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HISTOLOGY:

  EPITHELIA AND GLANDS

CONNECTIVE TISSUE PROPER

  CARTILAGE AND BONE
                       Olaleye O.O.
                       2B10
INTRODUCTION
The four basic types of tissues in the body are the:

            •Epithelial tissue

            •Connective tissue

            •Muscular tissue

            •Nervous tissue

These tissue exist and function in close association with one another.
Epithelia
Epithelia are a diverse group of tissues which cover or line all body

surfaces, cavities and

Tubes. They function as interfaces between different biological

compartments. As such, the mediate a wide range of activities such

as;

      •Selective diffusion

      •Absorption and/or secretion

      •Physical protection

      •Containment
They are closely bound to one another by a variety of membrane

specialisations called cell junctions which provide physical strength

and exchange of info and metabolites.

All epithelia are supported by basement membrane which separates

epithelia from underlying supporting tissues and are never penetrated

by blood vessels. Thus, epithelia are dependent on the diffusion of

oxygen and metabolites from adjacent supporting tissues.
Arrangement and structure of Epithelial cells

Epithelium is named according to:

• Shape

• Structure

• Arrangement of cells
Arrangement and structure of Epithelial cells

         • Squamous- thin and flat shaped cells

         • Cuboidal- cube shaped cells

         • Columnar- column shaped cells

         • Simple- single layer of cells

         • Stratified- multilayered cells

         • Pseudo-stratified- false stratified

         • Transitional- stretchable

         • Ciliated- cells possess cilia
Basement Memebrane


The basement membrane is a

thin,    noncellular   region   that

separates the epithelium from

the underlying conective tissue.

Can easily be seen with a light

microscope.
Classification of Epithelia tissues


Epithelium   is   traditionally   classified   according   to   three

morphological characteristics:

   •The number of cell layer: a single layer of epithelial cells is

   termed SIMPLE epithelium, whereas epithelia composed of

   several layers are termed STRATIFIED epithelium
•The shape of the component cells: This is based on appearance of

sections taken at right angles to the epithelial surface.

NB: In stratified epithelia the shape of the outermost layer of cells

determines the descriptive classification. Cellular outline are often

difficult to distinguish, but the shape of epithelial cells is usually

reflected in the shape of their nuclei.
•The presence of surface specialisation such as cilia and keratin:

   an example is the epithelia surface of skin whis is classified as

   stratified squamous keratinized epithelium.

NB: Epithelial maybe derived from ectoderm, mesoderm or

endoderm origin.
Glands Epithelia
Epithelium which is primarily involved in secretion is often arranged into

structures called GLANDS

Glands are merely invaginations of epithelial surfaces which are formed


during embryonic development by proliferation of epithelium into the

underlying tissues
There different types of glands:

Glands which maintain their continuity with the epithelial surface,

discharging their secretions onto the free surface via a duct, are called

EXOCRINE glands.

In some cases, the duct degenerates during development leaving

isolated islands of epithelial secretory tissue deep within other tissues.

The secretory products of such glands, known as ENDOCRINE or

DUCTLESS glands, pass into the bloodstream; their secretions are

know as hormones.
Glands are cells or aggregations of cells whose function is secretion.

Exocrine glands release the secretory product via a system of ducts that


opens upon one of the surfaces of the body which are in contact with the

external world (skin, gastrointestinal tract etc.).
Endocrine glands release their secretory product (typically hormones)


into the spaces between the secretory cells (extracellular space) from


which it enters the bloodstream.
Both endocrine and exocrine glands are developmentally derived from

epithelia, which form a down-growth into the underlying connective tissue.


The   cells   forming   this   down-growth   then   develop   the   special

characteristics of the mature gland.


