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© 2013 Pearson Education, Inc. Thyroid Gland Two lateral lobes connected by median mass called isthmus Composed of follicles that produce glycoprotein.

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Presentation on theme: "© 2013 Pearson Education, Inc. Thyroid Gland Two lateral lobes connected by median mass called isthmus Composed of follicles that produce glycoprotein."— Presentation transcript:

1 © 2013 Pearson Education, Inc. Thyroid Gland Two lateral lobes connected by median mass called isthmus Composed of follicles that produce glycoprotein thyroglobulin Colloid (thyroglobulin + iodine) fills lumen of follicles and is precursor of thyroid hormone Parafollicular cells produce the hormone calcitonin

2 © 2013 Pearson Education, Inc. Figure 16.9 The thyroid gland. Hyoid bone Thyroid cartilage Common carotid artery Inferior thyroid artery Trachea Aorta Gross anatomy of the thyroid gland, anterior view Epiglottis Superior thyroid artery Isthmus of thyroid gland Left subclavian artery Left lateral lobe of thyroid gland Colloid-filled follicles Follicular cells Parafollicular cells Photomicrograph of thyroid gland follicles (145x)

3 © 2013 Pearson Education, Inc. Thyroid Hormone (TH) Actually two related compounds –T 4 (thyroxine); has 2 tyrosine molecules + 4 bound iodine atoms –T 3 (triiodothyronine); has 2 tyrosines + 3 bound iodine atoms Affects virtually every cell in body

4 © 2013 Pearson Education, Inc. Thyroid Hormone Major metabolic hormone Increases metabolic rate and heat production (calorigenic effect) Regulation of tissue growth and development –Development of skeletal and nervous systems –Reproductive capabilities Maintenance of blood pressure

5 © 2013 Pearson Education, Inc. Synthesis of Thyroid Hormone Thyroid gland stores hormone extracellularly Thyroglobulin synthesized and discharged into follicle lumen Iodides (I – ) actively taken into cell and released into lumen Iodide oxidized to iodine (I 2 ), Iodine attaches to tyrosine, mediated by peroxidase enzymes

6 © 2013 Pearson Education, Inc. Synthesis of Thyroid Hormone Iodinated tyrosines link together to form T 3 and T 4 Colloid is endocytosed and combined with lysosome T 3 and T 4 are cleaved and diffuse into bloodstream

7 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 1 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 2 3 4 5 6 7 Golgi apparatus Iodide (I) Rough ER Capillary Iodide (I – ) is trapped (actively transported in). Lysosome Lysosomal enzymes cleave T 4 and T 3 from thyroglobulin and hormones diffuse into bloodstream. Thyroglobulin colloid is endocytosed and combined with a lysosome. Iodinated tyrosines are linked together to form T 3 and T 4. Iodide is oxidized to iodine. Iodine is attached to tyrosine in colloid, forming DIT and MIT. To peripheral tissues Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Thyro- globulin colloid T3T3 T4T4 T3T3 T4T4 T3T3 T4T4 Iodine DITMIT Colloid

8 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 2 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 Golgi apparatus Rough ER Capillary Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Colloid

9 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 3 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 Golgi apparatus Rough ER Capillary Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Colloid 2 Iodide (I) Iodide (I – ) is trapped (actively transported in).

10 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 4 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 Golgi apparatus Rough ER Capillary Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Colloid 2 Iodide (I) Iodide (I – ) is trapped (actively transported in). Iodine 3 Iodide is oxidized to iodine.

11 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 5 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 Golgi apparatus Rough ER Capillary Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Colloid 2 Iodide (I) Iodide (I – ) is trapped (actively transported in). Iodine 3 Iodide is oxidized to iodine. 4 Iodine is attached to tyrosine in colloid, forming DIT and MIT. Thyro- globulin colloid DITMIT

12 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 6 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 Golgi apparatus Rough ER Capillary Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Colloid 2 Iodide (I) Iodide (I – ) is trapped (actively transported in). Iodine 3 Iodide is oxidized to iodine. 4 Iodine is attached to tyrosine in colloid, forming DIT and MIT. Thyro- globulin colloid DITMIT 5 Iodinated tyrosines are linked together to form T 3 and T 4. T3T3 T4T4

13 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 7 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 Golgi apparatus Rough ER Capillary Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Colloid 2 Iodide (I) Iodide (I – ) is trapped (actively transported in). Iodine 3 Iodide is oxidized to iodine. 4 Iodine is attached to tyrosine in colloid, forming DIT and MIT. Thyro- globulin colloid DITMIT 5 Iodinated tyrosines are linked together to form T 3 and T 4. T3T3 T4T4 6 Lysosome Thyroglobulin colloid is endocytosed and combined with a lysosome.

