| AR | absolute risk; accounts receivable; achievement ratio; actinic reticuloid [syndrome]; active resista... |
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| ARA | Academy of Rehabilitative Audiometry; acetylene reduction activity; American Rheumatism Association;... |
| ARR | aortic root replacement |
| AWAR | anterior wall of aortic root |
| BOR | basal optic root; before time of operation; bowels open regularly; branchio-oto-renal [syndrome] |
| anterior layer of rectus abdominis sheath | The portion of the rectus sheath that lies anterior to the muscle, consisting in its upper two-thirds of contributions from the aponeuroses of the external and internal oblique muscles, and in its lower third (below the arcuralt line) of contributions from the aponeuroses of all three muscles of the anterolateral abdominal wall. Synonym: lamina anterior vaginae musculi recti abdominis. (05 Mar 2000) |
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| arcuate line of rectus sheath | A crescentic line, not always clearly defined, which marks the lower limit of the posterior layer of the sheath of the rectus abdominis muscle. Synonym: linea arcuata vaginae musculi recti abdominis, Douglas' line, linea saemicircularis, saemicircular line. (05 Mar 2000) |
| axillary sheath | Fibrous neurovascular sheath, formed as an extension of the prevertebral layer of deep cervical fascia through the cervicoaxillary canal, which enclosed the first part of the axillary artery, the axillary vein, and the brachial plexus. (05 Mar 2000) |
| carotid sheath | The dense fibrous investment of the carotid artery, internal jugular vein, and vagus nerve on each side of the neck, deep to the sternocleidomastoid muscle; the layers of cervical fascia blend with it. Synonym: vagina carotica. (05 Mar 2000) |
| rectus sheath | Sheath of the rectus abdominis, formed by the aponeuroses of the three anterolateral muscles of the abdominal wall that split to enclose the rectus and fuse medially to form the linea alba; it consists of an anterior lamina and a posterior lamina, the latter being absent below the arcuate line. See: aponeurosis of external abdominal oblique muscle, aponeurosis of internal abdominal oblique muscle. Synonym: vagina musculi recti abdominis. (05 Mar 2000) |
| giant cell tumour of tendon sheath | A nodule, possibly inflammatory in nature, arising commonly from the flexor sheath of the fingers and thumb; composed of fibrous tissue, lipid-and haemosiderin-containing macrophages, and multinucleated giant cells. Synonym: localised nodular tenosynovitis. (05 Mar 2000) |
| parotid sheath | The part of the investing cervical fascia that ensheaths the parotid gland and is fixed above to the zygomatic arch. Synonym: fascia parotidea, fibrous capsule of parotid gland, parotid sheath. (05 Mar 2000) |
| Mauthner's sheath | <cell biology> Plasma membrane of an axon. (12 Mar 1998) |
| caudal sheath | A group of microtubules arranged cylindrically around the caudal pole of the nucleus in a developing spermatozoon. (05 Mar 2000) |
| resectoscope sheath | An operative sheath through which transurethral electroresection of bladder tumours or prostate gland can be performed. (05 Mar 2000) |
| medullary sheath | <anatomy, neurology> An insulating layer surrounding vertebrate peripheral neurons, that dramatically increases the speed of conduction. It is formed by specialised Schwann cells, that can wrap around neurons up to 50 times. The exposed areas are called nodes of Ranvier: they contain very high densities of sodium channels and action potentials jump from one node to the next, without involving the intermediate axon, a process known as saltatory conduction. (18 Nov 1997) |
| Rouget-Neumann sheath | The amorphous ground substance between an osteocyte and the lacunar or canalicular wall. (05 Mar 2000) |
| microfilarial sheath | The membrane surrounding the embryos of certain blood-borne microfilariae, such as Wuchereria, Brugia, and Loa of humans; thought to be derived from the vitelline membrane. (05 Mar 2000) |
| mitochondrial sheath | The spirally arranged mitochondria in the middle piece of a spermatozoon; may control movement of the tail. (05 Mar 2000) |
| Waldeyer's sheath | The tubular space between the bladder wall and the intramural portion of the ureter as it courses obliquely through this structure; actually a space and not a true sheath. Synonym: Waldeyer's space. (05 Mar 2000) |