Connective tissue is composed of cells and an extracellular matrix. The extracellular matrix contains fibers such as collagen, elastic fibers, and reticular fibers embedded in a ground substance. Collagen is the most abundant protein and forms fibers that provide strength and structure. Elastic fibers allow tissues to stretch and return to their original shape. Reticular fibers form networks that support organs. The ground substance contains glycosaminoglycans and proteoglycans that lubricate and protect tissues. Fibroblasts are the most common cell type and produce the extracellular matrix.

1. CONNECTIVE TISSUE
FAMILY
Connective tissue
Adipose tissue

2. CONNECTIVE TISSUES
 The general characteristic – the same structure for all type of connective
tissues (cells and extracellular matrix), the same origin – mesenchyme
 Unlike epithelial cells, connective tissue cells are widely seperated by
components of extracellular matrix.
Epithelial
tissue
Closely aggregated polyhedral cells
and very little extracellular matrix
Epithelia are derived from all germinal
layers.
Cells of connective tissue + extracellular matrix [EM]
 Connective tissue proper
 Adipose tissue
 Cartilage
 Bone
 Blood and bone marrow

3. Structurally, connective tissue is composed of three elements:
 Cells
 Fibers −collagen fibers, elastic fibers, reticular fibers
 Ground substance
Fibers + ground substance = extracellular matrix
Cells of connective tissues (CTs)
 Connective tissue − fibroblasts, fibrocytes
 Adipose tissue – adipoblasts, adipocytes
 Cartilage – chondroblasts, chondrocytes
 Bone – osteoblasts, osteocytes
 Blood – formed elements (erytrocytes, leukocytes) produced
in the bone marrow – hematopoietic stem cells

4. The connective tissue cell lineage derived
from multipotential embryonic mesenchyme cells
In the bone marrow

5. Connective tissue (CT)
Cells
A variety of cells with different functions are present in CT
 The cells spend all their live in the tissue

Fibroblasts – originate locally from undifferentiated mesenchymal
cells

Fibrocytes – quiescent fibroblasts
 The cells which reside in the tissue

Mast cells (from hematopoietic stem cells - HSC)

Macrophages (HSC) – monocytes → macrophages

Plasma cells (HSC) – B lymphocytes → plasma cells

Leukocytes (HSC) – live in the tissue for a few days and die

Melanocytes – originate from neuroectoderm (neural crest)

6. Fibroblasts _ Fibrocytes
 Fibroblasts
 the most common cells in
connective tissue
 cells responsible for the
synthesis of extracelullar
matrix components
 an abundant and
irregularly
branched cytoplasm
 ovoid, large and pale
staining nucleus with
nucleolus
 rich in RER and well
developed Golgi complex
 produce the growth factors
→ influence growth and
cells differentiation
 proliferate when the
additional fibroblasts are
 Fibrocytes
 smaller than
fibroblasts
 fewer processes
 smaller, darker,
elongated nucleus
 small amount of RER
Two stages of activity
The active cells
↓
Fibroblasts
The quiescent cells
↓
Fibrocytes

7. The regenerative capacity for the connective tissue
 The regenerative capacity is observed when tissues are destroyed by inflammation
or traumatic injury.
 Fibroblast - the main cell type involved in repair
 During wound healing, the fibrocyte reverts to the fibroblast stage, and its synthetic
activities are reactivated.
Fibroblast
↔
Fibrocyte

8.  Myofibroblasts
 Macrophages
 Mast cells
 Leukocytes
 Plasma cells
 Melanocytes
The cells which reside in the tissue
Myofibroblasts
 The cells with features of fibroblasts and smooth muscle cells (SMC)
 They are observed during wound healing
 They have most of the morphological characteristics of fibroblasts but contain
increased amount of actin microfilaments and myosin and behave like SMC
 The activity of myofibroblasts is responsible for wound closure after tissue
injury – wound contraction

