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Questions and Answers
What is the primary function of Beta cells in the islets of Langerhans?
What is the primary function of Beta cells in the islets of Langerhans?
Which type of cell in the islets of Langerhans primarily secretes glucagon?
Which type of cell in the islets of Langerhans primarily secretes glucagon?
What structure surrounds each islet of Langerhans?
What structure surrounds each islet of Langerhans?
What percentage of the islet endocrine cells are constituted by Delta cells?
What percentage of the islet endocrine cells are constituted by Delta cells?
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Which type of diabetes is characterized by a lack of insulin production by Beta cells?
Which type of diabetes is characterized by a lack of insulin production by Beta cells?
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What feature distinguishes the capillary system within the islets of Langerhans?
What feature distinguishes the capillary system within the islets of Langerhans?
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Which of the following is NOT a type of cell found in the islets of Langerhans?
Which of the following is NOT a type of cell found in the islets of Langerhans?
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What symptom is primarily associated with diabetes mellitus?
What symptom is primarily associated with diabetes mellitus?
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What type of cells primarily make up the lining of thyroid follicles?
What type of cells primarily make up the lining of thyroid follicles?
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What is the primary hormone secreted by parafollicular cells?
What is the primary hormone secreted by parafollicular cells?
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Which organelles are indicative of the active protein synthesis and secretion in follicular cells?
Which organelles are indicative of the active protein synthesis and secretion in follicular cells?
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What is the sequence of stages for the synthesis and accumulation of thyroid hormones?
What is the sequence of stages for the synthesis and accumulation of thyroid hormones?
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Which component is responsible for transporting iodide into the follicular cavity?
Which component is responsible for transporting iodide into the follicular cavity?
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What feature differentiates parafollicular cells from follicular cells?
What feature differentiates parafollicular cells from follicular cells?
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The basophilic cytoplasm of follicular cells is primarily associated with what function?
The basophilic cytoplasm of follicular cells is primarily associated with what function?
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What is the appearance of the nuclei in parafollicular cells?
What is the appearance of the nuclei in parafollicular cells?
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What triggers the liberation of T3 and T4 in thyroid follicular cells?
What triggers the liberation of T3 and T4 in thyroid follicular cells?
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Which hormone is secreted by the parafollicular cells (C cells)?
Which hormone is secreted by the parafollicular cells (C cells)?
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What characterizes chief cells in the parathyroid glands?
What characterizes chief cells in the parathyroid glands?
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What primary function does melatonin serve in the pineal gland?
What primary function does melatonin serve in the pineal gland?
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Which zone of the adrenal cortex primarily secretes mineralocorticoids?
Which zone of the adrenal cortex primarily secretes mineralocorticoids?
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What is the main product of the zona fasciculata in the adrenal cortex?
What is the main product of the zona fasciculata in the adrenal cortex?
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The chromaffin cells within the adrenal medulla secrete which substances?
The chromaffin cells within the adrenal medulla secrete which substances?
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What is the undisputed role of oxyphil cells in the parathyroid gland?
What is the undisputed role of oxyphil cells in the parathyroid gland?
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Which statement correctly describes the islets of Langerhans?
Which statement correctly describes the islets of Langerhans?
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What directly influences the blood supply to the adrenal medulla?
What directly influences the blood supply to the adrenal medulla?
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What is the primary function of the adrenal medulla?
What is the primary function of the adrenal medulla?
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Which gland's hormone levels are notably high during darkness?
Which gland's hormone levels are notably high during darkness?
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Which type of cells are predominant in the adrenal cortex?
Which type of cells are predominant in the adrenal cortex?
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Which adrenal cortex zone is the thinnest and primarily produces sex steroids?
Which adrenal cortex zone is the thinnest and primarily produces sex steroids?
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Study Notes
Thyroid Gland
-
Follicular Cells (Principal Cells):
- Main cells in thyroid follicles, simple cuboidal epithelium
- Round central nuclei, basophilic cytoplasm
- Rest on basement membrane, apices reach follicular lumen
- Electron microscopy (EM): organelles for protein synthesis and secretion, phagocytosis, digestion are present, abundant rough endoplasmic reticulum (RER), well-developed Golgi bodies, secretory granules, lysosomes, apical microvilli.
- Synthesize and secrete thyroid hormones (T3 & T4) through 4 stages.
