Mitosis Health Dictionary

Mitosis: From 4 Different Sources


A type of cell division in which the chromosomes within the nucleus of a cell are exactly duplicated into each of 2 daughter cells.

Before cell division, the chromosomes duplicate themselves and coil up with the 2 copies joined together. The doubled chromosomes line up in the centre of the cell and are pulled apart to opposite ends of the cell, which then divides. Each daughter cell therefore has the same chromosome content as the original cell. (See also meiosis.)

Health Source: BMA Medical Dictionary
Author: The British Medical Association
The classic four-phased cellular division of somatic cells, wherein (when the dust settles) two new daughter cells contain full chromosomal information of the parent, complete nuclei, and half the cytoplasm. This is distinct from cloning (as in the bone morrow) and the chromosome splitting of miosis (ovum and sperm).
Health Source: Herbal Medical
Author: Health Dictionary
The process of cell division for somatic cells and for the ovum after fertilisation. Each chromosome becomes doubled by splitting lengthwise and forming two chromatids which remain held together by the centromere. These chromatids are exact copies of the original chromosomes and contain duplicates of all the genes they bear. When cell division takes place, the pull of the spindle splits the centromere and each double chromatid separates, one passing to one pole of the nucleus and the other to the opposite pole. The nucleus and the cell itself then also divide, forming two new daughter cells containing precisely the same 23 pairs of chromosomes and carrying exactly the same complement of genes as did the mother cell. (See CHROMOSOMES; FERTILISATION; GENES; HEREDITY.)
Health Source: Medical Dictionary
Author: Health Dictionary
n. a type of cell division in which a single cell produces two genetically identical daughter cells. It is the way in which new body cells are produced for both growth and repair. Division of the nucleus (karyokinesis) takes place in four stages (see prophase; metaphase; anaphase; telophase) and is followed by division of the cytoplasm (cytokinesis) to form the two daughter cells (see illustration overleaf). Compare meiosis. —mitotic adj.
Health Source: Oxford | Concise Colour Medical Dictionary
Author: Jonathan Law, Elizabeth Martin

Cell Division

The processes by which cells multiply. Mitosis is the most common form of cell division, giving rise todaughter cells identical to the parent cells.

Meiosis produces egg (see ovum) and sperm cells that differ from their parent cells in that they have only half the normal number of chromosomes.... cell division

Meiosis

A type of cell division that occurs in the ovaries and testes during the production of egg and sperm cells.

During meiosis in humans, a cell containing 23 pairs of chromosomes (46 in total) divides to form 4 sperm or egg cells, each with 23 single chromosomes.

First, the chromosomes are duplicated to produce 4 copies of each chromosome (92 in total).

Matching pairs of chromosomes line up and exchange genetic material.

The cell then divides twice to form 4 daughter cells, with each taking 1 copy of each chromosome.

Egg and sperm cells therefore have only half the usual chromosome content of a body cell, so that each parent contributes half of the child’s genetic material.

The exchange between chromosomes means that each daughter cell has a unique genetic make-up.

(See also mitosis).... meiosis

Antimetabolites

A group of drugs used in the treatment of certain forms of malignant disease. Chemically, they closely resemble substances (or METABOLITES) which are essential for the life and growth of CELLS. Antimetabolites are incorporated into new nuclear material in the cell or combine irreversibly with essential cellular enzymes, thus disrupting normal cellular division (see MITOSIS and MEIOSIS) and causing death of the cell. There is now a range of antimetabolites including CYTARABINE, METHOTREXATE, FLUOROURACIL and MERCAPTOPURINE.... antimetabolites

Colchicum Luteum

Baker.

Family: Liliaceae.

Habitat: The temperate Himalayas from Kashmir to Chamba. Major supplies of the drug are received from Kashmir.

English: Hermodactyls, Colchicum, Meadow Saffron, Golden Collyrium (Indian substitute). (C. luteum is a good substitute for C. autumnale L. which is official in the B.P.)

Ayurvedic: Hiranyatuttha.

Unani: Suranjaan Talkh.

Action: Non-steroidal antiinflammatory, anti-gout (relieves inflammation and pain of acute gout but does not increase expulsion of uric acid, is used with an alkaline diuretic), emetic, cathartic. Anti-chemotactic, antiphlogistic, inhibitor of mitosis. Highly toxic. Used for external application to lessen inflammation and pain.

Key application: In acute gout attack. (German Commission E.)

The fresh corms and aerial parts of a sample from Jammu yielded 0.94% and 070% of total alkaloids, the major being colchicine 0.40% and 0.20% respectively. Colchicine analogs— decteyl thiocolchicine (DTC), decetyl- methylcolchicine (DMC) and tri- methylcolchicinic acid (TMCA) were effective in the treatment of gout; DTC may elicit agranulocytosis.

Colchicine binds to tubulin, the protein subunit of microtubules. Its most important biological effect is the inhibition of processes that depend upon microtubule function by blocking polymerization. In preventing micro- tubule formation, colchicine has been shown to inhibit catecholamine secretion from adrenal medulla, iodine secretion from thyroid gland and pro- lactin secretion from pituitary tumour cells. It inhibits stimulated insulin secretion from isolated perfused pancreas and islets in vitro.

The use of Colchicum for long periods is not recommended owing to its toxicity in larger doses (even 7 mg of colchicine has caused death) and its depressant action upon central nervous system.

Prolonged use of Colchicum autum- nale may cause agranulocytosis, aplas- tic anaemia and peripheral nerve inflammation. (Sharon M. Herr.)... colchicum luteum

Eukaryote

A cell that has a NUCLEUS bounded by a membrane and with chromosomes containing DNA, RNA and proteins. The cell divides by MITOSIS and also contains MITOCHONDRIA. Animals, plants and cellular organisms made up of this type of cell are included in the biological superkingdom of Eukaryote.... eukaryote

Mosaicism

If non-dysjunction occurs after the formation of a ZYGOTE – that is, during a mitotic cell division and not a meiotic cell division (see MITOSIS; MEIOSIS) – some of the cells will have one chromosome constitution and others another. The term mosaicism describes a condition in which a substantial minority of cells in an individual’s body di?er from the majority in their chromosome content. How substantial this minority is will depend upon how early during cleavage the zygote undergoes nondysjunction. Mosaicism can cause disorders such as DOWN’S (DOWN) SYNDROME and TURNER’S SYNDROME. The proportion and type of abnormal cells affect the physical appearance of the affected individual. This may range from normal to the features typical of people with a chromosomal-abnormality syndrome.... mosaicism

Procarbazine

An antineoplastic drug used mainly to treat Hodgkin’s disease (see under LYMPHOMA). It acts by interfering with the process of MITOSIS, the method by which the cells of the body, including tumours, reproduce themselves.... procarbazine

Gene

A unit of the material of heredity. A gene corresponds to a particular area of DNA within a chromosome. There are about 30,000 different genes arranged on the 23 pairs of chromosomes. These genes control the development and functioning of organs and body systems, providing an “instruction manual” for an individual’s growth, survival, reproduction, and possibly also for aging and death. Genes also play a part, together with environmental factors, in determining a person’s intelligence, personality, and behaviour.

Genes fulfil these functions by directing the manufacture of proteins. Many proteins have a structural or catalytic role in the body. Others switch genes “on” or “off”. The genes that make these regulatory proteins are called control genes. The activities of control genes determine the specialization of cells; within any cell some genes are active and others idle, according to its particular function. If the control genes are disrupted, cells lose their specialist abilities and multiply out of control; this is the probable mechanism by which cancers form (see carcinogenesis; oncogenes).Each of a person’s body cells contains an identical set of genes because all the cells are derived, by a process of division, from a single fertilized egg, and with each division the genes are copied to each offspring cell (see mitosis; meiosis). Occasionally, a fault occurs in the copying process, leading to a mutation. The gene at any particular location on a chromosome can exist in any of various forms, called alleles. If the effects of an allele mask those of the allele at the same location on its partner chromosome, it is called dominant. The masked allele is recessive. (See also genetic code; inheritance.)... gene

