Histology Flashcards
Define endocrine cells
Specialized cells which secrete substances which affect other cells
What are the 5 major endocrine glands?
Pituitary, thyroid, parathyroid, adrenal, endocrine pancreas (islets)
What are the common features of endocrine tissues?
Ductless, vascular, organized into blocks/plates/cords, epithelial, polyhedral (cuboidal with prom cell borders), numerous organelles
What are the 5 characteristics of endocrine cells?
Specialized for secreting, secrete into interstitial fluid and then into bloodstream, do not require ducts, req proximity to blood vessels so they have a fine vascular network, fenestrated endothelium to allow for easy diffusion for larger mcs
What are the 4 patterns of endocrine cells
Epithelial
Mesenchymal
Neural
Individual cells
Which organs have an epithelial growth pattern?
Thyroid Parathyroid Ant pit Adrenal cortex Panc islets
What is the organization of epithelial endocrine cells?
Arranged in cords/clumps
Cells are attached to e.o
Ecto or endodermally derived (exception: adrenal cortex which is mesodermal)
What organs have a mesenchymal endocrine cells?
Leydig cells and ovarian stromal cells, granulosa and luteal cells
(connective tissue organization)
What are neural endocrine cells dervied from?
Neural crest
Where are neural endocrine cells?
Post pit
Adrenal medulla
What is the organization of the post pit
Organization of nervous system tissue
Secretory cells are supported by glial cells
–>neural endocrine cells
Describe the adrenal medulla
Sympathetic ganglion originate from neural crest and is innervated by preganglionic sympathetic axons
Lack axons, but function similar to sympathetic axons
–>neural endocrine cells
Where are individual endocrine cells?
Enteroendocrine cells of the GI tract which make a host of substances like gastrin and somatostatin
Also have neuroendocrine cells throughout the body
Juxtaglomerular cells (modified smooth muscle) of the renal cortex which make renin
Where is the pituitary located?
BAse of brain in sella tucica
What are the 2 parts of the pituitary? Where do they develop from?
Anterior: oral ectoderm
Posterior: neuroectoderm at the floor of the third ventricle
What can enlargement of the pituitary cause?
Visual disturbances due to prox to optic chiasm
Which part of the pituitary is the master gland?
Anterior: regulates most endocrine organs
What properties does the ant pituitary have?
Glandular and epithelial
What hormones does the ant pituitary secrete?
GH, prolactin, LH, FSH, TSH, ACTH
What regulates the ant pituitary?
Factors secreted by hypothalamic neurons
What is another name for the ant pituitary?
Adenohypophysis
What is another name for the post pituitary?
Neurohypophysis
What is the structure of the post pituitary?
Secretory endings of axons from nerve cells whose cell bodies are located in the hypothal
What hormones does the post pituitary secrete?
Oxytocin and ADH
What are the 3 parts of the ant pit
- Pars distalis
- Pars intermedia
- Pars tuberalis
Describe the pars distalis
Bulk of anterior pit, arises from thickened ant wall of the RP
Cystic spaces filled with eosinophilic material
Describe pars intermedia
Remnant of post wall of RP
Basophilic
Describe pars tuberalis
Arises from thickened lateral wall of RP, forms sheath around infundibulum
Contains veins from hypothalamus/thalamus
What are the parts of the post pit.?
- Pars nervosa
2. Infundibulum
Describe the pars nervosa
Contains neurosecretory axons and their endings
Biggest part of post pit
Describe infundibulum
Contains neurosec axons forming the hypothalamohypohysial tracts
What are the cell types of the pars distalis?
- Chemophils ( 2 kinds: acidophils and basophils)
2. Cromophobes
What do acidophils produce?
GH (50% of cells) and PRL
What do basophils produce?
ACTH, LH/FSH, TSH
What are the subtypes of acidophils?
Somatotropes (GH) and LActotropes (PRL)
What are the subtypes of basophils?
Corticotropes (ACTH), Gonadotropes (LH/FSH) and Thyrotropes (TSH)
What is the neurohypophysis?
Another name for posterior pituitary, includes median eminence, infundibular stalk, pars nervosa
What is the pars nervosa made of?
Unmeylinated nerve axons (cell bodies in hypothal) and supportive cells called pituicytes)
What does the pars nervosa secrete?
ADH (synth by neurons in supraoptic nuc) and oxytocin (synth in neurons in paraventricular nuc)
How do pars nervosa nerve endings differ from normal ones?
- Non-synaptic
2. Secrete hormones rather than NTs
What are the support cells of the pars nervosa?
Pituicytes (glial cells)
What does the pars nervosa do?
Serves as storage site for hormones which are stored in granules at axon terminals which are visible in light microscope as HERRING bodies
What are herring bodies?
Granules with hormones in them in the pars nervosa
What are the 4 parts of the thyroid?
