Connective tissue
Connective tissue is formed by the classes of 3
components:
1. Ground substance
2. Fibers: collagen, reticular and elastic
3. Cells:
The wide variety of C.T. types in the body reflects
variations in the composition and amount of the three
components that are responsible for the remarkable
structural, functional, and pathological diversity of
C.T.
The C.T. originate from the mesenchyme,
mesenchmal cell, the mesenchyme develops mainly
from the idle layer of the embryo, mesoderm
mesenchymal cell characterized by an oval
nucleuswith prominent and fine chromatin. They
possess many thin cytoplasmic processes and are
immersed in an abundant viscous extracellular
containing few fibers.
Cells of the C.T.
Fibroblast: synthesize collagen, elastin,
glycosaminoglycan, proteoglycans and multiadhesine
glycoproteins andare responsible for the synthesis of
extracellular matrix component.
Two stages of activity
1. Fibroblast
2. Fibrocyte
Fibroblast is also involved in the production of
growth factors that influence cell growth and
differentiation. Myofibroblast, a cell with features of
both fibroblasts and smooth m., and observed during
healing their activity is responsible for wound closure
after tissue injury, a process called wound contraction.
Macrophage: characterized by phagocytic ability
macrophage, monocytes are the same cell in different
stages of maturation tissue, macrophages can
proliferate locally, producing more cells.
Macrophages, which are distributed throughout the
body are present in most organs and constitute the
mononuclear phagocyte system.
Macrophages act as defense elements, and are also
antigen-presenting cells that participate in the
processes of partial digestion and presentation of
antigen to other cells.
Macrophages are also secretary cells that produce an
impressive array of substance including enzymes
e.g.: collagenase and cytokines.
Mast cells:oval to round c.t. cells, cytoplasm is filled with
basophilic secretary granules.
The principal function of mast cells is to storage of chemical
mediators of the inflammatory response. The secretary granules
contain preformed mediators.
1. Histamine
2. Heparin
3. Highly acidic, sulfated glycosaminoglycan
There are at least two populations of mast cells in c.t.
1. Connective tissue mast cell is found in the skin and
peritoneal cavity, their granules contain the
anticoagulant heparin.
2. Mucosal mast cell: is present in the c.t. of intestinal
mucosa and lung, their granules contain
chondroitin sulfate instead of heparin.
Medical application
Increased vascular permeability is caused by action of
vasoactive substances an example is histamine, which is
liberated from mast cells and basophilic leukocytes.
Increases is blood flow and vascular permeability are
responsible for local swelling (edema) redness and heat
pain is due mainly to the action of chemical mediators on
nerve ending chemotaks. The phenomenon by which
specific cell types are affricated by some molecules is
responsible for the migration of large quantities of
specific cell types to legions of inflammation, leukocytes
cross the walls of venules and capillaries by diapedesis,
invading the inflamed wears.
Plasma cells: are derived from B-lymphocytes and are
responsible for the synthesis of the antibodies.
Leukocytes: the normal c.t. contains leukocytes that
migrate from the blood vessels by diapedesis.
Diapedesis: leukocytes migrate through the walls of
capillaries and post-capillary venules from the blood to
c.t., this process increases greatly during inflammation
leukocytes do not return to the blood after having resided
in c.t., except for the lymphocytes that circulate
continuously in various compartments of the body (blood,
lymph, c.t., lymphatic organs).
Adipocytes: these cells can be found isolated or in small
groups within the c.t. itself.
These cells become specialized for storage of neutral fats
or for the production of heat
Medical application
Unilocular adipocytes can generate very common benign
tumors called Lipomas. Malignant adipocytes-derived
tumors liposarcomas are not frequent in humans.
Fibers
The c.t. fibers are formed by proteins that polymerize into
elongated structures. Fibers are collagen, reticular, elastic
the collagen and reticular are formed by the protein
collagen and the elastic fibers are formed by protein
elastin. These fibers are distributed unequally among the
types of c.t. there are two systems of fibers.
The collagen system consisting collagen and reticular
fibers, and elastic system consisting of elastic, elaunin and
oxytalan fibers.
Collagen fibers:are the most abundant protein in the
human body representing 30% of its day weight
Collagen synthesis: an activity originally believed to be
restricted of fibroblast, chondroblast, odontoblast, has
now been shown that many cells types producing this
protein the principal amino acids that make up collagen
use glycine, proline, hydroxyproline.
