| sickle cell C disease | A disease resulting from abnormal sickle-shaped erythrocytes (containing haemoglobin C and S) which appear in response to a lowering of the partial pressure of oxygen; characterised by anaemia, crises due to haemolysis or vascular occlusion, chronic leg ulcers and bone deformities, and infarcts of bone or of the spleen. (05 Mar 2000) |
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| sickle cell crisis | <haematology> Disease common in races of people from areas in which malaria is endemic. The cause is a point mutation in the allele that codes for the beta chain of haemoglobin with a substitution of (valine for glutamic acid at position 6. The defective haemoglobin (HbS) crystallizes readily at low oxygen tension. In consequence, erythrocytes from homozygotes change from the normal discoid shape to a sickled shape when the oxygen tension is low and these sickled cells become trapped in capillaries or damaged in transit, leading to severe anaemia. In heterozygotes, the disadvantages of the abnormal haemoglobin are apparently outweighed by increased resistance to Plasmodium falciparum malaria, probably because parasitised cells tend to sickle and are then removed from circulation. Symptoms include joint pain, acute abdominal pain, and ulcerations of the lower extremities. Origin: Gr. Haima = blood (18 Nov 1997) |
| sickle cell dactylitis | <syndrome> Recurrent painful swelling of the hands and feet occurring in infants and young children with sickle cell anaemia. Synonym: sickle cell dactylitis. (05 Mar 2000) |
| sickle cell disease | <haematology> Disease common in races of people from areas in which malaria is endemic. The cause is a point mutation in the allele that codes for the beta chain of haemoglobin with a substitution of (valine for glutamic acid at position 6. The defective haemoglobin (HbS) crystallizes readily at low oxygen tension. In consequence, erythrocytes from homozygotes change from the normal discoid shape to a sickled shape when the oxygen tension is low and these sickled cells become trapped in capillaries or damaged in transit, leading to severe anaemia. In heterozygotes, the disadvantages of the abnormal haemoglobin are apparently outweighed by increased resistance to Plasmodium falciparum malaria, probably because parasitised cells tend to sickle and are then removed from circulation. Symptoms include joint pain, acute abdominal pain, and ulcerations of the lower extremities. Origin: Gr. Haima = blood (18 Nov 1997) |
| sickle cell haemoglobin | <haematology> Haemoglobin S is an abnormal version of the protein haemoglobin. The sixth amino acid of the normal beta chain, glutamic acid, is replaced by valine with gluconic acid. This mutation causes the red blood cell to take on a sickle shape, and is the cause of the sickle cell trait condition (when the individual is heterozygous for this mutant haemoglobin) and the disease of sickle cell anaemia (when the individual is homozygous for this mutant haemoglobin). (09 Oct 1997) |
| sickle cell prep | <haematology, investigation> A test which looks at red blood cells under the microscope to detect sickle cells after an agent which lowers the oxygen content of the sample is added. A positive test is result is determined by the presence of sickle cells. Abnormal results indicate sickle cell anaemia or sickle cell trait. (27 Sep 1997) |
| sickle cell retinopathy | A condition marked by dilation and tortuosity of retinal veins, and by microaneurysms and retinal haemorrhages; advanced stages may show neovascularization, vitreous haemorrhage, or retinal detachment. (05 Mar 2000) |
| sickle cell test | <investigation> A test which looks at red blood cells under the microscope to detect sickle cells after an agent which lowers the oxygen content of the sample is added. A positive test is result is determined by the presence of sickle cells. Abnormal results indicate sickle cell anaemia or sickle cell trait. (27 Sep 1997) |
| sickle cell trait | <haematology> This condition occurs in people who have one of two possible genes (i.e., they are heterozygous forthe allele) that code for the defective haemoglobin responsible for sickle cell anaemia. The coditionis diagnosed by exposing an individual's red blood cells to a low oxygen environment, if the trait is present, the cells will turn to a sickle shape. People with this trait may suffer milder symptoms of sickle cell anaemia, or may have no symptoms. Some scientists believe the trait actually provides an evolutionary advantage in tropical environments because the slightly altered shape of the blood cells causes a person to be more resistant to malaria. (09 Oct 1997) |
| sickle cell-thalassaemia disease | Anaemia, clinically resembling sickle cell anaemia, in which individuals are compound heterozygous for the sickle cell gene and a thalassaemia gene; about 60 to 80% of haemoglobin is Hb S, up to 20% Hb F, and the remainder Hb anaemia. Synonym: sickle cell-thalassaemia disease. (05 Mar 2000) |
| sickle flap | A sickle-shaped flap from the anterior scalp and one side of the forehead, based on the opposite temporal artery. (05 Mar 2000) |
| sickle form | The male or female gametocyte(s) of Plasmodium falciparum, whose presence in human red blood cells is diagnostic of falciparum malaria. Synonym: crescent, sickle form. Myopic crescent, a white or grayish white crescentic area in the fundus of the eye located on the temporal side of the optic disk; caused by atrophy of the choroid, permitting the sclera to become visible. Synonym: myopic conus. Sublingual crescent, the crescent-shaped area on the floor of the mouth formed by the lingual wall of the mandible and the adjacent part of the floor of the mouth. (05 Mar 2000) |
| sickle scotoma | A comet-shaped scotoma, occurring in glaucoma, attached at the temporal end to the blind spot or separated from it by a narrow gap; the defect widens as it extends above and nasally curves around the fixation spot, and then extends downward to end exactly at the nasal horizontal meridian. Synonym: Bjerrum's sign, sickle scotoma. (05 Mar 2000) |
| sicklebill | <ornithology> Any one of three species of humming birds of the genus Eutoxeres, native of Central and South America. They have a long and strongly curved bill. Synonym: the sickle-billed hummer. A curlew. A bird of the genus Epimachus and allied genera. Source: Websters Dictionary (01 Mar 1998) |
| sickless | Free from sickness. "Give me long breath, young beds, and sickless ease." (Marston) Source: Websters Dictionary (01 Mar 1998) |