What is Connective Tissue ? Histology | Anjani Mishra

Connective tissue

or

                                             The connecting and supporting tissues

                             Written By Anjani Mishra

Tissue that connects and binds organs/parts or other tissues to maintain their relative position and furnish support and security to the body is called connective tissue (C.T.)

They are sometimes vary soft (Loose C.T.), sometimes firm (Cartilage), sometimes hard as stone (bone). These differences in firmness, hardness, and elasticity are dependent on the nature of the intercellular substances secreted by the cells.

 Fig:- Mesenchyme, Embryo, Chicken

1. Amorphous ground substance,  2, Mesenchymal cell

Composition:

Connective tissue (C.T.) elements or components are;

A. Cells

B. Intercellular substances

         a) Fibres- collagen, reticular, & elastic

         b) Amorphous ground substance (matrix)

•  Glycosaminoglycans
•  Proteoglycans
•   Multiadhesive glycoprotein

C. Tissue fluid (into which the elements are bathed)

[Amorphous- formless substance seen under light microscope, has a definite sub microscopic structure] 

A. CELLS

Fixed cells	Transient cells (Free or wandering)
a) Fibroblast cell	a) Macrophages (Histocytes/clasmocytes)
b) Adipose or fat cell (Adipocytes)	b) Plasma cells
c) Certain macrophages{Kupffer cells of         liver, dust cells of lungs}	c) Mast cells
d) Pigment cells	d) Leukocytes i) Agranulocytes        ii) Granulocytes        Lymphocytes               Neutroplil        Monocytes                   Eosinophil                                             Basophil

FIXED CELLS

a)  FIBROBLAST CELL

Fibro means 'fibre' blast means to 'produce', means fibre producing cells. They are young fibrocytes and very active. Older fibroblasts are called fibrocyte.

• Shape:- The cells are flattened or elongated
• Nucleus:- Ovoid, large
• Nucleolus:- Prominent
• Cell processes:- Many
• They are derived from mesenchymal cell

Mesenchyma: A diffuse network of cells forming embryonic mesoderm that gives rise to the connective tissue, blood & blood vessels, lymphatic system, and cells of reticulo-endothelial (R.E.) system.

                Fig:- Plasma cells, loose connective tissue, lamina propria, jejunum, dog

     1. Eosinophil, 2. Collagen fiber, 3. Neutrophil, 4. Plasma cell, 5. Lymphocyte,                   6. Fibroblast cell

b)  ADIPOSE/FAT CELL/ADIPOCYTE

These cells are fat storing cells. They are large, rounded cells with less cytoplasm, replaced by fat globules appear to be an empty space. The nucleus is pushed at periphery.

Fig:- Macrophages, loose connective tissue (L.C.T.), colon, pig

1. Adipocyte,  2. Macrophage,  3. Collagen fiber,  4.Eosinophil

c)   CERTAIN MACROPHAGES

• Kupffer cells of liver
• Dust cell/alveolar cell
• Microglia cells in CNS
• Osteoclast cells in bone
• Reticular cells in lymphoid tissue

d)  PIGMENT CELLS

They are also called melanocyte as they contain the pigment melanin. Pigment cells have irregular long cytoplasmic processes. The pigments remain either around the nucleus or may dispersed in the cytoplasm.
 Distribution: choroid coat of eye, skin

 Fig:- Nose, horse

1. Stratum basale,  2. Dermis,  3. Melanocyte,  4. Stratum spinosum

TRANSIENT CELLS/FREE/WANDERING CELLS

        a)  MACROPHAGES (Histocytes)

They are large irregular cells containing one or more nuclei. The nuclei are oval or kidney shaped. Some are fixed and some are motile or free.

They are phagocytic in nature, sometimes a group of phagocytic cells unite together to form a "foreign body giant cell" to engulf larger particles and therefore called, big eaters or macrophages.

They derive from bone marrow precursor cells that divide to produce monocyte.

                      

       b)  PLASMA CELL

Plasma cells are large oval cells, present in most C.T. cytoplasm is basophilic due to rich R.E.R. Nucleus is spherical, eccentrically placed, containing compact chromatin materials. This chromatin gives the nucleus of a plasma cell, the appearance of a clock-face, or the cart wheel.