14 © 2013 Pearson Education, Inc. Figure 16.10 Synthesis of thyroid hormone. Slide 8 Thyroglobulin is synthesized and discharged into the follicle lumen. 1 2 3 4 5 6 7 Golgi apparatus Iodide (I) Rough ER Capillary Iodide (I – ) is trapped (actively transported in). Lysosome Lysosomal enzymes cleave T 4 and T 3 from thyroglobulin and hormones diffuse into bloodstream. Thyroglobulin colloid is endocytosed and combined with a lysosome. Iodinated tyrosines are linked together to form T 3 and T 4. Iodide is oxidized to iodine. Iodine is attached to tyrosine in colloid, forming DIT and MIT. To peripheral tissues Colloid in lumen of follicle Thyroid follicular cells Tyrosines (part of thyroglobulin molecule) Thyro- globulin colloid T3T3 T4T4 T3T3 T4T4 T3T3 T4T4 Iodine DITMIT Colloid

15 © 2013 Pearson Education, Inc. Transport and Regulation of TH T 4 and T 3 transported by thyroxine-binding globulins (TBGs) Both bind to target receptors, but T 3 is ten times more active than T 4 Peripheral tissues convert T 4 to T 3

16 © 2013 Pearson Education, Inc. Transport and Regulation of TH Negative feedback regulation of TH release –Rising TH levels provide negative feedback inhibition on release of TSH –Hypothalamic thyrotropin-releasing hormone (TRH) can overcome negative feedback during pregnancy or exposure to cold

17 © 2013 Pearson Education, Inc. Hypothalamus TRH Anterior pituitary TSH Thyroid gland Thyroid hormones Target cells Stimulates Figure 16.8 Regulation of thyroid hormone secretion. Inhibits

18 © 2013 Pearson Education, Inc. Homeostatic Imbalances of TH Hyposecretion in adultsmyxedema; goiter if due to lack of iodine Hyposecretion in infantscretinism HypersecretionGraves' disease

19 © 2013 Pearson Education, Inc. Figure 16.11 Thyroid disorders.

20 © 2013 Pearson Education, Inc. Calcitonin Produced by parafollicular (C) cells No known physiological role in humans Antagonist to parathyroid hormone (PTH) At higher than normal doses –Inhibits osteoclast activity and release of Ca 2+ from bone matrix –Stimulates Ca 2+ uptake and incorporation into bone matrix

21 © 2013 Pearson Education, Inc. Parathyroid Glands Four to eight tiny glands embedded in posterior aspect of thyroid Contain oxyphil cells (function unknown) and parathyroid cells that secrete parathyroid hormone (PTH) or parathormone PTHmost important hormone in Ca 2+ homeostasis

22 © 2013 Pearson Education, Inc. Figure 16.12 The parathyroid glands. Parathyroid glands Parathyroid cells (secrete parathyroid hormone) Capillary Oxyphil cells Pharynx (posterior aspect) Thyroid gland Esophagus Trachea

23 © 2013 Pearson Education, Inc. Parathyroid Hormone Functions –Stimulates osteoclasts to digest bone matrix and release Ca 2+ to blood –Enhances reabsorption of Ca 2+ and secretion of phosphate by kidneys –Promotes activation of vitamin D (by kidneys); increases absorption of Ca 2+ by intestinal mucosa Negative feedback control: rising Ca 2+ in blood inhibits PTH release

24 © 2013 Pearson Education, Inc. Figure 16.13 Effects of parathyroid hormone on bone, the kidneys, and the intestine. Osteoclast activity in bone causes Ca 2+ and PO 4 3- release into blood Hypocalcemia (low blood Ca 2+ ) PTH release from parathyroid gland Ca 2+ reabsorption in kidney tubule Activation of vitamin D by kidney Ca 2+ absorption from food in small intestine Ca 2+ in blood Initial stimulus Physiological response Result

25 © 2013 Pearson Education, Inc. Homeostatic Imbalances of PTH Hyperparathyroidism due to tumor –Bones soften and deform –Elevated Ca 2+ depresses nervous system and contributes to formation of kidney stones Hypoparathyroidism following gland trauma or removal or dietary magnesium deficiency –Results in tetany, respiratory paralysis, and death

26 © 2013 Pearson Education, Inc. Adrenal (Suprarenal) Glands Paired, pyramid-shaped organs atop kidneys Structurally and functionally are two glands in one –Adrenal medullanervous tissue; part of sympathetic nervous system –Adrenal cortexthree layers of glandular tissue that synthesize and secrete corticosteroids

