2. Stress (cont.)

8. During stress, the priorities of the secretions of the hypothalamo-pituitary peripheral-endocrine axes are shifted in favor of the hypothalamo-pituitary-adrenocortical (HPA) axis. During stress: HPA GHRH GH GnRH FSH LH

9. Hypothalmo-Pituitary-Thyroid System

10. Figure 13-1: Diagrammatic representation of the thyroid gland

11. Figure 13-2

12. Table 13.3 Major Actions of Thyroid Hormones Calorigenesis Metabolism Brain maturation Behavior Growth & development

14. 3, 5, 3’, 5’ Tetraiodothyronine (thyroxine, T4) 3, 5, 3’ Triiodothyroine (T3)

15. Table 13-2: Some MORPHOLOGIC Changes in the Thyroid Gland with Aging FOLLICLES: - Are distended - Change in color - Epithelium flattened w/ reduced secretion Fewer mitoses Increased connective tissue; Fibrosis Atherosclerotic changes

16. Table 13-2 (con’t.): Some SECRETORY Changes in the Thyroid Gland with Aging Simultaneously decreased secretion and metabolic clearance of T4 with resulting essentially normal levels Failure of up-regulation of T3 nuclear receptors peripheral conversion of T4 to T3 TSH levels in 10% of the elderly, associated in antithyroid antibodies, present even in the absence of manifestations of hypothyroidism circulating T3 levels but generally within the normal (lower) range

17. Table 13-1: Some Critical Aspects of Thyroid Hormone Regulation 1.Major source of circulating T3 from peripheral deiodination of T4 (NOT from thyroid gland secretion) 2.The negative feedback at the pituitary anterior lobe is mainly through T4 (taken from circulation & converted into T3) 3.The peripheral deiodination of T4 depends on the physiological state of the organism. It allows an autonomy of response of the tissues to the hormones. 4.Deiodination can convert T4 (a less biologically active hormone) to T3 (a more active hormone). This conversion depends on the activity of the various deiodinating enzymes.

18. Figure 13-4

19. Basal Metabolic Rate from birth to 70 years old

20. Table 13-5 In the Elderly, Thermoregulatory Insufficiency Results from: heat production, body mass, muscle activity, shivering, sweating response, vasomotor responses, temperature perception.

21. Table 13-6 Autoimmune Diseases of the Thyroid Gland CharacteristicsGraves’ DiseaseHashimoto’s Thyroiditis Thyroid StatusHyperthyroidHypothyroid TSHGenerally undetectableNormal to elevated T4, T3 (serum)Above normalBelow normal Antibodies(ABs)Stimulatory ABs compete with TSH at receptor sites Loss of TSH control over thyroid function Some ABs block TSH actions Autoantibodies against thyroglobulin, T3, T4, thyroid destroy thyroid microsomal and nuclear components Generally present Lymphocytic InvasionLimitedMarked Female:Male RatioAs high as 10:1