I. Pituitary Gland
Slides #113 and #131 (Human
pituitary) Slide #131 is of very poor quality and consists
entirely of pars distalis (anterior lobe) and predominantly
acidophils. In Slide #113, many of you will not have the infundibulum
and/or pars tuberalis. In the pars distalis, identify the following
cell types: chromophobes and chromophils (acidophils
and basophils). Understand the functional relationships of chromophobes
and chromophils. You should know which cell types produce which
hormones even though you can only identify them at the level
of acidophil and basophil in this tissue. Realize
that the terms acidophil and basophil describe staining features
in the pituitary. To really identify which of the anterior pituitary
cells are producing specific hormones requires the use of sophisticated
immunocytochemical techniques and/or electron microscopy.
Understand the pars nervosa
is intimately connected to hypothalamic nuclei via "secretory
axons" from the cell bodies of the hypothalamus. What two
hormones are found in the pars nervosa that are produced in the
hypothalamus? Realize that the pituicytes are neuroglia
(supportive). "Herring bodies" (eosinophilic
colloid) can be seen in this part of the hypophysis and represent
secretory material concentrated at intervals along each axon.
They are located near capillaries of the pars nervosa.
The pars intermedia may
be identified between the pars distalis
and pars nervosa. Cords of basophilic cells
are readily seen. This portion of the gland produces MSH (melanocyte
stimulating hormone) in amphibians and fish. In the human, MSH
is produced in this region and there is some evidence that ACTH,
endorphins, and lipotropin are produced here as well. Some "follicles"
similar in appearance to those of the thyroid are seen in the
pars intermedia.
II. Pineal Body
Slide #101 (Human pineal) Note the connective tissue
capsule and its septa dividing the pineal into lobules. The parenchyma
consists of pinealocytes (chief cells), which have large round
nuclei with prominent nucleoli. What do the pinealocytes produce?
The glial (satellite) cells have flattened nuclei that stain
much more deeply than those of the chief cells. Try to find large
concretions called corpora arenacea or brain sand. These consist
of various calcium compounds, increase with age, and their significance
is not known. The pineal is the mind's eye and seat of the soul
-- just in case you were curious as to its primary function.
III. Thyroid and Parathyroid Glands
Slide #112 (Human thyroid)
Note the follicles filled with colloid and the interfollicular
connective tissue. The type (i.e., squamous or cuboidal) of epithelium
varies with the amount of colloid production and storage. The
vast majority of these cells are principle cells, but there are
a few parafollicular (C) cells. These are larger, stain
less intensely than the principle cells and if present, will
be found in the follicular epithelium or in the interstitium
between follicles. What is the function of C-cells? Don't spend
a lot of time looking for these cells if not immediately apparent.
What do the principle cells of the thyroid produce? What is the
effect of these products on the physiology of the animal? What
do the parafollicular cells produce? What is its physiological
effect? What controls the output of the thyroid gland? The parathyroid
is intimately associated with the thyroid and may be included
in some sections.
Slides #130 and #142 (Monkey
parathyroid) Note the connective tissue capsule sending thin
septa into the parenchyma. The parenchyma consists of principle(chief)
cells arranged in irregular cords. Oxyphil cells occur infrequently
and singly or in small clumps. These are larger and may have
distinct cell boundaries; they have a strongly acidophilic cytoplasm
clearly seen on Slide #130. The function of Oxyphil cells is
not known. What are the physiological effects of parathyroid
hormone?
I. Adrenal Gland
Slides #104 & #132 (Human
adrenal) Identify the capsule, cortex and medulla and note
the great vascularity of this organ. Within the cortex,
find its three layers (zones): (1) zona glomerulosa,
(2) zona fasciculata, and (3) zona reticularis.
You should be aware of which layers of the cortex are responsible
for the production of specific corticosteroids.
What does the medulla produce? What control is there
on the secretion from the medulla? Review the physiological effects
of all the hormones produced by the adrenal gland.
To the average individual, skin is taken for granted as an
organ that merely keeps our insides on the inside and one which
requires a great deal of attention for aesthetic reasons. Functions
of the skin seem minuscule when compared to the more intricate
and essential maneuvers of the heart, lungs, kidneys, etc. One
needs only observe a seriously burned patient to appreciate how
incorrect the above statement is. An intact, functioning integument
is vitally important to the livelihood of the individual. Skin
is the largest organ in the body (16% of total body weight).
Try to correlate functional activities of integument while learning
its normal architecture.
Slides #123 & #177 are sections of thick skin from
the palm or sole. When looking with low power, you see two different
layers: epidermis and dermis. The epidermis is the epithelial
layer (which type?) and the dermis is the connective tissue support
layer. At higher mag you should be able to identify the various
layers of epidermis (from basal to apical surface).
(1) stratum basale (germinativum) - darkly stained
packed cuboidal to low columnar cells, which lie right on the
basement membrane.
