Wednesday, July 29, 2020

Structural Organisation In Animals - Notes | Class 11 | Part 2: Animal Tissues | Connective Tissues




·   It links and supports other tissues/organs.

·   They are most abundant in complex animals.

·   All connective tissues except blood have fibroblast cells. They secrete structural fibrous proteins called collagen & elastin. They give strength, elasticity & flexibility to tissue.

·   The cells also secrete modified polysaccharides (matrix), which accumulate between cells and fibres.

·   Types of connective tissues: Loose, Dense & Specialised.

1. Loose Connective Tissues

In this, cells (fibroblasts, macrophages, mast cells etc.) and fibres are loosely arranged in a semi-fluid matrix.

It is 2 types: Areolar & Adipose.

o   Areolar tissue:

-    Present beneath the skin.

-    It serves as a support framework for epithelium.

Adipose tissue:

-    Seen mainly under skin.

-    Its cells (adipocytes) store fats.

-    Excess nutrients which are converted into fats are stored in this tissue.

2. Dense Connective Tissues

In this, fibres and fibroblasts are compactly packed. 2 types:

o   Dense regular connective tissues:

-    Show regular pattern of fibres.

-    Collagen fibres are present in rows between many parallel bundles of fibres.

-    E.g. tendons & ligaments.

               i.     Tendons: Attach muscles to bones.

              ii.     Ligaments: Attach one bone to another.

o   Dense irregular connective tissues:

Irregular pattern of fibres.

-   Fibroblasts & fibres (mostly collagen) are oriented differently.

-   This tissue is present in skin.


3. Specialized Connective Tissues

·   Cartilage:

o  In this, intercellular material (matrix) is solid and pliable (due to chondroitin salts) and resists compression.

o  Cartilage cells (chondrocytes) are enclosed in small cavities within the matrix secreted by them.

o  Most of the cartilages in vertebrate embryos are replaced by bones in adults.

o  Cartilage is present in the tip of nose, outer ear, joints in the vertebral column, limbs and hands in adults.

·   Bone:

o  It has hard and non-pliable matrix rich in calcium salts and collagen fibres which give bone its strength.

o  Bone cells (osteocytes) are seen in spaces called lacunae.

o  Functions:

§ It provides structural frame to the body.

§ Support and protect softer tissues and organs.

§ Limb bones serve weight-bearing functions.

§ Take part in locomotion and movements.

§ Blood cells are produced in bone marrow.

·   Blood:

o A fluid connective tissue containing plasma, red blood cells (RBC), white blood cells (WBC) and platelets.

o Helps in the circulation of various substances.

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