CDS (II) 2022 General Knowledge · Question 69 of 120

Correct — A, Adipose tissue. Adipose tissue is a loose connective tissue made mostly of adipocytes — cells whose interior is taken up almost entirely by a single droplet of stored lipid, pushing the nucleus and the rest of the cytoplasm out to a thin rim at the edge. Its main role is to store energy in the form of lipids, and it also cushions and insulates the body. It sits under the skin as subcutaneous fat, around the internal organs as visceral fat, in bone marrow, between muscles and in breast tissue. Fat is the body's dense energy store precisely because it is stored almost dry, without the water that accompanies glycogen, so a gram of it carries more than twice the energy of a gram of carbohydrate.

• (b)Red blood cells — Red blood cells are transport cells, not storage cells. A mature human red blood cell has lost its nucleus and most of its organelles to make room for haemoglobin, and it carries oxygen rather than storing fat.
• (c)Muscle tissue — Muscle tissue does hold a small quantity of lipid between and within its fibres, but its own storage fuel is glycogen, and it is contractile tissue rather than storage tissue. The body's fat depot is adipose.
• (d)Epithelial tissue — Epithelial tissue covers surfaces and lines cavities — skin, the gut lining, the ducts of glands. It protects, absorbs and secretes; it is not a storage tissue and it has very little intercellular material.

Animal tissues are grouped into four types — epithelial, connective, muscular and nervous. Connective tissue is defined by having relatively few cells set in a large amount of matrix, and it includes blood, bone, cartilage, tendon, areolar tissue and adipose tissue. Adipose is the specialised storage member of that family: its matrix is minimal and its cells are almost entirely fat droplet, which makes it both an energy reserve and, because fat conducts heat poorly, an insulating layer.

Two of the wrong options are quietly instructive. Blood is also a connective tissue, which surprises candidates the first time they meet it, and it is worth storing that alongside adipose so the category stops feeling like a list of hard structures. Muscle is the option that tempts anyone thinking about where fat is visible on a body; the distinction to hold is between a tissue that uses fuel and a tissue that keeps it. The insulating property is the other half of this topic and has been examined in its own right — subcutaneous fat is a barrier against loss of heat, not against loss of water or against infection.

• Adipose tissue is a loose connective tissue composed mostly of adipocytes.
• Its main role is to store energy as lipids; it also cushions and insulates the body.
• It is found subcutaneously, around viscera, in bone marrow, between muscles and in breast tissue.
• Blood is also classified as a connective tissue, despite having a fluid matrix.
• Muscle stores its own quick fuel as glycogen rather than as fat.

• Placing blood outside the connective tissues; its fluid matrix is still a matrix.
• Choosing muscle because fat is often described as sitting 'in' the body's muscles; muscle's own store is glycogen.
• Treating subcutaneous fat as a barrier to infection or to fluid loss; its documented barrier role is against loss of heat.

As a where-is-it-stored item, as a classify-the-tissue item, or as a function-of-subcutaneous-fat item.

• practice — not a real PYQ

  Which one of the following is classified as a connective tissue?

  • (a)Blood
  • (b)Skin epidermis
  • (c)Cardiac muscle
  • (d)Neuron

  Answer(a) Blood — it has few cells in a large fluid matrix, which is the defining feature of connective tissue.

• practice — not a real PYQ

  The nucleus of an adipocyte is pushed to one side of the cell because

  • (a)the cell has two nuclei
  • (b)a single large lipid droplet fills the interior
  • (c)the cell wall is rigid
  • (d)the cell is constantly dividing

  Answer(b) a single large lipid droplet fills the interior — the stored fat leaves only a thin rim of cytoplasm.