L28. Histology - Microanatomy of Endocrine Glands II
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Questions and Answers

Which of the following best describes the mechanism of action for steroid hormones?

  • They act through a second messenger system on the cell surface.
  • They are produced by enzymes in the smooth endoplasmic reticulum and mitochondria and require carrier proteins for blood transport. (correct)
  • They are released directly into the bloodstream and travel freely to target cells.
  • They are synthesized in the rough endoplasmic reticulum and stored in vesicles.

Which of the following is NOT a characteristic of peptide hormones?

  • They are packaged in the Golgi complex.
  • They are stored in secretory vesicles before release.
  • They are synthesized by the cooperative action of enzymes located in smooth endoplasmic reticulum and mitochondria (correct)
  • They are synthesized in the rough endoplasmic reticulum.

What is the primary difference between endocrine and paracrine signaling?

  • Endocrine signaling involves hormones binding to cell surface receptors, while paracrine signaling involves hormones entering the cell.
  • Endocrine signaling affects many different cell types, whereas paracrine signaling affects only a single cell type
  • Paracrine signaling involves rapid, short-term responses, while endocrine signaling results in long-term changes.
  • Endocrine hormones travel through the bloodstream to distant sites, while paracrine hormones act on neighboring cells via diffusion. (correct)

What describes an autocrine effect?

<p>Hormones act on the same cells that produce them. (A)</p> Signup and view all the answers

Based on the organization presented, what is a key shared characteristic between the thyroid and parathyroid glands?

<p>They have a defined section focused on cell types. (D)</p> Signup and view all the answers

According to the content, what do amino acid analogues and catecholamines have in common?

<p>They are in the same class of hormone. (C)</p> Signup and view all the answers

Based on the information provided, the adrenal gland is similar to the thyroid and parathyroid in which aspect?

<p>They all have the aspect of blood supply covered. (A)</p> Signup and view all the answers

In the adrenal gland, where do the thin-walled cortical capillaries, carrying hormone-rich but oxygen-poor blood, initially merge with oxygen-rich blood from medullary arterioles?

<p>At the cortico-medullary junction. (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the cells within the zona glomerulosa?

<p>They have a basophilic staining pattern. (C)</p> Signup and view all the answers

Which of the following best describes the mechanism of action for protein hormones?

<p>They interact with cell surface receptors, utilizing second messenger systems. (A)</p> Signup and view all the answers

What is the primary function of aldosterone, produced by the zona glomerulosa?

<p>To increase sodium uptake in the kidney. (D)</p> Signup and view all the answers

How do steroid hormones typically exert their physiological effects?

<p>By directly interacting with DNA, leading to the production of new proteins. (D)</p> Signup and view all the answers

Which of the following describes the order of zones in the adrenal gland cortex, from outermost to innermost?

<p>Zona glomerulosa, zona fasciculata, zona reticularis (A)</p> Signup and view all the answers

Which characteristic is associated with endocrine glands?

<p>They release their products into blood vessels via a dense plexus of fenestrated capillaries. (B)</p> Signup and view all the answers

How do the cells of the zona glomerulosa primarily obtain cholesterol, a precursor for steroid hormone synthesis?

<p>By means of receptor-mediated uptake. (C)</p> Signup and view all the answers

The pineal gland develops as a dorsal extension from which part of the brain?

<p>The posterior part of the roof of the diencephalon. (B)</p> Signup and view all the answers

What happens to the lumen of the pineal gland as it matures?

<p>It becomes obliterated as the walls of the gland thicken. (C)</p> Signup and view all the answers

What is the connective tissue covering that surrounds the pineal gland?

<p>The pia mater. (A)</p> Signup and view all the answers

How is the parenchyma of the pineal gland organized?

<p>It is partitioned into clumps of cells, or lobules, by septae and trabeculae. (B)</p> Signup and view all the answers

What is the major cell type found within the pineal gland?

<p>Pinealocytes. (B)</p> Signup and view all the answers

Which of the following is a distinct characteristic of pinealocytes?

<p>They are relatively large cells with deeply creased nuclei. (B)</p> Signup and view all the answers

Which ratio accurately represents the production of T4 to T3 by the thyroid gland?

<p>20:1 (C)</p> Signup and view all the answers

Where are T3 and T4 primarily transported within the body?

<p>Serum carrier proteins (A)</p> Signup and view all the answers

What is the key function of T3 and T4 hormones regarding metabolic processes?

