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Transcript
Endocrine System Martini Chapter 18 Functions of the Endocrine System Controls the processes involved in movement and physiological equilibrium Includes all tissues or glands that secrete hormones into the blood The number of receptors for a specific hormone can be altered to meet the body’s demand 2 Endocrine Glands Secrete products (hormones) into bloodstream Pituitary, thyroid, parathyroid, adrenal, pineal Other organs secrete hormones as a 2nd function Hypothalamus, thymus, pancreas,ovaries,testes, kidneys, stomach, liver, small intestine, skin, heart & placenta 3 Hormone Receptors “Lock and Key” approach: describes the interaction between the hormone and its specific receptor. Receptors for nonsteroid hormones are located on the cell membrane Receptors for steroid hormones are found in the cell’s cytoplasm or in its nucleus 4 Classification of Hormones Steroid Hormones Lipid soluble Derived from cholesterol Gonads: Androgens, Estrogens, Progestins Adrenal cortex: Corticosteroids, androgens Kidneys: calcitriol 5 Classification of Hormones Peptide Hormones Water soluble Glycoproteins and short polypeptides Pituitary Kidneys These all secrete Hypothalamus Water soluble Heart Peptide Hormones Pancreas Parathyroid 6 Classification of Hormones Amino Acid Derivatives Thyroid Hormone: Lipid soluble Catecholamines: Water Soluble Epinephrine Norepinephrine Dopamine 7 Hormone Receptors Hormones only affect target cells with specific membrane proteins called receptors 8 Number of Receptors Receptors are constantly being synthesized & broken down Down-regulation: is the decrease of hormone receptors which decreases the sensitivity to that hormone Receptors undergo endocytosis Up-regulation: deficiency of hormone, produces an increase in the number of receptors Target tissue more sensitive to the hormone 9 Hormone Transport in Blood Water soluble hormones circulate in free form in the blood Steroid (lipid) & thyroid hormones must attach to transport proteins synthesized by liver 10 Lipid Soluble Hormone Actions Pass through the cell membrane and binds to a receptors Then enters the nucleus to bind with DNA Activates certain genes (Direct gene activation). mRNA is synthesized → protein synthesis for: Enzymes as catalysts Tissue growth and repair Regulate enzyme function 11 Lipid Soluble Hormone Actions 12 Water Soluble Hormone Actions React with receptors outside the cell Activates G-protein in the membrane Leads to the formation of a second messenger (cAMP). cAMP can produce specific intracellular functions: Activates cell enzymes Change in membrane permeability Promote protein synthesis Change in cell metabolism Stimulation of cell secretions 13 Nonsteroid Hormone Actions Nonsteroid hormone 14 Amplification of Hormone Effects Response to a lipid soluble hormone is directly proportional to the number of hormone-receptor complexes available Response to a water soluble hormone is greatly amplified. Cells are highly sensitive to changes in the concentration of nonsteroid hormones Each target cell responds to hormone differently Liver cells: insulin stimulates glycogen synthesis Adipose: insulin stimulates triglyceride synthesis 15 Control of Hormone Secretion Regulated by signals from nervous system, chemical changes in the blood or by other hormones Negative feedback is the primary mechanism through which the endocrine system maintains homeostasis Disorders involve either hyposecretion or hypersecretion of a hormone 16 Hypothalamus It is the master of the Pituitary Gland 8 different releasing & inhibiting hormones This is the main interface between the nervous system and the endocrine system Located in the brain, this region controls most endocrine secretions Mainly regulatory hormones are released here. Most control the pituitary gland 18 Pituitary Gland Pea-shaped, 1/2 inch gland found in sella turcica of sphenoid