Amitosis

n. division of the nucleus of a cell by a process, not involving *mitosis, in which the nucleus is constricted into two.... amitosis

Anaphase

n. the third stage of *mitosis and of each division of *meiosis. In mitosis and anaphase II of meiosis the chromatids separate, becoming daughter chromosomes, and move apart along the spindle fibres towards opposite ends of the cell. In anaphase I of meiosis the pairs of homologous chromosomes separate from each other. See disjunction.... anaphase

Comfrey

Knitbone. Symphytum officinale, L. French: Grande consoude. German: Reinweld. Italian: Consolide maggiore. Part used: root and leaves. Considerable therapeutic versatility.

Constituents: allantoin, pyrrolizidine alkaloids (fresh young leaves and roots), mucilage, phenolic acids, steroidal saponins (root).

Action: astringent-demulcent, haemostatic, vulnerary. Rapid healer of flesh and bones by its property to accelerate mitosis (cell-division). Useful wherever a mucilaginous tissue restorative is required (repairing broken bones and lacerated flesh), especially in combination with Slippery Elm powder which prevents excess fluidity.

Uses: Ulceration anywhere along the gastrointestinal tract; colitis, hiatus hernia.

Bleeding from stomach, throat, bowel, bladder and lungs (haemoptysis) in which it reduces blood clotting time. Once used extensively for tuberculosis (pulmonary and elsewhere). Irritating cough, ‘dry’ lung complaints; pleurisy. Increases expectoration. Should not be given for oedematous conditions of the lungs.

Bones – fractures: to promote formation of a callus; rickets, wasting disease. Skin – varicose ulcers and indolent irritating sores that refuse to heal. Promotes suppuration of boils and gangrene as in diabetes. Bruises. STD skin lesions, internally and externally. Blood sugar control: assists function of the pancreas. Urine: scalding. Rheumatoid arthritis: improvement reported. Malignancy: cases of complete regression of sarcoma and carcinoma recorded. Rodent ulcer, (as a paste).

Preparations: thrice daily.

Tea: dried herb, one heaped teaspoon to each cup; or, 1oz to 1 pint boiling water; infuse 15 minutes, half- 1 cup for no more than 8 weeks.

Tincture (leaf). 1 part to 5 parts alcohol: dose 2.5-5ml. Maximum weekly dosage – 100ml for no more than 8 weeks.

Tincture (root). 1 part to 5 parts alcohol. Maximum weekly dosage – 80ml, for 8 weeks.

(National Institute of Medical Herbalists)

Poultice. A mucilage is prepared from fresh root in a liquidiser or by use of a rolling pin. For sprains, bruises, severe cuts, cleaning-out old ulcers and wounds.

Compress. 3 tablespoons crushed root or powder in 1 pint (500ml) water. Bring to boil; simmer gently 10 minutes. Saturate linen or suitable material and apply. Renew 2-3 times daily as moisture dries off. Ointment. 1 part powder, or liquid extract, to 10 parts base (cooking fat, Vaseline, etc).

Oil (external use). Ingredients: powdered Comfrey root in peanut oil and natural chlorophyll. (Henry Doubleday Research Association)

Notes. Contains trace element germanium, often given for cancer and arthritis. (Dr Uta Sandra Goodman) Helps eliminate toxic minerals. Neutralises free radicals that are created by toxic substances entering the body. Restores the body’s pH balance disturbed by highly acid foods such as meat, dairy products, refined foods and alcohol.

