Endocrine Organs: Thyroid and Parathyroid Glands
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| What is the functional units of the thyroid? | Secretory follicles
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| The thyroid gland develops as what? | A primordium originating as an endodermal thickening of the floor of the primitive pharynx.
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| During development the _______ grows ________ and forms a duct like invagination known as what? | Caudally, thyroglossal duct
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| During the downward migration the thyroglossal duct atrophies, leaving behind an embryonic remnant called what? | Pyramidal lobe
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| Around the 9th week of gestation, endodermal cells differentiate into plates of ________ that become arranged into ________. | Follicular cells, follicles
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| By week 14 follicles lined by follicular cells contain what? | Colloid
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| During the 7th week, epithelial cells lining the invagination of the 4th pharyngeal pouches are known as what? | Ultimobrachial bodies
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| Ultimobrachial bodies migrate toward the developing thyroid gland and become incorporated into what? | Lateral lobes
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| The ultiombrachial cells disperse among the thyroid follicles which gives rise to what? | Parafollicular cells
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| Follicles contain a gel-like mass called what? | Colloid
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| Follicular cells are responsible for the production of what? | Thyroid hormones (T3 and T4)
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| There is an extensive network of _________ ________ surrounding the capillaries. | Fenestrated capillaries
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| Thyroid hormone (T3 and T4) are what kind or hormones? | Iodinated tyrosine derivatives
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| What functions do thyroid hormone produce? | Regulate cell and tissue basal metabolism, heat production and influence body growth and development.
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| Thyroid hormone secretions are regulated by what? | TSH (released from the anterior pituitary gland)
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| What is the major component of colloid? | Thyroglobulin
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| 2 characteristics of colloid are? | 120 aa and it is strongly PAS positive.
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| Thyroglobulin is an inactive form of what? | Thyroid hormones
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| The thyroid is unique because it stores large amounts of its hormones in what manner? | Extracellularly
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| Thyroid hormones are absolutely essential for what? | Normal fetal growth
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| In normal pregnancy, both T3 and T4 cross the placenta and are critical for what? | Early brain development
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| Thyroid hormone deficiency during fetal development results in what? | Irreversible damage to the CNS (includes reduced neurons, defective myelination and mental retardation)
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| The combination of the CNS abnormalities and stunted body growth is known as what? | Congenital hypothyroidism (cretinism)
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| Parafollicular cells are also called what? | C cells
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| Parafollicular cells synthesize and secrete what? | Calcitonin (the thyroid gland also secretes calcitonin)
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| Calcitonin is the physiologic antagonist to what? | Parathyroid hormone
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| Calcitonin acts by suppressing what? | The resorptive action of osteoclast
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| Calcitonin also promotes what? | Calcium deposition in bones (increases the rate of osteoid calcification.
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| The secretion of calcitonin is regulated by what? | Blood calcium levels (high blood Ca levels stimulates secretion of calcitonin)
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| The parathyroid gland develops from what? | The 3rd and 4th pharyngeal pouches
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| The inferior parathyroid glands and the thymus are derived from what? | 3rd pharyngeal pouch
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| The superior parathyroid glands are derived from what? | 4th pharyngeal pouch
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| The principal (chief) cells differentiate during embryonic development and are functionally active in what? | Regulating fetal calcium metabolism
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| Principal (chief) cells are responsible for the secretion of what? | Parathyroid hormone (PTH)
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| Parathyroid glands secrete what? | PARATHYROID HORMONE
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| PTH has what effects? | Regulates calcium and phosphate levels in the blood (84 aa polypeptide)
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| Parathyroid hormone is absolutely essential for what? | LIFE
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| If the parathyroid is totally removed what happens? | Laryngeal muscles and other respiratory muscles go into tetanic contraction as blood calcium levels fall and death follows.
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| What effect does PTH have on bone? | Activates osteolysis by osteoclasts which releases calcium and phosphate into the blood.
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| What effect does PTH have on the kidney? | Excretion of calcium is decreased by PTH stimulation of tubular reabsorption which conserves calcium.
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| Urinary phosphate excretion is _______ by PTH secretion. | Increased
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| PTH regulates kidney conversion of 25-OH vit. D3 to what? | Hormonally active 1,25-(OH)2
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| How does PTH influence intestinal absorption? | Increases calcium absorption
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