Endocrine System Quiz
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Questions and Answers

What is the primary function of the endocrine system?

  • To coordinate muscle contractions.
  • To provide lubrication to joints.
  • To regulate body activities by releasing hormones. (correct)
  • To transmit nerve impulses rapidly.

    • Which hormone pathway affects nearby cells?

  • Neurocrine pathway
  • Paracrine pathway (correct)
  • Endocrine pathway
  • Autocrine pathway

    • Which type of hormone is primarily derived from cholesterol?

  • Steroid hormones (correct)
  • Amino acid-based hormones
  • Peptide hormones
  • Protein hormones

    • What must cells possess to respond effectively to hormones?

    <p>Specific membrane or intracellular receptors</p> Signup and view all the answers

    Which of the following glands is NOT classified as an endocrine gland?

    <p>Sweat gland</p> Signup and view all the answers

    What mechanism primarily regulates most hormone synthesis and release?

    <p>Negative feedback mechanisms</p> Signup and view all the answers

    Which of the following hormones are classified as lipid-soluble hormones?

    <p>Testosterone</p> Signup and view all the answers

    Which structure serves as the major integrating link between the nervous and endocrine systems?

    <p>Hypothalamus</p> Signup and view all the answers

    Which of the following best describes the histological organization of endocrine cells?

    <p>Arranged in cords or clusters</p> Signup and view all the answers

    Which type of stimuli can trigger hormone release from endocrine glands?

    <p>Humoral, neural, or hormonal stimuli</p> Signup and view all the answers

    What is the function of diffuse neuroendocrine cells?

    <p>To secrete hormones in various organs throughout the body</p> Signup and view all the answers

    What is a primary function of the pituitary gland?

    <p>To control the release of hormones from other glands</p> Signup and view all the answers

    Which glands are classified as part of the major endocrine system?

    <p>Adrenal glands and pancreas</p> Signup and view all the answers

    What is the primary cause of goiter formation due to iodine deficiency?

    <p>Accumulation of non-iodinated thyroglobulin in the lumen</p> Signup and view all the answers

    Which condition is characterized by fatigue, weight gain, and a puffy face?

    <p>Hypothyroidism</p> Signup and view all the answers

    What autoimmune disease is caused by the binding of anti-TSH receptor antibodies to TSH receptors?

    <p>Graves' disease</p> Signup and view all the answers

    Which hormones have opposing effects on blood calcium levels?

    <p>Parathyroid hormone and calcitonin</p> Signup and view all the answers

    Which cells primarily secrete parathyroid hormone (PTH)?

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

    What condition results from hypoparathyroidism?

    <p>Increased bone mineralization</p> Signup and view all the answers

    What is the effect of parathyroid hormone on the kidneys?

    <p>Promotes calcium reabsorption</p> Signup and view all the answers

    What is a possible outcome of hyperparathyroidism?

    <p>Calcium deposits in organs</p> Signup and view all the answers

    Which type of cells comprises the parathyroid gland's parenchyma?

    <p>Oxyphil cells and chief cells</p> Signup and view all the answers

    What is a potential complication of untreated congenital hypothyroidism in infants?

    <p>Cretinism</p> Signup and view all the answers

    Study Notes

    Endocrine Glands

    • Endocrine glands are ductless glands that release hormones into the extracellular space through diffusion.
    • Hormones have different pathways to exert their action: endocrine (enter blood stream), paracrine (affect nearby cells), and autocrine (act on the same cell that produced it).
    • Target cells must have specific membrane or intracellular receptors for hormones to bind.
    • Hormones are chemical signals secreted by endocrine cells to regulate metabolic functions of target cells.

    Types of Hormones

    • Amino acid-based hormones: example Thyroid & adrenomedullary hormones
    • Protein & peptide hormones: example all other hormones
    • Steroid hormones: derived from cholesterol; example sex hormones (testosterone, progesterone, estrogen) & adrenocortical hormones
    • Endocrine glands derived from mesoderm produce steroid hormones; those derived from ectoderm or endoderm produce amines, peptides, or protein hormones.