They are responsible for the synthesis of antibody and helps in the defense mechanism, of the body.

They are derive from B-lymphocyte

      c)  MAST CELL

They are large, round or oval C.T. cells filled with basophilic secretory granules in the cytoplasm. The nucleus is small, spherical, centrally located.

They are responsible for the production of heparin, histamine. Heparin acts as an anticoagulant where as histamine helps in smooth muscle contraction and allergic condition.

They are derive from bone marrow.

Fig:- Mast cells, loose connective tissue (L.C.T.), lip, cat

1. Mast cell,  2. Fibroblast cell,  3. Epithelium, lip

 d)  LEUKOCYTES 

i)   Agranulocyte (mononuclear leukocytes)

Lymphocytes (60-70%) megakaryocyte

They are white blood cells circulating in blood. They contain large spherical nucleus,

which occupies almost the entire cell. A small amount of cytoplasm found around the nucleus. The cytoplasm is slightly basophilic and the diameter is 6-18 mm.

Responsible for Ab production

Fig:- Blood, pig

1. Lymphocyte,  2. Monocyte,  3. Platelet

Monocyte (3-5%)

They are bone marrow-derived agranulocytes, with 12-20 mm in diameter.

The nucleus is large horse shoe-shaped, or kidney shaped. The cytoplasm is basophilic.

Responsible for phagocytic function

Fig:- Blood, cat

1. Monocyte

ii) Granulocytes (Polymorphonuclear leukocytes)

Neutrophil (30-35%) pus cell

These are most numerous of the leukocytes about 12-15 mm in diameter. The cytoplasm contain fine granules with nuclei having 2-5 lobes (usually 3 lobes) link to each other by thin nuclear extensions.

They are responsible for phagocytic function, especially bacteria and small particles, and hence it is called 'microphage'.

 Fig:- Buffy coat, cat

 1. Basophil, 2. Eosinophil, 3.  Neutrophil, 4. Lymphocyte, 5. Platelet

Eosinophils (2-4%)

• These are much less than neutrophils about same size, but with a characteristic bilobed nucleus and many large red "Specific granules" (about 200/cell) that are stained by eosin.
• They are attracted to the sites of allergic inflammation and parasite infection.

Basophil (0.5-1%)

• These cells are very less in number. They are about 12-15 mm in diameter. Their nucleus is  divided into two or more irregular lobes.
• The cytoplasm contain coarse spherical granules which is variable in size. Some granules overlie the nucleus. They stain dark with basic dye.
• These granules contain heparin, histamine, platelet activating factor etc.

 B. INTERCELLULAR SUBSTANCES

a) Fibers- The connective tissue fibers are hair or thread like structure found in the matrix of C.T. either arranged in bundles or in branched form. Three main types of connective tissue fibers are;

i) Collagen fiber

They consists of very fine fibrils (0.3-0.5um), which are smooth, unbranched, and usually wavy. Their chief constituent is the protein collagen (albuminous substances). There are more than 20 types of collagen in animal body. Collagen is the most abundant protein in the human body. It gives varying degress of rigidity, elasticity, and strength. They swell in acid and alkali and gradually dissolve.

Distribution: 

   Skin, bone, cartilage, Smooth muscle, basal lamina etc.

Fig:- Loose connetive tissue, mesentery, cat

1. Fibroblast cell,  2. Collagen fiber,  3. Elastic fiber,  4. Mast cell, 5. Erythrocyte in capillary

ii) Reticular Fiber

They are extremely thin (0.5-2um) which are branched and form no bundles, but latice-like network. They are considered as immature collagen fiber or mainly of collagen type III. They are more resistant to boiling, acids & alkalies than collagen fibers.
(Note:- Latice-like- A network formed by structure interwined usually at right angle with each other).

Distribution:

• Haematopoietic organs, such as bone marrow, lymphnode, spleen
• Parenchymal organs, such as liver, kidney, lungs, endocrine glands
• Intestinal muscle layers
• Uterus

iii) Elastic fiber

They may be very fine or very thick (18um). They are also branched but do not form bundles. They anastomose with other fibers to form an irregular network. They are elastic in nature that is they are extensible and return after stretching to their former length.