Infundibulum attaches it to brain (at the hypothalamus) Anterior lobe Secretes mainly regulatory hormones Posterior lobe Ends of axons of 10,000 neurons found in hypothalamus Neuroglial cells called pituicytes Secretes hormones, but manufactures none 19 Anterior Pituitary Hypothalamus Infundibulum Posterior Pituitary Sella Turcica 20 Flow of Blood to Anterior Pituitary Controlling hormones from hypothalamus enter blood Travel through the hypophyseal portal system of veins (2 capillary beds in series) Enter anterior pituitary at capillaries 21 Hypothalamus Releasing Hormones GHRH → GHIH (GH-Inhibiting-H) → CRH(corticotropin-RH) → → GnRH (gonadotropin-RH) PRH (PRL-releasing) PIH (PRL inhibiting) TRH (thyrotropin-RH) Anterior Pituitary → → → GH (growth hormone) (AKA: somatotropin) GH (growth hormone) ACTH (adrenocorticotropic) LH (luteinizing hormone) FSH (follicle-stimulating) PRL (prolactin) PRL (prolactin) TSH (thyroid stimulating) 22 23 Anterior Pituitary Growth Hormone (GH) The anterior pituitary releases bursts of GH every few hours. A major regulator is the blood glucose level During hypoglycemia, the hypothalamus secretes GHRH Anterior pituitary releases more GH, more glycogen broken down into glucose by liver cells 24 Growth Hormone GH Anterior Pituitary Within target cells increases synthesis of insulinlike growth factors that act locally or enter bloodstream ↑ cell growth & cell division Remember from the skeletal system, it stimulates cartilage and therefore bone growth in children ↑ lipolysis in adipose so fatty acids used for ATP ↓ glucose for ATP production so blood glucose levels remain high enough to supply brain 25 Anterior Pituitary Growth Hormone Effects 26 Hypothalamus Inhibition of Growth Hormone Growth hormone-inhibiting hormone (GHIH) suppresses the secretion. The hypothalamus releases this in response to hyperglycemia GHIH inhibits the anterior pituitary secretion of GH Less GH from anterior pituitary, glycogen does not breakdown into glucose 27 Anterior Pituitary Growth Hormone (GH) Diseases (refer to skeletal system notes from 231 for details) Too much GH in children leads to gigantism Too much GH in adults leads to acromegaly Too little GH in children leads to dwarfism Pituitary Dwarfism Acromegaly 28 29 Anterior Pituitary Thyroid Stimulating Hormone: TSH This pituitary hormone stimulates the thyroid gland synthesis & secretion of T3 and T4 Metabolic rate stimulated 30 Anterior Pituitary Adrenocorticotropic Hormone ACTH Pituitary secretion stimulated by CRH (corticotropin releasing hormone) from the hypothalamus ACTH works on the cortex of the adrenal gland to release glucocorticoids. Stress can increase CRH secretion which will increase ACTH secretion 31 Anterior Pituitary ACTH Negative Feedback 32 Anterior Pituitary Follicle Stimulating Hormone: FSH Initiates the formation of follicles within the ovary Stimulates follicle cells to secrete estrogen Stimulates sperm production in testes 33 Luteinizing Hormone LH Anterior Pituitary In females, LH stimulates Ovulation Formation of corpus luteum Secretion of progesterone In males, stimulates interstitial cells to secrete testosterone 34 Anterior Pituitary Prolactin: PRL In females, PRL promotes lactation Suckling reduces levels of hypothalamic inhibition and prolactin levels rise along with milk production In males, PRL decreases LH secretion (note that too much PRL would then decrease androgen levels and cause sterility) Controlled by both PRH and PIH from the hypothalamus 35 Posterior Pituitary (Neurohypophysis) Posterior Pituitary No hormones are made here. They are made in the hypothalamus and just released here. Consists of axon terminals of hypothalamic neurons Neurons release two neurotransmitters that enter capillaries Antidiuretic hormone Oxytocin 36 Antidiuretic Hormone ADH Posterior Pituitary AKA: Vasopressin ADH decreases urine formation by having kidneys conserve water ADH release triggered by osmoreceptors and inhibited by stretch receptors in blood vessels 37 Posterior Pituitary 38 Posterior Pituitary Diabetes Insipidus Caused by a lack of ADH Diabetes insipidus is caused by the inability of the kidneys to conserve water, which leads to frequent urination and pronounced thirst. 