50 Fun Facts About Histology

Which French anatomist, called the father of histology, identified 21 tissue types without a microscope?

Xavier Bichat thought the microscopes of his day too crude for medicine. He died at 30, probably of typhoid caught while examining decaying skin.

Hematoxylin, the nuclear dye in the standard H&E tissue stain, is extracted from the wood of which tree?

Logwood heartwood yields the dye, but it stains nothing until it has been oxidised and paired with a metal salt, most often aluminium.

Which large bone cell, usually holding several nuclei, dissolves old bone by secreting acid?

Osteoclast comes from Greek words for 'bone' and 'broken'. The cell pumps hydrogen ions into the space beneath it and leaves a shallow pit behind.

Which cells in the stomach's gastric glands secrete both hydrochloric acid and intrinsic factor?

Parietal cells pump acid against a gradient of three to four million to one, among the steepest ion gradients in any mammalian tissue.

Which tiny smooth muscles attached to hair follicles contract in the cold to raise goose bumps?

Arrector pili muscles contract without any conscious control. In furry mammals the raised hairs trap a layer of air that helps the animal hold on to heat.

Which cell type makes up about 90 percent of the cells in the human epidermis?

Keratinocyte life is a one-way trip: born in the deepest layer of the epidermis, each cell migrates to the surface and is shed some 40 to 56 days later.

Which instrument slices wax-embedded tissue into sections thin enough for light to pass through?

Microtome comes from Greek words for 'small' and 'to cut', and the finest models can shave a section just 50 nanometres thick.

In the H&E stain used on most biopsy slides, eosin colours the cytoplasm of cells which shade?

Pink is the mark of eosin, which clings to the proteins in cytoplasm and in the material between cells, while hematoxylin turns the nuclei blue-purple.

Light and dark human skin contain similar numbers of which pigment-producing cells in the epidermis?

Melanocytes are about equally common in every skin tone. The difference lies in how the pigment is packaged once it is handed to neighbouring skin cells.

Which cell in human blood ejects its nucleus as it matures, leaving more room for hemoglobin?

Erythrocyte is the formal name for a red blood cell, which circulates for about 100 to 120 days as little more than a flexible sack of hemoglobin.

Robert Hooke coined the biological term 'cell' in 1665 after examining a thin slice of which material?

Cork showed Hooke a structure of small walled enclosures under his microscope, and his book Micrographia handed biology the word.

Compact bone is built from cylinders of concentric lamellae around a central canal, each called what?

Osteon is the modern name for the Haversian system, after Clopton Havers, the 17th-century English physician who described the canals running through bone.

Which mature bone cell sits sealed inside a cavity called a lacuna, with a half-life of about 25 years?

An osteocyte is simply a bone-building cell that became trapped in the matrix it secreted. It never divides, but long branching arms keep it in touch with its neighbours.

Which tiny channels radiate between the lacunae of bone, linking the cells trapped in the hard matrix?

Canaliculi pass on materials picked up near blood vessels, spreading them through the bone matrix to cells that can never move to feed themselves.

Which mineral, also the main ingredient of tooth enamel, makes up about 70 percent of human bone by weight?

Hydroxyapatite crystals in bone are interspersed in a matrix of collagen, while in enamel the supporting proteins are amelogenins and enamelins instead.

Which membrane covers the outer surface of bones and, unlike bone tissue, contains pain-sensing nerves?

Periosteum also holds a reserve of progenitor cells that turn into bone- and cartilage-forming cells after a fracture, which makes it essential to healing.

Spongy bone gets its porous look from a network of thin bony struts known by which name?

Trabeculae line up along the loads a bone has to carry, so the lattice inside a femur is strongest in exactly the directions the stress runs.

Which cell stores one large lipid droplet that squashes its nucleus flat against the edge of the cell?

Adipocyte is the formal name for a fat cell, and the white kind is almost all droplet, with its cytoplasm reduced to a thin surrounding layer.

Which heat-producing tissue, abundant in newborns and hibernating mammals, is coloured by its mitochondria?

Brown fat makes heat without any shivering, and each of its cells holds numerous small lipid droplets packed among the mitochondria.

Heart muscle cells are joined end to end by which junctions, a microscopic hallmark of cardiac tissue?

Intercalated discs combine anchoring junctions with gap junctions, which lets the separate cells of the heart work as a single functional unit.

Which thin sheet of extracellular matrix anchors every epithelium to the connective tissue beneath it?

Basement membrane doubles as a supply route, since epithelium has no blood supply of its own and nutrients must diffuse across from the tissue below.

Which epithelium, also called urothelium, changes shape as the urinary bladder fills and empties?

Transitional epithelium looks cuboidal when relaxed and flattened when stretched, and it seals urine in so that wastes cannot seep back into the bloodstream.

Which hair-like projections on airway cells beat 10 to 20 times a second to sweep mucus toward the throat?

Cilia number around 200 on each airway cell, and their coordinated beat is nicknamed the mucociliary escalator because it carries mucus up to be swallowed or coughed out.

Which spindle-shaped cell, the most common in connective tissue, makes collagen and helps wounds to heal?

Fibroblast cells build the structural framework of animal tissues, laying down both the fibres and the surrounding matrix that everything else sits in.

Which granule-packed cells, named by the German scientist Paul Ehrlich, store the histamine released in allergies?

Mast cell is a misnomer: Ehrlich wrongly believed the granules fed the surrounding tissue, so he named them Mastzellen, German for well-fed cells.

