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Understanding Pineal, Thyroid, and Parathyroid Gland Functions

School
HKU SPACE - Kowloon East Campus**We aren't endorsed by this school
Course
BIOLOGY NEUROSCIEN
Subject
Biology
Date
Dec 12, 2024
Pages
18
Uploaded by BrigadierInternet15572
Chapter 17: Pineal, thyroid and parathyroid glandsLearning objectives:•Describe the function of the pineal gland•Understand the structure of the thyroid gland and the functions of the thyroid hormones (thyroxine and calcitonin)•Describe how calcitonin and parathyroid hormone regulate blood calcium levels•Describe the function of the thymus gland1http://healthpages.org/wp-content/uploads/2012/06/thyroid.jpghttp://www.shivayoga.net/wp-content/shivayoga//pineal.jpg
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The Pineal Gland2
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•Tiny pinecone-shaped •Located behind hypothalamus Secretesmelatoninduring the night•24-hour circadian rhythms (sleep-wake cycle)•Timing of puberty•Prevent premature sexual maturation•Mood •Disorder of melatonin secretion →DepressionTarget organ: Brainhttp://www.estatevaults.com/bol/biological_clock.jpghttp://www.ch.ic.ac.uk/local/projects/s_thipayang/melatoninchart.jpghttp://leavingbio.net/endocrine%20system/Endocrine%20System_files/image004.jpgPineal gland3
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The Thyroid Gland4https://nci-media.cancer.gov/pdq/media/images/719086.jpg
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Thyroid GlandThyroid hormones (T3and T4) are made in the colloid in response to TSH1.Thyroxine(tetraiodothyronine, or T4)–T4: 4 iodines (higher conc. in blood)2.Triiodothyronine(T3)–T3: 3 iodines (active form in target cells)T4→T3 in targetcellsA butterfly-shaped gland located in the neck, inferior to the larynxComposed of spherical sacs called thyroid folliclessurrounded by follicular cells •Provide iodine and tyrosine (amino acid) for thyroid hormone productionBetweenthyroid follicles are a nest of C cells (parafollicular cells)P.506, Saladin, (2010) Human Anatomy, 3rd Ed (McGrawHill Pub)5
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https://highered.mcgraw-hill.com/sites/0073378100/student_view0/chapter11/animations.html6https://www.youtube.com/watch?v=YUv9PFQper4
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Functions of Thyroid Hormones7
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Almost every cell in the body has TH receptors →Widespread effects1.Increase basal metabolic rate•the main determinant of the basal metabolic rate2. Tissue sensitivity to sympathetic activation•Increasing the heart’s responsiveness to catecholamines 3. Brain development and function 4. GrowthWhat are the functions of thyroid hormones (TH)?8https://media.istockphoto.com/photos/doctor-palpates-of-fat-mature-womans-neck-for-diagnostics-of-thyroid-picture-id1326326607?k=20&m=1326326607&s=612x612&w=0&h=j2hfM8MDxjWjy_sPD8r8_FxWtzjHO2LGosEB4eKltN0=https://media.istockphoto.com/photos/hormones-of-thyroid-gland-t3-and-t4-picture-id1093995914?k=20&m=1093995914&s=612x612&w=0&h=BQlSNzywk2NC87sHGLFBVoij-fmhEnpNJg88jcoG5OE=
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•Stimulate ATP and heat generation−TH is the most important factor that determines basal metabolic rate (i.e. O2consumption, energy and heat production at rest)−Cells burn more nutrients and produce more heat and ATP−A greater proportion of chemical energy from nutrients is converted into heat−Heat production > ATP production•Thermoregulation−TH release is stimulated by cold →Heat to regulate body temperature1. Increases Basal Metabolic Rate9
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•Permissive effects on catecholamines (i.e. epinephrine and norepinephrine)»With permissiveness, thyroid hormone must be present in adequate amounts to “permit” epinephrine and norepinephrine to exert their full effect•Thyroid hormone increases the no. of b-adrenergic receptors in epinephrine’s target cells→increasing the effectiveness of epinephrine and norepinephrineEffect on the cardiovascular system•↑ cardiac output by:1. ↑ stroke volume by increasing cardiac muscle contractility2. ↑ heart rate 2. Increases Target-cell Responsiveness to Catecholamines10
