histology

1. histology by.Dr.abdirahman
Gagajir
1

2. histology by.Dr.abdirahman
Gagajir
2

3. histology by.Dr.abdirahman
Gagajir
3

4. Connective tissue
o Connective tissues function primarily to
support the body and to bind or connect
together all types of tissue.
o This tissue also provide a mechanical
framework (the skeleton) which plays an
important role in locomotion.

5. o This mechanical function is important in
maintaining the form of the body, organs and
tissues.
o The tissue derives its name from its function
in connecting or binding cells and tissues.
Connective tissue is composed of:
(a) cells
(b) extracellular matrix.

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o Matrix consists of:
1.connective tissue fibers
2.Ground substance
3.Tissue Fluid

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Cells of the connective tissue
1. Fibroblasts
2. Adipose cells
3. Macrophage or Histiocytes
4. Mast cells
5. Plasma cells
6. Leukocytes

8. Histiocyte: A tissue macrophage; the
class includes hepatic Kupffer cells,
alveolar macrophages, giant cells of
granulomas, osteoclasts, and dermal
Langerhans cells.

9. oThe extracellular material of connective
tissue, which plays a major role in the
functioning of the tissue, is the dominant
component of the tissue.
o The dominance of the extracellular
material is a special feature that
distinguishes connective tissue from the
other tissues of the body.

10. o The extracellular matrix is composed of :
1. protein fibers (collagen fibers, reticular
fibers, elastic fibers)
2. amorphous ground substance
3. tissue fluid (not preserved in histological
preparations). The amount of tissue fluid is
fairly constant and there is an equilibrium
between the water entering and leaving the
intercellular substance of the connective tissue.
In pathological conditions (traumatic injury,
inflammation) fluid may accumulate in the
connective tissue, a condition known as edema.

11. FUNCTIONS OF CONNECTIVE
TISSUE
1. Structural support
The connective tissues serve several functions,
of which the most prominent function is
structural support to enable maintenance of
anatomical form of organs and organ systems.
Examples include the connective tissue capsules
surrounding organs (such as the kidney, lymph
nodes).

12. o The loose connective tissue acts to fill the
spaces between organs.
o The tendons (connecting muscles to bone)
and the elastic ligaments (connecting bones
to bones) are examples of specialized
orderly forms of connective tissue.
o The skeletal tissues (cartilage and bone) are
special forms of connective tissue.

13. 2. Metabolic functions
o The connective tissues serve a nutritive role.
All the metabolites from the blood pass from
capillary beds and diffuse through the adjacent
connective tissue to cells and tissues.
o Similarly waste metabolites from the cells
and tissues diffuse through the loose
connective tissue before returning to the blood
capillaries.

14. o The adipose tissue (especially that of the
hypodermis) serves as an energy store and also
provides thermal insulation.
o Surplus calories can be converted into lipid and
stored in adipocytes.
3. Blood components and blood vessels
o The hematopoietic tissues (blood-forming tissues)
are a further specialized form of connective tissue.
o These include the myeloid tissue (bone marrow)
and the lymphoid (lymphatic) tissue.
o The lining of the blood and lymphatic vessels
(endothelial cells) as well as the peripheral blood,
are also specialized forms of connective tissue.

15. 4. Defensive functions
o Various components of the connective tissue
play roles in the defense or protection of the
body including many of the components of
the vascular and immune systems (plasma
cells, lymphocytes, neutrophils, eosinophils,
basophils, mast cells).

16. o The various macrophages of the body are also
categorized as connective tissue cells.
o These all develop from monocytes and are
grouped as part of the Mononuclear
Phagocyte System of the body.
o Macrophages are important in tissue repair as
well as defense against bacterial invasion.

17. Cell type Chief function
Mesenchyme Embryonic source of all connective tissue cells
Fibroblasts
Chondroblasts
Osteoblasts
Structural support
Plasma cells
Lymphocytes
Neutrophils
Eosinophils
Basophils
Mast cells
Macrophages
Defense and immune
Adipocytes Metabolic
Energy storage
Thermal insulation

18. Between cells and fibers.
o The intercellular ground substance is an
amorphous, transparent material composed mainly
of glycoproteins and proteoglycans, with a fairly
high water content, that participate in binding cells
to the fibers of connective tissue
o Viscous clear substance that has a slippery feel
o It acts as a lubricant and a barrier to the
penetration to the tissues by foreign particles.

