Which one of the following is not a connective tissue?

Correct — C, Smooth muscle. Animal tissue falls into four classes — epithelial, connective, muscular and nervous. Smooth muscle belongs to the third: it is made of spindle-shaped contractile fibres in the walls of the stomach, intestine, blood vessels and iris, and it works without conscious control. Connective tissue is defined by the opposite arrangement — few cells scattered in a large amount of matrix — and ligament, tendon and cartilage are each built that way.

• (a)Ligament — A ligament is connective tissue with very little matrix and considerable elastic strength; it joins one bone to another at a joint.
• (b)Tendon — A tendon is fibrous connective tissue with great tensile strength and limited flexibility, joining muscle to bone. Its bundles are made of the protein collagen.
• (d)Cartilage — Cartilage is connective tissue with a solid but pliable matrix, found in the nose, ear, larynx, trachea and at the ends of long bones.

Connective tissue links, supports and packs other tissues, and its distinguishing feature is an abundant extracellular matrix in which relatively few cells sit. The family is wider than it first appears — bone, cartilage, tendon, ligament, areolar tissue, adipose tissue and blood all belong to it, blood being the odd member with a fluid matrix called plasma.

Three of the four options are structures a candidate meets in a diagram of a joint, so the list tempts you to hunt for the odd one out by location rather than by tissue class. The sorting rule that works is the matrix. Ligament, tendon and cartilage all have one; muscle has contractile fibres instead. Blood is the case worth rehearsing separately, since a fluid matrix still counts as connective tissue.

• The four animal tissue types are epithelial, connective, muscular and nervous.
• Connective tissue has few cells in a large extracellular matrix.
• Bone, cartilage, tendon, ligament, adipose tissue and blood are all connective tissues.
• Tendon joins muscle to bone; ligament joins bone to bone.
• Smooth muscle is involuntary and found in the walls of hollow internal organs; cardiac muscle is involuntary but striated; skeletal muscle is voluntary and striated.

• Sorting by anatomical location instead of by tissue class.
• Forgetting that blood and bone are connective tissues.
• Confusing tendon and ligament, which attach different things.

Asked as an odd-one-out across tissue classes; the sibling papers ask the same classification through blood, cartilage and the protein in tendons.

• practice — not a real PYQ

  Blood is classified as which type of tissue?

  • (a)Epithelial
  • (b)Connective
  • (c)Muscular
  • (d)Nervous

  Answer(b) Connective — its cells are suspended in a fluid matrix, the plasma.

• practice — not a real PYQ

  Muscle is attached to bone by

  • (a)a ligament
  • (b)a tendon
  • (c)cartilage
  • (d)areolar tissue

  Answer(b) a tendon — ligaments join bone to bone, tendons join muscle to bone.