27 © 2013 Pearson Education, Inc. Adrenal Cortex Three layers of cortex produce the different corticosteroids –Zona glomerulosamineralocorticoids –Zona fasciculataglucocorticoids –Zona reticularisgonadocorticoids

28 © 2013 Pearson Education, Inc. Figure 16.14 Microscopic structure of the adrenal gland. Medulla Cortex Capsule Zona glomerulosa Zona fasciculata Zona reticularis Adrenal medulla Adrenal gland Medulla Cortex Kidney Hormones secreted Aldosterone Cortisol and androgens Epinephrine and norepinephrine Photomicrograph (115x) Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla

29 © 2013 Pearson Education, Inc. Mineralocorticoids Regulate electrolytes (primarily Na + and K + ) in ECF –Importance of Na + : affects ECF volume, blood volume, blood pressure, levels of other ions –Importance of K + : sets RMP of cells Aldosterone most potent mineralocorticoid –Stimulates Na + reabsorption and water retention by kidneys; elimination of K +

30 © 2013 Pearson Education, Inc. Aldosterone Release triggered by –Decreasing blood volume and blood pressure –Rising blood levels of K +

31 © 2013 Pearson Education, Inc. Mechanisms of Aldosterone Secretion Renin-angiotensin-aldosterone mechanism: decreased blood pressure stimulates kidneys to release renin triggers formation of angiotensin II, a potent stimulator of aldosterone release Plasma concentration of K + : increased K + directly influences zona glomerulosa cells to release aldosterone ACTH: causes small increases of aldosterone during stress Atrial natriuretic peptide (ANP): blocks renin and aldosterone secretion to decrease blood pressure

32 © 2013 Pearson Education, Inc. Figure 16.15 Major mechanisms controlling aldosterone release from the adrenal cortex. Blood volume and/or blood pressure K+ in blood Stress Blood pressure and/or blood volume Hypo- thalamus Heart CRH Anterior pituitary Direct stimulating effect Initiates cascade that produces Renin Angiotensin II ACTH Atrial natriuretic peptide (ANP) Inhibitory effect Zona glomerulosa of adrenal cortex Enhanced secretion of aldosterone Targets kidney tubules Absorption of Na + and water; increased K + excretion Blood volume and/or blood pressure Kidney Primary regulators Other factors

33 © 2013 Pearson Education, Inc. Homeostatic Imbalances of Aldosterone Aldosteronismhypersecretion due to adrenal tumors –Hypertension and edema due to excessive Na + –Excretion of K + leading to abnormal function of neurons and muscle

34 © 2013 Pearson Education, Inc. Glucocorticoids Keep blood glucose levels relatively constant Maintain blood pressure by increasing action of vasoconstrictors Cortisol (hydrocortisone) –Only one in significant amounts in humans Cortisone Corticosterone

35 © 2013 Pearson Education, Inc. Glucocorticoids: Cortisol Released in response to ACTH, patterns of eating and activity, and stress Prime metabolic effect is gluconeogenesis formation of glucose from fats and proteins –Promotes rises in blood glucose, fatty acids, and amino acids "Saves" glucose for brain Enhances vasoconstriction rise in blood pressure to quickly distribute nutrients to cells

36 © 2013 Pearson Education, Inc. Homeostatic Imbalances of Glucocorticoids HypersecretionCushing's syndrome/disease –Depresses cartilage and bone formation –Inhibits inflammation –Depresses immune system –Disrupts cardiovascular, neural, and gastrointestinal function HyposecretionAddison's disease –Also involves deficits in mineralocorticoids Decrease in glucose and Na + levels Weight loss, severe dehydration, and hypotension

37 © 2013 Pearson Education, Inc. Figure 16.16 The effects of excess glucocorticoid. Patient before onset. Same patient with Cushings syndrome. The white arrow shows the characteristic buffalo hump of fat on the upper back.

