Proximal Sheath Research Articles

Flagellar apparatus absolute orientations and the phylogeny of the green algae

The absolute orientation of the flagellar apparatus in green algal motile cells is a feature of considerable value in studies of green algal systematics and phylogeny. The absolute orientation patterns found in those algae for which this feature is known or can be deduced are reviewed. Counterclockwise absolute orientation occurs in all classes except the Chlorophyceae and is considered primitive, while the clockwise absolute orientation present in most members of the Chlorophyceae is the result of progressive clockwise rotation of components during evolution. Extant intermediates documenting this rotation include Hafniomonas vegetative cells, which show counterclockwise absolute orientation, and Chaetopeltis quadriflagellate zoospores, in which the flagellar apparatus is strictly cruciate except for a slight clockwise offset of the microtubular rootlets. The V-shaped arrangement of the basal bodies in the flagellar apparatus, as well as the presence of proximal sheaths and of two layers of scales on the cell body, further identifies the Chaetopeltis zoospore as a primitive cell type within the Chlorophyceae. Trends towards the exsertion of basal bodies from a flagellar pit, either apically or laterally, the elimination of quadriflagellate cells, and, in the Chlorophyceae, an increasing amount of basal body offset, indicate advancement within the classes. Absolute orientation is conserved during flagellar apparatus replication and development. Events after flagellar apparatus division in the algae studied may be subdivided into component assembly, which is universal and preserves phylogenetically-useful features, and component reorientation, which occurs in relatively few green algae and adapts the flagellar apparatus to specialized functions. From these flagellar apparatus orientation studies, a major reevaluation of evolution within the Chlorophyceae is proposed, with weakly-thalloid algae possessing desmoschisis (e.g. Chaetopeltis) considered primitive, and most other types, including the Volvocales, considered more advanced. The evolution of wall formation does not preclude the formation of scales in primitive chlorophycean genera. In addition, one or more previously undescribed major lineages may exist within the green algae, including one, the Pleurastrum lineage, whose members possess dorsiventrally-flattened motile cells, counterclockwise absolute orientation of the flagellar apparatus, and a phycoplast at cytokinesis. The Chlorophyceae, the Ulvophyceae, and the Pleurastrum lineage are considered to have a common ancestor that resembled the modern genus Pyramimonas, while the Charophyceae is thought to be of more ancient derivation. The ancestors for all classes possessed counterclockwise absolute orientation of the flagellar apparatus and diamond-shaped scales.

Hair Loss in Children

PHYSIOLOGY OF NORMAL HAIR1,2Unlike the hair of most animals, human hair usually follows a random pattern of growth, rest, and shedding, followed by the growth and emergence of a new hair from the follicle. This cycle is related to histologic changes in the follicle: The anagen phase involves active growth (long follicle); the telogen phase is resting (short follicle); and the catagen phase is a transition between anagen and telogen.The duration of the growing phase (anagen) determines the ultimate length of the hair: normally longest on the scalp, followed in descending order of length by the hairs of the beard, pubis, axillae, body, eyebrows, and eyelid margins. Longer hair is associated with a higher ratio (10:1) of anagen to telogen follicles. Hair plucking is the most rapid, convenient path to examine this relationship: anagen hairs have a glistening, cylindrical proximal sheath, approximately 3 mm long (Fig 1) whereas the telogen follicle yields a hair with a short, 1-mm knob, appropriately called a club (Fig 2).The shape and color of hair are usually determined genetically. Straight hair is round in cross section, with curly and kinky (spiral) varieties becoming progressively more ellipsoid. Hair color may normally darken and shape change for the first five to ten years of life; this tendency is most commonly seen in the transformation of a curly haired blond child into a tow-headed or brunette adolescent.

Hair Loss in Children

PHYSIOLOGY OF NORMAL HAIR1,2 Unlike the hair of most animals, human hair usually follows a random pattern of growth, rest, and shedding, followed by the growth and emergence of a new hair from the follicle. This cycle is related to histologic changes in the follicle: The anagen phase involves active growth (long follicle); the telogen phase is resting (short follicle); and the catagen phase is a transition between anagen and telogen. The duration of the growing phase (anagen) determines the ultimate length of the hair: normally longest on the scalp, followed in descending order of length by the hairs of the beard, pubis, axillae, body, eyebrows, and eyelid margins. Longer hair is associated with a higher ratio (10:1) of anagen to telogen follicles. Hair plucking is the most rapid, convenient path to examine this relationship: anagen hairs have a glistening, cylindrical proximal sheath, approximately 3 mm long (Fig 1) whereas the telogen follicle yields a hair with a short, 1-mm knob, appropriately called a club (Fig 2). The shape and color of hair are usually determined genetically. Straight hair is round in cross section, with curly and kinky (spiral) varieties becoming progressively more ellipsoid. Hair color may normally darken and shape change for the first five to ten years of life; this tendency is most commonly seen in the transformation of a curly haired blond child into a tow-headed or brunette adolescent.

The aetiology of trigger finger: Explained on the basis of intratendinous architecture

Summary Studies of the intratendinous structure of the flexor tendons, and in particular the demonstration of the spiralling of the fibre components within the digits of the flexor tendons of the thumb and fingers, have allowed a new appreciation of the old problem of understanding trigger finger.The spiral arrangement of the intratendinous fibrous architecture lends itself to the development of a contour defect-or nodule-distal to a stenosed proximal sheath pulley. On release of the constriction the nodule can disappear by aprocess of unspiralling under the normal longitudinal forces acting on the tendon. Whether congenital, traumatic or rheumatoid inflammatory in origin, the relative stenosis of the proximal pulley of the digital tendon theca would appear to be the primary aetiological factor and the triggering only occurs when sufficient deformation of the tendon contour has been induced.