Posterior Pituitary Thyroid Parathyroid Glands Posterior Pituitary Gland Neurohypophysis o Does not synthesize hormones o Consists of axon terminals from two groups of hypothalamic neurons o These neurons release two peptide hormones that enter capillaries Antidiuretic Hormone ADH or vasopressin Oxytocin OT o The posterior pituitary resembles neural tissue with glial cells nerve fibers nerve endings and neurosecretory vessicles o Antidiuretic hormone ADH and oxytocin made in the hypothalamus are transported into the neurosecretory vesicles where they are stored until a signal comes to stimulate release Posterior Pituitary Gland Oxytocin Synthesis ADH secretion Hypothalamus Oxytocin OT Synthesis Antidiuretic Hormone ADH or Vasopressin synthesis Antidiuretic Hormone ADH signals from osmoreceptors o Actions o ADH produced by cells in supraoptic nucleus in the hypothalamus in response to Prevents diuresis decreases urine production by stimulating the kidneys to return more water back to the blood Prevents water loss in sweat glands Causes constriction of arterioles Vasopressin o Regulation of ADH Dehydration or high osmolarity of blood ADH released from posterior pituitary Overhydration or low osmolarity of blood ADH release inhibited ADH release inhibited by alcohol Lack of ADH results in diabetes insipidus Inability of the kidneys to conserve H2O Excessive urination Ocytocin o Produced by cells in the paraventricular nucleus of the hypothalamus o Two target tissues Uterus during labor Mammary glands after glands o Regulation during labor Stimulation of uterus by baby s head causing stretch of cervix Oxytocin release from posterior pituitary Uterine smooth muscle contracts As the baby s head is pushed into the cervix oxytocin release increases Muscle contraction which pushes the baby further and elicits even more oxytocin release When baby is born the positive feedback loop ceases o Regulation after delivery Effect on mammary glands Suckling and hearing baby s cry stimulates oxytocin release Oxytocin causes muscle contraction milk ejection Lactation is the process of milk production and ejection Milk production is stimulated by Prolactin Prolactin and Oxytocin work together in lactation Thyroid Follicles o Follicular cells produce thyroid hormones 1 T3 triiodothyronine 2 T4 thyroxine or tetraiodothyronine Formation of Thyroid Hormones o Iodide trapping by follicular cells o Synthesis of thyroglobulin TGB o Release of TGB into colloid o Iodination of tyrosine in colloid o Formation of T3 and T4 by combining T1 and T2 together o Uptake and digestion of TGB by follicle cells o Secretion of T3 and T4 into blood binds to thyroid binding globulin TBG Actions of Thyroid Hormones o Increased basal metabolic rate by stimulating the cellular use of O2 to produce ATP increased cellular catabolism of glucose glycolysis fatty acids beta oxidation triglycerides lipolysis o Increase synthesis of Na K ATPase more ATP is used to pump ions ATP use produces heat which raises body temperature called the calorigenic effect o Enhance some actions of sympathetic nervous system by up regulating beta receptors increased heart rate contractility and blood pressure o Stimulate growth in conjunction with hHG and insulin particularly during development Thyroid Gland Disorders Hyposecretion o During development infancy and or early childhood results in dwarfism and severe mental retardation congenital hypothyroidism or cretinism o In the adult results in edema low heart rate muscle weakness sensitivity to cold low body temperature weight gain and mental dullness myxedema Thyroid Gland Disorders Hypersecretion o Hyperthyroidism Graves disease Weight loss nervousness tremor increased heart rate and BP exophthalmos edema behind eyes high body temperature sweating Thyroid Gland Disorders Goiter o Enlarged thyroid usually due to dietary lack of iodine o Occurs because TSH levels are high stimulates growth of thyroid gland o Can be associated with hyperthyroidism hypothyroidism or euthyroidism o Dietary lack of iodine leads to low thyroid hormone T3 T4 production stimulates TSH by negative feedback stimulates thyroid gland growth Portion of Thyroid and Parathyoid o Calcitonin secreted by parafollicular C cells of the thyroid gland Lowers blood Ca2 levels by inhibiting osteoclasts o Parathyroid hormone secreted by chief cells of the parathyroid gland Raises blood Ca2 levels by stimulating osteoclasts Parathyroid Hormone o Raises blood calcium levels o Increases activity of osteoclasts o Increases reabsorption of Ca2 by kidney o Inhibits reabsorption of phosphate HPO4 2 o Promotes formation of calcitriol active vitamin D3 by kidney which increases absorption of Ca2 and Mg 2 by intestinal tract