Their principle constituent is the protein elastin (amino acids) and microfibrils (glycoprotein). They are resistant to boiling, acid and alkalies.

Distribution:

•  Ligamentum nuchae
• Arterial wall
•  Bronchi & bronchioles
• Interalveolar septa

Classification of C.T.

Adult C.T.                                                                               Embryonic C.T.

     A.  Connective tissue proper

i)                   Loose C.T.                                                      - Fascia

ii)                 Dense C.T.      –Irregular                                - Dermis

 –Regular                                  - Tendon, ligament, Aponeurosis

     B. Special C.T.

i)                   Reticular         - Bone marrow, lymphnode 

ii)                 Adipose           - subcutaneous tissue

      C. Cartilage

i)                   Hyaline           - Costal cartilage, trachea

ii)                 Fibrous            - Intervertebral disc

iii)               Elastic             - External ear, epiglottis

      D..Bone

i)                   Cancellons       - Extremities of long bone (spongy/soft bone)

ii)                 Compact          - shaft of long bone 

 Fig:- Mucous connective tissue (embryonic connective tissue), umbilical cord

            1. Amorphous ground substance,  2. Collagen fiber,  3. Fibroblast cell

A) CONNECTIVE TISSUE PROPER 

i) Loose C.T.

It is a very common type of C.T., sometimes called areolar connective tissue.

It consists of all main components of C.T., i.e. cells, fiber and ground substances

Cell: The most common cells are fibroblasts and macrophages.

Fiber: Collagen, reticular & elastic fiber

Ground substance: Moderate in amount which gives a delicate consistency to L.C.T.

Fig:-Loose and dense irregular connective tissue, dermis, cow

1. Loose connective tissue,  2. Fibroblast cell,  3. Collagen fiber,  4. Dence irregular connective tissue,  5. Eosinophil

Distribution:

•  Serous lining of peritoneum & pleural cavities
•  Mucous membrane that lines the hollow organs
•  Papillary layer of dermis, hypodermis
•  Sub-cutaneous tissue where fat is absent
•  Beneath the epithelial tissue.

 ii) Dense C.T.

It is composed of all the components of L.C.T., but there are fewer cells and a clear predominance of collagen fiber over ground substance.

A/to the arrangement of fibers, this tissue can be divided into two groups, i.e, irregular and regular dense C.T.

It appears white in colour due to richness in collagen fiber.

It is less flexible and  more resistant to stress than L.C.T.

Irregular dense C.T.

When the collagen fibers are arranged in bundles without a definite orientation, the dense C.T. is called irregular dense C.T.

This tissue often found closely associated with L.C.T.

Distribution:

• Dermis of skin
• Fibrous capsule of spleen, testis, ovary, kidney & lymph nodes
• Sub-mucosa of digestive tract
• Periosteum, perichondrium

Regular dense C.T.

When the bundles of collagen fibers are arranged in a definite pattern, the dense C.T. is called regular dense C.T.

Fibroblasts are the principal cells, although they are quite few in amount.

Have enormous tensile strength.

 Fig:- Dense regular connective tissue, tendon, nose,  pig

1. Tendon, l.s.
2. Fibroblast cell
3. Tendon, x.s.

Distribution:

• Tendon
• Ligament
• Aponeurosis

B) SPECIAL C.T.

i)  Reticular C.T.

It is a specialized C.T. consists of reticular fibers of type III collagen produced by specialized fibroblast cells called reticular cells.

Individual reticular fibers form delicate three-dimentional networks, that support cells in reticular tissue.

This create a sponge like structures within which cells and fluid are freely mobile.

Fig:- Reticular tissue, lymphnode, cow

1. Reticular fiber,  2. Lymphocyte

Distribution:

• Bone marrow
•  Lymphnode
•  liver
•  spleen

ii)  Adipose C.T.

It is also specialized type of C.T. in which adipose cell (Adipocytes) are predominate.

Adipose cells are found isolated or in small groups. They are found in large aggregates mostly. They are separated into lobes and lobules by the C.T. septa. Individual cells are surrounded by a network of reticular fibers.

Each adipose cell contains a large droplet of fat and the nucleus is pushed towards the periphery and is flattened. 

