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Transcript
Endocrine System Endocrine System and the nervous system often work together to bring about homeostasis Both use specific communication methods and affect specific target organs Their methods and effects differ Endocrine Glands & Hormones Excorine glands Secretions released into ducts opening onto an epithelial surface Endocrine glands Ductless organs that secrete their molecules directly into the bloodstream All endocrine cells are located within highly vascularised areas to ensure that their products enter the bloodstream immediately Overview of Hormones Molecules that have an effect on specific organs Only cells with specific receptors for the hormone respond to that hormone Called target cells, and the organs that contain them are called target organs. Organs, tissues, or cells lacking the specific receptor do not respond to the stimulating effects. Classification of Hormones Peptide hormones Formed from chains of amino acids Most of out body’s hormones are peptide hormones Longer chains are called protein hormones Example is growth hormone Steroid hormones Type of lipid derived from cholesterol Example is testosterone Biogenic amines Small molecules produced by altering the structure of a specific amino acid Example is thyroid hormone Negative Feedback Loop A stimulus starts the process, and eventually either the hormone that is secreted or a product of its effects causes the process to slow down or turn off Many hormonal systems work by negative feedback mechanisms One example is the regulation of the blood glucose level in the body Positive Feedback Loop Accelerated the original process, either to ensure that the pathway continues to run or to speed up its activities. Only a few positive feedback loops occur in the human endocrine system one example is the process of milk release form the mammary glands Hypothalamic Control of the Endocrine System As the master control center of the endocrine system the hypothalamus oversees most endocrine activity. Special cells in the hypothalamus secrete hotmones that influence the secretory activity of the anterior pituitary gland Called regulatory hormones because they are secreted into the blood to regulate secretion of most anterior pituitary hormones Releasing hormones (RH) Inhibiting hormones (IH) Hypothalamus has indirect control over these endocrine organs Hypothalamic Control of the Endocrine System Hypothalamus produces two hormones that are transported to and stored in the posterior pituitary Oxytocin Antidiuretic hormone (ADH) Hypothalamus directly oversees the stimulation and hormone secretion of the adrenal medulla An endocrine structure that secretes its hormones in response to stimulation by the sympathetic nervous system Some endocrine cells are not under direct control of hypothalamus Pituitary Gland Lies inferior to the hypothalamus Small, slightly oval gland housed within the hypophyseal fossa of the sphenoid bone Covered superiorly by the diaphragma sellae, which is one of the cranial dural septa that ensheathes the stalk of the infundibulum to restrict pituitary gland movement Connected to the hypothalamus by a tiny stalk, the infundibulum Partitioned both structurally and functionally into an anterior pituitary and posterior pituitary Called anterior lobes and posterior lobes Control of Anterior Pituitary Gland Secretions Anterior pituitary gland is controlled by regulatory hormones secreted by the hypothalamus Hormones reach the anterior pituitary via hypothalamo-hypophyseal portal system Essentially a “shunt” that takes venous blood carrying regulatory hormones from the hypothalamus directly to the anterior pituitary before the blood returns to the heart Thyroid Gland Located immediately inferior to the thyroid cartilage of the larynx and anterior to the trachea Distinctive “butterfly” shape highly vascularized, giving it an intense reddish colour Regulation of the thyroid hormones secretion depends upon a complex thyroid gland- pituitary gland negative feedback process Hyperthyroidism Too much thyroxine Enlargement of the thyroid (Goiter) Muscle weakness Increased metabolic rate Excessive heat production (dilation of blood vessels) Increased appetite Budging eyes Build up of fluid and entry of lymphocytes into orbital tissue Hyperthyroidism Treatments Removal of thyriod Thyroid blocking drugs Radioactive iodine Destyoys overactive thyroid tissue Injections of thyroid hormone Hypothyroidism Too little thyroxine Caused by iron deficiency Disrupts negative feedback loop with the pituitary Continuous production of TSH Reduced basal metabolic rate Decreased heat production Reduced tolerance to cold Decreased heart rate and output Weight gain (decreased appetite) Weakness & fatigue Parathyroid Glands Small, brownish-red glands located on the posterior surface of the thyroid gland Usually four small nodules some individuals may have as few as two or as many as six Parathoid hormone (PTH) Stimulates osteoclasts to reabsorb bone and release calcium ions from bone into the bloodstream Stimulates calcitriol hormone synthesis in the kidney Promotes calcium absorption in the small intestine Prevents the loss of calcium ions during the formation of urine Calatonin (thyroid Gland) Bones uptake Ca+ Negative Feedback loop for Blood Calcium (Ca+) Pancreas Located near the small intestine Exocrine Digestive enzymes to duodenum Endocrine 2 non-steriod hormones (produced by islets of Langerhans Insulin Glucagon Negative Feedback loop for Blood Glucose (sugar) Levels Type 1 Diabetes Immune system attacks the pancrease Insulin producing beta cells Body’s inability to produce insulin Type 2 Diabetes More Common form of diabetes (adult onset diabetes) 90% of diabetics are type 2 Body produces insulin Not enough Body doesn’t respond to it Diet and exercise Insulin injections (both type 1 and 2) Pineal Gland Small, pone cone shaped gland Located deep ion the center of the brain Hormone: Melatonin Causes us to feel sleepy Thymus Gland Located between the lungs in the upper chest cavity Immune System Regulated by pituitary gland Thymosin Stimulates the production of lymphocytes into T Cells Disappears after puberty Lymphocytes continue to be produced by spleen and lymph glands as adults Adrenal Glands 2 adrenal glands Located on top of each kidney 2 parts Outer Cortex Inner Medulla Each produces different hormones & acts like different organs Regulated by hypothalamus Adrenaline, noradrenalin, & cortisol Adrenal Medulla (think “middle”) Produces epinephrine and norepinephrine link between medulla and nervous system is that they both produce adrenaline these chemicals are released during stress situations Adrenal Medulla (continued) Epinephrine causes: blood sugar to go up, glycogen to be turned into glucose, heart rate increases, breathing rate increases, cell metabolism increases, blood vessels dilate, iris of the eye dilates… It’s fight or flight time! Adrenal Cortex Produces three different types of hormones: glucocorticoids, mineralocorticoids, and small amounts of sex hormones we’re only concerned about two hormones Cortisol One of the most important glucocoticoids helps the body recover from stress by increasing amino acid levels amino acids are either converted in to glucose (cell recovery) or protein (cell repair) Aldosterone The most important of the mineralocorticoids responsible for sodium levels, and therefore water levels in the body