Endocrine System Flashcards
What makes up the endocrine system?
Pituitary gland (adenohypophysis) Adrenal gland (suprarenal) Thyroid and parathyroid gland Pineal Gland Islet of Langerhans Diffuse neuroendocrine system (enteroendocrine cells of intestine, heart, kidney)
What is the pituitary attached to, and by what?
Attached to the hypothalamus by the infundibulum
What is the glandular portion of the pituitary called? What is it derived from?
Called the adenohypophysis and derived from the ectoderm of the primitive oral cavity.
What are the 3 parts of the adenohypophysis?
pars distalis, pars tuberalis, pars intermedia
What is the neural portion of the pituitary called? What is it derived from? What is this portion made up of?
Called the neurohypophysis. Derived from neuroectoderm. Made up of the pars nervosa and infundibulum.
What are the 2 parts of the pituitary infundibulum?
stem, median eminence
Where do neurons of the supraoptic and paraventricular nuclei synapse?
They synapse in the pars nervosa
Where do neurons of the dorsal medial, ventral medial, and infundibular nuclei synapse?
The primary capillary plexus just distal to the infundibulum
What does the superior hypophyseal artery perfuse?
The median eminence, upper part of infundibulum, and lower part of infundibulum via connection to inferior hypophyseal arteries
What does the inferior hypophyseal artery perfuse?
The pars nervosa
What makes up the anterior lobe of the pituitary?
pars distalis and pars tuberalis
What makes up the posterior lobe of the pituitary?
pars intermedia and pars nervosa
What stimulates or inhibits the release of hormones by cells in the anterior pituitary?
Release of peptide hormones from specialized neurons in hypothalamic nuclei (neurons of the dorsal medial, ventral medial, and infundibular nuclei) into the primary capillary plexus of the infundibulum
What hormones are secreted from the anterior pituitary?
thyrotropin
gonadotropin
growth hormone (somatotropin)
corticotropin
How is prolactin release regulated?
Peptide hormones (dopamine) secreted by the hypothalamus act on the primary capillary plexus of the infundibulum and inhibit the anterior pituitary from releasing prolactin.
Describe the blood supply to the hypophysis.
The superior and inferior hypophyseal arteries supply blood to the hypophysis. The inferior hypophyseal artery supplies blood to the pars nervosa, while the superior hypophyseal artery perfuses the upper infundibulum, median eminence, and lower infundibulum via the inferior hypophyseal artery.
The hypopheseal arteries end in capillary plexuses, which are then drained by hypophyseal portal veins
What does the pars distalis consist of?
Secretory cells within a connective tissue stroma with fenestrated capillaries
What are chromophobes? Describe them. Where are they found? How do they stain?
3 types of chromophobes which make up about 50% of cells in the pars distalis.
1) undifferentiated nonsecretory cells (stem cell?)
2) degranulated chromophils with few granules
3) connective tissue/follicular cells
Stain poorly - appear clear or white.
What is the function of the chromophobe subpopulation of connective tissue/follicular cells?
Follicular cells form a stromal network to support chromophil cells. May have some phagocytic functions.
How do acidophils stain? What is their function?
Acidophiles are chromophiles which stain orange with eosin and orange G, not PAS (PAS-orange G?). Acidophils secrete peptide hormones. Two examples of acidophils are somatotrophs and mammotrophs.
Are acidophils or basophils bigger? Which has more granules?
basophils are bigger. acidophils have more granules.
Describe the function and regulation of somatotrophs?
Somatotrophs are a type of acidophil which produce growth hormone (GH/somatotropin). They are under control of GH-releasing factor (released from hypothalamus) and GH-inhibiting factor (somatostatin, also released from the hypothalamus)
What do mammotrophs do? What regulates them?
Mammotrophs are a type of acidophil which produce prolactin, which stimulates and maintains lactation. Numbers of mammotrophs increase during lactation. Controlled by thyrotropin-releasing factor (TRF, stimulates production of prolactin) and prolactin-inhibiting factor (dopamine, tonic inhibition). Prolactin is secreted spontaneously in the absence of any hypothalamic stimulation.
How do basophils stain? What is their function?
Basophils stain with hematoxylin and other basic dyes. They secrete glycoprotein hormones - PAS positive. Examples of basophils are gonadotrophs, corticotrophs, and thyrotrophs.
