Endocrinology Notes PDF

ENDOCRINOLOGY Dr. Mobley AHS 2202  INTRODUCTION Endocrine & nervous system regulate body functions Both use chemical messengers send signals Endocrine system uses hormones produced in endocrine glands Hormones enter the blood stream to reach target...

ENDOCRINOLOGY Dr. Mobley AHS 2202  INTRODUCTION Endocrine & nervous system regulate body functions Both use chemical messengers send signals Endocrine system uses hormones produced in endocrine glands Hormones enter the blood stream to reach target tissues Minute amounts of hormones cause changes in the body  Hormones are produced by endocrine tissue Secreted into blood HORMONES stream Bind to receptors in or on cells (target cell)  HORMONE CHEMISTRY Peptide hormones Steroid hormones Monoamine hormones Chain of a few to 200+ Lipids synthesized from Derived from amino acids amino acids cholesterol and retain amino group Hydrophilic (water-soluble) Hydrophobic → bind to Catecholamines Receptor is on cell plasma proteins to travel (hydrophilic), thyroid membrane Receptor is INSIDE THE hormones (hydrophobic) CELL in the plasma or Receptor is on the cell mb nucleus for catecholamines, within the cell for thyroid C ELL MEM B RA NE RECEP TORS VS. IN TRACEL L UL AR RECEP TORS  CONTROL OF HORMONE SECRETION Feedback mechanisms control hormone secretion Negative feedback (most common): activity is decreased when hormone levels rise Positive feedback: activity is increased when hormone levels increase Positive feedback systems risk out of control upregulation Exception: Adrenal gland medulla does not use positive or negative feedback Regulated by the nervous system (sympathetic, fight-or-flight, releases epinephrine AKA adrenaline) L OC AT IO NS O F H O R MO NE P ROD UC T I ON  Hypothalamus MAJOR ENDOCRINE GLANDS Pituitary Gland Anterior pituitary Posterior pituitary  Diencephalon Functions Appetite control Temperature regulation HYPOTHALAMUS Wake-sleep cycle control Located dorsal to the pituitary gland, attached by a stalk Hypothalamus controls activity of the pituitary gland  Anterior pituitary (AP) Portal system of tiny vessels connects hypothalamus to AP Modified neurons of the hypothalamus secrete hormones into portal blood vessels HYPOTHALAMUS Releasing factors – PITUITARY Inhibiting factors CONNECTION Posterior pituitary (PP) Modified neurons in hypothalamus produce ADH & oxytocin These hormones travel down nerve fibers and are stored in the PP No hormones are produced in the PP HYPOTHALAMUS & ANTE RIOR PITUITARY HYPOTHALAMUS & POSTERIOR PITUITARY  AKA the hypophysis “Master endocrine gland” Size of a pea PITUITARY Lives ventral to the hypothalamus GLAND Housed in the pituitary fossa of the sphenoid bone Composed of 2 separate glands (anterior & posterior) Adenohyphophysis (anterior) → derived from endocrine tissue Neurohypophysis (posterior) → derived from nervous tissue  7 hormones Growth hormone Prolactin Thyroid-stimulating hormone ANTERIOR Adrenocorticotropic hormone PITUITARY Follicle-stimulating hormone (**gonadotropin**) Luteinizing hormone (**gonadotropin**) Melanocyte-stimulating hormone  AKA somatotropin Promotes growth (anabolism) and tissue regeration Regulates metabolism of macronutrients GROWTH Affects glucose metabolism & lipid metabolism HORMONE Mobilizes and breaks down tissue fats Inhibits glucose use by the cells, causing blood glucose to rise (GH) Opposite to the effect of insulin  CLINIC AL DISEASE: ACROMEGALY This Phot o by Unknown Author is licensed under CC BY-SA GH-producing anterior pituitary tumor Primarily affects cats Clinical signs: physical appearance (big head & body), diabetic difficult to regulate Diagnosis: Hormone blood test (IGF-1 levels), CT, MRI