Q.Enlist human endocrine glands. Describe the T.S. of thyroid gland and add a note on deficiency of thyroxine. OR Define 'evolution'. Give the principles of Darwin's theory of natural selection. Mention any 'one' objection to it.
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Start your 14-day free trial to unlock the full solution →Human endocrine glands: hypothalamus, pituitary, thyroid, parathyroid, adrenal, pancreas (islets of Langerhans), gonads, thymus, pineal.
The thyroid's follicular structure produces T3/T4 (deficiency causing cretinism/myxoedema/goitre). OR: Darwin's natural selection explains evolution through variation and differential survival, though it could not explain the source of variation itself.
Endocrine glands + thyroid + thyroxine deficiency: The major human endocrine glands are: the hypothalamus (neuroendocrine control centre), pituitary gland (master gland, controls other endocrine glands), thyroid gland, parathyroid glands, adrenal (suprarenal) glands, pancreas (specifically its islets of Langerhans), gonads (testes in males, ovaries in females), thymus gland, and pineal gland. In transverse section, the thyroid gland (a bilobed gland located on either side of the trachea, just below the larynx, with the two lobes joined by a narrow isthmus) shows a characteristic histology: it is made up of numerous small, spherical follicles, each lined by a single layer of cuboidal follicular epithelial cells and filled with a gel-like colloid substance, which stores the iodine-containing precursor protein thyroglobulin, from which the follicular cells synthesise and release the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Scattered singly or in small clusters between the follicles are parafollicular cells (also called C cells), which secrete a different hormone, calcitonin, involved in regulating blood calcium levels. Deficiency of thyroxine (hypothyroidism) has different effects depending on age of onset: in growing children, it causes cretinism, characterised by stunted physical growth, delayed skeletal development, and impaired mental development; in adults, chronic deficiency causes myxoedema, marked by a lowered basal metabolic rate, weight gain, lethargy, and puffiness of the face/skin due to fluid accumulation. A common underlying cause of thyroxine deficiency is dietary iodine deficiency, which additionally leads to simple goitre — a visible enlargement of the thyroid gland caused by compensatory hyperplasia of the follicular cells (stimulated by elevated TSH) attempting, unsuccessfully, to produce adequate hormone with insufficient iodine. …
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