organ1.pdf
PCB 4023 – Cell Biology
Lab 6: Organology I – Integument and its derivatives
Name: ____________________
SSN: _______________
Name: ____________________
SSN: _______________
N.B.
Since this document is in “pdf” format, the URLs (web addresses) cannot be linked. To use
them, simply highlight and copy the address and paste it into the address box of your browser.
------------------------------------------------------------------------------------------------------------------
Preparation assignment (to be completed before lab:
1)
2)
Kerr (1999) Chapter 8. Skin (pp. 145-161)
Kerr (1999) Chapter 12: Oral and Salivary Tissues (pp. 219-234)
Web resources:
N.B.
Again, you may wish to examine the “Integument and Breast” and “Oral Cavity and Esophagus”
modules at the University of Florida College of Medicine histology tutorial; there is an on-line quiz
available for the latter. As before, these modules may contain information that is not covered in
this course and you will not be held responsible for any information presented there. However,
you may wish to consider using them as additional preparation and/or review. The URL is as
follows:
http://www.medinfo.ufl.edu/year1/histo/index.html
Know of any other web sites pertaining to the integument and its derivatives that you have found
helpful or interesting? E-mail me the link at [email protected]. and let me know what and why you
found it informative and/or interesting.
------------------------------------------------------------------------------------------------------------------
I.
INTRODUCTION
Now that we have completed our study of the four major tissue types (epithelia, connective
tissue, muscle and nervous tissue), we will turn our attention to organs and organ systems.
You’ll recall from cell theory [M. Schleiden (1838) and T. Schwann (1839)] that all organisms
consist of cells and their products, and that cells form the fundamental units of life (i.e., the smallest
structural units capable of performing all living functions.) Cells form the basis of anatomical
organization, of which four hierarchical, interdependent levels can be recognized:
1)
cell - the fundamental unit of the organism; i.e., the smallest unit capable of performing all
functions vital to its survival; e.g., goblet cell - glandular epithelial cell of digestive and
respiratory tracts; there are 300 defined types in humans alone.
2)
tissue - a collection of cells and cell products that perform the same general function; e.g.,
mucosa (mucus membrane) of gut tract comprised of a mucous epithelium and its
underlying loose connective tissue (lamina propria).
3)
organ - a group of tissues that collectively perform a common function; e.g., the small
intestine consists of 4 tissue layers: mucosa, submucosa, muscularis externa, serosa.
4)
organ system - a series of organs which are functionally interrelated; the e.g., digestive
system = oral cavity, pharynx, esophagus, stomach, small and large intestines, rectum
and anus.
1
organ1.pdf
Time does not permit an examination of all the organ systems found in craniates nor is it
necessary. Once identification of the basic tissues has been accomplished, one can identify organs by
learning and recognizing their unique combination and arragnment of specific tissues and/or cells. Thus,
we’ll limit our examination of organology to a couple of examples to illustrate this principle. This week
we’ll examine the integument (skin) and, in deference to the dentist wannabe’s in the class, the oral
cavity. [Physician wannabe’s will be attended to next week.]
I.
Integument
Skin or integument (L., integumentum = covering) forms the boundary layer separating the
organism from the outside world. It is a complex organ comprised of a tremendous variety of tissues and
cells: lining epithelium, glandular epithelium, several types of connective tissue, smooth muscle, blood
vessels, sensory receptors and more. It is typically among the largest organs in most craniates (e.g.,
approximately 15% of body weight in humans; up to 40% or more in cetaceans) and serves an almost
innumerable number of functions. The following is an incomplete list:
1)
protection from external environment: abrasions, UV light, etc.
2)
passive immunological barrier to pathogens
3)
participates in water, ion and gas exchange
3)
sensory reception (typically mechanoreceptors and thermoreceptors)
4)
glandular secretions: protection (e.g., mucus,) defense (e.g., toxins), signaling (e.g.,
pheromones) , nutritive (e.g., mammary), cooling (sweat)
5)
vitamin D synthesis - vitamin D functions in depositing salts into bone; deficiency (rickets)
produces misshapen bones
6)
coloration in defense and communication and protection
7)
thermoregulation
figure: 3K6-1b
While skin varies considerably between
species and even between parts of the body, the
basic structure and development remains much the
same. Fundamentally, skin consists of two tissue
layers: An epidermis and dermis.
