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ANEQ305 Week 8 notes

by: Andrew Everitt

ANEQ305 Week 8 notes ANEQ305

Andrew Everitt

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Notes covering the endocrine system
Functional Large Animal Anatomy/Physiology
Dr. Hyungchul Han
Class Notes
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Popular in Functional Large Animal Anatomy/Physiology

Popular in Animal Science

This 7 page Class Notes was uploaded by Andrew Everitt on Sunday October 16, 2016. The Class Notes belongs to ANEQ305 at Colorado State University taught by Dr. Hyungchul Han in Fall 2016. Since its upload, it has received 14 views. For similar materials see Functional Large Animal Anatomy/Physiology in Animal Science at Colorado State University.


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Date Created: 10/16/16
ANEQ305 Week 8 10-10-16 Selection for Growth also changes muscle fiber type - Higher proportion of Type 2B fibers o Larger size o Lower protein turnover o Greater growth efficiency o White muscle fiber Thyroid gland is located in the throat below the larynx - Composed of follicular cells arranged in fluid-filled spheres (thyroid follicles) - Colloid serves as an extracellular storage site for thyroid hormones in the form of thyroglobulin, a large glycoprotein Thyroid hormone synthesis - Thyroglobulin (Tg) is synthesized y thyroid follicular cells (incorporating tyrosine) and secreted into colloid by exocytosis - Thyroid follicular cells efficiently capture iodide obtained from the diet, using an iodide pump - Iodide is activated and attached to tyrosine molecules on Thyroglobulin in colloid o Monoiodotyrosine (MIT) has 1 iodine o Diiodotyrosine (DIT) has 2 iodine - Iodinated tyrosines couple to form tetraiodothyronine (t4, thyroxine) and triiodothyronine (T3) Secretion of thyroid hormones - Follicular cells take up a piece of colloid (containing iodinated Tg) by phagocytosis - Lysosomal enzymes split off T4, T3, MIT and DIT in the process of breaking down Tg - T4 and T3 (biologically active thyroid hormones) diffuse across follicular cell membrane into blood, while MIT and DIT are recycles to iodide and tyrosine Mechanism of Thyroid Hormone Action - T3 is the major biologically active form of thyroid hormone - Most secreted T4 is activated by conversion to T3 by a deiodinase enzyme - T3 binds with nuclear receptors attached to thyroid-response elements of DNA - Alters transcription of specific mRNAs and synthesis of specific proteins - Iodine – major component in Thyroid hormone - Tyrosine – amino acid – second major component in Thyroid Hormone - Majority of thyroid hormone secreted as T4 - T3 is stronger and more potent - Lipophilic – steroids and thyroid hormones Effects of Thyroid Hormone - To increase basal metabolic rate – main function o Done through increased mitochondrial and Na+ - K+ pump activity - Modulate synthesis and degradation of metabolic fuel molecules - Molting in birds and mammals - Sympathomimetic effect – increase cell responsiveness to catecholamines - Increase heart rate and force of contraction - Essential for growth (permissive effect on GH) - Development of CNS - Required for metamorphosis in amphibians – tadpoles would not become frogs Regulation of Thyroid hormone secretion - Negative feedback loop involving hypothalamus-pituitary-thyroid axis o Thyroid-stimulating hormone stimulated almost every step of thyroid hormone synthesis and secretion o Hypothalamic thyrotropin-releasing hormone (TRH) stimulates TSH secretion by thyrotropes in anterior pituitary o Elevated T3 and T4 levels inhibit TSH secretion - Other factors affecting thyroid hormone secretion o Stress inhibits TSH secretion o Cold stimulates TSH secretion (infants) Abnormalities of thyroid function - Hypothyroidism – low thyroid activity o Lower metabolic rate o Causes  Primary failure of thyroid gland  Secondary to a deficiency of TSH (or TRH)  Inadequate dietary supply of iodine o Symptoms stem from reduced metabolic activity - Hyperthyroidism – high thyroid activity o Higher metabolic rate o Higher body temperature Adrenal glands are located above the kidneys - Outer layer of glands is called adrenal cortex and is