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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

Metabolic Action of Growth Hormone Figure 16.6

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

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

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

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

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

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

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

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

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