What is secreted by gonadotrophs? What are these hormones’ functions?
Follicle-stimulating hormone (FSH): stimulates the development of ovarian follicles and acts on Sertoli cells to stimulate production of androgen-binding protein.
Lutenizing hormone (LH): Stimulates steroidogenesis in ovarian follicles and corpus luteum. Controls rate of testosterone synthesis by Leydig cells.
What is secreted by corticotrophs? What is the function?
Adrenocorticotropin (ACTH) - stimulates growth and steroid synthesis in zona fasciculata and z. reticularis of adrenal cortex
What is secreted by thyrotrophs?
Thyrotropin (thyroid-stimulating hormone, TSH). Under control of TRF (secreted from hypothalamus; also stimulates prolactin release). Approximately 5% of cells.
What can H&E stain distinguish between?
acidophils, basophils, and chromophobes
What does the pars nervosa consist of?
Non-myelinated axonal processes (cell bodies located in paraventricular and supraoptic nuclei of hypothalamus) and pituicytes (astrocyte-like glial cells - contain glial fibrillary acidic proteins, often contain pigment granules)
What do neurons in the pars nervosa end close to?
the fenestrated capillary network
What are Herring bodies? Where are they found?
Large neurosecretory granule-filled dilations near axon terminals in pars nervosa. They are visible at LM level
What hormones do hypothalamic neurons release in the pars nervosa?
oxytocin and antidiuretic hormone (vasopressin). release near capillary plexus.
What produces oxytocin? What is its function?
Oxytocin is primarily produced by paraventricular nucleus cells and secondarily by supraoptic nucleus cells. It stimulates milk ejection in the mammary glands and uterine smooth muscle contraction during childbirth.
What produces antidiuretic hormone (ADH) and what is its function?
Produced mainly by supraoptic nucleus cells and secondarily by paraventricular nucleus cells. Stimulates water reabsorption by the renal medullary collecting ducts.
What is neurophysin?
It is a binding/carrying protein that complexes with neurohypophyseal hormones for transport down axons.
Describe the pars intermedia
Very small in humans. Contains basophil and chromophobe cells and Rathke’s cysts. Part of the posterior lobe of the pituitary
What are Rathke’s cysts?
Cuboidal epithelium lined cavities - remnants of Rathke’s pouch.
Describe the pars tuberalis
Highly vascular region - contains veins of hypophyseal portal system. Contains mostly gonadotropes. Part of the anterior lobe of the pituitary.
How do ACTH, TSH, FSH, and LH self-regulate?
Through feedback loops which impact both the pituitary and the hypothalamus.
What is acromegaly?
Excess growth hormone
What can a prolactin-secreting tumor cause?
Infertility - lack of ovulation
What is the most common cause of hypopituitarism in adults?
Pituitary tumors - adenomas
What is primary pituitary destruction? What is another name for this condition?
Also called intrinsic pituitary destruction. Hormone-secreting cells of the anterior pituitary are destroyed. Condition can involve some or all hormones.
What can poor anterior lobe function cause? Which hormones cause which symptom?
Failure of lactation (prolactin), amenorrhea (absence of menstruation - FSH or LH?), poor thyroid function (TSH), adrenal insufficiency (ACTH)
What can poor posterior lobe function cause?
Diabetes insipidus (impairment of water resorption in distal renal tubuli), polyuria (excessive urination), polydipsia (excessive thirst) - all caused by lack of ADH?
Describe the pineal gland.
Gland is covered by pia mater. No blood-brain barrier. Trabeculae (connective tissue septa) extend from capsule and divide Pineal gland into lobules. Consists of pinealocytes and glial cells (interstitial cells).
What is the major product of the pinealocytes? What is its function?
melatonin - regulates sleep cycle
How does the pineal gland stain?
Cells are slightly basophilic with irregular lobulated nuclei and distinct nucleoli. Silver stained cells appear to have long tortuous branches. May occasionally see brain sand in the gland.
What is brain sand? What is another name for brain sand?
Corpora arenacea = calcium phosphate or calcium carbonate granules. Irregular in shape, often lamellar in appearance (thin scaly rectangles? no idea what lamellar means). May be used by radiologist to localize gland.
What is the pineal gland innervated by?
