Hormonal Cascade System Connection of hypothalamus and pituitary

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