made of steroidogenic cells of mesodermal origin - Inner layer of gland is called adrenal medulla and is composed of chromaffin cells of neural crest origin - Steroidogenic and chromaffin tissues are intermingled in most non- mammalian species Steroid hormones of the adrenal cortex - Derived from cholesterol o Modified by stepwise enzymatic reaction - Glucocorticoids o Role in metabolism of glucose, proteins and lipids o Produced in zona fasciculate - Mineralocorticoids o Influenced mineral (electrolyte) balance o Produced in zona glomerulosa - Sex steroids o Androgenic (masculinizing) effects o Produced in zona fasciculata and zona reticularis Sympathetic controls blood glucose levels Effects of glucocorticoids - Metabolic effects – increase blood glucose, reducing fat and protein stores - Permissive action - Enhanced memory - Adaptation to long-term stress - Anti-inflammatory and immunosuppressive effects, especially at high doses Regulation of glucocorticoid secretion - Negative feedback loop involving hypothalamus-pituitary-adrenal axis o Adrenocorticotropic hormone (ACTH) stimulates cortisol secretion o Hypothalamic corticotropin-releasing hormone (CRH) stimulates ACTH secretion by corticotropes in the anterior pituitary o Elevatedd glucocorticoid levels inhibit CRH and ACTH secretion - Other factors affecting glucocorticoid secretion o Stress stimulates CRH secretion o circadian rhythm Abnormalities of adrenocortical function - Cushing’s symptom : excessive cortisol secretion o Most common cause: overstimulation by excess ACTH o Can have moon face – very round head o Consequences of excessive gluconeogenesis  High blood glucose and protein loss  Redistribution of fat in humans and dogs - Addison’s disease: deficiency of adrenal steroids o Most common cause: autoimmune destruction of the adrenal cortex o Aldosterone deficiency can be fatal o Cortisol deficiency causes poor response to stress, hypoglycemia, and lack of permissive actions Chromaffin cells in the adrenal medulla are modified postganglionic sympathetic neurons - Secrete norepinephrine and epinephrine o Derived from Tyrosine o Most synthetic steps take place in cytoplasm o Stored in chromaffin granules - Secretion by exocytosis - Secretion is stimulated by sympathetic nervous system Effects of adrenal catecholamines - Increased cardiac output - Vasodilation of coronary and skeletal-muscle arterioles - Dilation of respiratory airways - Inhibition of digestive activity - CNS arousal - Sweating - Mobilization of stored carbohydrates and fat - Dilation of pupils and flattening of lens Multifaceted stress response is coordinated by the hypothalamus - Hypothalamus receives input concerning physical and emotional stressors o Activates sympathetic nervous system o Secretes CRH o Secretes vasopressin - Chronic stress responses are detrimental o Breakdown of body structures o Reproductive failure o Increased susceptibility to disease Metabolism refers to all chemical reactions that occur within body cells - Anabolism – synthesis of larger organic molecules from smaller subunits o Requires energy in the form of ATP o Manufacture of molecules needed by the cell o Storage of nutrients - Catabolism – breakdown of organic molecules into smaller subunits o Hydrolysis of large organic macromolecules o Oxidation of smaller molecules to release energy for ATP production Glucose, fructose, galactose – 3 simple sugars – monosaccharides Sucrose and lactose – disaccharides Cellulose and starch – polysaccharide 1 gram of sugar = 4,000 calories or 4 Kcal (Cal) 1 gram of protein = 4,000 calories or 4 Kcal (Cal) 1 gram of fat = 9,000 calories or 9 Kcal (Cal) Water, vitamin, minerals, carbs, fat, proteins – 6 things found in food 90 milligram per 100 liters of blood = normal blood glucose level for humans Regulation of metabolic fuels - Dietary intake is usually intermittent - Absorptive state o After a meal o Excess nutrients are stored as glycogen or triglycerides - Post-absorptive state o Between meals o Fatty acids are the major energy source for most tissues o Endogenous energy stores are mobilized to provide energy Pancreas is composed of both exocrine and endocrine tissues - Exocrine portion secretes digestive enzymes