Connective Tissues Proper Skeletal Tissues Vascular Tissues
Cartilage Bone Blood Lymph
Compact Bone Spongy Bone
Hyaline Fibrous Calcified
Cartilage Cartilage Cartilage
White Fibrocartilage Elastic Cartilage
Areolar Adipose White Fibrous Yellow Elastic Reticular
Tissue Tissue Tissue Tissue Tissue
Connective Tissue Proper
● The connective tissueproperhasasoftgel-likematrix composed of proteoglycans, which are complex carbohydrates linked to proteins. They are of five major types : Areolar, Adipose, white fibrous, yellow elastic and reticular.
● Areolar tissue is the most widely distributed connec-
tive tissue in the body. They are also called loose
connective tissue. It fixes the skin with the muscles, attaches blood vessels and nerves with the surround- ing tissues. It forms the dermis of the skin and sub- mucosa in the wall of the alimentary canal.
● The areolar tissue consists of a transparent jelly-like matrix containing numerous fibres, cells and mucin. ● The white fibres occur in bundles called fascia and
are formed of collagen.
● Collagen is a rope-like protein that can bend but not stretch. These fibres are abundant in tendons, which join muscles to bones, and ligaments join muscles together.
● In genetic disorder called ‘Ehlers–Danlos Syndrome’, weakened collagen fibres in ligaments cause the bones of body joints to dislocate easily.
● The yellow fibres are fewer and thicker than the white fibres. They are straight and occur singly. ● Yellow fibres are flexible, elastic and branched, the
branches join with one another to form an irregular network. They are formed of a protein called elastin, which is resistant to boiling.
● Yellow fibres provide elasticity to the tissue. Collagen fibres formed at the injured site help in tissue repair.
Cells Present in Connective Tissue Matrix
● Fibroblasts are the principal cells of the areolar
tissues. They have abundant euchromatin, nuclei, rough endoplasmic reticulum and Golgi apparatus. ● When the tissue matures and stops growing, the cells
become less active and are called Fibrocytes. They are small and contain acidophilic cytoplasm.
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1609● Macrophages or histiocytes are almost as nume-
rous as the fibroblasts. They are large, long-lived amoeboid cells. They are capable of phagocytosis. Phagocytosis permits them to engulf and digest dead human cells and combat bacteria, viruses and other foreign pathogens that may cause disease.
● Mast cells secrete substances involved in defense
against foreign material or cells. One of these subs- tances—heparin, prevents blood clotting in the blood vessels. Another secreted substance—hista-
mine, causes blood vessels to enlarge in diameter
and become leaky. Both of these substances encourage white blood cells to move out of the blood vessels into the tissue to fight infection.
● Adipose tissue is connective tissue and functions as
storage. It differs from fibrous connective tissues in that it has very little ground substance and few fibres. It contains cells called adipocytes which are specia- lized to store fat.
● Brown adipose tissue (brown fat) comprises cells
whose granular cytoplasm is due to high concentra- tion of cytochromes and whose function appears to release heat in the neonatal mammals. Distributed around neck and between scapulae in hibernating mammals.
● White adipose tissue is distributed widely in the
body.
● The stored fat is largely composed of triglyceride. ● White fibrous tissue is specially rich in white colla-
gen fibres. These are similar but thicker than those found in the areolar tissue. This tissue is very tough and inelastic. It has two forms—cords and sheets. ● White fibres run parallel to form cords, called ten-
dons. They are arranged in bundles bound together by areolar tissue.
● The white fibres lie criscross in one plane to form
sheets. It occurs in the pericardium of heart, dura-
mater of the brain and spinal cord, sclerotic coat and cornea of the eye ball, capsule of the kidney, peri- chondrium of cartilage and periosteum of bone.
Differences between White and Yellow Fibres
White Fibres Yellow Fibres 1. Are abundant, very
fine and wavy.
1. Are fewer, thicker and straight.
2. Occur in bundles called fascia.
2. Occur singly. 3. Are inelastic and un-
branched.
3. Are elastic and bran- ched, branches join to form a network. 4. Formed of a protein
called collagen.
4. Formed of a protein called elastin. 5. Digested by pepsin. 5. Digested by trypsin. 6. Provide tenacity to the
tissues.
6. Provide elasticity to the tissues.
7. Composed of micro- fibrilshavingalternat- ing light and dark bands.
7. Not composed of microfibrils and lack striations.
● Yellow elastic tissue consists mainly of a loose
network of yellow elastic fibres. The fibres are much thicker but similar to those of areolar tissue. The fibroblasts are irregularly scattered.
● Elastic connective tissue has numerous bundles of elastic fibres, which impart their characteristics to the entire tissue, allowing it to stretch without deforming permanently.
