Endocrinology PDF

Endocrinology HORMONES I N T R O D U C T I O N ( C L A SS I F I C AT I O N A N D M E C H A N I S M ) Definitions: A hormone is a chemical substances that produced and secreted in blood by an organ or tissue to has an effect on target tissue, this target tissue is located usually but not always at...

Endocrinology HORMONES I N T R O D U C T I O N ( C L A SS I F I C AT I O N A N D M E C H A N I S M ) Definitions: A hormone is a chemical substances that produced and secreted in blood by an organ or tissue to has an effect on target tissue, this target tissue is located usually but not always at distant from the site of hormone production. Organ Targ or hormone et tissue tissu e example vitamin. D3 (1,25 dihydroxy vitamin D (1,25 DH) is synthesized in the skin and act on the intestine.and kidney Classification of hormone Classification according to: Chemical Nature: There are three types according to the chemical nature of hormones. 1-Steroid hormones 2-protien hormones 3-Amines hormones Steroid Hormones: All are synthesized from cholesterol. -They are fat soluble -Need protein carrier -They have long half –life from hours to minutes. Examples: 1-Sex hormones (Androgen, estrogen, progesterone.) Glucocorticoids (Cortisol )—mineralo cortico corticoid—(Aldosterone). Protein hormone: They include peptides, glycoprotein hormones. glycoprotein hormones : in this group the important ones are FSH, LH- they are gonadotropin coming from pituitary gland. TSH , HCG are glycoprotein each one of these hormones is formed ofα-chain and β- chain. α-chains are immunologically. Peptides hormones: They include insulin, glucagon, growth hormone and parathyroid hormones. All protein hormones are water soluble (hydrophilic) they don't need protein carrier, their half life is short mins. 5---60 Amines hormones: Include thyroid hormones, (T3 ,T4).catecholamine (adrenaline and nor - Adrenaline.)  they are synthesized from tyrosine..Thyroid hormone ----behave like steroid hormones (fat soluble, need protein carrier —have long half life period..Catecholamine ----behave like protein hormones. (water soluble (hydrophilic) they don't need protein carrier, their half life is short mins. 5---60). Depends on: 1- Location of the receptors 2-Nature of the signals used in site the cell 3-Solubility properties (either water or fat soluble) i.e lipophilic or hydrophilic. Lipophilic hormones (steroid, thyroid)- hydrophilic-(protein hormones peptide or glycoprotein and catecholamine. We can further classified hormone into: Classification based on the receptor site: group 1: In this group the hormone passed the plasma membrane and their receptors are present in site the cell they include: androgens, estrogens and progesterone (sex hormones) +glucocorticoids, mineral corticoid these hormones are synthesized by the adrenal gland and the sex hormones synthesized in the gonad(testes, ovary) and placenta. Group 11: Their site of receptors on the surface of the cell (hormone receptor complex) and need second messenger can be CAMP , CGMP( cyclic guanosine monophosphate) (synthesized by the enzyme adenyl cyclase), ca, or phosphate or both and other hormones their second messenger are unknown. Group 11: Devided to: A-The second messenger is Camp, the hormones are: TSH, ACTH (adrenocorticotropic hormone), ADH, glucagon, parathyroid hormones, calcitonin, gonadotropin (LH,FSH), Angoitensin11, and catecholamine. B- Their second messenger is CGMP, the only hormone is ANH (Atrial natriuretic----- hormone) control reg. of blood pressure. C-Their second messenger is ca2+ or phosphate or both- gastrin (git. Secretion produce git –HCL. -Chole cysto kinin (CCK) (gall bladder.) -Oxytocin (produced by posterior pituitary). Gonadotropin-Gn-releasing hormone (hypothalamus). D-The second messenger is unknown: -Insulin, GH, and prolactin. THANKS Hypothalam us and pituitary glands Hypothalamus The hypothalamus is located below the thalamus and sits just above the brainstem. Its primary function is to maintain homeostasis (stability of the.internal environment) in the body The hypothalamus links the nervous and the endocrine systems by the way of.pituitary gland Its function is to secrete releasing hormones and inhibiting hormones that stimulate or inhibit production of.hormones in the anterior pituitary Specialized neuron cluster called neurosecretory cells in the hypothalamus produce ADH and oxytocin (posterior pituitary hormones) and transport them to pituitary, where they are stored for.later release Pituitary gland Attached to the hypothalamus, the pituitary gland is pea – sized, reddish – gray body that stores hormones from the hypothalamus and releases them into the.bloodstream Hypothalamus Hormones: The hypothalamus synthesized hormones that transported by neuralfibres to be stored in the posterior pituitary. ADH: which is synthesized in the supraoptic nuclei of the hypothalamus enhances water reabsorption from the collecting ducts in the kidney. Oxytocin: is synthesized in the ventricular nuclei of the hypothalamus. The action of oxytocin is control the and have a role in initiating uterus contraction during delivery its used therapeutically