Module 13: The Endocrine System PDF

References: MLS 1104 LECTURE Module 13 The Endocrine System Reference: Seeley’s Essentials of Anatomy & Physiology 11th Edition by Vanputte, Regan Russ...

References: MLS 1104 LECTURE Module 13 The Endocrine System Reference: Seeley’s Essentials of Anatomy & Physiology 11th Edition by Vanputte, Regan Russo Prepared by: Cherry Grace A. Dabucon, MD 1 ENDOCRINE SYSTEM  Characteristics of the Endocrine System composed of endocrine glands and specialized endocrine cells located throughout the body Endocrine glands and cells secrete very small amounts of chemical messengers called hormones into the extracellular fluid. Hormones diffuse into the blood to be transported to their target & circulate through the bloodstream to specific sites called target tissues or effectors. At their target tissues, hormones stimulate a specific response ➔endocrine -derived from the Greek words endo, meaning “within,” and krino, “to secrete” Exocrine glands have ducts that carry their secretions to the outside of the body, or into a hollow organ, such as the stomach or intestines Endocrinology is the study of the endocrine system Chemical messengers allow cells to communicate with each other to regulate body activities stimulates the cell that originally secreted it Ex: cytokines secreted by white blood cells during an infection chemical messengers act locally on neighboring cells Ex: histamine, released by certain WBC (basophils) during allergic reactions secreted by neurons that activate an adjacent cell, whether it is another neuron, a muscle cell, or a glandular cell travel through the blood to their target cells  FUNCTIONS OF THE ENDOCRINE SYSTEM 1. Regulation of metabolism. Controls the rate of nutrient utilization and energy production. 2. Control of food intake and digestion. Regulates the level of satiation (fullness) and the breakdown of food into individual nutrients. 3. Modulation of tissue development. Influences the development of tissues, such as those of the nervous system. 4. Regulation of ion levels. Helps monitor blood pH, as well as Na+, K+, and Ca2+ concentrations in the blood. 5. Control of water balance. Regulates water balance by controlling the solute concentration of the blood as well as controlling membrane permeability. 6. Regulation of cardiovascular functions. Helps regulate the heart rate and blood pressure and prepare the body for physical activity. 7. Control of blood glucose and other nutrients. Regulates the levels of glucose and other nutrients in the blood. 8. Control of reproductive functions. Controls the development and functions of the reproductive systems in males and females. 9. Stimulation of uterine contractions and milk release 10. Modulation of immune system function  HORMONES “set into motion.” Chemical Nature of Hormones Hormones fit into one of two chemical categories ( based on their chemical composition, which influences their chemical behavior: (1) lipid-soluble hormones (2) water-soluble hormones entire basis of a hormone’s metabolism—its transport in the blood, its interaction with its target, and its removal from the body—is dependent on the hormone’s chemical nature Water-soluble hormones are polar molecules; they include protein hormones, peptide hormones, and most amino acid derivative hormones can dissolve in blood, many circulate as free hormones, meaning that most of them dissolve directly into the blood and are delivered to their target tissue without attaching to a binding protein short half-lives (Rapidly broken down in blood stream; Once the hormones are inside the target cell, lysosomal enzymes degrade them) Ex: GH, ADH, prolactin  HORMONES “set into motion.” Lipid-soluble hormones are nonpolar, and include steroid hormones, thyroid hormones, and fatty acid derivative hormones, such as certain eicosanoids Circulates unprotected thus easily removed by: 1. breakdown by enzymes in the liver or enzymes in the lungs 2. excretion into urine by the kidneys 3. breakdown by enzymes in the bloodstream Protects them: binding proteins which serve as “chaperone” of the hormone Ex: LH, FSH, androgens Three important modifications to protect them from being destroyed: 1. Having a carbohydrate attached to them. 2. Having a terminal end protected from protease activity. 3. Having binding proteins. Bound hormones circulate in the plasma longer than free water-soluble hormones do.  Stimulation of Hormone Release Control by Humoral Stimuli humoral stimuli- molecules and ions (chemicals) in the bloodstream can directly stimulate the release of some hormones word humoral refers to body fluids, including blood Ex: calcium stimulates the release of the hormone PTH elevated blood glucose levels directly stimulating the pancreas to secrete the hormone insulin elevated blood potassium levels directly stimulating the adrenal cortex to secrete the hormone aldosterone Control by Neural Stimuli neural stimuli - hormone secretion is due to a stimulus from a neurotransmitter Ex: Exercise➔sympathetic nervous system stimulates the Adrenal glands ➔ secrete epinephrine and norepinephrine, ➔increase heart rate ➔increase blood flow through the exercising muscles ➔ stop exercise then stops the neural stimulation releasing hormones - specialized neuropeptides stimulate hormone secretion from other endocrine cells Ex: hormones in the hypothalamus  Control by Hormonal Stimuli hormonal stimuli- hormone is secreted that, in turn, stimulates the secretion of other hormones Ex: hormones from the anterior pituitary gland, called tropic hormones (stimulate the secretion of another hormone) Inhibition of Hormone Release NOTE: inhibiting hormone release is also important Inhibition of Hormone Release by Humoral Stimuli companion hormone’s effects oppose those of the secreted hormone and counteract the secreted hormone’s action Ex: low blood pressure : adrenal cortex secretes the hormone aldosterone ➔ Increase BP Increase BP ➔ atria of the heart secrete atrial