    Mechanism of Hormone Action

    • Water-soluble hormones (all amino acid based hormones except thyroid hormone) exert effects by activating plasma membrane receptors and releasing intracellular second messengers.
    • Lipid-soluble hormones (steroids and thyroid hormone) diffuse into the cell, bind to intracellular receptors, migrate to the nucleus, and alter gene expression.

    Control of Hormone Release

    • Most hormone synthesis/release is regulated through negative feedback mechanisms.
    • Endocrine gland stimuli may be humoral, neural, or hormonal.

    Humoral Stimulus

    • Hormone release caused by altered levels of certain critical ions or nutrients.

    Neural Stimulus

    • Hormone release caused by neural input.

    Hormonal Stimulus

    • Hormone release caused by another hormone (a tropic hormone).

    Endocrine System

    • The major endocrine glands include pituitary, pineal, thyroid, parathyroid, adrenal, and endocrine pancreas.
    • Other endocrine components are found in the ovaries & testes, pancreas & kidneys, and diffuse neuroendocrine cells in the GIT & kidneys.
    • The histological organization of endocrine glands includes a capsule, stroma, septa, reticular fibers, and cells of the gland within the parenchyma.
    • Endocrine cells are specialized for secretion, with appearance dependent on secretory product (peptide or steroid).
    • Endocrine cells are commonly arranged into cords or groups and are closely associated with fenestrated capillaries.

    Hypothalamus

    • The hypothalamus is the major integrating link between the nervous and endocrine systems.
    • It oversees many internal body conditions.
    • It receives nervous stimuli from receptors throughout the body.
    • The hypothalamus stimulates cellular activity in various parts of the body by directing and regulating the release of hormones from the pituitary gland.

    Pituitary Gland

    • The pituitary gland (hypophysis) is located in the sella turcica of the sphenoid bone in the base of the skull.
    • It has two subdivisions that arise from different embryonic sources: adenohypophysis (anterior pituitary) and neurohypophysis (posterior pituitary).
    • The adenohypophysis develops from an evagination of the oral ectoderm (Rathke's pouch) and the neurohypophysis develops from neural ectoderm as a down growth of the floor of the diencephalon.
    • Blood supply to the pituitary gland involves superior and inferior hypophyseal arteries and the hypothalamo-hypophyseal portal system.

    Subdivisions of Hypophysis

    • Anterior Pituitary (adenohypophysis): Pars distalis, Pars tuberalis, and Pars intermedia.
    • Posterior Pituitary (neurohypophysis): Pars nervosa and infundibulum.

    Control of Secretion in the Adenohypophysis

    • Primarily controlled by hypothalamic hormones via the hypophyseal portal system (releasing and inhibiting hormones).

    Negative Feedback

    • A stimulus (e.g., low body temperature) causes the hypothalamus to secrete thyrotropin-releasing hormone (TRH), which acts on the anterior pituitary.
    • Thyrotropic cells in the anterior pituitary release thyroid-stimulating hormone (TSH).
    • TSH stimulates follicular cells of the thyroid gland to release thyroid hormone (TH).
    • TH stimulates target cells to increase metabolic activities resulting in an increase in basal body temperature.
    • Increased body temperature inhibits TRH secretion, inhibiting TSH synthesis and release, thereby dampening TH production.

    Pars Tuberalis

    • A funnel-shaped region surrounding the infundibulum.
    • Most cells are basophilic gonadotropic cells secreting follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
    • Highly vascularized by arteries and the hypophyseal portal system.

    Pars Intermedia

    • Lies between the pars distalis and the pars nervosa.
    • Contains colloid-filled cysts (remnants of Rathke's pouch).
    • In the fetus, basophils produce melanocyte-stimulating hormones (MSH) important for melanocyte activity.