● Elastic tissue is found in the walls of body organs that regularly change shape, such as the stomach, the lungs, the blood vessels and even the heart. Elastic tissue are also found in vocal cords and in the liga- ments that connect the bones of the spine.
Differences between Tendons and Ligaments
Tendons Ligaments
1. Are composed of white fibrous tissue.
1. Are composed of yellow elastic tissue.
2. Fibroblasts lie in almost continuous rows.
2. Fibroblasts lie scattered. 3. Are tough and inelastic. 3. Are strong but elastic. 4. Connect skeletal mus-
cles with bones.
4. Connect bones with one another. Also connect other parts together or support an organ.
● Reticular connective tissue has a finely branched
network of reticular fibres. It provides an internal framework of the cells that perform the functions of soft organs, for example, the liver, spleen, lymph- nodes and tonsils. It also forms the lamina propria of the gut wall. The reticular cells are phagocytic and form defense mechanism of the body.
● Skeletal tissues have a tough matrix. They form a rigid framework, which supports the body, protects the more vital organs, provides hand surface for the attachment of the tendons of the muscles and helps in locomotion in collaboration with the muscles. There are two types of skeletal tissue : Cartilage and bone. ● Cartilage has a high concentration of collagen fibres
like dense connective tissue. However, the ground substance of cartilage has a unique chemical com- position and special properties that permit it to absorb large amounts of bound water. This bound water makes cartilage resistant to compression.
● Cartilage lacks blood vessels, nerves and lymphatic vessels in its extracellular matrix. Due to absence of blood vessels, the injuries to cartilage are slow to heal.
● Chondroblast cells of cartilage become chondrocytes when surrounded by ground substance within the lacunae.
● The amorphous matrix (chondrin) contains glycopro- teins, basophilic chondroitin and fine collagen fibres, varying proportions of which determine whether it is
hyaline, elastic, or fibrocartilage.
● The surface of cartilage is surrounded by irregular connective tissue forming the perichondrium.
● The blood vessels that nourish cartilage are all loca- ted in perichondrium. There are three types of carti- lage present in the body, i.e., hyaline cartilage, fibro- cartilage and elastic cartilage.
● Hyaline cartilage is both flexible and strong. Front
part of nose is made of hyaline cartilage. It also covers the ends of many bones, providing a slippery surface for the movement of joints.
● It joins the ribs to the breast bone (sternum).
● Fibrocartilage is tougher and less flexible than hya-
line cartilage. Its collagen fibres are thicker and are arranged in dense bundles.
● Fibrocartilage joins bones together in areas where considerable stress may occur.
● Pads of fibrocartilage form the intervertebral discs between vertebral, where it acts as cushions.
● Elastic cartilages is more elastic and flexible than
any other type of cartilage. It readily recovers its shape after distortion. This cartilage is found in pinna (external ear) and external auditory canal of the ear, epiglottis, eustachian tubes.
● Bone is a living connective tissue composed of a
hard matrix material and bone cells.
● If a bone is kept in an acid for some time, its inorga- nic part is dissolved and organic part is left behind. Such a bone is said to be decalcified.
● Small bones are solid, while long bones have a cavity, the bone marrow cavity.
Differences between Bone and Cartilage
Bone Cartilage
1. Matrix is composed of a tough, inflexible material, the ossein.
1. Matrix is composed of a firm, but flexible material, the chondrin. 2. Matrix is always
impregnated with cal- cium salts.
2. Matrix may be free of or impregnated with calcium salts. 3. Bone cells lie in lacu-
nae singly.
3. Cartilage cells lie in lacunae singly or in groups of two or four. 4. Osteocytes are irregu-
lar and give off bran- ching processes in the developing bone.
4. Chondroblasts are oval and devoid of proces- ses.
5. Lacunae give off cana- liculi.
5. Lacunae lack canali- culi.
6. There are outer and inner layers of special bone-forming cells, the osteoblasts, that pro- duce new osteocytes, which secrete new lamellae of matrix.
6. There are no special cartilage-forming cells. Cartilage grows by division of all chondro- blasts.
7. Matrix occurs largely in concentric lamellae.
7. Matrix occurs in a homogenous mass. 8. Bone is highly vas-
cular.
8. Cartilage is nonvas- cular.
9. Bone may have bone marrow at the centre.
9. No such tissue is pre- sent.
● The substance of bone is distinguishable into 3 regions—periosteum, matrix and endosteum. Marrow cavity contains bone marrow.