natriuretic peptide (ANP), ➔ lowers BP aldosterone and ANP work together to maintain homeostasis of blood pressure. Inhibition of Hormone Release by Neural Stimuli inhibiting hormones prevent the secretion of other hormones Ex: hormones from the hypothalamus that prevent the secretion of tropic hormones from the ant. Pituitary gland  Regulation of Hormone Levels in the Blood Hypothalamus: TRH Two major mechanisms maintain hormone levels in the blood within a homeostatic range: TSH (1)NEGATIVE FEEDBACK hormone’s secretion is inhibited by the hormone itself once blood levels have reached a certain point and there is adequate hormone to activate the target cell Thyroid follicles A self-limiting system T3 and T4 EX: thyroid hormones (2) POSITIVE FEEDBACK stimulated by a tropic hormone, promote the synthesis and secretion of Hypothalamus: GnRH the tropic hormone in addition to stimulating their target cell➔stimulates further secretion of the original hormone. a self-propagating system Ex: prolonged estrogen stimulation promotes a release of the LH anterior pituitary hormone responsible for stimulating ovulation granulosa cells: Estrogen  HORMONE RECEPTORS AND MECHANISMS OF ACTION Receptors: target cell proteins where hormones exert their actions by binding to it hormone can stimulate only the cells that have the receptor for that hormone Receptor site: portion of receptor where hormone binds Specificity – tendency for each type of hormone to bind to one type of receptor, and not to others insulin binds to insulin receptors, but not to receptors for thyroid hormones epinephrine, can bind to a “family” of receptors that are structurally similar Because of high affinity of receptors to hormones ➔ hormone only a small concentration of a given hormone is needed to activate a significant number of its receptors Classes of Receptors 1. Lipid-soluble hormones bind to nuclear receptors lipid-soluble hormones enter their target cell, they bind to nuclear receptors, which are most often found in the cell nucleus Nonpolar molecules can freely cross the cell membrane Ex: Thyroid hormones and steroid hormones (testosterone, estrogen, progesterone, aldosterone, and cortisol) generally bind to nuclear receptors 2. Water-soluble hormones bind to membrane-bound receptors (proteins that extend across the cell membrane, with their hormone-binding sites exposed on the cell membrane’s outer surface) polar molecules and cannot pass through the cell membrane Ex: epinephrine and norepinephrine activated α subunits activate adenylate cyclase an enzyme that converts ATP activated to cAMP phosphodiesterase breaks transcription factor down cAMP to AMP Protein kinases are enzymes that, regulate the activity of other enzymes.  ENDOCRINE GLANDS AND THEIR HORMONES endocrine system consists of ductless glands that secrete hormones into the interstitial fluid ➔ blood richest blood supply are endocrine glands, such as the adrenal gland and the thyroid gland. Hypothalamus and Pituitary HYPOTHALAMUS serves as a control center for the autonomic nervous system as well as the endocrine system PITUITARY GLAND is also called the hypophysis known as the body’s master gland because it controls the function of so many other glands. It is a small gland about the size of a pea housed in a depression of the sphenoid bone inferior to the hypothalamus of the brain lies posterior to the optic chiasm and is connected to the hypothalamus by a stalk called the infundibulum divided into two parts: (1) The anterior pituitary is made up of epithelial cells derived from the embryonic oral cavity; (2) the posterior pituitary is an extension of the brain and composed of neurons.  Excess: Gigantism Deficiency: Dwarfism acromegaly : excess hormone is secreted after growth in bone length is complete, growth continues in bone diameter only. ➔the facial features and hands become abnormally large Influenced by: insulin-like growth factors (IGFs), or somatomedins MB rc Cortisol: Keeps the adrenal cortex from degenerating hydrocortisone MB rc & bind to melanocytes in the skin darkening of the skin MB rc LH: stimulates ovulation interstitial cells: Testosterone MB rc MB rc  MB rc inc BP aka vasopressin lack of ADH secretion causes Diabetes insipidus => dilute urine diuretic actions of alcohol are due to its inhibition of ADH secretion swift birth Pitocin: assist in childbirth and to constrict uterine blood vessels following childbirth (Nuc rc) Thyroid g:requires iodine to synthesize T4 thyroid follicles (parafollicular cells, or C cells) one of the largest endocrine glands shield-shaped contains numerous thyroid follicles(filled with thyroglobulin which T3 & T4 are attached), which are small spheres with walls composed of simple cuboidal epithelium Goiter: enlargement of the thyroid gland (due to deficiency of iodine) Hypothyroidism: lack of thyroid hormones Cretinism: developmental delay, short stature, and abnormally formed skeletal structures Graves disease is an autoimmune disease that causes Exophthalmos: excess hormones that accumulate in the hyperthyroidism eye's muscles and fatty tissues in Graves disease  Islets consist of three cell types, each of which secretes a separate hormone regulate the blood levels of nutrients, especially glucose (1) Alpha cells secrete glucagon (2) beta cells secrete insulin (3) Delta cells secrete somatostatin (inhibits the secretion of insulin and glucagon and inhibits gastric tract activity.) Elevated blood glucose levels stimulate beta cells to secrete insulin major target tissues for insulin are the liver, adipose tissue, muscles, and the area of the hypothalamus that controls appetite, called the satiety center (fulfillment of hunger) Diabetes mellitus is the body’s inability to regulate blood glucose levels within the normal range Type 1 DM occurs when too little insulin is secreted from the pancreas Type 2 DM is caused by either too few insulin receptors on target cells or defective receptors on target cells ENDOCRINE SYSTEM