 2 neurohormones Both are peptides (9 aa) transported in secretory vesicles via axonal transport Fig 7-12

12 Anterior Pituitary Secretes 6 Hormones (names?) A Trophic (tropic) hormone controls the secretion of another hormone Hypothalamic trophic hormones and the hypothalamic-hypophyseal portal system Fig 7-13

13 Negative Feedback Loops in the Hypothalamic-anterior pituitary axis Hypothalamus IC1 Ant. pituitary IC2 Endocrine gland IC3 Target tissue Hormones serve as negative feedback signals: Short-loop vs. long-loop negative feedback. Feedback patterns important in diagnosis of ES pathologies

14 Hormone Interactions Multiple hormones can affect a single target simultaneously Three types of hormone interactions: Synergism Permissiveness Antagonism

15 Synergism Combined action of hormones is more than just additive! Example: Blood glucose levels & synergistic effects of glucagon, cortisol and epinephrine Fig 7-18

16 Permissiveness Hormone A will not exert full effect without presence of hormone B. Example: Thyroid hormone & growth hormone Antagonism Antagonistic hormones have opposing physiological actions Hormone B diminishes the effect of hormone A (mechanisms?) Hormone Antagonists and Cancer: Tamoxifen

17 Endocrine Pathologies Unbalance leads to disease Due to: 1. Hypersecretion (excess) 2. Hyposecretion (deficiency) 3. Abnormal target tissue response

18 Hypersecretion: Due to? Iatrogenic (could lead to gland atrophy) Symptoms: Exaggerated Effects Examples: Cushing s Syndrome Gigantism Graves disease

19 Example: Hyperthyroidism (Review pp ) Most common cause: Graves' disease Autoantibodies (TSI) bind to TSH receptor and stimulate thyroid hormone production This activation by TSI is not subject to the normal negative feedback loop. Left exophthalmus in Graves disease

20 Hyposecretion: Due to? Symptoms: Normal effects of hormone diminished or absent Examples: Addison s disease Dwarfism Hypothyroidism

21 Example: Hypothyroidism Most common cause in US: chronic autoimmune thyroiditis (Hashimoto's thyroiditis = Chronic thyroiditis ) Other causes surgical removal of the thyroid gland radioactive iodine treatment external radiation a deficiency in dietary iodide consumption (=endemic or primary goiter)

22 Hypothyroidism cont. Symptoms: During childhood: stunted growth retardation lethargy low body temp. In adulthood: Bradycardia weight gain lethargy low body temp.

23 Abnormal Tissue Responsiveness Hormone levels normal, target unresponsive Due to: Abnormal hormone / receptor interaction Abnormal signal transduction

24 Diagnosis of Endocrine Pathologies Primary Pathology Defect arises in last integration center in the reflex Examples? Secondary Pathology Defect arises in one of the trophic integration centers Examples?

25 Which of the sets of lab values below would indicate Grave s disease? Explain. Patient Serum T4 Serum TSH A 6 µg/dl 1.5 µu/ml B 14 µg/dl.25 µu/ml C 2.5 µg/dl 20 µu/ml D 16 µg/dl 10 µu/ml Normal µg/dl µu/ml

26 Graves disease