 Fig:- Adipose tissue, soft palate, cow

1. Adipocyte

Distribution:

•   Sub-cutaneous fat
•   Intra abdominal fat
•  Surrounding the major joints

C)  CARTILAGE

i)                  i)  Hyaline cartilage (most common in the body)

The word hyaline is derived from Greek word "hyalos" means glass. It has translucent glass like appearance and contain type II collagen.

• Fresh hyaline cartilage is bluish-white and translucent
• It is characterized by small aggregation of chondrocytes embedded in the matrix of ground substances, surrounded by collagen fibers.
• Chondrocytes are elliptical in shape, having large spherical, centrally located nucleus.
• All hyaline cartilage is covered by a layer dense C.T., perichondrium except in the articular cartilage of joints.
•  It consists largely of collagen type-I fibers and contains numerous fibroblasts.
• The fibroblasts are in the inner layer of the perichondrium and are the precursors for chondroblast which divide and differentiate into chondrocyte.

 Fig:- Hyaline cartilage, trachea, cow

1. Territorial matrix
2. Chondrocyte in lacunae
3. Perichondrium, fibrous
4. Perichondrium, chondrogenic
5. Interterritorial matrix

Distribution:

•  Costal cartilage
•  Articular cartilage of joints
•  Thyroid, cricoid and arytenoid cartilage of the larynx
•   Tracheo-bronchial cartilage
•  Nasal Septum

ii)               ii)  Fibrous cartilage

•  Fibro-cartilage is a tissue intermediate between dense C.T. and hyaline cartilage, filled with dense bundles of type I collagen fibers.
• It is also called white fibro-cartilage.
• It is also associated with dense C.T. There is no perichondrium in fibrocartilage.
• It contains  chondrocytes and they are usually arranged in long rows, separated by the   collagen fibers.

Fig:- Fibrocartilage, intervertebral disc, horse

1. Chondrocyte
2. Matrix
3. Collagen fiber

Distribution:

• Intervertebral disc
• Symphysis pubis
• Articular cartilages of bones, eg; mandible, clavicles
•  Sternebrae

iii)            iii)   Elastic cartilage

•  The cartilage that contains branching elastic fibers in the matrix and highly flexible is called  elastic cartilage.
•  It is essentially identical to hyaline cartilage except that it contains an abundance network of fine   elastic fibers in addition to type-II collagen fibers.
•   Elastic cartilage has a yellowish colour due to the presence of elastin in the elastic fibers.
•   It is more flexible than hyaline cartilage. The surface is covered by perichondrium.

Fig:-Elastic cartilage, epiglotis, dog

1. Elastic fiber
2. Chondrocyte in lacunae

Distribution:

• The auricle (pinna) of the external ear
• The auditory tubes/canal
• The epiglottis

D)   BONE

  Bone is the hardest C.T. which forms the framework of the body. It is composed of;

                - Calcified intercellular material (bony matrix)

                - 3 cell types; osteocytes, osteoclasts & osteoblasts

• The calcified bony matrix is composed of fibers and ground substance.
•   Osteocytes are found in cavities  (lacunae) between layers (lamellae) of bony matrix.
•  Osteoblasts, which synthesize the organic components of the matrix.
• Osteoclasts which are multinucleated giant cells involved in the resoprtion and remodelling of bone tissue as well as phagocytic in nature.
•  There are very thin, cylindrical spaces that perforate the matrix, called canaliculi, through which exchanges between osteocytes and blood capillaries take place.
•   All bones are lined on the external surface by the periosteum, and in the internal surface by the endosteum, which are the layer of C.T. containing osteogenic cells.
•   Minerals deposits in the bony matrix to produce hard structures that protects various organs.
•   Bone contains a central cavity, the marrow cavity, which contains bone marrow.

Fig:- Compact bone, humerus, chicken

1. Haversian Canal
2. Osteocyte
3. Volkmann's Canal  

 If you have any questions you can ask me on :
mishravetanatomy@gmail.com 

Facebook Veterinary group link -  https://www.facebook.com/groups/1287264324797711/ 

Twitter - @MishraVet
Facebook - Anjani Mishra

Website: mishravetanatomy.blogspot.com