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Department of Natural SciencesUniversity of St. La Salle
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1.LOOSE CT esophagus, vagina, urinary bladder
Encountered in almost every microscopic
section of the body, it is the packing andanchoring material; binds other tissues and
organs together; allows a degree of mobility
between these parts due to its flexibility.
Found beneath thetunica propria of
organ cavities
Fibers are loosely
arranged in ameshwork as in the
loose areolar or
fibro-elastic types
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Collagenous and elastic fibers are both present
forming a loose, continuous and branching
meshwork; reticular fibers few and inconspicuous. Fibroblasts, macrophages, mast cells are relatively
very few and may include any or all of the different
varieties.
Ground substance is
fluid like, containingmany spaces capable
of becoming enlarged
and distended with
fluid.
These spaces or
areola is a synonym
for loose CT.
Richly supplied with blood vessels, lymphatics,
nerves.
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2.DENSE CT- has compactly
or closely packed fibers;
subdivided into:Dense regular:
a.Dense fibrous (white or
collagenous) CT- tendons
Found wherever firmness
and resistance are needed
in the body, such as in
tendons, flat sheets, cornea, fasciae and aponeurosis.
The fibers are oriented in a consistent pattern to meet
specific mechanical requirements. The predominant elements are oriented collagen
bundles with few, small blood vessels.
Ground substance is scanty in amount.
Blood vessels and nerves are found in CT sheaths.
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In tendons, each bundle is composed of a large
number of fibrils covered by a small amount of loose
CT, termed the endotendineum. Generally, several primary bundles are grouped
together into secondary fascicles bounded by a
coarser type of CT, the peritendineum.
The tendon is composed of a number of fascicles
ensheathed by thick CT called the epitendineum. Few, scattered fibroblasts
are found between the
layers of collagen.
Cell bodies appear rod-
shaped, but rectangular,
triangular or trapezoid in
surface view due to
pressure from the bundles of fibers.
In tendons, these are called tendon cells.
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Dense irregular- skin
Found typically in the dermis
of the skin, capsules of manyorgans, tendon sheaths and
nerves, in parts of the urinary
tract.
Essentially the same as the
loose type except that thefibers are thicker, woven into a compact feltwork
accompanied by extensive elastic networks.
Due to the compact arrangement of its fibers, this
tissue is stronger and offers more resistance than theloose variety.
Cells are located among the fibers. Macrophages are
easily identified by vital dyes; undifferentiated
mesenchymal cells are found along the small vessels.
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Form variants of loose CT. One type maybe transformedinto another depending on changes in local conditions so
that this classification should not be taken strictly.
1.RETICULAR CT- stroma of liver, bone
marrow, spleen, lymph nodes, thymus
Composed of typeIII
collagen; thesefibers are very fine, arranged in
slender bundles which anastomose
forming a delicate lattice network.
The stellate reticular cells are have
long cytoplasmic extensions that join other cells;mesenchyme cells may become actively phagocytic or
remain fixed as primitive reticular cells
Has a large population of resident macrophages adhering
to fibers; a few plasma cells, RBC and WBC are present.
CONNECTIVE TISSUE WITH SPECIAL PROPERTIES
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2. EMBRYONIC CT- uterus
A young form of CT occurring
in fetal life; during regenerationof adult destroyed CT areas
(uterine mucosa); dental pulp
and in certain tumors.
In the uterus, the tissue is
found in the tunica propria(corium) immediately beneath
the columnar epithelium lining of the uterus.
Very cellular, mostly fibroblasts of the spindle and
stellate variety, or the undifferentiated mesenchymal
type. Some blood cells and phagocytes are present. CT
fibers are obscured by coagulated ground substance.
This CT is highly vascular, blood vessels are numerous,
fully formed, containing non-nucleated RBC.
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3. MUCOUS CT- Whartons jelly of umbilical cord
Transient type of tissue that appears in the
development and differentiation of CT Found in the embryo, especially under the skin. In
adult animals, it is limited to the dermis and
hypodermis.
Fibroblasts, a few macrophages and lymphoid
wandering cells are present; fibers are thin,collagenous, increasing in number as the fetus
ages.
Very abundant, soft, jelly-like homogenous ground
substance. Residue contains granules and fibrillar precipitates
when fixed and exhibiting the staining reactions of
mucin.
It stains metachromatically with toluidine blue.
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In the umbilical cord, a
portion of the periphery
of the specimen far from
the 3 big umbilical
vessels will show a mass
of mucous CT called the
Whartons jelly which is
devoid of blood vessels. The specimen is
surrounded by the
amnion which is lined by
a single layer of
cuboidal cells. The CT fibers appear
indistinct showing the
coagulated gelatinous
ground substance.