<p>They regulate basal metabolism of carbohydrates, proteins, and fats. (A)</p> Signup and view all the answers

Which hormone directly controls all stages of T3 and T4 synthesis?

<p>TSH (C)</p> Signup and view all the answers

How is the release of TRH regulated?

<p>By negative feedback from T3 and T4 hormones. (C)</p> Signup and view all the answers

In which locations is T3 generated from T4?

<p>Kidney, liver, and heart (D)</p> Signup and view all the answers

What is a distinctive characteristic of parafollicular cells in terms of staining?

<p>They stain poorly with H&amp;E. (A)</p> Signup and view all the answers

Where can parafollicular cells be found within the thyroid gland?

<p>Within the wall of the follicle and in the interstitium (D)</p> Signup and view all the answers

What is the primary product secreted by parafollicular cells?

<p>Calcitonin (B)</p> Signup and view all the answers

Which of the following best describes the characteristic spatial arrangement of secretory granules in parafollicular cells?

<p>Located in close proximity to surrounding capillaries. (B)</p> Signup and view all the answers

Based on the provided information, what is the primary role of parathyroid hormone (PTH) when blood calcium levels are low?

<p>To stimulate the release of calcium from bone by activating osteoclasts. (A)</p> Signup and view all the answers

Which of the following best describes the appearance and characteristics of oxyphil cells in the parathyroid gland?

<p>Larger, acidophilic cells with many mitochondria and small nuclei. (A)</p> Signup and view all the answers

What is the functional relationship between calcitonin and parathyroid hormone (PTH) as described in the given content?

<p>The action of PTH is opposite to that of calcitonin. (B)</p> Signup and view all the answers

How does PTH indirectly stimulate osteoclast activity?

<p>By binding to osteoblasts, which then in turn drive the formation of activated osteoclasts. (B)</p> Signup and view all the answers

At what stage of life do oxyphil cells typically appear in the parathyroid gland, according to the text?

<p>Around 4-7 years of age, increasing with age. (B)</p> Signup and view all the answers

What cellular components are characteristic of oxyphil cells, based on the description in the given information?

<p>Numerous mitochondria, small nuclei, and an eosinophilic cytoplasm. (D)</p> Signup and view all the answers

Which cellular feature is identified within the chief cells of the parathyroid gland by the text?

<p>Prominent nuclei (D)</p> Signup and view all the answers

What is the primary source of the secretory granules mentioned in the parathyroid gland cells?

<p>Chief cells (C)</p> Signup and view all the answers

Besides bone, what other organ systems are targeted by Parathyroid Hormone (PTH) to help elevate blood calcium levels?

<p>Kidney tubules and intestines (C)</p> Signup and view all the answers

According to the provided content, what is a characteristic of the fenestrated capillaries in the parathyroid gland?

<p>They possess small pores or fenestrations that permit the exchange of molecules. (C)</p> Signup and view all the answers

Flashcards

Endocrine System

A group of organs that produce and release hormones into the bloodstream, regulating various bodily functions.

Hormones

Chemical messengers produced by endocrine glands that influence the activity of cells and organs.

Paracrine Hormones

Hormones that act on nearby cells in a local manner.

Autocrine Hormones

Hormones that act on the same cells that produced them.

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Peptide Hormones

Hormones primarily composed of amino acids, including peptides, proteins, and glycoproteins.

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Steroid Hormones

Hormones derived from cholesterol, including sex hormones and corticosteroids.

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Amino Acid Analogues & Derivatives

Hormones derived from amino acids, including catecholamines like adrenaline and noradrenaline.

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Pineal gland Location

The pineal gland extends from the roof of the diencephalon and is attached to the third ventricle.

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Pineal Lumen

The pineal gland's lumen is completely filled with cells as it ages, losing its hollow structure. The inside space disappears.

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Pineal Gland Covering

The pineal gland is covered by a protective layer derived from the pia mater that is continuous with the brain's outermost layer, extending into the gland.

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Pineal Parenchyma Structure

The pineal gland's parenchyma is made up of clumps of cells called lobules, separated by connective tissue.

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Pinealocyte Description

Pinealocytes are the main cell type, making up about 95% of the pineal gland. They are relatively large with deep folds in their surfaces, indicating active function.

