FUNCTIONAL ANATOMY The thyroid (from Gk. thyroid, meaning a shield, because it shields the trachea) gland

the intensity of color is measured with a spectrophotometer. When the concentration of serum hormone is high, the color will be more intense and vice versa. ELISA technic may be used to measure the peptide hormones as well as some steroid hormones (eg, progesterone, recall progesterone circulates in the blood being bound with a serum protein). LISA technic can be used to measure any protein in the serum, provided the protein is antigenic. By ELISA technic a screening may be made to detect sufferers from AIDS. Regarding the technology, other variants (other than the mentioned above) of ELISA are also available. Further, a new technic, closely related to ELISA is EMIT (not described here). By EMIT technic, trace quantities of protein (having low molecular wt, hence unsuitable for ELISA) can be measured. 3. Flurimetric analysis Plasma cortisol can be estimated by this method The analysis requires a flurimeter. This is currently the method of choice for plasma cortisol estimation. 4. Cytochemical assay More sensitive than RIA, the method is unfortunately very complicated and requires great expertise. However, its potentiality is great. 5. Dynamic tests In cases, where the endocrine malfunction is only very mild, estimation of concentration of the hormone level in blood may not give clear clue. In such case, a drug, which either stimulates or depresses the hormone's secretion may be given and after the drug administration the hormonal concentration measured. Such tests are called dynamic tests. An example is metyrapone test (chap. 4, sec. VI, in assessment of 'adrenocortical status'). Some older methods 1. Estimation of the urinary metabolites : Progesterone is metabolized and part of the metabolites appear in the urine as pregnanediol. Urinary pregnanediol can be estimated by column chromatography followed by colorimetry. Therefore, from a 24 hour urinary sample, daily secretion of progesterone in the body can be assessed. This method of assessment of progesterone status in the body is still somewhat popular, but similar others are not so. For example, estimation of urinary metabolites of suprarenal cortical hormones (e.g., 17 ketogenic steroids, 17 ketosteroids), for assessment of suprarenal status in the body, was very popular till the 1960s but are now practically obsolete, because superior methods are now available. 2. Whether an endocrine gland is hyper or hypo functioning, or functioning normally, car, be assessed (i.e , endocrinal status determinated) by many indirect methods. Examples are : serum cholesterol/BMR estimation, to assess the thyroid status. With the introduction of the modern methods, importance of the indirect methods have fallen considerably. HORMONE DEGRADATION A portion of the hormone is degraded in the target organ Apart from this, liver is the principal site of hormone degradation and the degraded hormones are often removed via the kidney through urine and are called urinary metabolites of the hormone. SUMMARY & HIGHLIGHTS Hormones may be (i) peptide, (ii) steroid and (iii) amines. Receptors for (i) peptide hormones are in the target cell membrane whereas (ii) those for steroid and thyroxine are in the cytosol or nucleus Membrane receptors combine with the hormone→activate G protein (coupling unit)→activate the catalytic unit --3- now a 2nd messenger is produced. The 2nd messenger ultimately produces the biological effect. However, some peptide messenger hormones are, till now, not known to produce 2nd messenger. cAMP, DAG, Ca++ etc. are examples of 2nd messenger. Adenyl cyclase, PLC etc are examples of catalytic unit. Steroid hormones and thyroxme do not prduce 2nd messengers. Instead they cause increased production of RNA → more proteins (= enzymes and/or structural proteins). Clinically blood concentrations of most hormones can be measured by RIA or ELISA technics. Normally, hormones are present in exact quantities, neither more nor less. Very often, hormones, regulation is achieved by (i) hypothalamus, (ii) ant. pituitary both of which are influenced by feed back (-ve, usually). However, some feed backs do not operate on the hypothalamus. Control of some other hormones (eg. insulin, PTH) is achieved by feed back by blood constituents (glucose, Ca++). I. Functional anatomy 2 Chemistry 3. Bio synthesis 4. Carriage of the thyroid hormones in the blood. 5. Functions 6. Mechanism of action 7. Control of secretion 8. Degradation of thyroid hormones 9. Applied physiology : (a) Hypofunction. (b) Hyperfunction (c) Goiter (d) Drugs used (e) Assessment of the thyroid function (status). FUNCTIONAL ANATOMY The thyroid (from Gk. thyroid, meaning a shield, because it shields the trachea) gland, first described by Wharton in the 19th century, weighs around 20 gms in adult. On its posterior side, there are four parathyroid glands. (Removal of thyroid gland therefore can cause unintended removal of the parathyroid glands as well, this is of clinical significance). The gland is very vascular and the blood vessels receive sympathetic supply. The thyroid begins to function from the midterm of fetal life. Food iodine deficiency in the mother's diet may lead to hypofunction of the thyroid in the fetus and its consequent hazards. Microscopically the gland contains about 3 million follicles (fig 6.2.1), diameter of each follicle being about 200 uM Each follicle contains a structureless material called 'colloid'. Each follicle is lined by epithelial cells When the activity of the gland is low or moderate, the epithelial cells are cuboidal and the amount