Which cartilage, the most common type in the body, forms the C-shaped rings of the trachea?

Hyaline cartilage also coats the ends of bones at joints, and it has no nerves or blood supply, so nutrients can reach its cells only by diffusion.

Which spot-like junctions bind cells together in tissues under heavy mechanical stress?

Desmosomes, whose name means 'binding body', are the target of the antibodies that cause the blistering skin disease pemphigus.

Which tissue-dwelling white blood cell engulfs and digests microbes, dead cells and other debris?

Macrophage cells were named by Élie Metchnikoff, who found such 'eating cells' by pushing thorns into starfish larvae and watching cells surround them.

Which single layer of flat cells lines the inside of every blood and lymphatic vessel in the body?

Endothelium cells are classed by what they touch: vascular where they meet blood, lymphatic where they meet lymph.

Which finger-like projections form the absorbing 'brush border' of the small intestine's lining cells?

Microvilli stand in their thousands on a single cell and are not the same as intestinal villi, which are far larger structures made of many cells.

Which outermost layer of the epidermis is made of 15 to 20 sheets of flattened dead cells with no nuclei?

Stratum corneum is Latin for 'horny layer', and the lipids packed between its cells are what keep the body from drying out.

The stratum lucidum, a thin clear layer of dead cells, is visible only in the thick skin of which areas?

Palms and soles are the body's areas of 'thick skin', and the extra layer takes the Latin word for 'clear' because it looks translucent under the microscope.

Which layer of skin lies beneath the epidermis and houses the hair follicles, sweat glands and nerves?

Dermis is mostly dense irregular connective tissue, and the papillae on its upper surface form ridges that greatly increase its contact area with the layer above.

Which immune cells of the epidermis were found by a 21-year-old student who mistook them for nerves?

Langerhans cells carry the name of Paul Langerhans, the German anatomist who also discovered the hormone-making islets of the pancreas.

Which pressure and vibration sensor found deep in the skin is built in concentric layers like an onion?

Pacinian corpuscle layers number 20 to 70 and slide past each other, so steady pressure soon fades and only changes such as vibration get through.

Which skin glands release an oily secretion by having whole cells rupture and disintegrate into it?

Sebaceous glands are most numerous on the face and scalp, and a rise in their sebum output at puberty is thought to lie behind teenage acne.

Type II cells in the lungs' air sacs secrete which substance to keep the sacs from collapsing?

Surfactant is a mix of phospholipids and proteins that spreads over the air-water boundary, keeping the sacs from collapsing at the end of each breath out.

Which cells of the small airways lost the name of their discoverer, Max Clara, an active Nazi Party member?

Club cells took their plain new name in 2013, after journal editors agreed the old eponym honoured a man who had studied tissue from executed victims of Nazi Germany.

Which cup-shaped lung cavities, about 480 million in a typical pair, are the site of gas exchange?

Alveoli give a pair of human lungs a combined gas-exchange surface of 70 to 80 square metres, all of it wrapped in a network of capillaries.

Which term describes the airway lining that looks many-layered although every cell rests on the same base?

Pseudostratified means 'falsely layered': each cell touches the base, but the nuclei sit at different levels and mimic several layers.

Chief cells in the stomach lining release which inactive enzyme precursor, later switched on by acid?

Pepsinogen turns into the protein-digesting enzyme pepsin only when it meets hydrochloric acid, which neighbouring cells in the same glands supply.

Which folds in the stomach lining flatten out so the organ can expand when food arrives?

Rugae let the stomach take on volume without a rise in pressure, because the coiled folds of its inner layers simply stretch outward as it fills.

Which spiral-shaped bacterium of the stomach lining won Barry Marshall and Robin Warren a Nobel Prize?

Helicobacter pylori has a helical body, thought to help it bore into the stomach's mucus layer, and it is classed as a cancer-causing bacterium.

The stomach wall has a third layer of muscle found nowhere else in the gut, running in which direction?

Oblique fibres form the innermost of the stomach's three muscle coats, and the extra layer lets the organ churn food as well as push it onward.

Which term names a cancer that develops from epithelial cells, such as those lining the skin or gut?

Carcinoma is one of several labels based on a tumour's cell of origin: cancers of connective tissue are sarcomas, and those of blood-forming cells are leukemias.

Reed–Sternberg cells, giants with an 'owl's eye' look on a slide, are the hallmark of which cancer?

Hodgkin lymphoma cannot be diagnosed without them: the giant cells measure 30 to 50 microns and carry either several nuclei or one two-lobed nucleus.

The Pap test, devised in the 1920s by a Greek physician, screens cells from which organ for cancer?

Cervix cells are collected with a small spatula or brush from the zone where outer squamous cells meet inner glandular ones, then checked for precancerous changes.

In Barrett's esophagus, acid exposure makes one cell type transform into another, a change called what?

Metaplasia replaces a lining with one better able to withstand the stress on it. It is not a cancer in its own right, but it can be an early step towards one.

Which German 'father of modern pathology' popularised the maxim that all cells come from cells?

Rudolf Virchow spread the maxim through his 1858 book Cellular Pathology, though the idea that cells arise only from other cells is now widely credited to Robert Remak.

Which glial cells wrap the nerve fibres of the peripheral nervous system in an insulating myelin sheath?

Schwann cell insulation covers just one axon each, and the name honours Theodor Schwann, the German physiologist who extended cell theory to animals.