Chapter 6: Practicum Guide: Identifying the Slides
The histology practicum for this block is an identification exam: you are shown a slide or a micrograph, often with an arrow or a label, and asked to name the tissue, a layer, a cell or a structure, sometimes followed by a question about its function. This chapter turns Chapters 1–5 into a routine you can run at the microscope, slide by slide.
A routine for any slide
- Scan at low power (4× or 10×) before anything else. Is it a sheet of one tissue, or an organ with layers? Is there a surface with epithelium on it?
- If there is a keratinized surface on top, it is skin. Go to the skin routine below.
- If the whole field is pink fibers or cells, it is probably muscle. Decide the plane of section, then use the muscle routine.
- Only then zoom in to answer the arrow: a layer, a cell or a structure.
- For a "function" follow-up question, name the job in two or three words: "light touch", "holocrine, sebum", "pressure and vibration".
Muscle routine
Step 1: plane of section. Long strips = longitudinal (membujur); a mosaic of round or polygonal profiles = transverse (melintang). In the atlas figure, OL = transverse and IC = longitudinal.
Step 2: striations and nuclei.
| You see | Answer |
|---|---|
| No striations, spindle cells, one central elongated nucleus | Smooth muscle |
| Striations, many nuclei at the periphery under the sarcolemma | Skeletal muscle |
| Striations, one central nucleus, branching, intercalated discs | Cardiac muscle |
Step 3: the follow-up questions, and their answers:
- Shape of smooth muscle cells? Fusiform (spindle).
- Position of the smooth muscle nucleus? Central.
- Innervation of smooth muscle? Autonomic nervous system (the junction is called a synapse).
- Position of skeletal muscle nuclei? Peripheral, beneath the sarcolemma.
- Neurotransmitter for skeletal muscle? Acetylcholine, at the motor end plate / neuromuscular junction.
- Island-like bundles of myofibrils in a cross-cut skeletal fiber? Cohnheim's areas.
- Connective tissue around one fiber? Endomysium. Around a fascicle? Perimysium. Around the muscle? Epimysium.
- Dark band? A band (anisotropic). Light band? I band (isotropic).
- Dark line in the middle of the I band? Z line. In the middle of the A band? M line. Light zone in the middle of the A band? H zone.
- Unit between two Z lines? Sarcomere.
- Dark irregular lines crossing cardiac fibers? Intercalated discs.
- Fibers that branch and rejoin in cardiac muscle? Anastomosis.
Traps
- Cardiac vs skeletal: both striated. Nuclei central + branches + discs = cardiac.
- Smooth vs cardiac in cross-section: both have central nuclei. Look for striations or discs in any longitudinal part of the field.
- Smooth muscle vs tendon or nerve: in tendon the flat nuclei sit between collagen bundles; in nerve the fibers are wavy and paler, with myelin spaces.
Skin routine
Step 1: thick or thin?
- Stratum lucidum present, very thick stratum corneum, no hair follicles → thick skin (palms, soles).
- No lucidum, thin corneum, hair follicles and sebaceous glands → thin skin.
Step 2: which layer is the arrow on? Count from the surface down:
| Layer | Clue |
|---|---|
| Stratum corneum | Pink, flaky, no nuclei |
| Stratum lucidum | Thin, glassy, pale band; thick skin only |
| Stratum granulosum | Flattened cells with dark granules |
| Stratum spinosum | Many layers of polygonal cells with "spines" |
| Stratum basale | One row of dark cuboidal/columnar cells on the basement membrane |
| Papillary dermis | Thin loose connective tissue in the papillae |
| Reticular dermis | Thick dense irregular connective tissue |
| Hypodermis | Fat and loose connective tissue beneath the dermis |
Step 3: the follow-up questions, and their answers:
- Type of epithelium of the epidermis? Keratinized stratified squamous epithelium.
- How is the epidermis nourished? By diffusion from the dermis (it has no blood vessels).
- Layer found only in thick skin? Stratum lucidum, whose cells contain eleidin.
- Spines on spinosum cells? Desmosomes (intercellular bridges); the fine strands running into them are tonofibrils.
- Pale cell among the basal cells? Melanocyte (makes eumelanin).
- Dendritic cell in the spinosum, no melanin, shown with special stains? Langerhans cell (immune, macrophage-like).
- Layer of dermis just under the epidermis? Stratum papillare (loose connective tissue).
- Deep fatty layer? Hypodermis (subcutis).
Nerve endings
| You see | Answer | Senses |
|---|---|---|
| Large oval "onion" of concentric lamellae, deep dermis or hypodermis | Vater-Pacini corpuscle | Pressure and vibration |
| Small cylindrical capsule filling a dermal papilla, transverse stacked cells | Meissner's corpuscle | Light touch |
| Unencapsulated nerve ending on a basal cell | Merkel's disc | Light touch |
| Small cylinder with spray-like branches, dermis | Ruffini ending | Pressure |
| Round, thick capsule, dermis | Krause end bulb | Pressure (practicum) |
Appendages
| You see | Answer | Follow-up |
|---|---|---|
| Circle of rings around a central hair | Hair follicle, transverse section | Hair layers inside out: medulla, cortex, cuticle |
| Clusters of large, pale, foamy cells next to a follicle | Sebaceous gland | Holocrine; opens into the follicle |
| Many small round tubules in the deep dermis, pale secretory and dark ducts | Eccrine sweat gland | Merocrine; opens onto the skin surface |
| Large tubules with wide lumens (axilla) | Apocrine sweat gland | Opens into a hair follicle |
| Flat cell between secretory cells and basal lamina | Myoepithelial cell | In the secretory portion only |
| Keratin plate on the back of a fingertip | Nail | Eponychium proximal, hyponychium distal |
Last-minute checklist
- Striations? Skeletal or cardiac. Nuclei peripheral? Skeletal. Discs and branches? Cardiac. Neither striations nor discs? Smooth.
- OL = transverse, IC = longitudinal.
- Epi- (whole muscle), peri- (fascicle), endo- (one fiber).
- A band dark, I band light, Z in I, M and H in A, Z to Z = sarcomere.
- Lucidum = thick skin. Eleidin in the lucidum, keratohyalin in the granulosum.
- Melanocyte (basale, pigment), Langerhans (spinosum, immune), Merkel (basale, touch).
- Papillary = loose, reticular = dense irregular.
- Meissner = papillae, light touch; Pacini = onion, pressure and vibration.
- Sebaceous = holocrine into the follicle; eccrine = merocrine onto the surface; apocrine = wide lumen into the follicle.