Endocrinology Week 10 PDF

ENDOCRINOLOGY 10 BIOLOGICAL COMMUNICATION Communication among cells, organisms & between organisms & their environment is absolutely central to life & reproduction. ENDOCRINE VS NERVOUS Major communication systems in the body Integrate stimuli and responses to changes in external and internal enviro...

ENDOCRINOLOGY 10 BIOLOGICAL COMMUNICATION Communication among cells, organisms & between organisms & their environment is absolutely central to life & reproduction. ENDOCRINE VS NERVOUS Major communication systems in the body Integrate stimuli and responses to changes in external and internal environment Both are crucial to coordinated functions of highly differentiated cells, tissues and organs Unlike the nervous system, the endocrine system is anatomically discontinuous. NERVOUS SYSTEM The nervous system exerts point-to-point control through nerves, similar to sending messages by conventional telephone. Nervous control is electrical in nature and fast. ENDOCRINE SYSTEM The endocrine system broadcasts its hormonal messages to essentially all cells by secretion into blood and extracellular fluid. Like a radio broadcast, it requires a receiver to get the message In the case of endocrine messages, cells must bear a receptor for the hormone being broadcast in order to respond. Together, the nervous and endocrine systems coordinate functions of all body systems. NERVOUS ENDOCRINE neurotransmitters HORMONES muscle contractions and glandular secretions metabolic activities , growth & development, reproduction acts in milliseconds acts in seconds to minutes to hours to days to months brief effects long-lasting effects ENDOCRINE PARACRINE AUTOCRINE NEURAL Interactions between the nervous and endocrine systems emphasize their coordinated communicative function. Endocrine system It is a network of ductless glands that secrete hormones directly into the blood. It is considered to be the regulatory system of the body. It is regulated by means of control of hormone synthesis rather than by degradation. Major endocrine glands Thyroid Parathyroid Pituitary Thymus Adrenals Pancreas Gonads testes (male) and ovaries (female) Kidney Erythropoietin, Renin Heart ATRIAL NATRIURETIC PEPTIDE Lungs PROSTAGLANDIN, ANGIOTENSIN CONVERTING ENZYME HORMONES These are chemical signals produced by specialized cells, secreted into the blood stream and carried to a target tissue. They play an important role in the growth and development of an individual. They are regulated by the metabolic activity either positive or negative feedback mechanism. Functions of HORMONES: 1. To maintain the constancy of chemical composition of extracellular and intracellular fluids 2. Control metabolism, growth, fertility, and responses to stress. FEEDBACK MECHANISMS 1. Positive feedback system It is a system in which an increased in the product results to elevation of the activity of the system and the production rate. Example: gonadal, thyroidal and adrenocortical hormones 2. NEGATIVE feedback system is a system in which an increased in the product results to decreased activity of the system and the production rate Example: Leutenizing hormone TYPES OF HORMONE ACTION 1. Endocrine It is secreted in one location and release into blood circulation binds to specific receptor to elicit physiological response. 2. Paracrine It is secreted in endocrine cells and released into interstitial space binds to specific receptor in adjacent cell and affects its function. 3. Autocrine is secreted in endocrine cells and sometimes released into interstitial space binds to specific receptor on cell of origin resulting to self-regulation of its function. 4. Juxtacrine It is secreted in endocrine cells and remains in relation to plasma membrane acts on immediately adjacent cell by direct cell-to-cell contact. 5. Intracrine It is secreted in endocrine cells and remained as well as function inside the synthesis of origin. 6. Exocrine It is secreted in endocrine cells and released into lumen of gut it affects their function. 7. Neurocrine It is secreted in neurons and released into extracellular space binds to receptor in nearby cell and affects their function 8. Neuroendocrine It is secreted in neurons and released from nerve endings, interacts with receptors of cells at distant site. classification of hormones accdg to composition & structure Peptides and Proteins These are synthesized and stored within the cell in the form of secretory granules and cleaved as needed. They cannot cross the cell membrane due to their large molecular size and thus; produce their effects on the outer surface of the cell. They are water soluble and not bound to carrier protein. Glycoprotein Polypeptides FSH, HCG, TSH, erythropoetin