Study Guide for Chapter 4, Tissues, for Marieb Human Anatomy and Physiology text, p. 118.
Tissues are groups of cells of similar
structure and
function. Several tissues are found in an
organ which also has its own blood and nervous supplies. An
organ system
performs related
tasks, e.g., the digestive system that includes the gut tube, pancreas
and liver.
See http://www.medinfo.ufl.edu/year1/histo/index.html
http://www.kumc.edu/instruction/medicine/anatomy/histoweb/index.htm
for on-line atlases.
TISSUE TYPES
- EPITHELIUM - avascular cell layers that cover or line organs. If cells are in a single layer,
the epithelium is
simple. If several layers thick, the epithelium is
stratified. See pg. 119.
TYPES
a.
Squamous
- cells are tile-like. Nucleus is round from a surface view and
squashed
top to bottom
b. Cuboidal - cells are box-like with a round nucleus.
Mostly it is
found as a
simple layer, i.e., thyroid follicles, bile and kidney ducts. In the
sweat
gland
ducts are lined with two-layers and are therefore stratified.
c. Columnar - Cells are shaped like columns. Simple
columnar
epithelium is lines the digestive tract
from the stomach to the rectum. In the small intestine food absorption
occurs
through this layer.
Ciliated columnar epithelium is found in the oviducts or
Fallopian
tubes. A more complex
pseudostratified columnar is found in the trachea, bronchioles
and
bronchi. In a pre cancerous stage
of lung cancer, this ciliated layer is replaced with a stratified
squamous
layer in the bronchioles.
Stratified columnar is found in the parts of the urethra that empties
the
bladder.
d. Transitional - a stratified layer with "dome" shaped
cells on the outer surface when the layer
is relaxed. When stretched, the layers looks squamous. It is found in
the
ureters and urinary bladder.
Too bad it doesn't stretch further in the kids you are hauling in the
family
car!
- CONNECTIVE TISSUES - it binds together and supports many tissues. It has three basic materials:
(1) ground substance is a secreted material outside the (2) connective
tissue cells and (3) fibers.
Matrix includes the ground substance and fibers. For instance,
calcium
phosphate is secreted onto
collagen fibers in developing bone tissue.
TYPES - See p. 126.
a. Mesenchyme - star-shaped cells that fill spaces in an embryo.
b. Fibrous Connective Tissues - composed mainly of collagenous
and
elastic fibers made by
fibroblasts.
Other cells include:
the macrophage
that eats bacteria and antibody labeled particles,
(e.g., viruses; the plasma cell that makes antibodies) and
the mast
cell that makes histamines
that make blood vessels leaky so that more immunecells and chemicals
from the
blood can enter tissues
to fight infections. Edema or tissue swelling results and the
area
becomes reddened with increased
blood flow (inflammation).
(1.) Loose irregular or areolar C.T. - fibers run in various
directions, it looks like cotton. It is found between muscles and the
skin.
(2.) Dense irregular C.T. - found in bundles under the
epidermis (epithelium) of the skin. Also, it is found in
scar tissue.
(3.) Dense regular C.T. - found in tendons and
ligaments where the collagen fibers are parallel.
(4.) Reticular - found as the network of fibers
supporting the spleen.
b. Cartilage - the avascular, solid matrix is a porous protein.
(1.) Hyaline cartilage
- a
clear, white cartilage composed of a somewhat brittle protein ground
substance secreted by chondrocytes
onto collagen fibers. See pg. //135.
It is found in the
nose and on
the ends of long bones where they come together and
make joints.
(2.) Elastic
cartilage -
has large numbers of elastic fibers. Found in
the ears and the epiglottis.
See pg.
//137.
(3.)