to induce labor (syndication). Hypothalamus have regulatory, stimulatory or inhibitory effect on hormones. Control anterior pituitary hormones synthesis or secretion e.g. Gn----releasing hormone, thytrotropin releasing hormone (TRH), adrenocorticotropin releasing hormone (ACT---RH), growth hormone – releasing hormone (GH---RH), and …..ect. HYPOTHALAMIC EFFECTS ON THE HORMONE ANTERIOR PITUITARY Thyrotropin-releasing hormone Stimulates release of TSH (TRH) (thyrotropin) and Prolactin Corticotropin-releasing hormone Stimulates release of ACTH (CRH) (corticotropin) Gonadotropin-releasing hormone Stimulates release of FSH and LH (Gn - RH) (gonadotropins) Growth hormone-releasing Stimulates release of growth hormone (GHRH) hormone Growth hormone-inhibiting Inhibits release of growth hormone (GHIH) hormone {Prolactin- releasing Stimulates release of hormone (PRH) prolactin Prolactin-inhibiting hormone Inhibits release of prolactin (PIH) Inhibitory hormones are called (Somatostatin). Hormones of anterior pituitary divided according to the types of cells, they divided into 1-Acidophils: Synthesized and secreted GH and prolactin. 2-Basophils: It secreted TSH and ACTH, Gonadotropin (LH, FSH) they act on the gonads (testes and ovary.). - ACTH: act in the adrenal cortex to stimulate synthesis and secretion of glucocorticoids (Cortisol). -TSH: ACTS in thyroid glands to stimulate synthesis and secretion of thyroid hormones. -Aldosterone: its not under the control of ACTH but under the control of rennin enjotensin. -Chromophobes: These cells of uncertain value of secretion hormones but tumors of Chromophobes cells are associated with increase cell secretion of prolactin. -hormones secreted by acidophil(GH,PRL) they act directly on the tissues and those secreted by basophilic (TSH,ACTH,LH,FSH) act on target endocrine glands and they are called trophic hormones. Mechanism of controls: Trophic hormones are control by negative feed back inhibition. Acidophil (GH, Prolactin) are control by neural control.  The Hypothalamus and negative feedback :mechanism :Hormone Regulation Hormone secretion in our body are regulated by 2 feedback mechanism to maintain their homeostasis in the blood:.Positive and negative :Negative Feedback Mechanism Most of hormonal secretion in our body is controlled by this mechanism only. All the hormones secreted in the hypothalamus are apart of negative feedback loop in the hypothalamus – pituitary – target organ For example. Let us consider the hypothalamus pituitary – thyroid gland axis. The pituitary gland is stimulated by TRH of hypothalamus to release thyroid – stimulated hormone (TSH). The TSH in turn triggers secretion of thyroid hormones from thyroid gland. Once thyroid hormone levels reach the threshold level in the blood, it sends negative signals to hypothalamus to secretion of TSH. After some time, the thyroid level drops signaling the hypothalamus to secrete TRH, pituitary to TSH, and the thyroid to thyroid hormones, and the mechanism thus continues thereby establishing a homeostasis of the.hormone level in the blood Disorder of Pituitary hormones: 1-Anterior Disorder of pituitary gland either be hypo function(low hormonal secretion) as a result of pituitary destruction it can be due to tumor, surgery, infection or infraction, hypo function can be of many hormones and called pan hypopituitorism. Deficiency in target organ give-----primary- deficiency in hypothalamus. Hyper function: Usually due to tumor usually benign (in case of malignant tumor at beginning case hyper function but at the last stage -------------- hypo function). Hormone Excess Defic GH Gigantism (children) short -Acromegaly in adults Prolactin lactoria, infertility, and.lactati amenorrhea ACTH Cushing syndrome s (high Cortisol) adrenocor TSH Hypothyroidism se hypothy :Deficiency or low TSH Generally, secondary hypothyroidism is associated with low TSH and low T3 and T4 (because the pituitary is damage). However TSH levels may also be normal or even slightly elevated. For this reason, TSH is often an unreliable measure of secondary hypothyroidism, and should not be used to assess the adequacy of :High TSH level High TSH level may lead to hypothyroidism, because when the thyroid gland does not produce enough hormones, the pituitary gland produces more TSH to.compensate Investigations: IF I suspected hypo or hyper function of pituitary gland or the target organs. 1-we do hormonal assays for pituitary hormones and the target organ hormones. 2-We can do radiological examinations 3-CT scan (computerized axial tomography). Most hormones are stable in the blood for hours or even days except few e.g. insulin , renin , PTH, ACTH, and Calcitonin these hormones should be estimated immediately and kept cool. If there suspecting of hypopituitorism estimate target organ hormones and trophic (TSH,ACTH,LH,FSH) hormones. -T4, TSH -LH, FSH, Oestradiol, (female) , Testosterone (male). -ACTH, Cortisol -GH -Prolactin. -If target hormones are low and pituitary hormones are high the defect is primary (in the target organ). If target hormones low and the pituitary hormones low the defect is secondary (in the thepituitary or.hypothalamus)