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CSU / Animal Sciences / ANEQ 305 / Where is the thyroid gland located anatomically?

Where is the thyroid gland located anatomically?

Where is the thyroid gland located anatomically?


School: Colorado State University
Department: Animal Sciences
Course: Functional Large Animal Physiology
Professor: Hyungchul han
Term: Fall 2016
Cost: 25
Name: ANEQ305 Week 8 notes
Description: Notes covering the endocrine system
Uploaded: 10/16/2016
7 Pages 130 Views 1 Unlocks

ANEQ305 Week 8 10-10-16  

Where is the thyroid gland located anatomically?

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

What is the role of thyroglobulin in thyroid hormone synthesis?

- 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  If you want to learn more check out What do infants learn in the sensorimotor stage?

- T4 and T3 (biologically active thyroid hormones) diffuse across follicular cell  membrane into blood, while MIT and DIT are recycles to iodide and tyrosine  

How does iodine get into follicular cells?

Don't forget about the age old question of What is the meaning of person-centered messages?

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  We also discuss several other topics like How do you convert molar mass?

- 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  If you want to learn more check out What happens when a thermosetting polymer is heated?

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  We also discuss several other topics like Who guards the guardians?

 - 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  We also discuss several other topics like Why are some investments planned and others unplanned?

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  


 - 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)  


- 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


Highlighted = extra lecture information  

Underlined = important info  

Bold= slide header  

Bold and underlined = chapter title

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