Animal tissues: epithelial, connective, muscle and nervous – Diversity of Specialised Tissues (Senior 4 Biology) | Ganzaa

Diversity of Specialised Tissues

Lessons

Senior 4 · Biology

Diversity of Specialised Tissues

4 lessons

Lesson 3 of 4

Animal tissues: epithelial, connective, muscle and nervous

25 min

Four tissues on a skewer

Order a brochette of goat meat in Kigali and you are eating, in one bite, all four basic kinds of animal tissue. The meat is mostly muscle. The tough white strands and the fat between the muscle fibres are connective tissue. Every small blood vessel in the meat is lined by a thin epithelium, and fine nerves once carried signals to the muscle fibres. Animal bodies, from a goat to you, are built from just these four tissue types, combined in different ways.

Definition

Epithelial tissue (epithelium): sheets of closely packed cells, with little material between them, covering body surfaces and lining tubes and cavities; it rests on a basement membrane and has no blood vessels of its own.

Connective tissue: cells scattered in a large amount of non-living matrix (ground substance plus fibres such as collagen and elastin), which supports, binds and protects other tissues.

Muscle tissue: long cells (fibres) containing the proteins actin and myosin, which contract to produce movement.

Nervous tissue: neurones, which carry electrical impulses, and supporting glial cells.

Epithelial tissue

Epithelia are named by the number of layers (simple: one layer; stratified: several) and the shape of the cells at the surface (squamous: flat; cuboidal: cube-shaped; columnar: tall). Figure 1 shows five common kinds.

Epithelium	Where	How its structure suits its function
Simple squamous	Alveoli of the lungs; lining of blood vessels (endothelium)	Very thin, so the diffusion distance for gases is short
Simple cuboidal	Kidney tubules; ducts of glands	Enough cytoplasm and mitochondria for secretion and absorption
Simple columnar with microvilli	Lining of the small intestine	Tall cells hold many mitochondria; microvilli give a huge surface for absorption
Ciliated columnar with goblet cells	Trachea, bronchi, oviducts	Goblet cells secrete mucus that traps dust and bacteria; cilia sweep it away
Stratified squamous	Skin (outer layer, keratinised), mouth, oesophagus	Many layers resist wear; surface cells are rubbed off and replaced from the bottom layer

Worked example 1: how much do microvilli add?

The free surface of a columnar cell from the small intestine is $10\,\mu\mathrm{m}$ by $10\,\mu\mathrm{m}$ . It carries 3000 microvilli, each a cylinder $1\,\mu\mathrm{m}$ long and $0.1\,\mu\mathrm{m}$ in diameter. Estimate how many times the microvilli increase the absorbing surface.

Flat surface without microvilli: $10 \times 10 = 100\,\mu\mathrm{m^2}$ .
Side area of one microvillus: $\pi d L = 3.14 \times 0.1 \times 1 = 0.314\,\mu\mathrm{m^2}$ . For 3000: $3000 \times 0.314 = 942\,\mu\mathrm{m^2}$ .
The tips of the microvilli cover roughly the original 100 µm², so the total is about $942 + 100 = 1042\,\mu\mathrm{m^2}$ .
Increase: $\frac{1042}{100} \approx 10$ times. The microvilli multiply the area for absorbing digested food about tenfold, without making the cell any wider.

Connective tissue

Connective tissue	Structure	Function and example
Loose (areolar)	Scattered cells, collagen and elastic fibres in a jelly-like matrix	Binds skin to muscle; holds organs in place
Adipose	Cells filled with a large fat droplet	Energy store, heat insulation, cushioning (around the kidneys)
Dense fibrous	Many parallel collagen fibres, few cells	Tendons (muscle to bone) and ligaments (bone to bone): strong in one direction
Cartilage	Cells (chondrocytes) in spaces (lacunae) in a firm, rubbery matrix; no blood vessels	Smooth, shock-absorbing surfaces of joints; supports the trachea and ear
Bone	Cells (osteocytes) in lacunae within a hard matrix of calcium phosphate and collagen, arranged in rings (osteons) around central canals carrying blood vessels	Support, protection, movement, mineral store
Blood	Red cells, white cells and platelets in a liquid matrix, plasma	Transport and defence

Muscle and nervous tissue

	Skeletal muscle	Smooth muscle	Cardiac muscle
Cells	Long cylindrical fibres with many nuclei	Spindle-shaped cells, one nucleus each	Branched cells, one or two nuclei, joined by intercalated discs
Stripes (striations)	Yes	No	Yes
Control	Voluntary	Involuntary	Involuntary; contracts on its own (myogenic)
Where	Attached to bones	Walls of the gut, blood vessels, uterus	Heart only
Fatigue	Tires quickly	Slow, sustained contractions	Never rests, does not tire

Nervous tissue is made of neurones, with long axons that carry impulses, and glial cells that support, insulate (forming myelin sheaths) and nourish them. It forms the brain, spinal cord and nerves.

