Differentiation Health Dictionary

An acute arbovirus (see ARBOVIRUSES) infection caused by a ?avivirus of the togavirus family, transmitted from animals to humans by various species of forest mosquito (jungle/sylvan yellow fever), and from human to human by Aëdes aegypti (urban yellow fever). Mosquito transmission was shown by Walter Reed and his colleagues in 1900. It is ENDEMIC in much of tropical Africa and Central and South America but does not occur in Asia. In the urban cycle, humans constitute the reservoir of infection, and in the jungle/sylvan variety, mammals – especially subhuman primates – are involved in transmission. Historically, yellow fever was enormously important, causing devastating epidemics (see EPIDEMIC); it also carried a high mortality rate in travellers and explorers. Differentiation from other infections associated with JAUNDICE was often impossible.

Clinically, yellow fever is characterised by jaundice, fever, chills, headache, gastrointestinal haemorrhage(s), and ALBUMINURIA. The incubation period is 3–6 (up to 10) days. Differentiation from viral hepatitides, other viral haemorrhagic fevers, severe Plasmodium falciparum malaria, and several other infections is often impossible without sophisticated investigative techniques. Infection carries a high mortality rate. Liver histology (biopsy is contraindicated due to the haemorrhagic diathesis) shows characteristic changes; a fulminating hepatic infection is often present. Acute in?ammation of the kidneys and an in?amed, congested gastric mucosa, often accompanied by haemorrhage, are also demonstrable; myocardial involvement often occurs. Diagnosis is primarily based on virological techniques; serological tests are also of value. Yellow fever should be suspected in any travellers from an endemic area.

Management consists of instituting techniques for acute hepatocellular (liver-cell) failure. The affected individual should be kept in an isolation unit, away from mosquitoes which could transmit the disease to a healthy individual. Formerly, laboratory infections were occasionally acquired from infected blood samples. Prophylactically, a satisfactory attenuated VACCINE (17D) has been available for around 60 years; this is given subcutaneously and provides an individual with excellent protection for ten years; international certi?cates are valid for this length of time. Every traveller to an endemic area should be immunised; this is mandatory for entry to countries where the infection is endemic.... yellow fever

A group of diseases characterized by the abnormal and unrestrained growth of cells in body organs or tissues. Tumour-forming cells develop when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells undergo a series of changes. A small group of abnormal cells develop that divide more rapidly than normal, lack differentiation (they no longer perform their specialized task), and may escape the normal control of hormones and nerves. Cancers differ from benign neoplasms (abnormal growths, such as warts) in that they spread and infiltrate surrounding tissue and may cause blockages, destroy nerves, and erode bone. Cancer cells may also spread via the blood vessels and lymphatic system to form secondary tumours (see metastasis).

Causes of cancer include environmental factors such as sunlight, smoking, pollutants, alcohol consumption, and dietary factors. These factors may provoke critical changes in body cells in susceptible people. Susceptibility to certain cancers may be inherited.

Many cancers are now curable, usually by combinations of surgery, radiotherapy, and anticancer drugs. For information on particular cancers, refer to the organ in question (for example lung cancer; stomach cancer).... cancer

n. a loss of normal cell characteristics or differentiation, which may be to such a degree that it is impossible to define the origin of the cells. Anaplasia is typical of rapidly growing malignant tumours, which are described as anaplastic.... anaplasia

n. a malignant tumour of the cervix, uterus, or vagina containing a mixture of *adenocarcinoma and cells with a sarcoma appearance, previously called malignant mixed Müllerian tumours (MMMT). These tumours are actually epithelial in origin and should be treated as high-grade adenocarcinomas. Sarcomatoid differentiation of epithelial cancers often indicates a poor prognosis.... carcinosarcoma

cluster of differentiation: a numerical system for classifying antigens expressed on the surface of lymphocytes. See also CD4.... cd

any developmental abnormalities resulting from anomalous metanephric differentiation (see metanephros). Most dysplastic kidneys are associated either with an abnormally located ureteral orifice or with urinary tract anomalies that are expected to produce unilateral, bilateral, or segmental urinary obstruction.... dysplastic kidneys

adj. 1. arising within or derived from the body. Compare exogenous. 2. formerly (until the 1980s), denoting a type of *depression (also known as melancholia) that was thought to arise totally biologically and therefore without any particular triggers. It stood in contrast to reactive depression, which was supposed to have been primarily triggered by stress or trauma. Today this differentiation is not usually made as the validity of separating these two types of depression could not be proven.... endogenous