Fibrocartilage - filled
with collagen fibers and a small amount
of cartilage ground
substance. In
the vertebral disc, it makes a tire-like circle
around the highly
vascularized,
gelatin-like central pulp. Also it is found in the pubic
symphysis which joins the
pelvic
bones anteriorly.
c. Bone - the ground substance is calcium phosphate secreted by osteoblasts onto collagenous fibers.
d. Adipose or fat - is found as yellow or white
fat in
the hollow portions (diaphyseal marrow cavity) of
bones, around the heart, and in the lowest layer of the skin. Yellow
fat cells
have a very large fat vacuole
and a very small amount of cytoplasm. Brown fat is rare as a
tissue. It
has lots of blood vessels and the
cells are filled with mitochondria. Brown fat is thought to regulate
fat
metabolism. See pg. //132.
e. Muscle - muscle cell moves tissues including bones
by
contracting or shortening. There are three types.
(1.) Striated
Skeletal
Muscle - stripes or striations are composed of the
contractile proteins actin and myosin. See the cell study guide. Cells
are
multi-nucleated
with the nuclei at the edges of the rod-like cells. They contract with
a great
deal of force
in moving bones as levers but, compared to the other types, fatigue
easily. See
pg. 138//140.
(2.) Smooth muscle - these
cells are
shaped like spindle rollers, round in the
center and pointed at the ends. They are called smooth because they are
not
striated or
stripped. They are found around the gut where they produce the food
moving,
squeezing
motion of peristalsis.
(3.) Cardiac muscle - found
in the
heart. It is striated but the rod-like cells are
shorter and have round, centrally located nuclei. Weaving with each
other, they
join at
intercalated discs. Cardiac muscle will not enter into a state
of
constant contraction
(tetanus) as does skeletal muscle and it is resistant to fatigue.
Cancer - See p. 146 of text.
The progression of normal cells to malignant cells is characterized by changes in cell structure and activity. Precancerous changes include a change in cell structure called (1) metaplasia (one normal tissue type to another normal type; e.g., the bronchial epithelium of smokers lungs changes from pseudostratified ciliated columnar to stratified squamous), 2.) dysplasia (cells are not cancerous, but they have abnormal structure, such as very large nuclei), or anaplasia (cells are dividing rapidly and have changed in function). When the cells lose control of mitosis, abnormally high cell division rates (hyperplasia) results in a tumor. If the cells of a tumor are abnormal in structure, the mass is called a neoplasm (new tissue).
Tumors are masses of cells that do not serve a normal purpose, e.g., tumors of the adrenal cortex may result in an over-secretion of the steroid hormones it produces, certain other types of tumors may decreases the secretion of an endocrine gland. A tumor may be benign or malignant. A tumor becomes malignant when the hyperplastic tissue cells invade other tissues. Tumors may be confined or nodular, or they may be diffuse, spreading gradually into normal tissues. Malignant cells secrete a growth/migration factors and metaloprotease enzymes that break down the collagen of basement membranes. When the tumor is larger, these cells secrete angiogenesis factors to vascularize (make blood vessels to serve) the tumor. Then the invasive cells make their way to blood vessels, lymph vessels and other stromal (under the basement membrane) tissues; thus, spreading to other locations and on to other organs in a process called metastasis. One newly developing tumor acts to supply seed cells for satellite tumors. Generally, the further away the satellite tumors are from the original tumor, the worse the prognosis for survival. Mutations of DNA are required for each stage (metaplasia, dysplasia or anaplasia, hyperplasia and metastasis). The current theory is that the mutations of suppressor genes cause the cells to revert to an "embryonic" state in that they lose control over mitosis and secrete the enzymes and growth factors that produce metastasis.
Intermediate Fibers and Malignant Tumors
GFAPs are found in glial cells of the brain.
When the GFAP
genes are over-expressed, the accumulation of GFAP is a "marker" the
diagnosis
of gliomas; specifically, astrocytes or
oligodentroctes. GFAP proteins are also found
superimposed over the neurofibrillary plaques of Alzheimer's disease.