● Periosteum covers the bone externally and is a
tough sheath composed of white fibrous tissue. Tendons of the muscles are attached to this sheath. ● Bundles of Collagen fibres, called Sharpey-Schafer
fibres, from the periosteum penetrates the bone to
provide a firm connection between the two and as a firm base for tendon insertions.
● The periosteum contains blood vessels, which send branches into the bone for providing nourishment. It also contains active bone-forming cells, the Osteo-
blasts, which produce new bone material.
● Endosteum lines the marrow cavity. It is composed
of white fibrous tissue and contains the bone-forming cells, which produce new bone material. The long bones thus grow in thickness from two sides.
● Matrix of bone is dense and hard. It is formed of a
protein called Ossein.
● Ossein is the collagen of bone and forms a streng- thening framework in the matrix.
● The hardness and rigidity of bone comes from the minerals primarily calcium and phosphate, which precipitate out of body fluids coating the collagen fibres.
● The main minerals (salts) include calcium phosphate, calcium carbonate, sodium chloride and magnesium phosphate.
● Bones thus contains both inorganic and organic matter.
● The matrix occurs as layers, the lamellae, which are largely arranged in concentric rings around narrow longitudinal cavities—the Haversian Canals.
● In the lamellae are found small fluid-filled spaces, the bone lacunae, which give off fine radiating channels called Canaliculi.
● A Haversian canal together with its lamellae, lacunae and canaliculi forms a Haversian system or Osteon. ● The Haversian canals are interconnected by trans-
verse channels, the Volkmann’s canals.
● In compact bone, the numerous bone cells or osteo-
cytes are embedded in a solid non-living matrix of
calcium phosphate that is deposited on collagen fibres.
● The osteocytes closer to the blood vessels obtain nutrients by diffusion and pass them to more distant osteocytes by means of their slender cellular exten- sions.
● Spongy bones also contain osteocytes, but they are
not arranged around Haversian canals. The bony bars and plates of spongy bone are not wider than a few cells, therefore, each osteocyte has intimate access to red marrow for the exchange of nutrient and wastes.
● Bone removing cells are called osteoclasts. Osteo- clasts are located on the surface of bone and remove bone by secreting enzymes and dissolve the solid calcium phosphate. As a result calcium and phos- phate ions are released in the blood when insufficient calcium and phosphate dietary is consumed.
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1611Types of Bone
● In compact bone, osteocytes are located in lacunae
that are arranged in concentric circles within Haver- sian system.
● Compact bone forms outer cylinder of shafts of long bones of limbs and is typified by Haversian system. Its cavity contains yellow bone marrow.
● Spongy bone is present at the end of long bones
and has entirely different structure.
Differences between Compact and Spongy Bones
Compact Bone Spongy Bone
1. Forms shaft (diaphysis) of long bones.
1. Forms epiphyses of long bones, besides forming skull bones, vertebrae and ribs. 2. Lamellae arranged in
regular Haversian sys- tems.
2. Lamellae arranged as interlacing network. 3. No gaps between
lamellae, hence com- pact bone.
3. Small spaces occur between lamellae, hence spongy bone. 4. Marrow cavity present. 4. Marrow cavity lacking. 5. Marrow cavity has
yellow marrow.
5. Spaces between lamellae contain red marrow.
6. Marrow stores fat. 6. Marrow produces red corpuscles and granu- lar white corpuscles.
● Spongy bone contains numerous bony bars and plates separated by irregular spaces. These spaces contain red bone marrow.
● Spongy bones form vertebrae, flat skull bones, and ends of long bones (epiphyses), typified by the pre- sence of traberculae.
TypesofBonesAccording totheir Source of For- mation
● The process of bone formation is called ossification. Bones are of the following types according to their source of formation—
(1) Cartilaginous or replacing bones—These bones develop from the pre-existing cartilage and particularly replace the cartilage. They are also called endochondrial bones. Examples— Humerus, Femur.
(2) Investing or dermal or membranous bones— These bones develop in the dermis of the integu- ment as thin plate and sink to get attached over the original cartilaginous endoskeleton. Example —Frontal, nasal, vomers and parietal of the skull. (3) Sesamoid bones—These bones are formed in the tendons at the joints. Example—Patella (Knee-cap).
(4) Visceral bones—These bones are formed in organs dissociated from rest of the skeleton. Examples—in the heart of some ruminants and called os cordis. Bone also develops as os
penis in the copulatory organs of most bats,
insectivores and rodents. Small bone also deve- lops as os palpebae in the eye lids of crocodile. ● Blood is a liquid connective tissue. Blood contains
approximately 22% solids and 78% water.