Right lobe, left lobe, isthmus, pyramidal lobe
Describe the follicles of the thyroid gland
Colloid (extracellular thyroglobulin) accumulates in the follicles which are the extracellular storage of secretory products (this is unique in the thyroid). It has a large lumen surrounded by simple cuboidal epithelium
What do the follicular cells store thyroglobulin for?
Store in follicles for subsequent use in production and secretion of T3 and T4
What are parafollicular cells?
Also called C cells, produce calcitonin
What is each gland surrounded by?
Connective tissue capsule
Where do capillaries run in thyroid?
Between adjacent follicular walls (each follicle is surrounded by a capillary network)
Where are parafollicular cells? What do they look like?
Interstitium, appear as pale staining cells occurring in isolation or small clusters
Larger than follicular cells
Hard to see
What is the most common pathology thyroid is removed for?
Nodules
What is the parathyroid?
There are about 4 of them, they are small, they sit behind the thyroid, they regulate Ca metabolism. 10% are within the thymus
What is the parathyroid derived from?
Lower glands derived from 3rd branchial arch (like thymus)
Upper glands derived from 4th branchial arch
Describe the parathyroid capsule
Thin, fibrous capsule that forms septae that divides the gland into lobules. The lobules separate densely packed cords of cells.
Describe fat in parathyroid
Fat cells in thyroid increase with age eventually fat makes up 60-70% of gland.
Describe the blood supply of parathyroid
Rich vascular network with fenestrated capillaries
What are the 3 types of parenchymal cells (ie functional cells) of the parathyroid?
- Principal/chief cells that secrete PTH (most numerous, present before birth)
- Oxyphil cells (unknown fxn, larger and acidophilic)
- Adipocytes (inc with age)
Describe parathyroid chief cells
Centrally located nuc, cytoplasm has glycogen, lipid droplets, dense vesicles with PTH
Describe parathyroid oxyphil cells
No known sec role, fxn not known, larger than chief cells, eosinophilic cytoplasm with lots of mitochondria
Where are the adrenal glands and what do they look like?
AKA suprarenal glands
Flattened triangular shape
Embedded in perirenal fat at superior poles of kidney
What are the 2 parts of the adrenal gland?
Outer cortex (90%) Inner medulla: cells similar to sump neurons which secrete catecholamines
Describe the structure of adrenal gland
Cords of steroid-secreting epithelial cells, separated by parallel sinusoids
What are the 3 zones of adrenal cortex and what does each produce?
From outside in:
- Zona glomerulosa (mineralocorticoids (ie aldosterone))
- Zona fasciculata (glucocorticoids, 80%)
- Zona reticularis (gonadocorticoids, androgenic steroids)
Poorly defined zones
Describe zona glomerulosa
- 15%
- Produces aldosterone
- Closely pack clusters and columns of cells
- Darkly stained nuclei
- Adrenal cortex
Describe zona fasciculata
- 80%
- Secrete glucocorticoids
- Large, arranged in long straight cords 1-2 cells thick separated by capillaries
- Small nuclei
- Numerous lipid droplets which contain fats, FAs, cholesterol, phospholipids (ie steroid hormone precursors)
- Adrenal cortex
Describe zona reticularis
- 5-7%
- Make dehydroepi-androsterone (DHEA) and some cortisol
- Smaller than cells of fasciculata
- Few lipid droplets
- Adrenal cortex
What is the most common adrenal tumor?
Adrenocortical adenoma
What is the adrenal medulla composed of?
Chromaffin cells arranged in groups or cords clustered around capillaries and venules
Modified neurons innervated by presympathetic sympathetic nerve fibers
Considered post-synaptic neurons which lack axons due to cortisol inhibition of chromaffin axonal growth. Cortisol also induces enzymes which convert norepi to epi
How do chromaffin products enter blood?
Fenestrated capillaries, numerous secretory vesicles
What are the 2 types of chromaffin cells?
Large dense core vesicles (secrete norepi)
Small less dense core vesicles (secrete epi)
What is pheochromocytoma?
Tumor of adrenal medulla that secretes epi//norpei
What is the pancreas?
An abdominal/retroperitoneal organ with both exocrine/endocrine fxn
What is exocrine panc made of
Acini and ducts that produce enzymes used in digestion (most of pancreas)
What is endocrine panc made of
Islands of neuroendocrine cells (islets)
What is the struc of islet cells
Nets/cords or endocrine cells scattered within panc
1-2% of panc volume
Where are islet cells most numerous?
Panc tail
When do islet cells dev gestationally
9-12wks
Each islet is made up of…
Several cell types:
Major
A
B (70%)
D (somatostatin)
Minor
PP
D-1
EC
What histologic features do endocrine organs share?
Vascularity, fenestrated capillaries, nested architecture