n. a malignant tumour of connective tissue, derived from *fibroblasts. Fibrosarcomas may arise in soft tissue or bone; they can affect any organ but are most common in the limbs, particularly the leg. They occur in people of all ages and may be congenital. The cells of these tumours show varying degrees of differentiation; the less well differentiated tumours containing elements of histiocytes have been recently reclassified as malignant fibrous histiocytomas.... fibrosarcoma

the grade (from one to five) given to an area of prostate cancer, reflecting the level of differentiation of the tumour. The tumour pattern is assessed by examining the gland at low magnification. Higher grades indicate poorer differentiation. [D. F. Gleason (1920–2008), US pathologist]... gleason grade

n. the basic unit of all living organisms, which can reproduce itself exactly (see mitosis). Each cell is bounded by a cell membrane of lipids and protein, which controls the passage of substances into and out of the cell. Cells contain *cytoplasm, in which are suspended a *nucleus and other structures (*organelles) specialized to carry out particular activities in the cell (see illustration).

Complex organisms are built up of millions of cells that are specially adapted to carry out particular functions. The process of cell differentiation begins early on in the development of the embryo and cells of a particular type (e.g. blood cells, liver cells) always give rise to cells of the same type. Each cell has a particular number of *chromosomes in its nucleus. The sex cells (sperm and ova) always contain half the number of chromosomes of all the other cells of the body (see meiosis); at fertilization a sperm and ovum combine to form a cell with a complete set of chromosomes that will develop into the embryo.... cell

n. a rare malignant tumour of the *bile ducts. Clinical features include abdominal pain, weight loss, pruritus, obstructive jaundice, and abnormal liver function tests. A tumour located at the junction of the right and left hepatic ducts within the liver is known as a Klatskin tumour. Primary sclerosing *cholangitis, *ulcerative colitis, chronic infection with specific liver flukes (such as Clonorchis sinensis), and exposure to the imaging contrast agent Thorotrast are potential risk factors for the development of cholangiocarcinoma. Differentiation from other causes of bile duct *stricture(s), e.g. sclerosing cholangitis, can be very difficult.... cholangiocarcinoma

a malignant tumour of the lining (*endometrium) of the uterus. Risk factors are nulliparity (never having given birth), obesity, and tamoxifen use as chemotherapy for breast cancer. The presenting symptom is usually *postmenopausal bleeding, but this cancer may present with postmenopausal discharge or *pyometra. The tumour invades the *myometrium and spreads down to the cervix and through the Fallopian tubes to the ovaries and peritoneal cavity and through the lymphatics to pelvic and aortic nodes. Prognosis depends on tumour differentiation, depth of myometrial invasion, extent of tumour spread, and involvement of retroperitoneal nodes. Treatment is laparoscopic abdominal *hysterectomy and bilateral *salpingo-oophorectomy, with *lymphadenectomy and radiotherapy if indicated.... endometrial cancer

n. the basic unit of genetic material, which is carried at a particular place on a *chromosome. Originally it was regarded as the unit of inheritance and mutation but is now usually defined as a sequence of *DNA or *RNA that acts as the unit controlling the formation of a single polypeptide chain (see cistron). In diploid organisms, including humans, genes occur as pairs of *alleles. Various kinds of gene have been discovered: structural genes determine the biochemical makeup of the proteins; regulator genes control the rate of protein production (see operon). Architectural genes are responsible for the integration of the protein into the structure of the cell, and temporal genes control the time and place of action of the other genes and largely control the *differentiation of the cells and tissues of the body.... gene

n. 1. the severity of a malignant tumour according to its degree of *differentiation. Low-grade tumours (grade 1) closely resemble normal tissues, are well differentiated, and have a good prognosis. High-grade tumours (grade 3) show a poor resemblance to normal tissues, are poorly differentiated, and have a poor prognosis. Benign tumours are not graded. 2. the severity of a non-neoplastic disease.... grade

n. the formation of new blood vessels resulting from the directed migration and differentiation of angioblasts (precursor cells) into endothelial cells. The primitive vessels undergo further growth and remodelling by *angiogenesis. Although largely confined to the embryo, vasculogenesis has recently been shown to occur in adults from circulating angioblasts.... vasculogenesis