hormonal cascade system connection of hypothalamus and pituitary
TRANSCRIPT
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Hormonal Cascade System
Connection of hypothalamus and pituitary
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• Hypothalamus to anterior pituitary to ultimate glands
– Releasing hormones– Amplification of signal– Negative feedback
• Posterior pituitary
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Some Major Hormones of Anterior Pituitary
Hormone Action
Thyrotropin (TSH) T4 and T3 release from thyroid
Luteinizing hormone (LH) Testosterone synthesis in Leydig cellsProgesterone synthesis in corpus luteum
Follicle-stimulating Spermatogenesis in Sertoli cellshormone (FSH) Estradiol synthesis in ovary; ovum maturation
Adrenocorticotropic Cortisol synthesis in adrenal cortexhormone (ACTH)
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Synthesis of Peptide Hormones
• Proopiomelanocortin is precursor polypeptide for eight hormones
• Other genes encode only one hormone
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Thyroid Hormone
• Iodination of tyrosine residues in thyroglobulin
• Proteolysis releases T3 and T4
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Epinephrine
• Adrenal medulla• Derived from tyrosine
or phenylalanine• Targets hepatocytes
and vascular smooth muscle cells
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• Begin with tyrosine or phenylalanine; hydroxylations
• Norepinephrine converted to epinephrine by PNMT
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Neuronal and glucocorticoid regulation
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Steroid Hormones
• Adrenal cortex, ovary and testes
• Derived from cholesterol• Cyclopentanoperhydro-
phenanthrene nucleus• Act on nuclear receptors
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Steroid Biosynthesis
• Begin by forming 5-pregnenolone• Further modifications for specific steroids• Involves cytochrome P450's
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Control of Steroid Synthesis
• Cell surface receptor activated• Stimulate conversion of
cholesterol
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Hormones that Stimulate Synthesis of Steroid Hormones
Steroid Hormone-producingHormone Structure Signal
Cortisol Adrenal cortex ACTH
Aldosterone Adrenal cortex Angiotensin II/III
Testosterone Leydig cell LH
Estradiol Ovarian follicle FSH
Progesterone Corpus luteum LH
1,25(OH)2 D3 Kidney Parathyroid hormone (PTH)
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Adrenal Hyperplasia
• 21-hydroxylase deficiency• Lack of cortisol and aldosterone• Buildup of androgens• Masculanization• Treated with cortisol
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Actions of Steroid HormonesHormone Target Tissue/Effects
Progesterone Uterine endometrium, mammary
Estradiol Female: gonadotropin secretion, uterine endometriumMale: inhibit testosterone synthesis
Testosterone Male: converted to dihydrotestosterone, Sertoli cells, secondary sex characteristics
Cortisol Stress adaptation, elevate liver glycogen, suppress immune responses
Aldosterone Kidney, Na+ reabsorption to raise blood pressure
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Vitamin D Synthesis
• D3 produced in skin• Further hydroxy-
lations to form active 1,25-(OH2)D
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Control of Serum Calcium Levels
• PTH produced in response to low serum calcium
• Synthesis of 1,25-(OH2)D induced by PTH
• 1,25-(OH2)D responsive genes in intestinal epithelial
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• 1,25-(OH2)D and PTH act together in response to low serum calcium
• High serum calcium calcium decreases PTH, inactive 24,25(OH2)D synthesized
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Vitamin D Deficiency and Toxicity
Deficiency• Rickets• Improper bone and cartilage formation
Toxicity• Hypercalcemia • Calcification in tissues, soft bones