Endocrine Histology

Question 1

what are the 2 embryological origins of the pituitary gland (hypophysis)?

Answer 1

adenohypophysis: derived from oral ectoderm, becomes anterior (pars distalis), intermediate (pars intermedia), and tuberal pituitary regions

neurohypophysis (pars nervosa): derived from neural ectoderm, becomes posterior pituitary

Question 2

fill in the blanks regarding the neurovascular link between the hypothalamus and pituitary gland:
_______ of blood vessels at the base of the hypothalamus (called the ________) allow secretory products to reach portal veins

blood then reaches the ________ in the anterior pituitary, which bathes the cells of the _______

Answer 2

primary plexus of blood vessels at the base of the hypothalamus (called the median eminence) allow secretory products to reach portal veins

blood then reaches the secondary plexus in the anterior pituitary, which bathes the cells of the adenohypophysis

Question 3

which (multiple) of the following adenohypophysial cells are basophilic (bind basophilic dyes)?
a. FSH
b. LH
c. TSH
d. MSH
e. ACTH
f. GH
g. PRL

Answer 3

glycoprotein hormones containing sialic acid are basophilic, including:
FSH, LH, and POMC-derived peptides (MSH, ACTH)

acidophilic: GH, PRL

Question 4

what are the hormones of the anterior (pars distalis) and intermediate (pars intermedia) lobes of the pituitary gland?

Answer 4

FLAT PEG + M:
FSH
LH
ACTH (from POMC)
TSH

PRL
endorphins
GH

MSH (from POMC)

Question 5

what are the 3 major cell types of the posterior pituitary (neurohypophysis)?

Answer 5

1. axonal process of unmyelinated nerves: cell bodies located in paraventricular nuclei (oxytocin) and supraoptic nuclei (vasopressin/ADH) of hypothalamus
2. pituicytes: glial-like support cells
3. endothelial cells: comprise fenestrated blood vessels

Question 6

from where do the axonal processes within the posterior pituitary (neurohypophysis) come from? how do they reach the posterior pituitary?

Answer 6

cell bodies of axons located in either paraventricular (oxytocin cells) or supraoptic (vasopressin cells) nuclei of hypothalamus

axonal fibers converge at median eminence to form hypothalamo-hypophyseal tract that enters posterior lobe of pituitary

Question 7

which 2 hormones are secreted from the posterior pituitary and from where are the cell bodies that produces these hormones?

Answer 7

1. paraventricular cells of hypothalamus produce oxytocin
2. supraoptic cells of hypothalamus produce vasopressin/ADH

Question 8

the storage granules found in the terminal portions of the axonal processes within the posterior pituitary are referred to as…

Answer 8

Herring bodies - can be visualized with a specific stain, contain hormones

Question 9

as precursor molecules, oxytocin (paraventricular nuclei) and vasopressin (supraoptic nuclei) are bound to _____

Answer 9

neurophysins I and II

hormones are cleaved free as they near the end of the axon, before release from Herring body granules

Question 10

what are the embryological origins of the thyroid gland?

Answer 10

thyroid gland derived from endoderm, begins as evagination from the floor of the mouth

also contains tubules derived from the fifth pharyngeal pouch - contain neural crest derived parafollicular/clear/C cells

Question 11

what is the function of the parafollicular or clear cells of the thyroid gland?

Answer 11

secrete calcitonin - “tones” down Ca2+ levels in the blood, opposes action of PTH

Question 12

describe the micro-anatomy of the thyroid gland

Answer 12

simple cuboidal epithelium surrounding ETC accumulation of colloid which is secreted by follicular cells and contains thryoglobulin (TG), the precursor to thyroid hormone

Question 13

______ is a glycoprotein composed of 2 subunits, which constitutes the major component of ______ that fills the thyroid follicles

Answer 13

THYROGLOBULIN is a glycoprotein composed of 2 subunits, which constitutes the major component of COLLOID that fills the thyroid follicles

Question 14

which form of thyroid hormone is most biologically active?

