| YS | yellow spot; yolk sac |
|---|---|
| ys | yellow spot; yolk sac |
| YST | yolk sac tumor |
| primitive streak | An ectodermal ridge in the midline at the caudal end of the embryonic disk from which arises the intraembryonic mesoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and gives a cephalocaudal axis to the developing embryo. Synonym: germinal streak. (05 Mar 2000) |
|---|---|
| neuroectodermal tumour, primitive | A malignant brain tumour sharing common features and biologic properties with medulloblastoma. Some pathologists and clinicians use the terms interchangeably: they both can disseminate throughout the nervous system and, in some cases, systemically. most lesions arise from the posterior fossa in children under five years of age. The tumour often produces hydrocephalus and symptoms of increased intracranial pressure. Papilledema is often present. (12 Dec 1998) |
| abdominal sac | The part of the embryonic celom that becomes the abdominal cavity. (05 Mar 2000) |
| air sac | <zoology> Thin-walled sacs or spaces which function as a part of the respiratory system in birds, fishes, insects, and mammals. The sacs are filled with air and connected with the air passages of the lungs; an air cell. Source: Websters Dictionary (04 Jul 1999) |
| allantoic sac | The dilated distal portion of the allantois; it forms part of the placenta in many mammals. (05 Mar 2000) |
| alveolar sac | Terminal dilation of the alveolar ducts that give rise to alveoli in the lung; a small air chamber in the pulmonary tissue from which the pulmonary alveoli project like bays and into which an alveolar duct opens; in birds, air-containing extensions of bronchi that connect with bone cavities. Synonym: sacculus alveolaris, air sac. (05 Mar 2000) |
| amniotic sac | <anatomy, obstetrics> Sac, enclosing the embryo of amniote vertebrates, that provides a fluid environment to prevent dehydration during development of land based animals. See: amnion. (18 Nov 1997) |
| anal sac | A vesicular cutaneous invagination opening by a duct on each side of the anal canal in carnivores (best developed in skunks, but absent in some bears, the raccoon, kinkajou, coati, and sea otter), each lying between the external and internal anal sphincter muscles, which aid in emptying the contents. The sac stores odouriferous scent markers produced by glands that line its wall or duct; frequently the sac becomes impacted in the dog or cat, requiring manual emptying. (05 Mar 2000) |
| aneurysmal sac | The dilated wall of an artery in a saccular aneurysm. (05 Mar 2000) |
| aortic sac | In mammalian embryos, the endothelially lined dilation just distal to the truncus arteriosus; it is the primordial vascular channel from which the aortic arches arise and is homologous to the ventral aorta of gill-bearing vertebrates. (05 Mar 2000) |
| rami laterales ramorum dorsalium nervorum cervicalium/thoracalium/lumbalium/sac | Lateral branch of dorsal primary rami of spinal nerves. See: lateral branches. (05 Mar 2000) |
| gestational sac | <radiology> Arises from blastocyst which implants into secretory endometrium surrounded by echogenic trophoblast sac size: 6th week = 17mm;, 8th week = 31 mm, fills chorionic cavity by 12th week visualization of gestational sac, relative to beta-hCG levels: transabdominal scan: greater than 1800 IU/l, transvaginal scan: less than 500 IU/l = 20%, 500-1000 IU/l = 80%, greater than 1000 IU/l = 100%, relative to menstrual age, transabdominal scan: earliest by 5.5 weeks (10-12mm), transvaginal scan: routinely seen by 5-5.5 weeks see: double decidual sac (12 Dec 1998) |
| gestation sac | The gestation sac is the fluid-filled sac in which the foetus develops, visible with an ultrasound exam. (09 Oct 1997) |
| vestibular blind sac | <anatomy> The lower extremity of the cochlear duct, occupying the cochlear recess in the vestibule. Synonym: caecum vestibulare, vestibular blind sac. (05 Mar 2000) |
| pericardial sac | <anatomy> A tough fibrous membrane that envelops and protects the heart. (27 Sep 1997) |