 Dear students, in this topic we shall discuss the synthesis and mechanism of release of catecholamine hormones. The catecholamines which include epinephrine and norepinephrine are synthesized from tyrosine. In this cycle, first, tyrosine is first converted into norepinephrine. This tyrosine is an amino acid which is converted into norepinephrine through a chain of reactions involving first transformation into dopa, then this dopa is transformed into dopa mine. This conversion occurs in the cytosol. The reactions are catalyzed by the enzymes tyrosine hydroxylase and dopa decarboxylase enzymes. Now dopa mine is incorporated into the granules where it is converted into norepinephrine. Since dopa mine is converted into norepinephrine into secretory granules and this enzyme is called beta hydroxylase, therefore dopa mine is converted into norepinephrine into granules. In the next step, norepinephrine becomes epinephrine. When there is methylation of norepinephrine, a methyl group is added to it and it is converted into epinephrine. This reaction is catalyzed by the enzyme phenyl ethanolamine and methyl transferase. This enzyme is actually in the cytosol, therefore, when norepinephrine is converted into epinephrine, then norepinephrine is first converted into cytoplasm from granules. In the cytoplasm, when it is converted into epinephrine, after this conversion epinephrine is again sent into the granules. Dear students, now we shall discuss the mechanism of release of catecholamine hormones from the granules and from the cell. Catecholamines are released as secretory granules from the chromaphen cells by exocytosis. Each chromaphen cell secretes either epinephrine or norepinephrine. The secretory granules, which contain epinephrine or norepinephrine, also contain ancafalin, ATP and a protein chromogranin. To this protein, the catecholamine hormones are bound. Once a pore is opened in the vasical, the catecholamine hormone liberates from the chromogranin protein and diffuses out of the vasical. This release of epinephrine or norepinephrine, it is controlled by pre-ganglionic sympathetic nerves. These nerves release acetylcholine as a neurotransmitter. When acetylcholine is released as a neurotransmitter, it causes chromaphen cells' conductance to calcium ions to increase. As a result of increased conductance of chromaphen cells for calcium ions, calcium influx into the cells occurs. As a result, calcium ions increase in the cells and the addition of calcium ions means that the action of the exocytosis of these hormones begins. Dear students, the release of catecholamine hormones is controlled by positive as well as negative feedback mechanisms. First, we shall discuss the positive feedback of catecholamine hormones. When catecholamine hormones release, they cause more blood flow to the adrenal glands. As a result, more secretion of these hormones occurs. This is the secretion of catecholamine hormones by increasing blood flow to the adenals. This is a positive feedback mechanism which increases the concentration of catecholamine. However, when large secretions of catecholamine are produced, then they cause negative feedback. This is a kind of self-control mechanism as we have seen that the catecholamine hormones release in the adenosine and its product of hydrolysis, that is adenosine, both have inhibitory effect on the release of catecholamine because they decrease the conductance of calcium ions into the chromophen cells. When the conductance of calcium ions of chromophen cells decreases, the result is that the exocytosis of secretive aziculose will decrease as a result of the release of catecholamine hormones.