9. φ 10 – 30 µm
Macrophages → the Mononuclear Phagocyte System
 Morphological features reflect functional activity of macrophages:
 they can be recognized by staining and by pseudopodia which are
found only in macrophages
 irregular surface with pleats and protrusions – pinocytotic and
phagocytic activity
 oval or kidney-shaped nucleus located centrally
 well-developed Golgi complex, many lysosomes, prominent rough
endoplasmic reticulum (RER)
 Macrophages derive from bone marrow precursor cells that divide producing monocytes
 Monocytes cross the wall of venules and capillaries to penetrate the connective tissue
 They mature and acquire morphological features of macrophages
 Macrophages are long-living cells, can proliferate locally and may survive for months in
tissues.
 The cells are distributed throughout the body, and in certain region have special names:
 histocytes – the connective tissue proper
 Kupffer cells – the liver
 microglia cells – the central nervous system
 Langerhans cells – the epidermis
 osteoclasts – the bone

10. Macrophages function
 phagocytosis of foreign substances and bacteria
 antigen processing and presentation to other cells
(Antigen Presenting Cells – APC)
 secretion of cytokines and other molecules
 cytokines participate in defensive and reparative functions
 enzymes, eg. collagenase
 removing cell debris and damaged extracellular components
 Macrophages when stimulated
 may increase in size and are arrangement in clusters forming epithelioid cells;
 may fuse to form multinuclear giant cells
 Epithelioid cells and giant cells are found only in pathological conditions.
Multinuclear giant cells

11. Mast cells
derive from progenitor cells in the bone marrow, they have a separate
stem cells than basophilic leukocytes
φ 10 – 13 µm
 Oval to round connective tissue cells
 The cytoplasm is filled with basophilic secretory granules
 Small, spherical nucleus, situated centrally
 Secretory granules of mast cells
 0.3 – 2.0 µm in diameter
 they contain mediators:
 histamine - promotes an increase in vascular permeability
 heparin - (sulfated glycosaminoglycan is blood anticoagulant)
 neutral proteases
 eosinophilic chemotactic factor for anaphylaxis (ECF-A)
 substances not stored in the granules:
 leukotriens (C4, D4, E4)
 slow-reacting substance for anaphylaxis (SRS-A)
 The surface of mast cells contains specific receptors for immunoglobulin E (IgE)
 The connective tissue mast cells
 skin and peritoneal cavity
 10 – 12 µm in diameter
 their granules contain anticoagulant
heparin
 The mucosal mast cells
 the connective tissue of the intestinal
mucosa and lungs
 5 – 10 µm in diameter
 their granules contain chondroitin sulfate

12. Eosinophil chemotactic
factor for anaphylaxis
Mast-cell secretion.
1: The first exposure to an antigen (eg, bee venom), IgE molecules are bound to the surface receptors.
2: After a second exposure to the antigen, IgE molecules bound to surface receptors
are cross-linked by the antigen.
3: These events lead to intracellular fusion of specific granules and exocytosis of their contents.
4: In addition, leukotrienes are produced.
The process of contents granules realizing does not damage the cell, cell synthesizes new granules.

13. Leukocytes
or white blood corpuscles
 the wandering cells of connective
tissue
 they migrate through the walls of
capillaries and postcapillary
venules from the blood to
connective tissue (diapedesis)
Diapadesis
 Granulocytes
 Lymphocytes B and T
Lymphocytes are found in small numbers throughout the connective tissues,
where they perform much of their immunological functions
Lymphocyte B
Lymphocyte B
Plasma cell

14. Plasma cells
 large, ovoid cells with basophilic cytoplasm, very well developed RER
 the Golgi complex and the centrioles occupy pale region in
histological slides
 spherical nucleus, placed excentrically containing compact, coarse
heterochromatin and lighter areas – the configuration resembles the face
of a clock (nucleus having a clock-face appearance)
 Average of plasma cells live is short, 10 – 20 days.
 B lymphocyte → plasma cell → synthesis of immunoglobulins
Plasma cells are widely dispersed throughout the connective tissues.
1] They are particularly abundant in the lamina propria of the alimentary canal
and respiratory passageways.
a} They are also found in the lymphoid organs.
b} They are rarely found in the blood

