 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. Because 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 is converted into epinephrine. When methylation of norepinephrine is added to a methyl group, it is converted into epinephrine. This reaction is catalyzed by the enzymes phenyl ethanolamine and methyl transferase. This enzyme is actually converted into cytosol. Therefore, when norepinephrine is converted into epinephrine, then norepinephrine is first converted into cytoplasm outside the granules. In this 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 chromophine cells by exocytosis. Each chromophine cell secretes either epinephrine or norepinephrine. The secretory granules which contain epinephrine or norepinephrine also contain n-cafalin, 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. 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 chromophine cells' conductance to calcium ions to increase. As a result, of increased conductance of chromophine cells for calcium ions, calcium influx into the cells occurs. As a result, calcium ions increase in the cells and the increase in 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 way, the secretion of catecholamine hormones increases by increasing blood flow to the adenals. This is a positive feedback mechanism that 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 just seen that the catecholamine hormones released from the vesicle also have ATP. This ATP 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. The release of catecholamine also decreases.