NB: Exocrine glands maintain the connection with the surface epithelium,

whereas the connection is lost by endocrine glands.
Exocrine glands


Exocrine glands may be classified according to cell number,


and/or the shape and branching pattern of their secretory portions


and ducts.
Unicellular Glands: consist of a single secretory cell. In mammals the


only example of unicellular exocrine glands are goblet cells, which occur


in the epithelium of many mucous membranes. Goblet cells secrete the


glycoprotein mucin, which by the uptake of water is converted into a slimy


substance, mucus.
Multicellular glands: The simplest form of a multicellular gland is a secretory


epithelial sheath - a surface epithelium consisting entirely of secretory cells (e.g.

the epithelium lining the inner surface of the stomach, where the mucous secretion

protects the stomach wall from the acidic contents of the stomach). Other


multicellular glands have their secretory portion embedded in the connective

tissue underlying the epithelium. The secretion is either discharged directly from


the secretory portion onto the epithelium or reaches the epithelium via a duct

system that consists of non-secretory cells.
The secretory portion may have a variety of shapes. Secretory cells


may form

tubes in tubular glands,

acini in acinar glands or


alveoli in alveolar glands
Combinations exist - the pancreas is a tubulo-acinar gland, in which each


section   of   the    secretory   system     has    a   specialized    function.


The precursors of digestive enzymes are produced by the acinar cells. Tubular


cells secrete the alkaline bicarbonate solution which eventually neutralizes the


acidic contents of the stomach that are released into the duodenum.
Multicellular    glands   with   an   unbranched     excretory    duct   are


called simple.


When the excretory duct is branched, it is called a compound gland.


Finally, the part of the gland consisting of secretory cells is branched in a


branched gland.
Secretory Mechanisms

The secretory cells can release their secretory products by one of three


mechanisms:


            • Merocrine secretion


            • Apocrine secretion


            • Holocrine secretion
Merocrine secretion: corresponds to the process of


exocytosis. Vesicles open onto the surface of the cell, and the


secretory product is discharged from the cell without any


further loss of cell substance.
Apocrine secretion: designates a mechanism in which part of the


apical cytoplasm of the cells is lost together with the secretory product.

The continuity of the plasma membrane is restored by the fusion of the


broken edges of the membrane, and the cell is able to accumulate the

secretory product anew. This mechanism is used by apocrine sweat

glands, the mammary glands and the prostate.
Holocrine secretion: designates the breakdown and


discharge of the entire secretory cell. It is only seen in


the sebaceous glands of the skin.
There are two additional mechanisms by which secretory cells can release their


products. Lipid soluble substances may diffuse out of the secretory cell (e.g.

steroid hormone-producing endocrine cells). Transporters (membrane proteins)


may actively move the secretory product across the plasma membrane (e.g. the

acid producing parietal cells of the gastric glands). These secretory mechanisms

may not involve any light microscopically visible specialisations of the cell.
Connetive Tissue Proper


This is the most widespread and abundant type of tissue in the human


body. Its function is primarily to support, anchor and connect various


parts of the body. Although connective tissue exists in a number of


forms,   all   types   have   three   basic   structural   elements   --


cells, fibres and intercellular substance (ground substance).
Connective tissue serves as:

     • Packing

     • Holds the cells of organs together

     • Passes on nutrients to other tissues from the blood

     • And active in fighting disease-causing organisms.

The cells in connective tissue are always well spaced in a thick, fluid base

substance, or matrix, in which there may also be long, thin threads called

fibers.
The most common cell types are fibroblasts, which produce fibres and other

intercellular materials. The two most common types of fibres are:

         • collagen (collagenous)

         • and elastic.

Collagen fibres are for strength while the elastic ones are for elasticity of the

tissue. Both the cells and the fibres are embedded in the intercellular

substance. The consistency of this substance is highly variable from gelatin-

like to a much more rigid material.
The proportions of the cells, fibres, and intercellular substance vary, depending

on a particular nature and function of the connective tissue. For example, a

strong connective tissue needs a greater proportion of the collagen fibres and

fewer cells. An example would be a dense regular connective tissue, which is

found in tendons and ligaments. On the other hand, a connective tissue

composed of mostly cells would not be very strong. An example would be an

adipose (fat) connective tissue.
CLASSIFICATION OF CONNECTIVE TISSUE


       • Connective tissue proper


       • Specialized connective tissues
Connective tissue proper: encompasses all organs and body cavities


connecting one part with another and, equally important, separating one


group of cells from another. This is a very large and diverse group of


tissues and includes adipose tissue (fat), areolar (loose) tissue, and


dense regular tissue, among others.
Specialized connective tissues: this group includes cartilage, bone,


and blood. Cartilage and bone form the skeletal framework of the body


while blood is the vascular (transport) tissue of animals.
Connective tissue proper