15. Adipose cells
 Adipose cells, adipocytes, fat cells
 the connective tissue cells for storage of neutral fats or for the production of heat.
Melanocytes
 are derived from neuroectoderm of neural crest
 synthesize and accumulate the melanin
 the skin

16. The extracellular matrix
 Ground substance
 Glycosaminoglycans
 Fibers
 Collagen fibers
 Elastic fibers
 Reticular fibers
 Proteoglicans
 Multiadhesive glycoproteins
Fibers
The connective tissue fibers are formed by proteins that polymerize into elongated structures.
The predominant fiber type is responsible for conferring specific properties of the tissue.
 Collagen fibers
 are formed by protein collagen
 the collagen is the most abundance protein in the human body (30% of dry weight)
 the collagens belong to a family of more than 25 members, produced by several cells type
 the collagens are distinguishable by their molecular composition, morphological features,
distribution, function and pathologies
are acidophilic; stain pink with eosin, blue with Mallory’s stain, green with
Masson’s trichrome stain, red with Sirius red.
eosin
Mallory’s

17.  The cell type responsible for collagen synthesis
 fibroblasts, chondroblasts, osteoblasts
 odontoblasts
 endothelial cells
 vascular smooth muscle cells
 The collagen profile
• the principal amino acids – glycine (33.5%), proline (12%), hydroxyproline (10%)
• amino acids that are characteristic of the collagen – hydroxyproline and hydroxylysine
Collagen types
 Type I − the abundant: skin, tendon, bone, dentin – resistance to tension
 Type II − cartilage, vitreous body – resistance to pressure
 Type III − skin, muscle, blood vessels, frequently together with type I –
structural maintenance in expansible organs
 Type IV − all basement membranes – support of delicate structure, filtration
(chicken-wire organization)
 Type V − fetal tissue, skin, bone, placenta, most interstitial tissues – participate
in type I collagen function
 Type VII – epithelia – anchors skin epidermal basal lamina to underlying stroma
(anchoring fibrils)

18. Collagen is a protein polymer composed of monomeric units of the protein Tropocollagen
Tropocollagen
Three α chains
 elongated protein 280 nm in length and 1.5 nm in width
Collagen gets it's strength from it's structural
arrangement.
a} Collagen is arranged into microfibrils.
b} Microfibrils are arranged into fibrils.
c} Fibrils are grouped into a fiber.
d} Fibers are grouped into a collagen bundle
Schematic drawing of an aggregate of collagen molecules, fibrils, fibers, and bundles.
There is a stepwise overlapping arrangement of rodlike tropocollagen subunits, each measuring 280 nm (1).
This arrangement results in the production of alternating lacunar and overlapping regions (2) that cause the
cross-striations characteristic of collagen fibrils and confer a 64-nm periodicity of dark and light bands when
the fibril is observed in the electron microscope (3). Fibrils aggregate to form fibers (4), which aggregate to
form bundles (5) routinely called collagen fibers. Collagen type III usually does not form bundles.

19. Collagen synthesis
 Procollagen synthesis
 Registration peptides on both
amino-terminal and
carboxy-terminal end
 precursor of tropocollagen
 Hydroxylation of proline and lysine
 peptidyl proline hydroxylase
 peptidyl lysine hydroxylase
Co-factors: O2, Fe, vit. C
Glycosylation of hydroxylysine
 transferases
Mn
Removing of registration peptides
 procollagen peptidases
 tropocollagen
Formation of covalent crosslinks between tropocollagen
molecules
 lysyl oxidase
Cu and O2 ions

20. Vitamin C (ascorbic acid) deficiency lead to the scurvy, disease characterized by
the degeneration of connective tissue.
Lack of vit. C → abnormal hydroxylation of procollagen → synthesis of
defective collagen