Dr H.E. Kirschner, well-known American physician, reported being called to the bedside of a patient with a huge advanced cancer of the breast. The odour was over-powering and the condition hopeless, but he advised poultices of fresh crushed Comfrey leaves several times daily to the discharging mass. Much to the surprise of all, the vile odour disappeared. The huge sore scaled over and the swelling subsided. Within three weeks the once-malignant sore was covered with a healthy scale and the pain disappeared. Unfortunately, treatment came too late; metastases had appeared in the liver which could not be reached by the poultices.

Claims that Comfrey is a toxic plant are unsubstantiated by a mass of clinical evidence to the contrary. Attempts to equate the effects of its isolated compounds apart from the whole plant yield conflicting results. For thousands of years the plant has been used by ancient and modern civilisations for healing purposes. Risks must be balanced with benefits.

There is a growing body of opinion to support the belief that a herb which has, without ill-effects been used for centuries and capable of producing convincing results is to be recognised as safe and effective.

Experiments reveal that in sufficient doses Comfrey can cause liver disease in laboratory animals. Its risk to humans has been a matter of serious debate since the 1960s, and is still unresolved. Although the overall risk is very low, a restriction has been placed on the plant as a precautionary measure. Fresh Comfrey leaves should not be used as a vegetable which is believed to be a health risk. It is believed that no toxicity has been found in common Comfrey (Symphytum officinale L). No restriction has been placed on use of dried Comfrey leaves as a tea. The debate continues.

It would appear that use of the root of Symphytum officinale may be justified in the treatment of severe bone diseases for which it has achieved a measure of success in the past, such as rickets, Paget’s disease, fractured bones, tuberculosis, etc, its benefits outweighing risks. Few other medicinal plants replenish wasted bone cells with the speed of Comfrey. (external use only) ... comfrey

Cytostatic

A herb which tends to slowdown mitosis (division and multiplication of cells) that can be of value as a supportive aid in malignancy.

Goldenseal, Mistletoe, Red Clover, Violet leaves. See also: ANTI-NEOPLASTIC. ... cytostatic

Aster

n. a star-shaped object in a cell that surrounds the *centrosome during mitosis and meiosis and is concerned with the formation of the *spindle.... aster

Astrocytoma

n. a brain tumour derived from non-nervous cells (*glia), which – unlike the neurons – retain the ability to reproduce themselves by mitosis. All grades of malignancy occur, from slow-growing tumours whose histological structure resembles normal glial cells, to rapidly growing highly invasive tumours whose cell structure is poorly differentiated (including anaplastic astrocytoma and *glioblastoma). In adults astrocytomas are usually found in the cerebral hemispheres but in children they also occur in the cerebellum.... astrocytoma

Centromere

(kinetochore) n. the part of a chromosome that joins the two *chromatids to each other and becomes attached to the spindle during *mitosis and *meiosis. When chromosome division takes place the centromeres split longitudinally.... centromere

Nucleic Acids

Substances found in all living matter that have a fundamental role in the propagation of life. Nucleic acids provide the inherited coded instructions (or “blueprint”) for an organism’s development.

There are 2 types of nucleic acid: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). In all plant and animal cells, including human cells, DNA permanently holds the coded instructions, which are translated and implemented by RNA. DNA is the main constituent of chromosomes, which are carried in the nucleus (central unit) of the cell.

DNA and RNA are similar in structure, both comprising long, chain-like molecules. However, DNA usually consists of 2 intertwined chains, whereas RNA is generally single-stranded.

The basic structure of DNA has been likened to a rope ladder, the chains forming the 2 sides, with interlinking structures in between forming the rungs.

The ladder is twisted into a spiral shape called a double helix.

Each DNA chain has a “backbone” consisting of a string of sugar and phosphate chemical groups. Attached to each sugar is a chemical called a base, which can be any of 4 types (adenine, thymine, guanine, and cytosine) and forms half a rung of the DNA ladder. The 4 bases can occur in any sequence along the chain. The sequence, which may be many millions of individual bases long, provides the code for the activities of the cell (see genetic code).

