Question

Which of the following statements is/are not correct regarding connective tissues? (i) Connective tissues are most abundant and widely distributed in the body of complex animals. (ii) They connect and support other tissues. (iii) They include such diverse tissues as bone, cartilage, tendons, adipose and loose connective tissues. (iv) They form the internal and external lining of many organs. (v) In all connective tissues except blood, the cells secrete fibres of structural proteins called collagen or elastin. (a) (iv) only (b) (v) only (c) (i) and (ii) (d) (iii) and (v)

Short answer

(a) (iv) only

Step-by-step solution

Understanding the function of connective tissues

Begin by recognizing the primary functions of connective tissues, such as connecting and supporting different tissues, and being widely distributed throughout the body of complex animals. They are known to contain various types of cells that can produce extracellular fibers such as collagen and elastin.

Recognizing the diversity of connective tissues

Acknowledge that connective tissues comprise an assortment of tissues including bone, cartilage, tendons, adipose, and loose connective tissues. This will help you confirm statements (i), (ii), and (iii) as correct.

Identifying incorrect statements about connective tissues

Understand that connective tissues do not form the internal and external lining of organs; those functions are primarily associated with epithelial tissues. Additionally, while most connective tissues secrete collagen or elastin fibers, it is important to note that blood is also considered a connective tissue although it does not have fibers as such.

Key concepts

Structural Proteins in Connective Tissue

Connective tissues, integral to the structural integrity of the body, are reinforced by two primary types of structural proteins: collagen and elastin. These proteins are secreted by the cells within the connective tissue matrix and are essential for providing strength, elasticity, and resilience.

Collagen, the most abundant protein in the animal kingdom, is known for its great tensile strength, which imparts rigidity and holds tissues together. Imagine collagen as the sturdy framework of a building, providing the structural support that keeps everything stable.

On the other hand, elastin is more like a rubber band, giving tissues the ability to stretch and then return to their original shape. This is paramount in tissues that undergo frequent stretching, such as blood vessels, lungs, and skin.

Defects or deficiencies in these proteins can lead to diseases such as scurvy, which is caused by a lack of collagen, or Marfan syndrome, associated with defects in elastin. Enhancing the understanding of these proteins is vital for comprehending how connective tissues sustain the stresses and strains of daily activity.

Types of Connective Tissue

Connective tissues are remarkably diverse and can be classified into three broad categories based on their characteristics and functions:

1. Proper Connective Tissues: These include loose connective tissues, such as areolar, adipose, and reticular tissues, which serve as a universal packing material between other tissues, and dense connective tissues, which form tendons and ligaments that neatly connect muscles to bones and bones to each other.

2. Specialized Connective Tissues: Within this group, we find cartilage and bone. Cartilage provides support and flexibility where it's needed, such as in the joints, ear, and nose, while bone is rigid and serves the critical role of supporting body structures and facilitating movement.

3. Fluid Connective Tissues: Blood and lymph fall into this category. Blood is unique as a connective tissue since it does not connect or give mechanical support. Its primary function is transport, delivering nutrients, oxygen, and hormones throughout the body while also removing waste products.

Recognizing the variety of connective tissues is crucial for understanding how they contribute to the overall architecture and operation of the body.

Functions of Connective Tissue

Connective tissues play a multitude of essential roles in the body. They are not only the 'glue' and 'support' for other tissues but perform several other critical functions that maintain the health and well-being of organisms.

For starters, connective tissues provide structural support, as seen in bones of the skeletal system. They are also crucial for protection, for instance, the skull protects the brain, and the rib cage safeguards the heart and lungs.

In addition to this, connective tissues are involved in insulation, where adipose tissue (body fat) helps to retain body heat and serves as an energy reserve. The transport of substances is another key function, exemplified by blood, which transports nutrients, gases, and wastes throughout the body.

To appreciate the significance of connective tissues, one must also understand their role in defending the body against pathogens. Components of the immune system are housed within connective tissues, where they detect and fight infections. These functions collectively highlight the indispensable nature of connective tissues in maintaining the body's integrity and responding to physiological demands.