2. 2 nd lecture: Communications among cells and tissues Classification of hormones in Several Ways: According to solubility According to chemical composition According to location of receptors

3. What Are Cell Signaling? Signal transduction at the cellular level refers to the movement of signals from outside the cell to inside The molecules responsible for Cell Signaling are called: Hormones (effector, ligand) They are signal molecules that communicate physiological and nutritional information between cells and tissues: The importance of Cell Signaling molecules: 1- To ensure coordinated function of the whole body. 2- To provide mechanisms through which the whole body can respond to environmental or nutritional changes.

4. definitions: Hormone is a substance that is synthesized in one organ and either: 1- Transported by the circulatory system to act on another tissue (paracrine action). 2- Or act on the cell in which they are synthesized without entering systemic circulation (autocrine action).

5. Hormone Receptors: Hormones initiate their biologic effects by binding to specific cell-associated recognition molecules called receptors. Hormone action is terminate when its molecules dissociate from the receptor. Target cell: It is the cell that possesses the ability to selectively bind a given hormone to its cognate(specific) receptor.

6. Hormones are classified according to several ways: 1) Solubility properties 2) Location Of Receptors: 3) Chemical composition. Classification Of Hormones

8. Hormones can be classified into two main groups: Group IIGroup I HydrophilicLipophilicSolubility Amino acids derivativesSteroids, Thyroid hormones Chemically NoYes Plasma Transport protein Short (minutes)Long (hours to days)Plasma half life Cell surface receptorIntracellular (cytosolic, nuclear) Receptor Second messengers: cAMP, Ca2+, phospho- inositols, tyrosine kinase Receptor-hormone complex Mediator

10. Hormones can be classified into three main groups: 1) Peptide hormones (Group-2): They are protein and glycoprotein in nature. 1-Pituitary hormones 2-Pancreatic hormones. 2) Steroidal hormones (Group-1): They are derivative of cholesterol : 1- Adrenal cortex hormones 2-The gonadal hormones 3- The placental hormones 3) Hormones derived from amino acids: They are derivative of amino acids. 1- Catecolamines (Group-2) 2- Thyroid hormones (Group-1).

12. A ccording to Mechanism Of Hormones Action Hormones can be classified into: A) Hormones acting through intracellular receptors B) Hormones acting through plasma membrane receptors

13. A) Hormones acting through intracellular receptors: They can be classified into : 1- Hormones acting through Cytoplasmic receptor: e.g. some Steroid hormones 2- Hormones acting through Nuclear receptor: e.g. Thyroid hormone (T3).

14. 1-The hormone is secreted from its specific endocrine gland into the circulation. 2- Carried with transport protein to its target cells. Glucocorticoid hormones ( ▲, G), Heat shock protein (hsp) 1)Hormones acting through Cytoplasmic receptor: Steroids hormones (Glucocorticoid)

15. 3- Hormone diffuse through cell membrane where it bind tightly to specific receptors in the cytoplasm. 4- binding of Hormone to the receptor forming to complex. 5- such binding dissociation of specific part from the receptor called heat shock protein (hsp 90) 6- This step called hormone-receptor activation. Glucocorticoid hormones ( ▲, G), Heat shock protein (hsp)

16. 7- the activated hormone-receptor complex moves into the nucleus and binds with high affinity to specific DNA sequence called Glucocorticoid- Response Element (GRE). 8- The Hormone- Receptor – GRE complex is now capable of binding one or more co-activator, resulting in activation of the gene transcription process. Glucocorticoid response element (GRE), Coativator (Δ+).

17. Activation of gene transcription mechanism production of specific mRNA leading to synthesis of specific protein (enzyme or other cellular component) exert its physiological effect on specific metabolic processes (activated or inhibited)

18. 2) Hormones acting through Nuclear receptor: e.g. Thyroid hormone 1-The hormone is secreted from the thyroid gland. 2- Binding with specific plasma transport protein till reach its target cells.. Thyroid hormones ( ● ), Thyroid response element (TRE), Corepressor 

19. 3- The hormone move directly into nucleus where: its receptor is already bind to (thyroid response element (TRE)+ Co-represor )Complex. 4- The hormone-receptor-TRE complex is capable of binding Co- activator activation of the gene transcription process.

20. 6- As a final result, the amount of specific protein is changed and consequently metabolic processes are influenced Thyroid hormones ( ● ), Thyroid response element (TRE), Coativator (Δ+) and Corepressor (  ).