Endocrinology | Hormones | Physiology PDF

Okay, here is the transcription of the provided text into a markdown format. ### Endocrinology * It is the science that deals with the study of the **endocrine system** (endo = internal, crine = secretion) * Endocrinology is the study of communication within a living organism through hormo...

Okay, here is the transcription of the provided text into a markdown format. ### Endocrinology * It is the science that deals with the study of the **endocrine system** (endo = internal, crine = secretion) * Endocrinology is the study of communication within a living organism through hormones. * Hormones are the chemical messengers of the endocrine system. | Endocrine glands | Exocrine glands | | :--------------------------------------------- | :---------------------------------------- | | ductless | have ducts | | Secrete their products (hormones) into the blood | Secrete their products to the outer surface or the lumen of GIT | | Can reach distant tissue | Can not | ### Control systems of the body The image depicts a flow chart comparing the nervous system and the endocrine system. * **Nervous System** * Fast * Stimulation of nerves → rapid effect * Secretes neurotransmitters * **Endocrine System** * Slow * Stimulation of glands → slow or delayed effect * Secretes chemical transmitters (hormones) The aim of these two control systems is to maintain homeostasis (maintenance of constant condition in internal environment). ### General endocrinology: 1. Definition of hormones. 2. Classification of hormones. 3. Properties of hormones. 4. Factors regulating the effect of hormones 5. Hormone cycle. 6. Biological half life of the hormone. 7. Regulation of hormone secretion. ### Hormones Hormones are chemical messengers released by: * **endocrine glands** (general Hs, transmitted by blood) or * **specialized tissues or cells** (local or tissue Hs, act locally) * in minute amount and regulate the functions of many organs. **Classification** 1. The site of release and the site of action 2. The chemical nature 3. The solubility ### 1. The site of release and the site of action | | | | :--------------------------------------------------------------- | :---------------------------------------- | | **General (endocrine) hormones** | **Local (tissue) hormones** | | secreted from endocrine glands | secreted from specialized tissues or cells in minute amount and act locally | | in a minute amount directly into the blood and regulate the function of many organs | | | Examples: | | | **Autocrine** (inhibin &follistatin)The secreted Hs can regulate the activity of the same cells that produce them | **Paracrine** (prostaglandins)The secreted hormone diffuses through the interstitial fluid usually to influence adjacent cells.. | | **Secreted from glands**: | **Neurocrine** (Ach) secreted from nerve cell and regulate the function of adjacent nerve cell or muscle via synapse or neuromuscular junction | | • Outside the CNS (Endocrine glands) | **solinocrine** (gastrin, secretin) secreted directly into lumen of gastrointestinal, respiratory and reproductive tracts | | • Inside the CNS (Neuro-endocrine glands) | | ### 2- The chemical nature | Protein | Polypeptide | Amino acid derivatives | Eicosanoids | Steroids | | :--------- | :---------------------- | :---------------------- | :------------------------------------------------------------------------- | :----------------------------------------------------------------------- | | More than 100 A.A. | Less than 100 A.A. | Derived from tyrosine: | derived from unsaturated fatty acid (arachedonic acid). Include: | They are lipid soluble, derived from **cholesterol**. They include:| | Water Soluble| Water soluble. | Dopamine, epinephrine, Norepinephrine, thyroid Hs. | Prostaglandins, Prostacyclin, Leukotriens, Thromboxane. | Androgens, Estrogens, Progesterone, Corticosteroids) | | Some anterior pituitary Hs.| Ex. | from histidine:- Histamine | | | | Ex. | hypothalamic RF, posterior pituitary hormones(oxytocin & ADH), Calcitonin, Parathormone, Insulin | from tryptophane: Serotonin, melatonin | | | | PRL, TSH, GH, FSH, LH | ### ### 3. The solubility * **Fat-soluble** * Steroids * Sex Hs. (female & male) * Adrenal cortex Hs.(corticosteroids) * Thyroid * $T_3 \& T_4$ * Fatty acid driv. * Prostaglandins * Prostacyclins * Leukotriens * Thromboxans * **Water-soluble** * All other hormones ### Properties of hormones * **Release**:Hormones are secreted in minute amount, synthesis and release are controlled by body needs. * **Specificity and high affinity**:Hormones affect specific target cells that have high affinity specific receptors to capture the low concentrated hormones from extracellular fluid * **Storage**:\ Water-soluble hormones are stored in the cytoplasm of producing cells in the form of granules and vesicles.