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Hormonal Cascade System
Connection of hypothalamus and pituitary
• Hypothalamus to anterior pituitary to ultimate glands
– Releasing hormones– Amplification of signal– Negative feedback
• Posterior pituitary
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)
Synthesis of Peptide Hormones
• Proopiomelanocortin is precursor polypeptide for eight hormones
• Other genes encode only one hormone
Thyroid Hormone
• Iodination of tyrosine residues in thyroglobulin
• Proteolysis releases T3 and T4
Epinephrine
• Adrenal medulla• Derived from tyrosine
or phenylalanine• Targets hepatocytes
and vascular smooth muscle cells
• Begin with tyrosine or phenylalanine; hydroxylations
• Norepinephrine converted to epinephrine by PNMT
Neuronal and glucocorticoid regulation
Steroid Hormones
• Adrenal cortex, ovary and testes
• Derived from cholesterol• Cyclopentanoperhydro-
phenanthrene nucleus• Act on nuclear receptors
Steroid Biosynthesis
• Begin by forming 5-pregnenolone• Further modifications for specific steroids• Involves cytochrome P450's
Control of Steroid Synthesis
• Cell surface receptor activated• Stimulate conversion of
cholesterol
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)
Adrenal Hyperplasia
• 21-hydroxylase deficiency• Lack of cortisol and aldosterone• Buildup of androgens• Masculanization• Treated with cortisol
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
Vitamin D Synthesis
• D3 produced in skin• Further hydroxy-
lations to form active 1,25-(OH2)D
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
• 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
Vitamin D Deficiency and Toxicity
Deficiency• Rickets• Improper bone and cartilage formation
Toxicity• Hypercalcemia • Calcification in tissues, soft bones
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