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.