Endocrine System PDF

# Endocrine System The endocrine system contains glands with no ducts, but their hormones are carried directly to the blood by blood sinusoids or fenestrated blood capillaries. It includes: - **Glands:** pituitary, supra renal, thyroid, parathyroid &pineal body. - **Masses of cells:** ovary, testis...

# Endocrine System The endocrine system contains glands with no ducts, but their hormones are carried directly to the blood by blood sinusoids or fenestrated blood capillaries. It includes: - **Glands:** pituitary, supra renal, thyroid, parathyroid &pineal body. - **Masses of cells:** ovary, testis, thymus. - **Scattered cells:** all over the body. ## Hormones are: - Chemical substances - Secreted by special cells - Affect distant organs - They regulate the biochemical reactions in the body - They regulate the processes of the body as the growth, maturation, regeneration & reproduction. ## Chemical structure of hormones: **1. Protein/Polypeptide Hormones:** - Follicle stimulating hormone (FSH) - Thyroid stimulating hormone (TSH) - Adrinocorticotrophic hormone (ACTH) - Leutinizing hormone (LH) - Prolactin (PRL) - Growth hormone (GH) - Antidiuretic hormone (ADH) - Oxytocin - Insulin & glucagon (pancreas) - Parathyroid hormone - Hypothalamic hormones - Calcitonin hormone **2. Steroid Hormones:** - Cortisol - Aldosterone - Estrogen - Progesterone - Testosterone **3. Amino acid Hormones:** - Thyroxine - Adrenaline - Noradrenaline ## Interrelation between the endocrine system & the Nervous system - Hypothalamo - Hypophyseal portal circulation - Hypothalamo - Hypophyseal tract ## Mechanism of action of hormones: The hormone to exert its action should bind to receptor. The receptors of hormones are: 1- Large proteins 2- Specific receptor for single hormone (key and lock) ## Locations of receptors - Surface of cell - for protein hormones - Cytoplasm - for steroid hormones - Nucleus - for thyroid hormones ## The receptors are dynamic. - **Up-regulation:** decrease hormone level - **Down-regulation:** increase hormone level. ## Mechanism of action of hormones: **1. Protein hormones & polypeptides, glycoprotein hormones (NON GENOMIC action):** - The hormone is named (1st messenger). - Hormone combines with a receptor on the cell membrane (protein can not cross the cell membrane), forming a hormone-receptor complex. - The hormone-receptor complex acts through a 2nd messenger formed, which can be: **a. Adenyl cyclase -- c-AMP - 2nd messenger system** - Hormone + receptor - Receptor binds to G protein - G protein activates ADENYL CYCLASE enzyme - Transformation of ATP to c-AMP (2nd messenger) - c-AMP activates PROTEIN KINASE - Phosphorylates proteins in the cell - Changes chemical reactions - Causes the effect - Phosphodiestrase breaks c-AMP to AMP **b. Inositol-diacyl glycerol - 2nd messenger system** - Hormone + receptor - Activates enzyme PHOSPHOLIPASE - C - This enzyme increases breakdown of phospholipid in the cell membrane into two 2nd messengers: - Inositol triphosphate (IP3): increases mobilization of Ca++ from mitochondria & endoplasmic reticulum (it performs the effect) - Diacyl glycerol (DAG): activates protein kinase C, which phosphorylates proteins. **c. c-GMP - 2nd messenger** - Activates the GENES to increase protein formation - form hormone action. **2. Steroid hormones (GENOMIC action):** - Steroid hormone passes the cell membrane to bind to a receptor in the cytoplasm, forming a hormone-receptor complex. - The hormone-receptor complex enters the nucleus, gets incorporated with the DNA; which causes transcription of DNA and forms mRNA (2nd messenger mRNA). - mRNA causes protein formation and forms hormone action. **3. Thyroid hormone (GENOMIC action):** - Thyroid hormones are very small and can pass the cell membrane. - They pass the cell membrane and nuclear membrane - They bind to a receptor in the nucleus - Increase transcription of DNA to form mRNA (2nd messenger) - Increase protein formation and form hormone action. ## Feed back control of hormones: **Def:** The mechanism by which the ENDOCRINE system maintains the level of the HORMONE secreted by certain glands constant in blood. - **Negative feed back:** If the HORMONE level increases in blood, the HORMONE inhibits the GLAND to decrease its secretion. ### Types of negative feed back: - **Short-short loop/Ultra short:** Hormone inhibits itself - **Short loop:** Hormone inhibits its releasing hormone - **Long loop:** Hormone inhibits