38 © 2013 Pearson Education, Inc. Gonadocorticoids (Sex Hormones) Most weak androgens (male sex hormones) converted to testosterone in tissue cells, some to estrogens May contribute to –Onset of puberty –Appearance of secondary sex characteristics –Sex drive in women –Estrogens in postmenopausal women

39 © 2013 Pearson Education, Inc. Gonadocorticoids Hypersecretion –Adrenogenital syndrome (masculinization) –Not noticeable in adult males –Females and prepubertal males Boys – reproductive organs mature; secondary sex characteristics emerge early Females – beard, masculine pattern of body hair; clitoris resembles small penis

40 © 2013 Pearson Education, Inc. Adrenal Medulla Medullary chromaffin cells synthesize epinephrine (80%) and norepinephrine (20%) Effects –Vasoconstriction –Increased heart rate –Increased blood glucose levels –Blood diverted to brain, heart, and skeletal muscle

41 © 2013 Pearson Education, Inc. Adrenal Medulla Responses brief Epinephrine stimulates metabolic activities, bronchial dilation, and blood flow to skeletal muscles and heart Norepinephrine influences peripheral vasoconstriction and blood pressure

42 © 2013 Pearson Education, Inc. Adrenal Medulla Hypersecretion –Hyperglycemia, increased metabolic rate, rapid heartbeat and palpitations, hypertension, intense nervousness, sweating Hyposecretion –Not problematic –Adrenal catecholamines not essential to life

43 © 2013 Pearson Education, Inc. Figure 16.17 Stress and the adrenal gland. Short-term stressProlonged stress Nerve impulses Spinal cord Preganglionic sympathetic fibers Adrenal medulla (secretes amino acid– based hormones) Catecholamines (epinephrine and norepinephrine) Short-term stress response Stress Hypothalamus Corticotropic cells of anterior pituitary To target in blood CRH (corticotropin- releasing hormone) Adrenal cortex (secretes steroid hormones) MineralocorticoidsGlucocorticoids ACTH Heart rate increases Long-term stress response Kidneys retain sodium and water Proteins and fats converted to glucose or broken down for energy Blood glucose increases Blood pressure increases Bronchioles dilate Liver converts glycogen to glucose and releases glucose to blood Blood flow changes, reducing digestive system activity and urine output Metabolic rate increases Blood volume and blood pressure rise Immune system supressed

44 © 2013 Pearson Education, Inc. Pineal Gland Small gland hanging from roof of third ventricle Pinealocytes secrete melatonin, derived from serotonin Melatonin may affect –Timing of sexual maturation and puberty –Day/night cycles –Physiological processes that show rhythmic variations (body temperature, sleep, appetite) –Production of antioxidant and detoxification molecules in cells

45 © 2013 Pearson Education, Inc. Pancreas Triangular gland partially behind stomach Has both exocrine and endocrine cells –Acinar cells (exocrine) produce enzyme-rich juice for digestion –Pancreatic islets (islets of Langerhans) contain endocrine cells Alpha ( ) cells produce glucagon (hyperglycemic hormone) Beta ( ) cells produce insulin (hypoglycemic hormone)

46 © 2013 Pearson Education, Inc. Figure 16.18 Photomicrograph of differentially stained pancreatic tissue. Pancreatic islet (Glucagon- producing) cells (Insulin- producing) cells Pancreatic acinar cells (exocrine)

47 © 2013 Pearson Education, Inc. Glucagon Major targetliver Causes increased blood glucose levels Effects –Glycogenolysisbreakdown of glycogen to glucose –Gluconeogenesissynthesis of glucose from lactic acid and noncarbohydrates –Release of glucose to blood

48 © 2013 Pearson Education, Inc. Insulin Effects of insulin –Lowers blood glucose levels –Enhances membrane transport of glucose into fat and muscle cells –Inhibits glycogenolysis and gluconeogenesis –Participates in neuronal development and learning and memory Not needed for glucose uptake in liver, kidney or brain

49 © 2013 Pearson Education, Inc. Insulin Action on Cells Activates tyrosine kinase enzyme receptor Cascade increased glucose uptake Triggers enzymes to –Catalyze oxidation of glucose for ATP production – first priority –Polymerize glucose to form glycogen –Convert glucose to fat (particularly in adipose tissue)

50 © 2013 Pearson Education, Inc. Figure 16.19 Insulin and glucagon from the pancreas regulate blood glucose levels. Stimulates glucose uptake by cells Insulin Stimulates glycogen formationw Pancreas Tissue cells Glucose Glycogen Liver Blood glucose falls to normal range. IMBALANCE Stimulus Blood glucose level BALANCE: Normal blood glucose level (about 90 mg/100 ml) Pancreas IMBALANCE Glucose Glycogen Liver Stimulates glycogen breakdown Blood glucose rises to normal range. Stimulus Blood glucose level Glucagon

51 © 2013 Pearson Education, Inc. Factors That Influence Insulin Release Elevated blood glucose levels – primary stimulus Rising blood levels of amino acids and fatty acids Release of acetylcholine by parasympathetic nerve fibers Hormones glucagon, epinephrine, growth hormone, thyroxine, glucocorticoids Somatostatin; sympathetic nervous system

