Histo endocrine sys II Flashcards
What is the origin of the thyroid?
Originates from endodermal epithelium in floor of embryonic pharynx, then secondarily loses epithelial connection to pharynx
What is the histological organization of the thyroid?
–Capsule of loose CT. Extensive blood and lymphatic supply.
–Spherical structures lined by epithelia forming follicles containing central colloid.
what is the thyroglobulin?
Extracellular storage of thyroglobulinin colloid. Thyroid hormones stored in a bound (inactive) form in colloid. pwhats gonna be T3 nad T4
What is th emajor regulator of the thyroid?
Hormone thyrotropin (TSH)
which are the epithelial cell types in thyroid follicles?
Thyroid follicular (principal) cells
Parafollicularor C cells
identify
colloids and nuclei of cells
describe the function and epithelium of thyroid folicular cells
Simple epithelium lining follicle (cell height varies in relation to functional activity) from columnar (active) to squamous (inactive)
They have the characteristics of cells that synthesize, secrete, absorb and digest proteins
Produce Thyroid hormones T3 (Triiodothyronine)and T4 (Thyroxine)
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Electron micrograph shows a single layer of epithelium containing low columnar follicular cells. The apical surfaces with visible microvilli (Mv) are in contact with the colloid, whereas basal surfaces of follicular cells rest on the basal lamina (FBL).
Accumulation of lysosomes (L) and colloid resorption droplets (CRD), extensive Golgi apparatus (G), rough endoplasmic reticulum (rER), and presence of enlarged intercellular spaces are indicative of intensive activity of follicular cells.
describe the function of parafollicular cells or C cells
Found as part of the epithelium or isolated cluster between thyroid follicles.
Secrete calcitonin (thyrocalcitonin) that lowers blood calcium inhibiting bone resorption.
Secretion is stimulated by elevation in blood calcium
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parafollicular cells or c cells (inacitive)
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parafolicular cells, with granules in colloid (active) T3 nad T4
Explain the mechanism of synthesis of thyroid hormones
1- Synthesis of thyroglobulin
The precursor of thyroglobulin is synthesized in the rER of the follicular epithelial cells. Thyroglobulin is post translationally glycosylated in the rER and the Golgi apparatus before it is packaged into vesicles and secreted by exocytosis into the lumen of the follicle.
2- The uptake of blood circulating iodide. Using ATP-dependent iodide transporters
Follicular epithelial cells actively transport iodide from the blood into their cytoplasm using ATPase-dependent sodium/iodide symporters (NIS). These cells are capable of establishing an intracellular concentration of iodide that is 30 to 40 times greater than that of the serum.
3- Iodination of thyroglobulin occurring at the microvillus surface of the follicular cell.
One or two iodine atoms are then added to the specific tyrosine residues of thyroglobulin. This process occurs in the colloid at the microvillar surface of the follicular cells and is also catalyzed by thyroid peroxidase (TPO)
4- Formation of T3 and T4 by oxidative coupling reactions
The thyroid hormones are formed by oxidative coupling reactions of two iodinated tyrosine residues in close proximity. For example, when neighboring DIT and MIT residues undergo a coupling reaction, T3 is formed; when two DIT residues react with each other, T4 is formed. After iodination, T4 and T3 as well as the DIT and MIT residues that are still linked to a thyroglobulin molecule are stored as the colloid within the lumen of the follicle
5- Upon stimulation by thyrotropin (TSH) → resorption of colloid by endocytosis → digested by lysosomal enzymes (proteases)
6- Release of T3 and T4 cross basolateral membrane and enter capillaries
Synthesis of thyroid hormones
production of T3 nad T4 is regulated through negative feedback system, explain
The follicular cells produce 20 times more T4 than T3; however, T4 is converted in the peripheral organs (e.g., liver, kidney) to a more active form of T3. Approximately 99% of T4 and T3 released from the thyroid gland into the circulation bind to specific plasma proteins. The remaining free (unbound) T4 and T3 exert negative feedback on the system and inhibit further release of T4 and T3. This inhibition occurs at the level of the anterior lobe of the pituitary gland and the hypothalamus. At the pituitary level, T4 and T3 inhibit secretion of TSH by thyrotropes
thyroid hormones are essential for:
normal fetal development
explain pathologicalc conditions involving the thyroid
- Iodine deficiency produces a condition called goiter
- Adult hypothyroidism
Can be secondary to hypothalamic failure
–Hashimoto thyroiditis presence of abnormal autoimmunoglobulinsdirected against thyroglobulin (TgAb), thyroid peroxidase (TPOAb), and the TSH receptor (TSHAb). Results in thyroid cell apoptosis and follicular destruction. - Children hypothyroidism = Cretinism
- Hyperthyroidism or thyrotoxicosis
-Graves’ disease: Immunoglobulins bind to the thyrotropin receptors mimicking thyrotropin stimulation
identify
Thyroid gland hyperactive, colloid being reabsorped
what is the parathyroid?