39 Posterior Pituitary Oxytocin Two target tissues both involved in neuroendocrine reflexes During delivery Baby’s head stretches cervix Hormone release enhances uterine muscle contraction Baby & placenta are delivered After delivery Suckling & hearing baby’s cry stimulates milk ejection Hormone causes muscle contraction & milk ejection 40 Posterior Pituitary Oxytocin During Labor Stimulation of uterus by baby Hormone release from posterior pituitary Uterine smooth muscle contracts until birth of baby Baby pushed into cervix increases hormone release More muscle contraction occurs When baby is born, positive feedback ceases 41 (GHIH) 42 Thyroid Thyroid Gland Located on the anterior surface of the larynx (neck) Has 2 lobes connected by the isthmus 43 Thyroid Histology of the Thyroid Follicle: sac of stored hormone (colloid) surrounded by follicle cells that produced it T3 & T4 Inactive cells are short In between cells called parafollicular cells Produce calcitonin 44 Thyroid Follicular Cells 45 Thyroid Formation of Thyroid Hormone 1. Iodide is actively transported into thy cytoplasm of the follicle cells 2. Iodide diffuses to apical surface of cell and is converted to I+ by thyroid peroxidase 3. Synthesis of thyroglobulin (TG) in the follicle cell 4. Release of TGB into colloid 5. Iodination of a tyrosine molecule on the TG in colloid forming T3 & T4 6. T3 & T4 re-enter the follicle cell by endocytosis 7. T3 & T4 diffuse into blood and attach to transport 46 proteins TGB 47 Thyroid Actions of Thyroid Hormones T3 & T4: thyroid hormones responsible for metabolic rate, synthesis of protein, breakdown of fats, use of glucose for ATP production Calcitonin: responsible for building of bone & stops reabsorption of bone (lower blood levels of Calcium) 48 Thyroid Control of T3 & T4 Secretion Negative feedback system Low blood levels of hormones stimulate hypothalamus It stimulates pituitary to release TSH TSH stimulates gland to raise blood levels 49 Thyroid Thyroid Negative Feedback T3 & T4 50 Thyroid Negative Feedback Calcitonin Thyroid Calcitonin production is not regulated by the anterior pituitary. It's secretion is stimulated by high calcium levels in the blood.51 Medical Example: Endemic (Colloid) Goiter Thyroid Occurs in people living in geographical areas within iodinedepleted soil, causing iodine deficiency. Remember: iodine is vital in the formation of thyroid hormone. Iodized table salt in the U.S. prevents this deficiency; however, it is still common in central Asia and Central Africa. 52 53 Hyperthyroidism: Grave’s Disease This is an autoimmune disease Thyroid Immune system over stimulates the thyroid gland Symptoms include insomnia, irritability, weight loss, heat sensitivity, increased perspiration, fine or brittle hair, muscular weakness, rapid heart beat, and hand tremors. Grave’s Disease is the only kind of hyperthyroidism that is associated exophthalmos Some patients will develop lumpy reddish thickening of the skin in front of the shins called pretibial myxedema 54 Thyroid Grave’s Disease Exophthalmos Pretibial Myxedema 55 Thyroid Hypothyroidism Hypothyroidism during infancy results in dwarfism & retardation called cretinism Hypothyroidism in adult produces sensitivity to cold, low body temp. weight gain & mental dullness and depression Hashimoto's Thyroiditis an autoimmune disease in which the immune system attacks and destroys the thyroid gland 56 Thyroid 57 Thyroid Hypothyroidism Endemic goiter and cretinism Cretinism 58 Parathyroid Parathyroid Glands These are 4 pea-sized glands found on back of thyroid gland Principal cells produce parathyroid hormone (PTH) PTH function Increases blood calcium (Ca2+) levels and decreases blood phosphate (PO42-) levels 59 Parathyroid Parathyroid Hormone Raise blood calcium levels ↑ activity of osteoclasts +2 by kidney ↑ reabsorption of Ca ↓ reabsorption of phosphate ↑ formation of calcitriol (vitamin D3) by kidney which increases absorption of Ca+2 and Mg+2 by intestinal tract Opposite function of calcitonin PTH is regulated by blood calcium levels, not by other glands! 