The epidermis is a superficial layer of
epithelia derived from the ectoderm. Like all
epithelia it rests upon a basement membrane. It is
stratified (i.e., consists of multiple layers) with the basal layer being the proliferative zone and the
superficial layers providing the function. It is largely avascular.
The dermis is an inner connective tissue layer derived from the mesoderm (predominantly the
dermatomes). It is composed of dense collagen (regular or irregular, varying within and between
species) and associated fibroblasts but also contains chromatophores (of neural crest origin, ask Dr. Kos;
but see below), sensory nerve cell endings, smooth muscle, vasculature, and varying degrees of
adiopocytes.
[N.B. In mammals and birds the chromatophores are located in the basal layer of the epithelium
rather than the dermis. Strange but true!]
Below the dermis is the hypodermis, a transitional layer of loose connective tissue and fat
between the dermis and the underlying muscle or skeleton. It is not considered part of the skin proper
and in gross anatomy is termed the superficial fascia.
figure: 3K6-3
2
organ1.pdf
As shown in this modification of Kresja’s famous illustration, interactions between the dermis and
epidermis give rise to a tremendous diversity of integumental structures. Teeth, bony scales, horny
(epidermal) scales, feathers, hair , and glands (e.g., sebaceous, sweat, mammary, etc.) all arise through
mesenchymal-epithelial interactions. This figure is incomplete as it does not include baleen, unguals
(claws, nails and hooves), horn, beaks and more.
figure: 3K-6-2Your text (Kerr, 1999) provides an excellent
description of the structure of human skin as an [atypical]
example of mammalian integument and only some of the
more unusual features are discussed here. This figure is
provided as a pictorial summary.
In mammals the epidermis is thick (five defined
layers or strata) with a multi-layered stratum corneum
whose enucleated cells are continuously exfoliated (i.e.,
there is no organized ecydysis). The chromatophores
(only melanocytes) are located within the basal layer of
the epithelium. Epidermal derivatives include teeth,
glands, hair, horns and unguals.
The dermis is typically thick (thus a good source of leather) and double layered with a (1)
superficial papillary layer consisting of finger-like projections into the epidermis (dermal papillae), and (2)
3
organ1.pdf
an inner reticular layer . The former is loose connective tissue and the latter is irregular dense connective
tissue (except in aquatic mammals where the collagen is regularly arranged into plies). The dermis of
mammals is extensively vascularized for thermoregulation. Hair follicles and glands (sebaceous and
sweat) project into the dermis. Associated with the hairs are smooth muscle arrector pilli. The dermis
provides the membranous precursor for the membrane (dermal) bones of the skull (dermatocranium) and
pectoral girdle (clavicle).
The hypodermis is relatively hypertrophied in mammals, presumably as an adaptation for
endothermy (insulation and energy storage).
Extending from the surface and embedded within the dermis are multicellular glands. There are
two major types: sebaceous and sweat. Sebaceous glands (L. sebum, tallow) are branched alveolar
[sac-like with obvious lumen] glands that produce an oily/waxy secretion (sebum). The ducts typically
open into hair follicles but are also found without hairs at special sites such as the eyelid (tarsal glands)
and in the external acoustical meatus.
Sweat glands are typically of limited distribution (the ubiquitous sweat glands of humans are
atypical) and absent in some species (cetaceans, sirenia and others). These are tubular glands
associated with myoepithelial cells which assist in secretion. There are two types which differ in (1) the
viscosity of the secretion, (2) their association with or without hair , and (3) developmental onset (pre or
post-puberty). Eccrine sweat glands secrete a watery solution (sweat) to the skin surface, are not
associated with hairs, and are present at birth. These function primarily in evaporative cooling, hence
their absence in aquatic forms. Apocrine sweat glands are morphologically similar but discharge a
thicker, odoriferous secretion, are associated with hairs , and form at puberty. Scent glands are modified
apocrine sweat glands whose pheromone secretions are used in marking trails and territories, courtship
and defense (e.g., skunk).