Small glands (4) behind the thyroid gland. Covered by the capsule. Occasionally embedded in the thyroid gland.
what cells are rpesent in the parathyroid?
- Chief cells (PRINCIPAL)
–Small polygonal cells
–Secretory granules containing parathyroid hormone (PTH) [aumenta concentracion de calcio] - Oxyphilcells
–Large cells, cytoplasm with many acidophilic mitochondria.
–Function not known
Adipose cells increase in numbers with age
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parathyroid gland on the right, vascular
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parathyroidlic cells and the violet dark are the chief cells
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parathyroid gland; chief cells dark pink and arrow is oxyphil
What is the function of PTH?
Promotes calcium release from bones. Binds to receptors in osteoblasts →produce osteoclast stimulating factor →promotes bone resorption →releases Ca2+ into the blood
Increases synthesis of vitamin D, that promotes reabsorption of calcium in kidney
Intestinal absorption of calcium is increased under PHT influence.
PHT and calcitonin have opposite effects in the regulation of calcium levels
explain pathologies involving PTH
Hyperparathyroidism
–Excessive high calcium in blood. Bone disease called Osteitis fibrosacystic
Hypoparathyroidism (en operaciones antes)
–Low calcium. Convulsions called Tetany
What is the embryological origin of adrenal glands?
Adrenal cortex: Coelomicintermediate mesoderm (steroid hormones)
Adrenal medulla: Neural crest (cathecholamines)
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adrenal gland
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adrenal gland
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adrenal gland
mention the fucntion of the adrenal cortex
Site of corticosteroid synthesis.
Hormones are not stored.
They are synthesized and released on demand. Precursors such as cholesterol are stored intracellular
explain the Zona glomerulosa of the adrenal gland
Beneath CT capsule. Cells forming arched cords. Acidophilic cytoplasm
Site of mineralocorticoidssynthesis (Aldosterone). This hormone regulates sodium and potassium concentrations in blood by acting on kidney distal tubules
Hormone secretion regulated mainly by renin-angiotensin system
identify zones
explain the zona fasciculata
Radiallyarranged cell columns.
Is the largest zone of adrenal cortex
Highly vacuolated cytoplasm (Spongyocytes)
Site of glucocorticoids synthesis (Cortisol)
Function: Regulates metabolism of carbohydrate, protein and fats Glyconeogenesisand glycogenesis
Anti-inflammatory activity suppressing Interleukins 1 and 2, production and some allergic reactions.
Hormone secretion controlled by ACTH (produced in adenohypophysis in corticotropics)
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zona fasciculata
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zona fasciculata
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SER, mitochondrias, precursor lipidico (L),
explain the zona reticularis
*Branching network of cell cords
*Adjacent to medulla
*Site of weak androgen synthesis:
*Dehydroepiandrosterone(DHEA)
*Region with numerous residual bodies.
*Function not clearly understood
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zona reticularis on top, zona medola bottom
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zona reticularis on top, zona medola bottom
exaplain the organization of blood supply of adrenal gland
The cortical arterioles form a cortical network of capillaries, which drain into a second capillary network in the medulla. The medullary capillary network is formed primarily by the medullary arterioles and drains into the central medullary vein.
exaplain adrenal dysfunction
Hyperadrenocorticism(Cushing syndrome)
Pituitary basophil tumor →Excessive production of ACTH secretion →Excess cortisol production →obesity, hirsutism, impotence, amenorrhea (afecta glucocorticoides)
Hypoadrenocorticism(Addison disease)
Destruction of adrenal cortex by infection. Symptoms: low blood pressure, weight loss, general weakness: may lead to death if no hormone therapy is given.
what si the origin of the adrenal medulla?