Postganglionic sympathetic nerves that arise in the superior cervical ganglia
How is the pineal gland function regulated?
External lighting leads to a signal from retinal neurons which inhibits secretion of melatonin from the pineal gland. Darkness stimulates melatonin secretion and light inhibits it.
What may a Pineal tumor cause?
Restriction of CSF flow through the aqueduct of Sylvius, causing hydrocephalus (buildup of fluid inside the skull leading to brain swelling)
What is the thyroid gland derived from?
The cephalic portion of the alimentary canal endoderm
What are the three parts of the thyroid gland?
2 lobes (right and left) connected by an isthmus
What are the thyroid lobes made up of?
Follicles lined by simple cuboidal epithelium (epithelium = principal cells). Follicles surrounded by extensive blood and lymphatic capillary network. Capillary endothelial cells are fenestrated.
Describe the principal cells in the thyroid gland.
Principal cells make up the follicular epithelium. The epithelium can appear more squamous during times of low activity, and more columnar during times of high activity. Principal cells secrete T3 and T4, and may have vesicles (colloidal reabsorption droplets).
What usually fills thyroid follicles? Describe this substance.
Acidophilic staining colloid (glycoprotein thyroglobulin - inactive storage form of thyroid hormones)
What are parafollicular cells? What do they secrete?
Also called C cells - somewhat larger than follicular cells. They are found as part of the follicular epithelium or as isolated clusters between thyroid follicles. At the ultrastructural level they contain numerous 100-180 nm granules. Stain poorly in humans - may appear clear or white. C cells secrete cacitonin.
What does calcitonin do? Where is it secreted from?
Calcitonin is secreted by C cells in the thyroid. It supresses bone resorption by inhibiting osteoclast activity. Elevated blood calcium levels stimulate calcitonin secretion, and secretion is suppressed when calcium concentration falls below normal.
What has a bigger role in regulating blood concentrations of calcium - calcitonin or PTH?
PTH! In humans, calcitonin has only a minor role in regulating blood concentrations of calcium.
Describe the synthesis of thyroglobulin (THY)
THY synthesized in rough ER, glycosylated in rough ER and golgi, and vesicles release contents into lumen of follicle.
Does iodide iodinate thyroglobulin in the cytoplasm?
NO! Thyroglobulin is oxidized in the cytoplasm, and tyrosine residues on the thyroglobulin are iodinated in the colloid.
How does iodide enter the cell?
It is actively transported across the membrane of the principal cell/follicular cell.
What process does TSH begin?
TSH (thyroid stimulating hormone) released from the anterior pituitary binds to TSH receptors on the principal cell. These cells then endocytose collid which combines with lysosomes. Then, iodinated residues are cleaved from the THY (?) and T3 and T4 are released into the cytosol and then at the plasma basal membrane.
What is T3?
triiodothyronine
What is T4?
thyroxine
What sorts of effects can thyroid hormones have in the body?
- Stimulate transcription of a variety of genes
- Cause a general increase in cellular metabolism
- Stimulate carbohydrate metabolism; decrease synthesis of cholesterol, phospholipids, and triglycerides; increase synthesis of fatty acids
What can excessive thyroid hormone production cause?
- Weight loss
- Increased heart rate, metabolism, respiration, and appetite
- Muscle tremors
- Tiredness
- Frequent or excessive menstrual bleeding
How do goiters occur?
Insufficient iodine uptake –> decreased T3, T4 production –> increased thyroid stimulating hormone (TSH) –> follicular hyperplasia = goiter
What is Graves disease?
Hyperthyroidism - thyroid hyperfunction due to immunologic dysfunction that produces a circulating immunoglobulin that has effects similar to TSH
What is Hashimoto’s disease?
Autoimmune destruction of thyroid resulting in hypothyroidism. Thyroid peroxidase autoantibodies produced. Thyroid infiltrated with lymphocytes and plasma cells. Lymphocytes may organize into germinal centers.
What is the relative frequency of thyroid cancer in men vs women?
Thyroid cancer occurs 3-4X as often in women compared to men.
What is myxedema? When does this happen?
Myxedema is a localized skin disorder with swelling. Myxedema is present in hypothyroidism and Hashimoto’s disease.
What is the parathyroid gland? Describe it.
4 small glands situated behind the thyroid gland. Each gland sits within a connective tissue capsule. Septa extend from the capsule into the gland.