60 Parathyroid ↓ Serum Ca+ ↑ Serum Ca+ 61 Parathyroid Hyperparathyroidism Stimulates excessive osteoclast activity Bones become soft and subject to spontaneous fractures; is most often caused by a tumor (parathyroid adenoma). Secondary hyperparathyroidism is caused by renal failure 62 Parathyroid 63 Parathyroid Hypoparathyroidism Symptoms include muscle cramps and seizures Most common cause is inadvertent surgical removal or injury after thyroid surgery. 64 Adrenal Adrenal Glands One on top of each kidney Cortex produces 3 different types of hormones from 3 zones of cortex Medulla produces epinephrine & norepinephrine 65 Adipose tissue Structure of Adrenal Gland Adrenal Capsule Zona Glomerulosa Zona Fasciculata Zona Reticularis Adrenal Medulla 66 Adrenal Adrenal Medulla Acts very much like a part of the sympathetic nervous system (fight or flight) Secretes the catecholamines Epinephrine & norepinephrine Stimulated by preganglionic neurons directly, so controlled by the hypothalamus as if part of the autonomic nervous system, NOT by tropic hormones 67 Adrenal Adrenal Cortex Secretes over 30 different steroid hormones (corticosteroids) Mineralocorticoids Aldosterone: maintains electrolyte balance Glucocorticoids Cortisol Gonadocorticoids Testosterone, estrogen, progesterone 68 Adrenal Adrenal Cortex 69 Adrenal Aldosterone Mineralocorticoid from the Zona Glomerulosa Functions + Decreases the amount of Na ,Cl , HCO3 and water excreted by the kidney + + ↑ excretion of K and H Hypersecretion: tumor producing aldosteronism High blood pressure caused by retention of Na+ and water in blood 70 Adrenal Aldosterone Secretion ↑ Plasma K+ ↓ Plasma Na+, blood pressure & blood volume ↑ Aldosterone Secretion ↑ Kidney K+ secretion (↓ Plasma K+) ↓ Kidney Na+ Excretion (↑ plasma Na+) 71 Adrenal Regulation of Aldosterone Blood plasma ion concentrations affect its secretion directly (but not always strongly) Kidney secretes renin in response to altered electrolyte levels, which triggers angiotensin activation in the blood, which leads to aldosterone secretion ACTH from the anterior pituitary can cause aldosterone secretion 72 Adrenal 73 Adrenal Cortisol Glucocorticoid from the Zona Fasciculata Functions to help regulate metabolism Overall effect is to help keep blood glucose within a normal range between meals Anti-inflammatory effects Decreases the permeability of capillaries Inhibits the synthesis of prostaglandins Stabilizes lysosomal membranes 74 Adrenal Cortisol Functions ↓ Synthesis of protein ↑ Release of fatty acids from adipose tissue Increases blood concentration of amino acids Increasing the fatty acids as an energy source and decreasing the use of glucose as an energy source It stimulates liver cells to synthesize glucose from noncarbohydrates (gluconeogenesis), such as circulating amino acids and glycerol, thus increasing blood glucose concentrations 75 Adrenal Brain ↑ Glucose available to brain 76 Adrenal Cushing Syndrome Hypersecretion of glucocorticoids Redistribution of fat (buffalo hump), spindly arms & legs due to muscle loss Moon Face Purple Striae (stretch marks) Wound healing is poor, bruise easily 77 Adrenal Addison’s Disease Hyposecretion of glucocorticoids Rare: 1 in 100,000 Hypoglycemia, muscle weakness, low BP, dehydration due to decreased Na+ in blood Mimics skin darkening effects of MSH Potential cardiac arrest 78 Adrenal DHEA: Androgens Hormones produced from DHEA are male (adrenal androgens) Some of them are converted into female hormones (estrogens) by the skin, liver, and adipose tissues. These hormones may supplement the supply of sex hormones from the gonads and stimulate early development of the reproductive organs. 