Lunula

Lunula (from the Latin lunule, meaning little moon)

Thumb nail, showing the lunula

Lunula is the white crescent shaped area at the base of the human finger or toe nail. Lunula is most obvious in the thumb, though not everyone's lunula is clearly visible. A lack of visible lunula is sometimes associated with certain pathologic conditions as in Terry's nails, where the nails appear white with a characteristic ground glass appearance and no lunula. This condition, thought to be due to decreased vascularity with increased connective tissue in the nail bed, is frequently found in hepatic failure, cirrhosis, diabetes, congestive heart failure, hyperthyroidism, and malnutrition.

Desmosome

Desmosome (from the Greek desmo & soma, "fiber body")

Desmosomes

Desmosomes are a special type of cell junction connecting adjacent cells together. Also known as macula adherens ("adhering spot"), desmosomes are a type of junctional complexes found in epithelial and muscle cells. They are made up of molecular complexes that attach cell adhesion proteins to intracellular keratin cytoskeletal filaments. Certain blistering diseases of the skin such as Pemphigus vulgaris are a result of genetic defects that result in abnormal desmosomal proteins, and hence defective cell-to-cell junctions.

Crenation

Crenation (from the Latin crenatus, scalloped or notched)

Crenated RBCs

The phenomenon of shrinking of cells when placed in a hypertonic environment (a hypertonic solution is one in which the concentration of solute is greater than that of the cells), as a result of osmosis (the diffusion of water across a semi-permeable membrane from a region of higher concentration to a region of lower concentration until dynamic equilibrium has been reached. Crenation is particularly noticable in red blood cells, which become scalloped and notched when placed in a hypertonic solution, losing their usual biconcae shape, and takng the appearance of a spiked ball, from which they take the name of echinocytes or burr cells.