Mucous tissue of an embryo showing
fibroblasts immersed in a very loose
extracellular matrix composed mainly of
molecules of the ground substances.
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4.ADIPOSE- skin, tongue
Stores fat, provide insulation against heat loss, and
mechanical support in certain regions of the body Plays an important role in maintaining a stable supply
of fuel by accumulating lipid in periods of excess food
intake and releasing fatty acids in periods of fasting.
Widely distributed as fat depots (e.g.panniculus adiposus of the belly and
buttocks in subcutaneous tissue,
yellow bone marrow, mesentery and
omenta) and may exhibit regional
differences in amount as influencedby certain factors like age and sex.
In the nervous system, eyelids, lungs
and penis, adipose tissue is absent.
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In the skin or tongue,
adipose CT can be
recognized readily
by the presence of
rounded clear spaces.
The clear spaces
represent the adipose
ghost cells, the fatcontent of which has
been washed away during the preparation of the slide.
These are closely spaced, separated by the thin
fibrous strands of both collagenous and elastic fibers,
pushed aside by expanding fat cells duringdevelopment to form the fibrous septa separating fat
lobules.
Within these septa are located other types of CT cells
and blood vessels.
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Two types are present:
Unilocular yellow or white
adipose tissue comprise the
bulk of body fat
Multilocular brown variety are
abundant in hibernating
species and newborn human
infants.
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Unilocular adipocytes can generate benign tumors
(lipomas), or malignantliposarcomas. Hibernomas
are relatively rare. In the multilocular type, mitochondria have a
transmembrane protein called thermogenin which
permits proton-motive backflow without passing the
ATP-synthetase system.
This releases heat that warms the body. It is notablethat in obese individuals, thermogenin is reduced in
quantity.
Obesity in adults may result from dietary excess,
resulting to an excessive accumulation of fat in
unilocular cells that become larger than usual
(hypertrophic obesity); or from an increase in the
number of adipocytes (hyperplastic obesity).
The latter typically occur in overnourished infants.
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Hormones that affect adipose tissues:
1.Insulin- increases uptake of glucose by adipocytes and
synthesis of triglycerides from carbohydrates2.Epinephrine, ACTH, glucagon, growth hormone,
thyroxine- promote varying degrees of lipolysis of
stored lipids and release of fatty acids.
ACTH results to localized hypertophy
of adipocytes in lower cervical regioncausing the buffalo hump condition.
3.Estrogens- influence pattern of
distribution of adipose tissue in females
Neural (sympathetic nerves of ANS) or humoral
mechanisms mobilize fats when the body issubjected to fasting periods or severe cold.
These factors stimulate adenylate cyclase,
activating the enzyme triglyceride lipase,
which breaks down triglyceride droplets.
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In general, adipocytes synthesize and store triglycerides.
In the fed state, an insulin:glucagon ratio stimulates
adipocytes to produce the following reactions:
a.Secrete lipoprotein lipase (LPL) into the capillaries of whiteadipose tissue. LPL catalyzes the digestion of triglycerides
(via VLDL and chylomicrons) into FA and glycerol. The former
enter the adipocyte to be stored; the latter travels to the liver.
b.Uptake and metabolize glucose and use it for energy and as a
source of the glycerol moiety of the stored triglycerides.
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In the fasted state, a decreased insulin: glucagon ratio and
epinephrine stimulate adipocytes to begin lipolysis due to
increased levels of cAMP which activate hormone-sensitive
lipase. This catalyzes the cleavage of FA from triglycerides.
The FA are used for ATP synthesis, and converted in the liver toketone bodies. The glycerol is used as a source of carbon for
gluconeogenesis.
Adipocytes secrete a hormone called leptin that has an anorexic
action . The action of the LEP gene is mediated through satiety
centers in the hypothalamus where their receptors are found.
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Hormones and Appetite
Produced byadipose (fat)tissue, leptin
suppressesappetite as its level
increases. When
body fat
decreases,
leptin levels fall,
and appetiteincreases.
Leptin
PYY
Insulin
Ghrelin
Secreted by the stomachwall, ghrelin is one of the
signals that triggers
feelings of hunger as
mealtimes approach. In
dieters who lose weight,
ghrelin levels increase,which may be onereason its so hard to
stay on a diet.
The hormone PYY,
secreted by the smallintestine after meals,
acts as an appetite
suppressant that
counters the appetite
stimulant ghrelin.
A rise in blood sugar
level after a mealstimulates the
pancreas to secreteinsulin. In addition to its
other functions, insulin
suppresses appetite by
acting on the brain.
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