anatomy and histology of endocrine glands Flashcards
general characteristics of epithelial tissue
- cell-cell adhesion
- cells form sheets/layers
- anchored to an extracellular matrix
- **avascular (but innervated)
- form glands
- barrier function
- cells are polarized
- high mitotic index/constant renewal
framework of a gland
connective tissue basement membrane of type IV/VII collagen epithelial secretory cells blood vessels connective tissue fibers (septa) formed in lobules
endocrine glands secrete into
bloodstream
exocrine glands secrete into
extracellular space (duct)
secretory cells of endocrine glands
- release products (hormones) into neighboring vascularized tissue
- no secretory duct
- typically epithelial, aggregates as cords or clusters
amino acid based hormones
- molecular size varies
- amines, peptides, proteinrs
- water soluble and cannot cross plasma membrane
- act on receptors in plasma membrane
steroid hormones
- synthesized from cholesterol
- lipid soluble and can cross plasma membrane
- act on receptors inside the cells
eicosanoids
leukotrienes and prostaglandins
lipid soluble hormones
- all steroid hormones and thyroid hormones
- made in adrenal cortex, gonads, & thyroid
- no secretory vesicle storage
- bound to plasma proteins
- long half life in blood–metabolized in liver
- receptors inside cell
- activate genes, causing synthesis of new proteins
water-soluble hormones
- all amino acid-based hormones except thyroid hormone
- made by all other endocrine glands
- stored in secretory vesicles
- usually free in plasma
- short half life (removed by kidneys)
- receptors on plasma membrane
- act through second-messenger systems
three types of stimuli that trigger hormone release
- humoral
- neural
- horomonal
humoral stimulus
- hormone release caused by altered levels of certain critical ions or nutrients
- stimulus: low concentration of Ca in capillary blood
- response: parathyroid glands secrete parathyroid hormone (PTH), which increases blood Ca
neural stimulus
- hormone release caused by neural input
- stimulus: action potentials in preganglionic sympathetic fibers to adrenal medulla
- response: adrenal medulla cells secrete epinephrine and norepinephrine
hormonal stimulus
- hormone release caused by another hormone (a tropic hormone)
- stimulus: hormones from hypothalamus
- response: anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones
- clear negative feedback loop
hypothalamus
- structure of diencephalon of brain located anterior and inferior to the thalamus
- manages pituitary
thyrotopin-releasing hormone (TRH)
stimulates release of thyrotropin (TSH)
gonadotropin-releasing hormone (GnRH)
stimulates the release of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
somatostatin
inhibits release of both somatotropin (GH) and TSH
growth hormone-releasing hormone (GHRH)
stimulates release of GH
dopamine
inhibits release of prolactin (PRL)
corticotropin-releasing hormone (CRH)
stimulates synthesis of pro-opiomelanocortin and release of both beta lipotropic hormone and corticotropin
anatomy of pituitary gland (hypophysis)
- master endocrine gland
- size of pea
- lies in depression of sphenoid bone (sella turcica)
- sphenoid air sinus lies inferiorly to gland
- superiorly covered by dura mater
- surrounded by thin connective tissue capsule
blood supply of pituitary gland
- two paired hypophyseal arteries–branches of internal carotid–have profuse anastomoses on the gland’s surface
- vessels give rise to network of portal venules–the hypophyseal portal system
development of pituitary gland
- during 3rd week, a hypophyseal pouch (rathke pouch) grows from oral ectoderm–> anterior pituitary
- the neurohypophysis forms from diencephalon –> posterior pituitary
2 main divisions of pituitary gland
- adenohypophysis
- neurohypophysis
adenohypophysis
- anterior pituitary
- pars distalis (anterior lobe of pituitary)
- pars tuberalis (surrounds infundibulum)
- pars intermedia (intermediate lobe)
- made of glandular epithelium
neurohypophysis (posterior pituitary)
- made of neural tissue–extension of hypothalamus
- pars nervosa (posteior lobe–main part)
- infundibular stalk (infundibulum)
- median eminence (attaches gland to hypothalamus)
cells in anterior lobe of pituitary and what they release
- somatotrophs –> GH
- lactotrophs–> prolactin
- corticotrophs–> ACTH and LPH
- thyrotrophs–> TSH
- gonadotrophs–> Lh and FSH
the pars distalis accounts for ____ % of the adenohypophysis
75%
main components of anterior lobe are cords or clumps of well-stained endocrine cells interposed with _____
fenestrated capillaries
acidophils
somatotrophs (GH)
lactotrophs (prolactin)
basophils
corticotrophs (ACTH)
thyrotrophs (TSH)
gonadotrophs (FSH, LH)
pars tuberalis
small funnel-shaped region surrounding the infundibulum of the neurohypophysis
-most of the cells are gonadotrophs (LH and FSH)
pars intermedia
- narrow zone lying between the pars distalis and pars nervosa
- contains basophils (corticotrophs) and chromophobes
- endorphins and melanocyte-stimulating hormone (MSH)
somatotrophs/acidophils
- -> somatotropin (growth hormone)
- stimulates growith in epiphyseal plates of long bones via insulin-like growth factors produced in liver
lactotrophs
- -> prolactin
- promotes milk secretion
gonadotrophs/basophils
- -> follicle stimulating hormone (FSH) and luteinizing hormone (LH)
- FSH promotes ovarian follicle development and estrogen and spermatogenesis
- LH promotes ovarian follicle maturation and progesterone secretion and interstitial cell androgen secretion in men