21. Reticular fibers
 consist mainly of type III collagen
 extremely thin with diameter between 0.5 to 2 µm
 they form extensive network in certain organs
 stain black by impregnation with silver salts – agyrophylic fibers
 Localization
 are particularly abundant in smooth muscle
 endoneurium
 framework in spleen, lymph nodes, bone marrow
 constitute a network around the cells of parenchymal organ, eg. liver,
endocrine glands
 the wall of arteries
Reticular fibers

22. Elastic fibers
 Elastin – the main component
 Precursor of elastin is proelastin
 Elastin is resistant to boiling, acid and
alkali extraction
 Elastin is hydrolyzed by pancreatic elastase
 Elastin is rich in glycin and proline
 Contains two unusual amino acids –
desmosine and isodesmosine formed by
covalent reaction between four lysine resiudes
 has rubberlike qualities
 stains brown with orcein and violet with
resorcine-fuchsin
 Elastoblasts
 Fibroblasts
 Chondroblasts
 Vascular SMC
 Endothelial cells
Elastin molecules are joined by covalent bonds to generate an extensive cross-linked network.
Because each elastin molecule in the network can expand and contract like a random coil, the
entire network can stretch and recoil like a rubber band.

23. The elastic fibers system
 Oxytalan fibers
 zonule fibers of the eye
 dermis
 do not contain elastin
 consist of a bundle of 10
nm
microfibrils composed of
glycoproteins:
fibromodulin I and II, and
large molecule – fibrillin.
 Elaunin fibers
 around sweet glands
 dermis
 irregular deposits of elastin
between the microfibrils
 mixture of elastin and
microfibrils without
preferential orientation
Microfibrils
Elastin
 Elastic fibers
 the wall of large arteries
 connective tissues
 elastin located centrally
and thin sheath of
microfibrils
 the most numerous
component of the elastic
fibers system

24. Ground substance
 highly hydrated, colorless and transparent complex mixture of macromolecules
 it fills the space between cells and fibers
 it is viscous and acts as lubricant and barrier to the penetration of invaders
 Glycosaminoglycans
 Proteoglycans
 Multiadhesive glycoproteins

25. Glycosaminoglycans (GAGs)
 called mucopolysaccharides
 are linear polysaccharides formed by repeating disaccharide units composed of uronic
acid and hexosamine.
 uronic acid – glucuronic or iduronic acid
 hexamine – glucosamine or galactosamine
 with the exception of hyaluronic acid GAGs are bound covalently to a protein core,
forming proteoglycans
 with the exception of hyaluronic acid all other GAGs are sulfated
 GAGs are intensely hydrophilic and act as polyanions
 dermatan sulfate
 chondroitin sulfate
 keratan sulfate
 heparan sulfate
 hyaluronic acid

26. Distribution of glycosaminoglycans in connective tissue
Glycosaminoglycan
Distribution
Hyaluronic acid
Umbilical cord, synovial fluid, vitreous humor,
cartilage
Chondroitin 4- sulfate
Cartilage, bone, cornea, skin, notochord, aorta
Chondroitin 6- sulfate
Cartilage, umbilical cord,skin, aorta (media)
Dermatan sulfate
Skin, tendon, aorta (adventitia)
Heparan sulfate
Aorta, lung, liver, basal laminae
Keratan sulfate (cornea)
Cornea
Keratan sulfate (skeleton)
Cartilage, nucleus pulposus, annulus fibrosus

27. Proteoglycans
 are composed of a core protein associated with the four main glycosaminoglycans
(without hyaluronic acid)
 proteoglycan (monomer) is three-dimensional structure (can be pictured as test
tube brush)
 Extracellular matrix (EM) proteoglycans
 aggrecan – the most important, the
dominant in cartilage
 syndecan
 fibroglycan
Proteoglycan
monomer
o Functions:
 structural component of EM
 anchoring cells to the EM
 as extracellular and surface proteoglycans
bind many protein growth factors (TGF-β
→ transforming growth factor)
Core protein
Proteoglycan aggregates
 Proteoglycans are degradated by several
cell types (lysosomal enzymes). The
lack of lysosomal enzymes causes
several disorders in humans

