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CSU - ANEQ 305 - Class Notes - Week 8

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CSU - ANEQ 305 - Class Notes - Week 8

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background image ANEQ 305 
Chapter 7: Endocrine 
7.4: Endocrine Control of Growth and Development in Vertebrates
​ (Continued)  ● Recall from last time: Growth Hormone administration  ○ Increase bone growth 
○ Increase muscle mass 
○ Increase milk production in dairy cattle 
● Higher proportion of  ​Type 2B fibers  ○ Larger size 
○ Decrease in protein turnover 
○ Greater growth efficiency 
7.5: Thyroid Gland  ● Located in throat below larynx  ○ Composed of  ​thyroid follicles​: follicular arranged in fluid filled spheres  ○ Colloid serves as  ​extracellular storage site​ in form of ​thyroglobulin​ (large  glycoproteins)   ● Thyroid Hormone synthesis  ○ Thyroglobulin ​ (Tg) synthesis by thyroid follicular cells by incorporates ​tyrosine  and secreted into colloid by exocytosis  ○ Thyroid follicular cells capture  ​iodide​ (I-) using iodide pump  ○ I-  ​activated​ and ​attached to tyrosine​ on Tg in colloid  ■ Monoiodotyrosine ​ (MIT) → 1 I-  ■ Diiodotyrosine ​ (DIT) → 2 I-’s   ○ Iodinated tyrosines couple to form tetraiodothyronine (T4, thyroxine) and  triiodothyronine (T3)  ● Secretion of thyroid hormone  ○ Follicular cells take up colloid (containing Tg) by  ​phagocytosis  ○ Lysosomal enzymes  ​split off​ T4, T3, MIT, and DIT in process of Tg breakdown  ○ T4 and T3 (biologically active blood hormone)  ​diffuse across follicular cell  membrane ​ into blood, while MIT and DIT are recycled to iodide and tyrosine  ● Mechanism of thyroid hormone  ○ T3 is  ​major biologically active​ form of thyroid hormone  ○ Most secreted T4 is  ​activated​ by conversion to T3 be ​deiodinase​ enzyme  ○ T3 binds with  ​nuclear receptors​ attached to ​thyroid-response-element  ○ Alters transcription of specific mRNAs and synthesis of specific proteins  ● Effects of thyroid hormones   ○ Increased  ​basal metabolic rate​ (BMR) through increased mitochondria and  Na+-K- pump activity  ○ Molting ​ in birds and mammals 
background image ○ Modulate synthesis and degradation of metabolic fuel molecules 
○ Sympathomimetic effect
​: increase target cell responsiveness to catecholamines  ○ Increased heart rate and force of contraction 
○ Essential for growth (
​permissive effect​ on GH)  ○ Development of CNS 
○ Metamorphosis in amphibians 
● Regulation of thyroid hormone secretion  ○ Negative feedback loop ​ involving ​hypothalamus-pituitary-thyroid axis  ■ Thyroid-stimulating hormone ​ (TSH) stimulates almost every step of  thyroid hormone synthesis and secretion  ■ Hypothalamic  ​thyrotropin-releasing hormone​ (TRH) stimulates TSH  secretion by thyrotropes in anterior pituitary  ■ Elevated T3 and T4 levels  ​inhibits​ TSH secretion  ○ Other factors affecting thyroid hormone secretion  ■ Stress ​ inhibits  ■ Cold ​ stimulates (in infants)  ● Abnormalities of thyroid function  ○ Hypothyroidism ​: low thyroid activity  ■ Causes  ● Primary failure of thyroid gland or 
● Secondary to a deficiency of TSH (or TRH) or 
● Inadequate dietary supply of iodine 
■ Symptoms stem from  ​reduced metabolic activity​ (ex. Weight gain, fatigue,  poor cold tolerance)  ○ Hyperthyroidism ​: elevated thyroid activity  ■ Symptoms stem from  ​increased metabolic activity​ (weight loss, increased  heart rate, anxiety)   7.6: Adrenal Gland  ● Located above kidneys  ○ Outer  ​adrenal cortex​ composed of ​steroidogenic​ cells of mesodermal origin  ○ Inner  ​adrenal medulla​ composed of ​chromaffin cells​ of neural crest origin  ○ Steroidogenic and chromaffin tissues are intermingled in most non-mammalian  species  ● Steroid hormone of adrenal cortex   ○ Derived from cholesterol  ■ Modified by stepwise enzymatic reactions  ○ Mineralocorticoids ​ (ex. ​aldosterone​)  ■ Influence mineral (electrolyte) balance 
■ Produced in 
​zona glomerulosa 
background image ○ Glucocorticoids ​ (ex. ​cortisol​)  ■ Role of metabolism of glucose, proteins, and lipids 
■ Produced in 
​zona fasciculata  ○ Sex steroids ​ (ex. ​dehydroepiandrosterone​)  ■ Androgenic (masculinizing) effects 
■ Produce 
​zona fasciculata​ and ​zona reticularis  ● Effects of glucocorticoids  ○ Metabolic effects ​: increase blood glucose, while reducing protein and fat stores  ○ Permissive actions ​ (ex. Permit catecholamines to induce vasoconstriction)  ○ 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  ■ Adrenocorticotropic hormone ​ (ACTH) stimulating cortisol secretion  ■ Hypothalamus  ​corticotropin-releasing hormone​ (CRH) stimulates ACTH  secretion by corticotrophs in the anterior pituitary   ■ Elevated glucocorticoid levels  ​inhibit​ CRH and ACTH secretion  ○ Other factors affecting glucocorticoid secretion  ■ Stress ​ stimulates CRH secretion  ■ Circadian rhythm   ● Abnormalities of adrenocortical function  ○ Cushing’s syndrome ​: excessive cortisol secretion  ■ Most common cause: overstimulation by excess ACTH 
■ Consequences of excessive gluconeogenesis 
● High blood glucose and protein loss 
● Redistribution of fat in humans and dogs 
○ Addison’s disease ​ (primary adrenocortical insufficiency)  ■ Most common cause: autoimmune destruction of adrenal cortex 
■ Aldosterone deficiency
​ can be fatal  ■ Cortisol deficiency ​ causes poor response to stress, hypoglycemia, lack of  permissive actions  ● Chromaffin cells ​ in ​adrenal medulla​ are modified postganglionic sympathetic neurons  ○ Secretes  ​NE​ and ​epinephrine​ (ratio varies between species)  ■ Both are catecholamines derived from tyrosine 
■ Most synthetic steps take place in cytoplasm 
■ Stored in 
​chromaffin granules  ○ Secretion by  ​exocytosis​ (similar to neurotransmitter secretion)  ○ Secretion is stimulated by  ​sympathetic system 

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School: Colorado State University
Department: Science
Course: Functional Large Animal Anatomy/Physiology
Professor: Hyungchul Han
Term: Fall 2016
Tags: anatomy, Physiology, Anatomyandphysiology, ANEQ305, and Colorado State University
Name: ANEQ305 Week 8
Description: These notes cover the last of Chapter 7- The Endocrine System
Uploaded: 03/05/2018
7 Pages 63 Views 50 Unlocks
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