(6pts)A space alien from the planet Terrestria comes to you with a supply of sma

Question

(6pts)A space alien from the planet Terrestria comes to you with a supply of small laboratory animals. They want to know the function of a gland found in the trachea region called xenoid. (a) Given your vast knowledge of the endocrine and nervous system briefly describe one experiment that you can use to determine if the gland is regulated by the nervous or endocrine system. (b) Given that the hormone produced by this substance is hydrophobic and is a prehormone, propose a mechanism of action for this hormone. 6

Explanation / Answer

Ans: a) The gland Xenoid is nothing but thyroid gland surrounding the trachea of the gut. Thyroid gland is endocrine gland. This gland is regulated by two harmones from the brain. The pituitary gland and hypothalamus both control the thyroid. Hypothalamus secretes TSH Releasing Hormone (TRH), which makes the pituitary to produce thyroid stimulating hormone (TSH). THS affects thyroid gland to produce two harmones namely T3 (80%) (tri-iodothyronine) and T4 (20%) (thyroxine). The experiment to see whether the thyroid gland is regulated by endocrine system, you can remove the pituitary gland in the brain which stops the. In particular anterior pituitary lobe of the gland can be removed, which does not stop the entire function of pituitary, but stops producing T3 and T4 and thyroid cannot be stimulated to produce T3 and T4 harmones. OR we can do one more experiment, These releasing hormones travel through a specialized blood vessel system (known as the hypothalamichypophysial portal system) that connects the hypothalamus to the anterior pituitary gland. From here, they stimulate the synthesis and secretion of anterior pituitary hormones, which include thyroid-stimulating hormone (TSH), luteinizing hormone (LH), folliclestimulating hormone (FSH), growth hormone (GH), adrenocorticotropin hormone (ACTH), and prolactin. We can cut of this portal blood vessel.

b). Triiodothyronine (T3) and thyroxine (T4) contain amino acid tyrosine hence hydrophobic. Thyroxine (T4) is very important pre-harmone, Upon entering cell cytoplasm through thyroxine receptors T4 is converted to the active T3 by deiodinases (5'-iodinase). There are two deiodinases. One named iodothyronine deiodinase removes one iodine on ortho position of benzene ring of tyrosine of thyroxine (T4) pre-harmone to produce active T3. These are further processed by decarboxylation and deiodination to produce active iodothyronamine (T1a) and thyronamine (T0a). These hormones function via nuclear receptors called thyroid hormone receptors with corepressor molecules bind DNA or genes named thyroid hormone response elements (TREs) and affecting transcription and gene expression.

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