Collagen types
1. Collagen type I: thick found in dermis, tendon, bone
dentin function resistance to tension
2. Collagen type II: loose aggregates of fibrils found in
cartilage [Hyaline and elastic] function resistance to
pressure
3. Collagen type III: thin, weakly found in skin, muscle,
blood frequently together with type I
Function: structural maintenance in expansible
organs.
4. Collagen type IV: frequently forms fiber together
with type I found in fetal tissues, skin, bone, placenta,
most interstitial tissue function participates in type I
collagen function.
5. Collagen type VI: small fiber found cartilage function
participates in type II collagen function found also in
basal lamina.
Reticular fiber: Consist mainly of collagen type III.
Reticular f. are extremely thin form an extensive network
in certain organ they stained black by silver salts
argyrophilic reticular f. abundant in smooth m.,
endoneurium and the frame work of hematopoietic organs.
Elastic fibers: are composed of 3 types of fibers oxytalan,
elaunin, elastic the structure of elastic fiber develop
through 3stages.
Subcutaneous tissue. (Elastic fibers labeled at right. )
Elastic fibres (or yellow fibres) are bundles of proteins (elastin)
found in extracellular matrix[1] of connective tissue and produced
by fibroblasts and smooth muscle cells in arteries. These fibers
can stretch up to 1.5 times their length, and snap back to their
original length when relaxed. Elastic fibers include elastin,
elaunin and oxytalan.
1. Oxytalan: the fiber consists of abundle of microfibrils
composed of various glycoproteins. oxytalan fibers
can be found in the zonule fibers of the eye.
2. The second stage of development, an irregular
deposition of the protein elastin appears between the
oxytalanmicrofibrils forming elaunin. These
structures found around sweat glands and in dermis.
3. During the third stage elastin gradually accumulates
until it occupies center of fibers bundles.
Ground substance:
The intercellular ground substance is a highly hydrated
colorless,
transparent
complex
mixture
of
macromolecules it fills the space between cells and fibers
of C.t. because it is viscous, acts as both a lubricant and
barrier to the penetration of invaders.
Grand substance is formed mainly of
Glycosaminoglycans, proteoglycans and multiadhsive
glycoproteins
Prcteoglycan consist of numerous GAGs covalently bond
to a core protein in a manner reminiscent of a test tube
brush the entire proteoglycan may in turn be bound to the
collagen and elastin fibers of C.T.
Grand substance components
Tissue fluid, minerals and proteoglycans
Minerals; mostlycalcium salts tissue fluid: water, gases wastes nutrients
which are transport from and to the cells of tissue
Odema : pathologic condition is characterized by
enlarged spaces, caused by the increase in liquid between
the components of the C.T.
Edema result from venous or lymphatic obstruction or
from a decrease in venous blood flow heart failure or
increased permeability of the blood capillary condition
resulting from chemical or mechanical injury or the
release of certain substances produced in the bodies
e.ghistamine .
Types of connective tissue :
A.Loose C.T.:
1- Areolar C.T.:
2-Reticular C.T.:
3-Adipose C.T.:
Embryonic connective tissue
1. mesenchyme : produce all permanent C.T2. mucous connective tissue : like mesenchyme but is a temporary it exists only
in the fetus . mucous almost entirely limited to substance ( Wharton's jelly)
mucous tissues have mainly fibroblast,
reticular tissue: very delicate tissue forms network that support cells .
areolar C.T.: found in every part of the body surrounds the B.V. , N., penetrate
with the into the small spaces of muscles
adipose tissue : occur singly or in small clusters in areolar t. the space between
fat cells is occupied by areolar t., reticular t, blood capillaries . white fat ; adipose
t. in adult
yellow ( brown fat ) : adipose t. in fetuses and infants , children . fat gets color
from an unusual abundance of blood v. and lysosomes . it stores lipid in the form
of multiple droplets rather than one large one .
obesity : is regarded as a condition in which a person as more than 20% above
the ideal weight for his or her sex , age .
hypertrophic obesity: excessive a accumulation of fat in unilocular t. cells that
become larger them usual
hyperplastic : an increase the number of adipocytes
lipomas : benign tumors which is generate from unilocular adipocytes
liposarcomas : malignant adipocyte derived tumors , are not frequent in human
4-Mucous C.T.:
5-Elastic C.T.:
B-Dense C.T.:
1- Irregular C.T.:
2-Regular C.T.: