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