    Neurohypophysis (Posterior Pituitary)

    • Consists of pars nervosa and infundibular stalk.
    • Unlike the pars distalis, it does not contain secretory cells.
    • Composed of unmyelinated axons, Herring bodies, pituicytes, and fenestrated capillaries.
    • Contains neurosecretory bodies (Herring bodies) that store and release oxytocin and ADH.

    Hormones of Pars Nervosa

    • Vasopressin (ADH) and oxytocin.
    • Released in response to respective stimuli (plasma osmolarity or uterine/mammary gland stimuli).
    • ADH increases water reabsorption in the kidney and oxytocin stimulates contraction of uterine muscle and myoepithelial cells around mammary glands during childbirth or nursing.

    Pineal Gland

    • Location: posterior of the third ventricle, attached to the brain by a short stalk
    • Origin: neuroectoderm in the roof of the diencephalon
    • Shape: cone or pine-shaped and covered by pia mater with septa of connective tissue
    • Pinealocytes: secretory cells, having slightly basophilic cytoplasm, secretory vesicles, mitochondria & long cytoplasmic processes
    • Produce melatonin (derived from serotonin), a low molecular-weight tryptophan derivative.

    Unmyelinated Sympathetic Nerve Fibers

    • Enter the pineal gland along its septa; associated indirectly with photoreceptive neurons in the retinas and running to the pinealocytes to stimulate melatonin release in darkness.
    • The pineal is involved in circadian rhythms.

    Interstitial Cells

    • Most closely resemble astrocytes.
    • Have elongated nuclei and cytoplasmic processes.
    • Found in perivascular areas and between groups of pinealocytes.
    • About 5% of cells in the gland.

    Corpora Arenacea

    • Characteristic feature of the pineal gland.
    • Variously sized concretions of calcium and magnesium salts.
    • Form by precipitation around extracellular protein deposits.
    • Increase in number and size with age and have no known function.

    Adrenal Gland

    • Paired organ near the superior poles of the kidneys; embedded in adipose tissue.
    • Shape: almond/triangular/flattened structures.
    • The right is pyramid-shaped and sits directly on top of the right kidney.
    • The left is more crescent-shaped and lies along the medial border of the left kidney.
    • Histological structure: covered by a dense capsule that sends thinner septa into the interior.
    • Two functionally different regions: cortex (yellowish peripheral layer) and medulla (reddish-brown central layer).

    Origin of Adrenal Gland

    • Adrenal cortex from mesoderm and adrenal medulla from neural crest, with sympathetic ganglion cells having the same origin.
    • The origin of the layers is important because they have different functions.

    Suprarenal Cortex

    • Accounts for 80-90% of the gland.
    • Contains cells that synthesize and secrete several steroid hormones, but do not store them.
    • Cells have characteristic features of steroid-secreting cells: central nuclei, acidophilic cytoplasm, and rich in lipid droplets, smooth ER with enzymes for cholesterol synthesis, mitochondria with tubular cristae .

    Adrenocortical Hormones

    • Mineralocorticoids, glucocorticoids, and androgens are synthesized from cholesterol and a component of low-density lipoproteins. -Hormone synthesis and release are by enzymes of SER & mitochondria.

    Organization of Adrenal Cortex

    • The cords of cortical cells are arranged differently and are specialized to produce different classes of steroid hormones.
    • Three concentric zones (glomerulosa, fasciculata, and reticularis) from the capsule inward

    Zona Glomerulosa

    • The outer small zone immediately inside the connective tissue capsule.
    • Forms 15% of the cortex
    • Cells are columnar, arranged in spherical or arched cords, and surrounded by fenestrated capillaries ( important for fluid and electrolyte homeostasis).