Worked example 2: identifying tissues from micrographs

Identify each tissue: (a) cells in small spaces in a hard matrix arranged in concentric rings around a central canal; (b) long cells with stripes, branching and joined end to end by dark bands; (c) several layers of cells, flattened at the free surface; (d) cells in small spaces in a smooth pink matrix with no blood vessels.

(a) Compact bone: osteocytes in lacunae, osteons around Haversian (central) canals.
(b) Cardiac muscle: striated, branched, with intercalated discs.
(c) Stratified squamous epithelium.
(d) Cartilage (hyaline): chondrocytes in lacunae, no blood vessels.

A stained section of the cartilage that covers the end of a bone in a joint: small cells (chondrocytes), often in pairs or short columns, each in a clear space (lacuna) within a smooth pink matrix with no blood vessels. Image: Bautista, Park, Mazur, Aaron and Bilgen (PLOS ONE, 2016), CC0, via Wikimedia Commons

CrashCourse: "Tissues, Part 1" (Crash Course Anatomy & Physiology #2). Note the four tissue types and how each is recognised under a microscope.

Warning

Common mistakes

Thinking blood is not a tissue. It is a connective tissue whose matrix is liquid plasma.
Mixing up tendons and ligaments: tendons join muscle to bone; ligaments join bone to bone.
Saying smooth muscle is striated. Only skeletal and cardiac muscle show stripes.
Naming an epithelium by its deepest cells. Stratified epithelia are named by the shape of the cells at the surface.

Tip

Exam technique. To identify a tissue, ask three questions: Are the cells packed together (epithelium) or scattered in matrix (connective)? Are they long fibres (muscle)? Are there long processes (nervous)? Then use the details: layers and cell shape for epithelia; type of matrix for connective tissue; stripes and nuclei for muscle.

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Practice: animal tissues

Name the four basic types of animal tissue and give one example of each.
Explain why the alveoli are lined by simple squamous epithelium, not stratified squamous.
Explain how goblet cells and ciliated cells work together in the trachea.
Compare skeletal and cardiac muscle in three ways.
State two differences between bone and cartilage.
Cartilage heals much more slowly than bone after injury. Suggest a reason.
A columnar cell surface of 80 µm² carries 2000 microvilli, each with a side area of 0.30 µm². Estimate the total surface area and the increase factor.

Show answersHide answers

Epithelial (lining of the alveoli), connective (bone, blood, tendon), muscle (skeletal muscle of the thigh), nervous (spinal cord).
Gases must diffuse across it quickly: one layer of very thin cells gives a short diffusion distance. Many layers would slow diffusion.
Goblet cells secrete mucus that traps dust and microorganisms; the cilia beat together and move the mucus up to the throat, where it is swallowed or coughed out.
Skeletal: unbranched fibres, many nuclei, voluntary, tires. Cardiac: branched cells with intercalated discs, one or two nuclei, involuntary and myogenic, does not tire.
Bone matrix is hard (calcium phosphate) and has blood vessels in canals; cartilage matrix is rubbery and has no blood vessels (also: bone in osteons, cartilage not).
Cartilage has no blood vessels, so nutrients and cells needed for repair reach it only slowly by diffusion through the matrix; bone has a blood supply.
Microvilli: $2000 \times 0.30 = 600\,\mu\mathrm{m^2}$ ; total $\approx 600 + 80 = 680\,\mu\mathrm{m^2}$ ; factor $\frac{680}{80} = 8.5$ .

Quick check

Match each tissue to where it is found.

Tap one on the left, then its partner on the right.

Key points

Four animal tissues: epithelial, connective, muscle, nervous.
Epithelia are named by layers (simple or stratified) and surface cell shape (squamous, cuboidal, columnar); each suits its job.
Connective tissues have cells in a matrix: loose, adipose, dense fibrous, cartilage, bone, blood.
Muscle: skeletal (striated, voluntary), smooth (unstriated, involuntary), cardiac (striated, branched, myogenic). Nervous tissue: neurones and glial cells.

Sources and credits

7.1.3: Animal Primary Tissues, from Biology 2e by OpenStax (Mary Ann Clark, Matthew Douglas, Jung Choi), via LibreTexts Biology, licensed under CC BY 4.0. Used for epithelial, connective, muscle and nervous tissues. Adapted by Ganzaa.
Figure 1, the worked examples, practice and quick check: written by Ganzaa.
Images: Schlawgclart, CC0; Athikhun.suw, CC BY-SA 4.0; Bautista and colleagues (PLOS ONE), CC0; all via Wikimedia Commons.
Video: "Tissues, Part 1: Crash Course Anatomy & Physiology #2", CrashCourse, embedded from YouTube.

1Four tissues on a skewer

2Epithelial tissue

3Connective tissue

4Muscle and nervous tissue

Four tissues on a skewer

Epithelial tissue

Connective tissue

Muscle and nervous tissue