Areolar (Loose) Connective Tissue

• Is the most widespread connective tissue of the body.


• It is used to attach the skin to the underlying tissue.

• It also fills the spaces between various organs and thus holds them in


  place as well as cushions and protects them.


• It also surrounds and supports the blood vessels.
• The fibres of areolar connective tissue are arranged in no particular


  pattern but run in all directions and form a loose network in the

  intercellular material. Collagen (collagenous) fibres are predominant.

• They usually appear as broad pink bands.


• Some elastic fibres, which appear as thin, dark fibres are also

  present.
• The cellular elements, such as fibroblasts, are difficult to distinguish in the

  areolar connective tissue.     But, one type of cells - the mast cells are

  usually visible.

• They have course, dark-staining granules in their cytoplasm.

• Since the cell membrane is very delicate it frequently ruptures in slide

  preparation, resulting in a number of granules free in the tissue

  surrounding the mast cells.

• The nucleus in these cells is small, oval and light-staining, and may be

  obscured by the dark granules.
Adipose Connective Tissue

The cells of adipose (fat) tissue are characterized by a large internal fat droplet,

which distends the cell so that the cytoplasm is reduced to a thin layer and the

nucleus is displaced to the edge of the cell.

These cells may appear singly but are more often present in groups.

When they accumulate in large numbers, they become the predominant cell

type and form adipose (fat) tissue.

Adipose tissue, in addition to serving as a storage site for fats (lipids), also pads

and protects certain organs and regions of the body.          As well, it forms an

insulating layer under the skin which helps regulate body temperature.
Dense (Fibrous) Regular Connective Tissue

•   Dense connective tissue is characterized by:


•   an abundance of fibres with fewer cells, as compared to the loose


    connective tissue.


•   It is also called fibrous or collagenous connective tissue because of the


    abundance of collagen (collagenous) fibres.


•   Little intercellular substance is present.
• Furthermore, in this tissue type, the fibres are organized in a regular, parallel

  pattern. Hence, the name – dense regular (fibrous or collagenous)


  connective tissue.

• In addition to the tendons, this type of tissue is also found in ligaments.


  Hence, the function of this tissue is to anchor skeletal muscle to bone, to

  attach bone to bone as well as to stabilize the bones within a joint.


  Fibroblasts are the only cells visible, and are arranged in rows between the

  fibres. These fibroblasts function to lay down or create the fibres of the tissue
Cartilage: Specialized Connective Tissues

Cartilage is a somewhat elastic, pliable and compact type of connective

tissue.

It is characterized by three traits:

              • lacunae,

              • chondrocytes,

              • a rigid matrix.

The matrix is a firm gel material that contains fibres and other

substances.
There are three basic types of cartilage in the human body:

         • hyaline cartilage,

         • elastic cartilage and


         • fibrocartilage.
The most common type of cartilage is the hyaline cartilage.

Most of the skeleton of the mammalian fetus is composed of hyaline cartilage.

As the fetus ages, the cartilage is gradually replaced by more supportive bone.

In the mammalian adult, hyaline cartilage is mainly restricted to:

    • the nose,

    • trachea,

    • Bronchi,

    • ends of the ribs,

    • and the articulating surfaces of most joints
The function of the hyaline cartilage is to provide

slightly flexible support and reduce friction within

joints. It also provides structural reinforcement.
The matrix appears as a smooth, solid, blue or pink-coloured

substance. Fine protein fibres, are embedded in the matrix, but

they are not visible with the light microscope since they do not

stain well.