Treatment: Radiation oncology, surgery, very high insulin dose compared to a normal diabetic  PROLACTIN Triggers and maintains lactation Continued teat stimulation will result in release of prolactin  AKA Thyrotropic hormone Stimulates growth and development of the thyroid gland THYROID STIMULATING HORMONE (TSH) Negative feedback mechanism TSH stimulates release of thyroid hormone → elevated thyroid hormone inhibits secretion of TSH When thyroid hormone drops, TSH is stimulated and released  CLINIC AL DISEASE: HYPOTHYROIDISM Disease summary: Autoimmune disease resulting in destruction of the cells that produce thyroid hormone. Body loses its ability to synthesize thyroid hormone. Clinical signs: Obesity, lethargy, skin issues Diagnosis: T4 (low), free T4 (low), TSH (high), thyroid This Phot o by Unknown Author is licensed under CC BY-SA antiglobulin (high) Treatment: Supplement thyroid hormone levothyroxine for life Prognosis: Excellent!  Stimulates growth and development of the cortex of the adrenal gland ACTH stimulates release of cortisol A D RE N O CO RT I C OT RO P IC H O R M O N E ( AC T H ) Negative feedback mechanism ACTH can be released in times of stress  Female Stimulates growth and development of follicles in the ovaries FOLLI CLE STIMULATING Stimulates lining cells of follicles to HORMONE secrete estrogens (FSH) Male Stimulates spermatogenesis in the seminiferous tubules  Female Rising estrogen (from FSH stimulation) has a negative feedback on FSH production FSH decreases, LH levels start to rise LH peaks and ovulation occurs LUTEINIZING LH stimulates the follicle to become the corpus luteum after ovulation HORMONE (LH) Corpus luteum produces progesterone Male LH stimulates interstitial cells to produce testosterone  Increases pigment production (melanocytes) MELANOCYTE- STIMULATING HORMONE (MSH) Other functions? Unknown  Technically produced by the hypothalamus and POSTERIOR stored in the posterior PITUITARY HORMONES pituitary Antidiuretic hormone Oxytocin  ANTIDIURETIC HORMONE (ADH) Increases renal reabsorption of water Prevents diuresis, maintains hydration of the body ADH is released when the hypothalamus detects dehydration ADH is inhibited by alcohol and caffeine Diabetes insipidus ADH deficiency Similar symptoms to diabetes → PU/PD Treatment: supplement ADH  OX YTOCIN Target tissues uterus & mammary glands Uterine contractions of myometrium during breeding & parturition Milk let-down after stimulation of the teat Myoepithelial cells of the alveoli contract Possible other behavioral roles in bonding with neonate THYROID GLAND  THYROID Two lobes on either side of the larynx, connected by the isthmus Microscopically: Thousands of follicles Follicle: sphere of simple cuboidal glandular cells surrounding globule of colloid (thyroid hormone precursor) Hormones produced by the thyroid: Thyroid hormone Calcitonin  Anterior pituitary releases TSH → stimulates thyroid gland to produce thyroid hormone T4 (tetriodothyronine/thyroxine) THYROID Biologically inactive form HORMONE Functions as a reservoir of T3 Converted to T3 in liver, kidney, muscle T3 (triiodothyronine) Biologically active form  THYROID HORMONE EFFECTS Calorigenic effect Heats the body Metabolism regulation Protein, carb & lipid metabolism Similar to GH Protein anabolism, Hyperglycemia, lipid catabolism Young animals CNS, bone, muscle development.  