Endocrine System

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Hormones: regulate the internal environment in three ways -

  1. by controlling the rates of enzymatic reactions,
  2. by controlling the transport of ions or molecules across cell membranes
  3. by controlling gene expression and the synthesis of proteins.
The internal environment controlled by hormones include:

  1. growth and development 
  2. metabolism
  3. regulation of the internal environment (temperature, water balance, ions), and 
  4. reproduction

Graves Disease: Tired and weak, loosing weight, and hot flushing. Hyperthyroidism. Increased appetite.
Goiter: Enlarged thyroid gland, lack of iodine
DM: Polyuria, Polydipsia, and Polyphagia.
Castration: reduced sex drive and rendered males infertile, less aggressive. Testis may be implanted and will continue to function as it is under hormonal control.
Organotherapy: Hypothyroidism treated with injected thyroid


Hormones:

  1. Glands
    1. Pineal gland - Amine - Melatonin has unclear targets,  Circadian rhythms
    2. Thyroid - Amine / Peptide - 
      1. Triiodothyronine and thyroxine (T3 and T4), acts on may tissues, Metabolism, growth and development
      2. Calcitonin, acts on bone, Plasma calcium levels (minimal effect in humans?)
    3. Parathyroid - Peptides - Parathyroid hormone (PTH), acts on the bone and kidney, regulates plasma calcium and phosphate levels
    4. Thymus - Peptides - Thymosin, Thymopeoitin - Acts on lymphocytes, Lymphocyte development
    5. Pancreas - Peptides - Insulin, Glucagon, Somatostatin (SS), pancreatic polypeptide - metabolism of glucose and other nutrients
    6. Adrenal cortex -Steroid - 
      1. Aldosterone, Acts on the Kidney, Sodium and Potassium homeostasis
      2. Cortisol, many tissues, stress response
      3. Androgens, Many tissues, Sex drive in females
    7. Adrenal Medulla - Amines - Epinetherine, Norepinepharine, acts on many tissues, fight or flight response
    8. Testis - Peptide Steroid - 
      1. Androgen, acts on many tissues, Sperm production, secondary sexual characteristics
      2. inhibin, Anterior pituitary, Inhibits FSH secretion
    9. Ovaries - Peptide Steroid - 
      1. Estrogen and Progesterone, acts on many tissues, Egg production, secondary sexual characteristics
      2. Ovarin Inhibin, acts on the Anterior pituitary, Inhibits FSH secretion 
      3. Relaxin (Pregnancy), acts on Uterine muscle, Relaxes muscle 
    10. Placenta - Peptide Steroid - 
      1. Estrogen and progesterine, acts on many tissues, Fetal and Maternal development
      2. Chorionic somatomammotropin (CS),  acts on many tissues, Metabolism
      3. Chorionicgonadotropin (CG), acts on the Corpus Luteum of the ovary, Hormone Secretion
  2. Cells
    1. Heart - Peptide - Atrial Natriuretic Peptide (ANP) - acts on the Kidneys - Increases sodium excretion
    2. Liver - Peptide  - 
      1. Angiotensin, acts on the Adrenal Cortex, blood vessels and the brain - Aldosterone secretion; increases blood pressure
      2. Insulin Like Growth Factors (IGF) - Acts on many tissues - Growth
    3. Stomach and small intestine - Peptide - Gastrin, cholecystokinin (CCK), Sectretin - Acts on the GI tract and pancreas - assists in digestion and absorption of nutrients
    4. Kidney - Peptide Steroid - 
      1. Erythropoitin (EPO) - acts on the bone marrow - red blood cell production
      2. 1,25 Didydroxi-vitamin D3 (calcepharol) - acts on the intestine - Increase calcium absorption
    5. Skin - Steroid - Vitamin D3 - Intermediate form of hormone - Precursor of 1,25 dihydroxy-vitamin D3
    6. Adipose tissue - Peptide - Leptin and others, acts on the hypothalamus and other tissues, Food intake, metabolism, reproduction
  3. Cluster of neurons
    1. Hypothalamus - Peptides - Trophic hormones, acts on the Anterior Pituitary - release and inhibit pituitary hormones
    2. Posterior pituitary - Peptides - Oxytocin, Vasopressin (ADH)  - 
      1. Oxytocin acts on Breast and Uterus and 
      2. ADH acts on the kidney for water reabsorption
    3. Anterior pituitary - Peptides - Prolacctin, Growth Hormone (somatotropin, Corticotropin ACTH, Thyrotropin (TSH), Folicular Stimulating Hormone (FSH), Luteinizing Hormone (LH)
      1. Prolacctin, acts on the Breast - milk production
      2. Growth Hormone (somatotropin), - acts on many tissues - Growth and metabolism
      3. Corticotropin ACTH, - acts on the Adrenal Cortex - Cortisol Release
      4. Thyrotropin (TSH), - Acts on the tyroid Gland - Thyroid hormone synthesis and release
      5. Folicular Stimulating Hormone (FSH), - Gonads - Egg or sperm production, sex hormone production
      6. Luteinizing Hormone (LH) - Gonads - Egg or sperm production, sex hormone production
Hormones are secreted by a Cell or a Group of Cells: 
  1. Classic glands 
  2. isolated endocrine cells
  3. Neuron secrete neurohormones
  4. Immune system secrete cytokines
Hormones are Secreted into the Blood
  1. Secretion is the movement of a substance from the intracellular compartment to the extracellular compartment or external environment
  2. Traditionally hormones excrete to the blood
  3. Ectohormone: signal molecules secrete into external environment. Pheromones act on other organisms of the same species to elicit a physiological or behavioral response - human armpit may secrete volatile steroid sex hormones - for attraction and synchronisation of menstruation  
Hormones are transported to a distant target
  1. Growth factors, act locally - autocrines or paracrines
  2. lipid-derived signal molecule called eicosanoid
  3. One hormone may be made in many sites and have many functions - Cholecystokine (CCK):
    1. found in extracts of intestine - causes contraction of the gall bladder
    2. found in neurons of the brain - acts as a neurotransmitter and a neuromodulator
    3. CCK - currently famous for controlling hunger
Hormones exert their effect at Very Low Concentrations
  1. hormones act nanomolar range
  2. histamine - uses large concentrations in allergic reactions on many cells throughout the body
  3. cytokines - are synthesised and released on demand - hormones are usually made in advance and stored in the parent endocrine cell. Erythropoietin, was a hormone and is now a cytokine!  
Hormones act by binding to Receptors
  1. cellular mechanism of action
  2. One hormone may have a number of effects on different tissues, at different ages. Insulin has varied effects:
    1. Muscle and adipose tissue, it alters glucose metabolism
    2. Liver, it modulates enzyme activity - but no direct effect on glucose matabolism
    3. Brain - glucose metabolism is independent of insulin
  3. Remember - glucose enters cells by through a membrane transport process called facilitated diffusion
Hormone Action must be Terminated
  1. Insulin Hormone action is limited by limiting secretion, removing or inactivating insulin circulating in the blood, and by terminating insulin activity in target cells
  2. hormones in the bloodstream are degraded into inactive metabolites by enzymes found in the liver and the kidney. The metabolites from the degredation are  then excreted in the bile or the urine. The rate of a hormones breakdown is the half-life in the circulation.



 Brown-Squard Injected
himself with testosterone from
Bull testis - organotherapy

Arnold A. Berthold
(Roosters with transplanted testis
 - AA Berthold - 1849)



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