L30-31: Endocrine Glands I-II Flashcards
Two populations of cells of hypothalamus. What does each release?
- ) Neurons: produces and releases NTs
2. ) Special neurons: produces and releases hypothalamic neurosecretory hormones – regulates activity of pituitary gland
Describe release and pathway of travel for hypothalamic neurosecretory hormones
- Stored at axon terminals of special neurons in hypothalamus, which terminate in the median eminence
- Released and passed into primary capillary plexus (fenestrated capillaries at median eminence)
- Drain into hypophyseal portal veins (in infundibulum)
- Pass into secondary capillary plexus (sinusoidal capillaries) located in anterior lobe of pituitary
- Pass into parenchyma of anterior lobe of pituitary to influence cells there
List and function of hypothalamic neurosecretory hormones
- ) GHRH: growth hormone releasing hormone stimulates secretion of somatotropin (growth hormone)
- ) PRH: prolactin-releasing hormone stimulates secretion of prolactin
- ) PIH: prolactin-inhibitory factor inhibits secretion of prolactin
- ) CRH: corticotropin-releasing hormone stimulates release of ACTH
- ) TSH-RH/TRH: thyroid-stimulating hormone-releasing hormone (aka thyrotropin-releasing hormone) stimulates secretion of thyroid stimulating hormone
- ) GnRH: gonadtropin-releasing hormone stimulates secretion of luteinizing hormone, stimulates secretion of follicle stimulating hormone
What do neurons of the supraoptic and paraventricular nuclei of the hypothalamus synthesize and secrete? Where do they secrete their product?
- Synthesize ADH and oxytocin. Synthesize neurophysin, a carrier protein of the two hormones ADH and oxytocin
- The axons from these neurons form the hypothalamohypophyseal tract, which carry these hormones to the posterior lobe of the pituitary gland where they are released and travel into general circulation
Pituitary gland. Two lobes and types of tissue found in each lobe?
- ) anterior lobe / aka adenohypophysis: glandular tissue
2. ) posterior lobe / aka neurohypophysis: neural tissue
Types of secretory cells of anterior pituitary. List the specific cells under each, their secretion and downstream target
1.) Chromophils
a. ) Acidophils:
- lactotropes/aka mammotropes secrete prolactin: acts on mammary gland during pregnancy to signal growth and to signal lactation following birth
- somatropes secrete somatropin (aka growth hormone): acts on long bones to influence growth, on muscle and adipose to increase cellular metabolism
b. ) basophils
- corticotropes secrete ACTH: acts on adrenal cortex to cause secretion of cortisol and corticosterones
- thyrotropes secrete TSH: acts on thyroid gland to cause secretion of T3 and T4
- gonadotropes secrete FSH and LH: acts on ovaries and testes respectively to cause estrogen/progesterone secretion and ovulation from ovaries and to signal spermatogenesis and androgen secretion from testes
2.) Chromophobes
What does excessive GH in children cause? In adults?
- Children: Gigantism
- Adults: Acromegaly (including prognathism)
• possibly through somatotropic adenomas
Histological feature(s) of posterior pituitary?
- Herring bodies: axon terminals of the hypothalamohypophyseal tract, which contain ADH and oxytocin
- Pituicytes (glia-like local cells) that are the supporting cells of the tissue here
Function of ADH and oxytocin?
- ADH: causes Na and therefore water absorption at the kidneys
- Oxytocin: contraction of myoepithelium at mammary glands a and also contraction of uterus during parturition
What is synthesized by the thyroid gland? By what cells?