(2) stratum spinosum - polyhedral cells above stratum
basale. Why is this layer call "spinosum"?
(3) stratum granulosum - thinner layer with more spindle-shaped
cells that contain keratohyalin granules. This layer may be difficult
to visualize in some of your sections. It shows up well on slide
#177.
(4) stratum lucidum - thin band of lighter staining
eosinophilic, or sometimes clear region of the stratum corneum
next to the granulosum, not always evident in all sections of
thick skin. Nuclei cease to exist in this layer.
(5) stratum corneum - extremely variable in size in
different areas of the body. It consists of dead, scale-like
keratinized cells. The layer above stratum corneum that is about
to be sloughed off is sometimes referred to as the stratum disjunctum.
The Dermis consists of
irregular connective tissue with several components. Two layers
exist but usually blend together sometimes making distinction
between the two difficult.
Papillary layer - thin clear layer of loose CT just
beneath epidermis. Its name derives from the fact that it extends
into the dermal papillae which extend into the epidermis.
Reticular layer - thicker, deeper layer of dense irregular
C.T.
What other connective tissue components can you identify in
this slide? Nerves? Remember those? Blood vessels, glands? You've
now seen the basic components of integument. Here comes the curve
. . there are many variations and additions not evident in this
slide (of course). For example:
Pacinian Corpuscles look like a slice through an onion
in histological sections. The layers of he corpuscle are connective
tissue and a neuronal process is located in the center. Because
they are located deep in the dermis or hypodermis they have been
thought to sense deep pressure. Recently some neurophysiological
experiments have shownArrector that Pacinian Corpuscles will
fire in synch. with vibrations over a wide range of frequencies.
Slides #92, #93 and #123 Look for Meissner's corpuscles
in the dermal papillae. Also look for Pacinian Corpuscles (previous
section) found deep in the dermis or in the hypodermis.
Meissner's Corpuscles are touch receptors located in
dermal papillae of the skin. They look like an elongated ball
of yarn. In the center of this structure is an axon (actually
a dendrite) of a sensory neurone. Where would you expect to find
the cell body of this sensory process?
Slide #177 In the epidermis, in addition to keratinocytes,
one may find melanocytes and Langerhans cells. Some features
that may help you identify them include: melanocytes usually
have round, oval, or otherwise very simple nuclei, whereas the
Langerhans cells usually have complex, lobed, dense staining
nuclei. Also, whereas melanocytes are usually (not always) found
in the stratum basale, Langerhans cells are more commonly (but
not always) found in the stratum spinosum.
Slide #177 Thin section of thick skin
Eccrine sweat glands are widely distributed throughout
the body of primates and are most numerous on the palms of the
hands and soles of the feet. They are located deep in the dermis,
are smaller, and more densely stained than sebaceous glands.
In the skin thin section, find myoepithelial cells associated
with secretory units. What is the function of these contractile
cells? The duct of eccrine glands is coiled, passing to the surface
through the dermis and all layers of the epidermis.
Slide #83 (Anal Canal) - there
shouldn't be much stratum corneum in this section. Where else
would you expect the epidermis to be thinner? Try to find other
examples of thin skin in your slide box (e.g. external ear).
Apocrine sweat glands (Slides 53 & 83, if you're lucky)
are much less abundant than the eccrine variety. They are most
numerous in the axillary and perianal regions of the body. See
Fig.21.21 (p.396) in Wheater. (If you don't get a demo, ask for
one.)
And another thing: both eccrine and apocrine sweat glands
are eccrine and merocrine, however, neither eccrine nor apocrine
sweat glands are apocrine. How do you explain that?
High magnification of apocrine sweat gland seen at
low mag in the above image of the perianal region of the human.
Apocrine is a type of secretion in which the top portion of the
cells are soughed off during secretion. These sweat glands were
misnamed apocrine when first discovered. We now know that their
mode of secretion is actually merocrine but the name apocrine
has stuck.
Hair and Glands
Slide #61 (Scalp) - demonstrates
hair shafts and follicles.
Sebaceous glands are associated with hair shafts and
are easy to identify by their large, foamy, pale staining cells.
In some cases you see the duct of the gland joining the hair
follicle. These are Holocrine glands. Can you identify
any Arrector pili muscles (smooth muscle) associated with
hair shafts? These muscles are responsible for "Goose pimples"
and also function in cases of "hair raising experiences"
like histology examinations. Sweat glands are classified
as either eccrine glands or apocrine glands. The
eccrine glands are the most common and are classified structurally
as simple coiled tubular glands. Eccrine sweat glands
are widely distributed throughout the body of primates and are
most numerous on the palms of the hands and soles of the feet.
They are located deep in the dermis, are smaller, and more densely
stained than sebaceous glands. In the skin thin section, find
myoepithelial cells associated with secretory units. What is
the function of these contractile cells? The duct of eccrine
glands is coiled, passing to the surface through the dermis and
all layers of the epidermis. See first image in this system (above).
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