28. Multiadhesive glycoproteins
 contain protein moiety with carbohydrates
 play an important role in the interaction between neighboring
adult and embryonic cells
 play role in the adhesion of cells to their substrate
 Fibronectin
 the product of fibroblasts and epithelial cells
 has sites to bind cells, collagen and GAGs, the interactions help
to mediate normal cell adhesion and migration
Protein
 Laminin
 participates in the adhesion of epithelial cells to basal lamina
 Matrix receptors – cell-surface molecules that bind to collagen, fibronectin, laminin
 Integrins – transmembrane linker protein, interact with the cytoskeleton (actin)
 Intracellular proteins – the interaction between integrins, EM, cytoskeleton elements
 Paxilin
 Vinculin
 Talin

29. Types of connective tissue

30. Mesenchyme
 The precursor embryonic tissue for all types of connective tissue
 Stellate undifferentiated cells and ground substance
 The lack of fibers
 Under specific stimuli the cells differentiate into the cells of connective tissue such
fibroblasts, chondroblasts, osteoblasts, blood cells
Embryo head

31. The connective tissue proper
 Loose connective tissue
 the very common type of connective tissue
 fills spaces between groups of muscle cells, supports epithelial tissue, forms layer
sheathing lymphatic and blood vessels.
 is found in papillary layer of dermis, in hypodermis, mucous membranes
 has delicate consistency, it is flexible, well vascularized, not very resistant to stress

32. Dense connective tissue (CT)
 is adapted to offer resistance and protection
 there are fewer cells than loose connective tissue and high amount of collagen fibers
 is less flexible and far more resistant to stress than loose connective tissue
 Dense irregular CT
 the collagen fibers are arranged in bundles without a definite orientation
 the collagen fibers form three-dimensional network
 provide resistance to stress from all directions
 is found in dermis, perichondrium, periosteum
Collagen fibers
Fibrocytes

33.  Dense regular CT
 the collagen bundles are arranged in the definite pattern
 the collagen fibers are alginated with the linear orientation of fibroblasts in response to
prolonged stresses exerted in the same directions
 it is found in tendons
Tendon
 the collagen fibers have parallel, closely packed bundles of
collagen separated by a small quantity of intracellular
ground substance
 fibrocytes have elongated nuclei parallel to the fibers
 the cytoplasm of fibroblasts stains the same color as the fibers
 The primary collagen bundles aggregate into larger bundles –
secondary bundles, enveloped by loose connective tissue with
blood vessels and nerves
Nuclei of fibrocytes
Collagen fibers

34. The connective tissue with special properties
 Elastic tissue
 is composed of bundles of thick parallel elastic fibers
 the spaces between the fibers are occupied by thin collagen fibers and flattened fibroblasts
 is found in yellow ligaments of the vertebrates column
 Reticular tissue
 the very delicate reticular tissue forms three-dimensional network that support cells
 consists of reticular fibers (type III collagen) and specialized fibroblasts named reticular
cells
 reticular tissue create the special microenvironment for hematopoietic organs and
lymphoid organs
Reticular cell
Reticular
fibers

35. The connective tissue with special properties
 Mucous connective tissue
 has a abundance of ground substance rich in hyaluronic acid
 is jellylike tissue containing very few fibers and a more viscous ground substance.
 the cells – mainly fibroblasts
 is found in umbilical cord and is referred to as Wharton’s Jelly
 is found in the pulp of young teeth
Umbilical cord

36. Adipose tissue
 Special type of the connective tissue with predomination of adipose cells
(adipocytes, fat cells)
 Adipocytes
 are found as isolated cells, in small aggregates (adipose tissue)
 Adipose tissue (the largest organ in the body)
 in men of normal weight represents 15 – 30% of the body
 in woman of normal weight = 20 − 25% of the body
Adipose tissue is found in a variety of places
such as:
1] the hypodermis
2] surrounding and protecting certain organs
3] the medullary cavity of long bones
Functions:
1] stores energy
2] insulates the body form heat loss
3] cushions the body and protects delicate
organs (ex; the kidney) from mechanical
trauma
Adipose tissue
 Uniocular adipose tissue
(common or yellow)
 Multiocular adipose tissue
(brown)