Produced by C cells in the thyroid gland Maintains blood calcium homeostasis C ALCITONIN Prevents hypercalcemia → excess calcium is deposited in the bones Calcitonin has the opposite effect of parathyroid hormone  Produced by the parathyroid glands Several small, pale nodules near the thyroid glands PARATHYROID HORMONE (PTH) PTH prevents hypocalcemia when iCa is too low Kidneys retain calcium Intestines absorb calcium Resorbs calcium from the bone THE ADRENAL GLANDS  Adrenals are located near the cranial ends of the kidneys ADRENAL GLANDS Actually composed of 2 glands of different embryologic origin Cortex Medulla  ADRENAL CORTEX Cortex: Outer gland originates from endocrine glandular tissue 3 groups of hormones produced in the cortex Glucocorticoids Mineralocorticoids Sex hormones  Named glucocorticoid due to hyperglycemic effect on blood glucose Cortisol, cortisone, cortisterone G LU C O C O RT I C O I D Gluconeogenesis HORM ONES Helps maintain BP Helps body adapt to stress  Regulate electrolytes (mineral salts) Aldosterone MI NE R A LO C ORT I C OI D H O R MO NE S Sodium, potassium, hydrogen ions Water reabsorption (via osmosis in the kidney) Kidney is the target organ  CLINIC AL DISEASE: ADDISON’S DISEASE (HYPOADRENOCORTIC ISM) Addison’s disease is a deficiency in the adrenal hormones Cortisol Aldosterone Symptoms: Electrolyte imbalance, hypoglycemia, hypotension Treatment: Stabilize, steroid injection, Oral prednisone & DOCP or percorten injections for life Prognosis: excellent with treatment. Death without treatment.  SEX HORMONES Small amounts of sex hormones Androgens Estrogens  Inner gland Develops from nervous tissue ADRENAL Regulated by sympathetic MEDULLA nervous system Norepinephrine Epinephrine Increased HR, increased cardiac output, bronchodilation THE PANCREAS  Exocrine pancreas → pancreatic enzymes Endocrine pancreas PANCREAS Small percentage of total pancreatic volume Glucagon Insulin Somatostatin  Large clumps of endocrine cells form pancreatic islets AKA Islets of Langerhans Alpha cells: glucagon PANCREATIC Beta cells: insulin ISLETS Delta cells: somatostatin Metabolism of glucose (glucagon & insulin) Inhibition of endocrine pancreas secretion (somatostatin)  Causes glucose, amino acids & fatty acids to be absorbed by the cells INSULIN Insulin lowers blood glucose  GLUCAGON Glucagon raises blood glucose (opposite of insulin) Stimulates liver cells to convert glycogen to glucose Stimulates conversion of protein & fat to glucose via gluconeogenesis GONADS  TESTES Interstitial cells produce androgens under the influence of LH Testosterone Male secondary sex characteristics Libido Spermatogenesis Anabolism  Controlled by FSH & LH from the anterior pituitary Estrogens OVARIES Progestins Relaxin (late pregnancy)  Female sex hormones Estradiol, estrone FSH stimulates follicles ESTROGENS Follicular cells produce & release estrogens Physical and behavioral changes associated with estrus FSH drops, LH peaks, ovulation occurs  LH stimulates development of the corpus luteum after ovulation Corpus luteum produces several PROGESTINS progestin hormones Progesterone is the primary hormone Steroid hormone Progestins are utilized in breeding programs to regulate timing of the cycle  Late pregnancy hormone RELAXIN Source of relaxin production depends on the species Corpus Placenta Uterus luteum  Kidneys Erythropoietin stimulates bone marrow to produce RBCs Stomach OTHE R HO RMO N E - Gastrin stimulates gastric glands to secrete HCl and digestive enzymes P RO D UC ING O RG ANS Small intestine Secretin stimulates pancreas to secrete sodium bicarbonate Cholecystokinin (CCK) stimulates pancreatic release of digestive enzymes Other functions related to bile release, stomach motility  Chorionic gonadotropin produced in humans and horses Placenta (pregnancy tests evaluate for it) Estrogen, progesterone, relaxin OTHE R HO RMO N E- Thymosin and thymopoietin P RO D UC ING Thymus cause cells in the thymus to develop into T lymphocytes O RG ANS Pineal Melatonin affects wake-sleep Body cycles (brain) THE END