Endocrine system General principle of endocrinology Co-ordinating system to regulate and integrate function of different cells - Nervous system -Endocrine system Neuro-endocrine system Hormone Molecules released by cell to act on the other cell 1 2 Mode of hormone delivery to target Mode of hormone delivery to target Endocrine (classical hormones) Neuroendocrine (neurohormone) Paracrine Autocrine Neurotransmitter 3 4 Endocrine glands and organs Endocrine cells usually grouped in glands Endocrine organs Thyroid gland Hypothalamus Thymus gland Adrenal gland Kidney ovary pituitary gland Stomach Pancreas testes 5 Endocrine glands and organs Endocrine glands Pituitary Thyroid Parathyroid Adrenal Endocrine organs Brain Heart Kidney Ovary Testes Pancreas ( islets) Placenta Liver GI tract 6
Hormone functions Maintain internal environment ( homeostasis) Chemical structure of hormones Protein: Growth hormone, Insulin Growth and development Glycoprotein: LH, FSH, TSH, HCG Energy production utilization & storage Reproduction Steroid: Vitamin D, Cortisol, Aldosterone Amine: Catecholamines,Melatonin, Thyroid H. 7 Eicosanoids: Prostaglandins, Thromboxanes 8 Feedback control of hormone secretion Negative feedback Positive feedback 9 10 Negative feedback system Positive feedback system + + Endocrine glands Target tissues Endocrine glands Target tissues - + 11 12
Example Mechanism of hormone action 1. Hormone recognition Cell surface receptors Specific Receptors Intracellular receptors Nucleus, cytoplasm, organells 13 14 H + receptor Hormone receptor complex Specificity Number Affinity Reversible Cell surface receptors Proteins, peptides, catecholamine and eicosanoids Binding of hormone to receptor initiates a series of events which leads to generation of so-called second messengers Intracellular receptors Steroids, Thyroid hormone and vitamin D Single H + Different R Different effects 15 the mechanism of action of these hormones is to modulate gene expression in target cells. 16 Mechanism of hormone action Secondary messengers 2. Signal transduction Cyclic AMP Cyclic GMP Hormone + hormone receptor Transducer protein ( G-protien) DAG 2nd messenger IP 3 Biological responses Calcium 17 18
Mechanism of hormone action 3. Biological responses Alter enzyme activity & concentration Alter cell protein Ion movement Cytoskeletal rearrangement Endocrine disorders 1. Hormone deficit 2. Hormone overproduction Endocrine gland/ Tumors (ectopic) 3. Hormone receptor defect Hormone resistance 19 20 Hypothalamus Hypothalamo-pituitary relationship Main function of hypothalmus is maintain body homeostasis Hypothalamic hormones 21 22 Hypothalamic Hormones Releasing hormones Inhibiting hormones Secreted into HT-PT portal system Hypothalamus-anterior pituitary relationship Stimulate or inhibit the anterior pituitary hormones 23 24
Hypothalamic H Corticotropin releasing Hormone (CRH) Pitutitary H ACTH Growth, development & metabolism Reproduction Thyrotropin releasing Hormone (TRH) TSH. Growth hormone releasing Hormone (GHRH) Growth H. Growth hormone inhibiting Hormone (GHIH) / Somotostatin Prolactin releasing Hormone (PRH) Prolactin inhibiting Hormone (PIH) /Dopamine Growth H. PRL PRL Gonadotropin releasing Hormone (GnRH) Gonadotropin H. 25 26 Posterior pituitary Hormones PVN SON 2 Hormones: Antidiuretic hormone (ADH) and Oxytocin Oxytocin & Vasopressin Synthesis in HT neurons PVN (oxytocin) & SON (ADH) Peptides, 9 amino acids, MW 1000 27 28 Vasopressin or Antidiuretic Hormones ADH increase insertion of water channels(aquaporins) Major role is antidiuretic action ADH + V 2 receptors camp Increase water permeability of collecting ducts via increase insertion of water channels (aquaporins) Increase water absorption via increase Sodium transport into medulla ADH cause vasoconstiction 29 30
ADH Abnormal ADH secretion ADH defect Plasma osmolarity Urine osmolarity Urine flow Water diuresis Diabetes inspidus (DI) (Pituitary or Nephrogenic types) 31 Urine volume Osmolarity & sp gr 32 Oxytocin Stimulation of milk ejection (milk letdown) - stimulates contraction of myoepithelial cells, causing milk to be ejected into the ducts and cisterns. Stimulation of uterine smooth muscle contraction at birth Sensitivity of uterus and breast to oxytocin during pregnancy Not necessary for intiation but slow labour in the absence of oxytocin Stop postpartum bleeding Establishment of maternal behavior 33 34 Stimulation physical stimulation of the nipples or cervix Inhibiting acute stress Catecholamine 35