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
thyrotrophs
- -> thyrotropin (TSH)
- stimulates thyroid hormone synthesis, storage, and liberation
corticotrophs
- -> adrenal corticotropin (ACTH) and lipotropin (LPH)
- stimulates secretion of adrenal cortex hormones
- helps regulate lipid metabolism
neurohypophysis contains more than 100,000 unmyelinated axons of large secretory neurons with cell bodies in _____ and _____ of the hypothalamus
supraoptic and paraventricular nuclei of the hypothalamus
paraventricular nucleus produces—
oxytocin
supraoptic nucleus produces–
ADH
the neurohypophysis contains —
highly branched glial cells called pituicytes
hormones accumulate in axonal dilations called neurosecretory bodies or Herring bodies (NB)
vasopressin/antidiuretic hormone (ADH)
increases water permeability of renal collecting ducts
Oxytocin
stimulates contraction of mammary gland myoepithelial cells and uterine smooth muscle
anatomy of thyroid gland
- begins in floor of pharynx as invag at foramen cecum
- descends inferiorly to final position with larynx
- may be connected to foramen cecum by thyroglossal duct (which disappears)
- divided into 2 lateral lobes connected by isthmus
follicular cells derived from —-
endoderm
parafollicular cells derived from
ultimobranchial body (fourth-sixth pouch)
blood supply of thyroid gland
- highly vascular organ
- arterial supply arises from superior and inferior thyroid arteries
- venous drainage forms from a plexus on the surface of the thyroid gland that drains into the superior, middle, and inferior thyroid veins
thyroid gland lies where?
roughly at level between 5th cervical and 1st thoracic vertebrae
thyroid gland is coved by _____
fibrous capsule from which septa extend into the parenchyma dividing it into lobules and carrying blood vessels nerves and lymphatics
lobules consist of
colloid-filled cuboidal epithelial follicles
each follicle is filled with lightly staining colloid of a large gelatinous protein called—-
thyroglobulin
what do follicular cells do?
- synthesize and exocytose thyroglobulin into lumen as component of colloid
- concentrate iodine from blood
overactive follicles have —
reduced colloid content
underactive follicles have —
increased amount of colloid
path of synthesis of thyroid hormone
- thyroglobulin synthesized and disacharged into follicle lumen
- iodide is trapped (actively transported in)
- iodide is oxidized to iodine
- iodine is attached to tyrosine in colloid, forming DIT and MIT
- iodinated tyrosines are linked together to form T3 and T4
- thyroglobulin colloid is endocytosed and combined with lysosome
- lysosomal enzymes cleave T4 and T3 from thyroglobulin and hormones diffuse into bloodstream
parafollicular cell
C cells
individually or in groups between follicular cells or in connective tissue
-secrete Calcitonin–triggered by elevated blood Ca levels and inhibits osteoclast activity
parathyroid glands
- four small ovoid masses on back of thyroid gland
- embedded in thyroid capsule
- microvasculature of each arises from inferior thyroid arteries
how is parathyroid hormone released?
stimulated by a decrease in blood calcium levels
- PTH is synthesized by chief cells
- oxyphil cells (aged chief cells–no longer secrete PTH)
function of PTH
- osteoblasts respond to PTH by producng RANKL, which increases the number and activity of osteoclasts
- resorption of calcified bone matrix and release of Ca increase concentration of circulating Ca, which suppressed PTH production (neg feedback)
- opposite of calcitonin
- in distal convoluted tubules of renal cortex, PTH stimulates Ca reabsorption
- indirectly increases Ca absorption in small intestine by stimulating Vit D activation
pineal gland
small, pine cone-shaped organ in posterior wall of third ventricle
-regulates daily rhythms of bodily activities
melatonin release from ____ is promoted by darness and inhibited by daylight
pinealocytes
adrenal (supraarenal) glands
paired organs located near to the superior poles of the kidneys embedded in pararenal adipose tissue and fascia
blood supply of adrenal glands
- superior suprarenal arteries
- middle suprarenal arteries
- inferior suprarenal arteries
each adrenal gland is drained by _____
a single vein (suprarenal vein)
2 regions of adrenal gland and their embryologic origins:
- adrenal cortex–mesoderm
2. adrenal medulla–neural crest cells
three concentric zones of adrenal cortex
- zona glomerulosa
- zona fasciculata
- zona reticularis
zona glomerulosa
- 15% of cortex
- consists of closely packed, rounded cords of columnar cells
- produces mineralocorticoids–aldosterone (mainly)
- affect uptake of Na, K, and water
- aldosterone secretion is stimulated by angiotensin II and also by an increase in plasma K concentration, but only weakly by ACTH
zona fasciculata
- 65-80% of cortex
- long cords of large cells (filled with lipid droplets)
- secretes mainly cortisol–affect carb metabolism stimulating glycogen synthesis in liver and gluconeogenesis in many cells
- secretes weak androgen-DHEA (dehydroepiandrosterone)
how is secretion controlled in the zona fasciculata?
controlled by ACTH with negative feedback proportional to the concentration of circulating glucocorticoids
zona reticularis
- 10% of cortex
- produce cortisol but primarily secrete the weak androgens, including DHEA that is converted to testosterone in both men and women
- secretion by these cells is also stimulated by ACTH with regulatory feedback
chromaffin cells
- from adrenal medulla
- arise from neural crest cells
- considered modified sympathetic post ganglionic neurons, lacking axons and dendrites
- secrete catecholamines (80% ep and 20% norep
dopamine
catecholamine made by hypothalamuc to inhibit prolactin
-reward and pleasure
epinephrine
increases heart rate, dilates bronchioles, dilates arteries of cardiac and skeletal muscle
norepinephrine
constricts vessels of digestive system and skin
increasing blood flow to heart, muscles, and brain
norepinephrine and epinephrine are produced by?
chromaffin cells in the adrenal medulla
chromaffin cells stimulate what?
glycogen breakdown, elevating blood glucose
pancreatic islets (islets of Langerhans)
compact spherical or ovoid masses of endocrine cells embedded within the exocrine part of the pancreas
4 types of cells in pancreatic islets
- alfa or A cells
- beta or B cells
- Delta or D cells
- PP cells
A cells
secrete primarily glucagon and are usually located peripherally
- act on several tissues to make energy available through glycogenolysis (decrease glycogen) and lipolysis (decrease lipids)
- increases blood glucose content
B cells
produce insulin
most numerous
located centrally
cause entry of glucose into cells and promote decrease of blood glucose
D cells
secrete somatostatin
scattered
much less abundant
inhibits release of GH and TSH in anterior pituitary and HCl secretion by gastric parietal cells
PP cells
<1% of islet cells
secrete pancreatic polypeptide
inhibits bile secretion, pancreatic enzyme, and bicarbonate secretion, and intestinal mobility
stimulates activity of gastric chief cells
all ___ are water soluble
peptides
what is the fundamental reproductive unit in the female?
ovaries
_____ cells secrete testosterone under the influence of _____
leydig cells secrete testosterone under influence of LH
sertoli cells
- in seminiferous tubules
- secrete androgen-binding protein in response to testosterone and FSH
Heart hormones
atrial natriuretic peptide (ANP) regulates salt water balance in kidney and blood pressure
renin
stimulates formation of angiotensin in blood and tissues, which in turn stimulates the release of aldosterone from the adrenal cortex
erythropoietin
(EPO)
key role in production of red blood cells
the kidney coverts calcidiol to _____
calcitriol (vitamin D)
adipokines
hormones made by fat calls
leptin
helps regulate and alter long-term food intake and energy expenditure