RNA is like a single strand of DNA; the main difference is that the base thymine is replaced by another base, uracil.When a cell undergoes mitotic (see mitosis) division, identical copies of its DNA must go to each of the 2 daughter cells. The 2 DNA chains separate, and 2 more chains are formed, side by side with the original chains. Because only certain base pairings are possible, the new double chains are identical to the original DNA molecule. Each of a person’s cells carries the same DNA replica that was present in the fertilized ovum, so the DNA message passes from one generation of cells to the next.... nucleic acids

Cell

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

Chromatid

n. one of the two threadlike strands formed by longitudinal division of a chromosome during *mitosis and *meiosis. They remain attached at the *centromere. Chromatids can be seen between early prophase and metaphase in mitosis and between diplotene and the second metaphase of meiosis, after which they divide at the centromere to form daughter chromosomes.... chromatid

Disjunction

n. the separation of pairs of homologous chromosomes during meiosis or of the chromatids of a chromosome during *anaphase of mitosis or meiosis. Compare nondisjunction.... disjunction

Euchromatin

n. chromosome material (see chromatin) that stains most deeply during mitosis and represents the major genes. Compare heterochromatin.... euchromatin

Heterochromatin

n. chromosome material (see chromatin) that stains most deeply when the cell is not dividing. It is thought not to represent major genes but may be involved in controlling these genes, and also in controlling mitosis and development. Compare euchromatin.... heterochromatin

Interphase

(interkinesis) n. the period when a cell is not undergoing division (mitosis), during which activities such as DNA synthesis occur.... interphase

Karyokinesis

n. division of the nucleus of a cell, which occurs during cell division before division of the cytoplasm (cytokinesis). See mitosis.... karyokinesis

Metaphase

n. the second stage of *mitosis and of each division of *meiosis, in which the chromosomes line up at the centre of the *spindle, with their centromeres attached to the spindle fibres.... metaphase

Chromosome

n. one of the threadlike structures in a cell nucleus that carry the genetic information in the form of *genes. It is composed of a long double filament of *DNA coiled into a helix together with associated proteins, with the genes arranged in a linear manner along its length. It stains deeply with basic dyes during cell division (see meiosis; mitosis). The nucleus of each human somatic cell contains 46 chromosomes, 23 of which are of maternal and 23 of paternal origin (see illustration). Each chromosome can duplicate an exact copy of itself between each cell division (see interphase) so that each new cell formed receives a full set of chromosomes. See also chromatid; centromere; sex chromosome. —chromosomal adj.... chromosome

Mitogen

n. any substance that can cause cells to begin division (*mitosis).... mitogen

Nondisjunction

n. a condition in which pairs of homologous chromosomes fail to separate during meiosis or a chromosome fails to divide at *anaphase of mitosis or meiosis. It results in a cell with an abnormal number of chromosomes (see monosomy; trisomy).... nondisjunction

Prophase

n. the first stage of *mitosis and of each division of *meiosis, in which the chromosomes become visible under the microscope. The first prophase of meiosis occurs in five stages (see leptotene; zygotene; pachytene; diplotene; diakinesis).... prophase

Spermatogonium

n. (pl. spermatogonia) a cell produced at an early stage in the formation of spermatozoa (see spermatogenesis). Spermatogonia first appear in the testis of the fetus but do not multiply significantly until after puberty. They act as stem cells in the walls of the seminiferous tubules, dividing continuously by mitosis and giving rise to *spermatocytes.... spermatogonium

Spindle

n. a collection of fibres seen in a cell when it is dividing. The fibres radiate from the two ends (poles) and meet at the centre (the equator) giving a structure shaped like two cones placed base to base. It plays an important part in chromosome movement in *mitosis and *meiosis and is also involved in division of the cytoplasm.... spindle

Telophase

n. the final stage of *mitosis and of each of the divisions of *meiosis, in which the chromosomes at each end of the cell become long and thin and the nuclear membrane reforms around them. The cytoplasm begins to divide.... telophase



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