\ Thyroid hormones (fat-soluble) are stored outside the cells producing them and inside follicles and surrounded by the producing cells\ Steroid hormones (fat-soluble) do not stored but synthesized according to the body needs. ### Pattern of Release | Nearly constant level | Pulsatile manner | Circadian rhythm | | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :------------------ | :------------------------------------------------ | | Thyroid hormones, prolactin in non-lactating animals, parathormone | (GH, GnRH, LH, FSH). | (glucocorticoids and ACTH) | | The image includes a graph with a stable horizontal line, this graph displays a nearly stable level | | | | | | | | The image includes a graph with a series of repeating spikes in the level, this graph displays a repeated spike pattern. | | | | | | | | The image includes a graph of level against time, with an oscillating wave-like shape, this graph displays the normal diurnal rhythm of hormones (e.g) cortisol | | | ### Factors regulating the effect of hormones The image is a cycle diagram showing factors regulating hormones 1. The concentration of the hormone 2. The presence of target tissue and active receptors 3. Hormone Interactions 4. The presence of specific antibodies against hormones 5. Vitamins ### Factors regulating the effect of hormones 1. **The concentration of the hormone:** * effect of some hormones is directly proportional with their concentration e.g., insulin. * effect of others are inversely proportional with their concentration e.g., estrogen. * Physiologically low estrogen level stimulates FSH, while physiologically high level inhibits FSH and stimulates LH, while abnormally high estrogen level inhibits both FSH & LH, this is called triple effect of estrogen). 2. **The presence of target tissue and active receptors** * Gonadotropic hormones do not affect castrated animals or if the receptors are inactive or occupied by any receptor blocker. * Insulin can not decrease blood glucose levels if its receptors decrease. 3. **Hormone Interactions** **(1) Synergistic effects** * When two or more hormones work together to produce a particular result * These effects may be additive or complementary * **Additive**: The action of epinephrine and norepinephrine on the heart. Each of these hormones separately produces an increase in cardiac rate; when acting together, they stimulate greater increase in cardiac rate * **Complementary effect**: The synergistic action of FSH and testosterone; each hormone separately stimulates a different stage of spermatogenesis during puberty. **(2) Permissive effects** * when it enhances the responsiveness of a target organ to the second hormone or when it increases the activity of the second hormone. * Ex: exposure of the uterus to estrogen, for example, induces the formation of receptor for progesterone, which improves the response of the uterus to progesterone. **(3) Antagonistic effects** * the actions of one hormone antagonize the effects of another. * Ex1: Lactation during pregnancy, is inhibited because the high concentration of estrogen in the blood that inhibits the secretion and action of prolactin. * Ex2; the action of insulin and glucagon. 4. **Presence of specific antibodies against hormones:** They come from the injection of protein or polypeptide Hs for a long period. The produced antibodies antagonize the hormone's action (e.g., insulin injection in diabetic patients). 5. **Vitamins:** * Vitamin Cis essential for the function of the adrenal gland Hs, * vitamin E for the action of gonadal Hs, * vitamin Bx for the function of thyroid gland Hs, * vitamin D is essential for the function of the parathyroid gland Hs. ### Hormone cycle * It is the period from the synthesis of the hormone by endocrine gland until its utilization by target tissue, inactivation and excretion from the body. The image shows a cycle diagram 1. Hormone synthesis:• Protein and peptide hormones are synthesized in rER of the cells producing them• Steroid hormones are synthesized by mitochondria and SER of the cells producing them• Thyroid hormones are synthesized in the colloid of thyroid follicles through lodination of tyrosine residues attached to thyroglobin 2. Storage. 3. Release (hypothalamic releasing Hs., pituitary tropic Hs. and hormone metabolite). 4. Transport (free in water soluble Hs. and bound on fat soluble Hs.) 5. Utilization (by target tissue inactivation and excretion ### 5. Hormone utilization, inactivation and secretion * When a hormone binds to its receptors and performs its function, It is known as hormone utilization. * Termination of the action of a hormone usually requires dissociation of the hormone from the receptor. * Some hormones are inactivated in liver and kidney where they are excreted in bile and urine. ### Biological half life ($t_{1/2}$) of a hormone * It is the time after which half the amount of the hormone available at a certain time (0 time) is cleared (disappeared) from the circulation. * Tissue utilization of the hormone * Frequency of hormone administration * i.e., decreased when the $t_{1/2}$ of the hormone is long | | | | :--------------------------------------------------------------- | :---------------------------------------------------------------------------------------- | | A relatively short biological $t_{1/2}$ as compared to normal Indicates Increased utilization of the hormone and vice versa. | For administration of exogenous hormone as a treatment, the frequency of hormone administration depends on its $t_{1/2}$ | ### Mechanism of hormone action | | | | | :------------------ | :--------------------------- | :---------------------- | | hypothalamus | Steroid H. | Derived from a.a. | | Adrenocorical | gonadal h. | & thyroid | | pancreatic | cytoplamic R | R nuclear | | Cell membrane r | | | | 2Ry messenger | | | | Change the | synthesis | Synthesis new proteins | ### Regulation of hormone secretion * I. Genetic * II. Environmental * III. Feed back * Negative (-ve) * Positive (+ve) ### I. Genetic control * **Genetic structure** is the primary factor that determines the activity of endocrine glands. * This