Question

In: Anatomy and Physiology

Describes how cortisol regulates metabolism of carbohydrate, protein and fat. States the stages in the formation...

  1. Describes how cortisol regulates metabolism of carbohydrate, protein and fat.
  2. States the stages in the formation of thyroid hormone and the critical enzyme.

Solutions

Expert Solution

Cortisol is the most important glucocorticoid secreted from the zona fasiculata from the adrenal cortex. It is secreted by the stimulation of ACTH or adrenocorticotropic hormone from the anterior pituitary. Cortisol is a steroid hormone which is also known by the name hydrocortisone. As it is a steroid hormone, it acts by stimulating DNA dependent mRNA synthesis in the nuclei of the target cell.

Cortisol and Carbohydrate metabolism-

  • This helps in glucose formation by stimulating the liver for gluconeogenesis.
  • It has anti-insulin action on peripheral tissues. This leads to an increase in blood glucose levels.
  • Glycogen synthetase is increased leading to glycogen synthesis.

Cortisol and Fat metabolism-

  • Lipolytic Action- Increases lipase activity by helping other hormones such as growth hormone, catecholamines, etc.
  • Metabolism of fatty acids takes place in the liver as fatty acids are transported from adipose tissue to the liver.

Cortisol and Protein metabolism-

  • This hormone causes protein breakdown(especially in the skeletal muscles).
  • Hepatic transaminase is activated by cortisol that leads to destination and transamination- finally contributing to gluconeogenesis. Eg,

Stages in the formation of thyroid hormone-

  • Iodide trapping- Iodine is ingested from dietary sources. This iodine(I2) is converted into iodide(I-) in the body. This iodide is absorbed into the blood and is taken up by thyroid to make hormones.
  • Oxidation of iodide- Once inside the thyroid follicular cell, iodide is oxidized to Iodine with the help of thyroid peroxide. ( You may wonder why iodine directly cannot enter? This is because Thyroid follicular cells cannot take iodine directly but they take it's iodide form, hence after entering the cell they again get oxidized to form iodine which will help in hormone production).
  • Iodination or organification- Iodine enters the colloid and gets bound to thyroglobulin. Now iodine gets attached to tyrosine(amino acid). If one tyrosine is attached MIT ( monoiodotyrosine) is formed. If another tyrosine gets attached, DIT( diiodotyrosine) is formed. Hence at the end of this step we have MITs and DITs that are attached to thyroglobulin. Here thyroid peroxidase comes into play.
  • Coupling reaction- Now in the colloid we have MITs and DITs bound to thyroglobulin. Two DITs combine to form T4 or thyroxine hormone and one DIT and one MIT combine to form T3 or triiodothyronine hormone. This is again done with the help of thyroid peroxidase.
  • Storage and Release- Thyroid hormones are stored in the colloid with the help of thyroglobulin. When our body needs hormones, this thyroglobulin is acted upon by protease to release free T3 and T4 in the circulation. Thyroglobulin is recycled to be used again.

We can say that thyroid peroxidase is the critical enzyme. It helps in the oxidation of iodide, indication, and coupling reaction.


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