OBJECTIVE QUESTIONS
11. Protein chondrin is found in— (A) Blood
(B) Areolar tissue (C) Bone
(D) Cartilage
12. Which of the following proteins, is not found in the connective tissue ?
(A) Collagen (B) Elastin (C) Ossein (D) Actin 13. Ligaments join—
(A) Muscle to bone (B) Bone to bone (C) Skin to muscles (D) Nerves to muscles
14. Osteoclasts are associated with—
(A) Bone formation (B) Bone breakdown (C) Muscle formation (D) Bone regeneration
15. The mast cells are found in— (A) Adipose tissue
(B) Yellow fibrous tissue (C) Areolar tissue (D) White fibrous tissue
16. The camel’s hump is composed of a tissue which provides water when oxidized. It is—
(A) Areolar tissue (B) Adipose tissue (C) Muscular tissue (D) None of these
17. The formation of cartilage is known as—
(A) Chondrogenesis (B) Diapendesis (C) Haemopoisis (D) Ossification
18. A bone which is formed by the transformation of the connective tissue, called—
(A) Replacing bone
(B) Investing bone (C) Cartilage bone (D) Reticular bone
19. The bone of mammals contains longitudinal Haversian canals, which are connected by trans- verse canals, called—
(A) Inguinal canal (B) Bidder’s canal (C) Volkmann’s canal (D) None of these
10. The pericardium of heart is com- posed of—
(A) Areolar tissue (B) Reticular tissue (C) White fibrous tissue (D) Yellow fibrous tissue
ANSWERS
1. (D) 2. (D) 3. (B) 4. (B) 5. (C) 6. (B) 7. (A) 8. (B) 9. (C) 10. (C) ●●●
Lamarckism
Lamarckism is also known as the theory of inheri- tance of acquired characters. Lamarckism is the first theory of evolution, and was proposed by Jean Baptiste de Lamarck (1744–1829), a French biologist. Although the outline of the theory was brought to notice in 1801, but his famous book 'Philosophic Zoologique' was published in 1809, in which he discussed his theory in detail. Lamarck coined the terms 'invertebrates' and 'Annelida'. The term 'Biology' was given by Lamarck and Treviranus. Lamarck also introduced the term 'Vertebrates'.
Lamarckian Postulates or Laws
The complete theory of evolution given by Lamarck (Lamarckism) is popularly known as the inheritance of acquired characters in organisms. It is in the form of four postulates or laws, as follows :
01. The internal forces of life tend to increase the size of an organism, i.e. the whole body and also the diffe- rent parts upto a limit determined by life itself. 02. The formation of a new organ or a part in the body is
the result of a new need or new want, which has arisen and continues to be left by the organism. 03. The development of an organ and its power of action
is directly proportional to its use, continuous and constant use strengthening the organ, while disuse results in its degeneration.
04. All the changes, which organisms acquire during their life time are transmitted to their offsprings by the process of inheritance. It means changes are cumula- tive over a period of time.
The fourth principle that is acquired characters are inherited, is the most attractive and controversial law, now known as 'Lamarckian doctrine'.
A more precise account of Lamarck’s theory may be given by the following factors, which according to him, played an essential role in evolution :
(1) Role of environmental factors—Lamarck be- lieved that various factors like soil, food, temperature etc. causing changes in environment act directly in case of plants, while indirectly in case of animals (since they possess nervous system). The environment influence leads to change in their habits which results in unusual activity of an organ or structure. Lamarck, thus assumed that living organisms react to external conditions and become modified.
(2) Effects of needs or physical wants—Lamarck thought that change of habits may bring about the modi- fication of existing organs or may initiate the formation of new organ.
(3) Use and disuse—The continuous and constant use of organs make them efficient and lead to their better
development, while disuse for a long time make them undeveloped and ultimately lead to their degeneration.
(4) Competition—There is a sort of competition in nature to avoid overcrowding on earth. The stronger orga- nisms try to destroy the weaker ones. The smaller multiply faster, while larger ones slowly, thus a balance is main- tained.
(5) Inheritance of acquired characters—The favou- rably structural changes gained by an individual due to use or disuse during its life time is preserved and are passed on to its offsprings. These changes become more and more pronounced if they are exposed to similar stress of the environment as was faced by their ancestors or parents. Such cumulative effects will finally result in the appearance of new species.
Cross breeding—These various peculiarities pro-
duced in the organisms will always appear in successive generations (provided breeding is confined to such unions only). As a result, crosses between individuals not acqui- ring these peculiarities, result in the disappearance of such characters acquired in particular circumstances.
Isolation—The separation of various generations
brings about their different features, which in the course of evolution, become specialized into particular species.
Analysis of Lamarck’s Theory
First law—The first law of Lamarck is merely the
growth process of the organism with which most scientists agree. The increase in size in living beings is common