Section 3 Medical Literature 第三部分 医学文献
Part 1.
The majority of blood cells originates from stem cells located inside the bone marrow:therefore the most “productive” areas correspond to the areas where red bone marrow is abundant:in an adult，this is found mostly inside cranial bones，vertebrae，ribs，inside the pelvis，the sternum and in the femurs.During infancy，all types of bones are involved，while during the fetal period，even the spleen and the liver are involved as well.Here，through long chains of cellular division and of successive differentiation,basophile1) white blood cells，neutrophil2) and eosinophils3) most of the lymphocytes and numerous monocytes and macrophagocytes，are constantly forming.
Here,even red blood cells and platelets reach full “maturation4)”.Lymphocytes(abundant inside the lymph)are also produced in the liver,the spleen and in the lymph nodes.
All the blood and lymph node cells have a predetermined lifespan:for example，after going from the bone marrow into the blood circulation，a red blood cell has an average life of about 120 days.During this time，it covers about 15000 km through the entire circulatory system and it usually ends up inside the liver or the spleen，which allows for the recycling of iron needed to mak up hemoglobin5).
If we consider that an average of 4 and million red blood cells circulate inside the body of an adult，and that every 120 days new ones are circulating，we are able to understand the efficiency and the speed of the cellular reproductive processes active inside the bone marrow，and the potential damage that this tissue can be exposed to，due to mutagen substances.Even the other cellular components have a set life span:after a relatively brief life they are phagocytized by the located inside spleen,the liver and the lymph nodes,digested by their enzymes and “recycled”as raw materials.
注释：
1）basophile 嗜碱（染色）的
2）neutrophil 中性白细胞
3）eosinophile 嗜酸细胞
4）maturation 成熟，化脓
5）hemoglobin 血红蛋白
Part 2.
The total amount of body water(TBW)may be considered as being contained in two compartments or spaces:the compartment of the intracellular fluid1)(ICF)，i.e.the fluid in the cells and the compartment of extracellular fluid2)(ECF)，i.e.the fluid outside the cells which are embedded.The TBW constitutes about 60(50-70)% of the body weight.Generally，there are two methods for measuring TBW.The direct method can only be used in the animal by drying the carcass completely and measuring the weight loss.In living animals or in human being，the indirect method is used.The principle of this method is based on dilution.In measuring TBW the substance injected must be freely diffusible throughout the body，and should not cause any toxic effect.Values at different ages are different.In adult，males have higher TBW values(about 62% of body weight)than females(51%)，because males generally have less adipose tissue and the adipose tissue has a low water content.It is therefore more reliable to relate measurements of TBW to the weight of lean body mass rather than the total body weight.
INTRACELLULAR FLUID
The ICF which constitutes about 25% of the TBW is inside the approximately 75 trillion cells of the body.The fluid of each cell contains its own individual mixture of different constituents but the concentration of these constituents is similar in most cells.ICF can not be measured directly，but is estimated as the difference between the values of TBW and ECF.
EXTRACELLULAR FLUID
The extracellular fluid is measured also by determining the dilution of a substance injected intravenously which remains extracellularly in its distribution.Examples are inulin,bromide3),sodium thiosulphate4) and thiocyanate5) which most nearly fulfill this requirement.However，the value obtained should be qualified by naming the substance used.For instance，it is thiosulphate space when thiosulphate is used.The thiosulphate space is about 17(15.4-19.0)% of the body weight in men and is slightly above 17% in women.
Interstitial fluid The volume of the interstitial fluid or tissue fluid is obtained by subtracting the plasma volume from that of ECF.It contributes about 12% of the body weight.
Plasma Blood consists of a pale amber coloured fluid，the plasma and the formed elements，red cells，white cells and platelets which are suspended in the plasma.Plasma is a part of the body fluid.The volume of plasma can also be measured by dye dilution or isotope dilution methods.A nontoxic dye，Evans blue is usually used to measure the plasma volume.However，it begins to leave the circulation in a few minutes.The use of labeled human albumin may therefore be more accurate.
