the cell, senses of taste, and over text of enghlis medical book

7/30/2019 the cell, senses of taste, and over text of enghlis medical book

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The cell

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit

of life that is classified as a living thing (except virus, which consists only from DNA/RNA covered byprotein and lipids), and is often called the building block of life.[1] Organisms can be classified as

unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and

animals). Humans contain about 10 trillion (1013) cells. Most plant and animal cells are between 1

and 100 m and therefore are visible only under the microscope.

There are two types of cells: eukaryotic and prokaryotic. Prokaryotic cells are usually independent,

while eukaryotic cells can either exist as a single celled organism or be found in multicellular

organisms.

All cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, separates its

interior from its environment, regulates what moves in and out (selectively permeable), and

maintains the electric potential of the cell. Inside the membrane, a salty cytoplasm takes up most of

the cell volume. All cells (except red blood cells which lack a cell nucleus and most organelles to

accommodate maximum space for hemoglobin) possess DNA, the hereditary material of genes that is

sitoated in nucleus an organit in the center of the cell.

Cell division involves a single cell (called a mother cell) dividing into two daughter cells. This leads to

growth in multicellular organisms (the growth of tissue) and to procreation (vegetative reproduction)

in unicellular organisms.

Prokaryotic cells divide by binary fission. Eukaryotic cells usually undergo a process of nucleardivision, called mitosis, followed by division of the cell, called cytokinesis. A diploid cell may also

undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular

organisms, fusing to form new diploid cells.

DNA replication, or the process of duplicating a cell's genome, always happens when a cell divides

through mitosis or binary fission.

A collection of cells of the same tape forms a tissue. Two or more different tissues associates in

performing some special function form an organ. An arangement of organs clossely allied to each

over and concerned to the same function fosrms a system.


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Sense of taste

The sense of taste is also called gustation. For food to have a taste, it must be dissolved in water.

There are four basic tastes: sweet, salty, sour and bitter.

All other tastes come from a combination of these four basic tastes. Actually, a fifth basic taste called"Umami" has recently been discovered. Umami is a taste that occurs when foods with glutamate (like

MSG) are eaten. Different parts of the tongue can detect all types of tastes.

The actual organ of taste is called the "taste bud." Each taste bud (and there approximately 10,000

taste buds in humans) is made up of many (between 50-150) receptor cells. Receptor cells live for

only 1 to 2 weeks and then are replaced by new receptor cells. Each receptor in a taste bud responds

best to one of the basic tastes. A receptor can respond to the other tastes, but it responds strongest

to a particular taste.

There are two cranial nerves that innervate the tongue and are used for taste: the facial nerve

(cranial nerve VII) and the glossopharyngeal nerve (cranial nerve IX). The facial nerve innervates the

anterior (front) two-thirds of the tongue and the glossopharyngeal nerve innervates that posterior

(back) one-third part of the tongue. Another cranial nerve (the vagus nerve, X) carries taste

information from the back part of the mouth. The cranial nerves carry taste information into the

brain to a part of the brain stem called the nucleus of the solitary tract. From the nucleus of the

solitary tract, taste information goes to the thalamus and then to the cerebral cortex. Like

information for smell, taste information also goes to the limbic system (hypothalamus and

amygdala). Another cranial nerve (the trigeminal nerve, V) also innervates the tongue, but is not used

for taste. Rather, the trigeminal nerve carries information related to touch, pressure, temperature

and pain.

The complete inability to taste is called ageusia, the reduced ability to taste is called hypogeusia, and

the enhanced ability to taste is calledhypergeusia. Ageusia is a rare disorder. It may be rare because

there are three different nerves that carry taste information to the brain. Older people have a

reduced sense of taste because their taste buds are not replaced as fast those in younger people.

Taste disorders can also be caused by drugs used to treat epilepsy, Parkinson's disease, diabetes and

high blood pressure. Damage to the areas of the brain such as the brain stem, thalamus and cerebral

cortex may also cause taste problems.


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REUMATIC FEVER

Rheumatic fever is caused by a combination of bacterial infection and immune system overreaction.

In some people, the body reacts with a massive immune system reaction to the affected areas. The

cells that normally kill invading bacteria become so active that they also attack the affected tissues.The result in the joints is temporary arthritis (inflammation of the joints). In the heart, they can

permanently damage heart valves, increasing the risk of heart problems later in life. Rheumatic fever

can also cause problems with the nervous system that are usually reversible.

The symptoms of rheumatic fever depend on whether the heart, joints, or nervous system are

affected. Most people with rheumatic fever have fever and joint pain. The joint pain (arthritis) usually

affects large joints such as the knees, elbows, ankles, or wrists. The joint pain characteristically

migrates from one joint to another, so that one or more joints may be swollen, red, and extremely

tender. The arthritis is usually reversible. The patients temperatures is usually elevated to 101-

102 Fahrenheit(frnhait), a moderate leukocytois is present and the eritrocyte sedimentationrate is increased.

Many people who develop rheumatic fever suffer damage to the muscle tissue of the heart, which

may include their heart valves (endocarditis), heart muscle (myocarditis), sac covering the heart

(pericarditis), or all three. This may cause no symptoms, but some people feel heart palpitations or

chest pain. Occasionally, there is heart failure, people die during a rheumatic fever episode.

The central nervous system may also be affected to produce a symptom known as chorea. Chorea

affects females more frequently and almost never occurs after puberty. The onset of chorea is

usually gradual, and it often first appears several months after the rheumatic fever has passed.

Occasionally, chorea is the only visible symptom of rheumatic fever. Teachers may be the first to

notice it and mistake it for clumsiness or restlessness. Symptoms of chorea may include: grimacing,

muscular weakness, involuntary- purposeless movements of the arms and legs, emotional

disturbances (crying and restlessness).

Infrequently only one side of the body is involved. The movement are increased by efort, excitement,

and fatigue but ceasewhen the patient isasleep. Marked muscular weaknes is freqweent so that hte

child is unable to walk, talk or even to sit up. Often the movements a so violent that hte patient has

to be placed in a padded crib to prevent injury.

Patient with choree usualy do not have fever, leucocytosis or a rapid erytrocyte sedimentation rate.The presents of fever and increased sedimentation rate is usually an indication of cardiac

involvement.

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the cell, senses of taste, and over text of enghlis medical book