Hair is a defining characteristic (synapomorphy or shared derived character) of mammals,
providing mechanical protection from abrasion, insulation, and sensory information. Each hairs consists
of a shaft of dead, cornified cells whose base is embedded in a hair follicle within the dermis. The follicle
consists largely of epidermal cells into whose base a dermal papilla protrudes, bringing nerve endings
and blood supply. Hairs elongate by adding new cells to the base of the hair shaft. Structurally a shaft
consists of a core (medulla) of shrunken dead cells, a thick cortex and outer cuticle of overlapping scaly
cells whose arrangement is often identifiable as to species. Hair color is a result of pigmentation within
cells of the cortex provided by melanophores within the follicle. The shaft of the follicle is usually oblique
to skin of surface and smooth muscle arrector pilli attaches to follicle to pull hair upright. These muscles
are under control of the sympathetic nervous system and function in the fight or flight response and to
increase the insulatory function. The pattern of hair replacement (or lack thereof) varies within and
between species with many species having seasonal coats of different coloration (e.g., minks, snow-shoe
hares, etc.)
Humans have a sparse covering of hair; fur or pelage, a thick covering of hair is typical of most
mammals and consists of long guard hairs underlain by shorter, denser underhairs. Guard hairs can be
modified into quills (defensive ) or vibrissae (“whiskers”; long, tactile hairs on the snouts).
III. ORAL REGION AND ORAL CAVITY
The oral regions includes the mouth, teeth, gingivae (gums), tongue, lips and cheeks, and palate
(hard and soft). The oral cavity or mouth represents the beginning of the digestive tract and is where
ingestion of food occurs. It consists of two parts: the vestibule and the mouth proper. The vestibule is
the slit-like space between the teeth and gingivae internally and the lips and cheeks externally. The
mouth proper extends from the teeth to the palatoglossal arches which mark the entry into the muscular
pharynx, the next portion of the digestive tract. In addition to its role in feeding / digestion, the mouth
plays an important role in speech, non-verbal communication (e.g., raspberries), sensory input (chemo(taste), mechano- and thermo-sensory), and humidification of inspired air.
4
organ1.pdf
figure: 3K13-3a
Of particular interest in the oral cavity
are the tongue, the salivary glands (major and
minor), and teeth. Included in this section but
actually located within the pharynx are the
tonsils. The relationship of these structures
along the sagittal plane is illustrated in the
accompanying figure.
Lab Assignment: Organology I – Integument
and its derivatives
Work through the following sections using your atlas as a guide. Make sure to answer the
questions (marked by “?”) at the end of the lab; these will be evaluated when you turn in your handout
next week. A list of structures which will form the basis for next week’s quiz is given at the end of the
handout.
To learn how to identify the structures, write down criteria which will assist you in your
identification (e.g., simple squamous epithelium: single layer, flat cells with flattened nuclei). Your text is
a good source for such material as well as your own observations. Some students find it helpful to make
rough sketches of the structure to assist in their learning.
N.B. Due to [unprogrammed] slide death, your slide box may not contain the required slide. If
this is the case, notify an instructor and they will provide a replacement or suggest an alternative. If you
end up borrowing a slide from one of your colleagues’, please don’t forget to return it to them.
I.
Skin
A.
skin (pig): H 2081 (trichrome); HI 1-3 (H&E)
Unfortunately our skin tissue is from fetal pigs, rather than mature human tissue. This presents
two problems: (1) A this age thehe epidermis is very thin and it will not be possible to distinguish the
classical five layers (strata germinativum, spinosum granulosum lucidum and corneum ); and (2) pigs,
unlike humans, have a very limited distribution of sweat glands and thus will probably not be visible in
your slide. With these caveats in mind, please try to identify the following:
Identify:
epidermis - keratinized stratifed squamous
stratum basale
melanocytes (chromatophore)
[strata spinosum, granulosum and lucidum]
stratum corneum
dermis
dermal papillae
reticular layer
collagen
fibroblasts
vessels
hypodermis
adipocytes
glands
sebaceous
[eccrine sweat (in a pig’s eye, maybe)]
hair
shaft
5
organ1.pdf
medulla
cortex
cuticle
follicle
dermal papilla
matrix cells
epidermal cells
[internal root sheath]
[external rooth sheath]
arrector pilli
B.