The large cartilage cells called chondrocytes, are trapped within

the matrix in spaces called lacunae (singular, lacuna).

Cartilage is a non-vascular tissue. As such, the chondrocytes rely

on blood vessels in the tissue surrounding the cartilage for nutrient

supply and waste removal.
BONE

Bone is the main component of the skeleton in the adult human.

Like cartilage, bone is a specialised form of dense connective tissue.

Bone gives the skeleton the necessary rigidity to function as attachment

and lever for muscles and supports the body against gravity.

Two types of bone can be distinguished macroscopically:

    • Trabecular or cancellous or spongy bone

    • Compact bone
Trabecular or cancellous or spongy bone consists of delicate bars


and sheets of bone, trabeculae, which branch and intersect to


form   a   sponge   like   network.   The   ends    of   long   bones


(or epiphyses) consist mainly of trabecular bone.
Compact bone does not have any spaces or hollows in the bone matrix


that are visible to the eye. Compact bone forms the thick-walled tube of


the shaft (or diaphysis) of long bones, which surrounds the marrow cavity


(or medullary cavity). A thin layer of compact bone also covers the


epiphyses of long bones.
Bone is, again like cartilage, surrounded by a layer of dense connective


tissue, the periosteum.

A thin layer of cell-rich connective tissue, the endosteum, lines the surface of


the bone facing the marrow cavity.


Both the periosteum and the endosteum possess osteogenic potency.

Following injury, cells in these layers may differentiate into osteoblasts (bone


forming cells) which become involved in the repair of damage to the bone.
Compact Bone

Compact bone consists almost entirely of extracellular substance, the matrix.

Osteoblasts deposit the matrix in the form of thin sheets which are

called lamellae.

Lamellae are microscopical structures.

Collagen fibres within each lamella run parallel to each other.

Collagen fibres which belong to adjacent lamellae run at oblique angles to each

other.

Fibre density seems lower at the border between adjacent lamellae, which

gives rise to the lamellar appearance of the tissue. Bone which is composed by

lamellae when viewed under the microscope is also called lamellar bone.
In the process of the deposition of the matrix, osteoblasts become encased in


small hollows within the matrix, the lacunae.

Unlike chondrocytes, osteocytes have several thin processes, which extend

from the lacunae into small channels within the bone matrix , the canaliculi.


Canaliculi arising from one lacuna may anastomose with those of other lacunae

and, eventually, with larger, vessel-containing canals within the bone.


Canaliculi provide the means for the osteocytes to communicate with each other

and to exchange substances by diffusion.
In mature compact bone most of the individual lamellae form concentric rings

around larger longitudinal canals (approx. 50 µm in diameter) within the bone


tissue.

These canals are called Haversian canals. Haversian canals typically run

parallel to the surface and along the long axis of the bone. The canals and the


surrounding lamellae (8-15) are called a Haversian system or an osteon. A

Haversian canal generally contains one or two capillaries and nerve fibres.
Irregular areas of interstitial lamellae, which apparently do not belong to any

Haversian system, are found in between the Haversian systems.


Immediately beneath the periosteum and endosteum a few lamella are found

which run parallel to the inner and outer surfaces of the bone. They are


the circumferential lamellae and endosteal lamellae.
A second system of canals, called Volkmann's canals, penetrates the


bone more or less perpendicular to its surface.


These canals establish connections of the Haversian canals with the inner

and outer surfaces of the bone.


Vessels in Volkmann's canals communicate with vessels in the Haversian

canals on the one hand and vessels in the endosteum on the other.


A few communications also exist with vessels in the periosteum.
Trabecular Bone

The matrix of trabecular bone is also deposited in the form of lamellae.

In   mature   bones,    trabecular   bone    will   also   be   lamellar   bone.

However, lamellae in trabecular bone do not form Haversian systems.

Lamellae of trabecular bone are deposited on pre-existing trabeculae

depending on the local demands on bone rigidity.

