2. The Endocrine System…
• This system is comprised of a variety of ductless glands.
• Some exist as discrete organs, while others are associated with
exocrine glands and/or found within complex organs.
• All endocrine glands secrete their products (hormones) into
the connective tissue surrounding the secretory elements; from
there, those products enter the blood or lymph, in which they
travel to their target organs.
• While protein and steroid hormones differ in mechanism,
the effects of both are mediated by specific receptors in their
target cells.
3. Hormones …
–
–
–
–
–
are “messenger molecules”
Circulate in the blood
Act on distant target cells
Target cells show receptors to respond to the hormones
The effects are dependent on the programmed response of
the target cells
– Hormones are just molecular triggers
• Basic categories of hormones…
– Amino acid based: modified amino acids (or amines),
peptides (short chains of amino acids), and proteins (long
chains of amino acids)
– Steroids: lipid molecules derived from cholesterol
3
6. 1.Hypophysis (Pituitary Gland)
• The hypophysis consists of glandular(Adenohypophysis) &
nervous portions(Neurohypophysis)
•
•
At low power, identify:
Adenohypophysis:
Pars anterior (pars distalis; anterior pituitary).
Pars intermedia( remnant of rathke pouch rudimentary in
human beings) .
Pars tuberalis
Neurohypophysis:
Pars nervosa ( posterior pituitary) consist of median eminence
and infundibulum.
8. Anterior Pituitary (Pars Distalis /Pars Anterior)
• Cells can be divided into two classes on the
basis of their staining characteristics:
• Chromophils ("color-loving"), and
chromophobes ("color-fearing").
• Chromophils are further classified as
acidophils and basophils.
• Each cell type produces only one type of
hormone.
• parenchyma consists of secretory epithelial
cells arranged in anastomosing cords and
clusters.
• Abundant sinusoidal capillaries with
fenestration
9. Anterior pituitory…
Chromophil:
Acidophils ;
strongly-staining, acidophilic
cytoplasm due to granules.
cells are larger,most abundant
than chromophobes.
well developed cell outline
Basophils-
Cells are variable in sixe and
shape with basophilic
cytoplasm.
secretory granules responsible
for the staining characteristics
of these cells are.
10. Anterior pituitory…
Chromophobe clear, faintly-staining, sparse
cytoplasm.
Do not have granules
Indistinct cell outline
Represent chromophil
without granules or stem
cells
Sinusoidal Capillaries in
Anterior Pituitary
Chromophil granules are
dense cored vesicles
11.
12. Pars Intermedia…
• Intermediate portion of
pituitary
• part of the adenohypophysis,
• is non-neural.
• composed of a thin layer of
epithelial cells, which enclose
colloid-filled spaces.
• Identify colloid vesicles, and
the surrounding low columnar
cells .
13. Pars Nervosa…
• is a downgrowth from the
hypothalamus
• Exhibits characteristics of nervous
tissue.
• Axon terminals within this area
originate from cells in the
hypothalamus; those in the
supraoptic nucleus produce ADH
(vasopressin), while those in the
paraventricular nuclei produce
oxytocin.
• Cell bodies of these neurons are
located in the hypothalamus,
• The pars nervosa contains no
neuronal cell bodies.
14. Pars nervosa…
• Pituicytes :
Glial cells, variable in cell size
and shape.
barely visible having orange
stained cytoplasm.
• Herring bodies:
large unmyelinated axon
terminals, containing large
numbers of neurosecretory
granules.
Rich capillary network present
in pars nervosa
16. Thyroid Gland-General Structure
•
It stores the inactive form of
hormone extracellularly in
follicles .
• General Structure. Identify …
connective tissue capsule .
connective tissue septa that
divide the bilobed gland into
lobules .
17. follicles -of various sizes,
filled with pink-stained colloid
and lined by cuboidal epithelial
cells. These are the
functional units of the thyroid
gland.
follicle size varies inversely
with secretory activity.