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Parafollicular Cells (C Cells):
- Located between follicular cells and basement membrane, do not reach lumen
- Larger and paler than follicular cells
- EM: rounded nuclei, Golgi apparatus between nucleus and lumen, lipid droplets, colloid resorption droplets, short irregular microvilli, dense granules (indicating calcitonin)
- Synthesize and secrete calcitonin (lowers blood calcium)
Thyroid Hormone Synthesis & Release
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Synthesis stages:
- Thyroglobulin/colloid synthesis in follicular cells, similar to other protein export.
- Iodide uptake (Na exchange) via basolateral membrane protein in follicular cells.
- Iodide transport into follicular lumen through pendrin, oxidized by thyroid peroxidase to iodine in the lumen.
- Tyrosine residues of thyroglobulin are iodinated and stored until needed in the follicular lumen.
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Release (T3 & T4):
- Thyrotropin stimulation leads follicular cells to take up colloid by endocytosis.
- Lysosomal enzymes digest colloid in endocytic vesicles, releasing T4 and T3 into cytoplasm.
- Free T4 and T3 cross basolateral membrane into capillaries.
Parathyroid Glands
- Composed of chief cells (predominant) and oxyphil cells.
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Chief Cells (Principal Cells):
- Predominant cell type, small polygonal cells in cords, separated by fenestrated capillaries.
- Round nuclei, pale-staining cytoplasm, few secretory granules containing parathyroid hormone (PTH).
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Oxyphil Cells:
- Less common, larger than chief cells, often in clusters.
- Very acidophilic cytoplasm due to high mitochondria content.
- Possible derivatives of chief cells, unknown function.
Pineal Gland
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Pinealocytes:
- Epithelioid cells, basophilic, branching, with long processes ending in flattened dilatations.
- Supported by interstitial cells.
- Secrete melatonin (high during darkness, low during day), possible antigonadotropic function, and antioxidant.
Adrenal Glands
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Adrenal Cortex:
- Steroid-secreting cells, surrounded by fenestrated capillaries, synthesized on demand from cholesterol (not stored).
- Three zones:
- Zona glomerulosa: Rounded/arched clusters of columnar acidophilic cells, mineralocorticoids (e.g., aldosterone).
- Zona fasciculata: Long cords of large polyhedral cells with lipid droplets, glucocorticoids (e.g., cortisol).
- Zona reticularis: Small polyhedral cells in irregular cords, adrenal sex steroids (weak androgens, e.g., DHEA).
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Adrenal Medulla:
- Composed of chromaffin cells and ganglionic cells.
- Chromaffin cells: secrete catecholamines (epinephrine, norepinephrine), differentiated by secretory granule density (noradrenaline granules darker), ~80% are adrenaline-secreting.
- Ganglionic cells: Larger, regulate catecholamine secretion.
- Double blood supply: from medullary arterioles (systemic arterial blood) and from cortical capillaries (venous blood rich in steroid hormones).
- Composed of chromaffin cells and ganglionic cells.
Endocrine Pancreas (Islets of Langerhans)
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Islets of Langerhans:
- Clusters of endocrine cells (less than 5% of pancreas) amid exocrine acinar cells.
- Surrounded by a thin capsule of reticular fibers.
- Lightly stained polygonal or rounded cells arranged in cords separated by fenestrated capillaries.
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Cell Types:
- Beta cells (70%): Insulin.
- Alpha cells (20%): Glucagon.
- Delta cells: Somatostatin
- PP cells
- G cells
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Islet Blood Circulation:
- Allows islet hormones to control exocrine secretion. Most pancreatic arterial blood first passes through islet endocrine cells before neighboring exocrine tissue.
Clinical Correlations (Diabetes Mellitus)
-
Diabetes Mellitus: Hyperglycemic disorder due to insulin deficiency or defective insulin receptors
- Type 1 (insulin-dependent): usually younger than 20, lack of insulin production
- Type 2 (non-insulin-dependent): usually older than 40, defective insulin receptors
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Description
Explore the intricate details of the thyroid gland, focusing on the function and structure of follicular and parafollicular cells. This quiz covers thyroid hormone synthesis, secretion mechanisms, and the role of calcitonin in calcium homeostasis. Test your understanding of these essential concepts related to human physiology.