Osteocytes, lacunae and canaliculi in trabecular bone resemble those in

compact bone.

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HISTOLOGY: EPITHELIA AND GLANDS CONNECTIVE TISSUE PROPER CARTILAGE AND BONE

  • 1. HISTOLOGY: EPITHELIA AND GLANDS CONNECTIVE TISSUE PROPER CARTILAGE AND BONE Olaleye O.O. 2B10
  • 2. INTRODUCTION The four basic types of tissues in the body are the: •Epithelial tissue •Connective tissue •Muscular tissue •Nervous tissue These tissue exist and function in close association with one another.
  • 3. Epithelia Epithelia are a diverse group of tissues which cover or line all body surfaces, cavities and Tubes. They function as interfaces between different biological compartments. As such, the mediate a wide range of activities such as; •Selective diffusion •Absorption and/or secretion •Physical protection •Containment
  • 4. They are closely bound to one another by a variety of membrane specialisations called cell junctions which provide physical strength and exchange of info and metabolites. All epithelia are supported by basement membrane which separates epithelia from underlying supporting tissues and are never penetrated by blood vessels. Thus, epithelia are dependent on the diffusion of oxygen and metabolites from adjacent supporting tissues.
  • 5. Arrangement and structure of Epithelial cells Epithelium is named according to: • Shape • Structure • Arrangement of cells
  • 6. Arrangement and structure of Epithelial cells • Squamous- thin and flat shaped cells • Cuboidal- cube shaped cells • Columnar- column shaped cells • Simple- single layer of cells • Stratified- multilayered cells • Pseudo-stratified- false stratified • Transitional- stretchable • Ciliated- cells possess cilia
  • 7. Basement Memebrane The basement membrane is a thin, noncellular region that separates the epithelium from the underlying conective tissue. Can easily be seen with a light microscope.
  • 8. Classification of Epithelia tissues Epithelium is traditionally classified according to three morphological characteristics: •The number of cell layer: a single layer of epithelial cells is termed SIMPLE epithelium, whereas epithelia composed of several layers are termed STRATIFIED epithelium
  • 9. •The shape of the component cells: This is based on appearance of sections taken at right angles to the epithelial surface. NB: In stratified epithelia the shape of the outermost layer of cells determines the descriptive classification. Cellular outline are often difficult to distinguish, but the shape of epithelial cells is usually reflected in the shape of their nuclei.
  • 10. •The presence of surface specialisation such as cilia and keratin: an example is the epithelia surface of skin whis is classified as stratified squamous keratinized epithelium. NB: Epithelial maybe derived from ectoderm, mesoderm or endoderm origin.
  • 12. Epithelium which is primarily involved in secretion is often arranged into structures called GLANDS Glands are merely invaginations of epithelial surfaces which are formed during embryonic development by proliferation of epithelium into the underlying tissues
  • 13. There different types of glands: Glands which maintain their continuity with the epithelial surface, discharging their secretions onto the free surface via a duct, are called EXOCRINE glands. In some cases, the duct degenerates during development leaving isolated islands of epithelial secretory tissue deep within other tissues. The secretory products of such glands, known as ENDOCRINE or DUCTLESS glands, pass into the bloodstream; their secretions are know as hormones.
  • 14. Glands are cells or aggregations of cells whose function is secretion. Exocrine glands release the secretory product via a system of ducts that opens upon one of the surfaces of the body which are in contact with the external world (skin, gastrointestinal tract etc.).
  • 15. Endocrine glands release their secretory product (typically hormones) into the spaces between the secretory cells (extracellular space) from which it enters the bloodstream.
  • 16. Both endocrine and exocrine glands are developmentally derived from epithelia, which form a down-growth into the underlying connective tissue. The cells forming this down-growth then develop the special characteristics of the mature gland. NB: Exocrine glands maintain the connection with the surface epithelium, whereas the connection is lost by endocrine glands.
  • 17. Exocrine glands Exocrine glands may be classified according to cell number, and/or the shape and branching pattern of their secretory portions and ducts.
