Lect.3.Connective tissue.ppt for the bams

Connective tissue

1. Connective tissue
Functions of CT:
a. Structural support
b. A medium for exchange (so it is vascular).
c. Helps in defense & protection of the body.
d. A site for storage of fat.
TYPES:
1.CT. proper. 2. Embryonic CT.
3. Specialized CT (cartilage, bone and blood).
Components of CT:
1-Cells.
2-Extracellular matrix (ground substances and fibers).

2. Extracellular Matrix
I-Ground substance
It is a hydrated, amorphous material that is composed of:
Glycosaminoglycans, proteoglycans and adhesive
glycoproteins as laminin, chondronectin, osteonectin
and fibronectin.
II-Fibers
*Collagen fibers, are inelastic and possess great tensile
strength. Each fiber is composed of fine subunits called
tropocollagen molecule.
Most of the fibers show axial periodicity by EM.
There are six major collagen types:
Type I: in CT proper, bone, dentin and cementum

3. Type II: In hyaline and elastic cartilage.
Type III: reticular fibers.
Type IV: Lamina densa of the basal lamina.It does not
possess a periodicity and not assembled into fibers.
Type V: Associated with type I collagen and in the
placenta.
Type VII: Attaching the basal lamina to the lamina
reticularis.
The previous types of collagen show fibrillar structure
except type IV that form meshwork.
*Elastic fibers: Are composed of elastin and
microfibrils.They are formed by fibroblasts as well as
smooth muscle cells of blood vessels.

4. CT.Cells
I-Fixed cells: 1.Fibroblasts
2.Adipose cells.
3.Pericytes.
4.Mast cells.
5.Macrophages.
II-Transient cells:
1.Plasma cells.
2.Lymphocytes.
3.neutrophils, eosinophils and basophils.
4.Macrophages.
5.Monocytes.

5. Fixed CT. Cells
I-Fibroblasts
They are the most abundant CT. cells and derived from
undifferentiated mesenchymal cells.
Types:
1-Active fibroblasts: are elongated, fusiform cells with
pale-staining cytoplasm rich in RER and dark-stained
large ovoid nucleus containing well-defined nucleolus.
2-Inactive fibroblasts (fibrocytes): are smaller and are
more ovoid with more acidophilic cytoplasm.
* Fibrobalsts are responsible for the synthesis of almost of
extracellular matrix.

6. II-Adipose cells (fat cells or adipocytes):
They are derived from undifferentiated mesenchymal cells.
They are fully differentiated and do not undergo cell division.
There are 2 types:
A-Unilocular fat cells, form white adipose tissue: they are large
cells, they store fat as one droplet, which enlarge pushing the
cytoplasm and the nucleus peripherally against cell membrane
(signet-ring appearance). They have few mitochondria. The fat
droplet is not bounded by a membrane.
B-Multilocular adipocytes, form brown adipose tissue:
Are small cells with multiple fat droplets, central spherical nucleus
and many mitochondria.
* They function in the synthesis, storage and release of fat.

7. IV.Mast cells:
They are derived from bone marrow stem cells.
Their cytoplasm is rich in membrane-bound granules
that stained metachromatically with toluidine blue.
The granules contain heparin, histamine, eosinophil
chemotactic factor and neutrophil chemotactic factor.
They are present in subepithelial CT.,CT. around small
blood vessels, and subepithelial CT. of digestive and
respiratory tracts (mucosal mast cells that secrete
histamine).
* Histamine causes vasodilatation and increase
permeability of blood vessels. It causes bronchospasm
and increase mucus production.

8. V-Macrophages
They are active mononuclear phagocytes.
Some are fixed and others are transient .
They are irregular in shape and have filopodia.
Their cytoplasm Is basophilic with small eccentric
indented nucleus, prominent RER, well developed Golgi
and an abundance of lysosomes.
They derived from monocytes that localized in different
regions, EX. in liver (Kupffer cells), in lung (dust cells),
in CT.(macrophage), in skin (Langerhans cells) and in
blood (monocytes).
Several monocytes can fuse together forming foreign-
body giant cell.
They phagocytose foreign substances and debris.

9. Transient CT. cells
I-Plasma cells
They are derived from B-lymphocytes after exposure to an
antigen.
They secrete antibodies.
They are large ovoid cells with intensely basophilic cytoplasm
that is rich in RER and Golgi (pale-staining region adjacent
to the nucleus that has chromatin radiating out from the
center (clock-face appearance).

10. II-Leukocytes
They are white blood cells that circulate in blood stream then
migrate through capillaries to enter CT. during
inflammations, invasion by foreign elements and immune
response.

11. Classification of CT.
A-Embryonic CT:
1.Mesenchymal CT: Is present only in the embryo (in adult
in pulp of teeth) and consists of mesenchymal cells in a
gel-like ground substance containing scattered reticular
fibers.
Mesenchymal cells are small cells with pale staining
cytoplasm with small processes and a small pale nucleus
with prominent nucleolus.
2.Mucous tissue:
It is formed of hyaluronic acid, collagen types I &III and
fibroblasts.
It is known as Wharton’s jelly and is found in umblical
cord and sub-dermal CT. of the embryo

12. B-Connective tissue proper
1-Loose (areolar CT):
It fills in the spaces of the body just deep to the skin,
below the mesothelium lining of internal body cavity,
adventitia of blood vessels and surrounds the
parenchyma of glands.
The loose CT of mucous membranes is called lamina
propria.
It is characterized by abundant ground substance and
tissue fluid housing the fixed CT. cells, undifferentiated
cells and collagen, reticular and elastic fibers.

13. 2.Reticular CT:
Type III collagen is its major component. Collagen forms mesh-
like networks interspersed with fibroblast and macrophages.
It forms the architectural framework of liver sinusoids,
adipose tissue, lymph nodes, spleen, smooth muscle and
islets of Langerhans
.3.Adipose tissue:It is divided into white (unilocular)
adipose tissue and brown (multilocular) adipose tissue.
It is rich in blood vessels

14. 4. Dense CT:
It has many more fibers and fewer cells than ordinary
CT.It is formed of three types:
a.Dense irregular collagenous CT: it is formed of
randomly arranged collagen fibers, few ground
substances and fibroblasts scattering between collagen
fibers. It constitutes the dermis of skin, the sheath of
nerves and capsules of spleen, testes, ovary and lymph
nodes.

15. b. Dense regullar collagenous CT:
it is composed of coarse collagen bundles that
oriented into parallel sheets. It has few ground
substances and fibroblasts between collagen
bundles.Ex. Tendons, ligaments and
aponeuroses.

16. c.Dense regular elastic CT: it has coarse branching
elastic fibers with only collagen fibers forming
networks and scattered fibroblasts. Elastic fibers are
arranged parallel to one another and form either thin
sheets or fenestrated membranes as in large blood
vessels, ligamenta flava and suspensory ligament of
penis.

17. Basement membrane
It is a cellular region that interface between epithelium
and the underlying CT. It is visible by light microscope
and stained by PAS.
External lamina, is similar to basement membrane and
surrounds smooth muscle, skeletal muscle, adipocytes
and Schwann cells.
By EM. It is composed of: 1. Basal lamina which is
formed by the epithelium and it is consists of two layers :
A. Lamina lucida. It consists of extracellular
glycoproteins laminin and entactin.
B. Lamina densa, comprises a meshwork of type IV
collagen.

18. 2. Lamina reticularis: which is composed of type I &III
collagen that manufacture by fibroblasts of underlying
CT. It is thick in skin and very thin around alveoli.