37. Uniocular (common or yellow) adipose tissue
 The color varies from white to dark yelow (depends on diet – carotenoids)
 It is found throughout the human body except
 eyelids, the penis, the scrotum, the entire auricle of the external ear (without the lobule)
 The distribution is determined by age and sex
 in the newborn has uniform thickness in the body
 its distribution is partly regulated by sex hormones and adrenocortical hormones
(different distribution in male and female body)
Spherical, isolated, cell
Signet ring cells
Sudan III
Lipid droplet
Lipids are removed
in routine histological
techniques
Nucleus
Cytoplasm
Polyhedral cells
in adipose tissue

38. Uniocular (common or yelow) adipose tissue
 Cytoplasm
 Golgi complex
 mitochondria
 poorly developed RER
 SER
 free polyribosomes
 pinocytotic vesicles
φ 50 – 150 µm
Basal lamina
Vimentin intermediate filament
 Adipose tissue
 is richly vascularized

39. Uniocular (common or yelow) adipose tissue
 Large depot of energy for organism
 Lipids in adipose cells – triglycerides (esters of fatty acids), glycerol
 Adipose cells can synthesize fatty acids from glucose → insulin
 Metabolism of adipose tissue is regulated by hormones
 nonepinephrine, growth hormone, glucocorticoids, prolactin,
corticotropin, insulin and thyroid hormone
 The autonomic nervous system plays important role in mobilization of
fats
Adipose tissue as a secretory organ
 synthesis of several molecules – lipoprotein lipase
 leptin
 protein participating in the regulation of the amount of adipose tissue
in the body and in the food ingestion
 receptor for leptin in the brain and other tissues
 adiponectin
 adipsin
 TNFα (Tumor Necrosis Factor α)

40. Histogenesis of uniocular adipose tissue
 during a finite postnatal period, nutritional
and other influences can result in the increase in
number of adipocytes
 after the period the cells do not increase
in the number
 Adipocytes accumulate more lipids only under
conditions of excess caloric intake (overfeeding)
 The early increase in the number of adipocytes
may predispose an individual to obesity in latter
life

41. Multiocular adipose tissue (brown fat)
 Multiocular tissue cells are polygonal and smaller than
uniocular adipose cells
 The cytoplasm contains
 great number of lipid droplets of various sizes
 spherical and central nucleus
 numerous mitochondria with abundant long cristae
(containing colored cytochromes)
 The cells receive direct sympathetic innervation
 The tissue is rich in capillaries

42. Distribution of multiocular adipose tissue
 The tissue is more abundant in hibernating animals – hibernating gland
 In humans the tissue is important mainly in the first postnatal life (produces heat and
protects the newborn against cold)
 It is greatly reduced in adulthood
In human newborn the multiocular adipose tissue constitutes 2 - 5% of the body weight
 Mainly around the shoulder blades and kidneys

43. Function of the multiocular adipose tissue
 The main function is to produce heat
 The production is stimulated when animals or human newborns are exposed to the cold
environment
 Nerve impulses release epinephrine → the stimulation of lipase in adipocytes → the
release of fatty acid, that are metabolized → heat production (temperature of tissue is
elevated)
 Mitochondria of multiocular adipocytes contain transmembrane protein – thermogenin
 The energy is not used to synthesize ATP but is dissipated as heat
 Warmed blood circulates throughout the body

44. Slides
 Mesenchyme

45.  Mucous tissue
The umbilical cord - Warthon’s jelly
Vein
Arteries

46.  Loose connective tissue
 Nuclei of fibrocytes and others cells
 Collagen fibers
 Elastic fibers
Collagen fibers
Elastic fibers

47.  Dense connective tissue
 Dense regular CT
 Dense irregular CT
Trachea
Tendon
Perichondrium

48.  Adipose tissue
Sudan III
Signet ring cells