    Function of Zona Glomerulosa

    • Secrete mineralocorticoids, primarily aldosterone, to regulate salt and water balance.
    • Aldosterone stimulates Na+ reabsorption and water, in the distal convoluted tubules;
    • It also increases Na+ absorption by the intestine.
    • Decrease Na+ & increase K+ content of sweat & saliva.
    • Aldosterone secretion is stimulated by angiotensin II and also by an increase in plasma K+ and decrease Na+ concentrations; weakly by ACTH

    Renin-Angiotensin Mechanism

    • A mechanism related to blood pressure regulation.
    • Decreased blood pressure triggers renin release from the kidney, which initiates a cascade that results in aldosterone secretion.

    Zona Fasciculata

    • The intermediate layer of cells in the suprarenal cortex
    • The largest layer, accounting for up to 80% of the cortex.

    Zona Fasciculata Consists of:

    • Polyhedral cells larger than zona glomerulosa cells.
    • Arranged in radial columns (one to two layers thick).
    • Stain lightly acidophilic.
    • Sinusoidal capillaries between the columns of cells.
    • Many lipid droplets (appear vacuolated called spongiocytes)

    Function of Zona Fasciculata

    • Secrete glucocorticoids, especially cortisol and a small amount of androgens, regulating carbohydrate, fat, and protein metabolism.
    • Cortisol has an anti-inflammatory effect and suppresses the immune response.
    • Secretion is controlled by ACTH from the anterior pituitary and negative feedback.
    • Stress and catecholamines stimulate secretion.

    Zona Reticularis

    • The innermost layer of the suprarenal cortex, constituting about 7% of the cortex
    • Darkly staining acidophilic cells.
    • Arranged in anastomosing cords.
    • Similar to spongiocytes but smaller
    • Fewer lipid droplets and more lipofuscin pigment.
    • Several cells near the suprarenal medulla are dark with electron-dense cytoplasm and pyknotic nuclei, which suggests that this zone contains degenerating parenchymal cells.

    Function of Zona Reticularis

    • Produces glucocorticoids (mainly cortisol) but primarily secretes the weak androgen dehydroepiandrosterone (DHEA).
    • DHEA gets converted to testosterone in other tissues.
    • ACTH stimulates secretion and negative feedback system regulated with the pituitary and hypothalamus.

    Fetal Adrenal Cortex

    • A layer comprising 80% of the total gland, thick, containing cells secreting sulfated DHEA, controlled by fetal pituitary
    • DHEA gets converted to active estrogens and androgens, primarily entering maternal circulation..
    • After birth, the provisional cortex involutes and the permanent cortex develops in three layers (zones).

    Clinical Applications of Adrenal Gland

    • Hyperfunction: Cushing's syndrome (excess glucocorticoids), Conn's syndrome (excess aldosterone), and excessive adrenal androgens which may lead to precocious puberty (boys) and hirsutism/virilization in girls.
    • Hypofunction: Addison's disease (destruction of the adrenal cortex).

    Blood Supply of Adrenal Gland

    • Capsular arteries and cortical arterioles (supplying the cortex).
    • Medullary arterioles (branching into medullary capillary network).
    • Adrenal medulla has a more vascular supply with dual blood supply, arterial blood from medullary capillaries, and blood of cortical capillaries, which carries cortical hormones.

    Adrenal Medulla

    • Composed of chromaffin cells (pheochromes) – large, pale-staining polyhedral cells arranged in cords or clumps.
    • Few parasympathetic ganglion cells, alongside a profuse supply of sinusoidal capillaries.
    • Secretion through chromaffin reaction.

    Origin of Medullary Cells

    • Chromaffin cells arise from neural crest cells, the same origin as postganglionic neurons in sympathetic and parasympathetic ganglia.
    • They are modified sympathetic postganglionic neurons without axons/dendrites, specialized as secretory cells.

    Medullary Hormones

    • Secrete catecholamines like epinephrine and norepinephrine, derived from tyrosine.
    • Epinephrine, the major product (80%).
    • Granules in chromaffin cells (epinephrine granules, less electron dense & smaller), contain catecholamines, Ca2+, ATP & proteins called chromogranins.