79 Congenital Adrenal Hyperplasia (CAH) Adrenal Autosomal recessive disorders that have complete or partial deficiency of an enzyme involved in cortisol or aldosterone synthesis. The precursors are turned into DHEA (androgen) Male infants: present at 3-4 with salt wasting with vomiting, diarrhea, dehydration Female infants: present at birth with ambiguous genitalia because of virilization due to excess androgens This is a GIRL80 Pancreas Pancreas Organ (5 inches) consists of head, body & tail Cells (99%) in acini produce digestive enzymes Endocrine cells in pancreatic islets produce hormones 81 Pancreas 82 Pancreas Pancreas Histology Acini produce digestive enzymes (exocrine) 83 Pancreatic Islets (Islets of Langerhans) Pancreas Alpha cells (20%) produce glucagon Increase Glucose Beta cells (70%) produce insulin Decrease Glucose Delta cells (5%) produce somatostatin Inhibits Glucagon and Insulin 84 Pancreas Glucagon It works on the liver to cause the production of glucose via: It is regulated by blood glucose levels directly: Glycogenolysis (break down glycogen) Gluconeogenesis (break down glucose) Secreted when blood glucose drops (before next meal) Prevents hypoglycemia 85 Pancreas Insulin It works on the liver to remove glucose from the blood via: Making glycogen Preventing gluconeogenesis Increasing glucose transport into cells It is also regulated by blood glucose levels directly Prevents hyperglycemia 86 Pancreas Note: glucagon and insulin work in opposition, and their combined effects control blood glucose 87 Pancreas Diabetes Type 1: Insulin Dependent Diabetes AKA: juvenile diabetes Caused by a lack of insulin Autoimmune disorder Immune system destroys beta cells in the pancreas 88 Pancreas Diabetes Type 2: Non-Insulin Dependent Caused by an insensitivity of cells to insulin. (Down regulation of receptors) Diabetes mellitus marked by hyperglycemia ↑ urine production (polyuria) ↑ thirst (polydipsia) ↑ eating (polyphagia) 89 Pineal Gland Secretes only one hormone: melatonin Involved in circadian rhythms (Recognition of day and night times) Day ↓ melatonin Night ↑ melatonin Melatonin secretion produces sleepiness 90 Other Endocrine Hormones We will be covering these in great detail when we study the other systems. Reproductive system: Renal System LH, FSH, Estrogen, Progesterone, Testosterone Renin, Angiotensin Heart Atrial natriuretic peptide 91 Stress Stress & General Adaptation Syndrome Stress response is a set of bodily changes called general adaptation syndrome (GAS) Any stimulus that produces a stress response is called a stressor Stress resets the body to meet an emergency As a result of the general response to stress, the blood concentration of epinephrine, cortisol, and aldosterone increase. 93 94 Alarm Phase Immediate response to stress Directed by the sympathetic nervous system “Fight or Flight response” Epinephrine plays the dominant role 95 Resistance Phase Initiated by hypothalamic releasing hormones (long-term reaction to stress) Corticotropin, growth hormone & thyrotropin releasing hormones Allow body to continue to fight a stressor 96 Resistance Phase Glucocorticoids are released (↑ cortisol so protein catabolism is increased & other sources of glucose are found) ↑ Aldosterone Mobilize lipid and protein reserves Conserve glucose for neural tissue Elevate and stabilize blood glucose concentrations Conserve salts and water Eliminate K+ and H+. ↑ Thyroid hormone to ↑ metabolism 97 Exhaustion Resources of the body have become depleted Resistance stage can not be maintained Prolonged exposure to resistance reaction hormones Wasting of muscle Suppression of immune system Ulceration of the GI tract Failure of the pancreatic beta cells 98 The End