  • 18. Unicellular Glands: consist of a single secretory cell. In mammals the only example of unicellular exocrine glands are goblet cells, which occur in the epithelium of many mucous membranes. Goblet cells secrete the glycoprotein mucin, which by the uptake of water is converted into a slimy substance, mucus.
  • 19. Multicellular glands: The simplest form of a multicellular gland is a secretory epithelial sheath - a surface epithelium consisting entirely of secretory cells (e.g. the epithelium lining the inner surface of the stomach, where the mucous secretion protects the stomach wall from the acidic contents of the stomach). Other multicellular glands have their secretory portion embedded in the connective tissue underlying the epithelium. The secretion is either discharged directly from the secretory portion onto the epithelium or reaches the epithelium via a duct system that consists of non-secretory cells.
  • 20. The secretory portion may have a variety of shapes. Secretory cells may form tubes in tubular glands, acini in acinar glands or alveoli in alveolar glands
  • 21. Combinations exist - the pancreas is a tubulo-acinar gland, in which each section of the secretory system has a specialized function. The precursors of digestive enzymes are produced by the acinar cells. Tubular cells secrete the alkaline bicarbonate solution which eventually neutralizes the acidic contents of the stomach that are released into the duodenum.
  • 22. Multicellular glands with an unbranched excretory duct are called simple. When the excretory duct is branched, it is called a compound gland. Finally, the part of the gland consisting of secretory cells is branched in a branched gland.
  • 23. Secretory Mechanisms The secretory cells can release their secretory products by one of three mechanisms: • Merocrine secretion • Apocrine secretion • Holocrine secretion
  • 24. Merocrine secretion: corresponds to the process of exocytosis. Vesicles open onto the surface of the cell, and the secretory product is discharged from the cell without any further loss of cell substance.
  • 25. Apocrine secretion: designates a mechanism in which part of the apical cytoplasm of the cells is lost together with the secretory product. The continuity of the plasma membrane is restored by the fusion of the broken edges of the membrane, and the cell is able to accumulate the secretory product anew. This mechanism is used by apocrine sweat glands, the mammary glands and the prostate.
  • 26. Holocrine secretion: designates the breakdown and discharge of the entire secretory cell. It is only seen in the sebaceous glands of the skin.
  • 27. There are two additional mechanisms by which secretory cells can release their products. Lipid soluble substances may diffuse out of the secretory cell (e.g. steroid hormone-producing endocrine cells). Transporters (membrane proteins) may actively move the secretory product across the plasma membrane (e.g. the acid producing parietal cells of the gastric glands). These secretory mechanisms may not involve any light microscopically visible specialisations of the cell.
  • 28. Connetive Tissue Proper This is the most widespread and abundant type of tissue in the human body. Its function is primarily to support, anchor and connect various parts of the body. Although connective tissue exists in a number of forms, all types have three basic structural elements -- cells, fibres and intercellular substance (ground substance).
  • 29. Connective tissue serves as: • Packing • Holds the cells of organs together • Passes on nutrients to other tissues from the blood • And active in fighting disease-causing organisms. The cells in connective tissue are always well spaced in a thick, fluid base substance, or matrix, in which there may also be long, thin threads called fibers.
  • 30. The most common cell types are fibroblasts, which produce fibres and other intercellular materials. The two most common types of fibres are: • collagen (collagenous) • and elastic. Collagen fibres are for strength while the elastic ones are for elasticity of the tissue. Both the cells and the fibres are embedded in the intercellular substance. The consistency of this substance is highly variable from gelatin- like to a much more rigid material.
  • 31. The proportions of the cells, fibres, and intercellular substance vary, depending on a particular nature and function of the connective tissue. For example, a strong connective tissue needs a greater proportion of the collagen fibres and fewer cells. An example would be a dense regular connective tissue, which is found in tendons and ligaments. On the other hand, a connective tissue composed of mostly cells would not be very strong. An example would be an adipose (fat) connective tissue.