    Medullary Hormones - Function

    • Medullary hormones deal with physical/emotional stress (fight-or-flight).
    • Increase blood pressure, blood glucose, vasoconstriction, and heart rate, as well as metabolic effects
    • Disorders: Pheochromocytoma is tumor of chromaffin cells, leading to hyperglycemia and transient elevation of blood pressure.

    Endocrine Pancreas

    • Composed of spherical aggregates, called islets of Langerhans, scattered among the exocrine acini.
    • More than a million islets in the human pancreas, concentrated at the tail.
    • Very thin capsule of reticular fibers surrounds each islet.
    • Origin: Endodermal (epithelial tissues).

    Islets of Langerhans Cells

    • Each islet consists of polygonal/rounded cells that are smaller and lightly stained than the surrounding acinar cells.
    • Arranged in cords that are separated by capillaries
    • Autonomic nerve fibers contact some of the endocrine cells and capillaries.

    Pancreatic Islet Cells

    • Four cell types:
      • Alpha cells (20%): Secrete glucagon; near periphery, stained pink with Gomori; granules with homogenous electron-dense core and lower density peripheral zone
      • Beta cells (70%): Secrete insulin; centrally located; smaller; numerous; stains blue with Gomori; granules with one or more dense crystals in a low density matrix.
      • Delta cells (5–10%): Secrete somatostatin; scattered and less abundant; larger granules, less electron dense
      • F/PP cells (<5%): Secrete pancreatic polypeptide; more common in islets of the head of the pancreas; granules with smaller sizes and variable density.

    Pancreatic Hormones

    • Insulin: anabolic hormone, increases the storage of glucose, fatty acids, and amino acids in cells and tissues, lowering blood sugar.
    • Glucagon: catabolic hormone that mobilizes glucose, fatty acids, and amino acids from stores into blood, raising blood sugar

    Neuronal Control of Glucagon & Insulin

    • Sympathetic fibers during stressful situations, emergencies, and exercise increase glucagon release and inhibit insulin release.
    • Parasympathetic fibers during restful times and digestion stimulate insulin release..

    Cell Types & Function

    • Alpha cells (glucagon): Increase blood glucose.
    • Beta cells (insulin): Decrease blood glucose.
    • Delta cells (somatostatin): Paracrine; inhibits hormone release; inhibits GH & TSH.
    • F cells (pancreatic polypeptide): Stimulates gastric chief cells; inhibits bile/pancreatic enzyme/bicarbonate secretion & intestinal motility

    Medical Applications

    • Insulin-dependent (type 1) diabetes: autoimmune destruction of beta cells, resulting in insulin insufficiency.
    • Insulin-independent (type 2) diabetes: failure of cells to respond to insulin (insulin resistance), often associated with obesity.

    Thyroid Gland

    • Location: cervical region, anterior to the larynx, two lobes united by an isthmus.
    • Surrounded by dense, irregular collagenous CT capsule; lobules.
    • Embedded in capsule: parathyroid glands.

    Thyroid Gland Origin

    • Main bulk from the primitive pharynx (endodermal lining).
    • Parafollicular cells (C-cells) from neural crest.
    • Develops between the first and second pharyngeal pouches.

    Cellular Organization

    • Thyroid follicle is the structural/functional unit (20-30 million).
    • Follicular cells (98%): cuboidal basophilic; central nucleus. Parafollicular cells (2%): larger, less intensely stained.
    • Central lumen is colloid (acidophilic, gelatinous substance).

    Follicular Cells

    • Single layer of cuboidal basophilic cells.
    • Protein secreting cells.
    • Contain apical secretory granules and abundant lysosomes & surface microvilli.
    • Shape (squamous to low columnar) varies with functional activity; active glands have low columnar epithelium & glands with squamous follicles are considered hypoactive.
    • Produce thyroid hormones (T3 & T4).

