1.DAFINITION The word hormone is derived from the Greek word bormaein which means to execute or to arouse. In the classic definition hormones are secretory products of the ductless glands, which are released in catalytic amounts into blood stream and transported to specific target cells(or organs), where they elicit physiologic, morphologic and biochemical responses. The chemical messengers which perform hormonal functions are defined as Pic.

2. Endocrine hormones. These are the chemical messengers whose function is the transmission of a molecular signal from a classic endocrinal cell through the blood stream to a distant target cell. Neurocrine hormones. Neurohormones or peptides are released from a neurosecretory neuron into the blood stream and then carried to a distant target cells Example of such neurocrine substances are oxytocin and antidiuretic hormone (ADH). 3. Paracrine hormones. These are chemical messengers which after getting secreted by a cell are carried over short distance by diffusion through the interstitial spaces (extra cellular fluid) to act on the neighboring different cell types. For example, in islets of Langerhans somatostatin secreted by the delta cells acts on the alpha and beta cells. Autocrine hormones. These refer to those chemical messengers which regulate the activity of neighboring similar type of cells. Examples of autocrine hormones are prostaglandins. 4. Typesofgroupiihormonesbasedonthechemicalnatureof secondmessengerinvolvedintheirmechanismofaction 5. MCQ The following hormones increase the level of intracellular cAMP except? a) vasopressin b) glucagon c) parathyroid hormone d) 1,25-DHCC 6. A. Depending upon the chemical natuere 7. Hormone transport 8. 1. Feedback control 9. SPECIFICITY OF HORMONE ACTION IS BECAUSE OF SPECIFIC RCEPTORS. 10. The main mechanisms of hormone actions are: 11. Mechanism of action of hormone via tyrosine kinase activation 12. Mechanism of action of hormone via tyrosine kinase activity: A, by receptors that possess intrinsic tyrosine activity: and B, by receptors that do not possess intrinsic tyrosine activity. 13. MEASUREMENT OF HORMONES 14. Enzyme- linked immunosorbent assay method 15. THE END