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Chemical Control in Mammals

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Mammals secrete hormones via their endocrine glands to control many functions in the body including the stress response, digestion, reproduction, etc. Hormones are chemicals which bind to specific receptors on cells if present, and initiate a response. This is either directly by entering cells and binding transcription factors, or indirectly via a second messenger which then cascades the signal down and activates enzymes.



You love cats don’t lie. The pituitary gland secretes many different hormones as the master gland, with the ability to control other glands. These include growth hormones, thyroid stimulating hormones and hormones involved in reproduction and lactation. The thyroid gland secretes hormones involved in metabolism and protein synthesis, while the nearby parathyroid glands secrete hormones that control blood and bone calcium content.


The adrenal glands secrete hormones such as adrenaline and cortisol, involved in metabolism and immune function, while the pancreas secretes insulin and glucagon to maintain a steady blood glucose concentration. Finally, the ovaries and testes secrete hormones such as oestrogen, progesterone and testosterone at the direction of hormones produced by the pituitary. These act on the production of gametes, secondary sexual characteristics and metabolism.


Adrenaline mode of action via secondary messenger

Adrenaline is secreted by the adrenal glands in times of stress or exercise. It has the same effect as glucagon. Both of these hormones act via a second messenger. That is, they bind to the plasma membrane of cells and exert their influence from the outside by causing a cascade of enzymatic reaction events inside the cell which ultimately end up in their response. They chicken out of it, don’t blame the messenger.


The second messenger model includes adenylate cyclase, cyclic AMP (cAMP) and protein kinase. Epinephrine is another word for adrenaline.



Oestrogen mode of action via direct binding of transcription factors

Transcriptional factors are molecules which can bind DNA and thus initiate transcription. Most of the time these are inactive in the cytoplasm because they have an inhibitor attached to them.


Hormones like oestrogen which are crucial to immunity, bone development, female reproduction, etc. can bind to transcriptional factors and release their inhibitor. Oestrogen crosses the plasma membrane freely as it is lipid-soluble.


This enables the transcriptional factor to migrate from the cytoplasm into the nucleus via the nuclear pore, bind DNA and initiate transcription of specific genes.






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