Several
types of keratin fibers fill up cells in the glassy layer of the skin
(stratum
lucidum). Hyperkeratosis is considered to be a pre-cancerous
condition
if it occurs on the lip. Carcinomas are cancers of epithelial
cell
origin. The genes that produce certain types of keratin are
over-expressed in
carcinoma cells, particularly in those on the outside edge of the
tumor. The
excess keratin is needed for the movement or invasiveness of the cancer
cells.
Keratin may also help cancer cells resist the tumor necrosis (rotting)
toxin
produced by macrophages.
Vimentin is an intermediate fiber found the cells
that are
formed from the embryonic tissue mesoderm. Mesoderm forms blood
vessels,
muscle, connective and neural tissues. A sarcoma is a cancer of
certain
cells in bone or "soft tissues." Vimentin
genes are over-expressed in cells of sarcomas.
Desmin and laminin are found in muscle cells. If a sarcoma has large amounts desmin and laminin in the tumor cells, the origin of the
cancer was from muscle cells (leiomyocytoma). Malignant fibrous histiocytomas are cancerous tumors that originate from fibroblasts. They will contain large amounts of vimentin as practically the only intermediate filament.
http://www.fhcrc.org/science/education/courses/cancer_course/basic/img/colon.gif
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Questions to ponder
1. A sarcoma was biopsied and the cells were tested for the presence and amount of keratin, vimentin, desmin, laminin and myoglobin. What kind of cells produced the sarcoma if the first test was negative, the second normal positive, third and fourth and fifth positive.
Genetic Engineering
Normal genes can be cut out of cellular DNA or RNA. These can be
spliced
into the genes of
harmless viruses. The normal genes can "jump" from the viral DNA or
indirectly through the
viral RNA to the host cell DNA, thereby carrying good genes into the
cells
containing defective
ones. Gene replacement therapy shows promise in treating diseases like
Duchienne muscular
dystrophy (due to a defective Ca++channel) and cystic
fibrosis
(caused by a defective Cl-
channel).
Aging Theories
- Loss of telomeres - short pieces of the ends of chromosomes are lost with each mitotic
division. When the telomere has been shortened, a signal cannot be
transmitted
to start
cell division. The cell becomes senescent and dies. Each cell type is
thought
to have a set
number of times to divide. Cancer cells are the exception, they are
immortal if
maintained in
culture. They have an enzyme called telomerase that reconstructs the
telomeres.
There are
breast cancer cells alive today that were taken from a woman who died
of that
disease in 1968.
- Accumulation of Mutations - not only is series of mutations a cause of cancer but they are
also speculated to be a cause of cellular senescence. Cell death and
other
chemical processes
produce highly reactive "free radicals" (peroxide groups and
chemicals that have oxygen
atoms with unpaired electrons). These can damage genes and structural
proteins.
By
stimulating cell divisions, mitogens like nicotine, encourage the
accumulation
of mutations.
In general tumor suppressor genes are first mutated, that may then
allow for
the activation of oncogenes.
See the figure on page //146.
- Accumulation of "Clinkers" - lipofuscin, undigested/yellowish fatty deposits accumulate
in cells over a lifetime. These interfere with cell metabolism and
function.
- Genetics - most species of plants and animals have a relatively narrow range of life expectancy.
If you want to live a long time, do a better job of picking your
parents.
- Glucose Cross-linking of Collagen - stiffens tendons and ligaments.
- Decreases in neural conduction and secretion of hormones - as one ages, secretions of
growth hormone, testosterone and estrogen decline. Changes
include a
decrease in muscle
mass and a corresponding increase in fat, and a thinning of the bones (osteoporosis)
making
fractures more common and slow to heal.
Why do dogs only live 10-12 years?
Study Questions
1. Explain how nicotine and anabolic steroids do not cause cancer but
rather
encourages
the development and spread of tumors.
2. Where is each type of epithelium found (one prominent location for
each)?
3. Where is each type of connective tissue found?
4. Where is each type of muscle found?
5. Compare and contrast the functions of (1) elastic and collagen
fibers, (2)
bone
and cartilage, and (3) smooth, cardiac and skeletal muscle.
Email:jaliff
@
gpc.edu