What are the 2 main types of cells in the parathyroid gland?
chief cells and oxyphil cells
Describe the chief/principal cells of the parathyroid gland.
They have irregular granules (200-400 nm in diameter) that contain parathyroid hormone (PTH)
Describe the oxyphil cells of the parathyroid gland.
Oxyphil cells stain intensely with eosin due to large numbers of mitochondria. Appear after purberty. Function unclear (transitional chief cells?)
Which is bigger - oxyphil cells or chief cells?
Oxyphil cells
How does PTH work?
PTH increases Ca++ in blood by 3 methods:
1) PTH stimulates the number and activity of osteoclasts, which reabsorb the calcified bone matrix and release Ca++.
2) PTH enhances resorption of Ca++ from kidney distal tubules and increases phosphate excretion.
3) PTH increases intestinal absorption of Ca++ from food by stimulating vitamin D synthesis, which then stimulates synthesis of calcium binding protein in intestine.
Is calcitonin or PTH a more important regulator of blood calcium?
PTH
What is hyperparathyroidism? What causes it?
Adenoma (80%), carcinoma (1-2%), hyperplasia (15%)
Blood calcium is increased and blood PO4 is low. Bone cysts may develop (osteitis fibrosa cystica - rubbery deformed bones, kidney stones, pancreatitis, peptic ulcers, hypertension)
What is hypoparathyroidism?
Decreased serum Ca++ and increased serum PO4. Symptoms are tetany (spasms and cramps, typical with low Ca++), muscle cramps, exaggerated tendon reflexes, jaw locks
What are the two layers of the suprarenal (adrenal) gland? Where are these two layers derived from?
Cortex - derived from the mesoderm
Medulla - derived from the neural crest
Describe the adrenal medulla.
Cells are arranged in cords or clumps supported by a reticular fiber network. Contains parenchymal/chromaffin cells and sometimes sympathetic ganglionic nerve cells.
Describe medullary parenchymal/chromaffin cells.
Have numerous secretory granules (140-350nm) that contain epinephrine or norepinephrine.
Are granules smaller in cells secreting epinephrine or norepinephrine?
epinephrine (word is smaller too?)
What are the three layers of the adrenal cortex, from outside to inside?
Zona glomerulosa
Zona fasciculata
Zona reticularis
What is secreted by the zona glomerulosa? What stimulates this?
Mineralocorticoids (aldosterone). Synthesis is stimulated by angiotensin II and ACTH.
What is secreted by the zona fasciculata?
Glucocorticoids (cortisol, corticosterone). ACTH stimulates secretion.
How is the zona fasciculata arranged?
Sinusoidal capillaries are arranged longitudinally between columns of parenchymal cells.
What are the layers of the adrenal gland, from outside to inside?
capsule
zona glomerulosa - secretes mineralocorticoids
zona fasciculata - secretes glucocorticoids
zona reticularis - secretes gonadocorticoids
adrenal medulla - secretes adrenalin and noradrenalin
What is secreted by the zona reticularis?
Gonadocorticoids (DHEA - dehydroepiandrosterone, androstenedione)
How do noradrenalin secreting chromaffin cells stain with a chrome salt fixation?
brownish color
What is a pheochromocytoma?
Adrenal medulla tumor that causes hyperglycemia and transient elevations in blood pressure. This is the most common adrenal tumor in adults.
What is a neuroblastoma?
An adrenal medulla tumor that is common in children. It does not affect blood pressure.
What is Cushing’s syndrome?
Excess secretion of cortisol (from the zona fasciculata). Causes round “moon face,” high blood sugar, diabetes mellitus, amenorrhea, hirsutism (male-pattern hair growth in women), and acne. Patients are also emotionally labile (mood fluctuations)
What is Conn’s syndrome?
Excess production of aldosterone (from the zona glomerulosa). Leads to excess H2O retention, causing hypertension and hypokalemia.
What is Addison’s disease?
(Chronic) adrenocortical insufficiency - causes weakness, nausea, weight loss, and elevated ACTH levels (because no negative regulation by glucocorticoids on hypothalamus or pituitary) (causes hyperpigmentation)
What is Waterhouse-Friderichsen syndrome?
Acute cortical destruction. Can lead to meningococcal sepsis and endotoxic shock.