Interfollicular regions –
the presence of connective
tissue, sinusoidal capillaries
into which hormone is released)
parafollicular cells
18. Thyroid Follicles
• Follicular epithelium:
vary from high cuboidal to low
cuboidal ; reflects the level of
follicle secretory activity.
follicle cells (principal cells)
have large, centrally- or
basally-located nuclei,
cells active in protein secretion.
Storage and release of thyroid
hormones involves the protein
thyroglobulin .
19. Parafollicular Cells
Found scattered singly or in
small groups present in
periphery of the follicles ,
cells are responsible for
production of calcitonin, a
peptide hormone that is
synthesized and secreted
independently of thyroid
hormone.
Also called C, clear, or light
cells.
20. Parafollicular Cell…
can be distinguished from
follicular cells because
they are large oval have
eccentrically-placed
nuclei and extensive, but
lightly-stained cytoplasm.
They are placed in
periphery of follicles
22. Parathyroid Glands…
General Structure :
Thin C.T. capsule that
surrounds each gland and
gives rise to internal septa.
glands are actually embedded
in the capsule of the thyroid
gland.
23. Parathyroid Glands-Parenchyma
present as a mass of crowded
single cells, not arranged as
follicles. It consist of 2 type of
cells:
Chief cells (principal cells):
Numerous ,small cells with
prominent nuclei, and the
pale,scant cytoplasmic
staining.
24. Parathyroid Glands…
Oxyphil cells:
single or clumps of larger
cells with acidophilic
(oxyphilic), cytoplasm
with dark staining nucleus.
Number inrease with age.
Oxyphil cells are not
always present in a section
of parathyroid gland.
26. Adrenal Glands…
Like the pituitary, they are composed
of two distinctly different components,
one of mesothelial origin and one of
neural origin .
General Structure
• outer cortex , and the inner medulla .
These zones are readily observed even
in a fresh, unstained section.
• 3 histological zones of the cortex.
• tough connective tissue capsule and
radial trabeculae that extend into the
cortex.
• Prominent central vein in the medulla.
27. Adrenal Cortex…
• The cortex is divided into three layers:
– Zona glomerulosa
– Zona fasciculata
– Zona reticularis
medulla
capsule
reticularis
28. Adrenal Cortex: Zona Glomerulosa
Identify…
• outermost cortical layer , and
note the presence of columnar
epithelial cells arranged in
long cords that appear as ovoid
clumps when cut in crosssection.
• cytoplasm is pink and relatively
scant contain lipid droplets.
• capillary sinusoids are abundant.
29. Adrenal Cortex: Zona Fasciculata…
• Note that this is the broadest,
lightest-staining of the three
cortical zones, with epithelial
cells that have large,
abundant, poorly-stained
cytoplasm.
• Cells are arranged in vertical
columns of radial plates
• Identify capillary sinusoids
between cords of secretory
cells.
30. Adrenal Cortex: Zona Reticularis…
• Note that the epithelial cells of
this innermost, prominently
stained zone are arranged in
irregular, anastomosing cords
and clumps with wide capillary
sinuses intervening.
• Note that the secretory cells are
small, with relatively darkly
stained cytoplasm that may
contain yellow pigment.
31. Adrenal Medulla: Chromaffin Cells
• Derived from neural crest, cells
of the medulla are functionally
equivalent to postganglionic
sympathetic neurons.
• Chromaffin cells. The
secretory cells of the medulla
contain catecholamines
(norepinephrine and
epinephrine) in cytoplasmic
granules that are oxidized to a
brown color by potassium
bichromate (the chromaffin
reaction).
32. Adrenal Medulla: Chromaffin Cells
Note that chromaffin cell
cytoplasm is quite
basophilic, compared to
the acidophilia of the
adjacent zona reticularis.
Note that the cells are
arranged into tight
clumps, with wide
capillaries and venous
channels intervening .
