Endocrine System PDF

The Endocrine System The Endocrine System Hormones – Messenger Substances in the Mammalian Organism  Endocrine vs. Exocrine Cells The Endocrine System  Hormones bring about...

The Endocrine System The Endocrine System Hormones – Messenger Substances in the Mammalian Organism  Endocrine vs. Exocrine Cells The Endocrine System  Hormones bring about their effects by altering the activity in the target cells. That is, they affect the ongoing metabolic activities of those cells. 1. By altering membrane permeability (or electrical state) 2. By stimulating the production of proteins or regulatory molecules in cells 3. By activating/deactivating enzymes in cells 4. By stimulating target cell to secrete itself The Endocrine System  Peptide and Steroid Hormones The Endocrine System Principles and Mechanisms of Action  Peptide Hormones Peptide hormones exert their effects by binding to specific receptors on the cell surface, initiating a signaling cascade inside the cell. This typically involves activation of second messenger systems such as cyclic AMP (cAMP), and calcium ions (Ca2+), leading to various cellular responses. Peptide hormones are water-soluble and cannot pass through the cell membrane, so they rely on these receptors to Examples transmitof peptide their The Endocrine System signals. hormones: Insulin, Growth hormone (GH),Thyroid stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH), Follicle-stimulating hormone (FSH) and luteinizing hormone (LH), Oxytocin, Antidiuretic hormone (ADH), T3  Water soluble Hormones (Peptide Hormones) They are generally 3 - 180 amino acids long Unlike steroid hormones, these do not cross the cell membrane but rely instead on a second messenger (a chemical equivalent inside the cell) The Endocrine System Cyclic AMP, Calcium ion, Cyclic GMP are known to act as second messengers. There are typically 2000-100,000 receptor proteins on the target cell membrane. When the hormone binds to the receptor on the target membrane, a trigger mechanism causes adenylate cyclase enzyme to make cAMP on the inner side of the membrane. cAMP activates protein kinase enzymes in the cytol which then carry on the desired metabolic reaction. E Steroid Hormones Steroid hormones enter the cell and bind to receptors in the cytoplasm. The hormone-receptor complex enters the nucleus where it binds with chromatin and activates specific genes. Genes (DNA) contain information to produce protein as diagrammed below. When genes are active, protein is produced. The Endocrine System Steroid hormones act more slowly than peptide hormones because of the time required to produce new proteins as opposed to activating proteins that are already present. Examples of Steroid Hormones: All sex hormones ( Testosteron, Oestrogen, Progesteron), Cortisol, Aldosteron  Lipid soluble hormones (The Steroids) This group includes sex hormones (e.g. testosterone, estrogen) and corticoids (hormones related to stress management) Being lipid soluble, they move easily from the blood stream, to the ECF, and penetrate the cell itself. Once inside the cell, they are free to bind to receptor sites directly on the DNA (or to some intermediate in the cytoplasm). Some may act by affecting membrane properties. The Endocrine System The hormone-DNA binding either inhibit or stimulate transcription of specific genes. The proteins so produced bring about the observable response. c Cholesterol and Steroid Hormones The Endocrine System The Endocrine System The Endocrine System  Glands Hormones adrenal cortex adrenocorticotropic hormone adrenal medulla aldosterone anterior pituitary antidiuretic hormone ovaries calcitonin testes cortisol pancreas epinephrine, norepinephrine parathyroid estrogen pineal FSH (follicle stimulating hormone) posterior pituitary glucagon The Endocrine System thymus gonadotropic hormones (FSH, LH) thyroid growth hormone insulin LH (lutinizing hormone) melatonin oxytocin parathyroid hormone prolactin progesterone testosterone thymosins thyroid stimulating hormone thyroxin triiodothyronine The Endocrine System  Hypothalamus and Pituitary Gland The Endocrine System hypothalamus Anterior pituitary gland Posterior pituitary gland  Hypothalamus and Pituitary Gland The Endocrine System The Endocrine System  Anterior Pituitary Hormones that Directly Affect the Body + Growth Hormone (GH or Somatotropic Hormone) stimulates body cells to grow. If too little hormone is produced, pituitary dwarfism results. The secretion of too much hormone results in a pituitary giant. Acromegaly is a genetic disease in which growth hormone is produced throughout a persons lifetime. + Prolactin The Endocrine System Prolactin is produced in quantity after childbirth. It stimulates the development of the mammary glands and the production of milk. It is also involved in the metabolism of fats and carbohydrates. + Melanocyte-Stimulating Hormone (MSH) This hormone causes skin color changes in some fishes, amphibians, and reptiles. In humans, it stimulates the melanocytes to synthesize melanin.  Anterior pituitary hormones that regulate other glands The pituitary also controls other glands and is often referred to as the "master gland". Three kinds of pituitary hormones that regulate other glands are discussed below. The glands that they regulate will be discussed in the following section. The Endocrine System Thyroid Stimulating Hormone (TSH) ® thyroid ® thyroxin Adrenocorticotropic Hormone (ACTH) ® adrenal cortex ® cortisol Gonadotropic Hormones (FSH and LH) ® ovaries and testes ® sex hormones; controls gamete production The Endocrine System  Anatomy of the Thyroid Gland I 1.Thyroid gland The Endocrine System 1a. Right lobe 1b. Left lobe 1c. Isthmus 2. Thyroid cartilage 3. Trachea 4. Subclavian artery  Anatomy of the Thyroid Gland II The Endocrine System  The thyroid produces thyroxin (also called T4 because it 4 contains 4 iodine atoms) and triiodothyronine (also called T3 because it contains 3 iodine atoms). Both T 4 and T3 have similar effects on target cells. In most target tissues, T4 is converted to T 3. They influence