through the pancreatic duct into the digestive tract lumen - Islets of Langerhans are integrators of endocrine regulatory responses and secrete hormones o Pancreatic hormones are the dominant hormonal regulators of glucose homeostasis  Beta cells secrete insulin  Alpha cells secrete glucagon  Delta cells secrete somatostatin  F cells secrete pancreatic polypeptide Effects of insulin - Lowers blood glucose and promotes storage of carbohydrates o Facilitates glucose transport into most cells o Stimulates glycogenesis in skeletal muscle and liver o Inhibits glycogenesis in liver o Inhibits gluconeogenesis in liver - Lowers blood fatty acids and promotes storage of triglycerides o Stimulates production of fatty acids from glucose o Inhibits lipolysis - Lowers blood amino acids and enhances protein synthesis o Promotes uptake of amino acids into cells - Insulin higher shortly after eating - Glucagon higher after long period after eating - Insulin lowers blood glucose to normal level Excretion of glucose is not under glucose control Diabetes means sugar in pee Regulation of Insulin secretion - Direct negative feedback system between pancreatic Beta cells and the blood glucose level o During absorption of a meal, insulin secretion increases - Other factors that stimulate insulin secretion: o Increased blood amino acids o Gastrointestinal hormones: glucose-independent insulintotropic peptide (GIP), glucagon-like peptide (GLP) o Increased parasympathetic activity Glucagon - Opposite effect of insulin o Increases hepatic glucose production and raises blood glucose levels o Promotes fat breakdown and inhibits triglyceride synthesis, raising fatty acid levels in blood o Promotes protein breakdown in liver, but does not affect muscle protein - Glucagon secretion is increased during the post-absorptive state when blood glucose levels are low Diabetes Mellitus - Elevated blood glucose levels - Glucose in urine attracts water to cause excessive urination - Type 1 o Lack of insulin secretion by pancreatic Beta cells o Requires administration of insulin - Type 2 o Not insulin dependent o Normal or elevated insulin levels o The receptors for insulin don’t function properly  Reduced sensitivity of target cells to insulin Importance of Calcium - 99% of calcium is stored in skeleton and teeth o Only free Ca2+ in plasma is biologically active and subject to regulation - Both Ca2+ homeostasis and Ca2+ balance must be regulated - Ca2+ plays a vital role in: o Neuromuscular excitability o Excitation-contraction coupling in cardiac and smooth muscle o Stimulus-secretion coupling o Maintenance of tight junctions between cells o Clotting of blood - Other 1% is free calcium and is used in physiological function Parathyroid Hormone - Released from parathyroid glands, located near the thyroid gland - Essential for life - Raises plasma Ca2+ levels o Promotes transfer of Ca2+ from bone fluid into plasma o Promotes reabsorption of bone by osteoclasts o Increases reabsorption of Ca2+ in the kidneys o Indirectly increases Ca2+ absorption from the small intestine by activating vitamin D - PTH secretion is increased in response to a fall in plasma Ca2+ levels - Acts on bone, kidneys, and small intestine (indirectly) Calcitonin - Produced by C cells of the mammalian thyroid gland, ultimobranchial glands in birds, and connective tissue sheets around the heart in fishes - Decreases plasma Ca2+ levels o Decreases transfer of Ca2+ from bone fluid into plasma o Decreases bone resorption by inhibiting activity of osteoclasts o Ability to lower blood Ca2+ is especially important in marine fishes because of Ca2+ in sea water - Calcitonin secretion is increased in response to an increase in plasma Ca2+ levels Vitamin D (cholecalciferol) - Produced in skin from 7-dehydrocholesterol on exposure to sunlight o Can also be obtained in the diet - Activated by sequential alterations in the liver and kidneys, forming 1,26- (OH)2-vitamin D3 (calcitriol) - Promotes Ca2+ absorption in the intestine - Increases sensitivity of bone to PTH Key Highlighted = extra lecture information Underlined = important info Bold= slide header Bold and underlined = chapter title


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