means that errors in genetic structure may result in disorders of endocrine secretion. * These disorders may be hypofunction or hyperfunction secretion of abnormal Hs ### Environmental Factors | High temperature | Emotion | Intake of food | Prolonged excercise | Sleep | | :-------------------- | :------------------------------------------------------------------------------------------------------ | :------------------- | :------------------------------- | :------------- | | Inhibit TRH, TSH, T3 & T4| Stimulates adrenaline, glucocorticoids, ACTH, PRL, and GH release | Increases gut hormones | increases GH & PRL while decreasing sex Hs | Increases GH, PRL| ### Feedback Control of Hormone Production * Synthesis and secretion of most hormones are under feedback control. * Feedback control means regulation of hormonal secretion from an endocrine gland by an Effect of the circulating hormone that he gland itself produces. This may be direct or Mediated by another hormone, a metabolite produced by the hormone, Or a physical factor. * The result if this type of regulation can generate more hormone (positive feedback) or less hormone (negative feedback). ### III. Feed back **(a) Negative (-ve) feed back:** * Negative feedback acts to decrease the level of the hormone in the blood is when it increases above normal. * It is important in maintaining homeostasis * All endocrine glands are under the control of negative feedback mechanisms. * Negative feedback mechanisms act like a thermostat. * It is controlled by the by the level of the hormone or its metabolite in the blood ### FEEDBACK CONTROL OF HORMONE PRODUCTION * A classic example of this process involves the hypothalamus- pituitary- thyroid axis. In the euthyroid (normally functioning thyroid gland) animal, thyrotropin releasing hormone (TRH) from the hypothalamus and TSH from the pituitary gland are secreted in a state of equilibrium. * When thyroid hormone concentrations in the blood are inadequate, TRH secretion increases to stimulate TSH secretion, and TSh stimulates the thyroid gland to produce more T3, and T4. The increased blood concentrations of thyroid hormones feed back negatively on the hypothalamus and pituitary gland so that secretions of TRH and ThS are reduced. * Glucocorticoids also affect ACTH secretion by similar negative feedback mechanisms in the pituitary and/or hypothalamus. ### Feedback mechanism: (metabolite) * The diagram illustrates feedback from the body #### Feedback CONTROL OF HORMONE PRODUCTION * Some hormones are under feedback control by metabolites and physical factors as well as other hormones , Ionized clacium negatively controls PTH secretion , glucose negatively controls glucagon and positively controls insulin secretion, and the volume of extracellular fluid negatively controls aldostrone production by feedback mechanisms. #### _(2) Positive feed backregulation of hormones also exists, although they are much less common than negative feedback regulation._ * _In .feed the hormone regulates in a negative way Hormones cannot tell on what to do._ * _in a positive the hormone regulates the level in another direction._ * *A feed back mechanism always must to be in one direction or the other with the horomone or not it will not survive.* **(Examples of positive feed back:** * **A .Two different horomons increase or decreaswe together:** 1. One exsample is to preovulatory release of the follicle .increased to the estrogen levels.**preavulatory LH surge**)**. ### Types of endocrine gland stimuli * **(a) Humoral Stimulus Hormone** * release caused by altered levels\ of certain critical ions or nutrients. * **(b) Neural StimulusHormone** * release caused by neural input. * **(c) Hormonal StimulusHormone** * release caused by another hormone (a tropic hormone). ### Endocrine Glands The image is the illustration of endocrine glands in a female cow and a male cow * Pineal * Hypothalamus * Adrenal Gland * Ovary * Placenta * Kidney * Pituitary * Parathyroid * Located a base of brain * pancreas * Thyroid. Glands secreting general hormones (Endocrine and neuroendocrine) 1. **The hypothalamus** > It is a neuroendocrine gland that secretes: 1. Releasing and inhibiting hormones (a group of hormones stimulate or inhibit the release of tropic hormones from the pituitary gland). 2. Oxytocin. 3. Vasopressin (it is also called antidiuretic hormone, ADH). * The hypothalamus is located below the thalamus andabove the pituitary gland. * It is divided into a variety of nuclei (the nucleus is aggregation of nerve cells inside the CNS). * It is connected to the pituitary gland by the pituitary stalk (infudibulum). ### Connection between the hypothalamus and pituitary gland * **Hypothalamo-hypophyseal portal system**The vascular link between the median eminence and the anterior pituitary through which the releasing and inhibiting hormones pass from the hypothalamus to the ant. Pituitary gland. * **Hypothalamo-hypophysea l tract**Between hypothalamus and posterior pituitaryBoth of the posterior pituitary hormones-antidiuretic hormone andoxytocin-are actually produced in neuron cell bodies of the Supraoptic nuclei and paraventricular nuclei of thehypothalamus and transported along axons of the hypothalamus to the pituitary when stored in ready to used * Releasing and inhibiting hormones <table><thead><tr><th></th><th>Structure</th><th>Action</th><th>Action</th></tr></thead><tbody><tr><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td></tr></tbody>