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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Nephelometry - Nephrotic Syndrome
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Negative self-regulation
See negative autogenous regulation.
Negative staining
A staining technique used in electron microscopy in which a reverse or negative image of the object is generated.
Negative supercoiling
The twisting of duplex DNA in a direction opposite to the intrinsic coiling of the double helix.
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Neighbour joining
A hierarachical clustering method similar to UPGMA, which is used in the CLUSTAL W/X programme.
Nematodes
A class of unsegmented worms which are often parasitic. Also called eelworms, especially when phytoparasitic.
Neoformation
Organogenesis; production of newly formed structures, such as tissues, meristems and embryos.
Neomycin
A synthetic antibiotic derived from streptomycin that inhibits bacterial protein synthesis.
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Neonatal hypoglycaemia
Hypoglycaemia that occurs in newborns. This is seen in the following conditions: 1. Transiently in normal babies, especially those suffering from severe infections, respiratory distress and brain damage. 2. Premature and small-for-dates babies because of low glycogen stores. 3. Infacts of diabetic mothers due to foetal exposure to hyperglycaemia. This leads to foetal islet cell hyperplasia with consequent hyperinsulinaemia and hypoglycaemia following parturition. 4. Erythroblastosis foetalis, which is associated with islet cell hyperplasia. 5. Infants suffering from intrauterine malnutrition.
Neonatal jaundice
Retention jaundice that occurs in the newborn, especially in pre-mature infants. It is referred to as "physiological jaundice" and results from excessive haemolysis coupled with an immature hepatic system for the uptake, conjugation and secretion of bilirubin. The activity of UDP-glucuronyl transferase is decreased and synthesis of UDP-glucuronic acid, the substrate for the enzyme may also be reduced. Unconjugated hyperbilirubinaemia develops during the first few days of life and may be as high as 30 mg/dL (517 μmol/L).
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When bilirubin concentration exceeds the binding capacity of albumin, the lipid-soluble unconjugated bilirubin penetrates the blood-brain barrier resulting in hyperbilirubinaemic toxic encephalopathy or kernicterus. This can eventually lead to brain damage and death. The condition may be exacerbated by drugs, which cause haemolysis, displace bilirubin from albumin (sulphonamides) or inhibit glucuronyltransferase (novobiocin). Phenobarbital administration is effective in the treatment of neonatal jaundice. Exposure to visible light by an unknown mechanism can promote hepatic excretion of unconjugated bilirubin.
Neonate
Newborn.
Neoplasm
Abnormal uncontrolled growth. A tumour, which may be benign or malignant.
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Neoteny
The retention of juvenile body characters in the adult state, or the presence of adult characters in the juvenile state.
Nephelometry
A technique that measures the intensity of light scattered by the particles in suspension. This is measured at right angles to the direction of incident light. This method is more sensitive for low concentration. Nephelometry is useful to estimate the concentration of microorganisms, anlayse waste water and evaluate the amount of haze present in beverages and pharmaceuticals.
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Nephrolithiasis
(renal calculi, renal stones) Renal calculi may be formed in the urinary tract due to an imbalance between conservation of water an excretion of insoluble substances. Factors favouring stone formation include high concentration of one or more normal constituents of the glomerular filtrate, alterations in urinary pH due to bacterial infection, obstruction of urinary flow and absence of inhibitors of crystal growth. The substances present in stones include calcium salts, struvite, uric acid or cystine.
Nephron
The functional unit of the kidney. Each kidney contains about a million nephrons, each composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a thin-walled sac like structure called the Bowman's capsule. The afferent arteriole, a branch of the renal artery, forms a capillary network called the glomerulus in the Bowman's capsule. From these capillaries, blood is drained into the efferent arteriole, which supplies the tubule. Beyond the capsule, the nephron becomes tubular and convoluted. This is known as the proximal convoluted tubule (PCT).
The PCT dips into the medulla to form the loop of Henle, which consists of the descending and ascending limbs. The tubule then curves back into the cortex to form the distal convoluted tubule (DCT). Between the DCT and the afferent arteriole is the juxtaglomerular apparatus, which elaborates renin. Several distal tubules merge in the renal cortex to form a collecting duct, which is joined by other ducts to open into the pelvis.
The Structure of Nephron
| 1. |
Afferent Arteriole |
2. |
Glomerulus |
| 3. |
Bowman's Capsule |
4. |
Proximal covoluted tubule |
| 5. |
Cortex |
6. |
Medulla |
| 7. |
Juxtaglomerular Apparatus |
8. |
Distal Convoleted Tubule |
| 9. |
Afferent Arteriole |
10. |
Collecting Duct |
| 11. |
Loop of Henle |
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Nephropathy
Kidney disease.
Nephrotic syndrome
A renal disorder characterised by albuminuria, hypoalbuminaemia and oedema. The primary defect in nephrotic syndrome is an increase in glomerular permeability. This causes albuminuria, loss of IgG and antithrombin III. Nephrotic syndrome is associated with thrombotic tendency, susceptibility to infection and hyperlipidaemia. Management involves low salt diet and diuretic therapy.
Nernst equation
An equation relating the redox potential to the standard redox potential and the concentrations of oxidised and reduced form of the couple.
 Nernst equation
Nerve cell
See neuron.
Nerve growth factor (NGF)
A factor isolated from a tumour transplanted into a chicken embryo. NGF is required for the growth and survival of sensory and sympathetic neurons.
Nesidioblast
A cell that gives rise to the pancreatic islet cell.
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- Dictionary of Bioinformatics, Biotechnology, Biochemistry Part 4
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