33. Adrenal Medulla: Blood Supply
• The medullary capillary
network receives blood from a
capsular plexus both indirectly,
via cortical capillary sinusoids,
and directly, via small arteries
passing through the cortex from
the capsule.
• Identify the extensive network
of dilated capillaries in the
medulla.
34. Pineal Gland-General Structure
• The pineal gland is an evagination of the
diencephalon of the brain, and contains highly
modified neurons called pinealocytes.
General structure
• Under low power, identify trabeculae that
arise from pia mater. Trabeculae divide the
pineal parenchyma into indistinct lobules.
35. Pineal Gland-Parenchyma
• The parenchyma contains two cell types,
pinealocytes and neuroglia.
• The pinealocytes are modified neurons.
• You will not need to distinguish these two cell
types.
36. Pineal Gland-Pineal Sand
• Basophilic, extracellular
concretions . They are often
calcified, which makes the
pineal gland an excellent
radiological marker,
particularly of the midline.
37. Epiphysis (Pineal Gland)
• The pineal is innervated by
unmyelinated axons of
postganglionic sympathetic
neurons. This is an unusual
example of a central nervous
system structure that receives
sympathetic innervation.
• Presence of a rich vascular
supply characteristic of all
endocrine glands.
38. Endocrine Pancreas: Islets of Langerhans
• The pancreas is a mixed exocrine
and endocrine gland.
General Structure
• Note that islet cells are found as
clumps of small secretory cells
with relatively lightly-stained
cytoplasm present in connective
tissue .
• Compare their appearance to that of
the prolific protein-secreting cells
of exocrine pancreatic acini .
• Identify the rich network of
capillaries that characterize all
endocrine organs.
39. Islet of Langerhans…
• Consist of 3 types of cells
Alpha cells (30%)
Stains pinks present
more on peripheral region
Beta cells (70%)
Stains blue
More in the centre
Delta cells
Least in no.
40. Clinical Histology
1.Goiter (Multinodular)
•
common cause of overactivity
of the thyroid gland
(hyperthyroidism).
• Increased TSH production
results in the formation of
characteristic large nodules .
• Rx- surgical removal of part
of the thyroid, or by injection
of radioactive iodine
2.Graves Disease (hyperthyroid)
– Follicles are very small (little
colloid)
– Colloid appears to have open
spaces along its edge
scalloped edges (common to
hyperthyroidism
41. 3. Hashimoto's Thyroiditis:
• Autoimmune condition in
which the immune system
attacks the thyroid, causing
a reduction in the number
and size of follicles.
• Rx replacement/ admin. of
thyroid hormone.
42. 4.Adrenal Atrophy:
– Hypoplasia (decrease in cells) usually in the cortex but
also gaps in the medulla
– Proliferation of parenchymal cells
5.Adrenal Pheochromocytoma:
– Benign condition where Medulla is enlarged and
represents the majority of the adrenal gland
– Large, bizarre looking nuclei (large and dark-staining)
– Large vascular spaces
43. 5.Hyperparathyroidism (bone):
– Within the bone spicules, you can see osteoclasts
degrading the bone (more osteoclasts than usual)
– osteoclasts are multinucleate
6.Parathyroid Oxyphil Adenoma:
– Identify healthy parathyroid for its darkly staining
chief cells, pink oxyphil cells, and fat throughout
– Tumor is made entirely of oxyphil cells
– Monoclonal proliferation= tumor composed of 1 type
of cell )
44. 7.Pituitary Acidophilic Adenoma:
– Tumors tend to be in the anterior pituitary; monoclonal
proliferations of 1 of the 3 common anterior pituitary
cells
– In this case, it is an acidophilic adenoma so the
cytoplasms are predominantly pink-staining
– Acidophils make hormones that serve non-endocrine
glands (ex. Mammary gland)
8.Type II Diabetes (pancreas):
– Enlarged islets of Langerhans
– Hyaline deposits in the islets (pinker than usual)