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Pineal Gland Function

The pineal gland is an endocrine gland. This means it secretes hormones directly into the bloodstream. It does not use ducts.

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Pineal Gland Hormone

The pineal gland secretes melatonin, a hormone that regulates sleep cycles and circadian rhythms.

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How Steroid Hormones Work

Steroid hormones enter cells and bind to DNA, causing the production of new proteins specific to the hormone.

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How Protein Hormones Work

Protein hormones mostly work by binding to cell surface receptors and triggering the production of second messengers.

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How are T3 and T4 Transported?

T3 and T4 are transported in the blood by carrier proteins in the serum.

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What Happens to MIT and DIT?

MIT and DIT, precursors to T3 and T4, are recycled by the thyroid gland.

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What Regulates T3 and T4 Production?

Thyroid-stimulating hormone (TSH) regulates all stages of T3 and T4 synthesis.

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How is TRH Release Regulated?

The release and synthesis of TRH is controlled by a feedback mechanism involving T3 and T4.

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What is the Ratio of T4 and T3 Production?

The thyroid gland produces T4 and T3 in a 20:1 ratio.

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Which is More Active: T3 or T4?

T3, although produced less, is 5 times more active than T4.

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Where is T4 Converted to T3?

The kidneys, liver, and heart convert T4 into T3.

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What is the Function of T3 and T4?

T3 and T4 regulate tissue metabolism, affecting carbohydrates, proteins, and fats.

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How do T3 and T4 Affect Body Temperature?

T3 and T4 play a role in heat production, regulating body temperature.

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How do T3 and T4 Affect Growth?

T3 and T4 are involved in tissue growth and development.

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Zona Glomerulosa

The outermost zone of the adrenal cortex, characterized by rounded clumps of cells near fenestrated capillaries, responsible for producing aldosterone.

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Aldosterone

A mineralocorticoid hormone produced by the zona glomerulosa that increases sodium reabsorption in the kidneys, playing a crucial role in regulating blood pressure and fluid balance.

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Angiotensin II

A peptide hormone that stimulates the zona glomerulosa to produce aldosterone, primarily acting through the renin-angiotensin-aldosterone system.

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Venous Return in the Adrenal Gland

The process of oxygen-poor, hormone-rich cortical blood mixing with oxygen-rich medullary blood, forming the venous blood supply to the adrenal medulla.

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Adrenal Cortex Zones

The adrenal cortex is composed of three distinct zones: the zona glomerulosa, zona fasciculata, and zona reticularis, each responsible for producing different hormones.

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Chief cells

Cells found in the parathyroid gland responsible for producing and secreting parathyroid hormone (PTH). They are smaller, more numerous, and stain less intensely than oxyphil cells.

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Oxyphil cells

Larger cells in the parathyroid gland that appear later in life and have a distinct eosinophilic staining pattern due to their abundant mitochondria.

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Parathyroid hormone (PTH)

A hormone produced by the parathyroid gland that plays a crucial role in regulating blood calcium levels. It increases blood calcium by stimulating bone breakdown, enhancing calcium reabsorption in the kidneys, and promoting intestinal calcium absorption.

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Bone resorption

The process by which bone tissue is broken down by specialized cells called osteoclasts, releasing calcium into the bloodstream.

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Osteoclasts

Cells responsible for breaking down bone tissue.

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Osteoblasts

Special cells in bone tissue that help build new bone and are involved in regulating osteoclast activity.

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Kidney tubular reabsorption

The process by which the kidneys filter waste products from the blood and reabsorb essential substances like calcium.

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Intestinal calcium absorption

The process by which the small intestine absorbs calcium from ingested food.

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Calcitonin

Hormone produced by the thyroid gland that lowers blood calcium levels by inhibiting bone resorption and increasing calcium excretion in the kidneys.

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PTH and calcitonin interaction

The opposing actions of PTH and calcitonin in maintaining blood calcium balance.

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Study Notes

Microanatomy of Endocrine Glands II

  • Pineal Gland (Epiphysis Cerebri):

    • Located as a dorsal extension from the posterior part of the diencephalon's roof.
    • Its lumen is obliterated as the walls thicken with age.
    • It remains attached to the roof of the third ventricle.
    • Covered by a capsule, extending into the gland as septae and trabeculae.
    • Contains pinealocytes (95%) which are large cells with creased nuclei, prominent nucleoli, and long cytoplasmic processes.
    • Contains glial cells (5%) which have long cytoplasmic processes forming a supporting network with blood capillaries.
    • Contains corpora arenacea (brain sand) which are concretions of calcium phosphate located in glia and stroma. Their number and size increase with age.
    • Primarily responsible for producing serotonin, melatonin, and other specific peptides(neurohormones). -May play a role in regulating gonadal function and adapting to day-length changes (jet lag) and seasonal affective disorder (SAD).