Origen: Neural crest origin
The adrenal medulla cells are innervated by presynaptic sympathetic neurons, therefore can be regarded as modified sympathetic postganglionic neurons that have become secretory
what si the arangement of the adrenal medulla?
Arranged as clusters and cords of cells. Called Chromaffincells, because stain specifically with bichromatesalts = Chromaffinreaction
what is the secretory function of the adrenal medulla?
Epinephrine and norepinephrine
Release of hormones is triggered by acetylcholine from the presynaptic sympathetic axons that synapse with each chromaffin cells.
*Secreted two hormones by two different cell types
*Accumulate and store hormones in granules
*Catecholamines(epinephrine and norepinephrine)
identifyq
adrenal medulla
describe epinephrine and norepinephrine
Epinephrine
*Small, less dense granules. Prepares body for “fight or flight”
*Increases heart rate, brain alertness, liver, skeletal muscle function.
Norepinephrine
*Large dense core vesicles. Elevation of blood pressure by vasoconstriction
identify
adrenal medulla; norepinephrine and epinephrine
explain the blood supply of adrenal medulla
Dual blood supply to medulla
*Indirect: via cortical sinusoids.
*Direct: via long, medullary arteries, which course through cortex without supplying it.
what do glucocorticoids do in the adrenal medulla?
Glucocorticoids induce the conversion of norepinehrineto epinephrine in the chromaffin cells
what is one disorder of the adrenal medulla?
Pheochromocytoma, a tumor that causes hyperglycemia and transient elevations of blood pressure.
what are islets of langerhans?
Scattered, well-vascularized, epithelioid cell islands within exocrine pancreas.Four different hormone secreting cells:
Alpha cells (A)
–Secrete glucagonwhich increases blood sugar levels
Beta (B)
–Secrete insulin which lowers blood sugar
Delta cells (D)
–Secrete somatostatin: Inhibits release of insulin and glucagon in a paracrine action
F cell
–Secretes pancreatic polypeptide. Stimulates gastric chief cells. Inhibits bile secretion and intestinal motility.
Difficult to identify specific cell types at light microscopy level.
Antibodies against specific hormones is the best method.
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Pancreas endocrine and exocrine (islets 1-3 million)
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In this H&E preparation, it is difficult to identify specific islet cell types without special stains. At best, one can identify small cells (arrows) at the periphery of the islet that are probably A cells.
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This photomicrograph shows an islet of Langerhans from rat pancreas stained with a special silver stain that reacts with glucagon-secreting cells (A cells)
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This immunofluorescence image shows the islet of Langerhans and distribution of glucagon-secreted A cells (green) and insulin-secreted B cells (red) in the adult pancreas. Cells were counterstained with 4′,6-diamidino-2-phenylindole (DAPI) stain that reacts with nuclear DNA and exhibits blue fluorescence over the nuclei. Note that B cells comprise most of the islet cells and A cells are scattered throughout the islets.
identify
B cells-Secretory granules with insulin crystals (se cristaliza la insulina)
what is the innervation of the islets of langerhan?
The islets have both sympathetic and parasympathetic innervation. Aprox.10% of the islet cells have nerve endings contacts. Network of gap junctions are located between islet cells allows communication.
explain diabetes mellitus
Absence or inadequate amounts of insulin lead to elevated blood glucose levels and the presence of glucose in the urine, a condition known as diabetes mellitus.
Insulin resistance characteristic of diabetes mellitus is linked to neural degeneration, cognitive dysfunction, and dementia.
explain where those IGF are found
It has been found expression of insulin and insulin growth factors (IGF I and IGF II) in nerve cells in several regions of the brain.
an early symptom of Alzheimer’s disease (AD):
The reduced rate of insulin and IGF production in the brain contributes to the degeneration of brain cells
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Pathological conditions:
Pancreatic tumors
Diabetes type I (Autoimmune disease, antibodies against B cells)
queda como connective tissue (it has been replaced, los islets se llenan de CT)