19. o H+E staining: lost during preparation and appears
empty.
o Ground substance: Proteglycans and Hyaluronic
acid
o Proteoglycans: Proteins and Glucosamine glycans
o The main proteoglycans consist of a core protein
associated with sulfated glycosaminoglycan's (GAGs).
The main GAGs include : chondroitin-4-sulfate,
chondroitin-6-sulfate, keratin sulfate, heparan
sulfate) and the non-sulfated hyaluronic acid.
o All substances passing to and from cells must pass
through the ground substance.
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20. CONNECTIVE TISSUE FIBERS
Connective tissue fibers are composed of
structural proteins. The three main types of
fibers are:
1. collagen fibers
2. reticular fibers
3. elastic fibers.

21. Collagen fibers
o Collagen is the most abundant protein in the
body (up to 30% dry weight).
o There are more than 12 different types of
collagen, though the most common types are
Types I to V.
o Collagen is synthesized by a wide number of cell
types (including: fibroblasts, osteoblasts,
Chondroblasts, odontoblasts, reticular cells,
epithelial cells, endothelial cells, smooth muscle
cells, Schwann cells).

22. o The main amino acids of collagen are:
1. glycine (33.5%)
2. proline (12%)
3. hydroxyproline (10%)
o The amino acids, hydroxyproline and
hydroxylysine are characteristic of collagen.
It is the only naturally occurring protein with
both these amino-acids.

23. Collagen type Main sites Special features
Type I Bones, tendons, organ
capsules, dentin
Most abundant,
Typical collagen fibers
(64nm banding)
Type II Hyaline cartilage
Elastic cartilage
Very thin fibrils
Type III Reticular fibers ,smooth
muscle,arteries,uterus
,liver,spleen,kidney and
lungs
Often associated with Type I
Type IV Basal lamina associated
with epithelial and
endothelial cells
Amorphous (non-
fibrous)
Type V Basal lamina associated
with muscle
Amorphous (non-
fibrous)

24. o Collagen fibers consist of closely packed
orderly fibrils and when seen in bundles (as
in tendons, aponeuroses) appear white.
o In histological preparations after regular
staining they are acidophilic (pink staining
with eosin).
o Collagen fibers are flexible, but very inelastic
with extremely high tensile strength.

25. Reticular fibers
o Reticular fibers are very thin (diameters
between 0.5 - 2m) and are not visible in
normal histological preparations after
regular staining (H & E), however they can
be visualized and stained black after
impregnation with silver salts.
oThis affinity for silver is called
argyrophilia.

26. oReticular fibers are also stained with the
PAS reaction due to the high content of
glycoproteins associated with the fibers (6-
12% hexoses as opposed to 1% in
collagen fibers).
oIt is now recognized that reticular fibers
are a special form of collagen (Type III).

27. o Reticular fibers form fine-meshed networks
around cells and cell groups.
o in diverse organs. They are abundant in
lymphatic organs (lymph nodes, spleen),
smooth muscle (in the sheath surrounding each
myocyte), in endoneurium (connective tissue
surrounding peripheral nerve fibers), and
supporting epithelial cells of several glands
(liver, endocrine glands).

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Reticular fibers

30. Elastic fibers
o Elastic fibers, as the name suggests, are highly
elastic and stretch in response to tension.
o In particular they are formed from the protein
elastin.
o The amino acid composition of elastin, similar
to collagen, is rich in glycine and proline, but in
addition has two unusual amino acids,
desmosine and isodesmosine.
o Elastic fibers also have a high content of
valine.

31. oElastic fibers are very prominent in elastic
tissues such as the elastic ligaments.
oWhen present in high concentration, the
elastin imparts a yellow color to the tissue.
The elastic laminae of arterial blood
vessel walls are composed of a non-
fibrillar form of elastin.
oSites: Vertebral ligament, Larynx and
Elastic arteries.