52 © 2013 Pearson Education, Inc. Homeostatic Imbalances of Insulin Diabetes mellitus (DM) –Due to hyposecretion (type 1) or hypoactivity (type 2) of insulin –Blood glucose levels remain high nausea higher blood glucose levels (fight or flight response) –Glycosuria – glucose spilled into urine –Fats used for cellular fuel lipidemia; if severe ketones (ketone bodies) from fatty acid metabolism ketonuria and ketoacidosis –Untreated ketoacidosis hyperpnea; disrupted heart activity and O 2 transport; depression of nervous system coma and death possible

53 © 2013 Pearson Education, Inc. Diabetes Mellitus: Signs Three cardinal signs of DM –Polyuriahuge urine output Glucose acts as osmotic diuretic –Polydipsiaexcessive thirst From water loss due to polyuria –Polyphagiaexcessive hunger and food consumption Cells cannot take up glucose; are "starving"

54 © 2013 Pearson Education, Inc. Homeostatic Imbalances of Insulin Hyperinsulinism: –Excessive insulin secretion –Causes hypoglycemia Low blood glucose levels Anxiety, nervousness, disorientation, unconsciousness, even death –Treated by sugar ingestion

55 © 2013 Pearson Education, Inc. Table 16.4 Symptoms of Insulin Deficit (Diabetes Mellitus)

56 © 2013 Pearson Education, Inc. Ovaries and Placenta Gonads produce steroid sex hormones –Same as those of adrenal cortex Ovaries produce estrogens and progesterone –Estrogen Maturation of reproductive organs Appearance of secondary sexual characteristics With progesterone, causes breast development and cyclic changes in uterine mucosa Placenta secretes estrogens, progesterone, and human chorionic gonadotropin (hCG)

57 © 2013 Pearson Education, Inc. Testes Testes produce testosterone –Initiates maturation of male reproductive organs –Causes appearance of male secondary sexual characteristics and sex drive –Necessary for normal sperm production –Maintains reproductive organs in functional state

58 © 2013 Pearson Education, Inc. Other Hormone-producing Structures Adipose tissue –Leptin – appetite control; stimulates increased energy expenditure –Resistin – insulin antagonist –Adiponectin – enhances sensitivity to insulin

59 © 2013 Pearson Education, Inc. Other Hormone-producing Structures Enteroendocrine cells of gastrointestinal tract –Gastrin stimulates release of HCl –Secretin stimulates liver and pancreas –Cholecystokinin stimulates pancreas, gallbladder, and hepatopancreatic sphincter –Serotonin acts as paracrine

60 © 2013 Pearson Education, Inc. Other Hormone-producing Structures Heart –Atrial natriuretic peptide (ANP) decreases blood Na + concentration, therefore blood pressure and blood volume Kidneys –Erythropoietin signals production of red blood cells –Renin initiates the renin-angiotensin- aldosterone mechanism

61 © 2013 Pearson Education, Inc. Other Hormone-producing Structures Skeleton (osteoblasts) –Osteocalcin Prods pancreas to secrete more insulin; restricts fat storage; improves glucose handling; reduces body fat Activated by insulin Low levels of osteocalcin in type 2 diabetes – perhaps increasing levels may be new treatment Skin –Cholecalciferol, precursor of vitamin D

62 © 2013 Pearson Education, Inc. Thymus –Large in infants and children; shrinks as age –Thymulin, thymopoietins, and thymosins May be involved in normal development of T lymphocytes in immune response Classified as hormones; act as paracrines Other Hormone-producing Structures

63 © 2013 Pearson Education, Inc. Developmental Aspects Hormone-producing glands arise from all three germ layers Most endocrine organs operate well until old age Exposure to pesticides, industrial chemicals, arsenic, dioxin, and soil and water pollutants disrupts hormone function Sex hormones, thyroid hormone, and glucocorticoids are vulnerable to the effects of pollutants Interference with glucocorticoids may help explain high cancer rates in certain areas

64 © 2013 Pearson Education, Inc. Developmental Aspects Ovaries undergo significant changes with age and become unresponsive to gonadotropins; problems associated with estrogen deficiency occur Testosterone also diminishes with age, but effect is not usually seen until very old age

65 © 2013 Pearson Education, Inc. Developmental Aspects GH levels decline with age - accounts for muscle atrophy with age TH declines with age, contributing to lower basal metabolic rates PTH levels remain fairly constant with age, but lack of estrogen in older women makes them more vulnerable to bone- demineralizing effects of PTH


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