Plasma contains numerous dissolved materials including proteins，carbohydrates，lipids，electrolytes，pigments，hormones and others.The plasma proteins(albumins,globulins and fibrinogen)can be separated and quantified by means of electrophoresis.The total plasma protein concentration is 5-7g/dl，with albumin at a concentration of 3-4g/dl，the globulin at about 1.5-2.0g/dl and fibrinogen at a 0.2-0.4g/dl.(https://www.daowen.com)
Many of the physical and chemical properties of plasma are influenced by the plasma proteins.They are responsible for the specific gravity of plasma which is 1.028 as well as the plasma viscosity.Albumin and globulin substantially determine the colloidal osmotic pressure of plasma.Globulin and fibrinogen decide the suspension stability of the red blood cells in plasma.Fibrinogen is essential for coagulation.The globulins are important in antibody formation.The plasma proteins also act as substrates for the release of peptides such as angiotensin and bradykinin and as binding vehicles for the transport of substance such as metal ions，fatty acids，steroids，hormones and drugs.All the proteins contribute to the buffering capacity of blood.
Other extracellular fluids Lymph,cerebrospinal fluid,fluid in abdominal,pleural and joint cavities,and aqueous humor of the eye hall are all examples of specialized interstitial fluid.Not only each fluid is different in composition from the plasma dialysate，but also in some respects they differ from each other.For example,cerebrospinal fluid has higher Cl-concentration than plasma dialysate,while the concentrations of K+ and Ca2+ are significantly lower in this fluid.
注释：
1）intracellular fluid 细胞内液
2）extracellular fluid 细胞外液
3）bromide 溴化物
4）sodium thiosulphate 硫代硫酸钠
5）thiocyanate 硫氰酸盐
Part 3.
AIDS The irony of AIDS is that the human immunodeficiency virus1)(HIV)attacks the very cells whose job is to fight off infection.
One of the most obvious abnormalities in the blood of someone with AIDS is the lack of the white blood cells known as T-helper cells.These cells have a key role in the body’s defense against infection.Their number declines as AIDS progresses，until virtually none remains.At this stage the person’s chances of survival rapidly diminish，as he or she falls prey to a whole range of infections as well as certain cancers.
Scientists established several years ago that HIV can infect the T-helper cell.Yet this is only part of the story.In someone with AIDS，only a small proportion of T-helper cells are infected with the virus.Other infected white cells(called macrophages2))may also be blame.Scientists now know that HIV infects a much higher proportion of macrophages than T-helper cells.Instead of killing them，the virus seems to sit quietly in these cells for many months before reproducing itself.
The more scientists find out about the way in which HIV infects people，and how it goes about damaging the immune system，the more complicated the whole process seems.At the Fourth International Conference on AIDS held in Stockholm in Jun，researchers heard that there can be a long interval between infection with the virus and appearance of antibodies against it.
Doctors usually advise people that the period between infection and the appearance of antibodies can be about three months.A new，highly sensitive test suggests that，in certain cases，antibodies take much longer to develop.
The human immunodeficiency virus is not easy to catch.It is less infectious than the hepatitis B virus，for example.Only about one in 100 health-care workers who have stabbed themselves with a needle known to contain blood form someone infected with HIV have become infected as a result.However，there have been a handful of reports of people who became infected after they spilled blood from infected people on their hands or splashed it in their eyes or mouth.
The number of people who have become infected by such routes is minute when compared to the millions infected as a result of sexual intercourse3) with an infected person，or the thousands who have caught the virus because they shared needles for injecting drugs with infected people.
Throughout the world，sexual intercourse between heterosexuals is probably the main route of transmission.In the US，where heterosexual transmission now accounts for about 3.5 percent of cases of AIDS，some scientists believe that heterosexuals will account for 10 percent of cases within the next 10 years.Infection with HIV does not seem to be inevitable following heterosexual intercourse with an infected person.In some heterosexual4) couples,the uninfected parter remains uninfected despite,in some cases，unprotected intercourse over along period of time.Yet there have been some reports，including two in Britain，where women have become infected after just one or two acts of intercourse with a man infected with HIV.
注释：
1）human immunodeficiency virus 人类免疫缺陷病毒（AIDS病毒）
2）macrophages 巨噬细胞
3）sexual intercourse 性行为，性交
4）heterosexual 异性的，异性恋的