Course 32.1Lesson 3 of 3

Connective tissue: loose, dense, cartilage, bone and blood

Bone, blood, fat and the tendon at the back of your ankle seem to have little in common. Yet they are all connective tissue, and all have cells in a matrix. This lesson sorts connective tissue into loose, dense and specialised kinds, and takes a close look at cartilage, bone and blood.

about 25 min1 simulation1 practice question

Lesson 3 of 3Show all lessons

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The tissue that links

Think of the packing in a box of fragile things. The packing fills gaps, holds each thing in place and protects it. The connective tissue of the body does the same, and more. It links tissues together, supports them, fills the spaces and, in the case of blood, carries things around.

Every connective tissue has three parts.

Cells. They differ from one kind of tissue to another.
Fibres. The commonest is collagen, which is strong. Elastin gives stretch.
Ground substance, the matrix. In most connective tissues the cells lie in a large amount of matrix. This is different from epithelium, which has very little.

NCERT sorts connective tissue into three groups: loose, dense and specialised.

Six small drawings of connective tissue. Areolar tissue: loose network of fibres with a fibroblast, a macrophage and a mast cell. Adipose tissue: large round cells almost filled with a fat droplet and a nucleus pushed to the edge. Dense regular tissue: rows of parallel thick fibres with flat fibroblasts between them, as in a tendon. Cartilage: round cells in small cavities (lacunae) in a smooth solid matrix. Bone: rings of hard matrix with small cells in cavities around a central canal. Blood: red biconcave cells without a nucleus, a larger white cell with a nucleus, small platelets and a pale fluid plasma around them.

Loose connective tissue

The cells and fibres are loosely arranged in a semi-fluid ground substance.

Areolar tissue lies beneath the skin and supports the epidermis. It has fibroblasts, which make fibres, macrophages, which engulf germs, and mast cells, which release histamine in an allergy.
Adipose tissue lies beneath the skin. Its cells are specialised to store fat. A large droplet fills almost the whole cell and pushes the nucleus to the edge. Fat is a store of energy, and it also insulates the body.

Dense connective tissue

Fibres and fibroblasts are packed tightly, with little ground substance.

Dense regular tissue. Collagen fibres lie in parallel rows with fibroblasts between them. Tendons join skeletal muscle to bone. Ligaments join one bone to another.
Dense irregular tissue. Fibres run in many directions, so it can stand a pull from any side. It is found in the skin.

An easy way to remember: a tendon takes the pull of a muscle, and a ligament holds a joint.

Specialised connective tissue

Cartilage. The matrix is solid but pliable, and it resists compression. The cells, chondrocytes, lie in small cavities called lacunae in the matrix. The cartilage in an embryo is mostly replaced by bone in an adult. It remains in the tip of the nose, the outer ear joints, between the bones of the vertebral column, and in the limbs and hands.

Bone. The matrix is hard, rich in calcium salts and in collagen fibres. The salts give hardness and the collagen gives strength. Bone supports and protects soft organs, and the limb bones help in movement. The bone marrow of some bones makes blood cells.

Blood. Blood is a fluid connective tissue. Its matrix is the liquid plasma, and it holds red blood cells (RBCs), white blood cells (WBCs) and platelets. It is the main circulating fluid, and it carries gases, nutrients, wastes and hormones.

Part of blood	Usual count in an adult	Main work
Red cells	about 5 million in each microlitre	carry oxygen
White cells	about 4000 to 11 000 in each microlitre	defence
Platelets	about 150 000 to 400 000 in each microlitre	clotting

NCERT states 6000 to 8000 for the white cells as the usual average. The wider range above is the one used in medicine. A microlitre is the same as a cubic millimetre.

Plasma is mostly water with dissolved proteins, salts and nutrients. Because the red cells fill less than half of the blood, the plasma is the larger part.

Try it in Python

The program counts the red cells in the blood and finds the plasma.

Practise with new numbers

Common mistakes

Putting a tendon and a ligament the wrong way round. A tendon joins muscle to bone. A ligament joins bone to bone.
Saying that bone is hard because of collagen. Calcium salts give hardness. Collagen gives strength.
Saying that blood is not a connective tissue. It is a fluid connective tissue.
Thinking that cartilage is hard like bone. Its matrix is solid but pliable.
Calling fat cells blood cells. Adipose tissue stores fat. It is a loose connective tissue.

Remember these

Connective tissue: cells, fibres and matrix. It links, supports and fills spaces.
Loose: areolar (fibroblasts, macrophages, mast cells) and adipose (fat). Dense: regular (tendons, ligaments) and irregular (skin).
Specialised: cartilage (chondrocytes in lacunae), bone (calcium salts and collagen) and blood (plasma, RBC, WBC, platelets).

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

Name the three parts of a connective tissue.

Which cells of areolar tissue make fibres?

What does a tendon join, and what does a ligament join?

What makes bone hard, and what makes it strong?

Why is blood called a fluid connective tissue?

References

OpenStax Biology 2e, chapter 33, The Animal Body: Basic Form and Function, section 33.2 Animal Primary Tissues.
NCERT (2023). Biology, Textbook for Class XI, chapter 7, Structural Organisation in Animals.