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Thyroid hormones are critical for normal brain development•Essential for normal CNS development (fetal and early life)- Insufficient TH secretion (hypothyroidism) →Mental retardation→Retarded growth and development- Can be partially reverted if treated quickly after birth with iodineand/or TH replacement•Brain function: Behavior / mental status-Due to effect of TH on regulation of gene expression (e.g. increase no. of β-adrenergic receptors)-High TH →Nervousness, anxiety, stress, irritability, marked impatience, restlessness-Low TH →Lack of energy and motivation, depression3. Brain Development and Function11
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Thyroid hormone is essential for normal growth because of its effects on growth hormone (GH) and insulin-like growth factor (IFG)•Thyroid hormone stimulates GH secretion and increases production of IGF by the liver•Promotes the effects of GH and IGF on the synthesis of new structural proteins and on skeletal growth–thyroid-deficient children have stunted growth and mental retardation (cretinism) that can be reversed by thyroid replacement therapy–Unlike excess GH, excess thyroid hormone does not produce excessive growth4. Growth12https://ars.els-cdn.com/content/image/1-s2.0-S1521690X09001031-gr2.jpgCongenital hypothyroidismAbsence of T3or T4
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Thyroid Hormone is Regulated by Hypothalamus-pituitary-thyroid Axis•Negative feedback usually prevents large variations in the blood’s thyroid hormone concentrations•Coldand stressmodify production by altering the secretion of TRH and TSH•Inadequate intake of iodine leads to inadequate thyroid hormone production, more TSH secretion and resulting in goiter(enlargement of the thyroid)13https://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/Thyroid_system.svg/1200px-Thyroid_system.svg.png
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14https://www.clevelandclinic.org/healthinfo/ShowImage.ashx?PIC=4271https://i0.wp.com/post.medicalnewstoday.com/wp-content/uploads/sites/3/2020/11/GettyImages-1220858563-header-1024x575.jpg?w=1155&h=1528
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Thyroid Gland and CalcitoninC cellsSecrete calcitoninfrom parafollicularcells–Promotes deposition of Ca2+ on bone and lower blood calcium concentrationTarget organs: Bone and kidneyCalcitonin1.Inhibits osteoclast activity (osteoclasts break down the bone tissue: bone resorption)→Release less Ca2+from the bone2.Stimulates osteoblast activity (osteoblasts build up the bone tissue)→Absorb more Ca2+from the blood3.Promote excretionof Ca2+ from kidneyOverall result →↓ blood (plasma) [Ca2+]P.506, Saladin, (2010) Human Anatomy, 3rd Ed (McGrawHill Pub)works together with parathyroid hormone to control plasma calcium level15
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Parathyroid gland4 parathyroid glands embedded in the posterior side of the thyroid →parathyroid hormone (PTH)PTH increases plasma [Ca2+] by: 1.Promoting Ca2+ release from the bone (boneresorption)2.Increasing Ca2+reabsorption by kidneys3.Promoting absorption of Ca2+ from gut•Indirectly through stimulating the production of active form of vitamin D(calcitriol)Target organs: Bone, KidneyControl of PTH release:-Regulated by plasma [Ca2+ ] (-ve feedback)-Parathyroid glands contains Ca2+chemoreceptors on the plasma membrane to detect plasma Ca2+ level P.507, Saladin, (2010) Human Anatomy, 3rd Ed (McGrawHill Pub)16
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PTH opposes the function of calcitoninP. 347, Vander A., Sherman, J and Luciano, D. (2010) Human Physiology, 12th ed. (McGraw Hill)17
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Thymus•A bilobed gland above the heart in the mediastinum•Endocrine, lymphatic and immune•Secretesthymus hormones→Stimulate the development of other lymphatic organs→Regulate the development and activity ofT lymphocytesTarget cells: T lymphocytesP.505, Saladin, (2010) Human Anatomy, 3rd Ed (McGrawHill Pub)18
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