Answer 14

T3 (thyroxine) is most biologically active - binds TH receptor with high affinity

T4 (triiodothyronine) is secreted in greater amounts by the thyroid follicular cells, but it is usually metabolized to T3 in peripheral tissues

Question 15

T3 and T4 secretion are controlled by negative feedback, such that they inhibit secretion of ____ from the hypothalamus and ____ from the anterior pituitary

Answer 15

T3 and T4 secretion are controlled by negative feedback, such that they inhibit secretion of TRH from the hypothalamus and TSH from the anterior pituitary

Question 16

what is the effect of congenital hypothyroid (previously termed cretins)?

Answer 16

low/absent thyroid hormone or iodination of thyroid hormone —> short stature, cognitive deficits

this is because thyroid hormone is necessary for proper growth

Question 17

how does a congenital deficiency in thyroid hormone vs growth hormone present?

Answer 17

lack of TH (or iodination) —> short stature, cognitive defects

lack of GH —> dwarfism (defective long bone growth)

Question 18

how does low dietary intake of iodine cause goiter?

Answer 18

goiter: thyroid gland hypertrophy

lack of iodine induces TSH stimulation of thyroid follicle proliferation —> increase in gland size

Question 19

Graves’ disease

Answer 19

hyperthyroid condition in which antibodies constitutively activate the thyroid receptor

accompanied by thryotoxicosis and exopthalmia (bulging eyes)

Question 20

Hashimoto’s disease

Answer 20

autoimmune disease against thryoglobulin (thyroid hormone precursor) or other thyroid components —> resulting hypothyroidism

Question 21

which 2 cell types are found in the parathyroid glands?

Answer 21

1. principal/ chief cells: most abundant, pale-staining, produce/secrete PTH (stored in granules)
2. oxyphilic cells: stain intensely acidophilic, lack granules, function unknown

Question 22

which cells make up the adrenal medulla, from what embryonic tissue are they derived, and what hormones do they secrete?

Answer 22

chromaffin cells (derived from neural crest cells), secrete epinephrine and norepinephrine

cells secreting NE are very granular, cells secreting Epi are more homogenous and stain less densely

Question 23

explain how the adrenal medulla has a dual blood supply

Answer 23

1. superior, middle, and inferior suprarenal arteries form a plexus that distributes blood to the outermost zona glomerulosa via fenestrated capillaries, and blood travels inward to medulla via sinusoids
2. medullary arterioles (direct supply)

Question 24

a single central vein drains the entire adrenal gland, draining into the ______ vein on the left and the _____ on the right

Answer 24

a single central vein drains the entire adrenal gland, draining into the RENAL vein on the left and the VENA CAVA on the right

Question 25

contrast the functions of the zona glomerulosa, zona fasciculata, and zona reticularis

Answer 25

zona glomerulosa: secretes mineralocorticoids (primarily aldosterone)

zona fasciculata: secretes glucocorticoids (primarily cortisol)

zona reticularis: secretes gonadocorticoids or sex steroid (androgens)

Question 26

in the adrenal cortex,
_____ secretes aldosterone
_____ secretes cortisol
_____ secretes androgens

Answer 26

zona glomerulosa: secretes mineralocorticoids (primarily aldosterone)

zona fasciculata: secretes glucocorticoids (primarily cortisol)

zona reticularis: secretes gonadocorticoids or sex steroid (androgens)

Question 27

contrast the histological appearance of the zona glomerulosa, fasciculata, and reticulata

Answer 27

zona glomerulosa - round cells in clusters separated by connective tissue and lipid droplets, dark staining/ acidophilic nuclei

zona fasciculata - arranged in cords one layer thick, separated by connective tissue and capillaries, vacuolated cytoplasms due to high lipid content (“spongiocytes”)

zona reticulata - small cells in irregular network, surrounded by blood vessels and connective tissue