Epithelial and Connective Tissues: Quick Revision

A brief note on Epithelial and Connective Tissues. Read it before a test. Try each question at the end before you open its answer.

Epithelial tissue

• Features: cells close together, little matrix, a basement membrane, no blood vessels.
• Simple: one layer. Compound (stratified): more than one layer.
• Squamous: air sacs and blood vessels. Cuboidal: gland ducts and kidney tubules. Columnar: stomach and intestine. Ciliated: bronchioles and fallopian tubes. Compound: skin, mouth, pharynx.
• Diffusion: the rate across a layer is inversely proportional to its thickness.

Junctions and glands

• Tight junction: stops leakage. Adhering junction: cements cells. Gap junction: joins the cytoplasm of cells.
• Gland: cells that secrete. Goblet cell: unicellular. Salivary gland: multicellular.
• Exocrine: product through a duct. Endocrine: no duct, hormones into the fluid around the gland.

Connective tissue

• Parts: cells, fibres and matrix.
• Loose: areolar tissue (fibroblasts, macrophages, mast cells) and adipose tissue (stores fat).
• Dense regular: tendons (muscle to bone) and ligaments (bone to bone). Dense irregular: skin.
• Cartilage: chondrocytes in lacunae, a pliable matrix. Bone: calcium salts and collagen. Blood: plasma with red cells, white cells and platelets.

A worked example

A blood test shows 5000 white cells in each microlitre. How many are in 2 mL of blood?

1. Two millilitres are 2000 microlitres.
2. The number of cells is $5000 \times 2000 = 10\,000\,000$.

Practice with new numbers

A program to try

The program names the tissue that joins two body parts.

Mistakes to avoid

• Saying that epithelium has blood vessels. It has none.
• Swapping tendon and ligament. A tendon joins muscle to bone.
• Forgetting that endocrine glands have no duct.
• Saying that blood is not a connective tissue.

Check yourself

1. Which epithelium lines the air sacs of the lungs?

2. Which junction lets ions pass between two cells?

3. What does a tendon join?

4. Name the matrix of blood.

Sources

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