  • 32. CLASSIFICATION OF CONNECTIVE TISSUE • Connective tissue proper • Specialized connective tissues
  • 33. Connective tissue proper: encompasses all organs and body cavities connecting one part with another and, equally important, separating one group of cells from another. This is a very large and diverse group of tissues and includes adipose tissue (fat), areolar (loose) tissue, and dense regular tissue, among others.
  • 34. Specialized connective tissues: this group includes cartilage, bone, and blood. Cartilage and bone form the skeletal framework of the body while blood is the vascular (transport) tissue of animals.
  • 35. Connective tissue proper Areolar (Loose) Connective Tissue • Is the most widespread connective tissue of the body. • It is used to attach the skin to the underlying tissue. • It also fills the spaces between various organs and thus holds them in place as well as cushions and protects them. • It also surrounds and supports the blood vessels.
  • 36. • The fibres of areolar connective tissue are arranged in no particular pattern but run in all directions and form a loose network in the intercellular material. Collagen (collagenous) fibres are predominant. • They usually appear as broad pink bands. • Some elastic fibres, which appear as thin, dark fibres are also present.
  • 37. • The cellular elements, such as fibroblasts, are difficult to distinguish in the areolar connective tissue. But, one type of cells - the mast cells are usually visible. • They have course, dark-staining granules in their cytoplasm. • Since the cell membrane is very delicate it frequently ruptures in slide preparation, resulting in a number of granules free in the tissue surrounding the mast cells. • The nucleus in these cells is small, oval and light-staining, and may be obscured by the dark granules.
  • 38. Adipose Connective Tissue The cells of adipose (fat) tissue are characterized by a large internal fat droplet, which distends the cell so that the cytoplasm is reduced to a thin layer and the nucleus is displaced to the edge of the cell. These cells may appear singly but are more often present in groups. When they accumulate in large numbers, they become the predominant cell type and form adipose (fat) tissue. Adipose tissue, in addition to serving as a storage site for fats (lipids), also pads and protects certain organs and regions of the body. As well, it forms an insulating layer under the skin which helps regulate body temperature.
  • 39. Dense (Fibrous) Regular Connective Tissue • Dense connective tissue is characterized by: • an abundance of fibres with fewer cells, as compared to the loose connective tissue. • It is also called fibrous or collagenous connective tissue because of the abundance of collagen (collagenous) fibres. • Little intercellular substance is present.
  • 40. • Furthermore, in this tissue type, the fibres are organized in a regular, parallel pattern. Hence, the name – dense regular (fibrous or collagenous) connective tissue. • In addition to the tendons, this type of tissue is also found in ligaments. Hence, the function of this tissue is to anchor skeletal muscle to bone, to attach bone to bone as well as to stabilize the bones within a joint. Fibroblasts are the only cells visible, and are arranged in rows between the fibres. These fibroblasts function to lay down or create the fibres of the tissue
  • 41. Cartilage: Specialized Connective Tissues Cartilage is a somewhat elastic, pliable and compact type of connective tissue. It is characterized by three traits: • lacunae, • chondrocytes, • a rigid matrix. The matrix is a firm gel material that contains fibres and other substances.
  • 42. There are three basic types of cartilage in the human body: • hyaline cartilage, • elastic cartilage and • fibrocartilage.
  • 43. The most common type of cartilage is the hyaline cartilage. Most of the skeleton of the mammalian fetus is composed of hyaline cartilage. As the fetus ages, the cartilage is gradually replaced by more supportive bone. In the mammalian adult, hyaline cartilage is mainly restricted to: • the nose, • trachea, • Bronchi, • ends of the ribs, • and the articulating surfaces of most joints
  • 44. The function of the hyaline cartilage is to provide slightly flexible support and reduce friction within joints. It also provides structural reinforcement.