metabolic rate, growth, and development. Thyroxin production is regulated by a negative feedback The Endocrine Sstem mechanism in which it inhibits the hypothalamus from stimulating the thyroid. Thyroglobulin is a protein produced by the thyroid gland. It serves as a precursor in the synthesis of thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Thyroglobulin levels can be measured in blood tests to assess thyroid function and to monitor treatment for thyroid disorders, such as thyroid cancer. Not to be confused with the thyroxin binding globulin:TBG binds thyroid hormones in circulation. It is a transport protein responsible for  Actions of T3 and T4. T3 and T4 regulate growth and development, especially critical for the fetus, with requirements lasting past the time of birth. T3 and T4 impact upon numerous systems including muscle, bones, CNS development, myelination, dendritic formation, and synapse formation. T3 and T4 act as metabolic stimulants (calorigenic effects) to increase the rate of oxygen consumption by the heart, skeletal muscle, liver, and kidney. In adults, brain, spleen, and gonad metabolism is less susceptible to the effects of The Endocrine System T3 and T4. CNS input through the hypothalamus (TRH) in cold temperatures increase T3 and T4 secretion to increase metabolic rates. How the hormones increase metabolic rates has yet to be established. T4 and T3 have cardiovascular effects, increasing the heart rate and force of contraction to achieve increased cardiac output. In hyperthyroidism, the number of b-adrenergic receptors in the heart is increased (so sometimes b- adrenergic receptor antagonists are used as part of treatment).  Calcium Metabolism Calcitonin The thyroid gland also secretes calcitonin, which stimulates calcium deposition in the bones. This is the opposite of the action of parathyroid hormone. Calcitonin production is not regulated by the anterior pituitary. It's secretion is stimulated by high The Endocrine System calcium levels in the blood. Parathyroid glands The parathyroid glands are 4 small glands embedded in posterior surface of the thyroid gland.They secrete parathyroid hormone (PTH), which increases blood levels of Ca++.Bone tissue acts as a storage reservoir for calcium and PTH stimulates the removal of calcium from the bone to increase levels in the blood. It increases the kidney’s reabsorption of Ca++ so that less is lost in urine. It activates vitamin D which enhances Ca++ absorption from food in the gut. Secretion is regulated by the Ca++ level in the blood, (not hypothalamic or pituitary hormones). Organs involved in the metabolism of calcium Bones: The primary reservoir of calcium in the body, where it is stored in the form of hydroxyapatite crystals. Intestines: Responsible for absorbing calcium from the diet into the bloodstream. Vitamin D plays a crucial role in enhancing calcium absorption in the intestines. Liver: The liver plays a role in calcium metabolism by producing a hormone called calcidiol, which is then activated to calcitriol, the acive form of vitamin D, in the kidney. Calcitriol helps regulate calcium absorption in the intestines, thus influencing calcium levels in the bloodstream. Additionally, the liver stores and releases calcium as needed, contributing to overall calcium homeostasis in the body. Kidneys: Regulate calcium levels in the blood by excreting excess calcium through urine or retaining it when levels are low. Parathyroid glands: Secrete parathyroid hormone (PTH), which helps regulate calcium levels by stimulating the release of calcium from bones, increasing calcium absorption in the intestines, and  Vitamin D and Calcium Metabolism The Endocrine System The Endocrine System Calcium Metabolism  Adrenal/ Suprarenal Glands The Endocrine System  AdrenalCortex The outer layer of an adrenal gland is the adrenal cortex. It produces three kinds of steroid hormones. These are glucocorticoids, mineralocorticoids, and small amounts of sex hormones. The major glucocorticoid is cortisol and the major mineralocorticoid is aldosterone. Cortisol (A Glucocorticoid) The Endocrine System Glucocorticoids are produced in response to stress. Cortisol raises the level of glucose in the blood by stimulating the liver to produce glucose from stored non-carbohydrate sources such as proteins and lipids and to release it into the blood. Cortisol reduces swelling by inhibiting the immune system.. The drug prednisone, derived from cortisol, is used to treat inflammation.  Aldosterone (AMineralocorticoid) Aldosterone secretion is not under the control of the anterior pituitary. It acts primarily on the kidney to promote absorption of sodium and excretion of potassium. Increased sodium levels contribute to the retention of water and thus increased blood volume. In the absence of aldosterone, sodium is excreted The Endocrine System and the lower sodium levels result in decreased blood volume and lower blood pressure. The presence of too much blood in the circulatory system stimulates the heart to produce atrial natriuretic factor. This hormone inhibits the release of aldosterone by the adrenal cortex and ADH by the posterior pituitary causing the kidneys to excrete excess water. The loss of water and sodium contribute to lowering the blood volume.  Adrenal Medulla The adrenal medulla is composed of modified neurons that secrete epinephrine and norepinephrine (adrenaline and noradrenaline) under conditions of stress. These hormones are released in response to a variety of stresses and stimulate the fight- or- flight The Endocrine System response of the sympathetic nervous system. It results in a faster heart rate, faster blood flow, and dilated airways to facilitate oxygen flow to the lungs. In addition, the level of glucose in the blood is increased to make energy more available. Their secretion is controlled by brain centers (including hypothalamus) via sympathetic nerves, not by pituitary hormones.  The “Stress Reaction“ The Endocrine System  Sexual Hormones, Fertility,Reproduction and Pregnancy The Endocrine System The Endocrine System