Endocrine Histology

Question 1

Embryonic origin and parts of anterior pituitary

Answer 1

• outgrowth of endoderm called “Rathke’s pouch”

- made up of pars distalis, pars intermedia, pars tuberalis

Question 2

Posterior pituitary is an extension of

Answer 2

the brain (hypothalamus)

• infundibular stem/stalk
• median eminence

Post pit is called “pars nervosa”

Question 3

Pars distalis: makes/secretes/cell types

Answer 3

• Part of AP
• made of cells that synthesize and release GH, PRL, ACTH, TSH, and FSH and LH

cell types:
somatotrophs (GH): 50% of secretory cells
lactotrophs (PRL)
Gonadotrophs (FSH, LH)
Corticotrophs (ACTH)
Thyrotrophs (TSH)

three cell classes:
acidophils (GH, PRL)
basophils (TSH, ACTH, LH or FSH containing)
chromophobes (lacking granules)

Question 4

Pars tuberalis

Answer 4

• collar of cells around the infundibular stalk contains blood vessels that lead from capillaries of the median hypothalamic eminence to small vessels/capillaries of the pars distalis
• blood entering median eminence comes from superior hypophyseal arteries
• This is how hypothalamus delivers regulatory factors to AP (TSHRH, GnRH, CRH, GHRH, and inhibitory somatostatin and dopamine)

Question 5

Pars intermedia

Answer 5

• poorly devel in humans
• consists of colloidal cysts
• hormones: ADH (ie vasopressin) and oxytocin
• released from ends of axons that have cell bodies in hypothalamus

Question 6

Thyroid gland

Answer 6

multi-lobed
series of follicles w/ single layer of epithelial cells surrounding central chamber called the colloid
-scattered cells b/t follicles produce calcitonin
-blood supply: superior and inferior thyroid artery
-iodide converted to iodine
-thyroid hormones and thyroglobulin released into blood

Question 7

Parathyroid glands

Answer 7

• closely associated with the thyroid gland; 4-8 may be present in any individual
  1. Chief cells (produce PTH; increases osteoclasts release of calcium from bone, and increases clacium uptake in GI tract and by kidney)
  2. oxyphil cells (contain many mitochondria)
  3. Adipose cells

Question 8

Adrenal gland

Answer 8

• houses two distinct organs: cortex and medulla
• cortex: produce/release various steroids
• medulla: aa derived hormones like epi, norepi, enkephalins
• blood delivered via sup, mid, inferior suprarenal a. (via cortical arteries)

Question 9

Adrenal Cortex

Answer 9

3 layers (out to in)

1. zona glomerulosa (mineralocorticoids, notably aldosterone)
2. zona fasciculata: glucocorticoids such as cortisol
3. zona reticularis: androgens

Fasciculata and reticularis are controlled by ACTH.
Glomerulosa regulated thru angiotensin system

Question 10

Adrenal medulla

Answer 10

• contains epi, norepi producing cells
• symp/parasymp control
• clusters around venous channels that drain toward central medullary vein
• enkephalins and chromagranins also released by theses cells

Question 11

Development of pituitary gland

Answer 11

• neural ectoderm gives rise to tissues as far back as the pharynx
• 4 weeks: an evagination of the lower part of the neural ectoderm of primitive diencephalon forms the beginnings of the posterior pit and central portion of infundibular stalk
• Oral ectoderm from upper part of mouth evaginates (Rathke’s pouch) and comes in contact with the neural ectoderm
• third month, pituitary takes on typical shape
• pars distalis, intermedia and tuberalis are derived from Rathke’s pouch
• posterior (pars nervosa and infundibular stalk) are derived from neural ectoderm
• CT develops around pit (sella turcica)
• mesoderm infiltrates gland for vasculature of the hypophyseal portal system

Question 12

Development of thyroid/parathyroid glands

Answer 12

• thyroid contains cellular components that derive from the endoderm (thyroid follicle epithelial cells), neural crest (originally ectodermal, calcitonin secreting cells), and mesoderm (vasculature), but originate from different locations along the developing pharynx
• develops as a set of 4 bilateral lobed pouches
• thyroid begins as medial evagination of endoderm called thyroid diverticulum (extends b/t 1st and 2nd pharyngeal pouches)
• parts of parathyroid develop from clefts b/t 3rd and 4th pouches (inf parathyroids) and after 4th pouch (superior parathyroids)
• ultimobranchial body develops after 4th pouch: gets populated by neural crest cells, give rise to calcitonin-secreting or parafollicular cells of the thyroid
• thyroid diverticulum enlarges, descends along pharynx, developing thyroid attached via thyroglossal duct
• mesoderm eventually infiltrates and gives rise to vasculature

Question 13

Development of adrenal glands

Answer 13

• cortex originates from mesoderm
• medulla is from ectoderm
• 4 weeks (under induction by mesonephric duct) cells in cleft proliferate and migrate into the mesenchyme just dorsal to it.
• b/t 2-3 mo, another wave of cells from coelomic epithelium enter the mesenchum and surround the outer part
• First early set of cells will become cells of reticularis of cortex, second group into fasciculata and glomerulosa
• For medulla: neural crest cells (ectoderm) migrate to a region that will become the sympathetic ganglia.
• cells are called sympathogonia early on, and some migrate into center of cup that will become medullary region of adrenal (stain yellow, called “chromaffin cells”), progenitors of norepi/epi producing cells