ACTH, ADH, GH, angiotensin, calcitonin, cholecystokinin, gastrin/glucagon, insulin, melanocytestimulating hormone (MSH), oxytocin, PTH, prolactin, somatostatin Steroids These are lipid molecules that have cholesterol as a common precursor. They are produced by adrenal glands, ovaries, testes and placenta. They are water insoluble (hydrophobic) and circulate bound to a carrier protein. Examples: aldosterone, cortisol, estradiol, progesterone, testosterone and activated vitamin D3. Amines They are derived from an amino acid and they are intermediary between steroid and protein hormones Examples: epinephrine norepinephrine, triiodothyronine thyroxine, hypothalamus It is the portion of the brain located in the walls and floor of the third ventricle. It is the link between the nervous system and the endocrine system. The supraoptic and paraventricular nuclei produce vasopressin and oxytocin. The neurons in the anterior portion release the following hormones: thyrotropin-releasing hormone (TRH) gonadotropin-releasing hormone(Gn-RH) somatostatin (aka growth hormone inhibiting hormone) (GH-IH); growth hormone releasing hormone (GH-RH) and prolactin-inhibiting factor (PIF). Endocrine glands 1. PINEAL GLAND It is attached to the midbrain. It secretes melatonin that decreases the pigmentation of the skin. Secretions are controlled by nerve stimuli. 2. PITUITARY GLAND It is known as the "Master Gland" located in a small cavity in the sphenoid bone of the skull called the sella turcica or Turkish saddle. All pituitary hormones have circadian rhythms. pituitary gland A. Anterior Pituitary It is the "true endocrine gland". It regulates the released and production of hormones such as prolactin, growth hormone, gonadotropins (FSH and LH), TSH and ACTH. The hormones secreted by this anterior lobe are either peptides or glycoproteins. B. posterior Pituitary It is capable of releasing the hormones oxytoxin and vasopressin but not capable of producing it. The release of the hormones occurs in response to serum osmolality or by suckling. anterior pituitary gland 1. Growth Hormone (GH)/Somatotropin It is the most abundant of all pituitary hormones. It is controlled by GH-RH (the amount released) and somatostatin (governs the frequency and duration of secretory pulse). Its overall metabolic effect is to metabolize fat stores while conserving glucose. Major stimulus: Major inhibitor: Physiologic stimuli: Increased: Decreased: deep sleep (markedly increased GH) somatostatin stress, fasting and high protein diet acromegally, chronic malnutrition, renal disease, cirrhosis and sepsis hyperglycemia, obesity and hypothyroidism Disorders Low: Idiopathic or Pituituary Adenoma (most common in adults) High: Acromegaly Diagnostic Tests Physical activity test Screening test for GH deficiency Insulin Tolerance Test Gold Std test for GH deficiency Arginine stimulation test 2nd Confirmatory test for GH deficiency Somatomedin C or insulin-like growth factor 1 Screening test for Acromegaly Oral Glucose Tolerance test Confirmatory test for Acromegaly 2. Gonadotropins a. Follicle stimulating hormone (FSH) Male: aids in spermatogenesis Female: elevation can help diagnose premature menopause b. leutenizing hotmone (LH) Male: helps leydig cells to produce testosterone Female: ovulation 3. Thyroid Stimulating Hormone (TSH) It is also known as thyrotropin. It is the main stimulus for the uptake of iodide by the thyroid gland. stimulates thyroid hormone synthesis Blood levels may contribute in the evaluation of infertility. 4. Adrenocorticotrophic Hormone (ACTH) It is produced in response to low serum cortisol It is a regulator of adrenal androgen synthesis. deficiency of ACTH will lead to atrophy of the zona glomerulosa and zona reticularis Increased in: Addison's disease ectopic tumors after protein-rich meals 5. prolactin It is a pituitary lactogenic hormone; a stress hormone; a direct effector hormone. It functions in the initiation and maintenance of lactation. It also acts in conjunction with estrogen and progesterone to promote breast tissue development. Major inhibitor: dopamine Prolactin excess: hypogonadism POSTERIOR pituitary gland 1. Oxytoxin It is nonapeptide, very similar in composition to ADH. It is secreted in association with a carrier a protein. It stimulates contraction of the gravid uterus at term - "Fergusson reflex." It plays role in hemostasis at the placental site following delivery. It stimulates muscle contraction during delivery and lactation 2. Anti-Diuretic Hormone (ADH)/Arginine Vasopressin (AVP) It is a nonapeptide that acts on the distal convoluted and collecting tubules of the kidneys. It regulates water balance It decreases the production of urine by promoting reabsorption of water by the renal tubules It increases blood pressure