CDS Biology · Human Physiology
Tissues and Muscles
The tissues every organ is built from: the epithelium that lines it, the connective tissues that store fat and hold it together, and the three kinds of muscle.
Why this matters
Six CDS questions from 2018 (I) to 2026 (II). Two ask where fat is stored (2018 (I) and 2022 (II)), two ask about the kinds of muscle, one about the lining of the mouth and one about the protein of cartilage.
Concept 1 of 2: Epithelial and connective tissue
A tissue is a group of similar cells doing one job. Epithelium covers and lines: the skin, the inside of the mouth, the gut. Connective tissue joins and supports: bone, cartilage, the tendons and ligaments, the fat under the skin, and even the blood. Each has its own kind of cell, and the cell names give the answers away once you know them.
Definition
Four kinds of animal tissue: epithelial, connective, muscular and nervous.
Epithelium:
- Squamous: thin, flat cells. Lines the mouth, oesophagus and blood vessels; many layers of it (stratified) form the skin.
- Cuboidal: cube-shaped cells, in kidney tubules and glands.
- Columnar: tall cells lining the intestine; ciliated ones line the windpipe.
Connective tissue:
- Adipose tissue: fat stored in cells called adipocytes, below the skin and around organs.
- Cartilage: flexible, made by chondrocytes in a matrix with collagen fibres (nose, ear, ends of bones).
- Bone: hard, made by osteocytes. Tendons join muscle to bone; ligaments join bone to bone.
- Blood is a fluid connective tissue. A reticulocyte is a young red blood cell.
| Tissue | Where it is found | Its cell or key part |
|---|---|---|
| Squamous epithelium | Lining of the mouth and oesophagus; skin | Thin, flat cellsQ CDS 2022 (I): an injury to the delicate lining of the mouth and oesophagus damages squamous epithelium. |
| Cuboidal epithelium | Kidney tubules, glands | Cube-shaped cells |
| Adipose tissue | Below the skin, around organs | Adipocytes, which store fatQ Asked twice, CDS 2018 (I) and 2022 (II): fat is stored in adipose tissue, in adipocytes. |
| Cartilage | Nose, ear, ends of bones | Chondrocytes, with collagen fibresQ CDS 2026 (II): collagen matters for cartilage and is not a globin. |
| Bone | Skeleton | Osteocytes |
| Blood | Inside the blood vessels | A fluid connective tissue |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
CDS · 2022 · CDS (I) 2022 — General Knowledge · Q15Moderate
Example 1 · Human Physiology · Tissues and Muscles
Suppose, due to an accident, the delicate lining of the mouth and the oesophagus of a person is injured. In this case, which one of the following tissues will be affected ?
Adipocyte stores fat; the other '-cytes' do not
Adipocytes store fat. Chondrocytes make cartilage, osteocytes are bone cells, and a reticulocyte is a young red blood cell.
Collagen is not a globin
Haemoglobin and myoglobin are globins that carry oxygen. Collagen is the fibrous protein of cartilage, bone and tendon, and keratin is the protein of hair and nails.
Concept 2 of 2: The three kinds of muscle
Muscles that move your bones, like the biceps, work when you decide: they are voluntary, and their cells look striped. The muscles in the walls of your gut, bladder tubes and airways work on their own; they are smooth, without stripes. Heart muscle is striped like skeletal muscle but works on its own like smooth muscle, and its cells branch and join so the whole heart beats together.
Definition
Three kinds of muscle:
- Skeletal (striated): voluntary, attached to bones (biceps, triceps). Cells are long cylinders, unbranched and multinucleate.
- Smooth (unstriated): involuntary, in the walls of the gut, ureters, bronchi, blood vessels and the iris of the eye. Cells are spindle-shaped with one nucleus.
- Cardiac: involuntary, only in the heart; it beats rhythmically all through life. Cells are cylindrical, branched and uninucleate, with stripes.
| Feature | Skeletal | Smooth | Cardiac |
|---|---|---|---|
| Control | Voluntary | Involuntary | Involuntary |
| Stripes | Striated | Unstriated | Striated |
| Cell shape | Cylindrical, unbranched | Spindle-shaped | Cylindrical, branchedQ CDS 2021 (I): a cardiac muscle cell is cylindrical, branched and uninucleate. |
| Nuclei per cell | Many | One | One |
| Found in | Biceps and other limb muscles | Ureters, iris, bronchi, gut | HeartQ CDS 2019 (II): the biceps has no smooth muscle; the ureters, iris and bronchi do. |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
CDS · 2021 · CDS (I) 2021 — General Knowledge · Q112Moderate
Example 2 · Human Physiology · Tissues and Muscles
Which one of the following is the structure of a cardiac muscle cell ?
The biceps is skeletal muscle
Organs with walls that squeeze on their own (ureters, bronchi, gut, iris) use smooth muscle. The biceps moves a bone at your command, so it is skeletal.
Branched means cardiac
Only cardiac cells are branched. Skeletal cells are unbranched and multinucleate; smooth cells are spindle-shaped (some options misprint this as 'spinal shaped').
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Epithelial and connective tissue6 rows
| Tissue | Where it is found | Its cell or key part |
|---|---|---|
| Squamous epithelium | Lining of the mouth and oesophagus; skin | Thin, flat cellsQ CDS 2022 (I): an injury to the delicate lining of the mouth and oesophagus damages squamous epithelium. |
| Cuboidal epithelium | Kidney tubules, glands | Cube-shaped cells |
| Adipose tissue | Below the skin, around organs | Adipocytes, which store fatQ Asked twice, CDS 2018 (I) and 2022 (II): fat is stored in adipose tissue, in adipocytes. |
| Cartilage | Nose, ear, ends of bones | Chondrocytes, with collagen fibresQ CDS 2026 (II): collagen matters for cartilage and is not a globin. |
| Bone | Skeleton | Osteocytes |
| Blood | Inside the blood vessels | A fluid connective tissue |
The three kinds of muscle5 rows
| Feature | Skeletal | Smooth | Cardiac |
|---|---|---|---|
| Control | Voluntary | Involuntary | Involuntary |
| Stripes | Striated | Unstriated | Striated |
| Cell shape | Cylindrical, unbranched | Spindle-shaped | Cylindrical, branchedQ CDS 2021 (I): a cardiac muscle cell is cylindrical, branched and uninucleate. |
| Nuclei per cell | Many | One | One |
| Found in | Biceps and other limb muscles | Ureters, iris, bronchi, gut | HeartQ CDS 2019 (II): the biceps has no smooth muscle; the ureters, iris and bronchi do. |
Watch out for (4)
- Adipocyte stores fat; the other '-cytes' do not→ Epithelial and connective tissue
- Collagen is not a globin→ Epithelial and connective tissue
- The biceps is skeletal muscle→ The three kinds of muscle
- Branched means cardiac→ The three kinds of muscle
Test yourself on Human Physiology
15 past CDS questions from this chapter, timed at 15 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.