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Elastic Fibers
Aorta is the example

33. CONNECTIVE TISSUE CELLS
Fibroblasts
o Fibroblasts are the most common cell type
found in connective tissue.
o The term "fibroblast" is commonly used to
describe the active cell type, whereas the more
mature form, which shows less active synthetic
activity, is commonly described as the
"fibrocyte".
o Fibroblasts are elongated, spindle-shaped cells
with many cell processes.

34. o They have oval, pale-staining, regular nuclei
with prominent nucleoli.
o Abundant rough endoplasmic reticulum and
active Golgi bodies are found in the cytoplasm.
o Fibroblasts synthesize collagen, reticular and
elastic fibers and the amorphous extracellular
substance (including the glycosaminoglycans
and glycoproteins).

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FIBROBLASTS
o Fusiform shaped
o Most common connective tissue cell
o Produces Collagen
i. Reticular fibers
ii. Elastic fibers
iii. Extra cellular matrix

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FIBROBLASTS

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Fibroblasts
Fusiform cell with elliptical nuclei

38. Macrophages
o Macrophages show pronounced
phagocytotic activity.
o This can be demonstrated following injection
of vital dyes such as trypan blue or Indian ink
and the uptake of the particulate matter.
Macrophages originate from monocytes (from
precursor cells in bone marrow), which migrate
to connective tissue and differentiate into
tissue macrophages.

39. o the various macrophages of the body are
grouped in a common system called the
Mononuclear Phagocyte System (MPS).
o A wide range of macrophages are included in
the MPS and include : Kupffer cells of the
liver, alveolar macrophages of the lung,
osteoclasts, microglia etc.

40. o The main functions of macrophages are
ingestion by phagocytosis of microorganisms
(bacteria, viruses, fungi), parasites, particulate
matter such as dust, and they also participate in
the breakdown of aged cells including
erythrocytes.
o The intracellular digestion occurs as a result of
fusion of lysosomes with the phagosome
(ingested body).
o of the foreign body and sites of inflammation

41. o Macrophages are normally long-lived and
survive in the tissues for several months.
o In some cases where a foreign body (such as a
small splinter) has penetrated the inner tissues
of the body, several macrophages may fuse
together to form multinuclear foreign body
giant cells.
o These large cells accumulate at sites of
invasion.

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Macrophages /Histiocytes
o Resembles Fibroblasts
o Phagocytic
o Ingests Bacteria, cell debris and other
foreign matter

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MACROPHAGE

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MACROPHAGE

45. Mast cells
o Mast cells are oval or round cells (20-30m
diameter) in connective tissue characterized by
cytoplasm packed with large round basophilic
granules (up to 2m diameter).
o The granules are stained metachromatically
(purple after toluidine blue staining).
o Two of the main components of mast cell
granules are histamine and heparin.

46. o The granules of mast cells are released in
inflammatory responses.
o Mast cells are abundant in loose connective
tissue (especially adjacent to blood vessels), in
the dermis, and in the lamina propria of the
respiratory and digestive tracts.

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MAST CELL
o Spherical to round
o Sites: CT of Skin, Digestive tract and respiratory tract
o Functions: Secrets Heparin and Histamine
Heparin is anticoagulant and Histamine is mediator of
inflammation

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Mast cell

49. Plasma cells
o are responsible for antibody production.
o These large cells have eccentric nuclei, basophilic
cytoplasm (much rough endoplasmic reticulum
associated with protein synthesis) and well-
developed Golgi bodies.
o Plasma cells are relatively short-lived (10-20 days)
and are found in sites of chronic inflammation or
sites of high risk of invasion by bacteria or foreign
proteins (such as the lamina propria of the
intestinal and respiratory tracts).

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o Sites :Respiratory and Digestive tract
o Arises from Lymphocytes
o Functions: Secretes antibodies into
circulation
Participate in the defense
mechanism

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Plasma cell
Almost oval shape and large, offset nucleus with chromatin
clumped in a "clockface" pattern, and an adjacent pale patch of
clear cytoplasm.