  • 45. The matrix appears as a smooth, solid, blue or pink-coloured substance. Fine protein fibres, are embedded in the matrix, but they are not visible with the light microscope since they do not stain well. The large cartilage cells called chondrocytes, are trapped within the matrix in spaces called lacunae (singular, lacuna). Cartilage is a non-vascular tissue. As such, the chondrocytes rely on blood vessels in the tissue surrounding the cartilage for nutrient supply and waste removal.
  • 46. BONE Bone is the main component of the skeleton in the adult human. Like cartilage, bone is a specialised form of dense connective tissue. Bone gives the skeleton the necessary rigidity to function as attachment and lever for muscles and supports the body against gravity. Two types of bone can be distinguished macroscopically: • Trabecular or cancellous or spongy bone • Compact bone
  • 47. Trabecular or cancellous or spongy bone consists of delicate bars and sheets of bone, trabeculae, which branch and intersect to form a sponge like network. The ends of long bones (or epiphyses) consist mainly of trabecular bone.
  • 48. Compact bone does not have any spaces or hollows in the bone matrix that are visible to the eye. Compact bone forms the thick-walled tube of the shaft (or diaphysis) of long bones, which surrounds the marrow cavity (or medullary cavity). A thin layer of compact bone also covers the epiphyses of long bones.
  • 49. Bone is, again like cartilage, surrounded by a layer of dense connective tissue, the periosteum. A thin layer of cell-rich connective tissue, the endosteum, lines the surface of the bone facing the marrow cavity. Both the periosteum and the endosteum possess osteogenic potency. Following injury, cells in these layers may differentiate into osteoblasts (bone forming cells) which become involved in the repair of damage to the bone.
  • 50. Compact Bone Compact bone consists almost entirely of extracellular substance, the matrix. Osteoblasts deposit the matrix in the form of thin sheets which are called lamellae. Lamellae are microscopical structures. Collagen fibres within each lamella run parallel to each other. Collagen fibres which belong to adjacent lamellae run at oblique angles to each other. Fibre density seems lower at the border between adjacent lamellae, which gives rise to the lamellar appearance of the tissue. Bone which is composed by lamellae when viewed under the microscope is also called lamellar bone.
  • 51. In the process of the deposition of the matrix, osteoblasts become encased in small hollows within the matrix, the lacunae. Unlike chondrocytes, osteocytes have several thin processes, which extend from the lacunae into small channels within the bone matrix , the canaliculi. Canaliculi arising from one lacuna may anastomose with those of other lacunae and, eventually, with larger, vessel-containing canals within the bone. Canaliculi provide the means for the osteocytes to communicate with each other and to exchange substances by diffusion.
  • 52. In mature compact bone most of the individual lamellae form concentric rings around larger longitudinal canals (approx. 50 µm in diameter) within the bone tissue. These canals are called Haversian canals. Haversian canals typically run parallel to the surface and along the long axis of the bone. The canals and the surrounding lamellae (8-15) are called a Haversian system or an osteon. A Haversian canal generally contains one or two capillaries and nerve fibres.
  • 53. Irregular areas of interstitial lamellae, which apparently do not belong to any Haversian system, are found in between the Haversian systems. Immediately beneath the periosteum and endosteum a few lamella are found which run parallel to the inner and outer surfaces of the bone. They are the circumferential lamellae and endosteal lamellae.
  • 54. A second system of canals, called Volkmann's canals, penetrates the bone more or less perpendicular to its surface. These canals establish connections of the Haversian canals with the inner and outer surfaces of the bone. Vessels in Volkmann's canals communicate with vessels in the Haversian canals on the one hand and vessels in the endosteum on the other. A few communications also exist with vessels in the periosteum.
  • 55. Trabecular Bone The matrix of trabecular bone is also deposited in the form of lamellae. In mature bones, trabecular bone will also be lamellar bone. However, lamellae in trabecular bone do not form Haversian systems. Lamellae of trabecular bone are deposited on pre-existing trabeculae depending on the local demands on bone rigidity. Osteocytes, lacunae and canaliculi in trabecular bone resemble those in compact bone.