the hypothalamus and pituitary - **Positive feed back:** Increase the LEVEL of hormone - stimulates secretion of the other hormone. - Eg increase estrogen increase LH ## Development of pituitary The pituitary gland develops from two sources: **Rathke's pouch** (at the roof of the stomodeum or future mouth) and **infundibulum** (at the floor of the diencephalon or future hypothalamus). - **Rathke's pouch** grows towards the diencephalon. The part connecting it to the stomodeum disappears while the cranial part enlarges, forming the ant lobe of the pituitary. - **Infundibulum** extends from the floor of diencephalon, descends to meet the pouch, and forms the post lobe of the pituitary. The infundibulum between the diencephalon and the pituitary remains containing the nerve fibers connecting both. It is the **Master of the endocrine gland**, measuring 12 x 8 x 6 mm and weighing 0.5 gm. ## Relations: The pituitary gland lies in the pituitary fossa with the following relations: - **Ant:** tuberculum sellae - **Post:** dorsum sellae. - **Sup:** diaphragma sellae and optic chiasma - **Inf:** sphenoid air sinuses. - **Lat:** cavernous venous sinus. ## Histology of the pituitary gland **A- Adenohypophysis:** - Adenohypophysis: (Pars distalis - anterior lobe, Pars tuberalis, & Pars intermedia) **B- Neurohypophysis:** - Neurohypophysis: It includes Pars nervosa, & infundibulum ### Pars distalis - It is formed of cells classified into 2 groups: - **Chromophobes (52%):** - Small cells with pale cytoplasm which has mild affinity for stains. - Some cells are granular may secrete hormones. - Some cells are non-granular & are considered stem cells. - **Chromophils (48%):** - They are classified into Acidophils (37%) and Basophils (11%) #### Acidophils (37%) - They are medium sized cells between chromophobes &basophils - They contain somatotrophs and mammotrophs. **a. Somatotrophs:** - Secrete growth hormone: - If increased before closure of epiphysis, it causes gigantism. - If increased after closure, it causes acromegaly. - If decreased, it causes dwarfism. - Spherical cells with central rounded nuclei and acidophilic granules. - **Special stain:** Orange G or Orangeophil **b. Mammotrophs:** - Secrete prolactin for milk secretion. - Oval cells with oval nuclei and acidophilic granules. - **Special stain:** Carminophil #### Basophils (11%) - They are the largest cells classified into 3 types: thyrotrophs, corticotrophs and gonadotrophs. **a. Thyrotrophs:** - Secrete Thyroid stimulating hormone (TSH), T3 and T4. - Rounded cells with rounded nuclei. - All cells have mitochondria, golgi, rER & secretory granules. **b. Corticotrophs:** - Secrete ACTH. - Rounded cells with eccentric nuclei. - Secrete endorphin and lipotropic factor. **c. Gonadotrophs:** - Secrete FSH and LH - Rounded cells with rounded nuclei. - All cells have mitochondria, golgi, rER & secretory granules. ### Pars Tuberalis - Basophilic cells. - Unknown function. - Some secrete gonadotrophins (FSH&LH). ### Pars Intermedia - Basophilic cells. - Rudimentary in humans, but in some species, they secrete melanocyte stimulating hormone. ## Neurohypophysis - It is formed of two parts: - **Infundibulum:** connects the hypothalamus with pars nervosa. - **Pars Nervosa:** does not secrete hormones. - It contains: - **Pituicytes:** supporting neuroglial cells. - **Nerve fibers:** No nerve cells, but axons of secretory cells from the hypothalamus, which carry neurosecretion to blood capillaries. - **Herring bodies:** acidophilic bodies, which are the accumulated secretions of nerve fibers. They contain oxytocin & vasopressin. - **Fenestrated blood capillaries:** surrounded by Herring bodies. ### Functions of pars nervosa - It stores ADH and Oxytocin secreted by the supraoptic & paraventricular nuclei of the hypothalamus. ## Hormones secreted by the anterior pituitary: - Thyroid stimulating hormone (TSH) - Adrenocorticotropic hormone (ACTH) - Follicle stimulating hormone (FSH) - Luteinizing hormone (LH) - Growth hormone (GH) - Prolactin (PRL) ## Hormones secreted by the posterior pituitary: - Antidiuretic hormone (ADH) or Vasopressin - Oxytocin **Important:** There are additional details within the images about specific functions of each hormone as well its controls. Let me know if you would like me to elaborate on any specific part of the information presented. I can also expand on the specific control mechanisms of the hormones provided they are available in the images.