Histology - Endocrine System Flashcards
Egs of peptide hormones
Glycoproteins -> TSH, LH, FSH
Short polypeptides -> ADH, Oxytocin, Prolactin, GH
Egs of amino acid derived hormones
Tyrosine -> thyroid hormone, catecholamines (E,NE,dopamine)
Tryptophan -> melatonin
Egs of lipid derived hormones
Steroid -> androgens, estrogens, progestins, calcitriol, corticosteroids
Eicosanoids ->. Leukotrienes, prostaglandins
Routes of communication in endocrine system
Endocrine
Paracrine
Autocrine
Synaptic
Features of endocrine system
One gland many hormones
One hormone many glands
One hormone, many targets, many effects
One hormone different messenger type
How are islet cell types identified
Cell distribution
Immunohistochemistry/ flourescence
EM
Two vascular systems in the pancreas
Insuloacinar portal system
Acinar vascular system
How are islet cells regulated
- Neural - arteriole wall inner action regulates blood flow
- Paracrine secretions - alpha cells regulate insulin release. Somatostatin inhibits insulin and glucagon release.
- Autocrine - neoropeptide release that acts on same cell to release hormone (eg alpha cells release glutamate to stimulate glucagon release)
Alpha cells release
Glucagon
Beta cells release
Insulin
Delta cells release
Somatostatin and gastrin
F-cells release
Pancreatic polypeptide
When are D cells stimulated
After protein rich meal
What hypothalamic nuclei releases ADH
Supra optic nucleus
What hypothalamic nuclei release OXY
Para ventricular nucleus
How is the pituitary formed
Down growth of floor of diencephalon joins to Rathke’s pouch (up growth of ectodermal lining of future oral cavity)
What separates the two lobes of the pituitary
Pars intermedia
What are the separate parts of the pituitary
Infundibular stem Pars tuberalis Pars distalis (anterior) Pars intermedia (Rathke's cyst) Pars nervosa (posterior)
Blood supply to pituitary
Superior hypophyseal artery -> 1ry cap plexus -> portal veins -> 2ndry cap plexus -> hypophyseal veins
Note inferior hypophyseal artery supplies pars nervosa
Function of hypothalamo-hypophyseal portal system
- Hormones from 1ry cap plexus can act on anterior hypophysis
- Secretions from ant hypophysis can enter general circulation
- Allows for functional integration of hypothalamus with anterior hypophysis
Three components of anterior pituitary
Cords of epithelial cells (chromophils and chromophobes)
Delicate connective tissue stroma
Fenestrated caps
What are the acidophilic cells in the ant pit lobe and what do they release
Somatotrophs (GH - somatotropin)
Lactotrophs (Prolactin)
Somatotrophs inhibited by … and stimulated by …
Somatostatin. Increased blood glucose.
GHRH. Decreased IGF-1.
Function of GH
Stimulate secretion of IGF-1 by liver
Lactotrophs inhibited by … and stimulated by …
Dopamine
Prolactin releasing hormone (PRH) thyrotropin releasing hormone (TRH)
What are the basophilic cells in the ant pit lobe and what do they release
Gonadotrophs - FSH, LH
Thyrotrophs - TSH
Corticotrophs - ACTH
What is the role of pituicytes in the release of hormones
They have retracting cell processes that allow passage of hormones into pericapillary space
Absence of thyroid leads to what childhood feature
Cretinism
Morphology of hypothyroid gland
Large colloid filled follicles
Flattened principle cells
Sparse resorption vacuoles
Morphology of hyperthyroid
Numerous small irregular shaped follicles
Columnar principle cells
Many resorption vacuoles
Function of C cells in thyroid
Release calcitonin to suppress Ca resorption from bone.
Describe exocrine phase of thyroid hormone synthesis
Iodide diffuses across cell and is converted to iodine by thyroid peroxidase.
Thyroglobulin is released into colloid and its tyrosyl residues are linked to two iodine molecules each = iodothyroglobulin
Describe the endocrine phase of thyroid hormone synthesis
Iodothyroglobulin colloid droplet is endocytosed and fused with a lysosome. Proteolytic action of lysosomal enzymes release T3 and T4 which diffuse into the blood stream
What will removal of the parathyroid glands cause
Tetany
Thoracic and laryngeal muscle spasm = death
What does PTH do
Resort Ca from bone
Stimulate kidney resorption of Ca
Activate Vit D
Functional cells of the parathyroid gland
Chief cells
Oxyphil cells
What can be seen on EM of a steroid cell
Lipid droplets
Mitochondria ++
Abundant sER
General steroid synthesis path way
Cholesterol -> via StAR -> mitochondria -> sER -> mitochondria (not DHEA, androstenedione) -> extracellular
Blood supply to adrenal gland
Capsular artery
1. Medullary arteriole
2. Cap bed in each zone
Therefore dual blood supply
Mechanism of hot flashes
High GnRH, FSF, LH
Low estrogen
What happens following estrogen withdrawal
Vasomotor disturbances Atrophy vaginal epithelium Decreased vaginal secretions Decreased circulation to vagina/ uterus Loss of vaginal tone (pelvic relaxation) Cardiovascular risk increased
Why does increased fat help in menopause
Androstenedione and DHEA can be converted to estrone by adipose tissue