  • Thyroid Gland:

    • Composed of two lateral lobes connected by an isthmus that crosses the midline of the larynx/upper trachea.
    • Usually has a pyramidal lobe extending from the isthmus.
    • Typically weighs around 40 grams.
    • Covered by connective tissue forming a thin capsule that extends to subdivide the gland into lobules.
    • Follicular organization comprises spherical follicles ranging up to 1mm in diameter.
    • Follicles are lined with simple cuboidal epithelium resting on a basement membrane.
    • The lumen of follicles is filled with colloid which is the stored secretory product of follicular cells, iodinated thyroglobulin.
    • Thyroid follicular cells produce thyroxine (T4) and triiodothyronine (T3).
    • These cells are the only endocrine cells for extracellular storage of secretory product.
    • Follicular cells concentrate iodide 30-fold via ATP-dependent iodide transporters.
    • Rough ER synthesizes thyroglobulin.
    • Thyroid peroxidase is inserted into the apical membrane to facilitate the oxidation of iodide to free iodine and iodination of thyroglobulin.
    • Iodinated thyroglobulin (colloid) is stored in follicle lumen and then taken into follicular cells by endocytosis.
    • Colloid is hydrolyzed by lysosomal enzymes and T3 and T4 are released into the blood; MIT and DIT are recycled.
    • T3 and T4 act to regulate tissue basal metabolism of carbohydrates, proteins, and fats.
    • Parafollicular cells are large cells that stain poorly with H&E and are found within the wall of follicles, underneath the follicular cells and in small clusters within the interstitium.
    • They produce calcitonin/thyrocalcitonin which depresses osteoclast activity and increases renal and intestinal calcium excretion; lowering blood calcium levels.

  • Parathyroid Glands:

    • Two small glands located on the dorsal surface of the thyroid gland lobes.
    • Composed of two cell types; chief (principal) cells and oxyphil cells.
    • Chief cells are relatively small with large nuclei and few small secretory granules and create parathyroid hormone (PTH).
    • Oxyphil cells appear later in life (4-7 years), are larger, acidophilic (stain darker) and have numerous mitochondria.
    • PTH (parathormone) is produced by chief cells; it's crucial for calcium homeostasis. PTH opposes calcitonin in its action.
    • Low blood calcium stimulates PTH to activate osteoclasts to release calcium from bones, and to increase calcium resorption in the kidney tubules and intestines.

  • Adrenal Glands (Suprarenal glands):

    • Located at the cranial pole of each kidney, each is made up of two separate endocrine organs: adrenal cortex and adrenal medulla.
    • The cortex is comprised of three zones: zona glomerulosa, zona fasciculata, and zona reticularis each having different types of cells that produces hormones.
    • The zona glomerulosa is the outer zone and consist of rounded clumps of cells and produces aldosterone; important for maintaining sodium balance.
    • The zona fasciculata is the middle zone, consisting of organized straight cords/columns of cells that produce glucocorticoids, mainly cortisol, critical for metabolism and reducing inflammation.
    • The zona reticularis is the inner zone and is highly organized and produces gonadocorticoids, mostly dehydroepiandrosterone and some cortisol.
    • The adrenal medulla consist of a network of polyhedral cells, surrounded by capillaries and cortical veins.
    • The cells are modified postganglionic sympathetic neurons which are part of the chromaffin system and stain with dichromate salts.
    • The adrenal medulla cells produce epinephrine (80%) and norepinephrine (20%), important for the fight-or-flight response.
    • Glucocorticoids suppress axon formation of adrenal medullary cells.
    • Clinical correlations: include Hypoadrenocorticism (Addison's disease), Hyperadrenocorticism (Cushing's syndrome) and Pheochromocytomas.

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Test your knowledge on endocrine principles with this quiz focusing on hormone mechanisms, characteristics of peptide and steroid hormones, and gland functions. You'll explore the differences between autocrine and paracrine signaling, as well as the roles of key glands in hormone production.

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