    Parafollicular (C) Cells

    • Found inside the basal lamina or clusters between follicles.
    • Derived from neural crest cells.
    • Larger and less intensely stained than follicular cells.
    • Contain fewer rough ER, larger Golgi complexes, numerous small granules with polypeptide hormone (calcitonin)

    Thyroid Hormone (T3 & T4) Synthesis & Secretion

    • Regulated by: iodide levels in follicular cells; binding of TSH to TSH receptors.
    • Steps:
    • Thyroglobulin synthesized/released into lumen.
    • Iodide uptake/oxidation.
    • Iodinated tyrosines (DIT, MIT) form T3 & T4 in colloid.
    • Endocytosis & hydrolysis of thyroglobulin by lysosomal enzymes.
    • T3 & T4 released into blood.

    Thyroid Hormone (T3 & T4)

    • T4 is more abundant (90%) and a prohormone/reservoir for active T3.
    • T3 is more active form (2-10x stronger), with a shorter half-life (1.5 days vs. week).
    • Most circulating thyroid hormone is bound to transport proteins.

    Thyroid Hormone Function

    • Important for growth, cell differentiation, basal metabolic rate, and oxygen consumption in cells.
    • Affects protein, lipid, and carbohydrate metabolism.

    Thyroid Hormone Secretion Control

    • TSH from anterior pituitary stimulates synthesis/release.
    • TSH increases epithelium activity/height.
    • TSH receptors at follicular cell bases.
    • Negative feedback.
    • Iodine levels.

    Medical Applications

    • Iodine deficiency goiter: thyroid gland enlargement due to iodine deficiency, resulting in accumulation of non-iodinated thyroglobulin Hypothyroidism: leads to cretinism in infants; autoimmune disorders; fatigue, weight gain, pale or puffy face; cold intolerance, joint/muscle pain
    • Hyperthyroidism: Grave's disease; autoimmune; TSH receptors stimulated; continuous thyroid hormone release; bulging eyes (exophthalmos)

    Parathyroid Gland

    • Usually 4 in number.
    • Located on posterior surface of the thyroid gland.
    • Superior & inferior glands..
    • Usually embedded in thyroid capsule
    • Derived from pharyngeal pouches.

    Parathyroid Gland Structure

    • Capsule, septa, and clusters of secretory cells.
    • As age increases, Chief Cells are replaced by adipocytes..
    • Two cell types: Chief cells and oxyphil cells

    Chief Cells

    • Polygonal cells with round nuclei and pale-staining, slightly acidophilic cytoplasm.
    • Cytoplasm contains secretory granules with parathyroid hormone (PTH).
    • Main target cell of PTH are osteoblasts which release osteoclast-stimulating factor, causing increase in the number & activity of osteoclasts.

    PTH Action

    • Increase blood calcium by increasing the number and activity of osteoclasts; increases Ca2+ & Mg2+ reabsorption from the distal tubules;
    • Inhibits HPO4⁻² reabsorption so more is in Urine;
    • Promotes activation of vitamin D, increasing Ca2+ and Mg2+ absorption from the gastrointestinal tract

    Oxyphil Cells

    • Less numerous, larger than chief cells.
    • Stain deeply with eosin.
    • Appear in groups/isolated cells, have more mitochondria, little RER & glycogen in cytoplasm.
    • Possibly inactive phase of chief cells.
    • Appear around puberty and increase in number; unknown function.

    Medical Applications

    • Hyperparathyroidism: decreased blood phosphate, increased blood calcium.
    • Osteitis fibrosa cystica: bones are less stress-resistant; prone to fractures
    • Hypoparathyroidism: increased blood phosphate, decreased blood calcium.
    • Generalized convulsions (spasam/tetany)
    • Treated with Calcium salts & Vit D to promote Ca2+ uptake in gut

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