Mammary gland
mammary gland, active: 93W5051(extras available)
Mammary glands are thought to have evolved from either sweat or sebaceous glands,
possessing properties of each (compound alveolar morphology like sebaceous, myoepithelial like sweat).
These glands develop embryologically from a continuous epithelial milk ridge which extends from the
axilla to groin and which invaginates into the dermis. Mammary glands potentially develop anywhere
along this line, the number varying between and within species (c.f. humans vs cats or dogs). Each
glands or lobe consists of numerous lobules, each lobule a cluster of secretory alveoli which empty into
storage ducts. Under hormonal influence, the glands secrete milk (a watery mixture of fats,
carbohydrates and proteins) to nourish the offspring. A build up of adipose tissue around the glands
produces structures called breasts (L., mammae; hence, mammals).
Only the glandular portion of the breast is illustrated in this slide.
Identify
mammary gland
alveoli
milk
duct
connective tissue
adipocytes
II. Oral Cavity
Our pickings here are a bit slim and thus the examination will be far from comprehensive (e.g., no
lips). We will examine the tongue, epiglottis, salivary gland, tonsil, and both developing and developed
(i.e., mineralized) teeth.
A.
Tongue
tongue, cat, ls (H&E): H2690
alternative: tongue, cs (trichrome stain): HD 2-212
alternative: tongue; ls: HK 2-26
lingual salivary glands: HK 4-4
This muscular organ also contains the taste buds and other sensory organs, lymphatic tissue
(lingual tonsils) and the lingual salivary glands (serous, mucous and mixed. Along with the rest of the oral
cavity it is lined by a mucous membrane consisting of an epithelium and underling an underlying
connective tissue called the lamina propria. The dorsum is lined with a keratinized stratified squamous
epithelium which is folded into projections called papillae which come in a variety of shapes. The ventral
mucous membrane of the tongue is lined by a non-keratinized stratified squamous epithelium.
6
organ1.pdf
Identify:
mucous membrane
epithelium
lamina propria
papillae
skeletal muscle fibers
salivary glands
serous
mucous
B.
sublingual gland: H2735
The major salivary glands are the paired parotid, submandibular and sublingual glands. The
minor salivary glands are found within the tongue (lingual) and within the oral mucosa of the labial, buccal
and palatal surfaces. The minor glands account for only 10% of the total volume of saliva in humans, but
account for the majority of it mucous component.
The sublingual gland is composed of a mixture of serous, mucous and combined seromucous
secretory units.
Identify:
mucous cells
serous demilunes
ducts
[seromucous acini - may be absent]
C.
Tonsils
palatine tonsil: H1900(extras available); HH 1-2
alternative: pharyngeal tonsil: H8833 (extras available)
Aggregations of lymphoid tissues in the proximal portion of the digestive tract are called tonsils.
Forming a ring (of Waldeyer) around the pharyngeal passage, the tonsils are subdivided into pharyngeal
(or adenoids; dorsal midline), palatine (bilateral) and lingual (ventral midline). The three can be
distinguished by the nature of their covering oral mucosa. Each is characterized by numerous nodules or
follicles with germinal centers of lymphocyte proliferation.
Identify:
lymphoid follicles (nodules)
germinal centers
lymphocytes
connective tissue septa
D.
Developing tooth
developing tooth, fetal pig: H2626 series (A-G; use F or G); DEMONSTRATION
Early in their development, prior to the replacement of their protein matrix by inorganic salts, the
mineralized tissues of the tooth can be demonstrated in paraffin sections. Teeth develop through a series
of epithelial-mesenchymal interactions. The enamel crown is derived from the oral ectoderm which grows
into the mesenchyme of the developing jaws to form the enamel organ. The inner layer of this enamel
organs gives rise to the enamel secreting cells, the ameloblasts. The dentin, cementum and periodontal
ligament are all derived a condensation of the mesenchyme produced by the oral ectoderm, the dental
papilla. The dentin, which forms the core of the tooth, is laid down by specialized secretory cells called
odontoblasts. Interestingly, at least to Dr. Kos and her ilk, the dental papilla is of neural crest origin.
Identify:
7
organ1.pdf
dental papilla
odontoblasts
dentin
ameloblasts
enamel
figures: 3K13-6
E.
