ENDOCRINE SYSTEM PHYSIOLOGY INTRODDUCTION TO ENDOCRINE PHYSIOLOGY HORMONES

ENDOCRINE SYSTEM

PHYSIOLOGY

INTRODDUCTION TO ENDOCRINE PHYSIOLOGY

HORMONES ▪ CHEMICAL SUBSTANCES PRDUCED IN THE BODY THAT CONTROLS AND REGULATES THE ACTIVITY OF CERTAIN CELLS AND ORGANS. ▪ TRAVEL TO TARGET ORGANS VIA THE BLOODSTREAM ▪ SECRETED BY GLANDS ▪ BIND TO RECEPTOR SITES ON TARGET ORGANS ▪ ONE OF THE WAYS BY WHICH CELLS IN THE BODY COMMUNICATE WITH EACH OTHER ▪ PRODUCED BY ENDOCRINE GLANDS

FUNCTIONS OF HORMONES ▪ GROWTH AND DEVELOPMENT ▪ METABOLISM (PRODUCTION OF ENERGY) ▪ SEXUAL FUNCTION ▪ REPRODUCTION

CLASSIFICATION OF HORMONES THERE ARE THREE GENERAL CLASSES OF HORMONES ▪ PROTEINS & POLYPEPTIDES – PITUITARY HORMONES, PANCREATIC HORMONES ETC ▪ STEROIDS – THOSE SECRETED BY THE ADRENAL CORTEX, OVARIES, TESTES & PLACENTA ▪ DERIVATIVES OF TYROSINE (AMINES) – THYROXINE, TRIODOTHRYONINE, NOREPINEPHRINE, EPINEPHRINE

CLASSIFICATION OF HORMONES ▪ STEROID HORMONES – TESTOSTERONE, ESTROGEN, PROGESTERONE ▪ AMINE HORMONES – T 3, T 4, EPINEPHRINE, NOREPINEPHRINE ▪ PEPTIDE HORMONES – OXYTOCIN AND VASOPRESSIN ▪ PROTEIN HORMONES – INSULIN, GLUCAGON ▪ GLYCOPROTEIN HORMONES – LH, FSH, TSH ▪ EICONSANOIDS HORMONES - PROSTAGLANDINS In general, polypeptides with 100 or more amino acids are called proteins, and those with fewer than 100 amino acids are referred to as peptides

PROPERTIES OF HORMONES ARE SIMILAR TO ENZYMES, BUT: ▪ ENZYMES ARE NORMALLY PROTEINS ▪ HORMONES CAN BE PEPTIDES, AMINES OR STEROIDS

CELLULAR COMMUNICATION ▪ GAP JUNCTION ▪ AUTOCRINE ▪ PARACRINE ▪ ENDOCRINE ▪ NERVOUS ▪ NEUROENDOCRINE

HORMONES EXERT THEIR ACTIONS AS: ▪ PARACRINE ACTION ▪ ENDOCRINE ACTION ▪ AUTOCRINE ACTION

PARACRINE SIGNALING ▪ LOCALLY ACTS BETWEEN CELLS THAT ARE CLOSE TOGETHER ▪ MOVE BY DIFFUSION THROUGH THE EXTRACELLULAR MATRIX ▪ THE SIGNALS ELICIT QUICK RESPONSES AND LAST ONLY A SHORT AMOUNT OF TIME ▪ PARACRINE LIGAND MOLECULES ARE NORMALLY QUICKLY DEGRADED BY ENZYMES OR NEIGHBOURING CELLS – IN ORDER TO KEEP THE RESPONSE LOCALIZED EXAMPLE IS THE TRANSFER OF SIGNALS ACROSS SYNAPSES BETWEEN NERVE CELLS

ENDOCRINE SIGNALING ▪ SIGNALS FROM DISTANT CELLS ▪ ORIGINATE FROM ENDOCRINE CELLS ▪ USUALLY PRODUCE A SLOWER RESPONSE, BUT HAVE A LONGER-LASTING EFFECT ▪ LIGANDS RELEASED ARE CALLED HORMONES

AUTOCRINE SIGNALING ▪ PRODUCED BY SIGNALING CELLS THAT CAN ALSO BIND TO THE LIGAND THAT IS RELEASED ▪ THEREFORE THE SIGNALING CELL AND THE TARGET CELL CAN BE THE SAME OR A SIMILAR CELL ▪ OFTEN OCCURS DURING EARLY DEVELOPMENT OF AN ORGANISM ▪ REGULATES PAIN SENSATION AND INFLAMMATORY RESPONSES ▪ CELL CAN SIGNAL ITSLEF TO UNDERGO PROGRAMMED CELL DEATH IF INFECTED

DIRECT SIGNALING ACROSS GAP JUNCTIONS ▪ CONNECTIONS BETWEEN PLASMA MEMBRANES OF NEIGHBOURING CELLS ▪ ALLOW SMALL SIGNALING MOLECULES TO DIFFUSE BETWEEN CELLS ▪ SMALL MOLECULES (Ca 2+), ARE ABLE TO MOVE BETWEEN CELLS ▪ LARGE MOLECULES (PROTEINS AND DNA), CANNOT

CONTROL IN THE ENDOCRINE SYSTEM WITH FEEDBACK

MECHANISM OF ACTION OF HORMONES Hormone receptors: ▪ On the surface of the cell membrane, e. g. for peptides and amines. ▪ In the cytoplasm, e. g. for steroids. ▪ In the nucleus, e. g. for thyroid hormone or steroids.

MECHANISM OF ACTION OF HORMONES Intracellular signaling: ▪ Ion channel-linked receptors ▪ G-Protein-linked receptors ▪ Enzyme-linked receptors ▪ Intracellular hormone receptors and activation of genes.

MECHANISM OF ACTION OF HORMONES Second messenger mechanisms: ▪ Adenylyl cyclase triggering c. AMP second messenger system. ▪ Cell membrane phospholipid second messenger system.

MECHANISM OF ACTION OF HORMONES Some Hormones That Use the Adenylyl Cyclase–c. AMP Second Messenger System Adrenocorticotropic hormone (ACTH) Angiotensin II (epithelial cells) Calcitonin Catecholamines (b receptors) Corticotropin-releasing hormone (CRH) Follicle-stimulating hormone (FSH)

MECHANISM OF ACTION OF HORMONES Human chorionic gonadotropin (HCG) Luteinizing hormone (LH) Parathyroid hormone (PTH) Secretin Somatostatin Thyroid-stimulating hormone (TSH) Vasopressin (V 2 receptor, epithelial cells)

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