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THE TISSUES (HISTOLOGY) p. 49
In order to examine the anatomy of representative tissue types found in the
human body, prepared slides are made by slicing extremely thin sections from
various mammal organs, staining them with appropriate dyes, and mounting them
permanently on glass slides. With the aid of a standard bright-field
microscope, the cellular size, shape, and arrangement within the tissue can be
observed. Also of interest are characteristics of intercellular matrix.
A common staining procedure used is the hematoxylin-eosin technique
which leaves
cytoplasm pink, while staining nuclear material and protein aggregates
blue-purple. It is wise to avoid trying to recognize tissues by color, since
the shades may vary from slide to slide. When slides are prepared, the contents
of tubes, cavities, vacuoles, and some cells often rinse out, leaving an empty
space. The space is unstained, of course, and appears white in bright-field
microscopy.
The slides available to you for study are:
1. Kidney (human or other mammal): The overall purpose of the simple
epithelium
within the kidney is to allow filtration of wastes and excess
materials from the blood
passing through the kidney.
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This organ is composed of a myriad of intertwined tubules, the walls of which
are made of simple epithelium. Some of the tubules are lined with simple
squamous epithelium, others with simple cuboidal epithelium. As the
kidney tissue is sliced, some tubules are cut in transverse (cross) section
and appear as perfect circles around an empty cavity (lumen). The empty
cavity appears white.
At the periphery of the organ are specialized capillary clusters called
glomeruli. You will notice a white space* adjacent to this cluster. It is
known as the renal (Bowman's) capsule and the walls of it are
composed of simple squamous epithelium.
2. Trachea: Hyaline cartilage rings which support the
trachea are observed as oval
fields or patches of evenly stained matrix. The chondrocytes
(cartilage cells) are
isolated in scattered spaces called lacunae which often appear
white (empty)
after staining.
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Pseudostratified ciliated columnar epithelium tissue lines the trachea. Goblet cells, fibrous connective, smooth muscle, or adipose tissue may also be observed.
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3. Intestine (human or other mammal): The tissue layer which lines
the lumen is
simple columnar epithelium. The foldings (called villi)
increase the surface area for
absorption. Also visible in a slide of intestinal tissue is
smooth muscle.
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4. Loose connective tissue (areolar): its function is
connecting and binding.
The matrix of loose connective tissue contains several fiber types.
Identify the
thin Elastic fibers and thick Collagen fibers, and the
fibroblast cells.
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5. Compact bone: NOTE: This slide is labeled "Ground Bone". Identify
the following
structures: lamellae (bony layers), lacunae (spaces
containing osteocytes)
NOTE: The osteocytes are not distinguishable in the dark lacunae.
Haversian canal (central space for capillary) and canaliculi
(fine, wavy lines
showing location of minute canals)
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6. Skin: Try to look at several examples: thick skin, thin skin,
scalp. In each, look at
the free border, then scan from the border deeper into the organ. Skin
is an organ of
the integumentary system and it will consist of several tissue types.
There are
several accessory organs related to the skin and located within it, these
include the
hair follicles, oil glands, and sweat glands. Functions of the skin
include protection,
excretion, and sensation.
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The epidermis is composed of stratified squamous keratinized epithelium.
The outermost, dead, flat layer (often torn or detached) is the stratum
corneum. The other layers of the epidermis (usually a darker purple
border) have cytoplasm and nuclei and take up the stain better. The base layer
of the epidermis is the stratum
basale. In some slides the brown pigment melanin in the stratum basale
demonstrates melanocyte activity. Notice that the area where the
epidermis and dermis join is ridged, this is the papillary layer
of the dermis. The dermis is composed of irregular dense fibrous connective tissue;
the dermis has dense irregular fibers and accessory structures such as hair
follicles, sweat glands, and oil glands. Notice the hair follicles or a
space containing a hair shaft and root. Recognize the
sebaceous (oil) glands producing sebum (oil), and the sweat (sudoriferous)
glands Below the dermis is subcutaneous loose connective tissue
which may contain some adipose tissue.
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7. Skin Model: You must be able to correctly label and identify the following
layers
and structures.
8. Muscle Tissue:
A. skeletal--long parallel striated fibers,
multi-nucleated,
peripheral nuclei underneath sarcolemma;
recognize endomysium, perimysium, and epimysium
B. smooth--non-striated spindle-shaped cells, single
nucleus
C. cardiac--branched, striated fibers with central nuclei
between intercalated discs
ADDITIONAL LAB STUDY FOR HISTOLOGY INVOLVES GROSS STUDY OF TISSUES. In order to achieve an overall understanding of the various tissue types, it is helpful to study them as they appear to the unaided eye in a "fresh" specimen. This type of study is called gross anatomy rather than microscopic anatomy.
In order to facilitate this study, you have been asked to bring a small piece of fresh (or frozen and thawed) uncooked chicken to the lab. This item is something with which most people have had prior experience and familiarity. You will now be asked to separate (dissect) the chicken sample into its component organs and tissues, recognizing and naming them as instructed. You will be provided dissection tools.
SAFETY NOTES:
1. SCALPELS AND TEASING NEEDLES ARE SHARP OBJECTS!
HANDLE THEM CAUTIOUSLY WHILE TRANSPORTING THEM,
DURING THE DISSECTION, AND WHEN CLEANING THEM.
2. RAW CHICKEN can transport Salmonella sp., a microorganism
associated
with gastrointestinal illnesses. Take care when handling the chicken
and wash your
hands thoroughly after the exercise. Do not eat or drink, or
accidentally place items
(fingers, pencils, etc.) in your mouth until you have cleaned up after
the chicken
dissection.
INSTRUCTIONS:
1. Look at the skin as you pull it off. You will find
papillae evident, as well as "hair
follicles", feathers being a modified skin appendage as are hairs.
2. Notice the filmy loose (areolar) connective tissue as you pull
the skin off.
3. The oily yellow patches between skin and muscles are adipose tissue.
4. Look at the muscles (the fleshy part you eat.) You can see
the parallel
arrangement of the muscle fiber bundles.
5. The muscles will be attached to bone by long silvery-white
tendons (dense
regular connective tissue).
6. Look for the articular hyaline cartilage over the ends of
bone at a joint
(particularly obvious on a leg or thigh).
7. Look for the dense fibrous connective tissue periosteum of the bone.
8. Break or cut one of the bones at its epiphysis and identify
cancellous and
compact bone.
9. Look in the marrow cavity for red and/or yellow marrow.
10. Observe blood vessels.
11. You may find the cut end of a ligament near a joint.
12. Look for a nerve. The thigh is a good place to find a
large nerve (the sciatic).
It travels along the same path as the major blood vessels and can
be dissected free
from them. It is white, and may be mistaken for a tendon. Follow
it to satisfy
yourself that it does not attach to muscle as the tendon would.
13. Wrap your chicken in paper towels and discard it in the
plastic-lined waste can
nearest the door. Thoroughly wash and dry all dissection equipment
used,
including the tray.
NOTE: FOR THE LAB PRACTICAL, BE ABLE TO RECOGNIZE AND NAME ANY OF THE
STRUCTURES DESCRIBED ABOVE.