Tooth, mineralized ground section
human mandibular canine or
premolar, ground section:
DEMONSTRATION
In ground sections only the
mineralized tissues (enamel, dentin,
cementum and bone) are preserved; the
organic components (e.g., cells, periodontal
ligament) are not. As shown in the
illustration, a tooth is composed of an
enamel-covered crown and cementumcovered root. The core of both the crown and root is composed of dentine which surrounds the pulp
cavity. The crown of the tooth protrudes into the oral cavity and the roots project into bony sockets within
the alveolar bone of the upper and lower jaws. The periodontal ligament (not preserved here) connects
the cementum to the alveolar bone.
figures: ss116
Enamel is the most densely mineralized
of the connective tissues (96%+ inorganic
salts). It is laid down in prisms by the
ameloblasts moving in an undulating pattern
starting from the dento-enamel junction (DEJ)
and terminating at the crown surface. The
pattern of undulating deposition results in the
formation of two structures: the striae of
Retzius and the Hunter-Schreger bands (see
photograph). The Hunter-Schreger bands are
comprised of bundles of prisms in sectioned in
alternative planes (cross and semi-longitudinal).
These are best seen along the DEJ. The striae
of Retzius are seen as fine lines running from
the DEJ to the crown surface parallel to the
contour of the dentin core.
Dentin is typically composed of 80%
inorganic salts and is deposited by the odontoblasts moving from the DEJ to the pulp cavity. A
cytoplasmic process is trailed behind the odontoblasts resulting in the formation of the dentin tubules.
Cementum is very similar to bone in composition, structure and behavior but is typically more
heavily mineralized (70% inorganic salts). It is largely , but not completely, acellular. Collagen fibers
embedded within the cement and extending into the adjacent alveolar bone form the periodontal
ligament.
Identify:
enamel
8
organ1.pdf
prisms
striae of Retzius
Hunter-Schreger bands
dentin
dentine tubules
pulp cavity
cementum
[alveolar bone]
III. Questions (Due the following lab)
?
Which component of skin, epidermis or dermis, differs the most between thick and thin skin?
?
How can you tell if a stratified squamous epithelium is keratinized?
?
The cells of which layer(s) (strata) of the epidermis remains mitotically active?
?
In the stratum granulosum, how can keratin synthesis occur in the absence of an intact nucleus?
?
What three factors determine skin color?
?
What two cell types are capable of cell division in the stratum basale?
?
What type of connective tissue is found in the papillary layer of the dermis? In the reticular layer?
?
What three types of fibers are found in the dermis? Which is most abundant?
?
In what layer of the skin are the sweat glands found?
?
What special cells assist in the expulsion of sweat from eccrine glands? What controls these
cells?
?
How would you distinguish apocrine from eccrine glands in a histological section?
?
How would you distinguish eccrine from sebaceous glands in a histological section?
?
In what structure are the proliferative cells of a hair found?
?
How can you distinguish histoloigcally between mucous-secreting and serous-secreting salivary
gland cells?
?
What is a serous demilunes?
?
What component of the nervous system regulates salivation? What special cells assist in the
expulsion of saliva?
?
The two sets of teeth found in mammals are properly called deciduous and succendaneous?
Why deciduous? Why is succendaneous a better term than “permanent.” [Hint: Count your
teeth; are there 32? Nothing permanent about them, is there?] The condition of having only
two sets of teeth is called diphyodonty and is unique to mammals. Most craniates are
polyphyodont. What does this mean?
?
Rank order the following mineralized tissues from most mineralized to least: bone, cementum,
dentin, enamel.
?
What type of tissue and cells are found in the pulp cavity of a tooth.
9
organ1.pdf
?
Why isn’t any enamel observed in paraffin sections of mature (fully developed) teeth?
?
In regards to cementum, dentin and enamel, which are continuously laid down throughout life and
which are not? What biological response occurs when you chip your enamel?
?
What is the inorganic element in bone, dentin, cementum and enamel called?
?
Who was Retzius? In what organisms are the Retzius cells found? [Hint: Think of and then ask
Dr. Kos.]
IV.
Quiz: Be prepared to identify all of the structures listed in Part II.:
10