52. Leukocytes
o The white blood corpuscles are commonly
found in connective tissue.
o They migrate from the blood vessels to the
connective tissue, especially to sites of injury or
inflammation.

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o Neutrophils: Bacterial invasion
o Eosnophils: Allergic reaction
o Basophils:Heparin and
histamines
o Lymphocytes: Defense
o Monocytes: Defense

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Adipose cells
o Single or in groups
o Forms adipose tissue
o Functions: 1. stores fat
2.Protective packing material

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Classification of Connective
tissue
1. Connective tissue proper
2. Specialized Connective Tissue
3. Supportive Connective Tissue

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Classification of Connective
tissue proper
1. Loose Connective tissue
2. Dense connective tissue
irregular
Regular

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Specialized Connective tissue
o Adipose tissue
o Blood
o Bone
o Cartilage
o Lymphatic tissue
o haemopoetic tissue

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Supportive Connective tissue
1. Cartilage
2. Bone

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Loose connective tissue
(Cellular Connective tissue)
o Abundance of cells
o Loosely arranged fibers
o Abundant Ground Substance
Sites: Beneath the epithelia that line the
internal surfaces of the body.

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Fibroblasts seen in plenty

63. Dense Connective Tissue
• Dense irregular connective tissue(variable
orientation of fibers)
• Dense Regular connective tissue( Fibers are
arranged in orderly manner)
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64. Dense Irregular Connective
tissue
o Abundance of fibers and few cells
o Sparse cell population
o Provides significant strength(note high content
of collagen fibers)
o Sites: Submucosa in the intestinal part Skin
Dermis.
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Dense irregular connective
tissue
Note the skin with irregular connective tissue

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Tendon
Note the arrangement of regular pattern
with Fibroblasts

67. Dense Regular Connective
Tissue
oOrderly and densely packed arrays of fibers
and cells.
eg: Tendons, ligaments and
aponeurosis
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CARTILAGE

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Cartilage basics
o Special form of connective tissue
o Main function is to support soft tissues
o Consists of cells and matrix
o Matrix contains collagen(Type 2) or elastic
fibers which gives the cartilage firmness
and resilience.
o Cartilage exhibits tensile strength, provides
structural support and allows flexibility
without distortion.

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o Cells: Chondrocytes
o Highly specialized ECM
o Avascular
o Matrix is solid and firm.
o Glycosaminoglycans in the matrix permits
diffusion of substances.
o Hyaluronic acid makes it well adapted for
weight bearing capacity(Synovial joints)

72. Cartilage Matrix(GAG)
o Hyaluronic acid
o Chondrotin Sulfate
o Keratan Sulfate
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Hydrated matrix explains the resilence of the
cartilage

73. Classification
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1. Hyaline
2. Elastic
3.Fibrocartilage

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Hyaline Cartilage
Homogenous matrix, small nests of chondrocytes,
surrounding perichondrium
Lacunae

75. Sites
o Articular surface of bones
o Costal cartilages
o Trachea
o Nose
o Larynx
o Bronchus
o Embryo: Skeletal model for most bones
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Elastic cartilage
Numerous elastic fibers

78. Sites
o External Ear
o Auditory Tube
o Epiglottis
o Larynx
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Fibrocartilage

81. Sites
o Intervertebral Disc
o Symphisis Pubis
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83. Growth of cartilage
o Appositional growth(From perichondrium)
o Interstitial growth(From division of
chondrocytes within their lacunae)
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84. Bone
o Specialized form of connective tissue
o Cells, fibers and matrix
o Mineralized
o Provides attachment
o Provides protection
o Haemopoesis/reservoir of ca and P
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85. Types of Bone
1.Osteoprogenitor cells/Mesenchyme
2.Osteoblasts/Immature bone cells
3.Osteocytes/ Main cell
4.Osteoclasts/ large multinucleated
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86. o Osteons or haversian systems(structural
unit of bone between internal and
external circumferential lamellae)
o Lamellar arrangement
o Lacunae
o Canaliculi
o Central( Haversian Canals)
oPerforating ( Volkmann's canal)
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