- T3/T4 by the follicular cells
- Calcitonin by the parafollicular cells
Histological features of the thyroid gland
- ) Capsule: dense irregular collagenous CT, gives rise to trabeculae/septa that partions gland into lobules, carries BVs, lymphatics and nerves – parathyroid glands located in this capsule on posterior surface
- ) Thyroid follicles: surrounded by basal lamina, reticular fibers and fenestrated capillary plexus, glandular secretion stored in follicular lumen (colloid consists of thyroglobulin bound to T3/4) lined by follicular epithelium (follicular cells or principal cells) which have different shape depending on their level of activity
- ) Parafollicular cells (aka clear cells or C cells) wedged between follicles are light-staining with round nucleus with granules containing calcitonin
Briefly describe synthesis and release of thyroid hormones (T3 and T4)
- Thyroglobulin is synthesized at RER, also glycosylated there
- Transported to Golgi where it is glycosylated
- Transported to luminal aspect of cell and exocytosed
- Iodine is reduced to iodide in GI
- Enters bloodstream and is absorbed preferentially by thyroid gland
- Enters via sodium/iodide symporter at basal membrane of follicular cells
- Diffuses toward apical cell membrane
- Oxidation of iodide takes place via thyroid peroxidase, membrane bound enzyme on apical cell membrane (with peroxide)
- Iodination of thyroglobulin’s tyrosine residues occur where luminal microvillar aspect of follicular cell contacts colloid producing MIT and DIT
- MIT+DIT = triiodinated tyrosine
- DIT+DIT = tetraiodinated tyrosine
- TSH secreted from thyrotropes in anterior pituitary and released into general circulation
- Binds to TSH receptors on basal membrane of thyroid follicular cells
- Filopodia form at luminal surface of follicular cells
- Endocytosis of colloid occurs
- Vesicles unit with endosomes, contain proteases and cleave iodinated tyrosine residues from thyroglobulin (T3/T4, MIT and DIT), released into cytoplasm. T3 and T4 are liberated from cell basal membrane in surrounding CT and are picked up by blood and lymphatics. T4 converted to T3 by liver, kidney and heart
- T3 = triiodothyronine, T4 = tetraiodothyronine
Histology of parathyroid gland
- Covered by a collagenous CT capsule that send BVs, lymphatic vessels and nerve fibers into glands, septa and reticular fibers form supporting framework
- Fenestrated capillary network
- Adipose present in adults
- Parenchyma = cords and clusters of epithelial cells. Chief cells are eosinophilic and oxyphil cells are intensily eosinophilic (d/t mitochondria) and larger than chief cells
Function of calcitonin
- Causes lowers calcium in serum through inhibition of osteoclast activity
- Also causes calcium deposition in bone through osteoid calcification
Cells of parathyroid glands. What does each secrete?
- ) Chief cells: secretes PTH
- ) Oxyphil cells: unknown function
- ) Intermediate cell: unknown function
Function of PTH? How?
- PTH increases blood calcium level and simultaneously decreases serum phosphate
- Low levels of calcium trigger release of PTH
- High level inhibit its release
- In bone: PTH attaches to osteoblast receptors, causing them to release osteoclast-stimulating factor, which triggers osteoclast activity
- In kidney: PTH prevents calcium loss in urine and promotes phosphate loss
- In GI: PTH controls rate of calcium absorption from GI by regulating formation of vitamin D, which facilitates calcium absorption
What occurs with an accidental complete parathyroidectomy?
- Dangerous drop in blood calcium levels leading to tetanic contraction of muscles, including laryngeal and respiratory muscles resulting in death
List the endocrine cells of the pancreas. What are their secretions and the functions of those?
- These cells are found in the islets of Langerhans
1. ) Alpha cells: glucagon – increases blood glucose levels
2. ) Beta cells: insulin – decreases blood glucose levels
3. ) Delta cells: somatostatin – reduces SM contraction of digestive tract and gallbladder
4. ) G cells: gastrin – stimulates HCl synthesis by parietal cells in stomach mucosa
5. ) F cells (PP cells): pancreatic polypeptide – inhibits pancreatic exocrine secretions
Two regions of the parenchyma of the adrenal glands. What does each synthesize and secrete?
- Cortex: produces mineralcorticosteroids, glucocorticoids and weak androgens
- Medulla: produces catecholamines (Epi and NE)
Layers of the adrenal gland’s cortex. What does each synthesize?
1.) Zona glomerulosa (outer zone): mineralcorticosteroids, mainly aldosterone
2.) Zona fasciculate (intermediate zone): glucocorticoids such as cortisol and corticosterone
3.) Zona reticularis (inner zone): weak androgens such as dehydroepiandrosterone and androstenedione
Think GFR - ie. glomerular filtration rate - you are right next to the kidney
Function of aldosterone
- DCT of kidney, stimulating water balance – absorption of sodium and excretion of potassium
Function of cortisol and corticosterone
- Control of CHO, fat and protein metabolism
What is Cushing’s syndrome?
- aka hyperadrenocorticism
- small tumors of the basophils in the anterior pituitary gland – tumors produce excess ACTH, which overstimulate adrenal cortex causing excessive production of cortisol
- result: obesity in face, nack and trunk. Also impotency in males and amenorrhea in females
Describe cells of the adrenal medulla
- ) Chromaffin cells: modified postganglionic sympathetic cells that synthesize and secrete catecholamines: Epi and NE
- ) Sympathetic ganglion cells: send their axons to the cortex where they modulate cortical activity and innervate blood vessels
