1. Endocrine Control of Growth and Metabolism
Chapter 23
Endocrine Control of Growth and Metabolism

2. About this Chapter
How several key hormone pathways influence metabolism
How cortisol is produced & regulated; how it impacts many tissues
How thyroid hormones are regulated and their effect on targets
The role of growth hormone in growth & development
Calcium metabolism and its role in bones and cell regulations

3. Endocrine Control in Review
Hypothalamic – pituitary: feedback loop & trophic control
Hormones can have receptors on many diverse tissues
Usually initiating protein change or synthesis in target cells
Problems come from too much or too little hormone

4. Adrenal Cortex: Steroid Hormone Production
Figure 23-2: Synthesis pathways of steroid hormones

5. Cortisol Effects: Body Responses to Stress
Permissive effect on glucagon
Memory, learning & mood
Gluconeogenesis
Skeletal muscle breakdown
Lipolysis, calcium balance
Immune depression
Circadian rhythms

6. Cortisol Effects: Body Responses to Stress
Figure 23-4: Circadian rhythm of cortisol secretion

7. Control of Cortisol Secretion: Feedback Loops
External stimuli
Hypothalamic
Anterior Pituitary
Adrenal cortex
Tissues
Figure 23-3: The control pathway for cortisol

8. Endocrine Control: Three Levels of Integration
Figure 7-13: Hormones of the hypothalamic-anterior pituitary pathway

9. Cortisol: Role in Diseases and Medication
Use as immunosuppressant
Hyperimmune reactions (bee stings)
Serious side effects
Hypercortisolism (Cushing's syndrome)
Tumors (pituitary or adrenal)
Iatrogenic (physician caused)
Hypocortisolism (Addison's disease)

10. Thyroid Gland: Hormones and Iodine Metabolism
C-cells – calcitonin (covered later)
Follicle cells
Amine hormones:
thyroxine, T1, T2 & T3
 growth
 metabolism
Thermogenic

11. Effects of Thyroid Hormone
TH is concerned with:
Glucose oxidation
Increasing metabolic rate
Heat production
TH plays a role in:
Maintaining blood pressure
Regulating tissue growth
Developing skeletal and nervous systems
Maturation and reproductive capabilities

12. Thyroid Hormone Thyroid hormone – the body’s major metabolic hormone
Consists of two closely related iodine-containing compounds
T4 – thyroxine; has two tyrosine molecules plus four bound iodine atoms
T3 – triiodothyronine; has two tyrosines with three bound iodine atoms

13. Thyroid Gland: Hormones and Iodine Metabolism
Figure 23-7b: The thyroid gland

14. Thyroxine and its precursors: Structure & Synthesis
Figure 23-8: Thyroid hormones are made from tyrosine and iodine

15. Thyroxine and its precursors: Structure & Synthesis
Figure 23-9: Thyroid hormone synthesis

16. Synthesis of Thyroid Hormone
Thyroglobulin is synthesized and discharged into the lumen
Iodides (I–) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen
Iodine attaches to tyrosine, mediated by peroxidase enzymes, forming T1 (monoiodotyrosine, or MIT), and T2 (diiodotyrosine, or DIT)
Iodinated tyrosines link together to form T3 and T4
Colloid is then endocytosed and combined with a lysosome, where T3 and T4 are cleaved and diffuse into the bloodstream

17. Transport and Regulation of TH
T4 and T3 bind to thyroxine-binding globulins (TBGs) produced by the liver
Both bind to target receptors, but T3 is ten times more active than T4
Peripheral tissues convert T4 to T3
Mechanisms of activity are similar to steroids
Regulation is by negative feedback
Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback

18. T3 & T4 Control Pathways & Diseases from Malfunction
Hypothalamus
Anterior Pituitary
Thyroid
Hypothyroidism
Goiter (TSH )
Grave's disease

20. T3 & T4 Control Pathways & Diseases from Malfunction
Figure 23-12: Thyroid hormone pathway

21. Growth Hormone (GH): Functions & Malfunctions
Polypeptide H from hypothalamus/anterior pituitary
 growth (with T4, sex Hs, paracrines)
 metabolism
 protein & bone synthesis
Regulation – hypothalamus
Dwarfism
Acromegaly

22. Metabolic Action of Growth Hormone
Figure 16.6

23. Growth Hormone (GH): Functions & Malfunctions
Figure 23-16: Growth hormone pathway

24. Multiple Hormones Can Target a Cell/Tissue
Growth H
Somatomedins
Thyroxin
All have receptors on many tissues
Stimulate pathways for growth
Figure 7-17: A complex endocrine pathway

25. Bone Growth and Calcium Metabolism
Epiphyseal plate – new bone growth site
Chondrocytes, osteoblasts & calcification build bone

26. Bone Growth and Calcium Metabolism
Figure 23-19: Bone growth at the epiphyseal plate

27. Calcium Metabolism:
Maintain [plasma]: from diet, from bone "storage", recycled
Key roles: muscle contraction, bone support, cell signaling

29. Figure 23-20: Calcium balance in the body
Calcium Metabolism:
Figure 23-20: Calcium balance in the body

30. Control of Calcium Balance & Metabolism
Parathyroid H
Calcitrol
Vitamin D
Sun/diet
Calcitonin
Thyroid
C-cells
(Phosphate balance)
Figure 23-23: Endocrine control of calcium balance

33. Osteoporosis: Disease of Bone Growth & Calcium Metabolism
Bone reabsorption exceeds deposition
Osteoclasts mobilize Ca++ to plasma
Factors: inadequate Ca++ intake, genes, hormones, smoking
Figure 23-21: Osteoclasts are responsible for bone resorption

34. Summary
In addition to insulin and glucagon, metabolism is influenced by hormones from adrenal, thyroid, parathyroid and hypothalamus
Cortisol  catabolic activities responding to stress
Growth H  anabolic activities to promote growth
PTH, cacitrol, & calcitonin balance plasma [Ca++] for bone synthesis, muscle contraction, & cell signaling
Endocrine diseases result from pathway or glandular hypo or hyper secretion