Mode of hormone action through intracellular receptors, Biology

MODE OF HORMONE ACTION THROUGH INTRACELLULAR RECEPTORS -

  • Steroid hormones are lipid-soluble and easily pass through the cell membrane of a target cell into the cytoplasm.
  • In the cytoplasm they bind to specific intracellular receptors (proteins) to form a hormone receptor complex that enters the nucleus.
  • In the nucleus, the hormone receptor complex binds to a specific regulatory site on the chromosome and activates certain genes (DNA).
  • The activated gene transcribes mRNA which directs the synthesis of proteins and usually enzymes in the cyto- plasm. The enzymes promote the metabolic reactions in the cell.
  • The actions of lipid soluble hormones are slower and last longer than the action of water-soluble hormones.

1325_hormonal action by intracellular receptor.png

Hormones as Regulators (Feed Back Control). Hormones help in maintaining internal environment of the body. When the secretion of hormones is under the control of factors or other hormones it is called feed back control. The regulation of secretion of thyroxine from the thyroid gland is an example of such feed back control mechanism.

Feed back control is of two types.

(i) Positive Feed Back Control. If the level of thyroxine is less than normal limits in the blood, thyroxine level stimulates the hypothalamus to secrete more of TRH which results in increased secretion of TSH which in turn stimulates increased secretion of thyroxine. Such regulatory effect is called positive feed back control.

(ii) Negative Feed Back Control. The thyrotropin releasing hormone (TRH) horn the hypothalamus stimulates the anterior lobe of the pituitary gland to secrete the thyroid stimulating hormone (TSH). The TSH in turn stimu- lates the thyroid gland to secrete thyroxine. A high amount of thyroxine in the blood exerts an inhibitory effect on hypothalamus in such a way that less of TRHand TSH is produced respectively. This eventually results a decrease in thyroxine. This is called negative feed back control.

2171_hormonal action by intracellular receptor1.png

Posted Date: 10/2/2012 7:42:17 AM | Location : United States







Related Discussions:- Mode of hormone action through intracellular receptors, Assignment Help, Ask Question on Mode of hormone action through intracellular receptors, Get Answer, Expert's Help, Mode of hormone action through intracellular receptors Discussions

Write discussion on Mode of hormone action through intracellular receptors
Your posts are moderated
Related Questions
Q. From which germ layer do the liver and the pancreas originate? What are other organs and tissues made from that germ layer? The pancreas and the liver are originated from th

Out of 67,410 randomly selected surgeries tracked in a study in the UK, 2832 were followed by surgical site infections. a.    What is the best estimate of the probability of an

what are the general characteristicss of porifera

PROTOPLAST Cell without cell membrane (Henstein) It contains 1 or more vacuoles. In mature plant cells protoplast forms a peripheral layer called Primordial utricle.

The immune response involves the activities of proteins, cells, and the lymphatic system.

Explain Class Oligochaeta - Earthworms in details? This group of annelids includes the earthworms. Oligochaetes live in the soil or in fresh water habitats, and a few inhabit m

Define Phosphorous distribution in plasma? In plasma, phosphorus is distributed in different forms. Figure: Phosphorous distribution in plasma Inorg

Interaction of insect hormones in the process of metamorphosis The organs and the hormones usually included in metamorphosis of insects. This is since despite the fact that t

Which of the following serves as a controlled variable in a negative feedback system? A. Levels of hydrogen ions in the interstitial spaces of the brainstem. B. Blood plasma

Isoniazid  Serum aminotransferase activity increases in 10% to 20% of patients taking isoniazid, especially in the early weeks of treatment, but often returns to normal even wh