Perawatan Mesin Penggerak Utama

Kegiatan perawatan ini pada dasarnya dilakukan apabila waktu yang telah ditentukan oleh catatan perawatan motor induk tiba pada waktunya. Biasanya kegiatan perawatan ini dilakukan bersamaan dengan kegiatan docking kapal. Namun perawatan tidak mengenal waktu artinya dapat dilakukan setiap saat bila diperlukan. Perawatan mesin induk dibagi menjadi perawatan harian, perawatan berkala. Disini dapat disampaikan beberapa bagian mesin induk dengan sistem perawatannya antara lain : Perawatan 10 jam (harian) : Sistem bahan bakar : periksa isi bahan bakar pada tangki harian, tambah jika kurang, jika perlu ganti saringan bahan bakar, Sistem pelumasan : periksa isi minyak pelumas jika kurang tambah, jika perlu ganti saringan pelumas, ganti oli karter, Perawatan setiap 60 jam - Bak minyak pelumas : ganti minyak pelumas, buang minyak dari saringan minyak pelumas dan pendingin minyak pelumas, ganti elemen saringan minyak pelumas - Bak minyak pelumas dan pompa penyemprotan bahan bakar : periksa dan tambah - Governor (mekanik) : periksa dan tambah - Governor (pnumatik) : periksa dan tambah - Sistem pendingin : saringan minyak pelumas cuci rumah saringan, saringan bahan bakar buang bahan bakar yang tercampur dengan kotoran dan air - Sistem bahan bakar : tangki bahan bakar periksa dan kuras bebaskan kotoran dan air bersihkan Perawatan setiap 120 jam - Bak minyak pelumas : ganti minyak pelumas, buang minyak dari saringan minyak pelumas dan pendingin minyak pelumas, ganti elemen saringan minyak pelum - Bak minyak pelumas dan pompa penyemprotan bahan bakar : ganti minyak pelumas - Governor (mekanik) : periksa dan tambah,ganti minyak pelumas - Governor (pnumatik) : lumasi diafragma - Saringan udara (minyak pelumas) : ganti minyak pelumas dan cuci bak minyak - Puli penarik kipas : periksa - Sistem pendingin saringan minyak pelumas : ganti elemen saringan bersamaan pada waktu ganti minyak pelumas atau lampu tanda peringatan tekanan minyak pelumas menyala dan cuci rumah saringan - Pompa pengisi bahan bakar : bersihkan saringan - Sistem bahan bakar penyemprotan bahan bakar : Periksa tekanan penyemprotan dan kondisi pengabutannya, bersihkan kerak karbon dan kotoran, bersihkan tangki bahan bakar dari air dan kotoran Perawatan 250 jam - Sistem bahan bakar penyemprotan bahan bakar : Periksa tekanan penyemprotan dan kondisi pengabutannya, bersihkan kerak karbon dan kotoran, bersihkan tangki bahan bakar dari air dan kotoran Perawatan 500 jam - Motor starter : periksa dan bersihkan pada umumnya - Sistem pendingin : cuci bak minyak pelumas dan saringan isap minyak pelumas, pendingin minyak pelumas - Sistem bahan bakar : cuci tangki bahan bakar Perawatan 1000 jam - Sistem pendingin : saringan bahan bakar ganti elemen saringan

UAN SMP Bahasa Inggris (sample)

Chose the best answer!

1. Windi : I'd like to buy a shirt.
Shop assistant : Which shirt do you like, the one with long sleeves or short sleeves?
Windi : ……………. It’s nice

A. I like the shirt with long sleeves
B. I don't like either of them
C. I don't like both
D. I don't like it

2. Rosi : Yesterday morning my mother saw you in the market. What did you buy there?
Atik : I ... a head of cabbage.

A. buy B. bought
C. am buying D.will buy

3. The plant has short stiff leaves. It can be planted in the ground and grows quite tall. Usually it is put in a hanging pot. It has beautiful flowers which are mostly purple and red. The flowers last a long time before they die. What flower is it? It is ...

A. a rose B. a lily
C. an orchid D. a jasmine

4. Ary : Why didn’t you come with, us to the Safari Park yesterday?
Mary : My mother was seriously ill and I had to stay, home to be with her
Ani : ... I hope she will get better soon.

A. That's great
B. That's wonderful
C. Thank’ you for that
D. I am sorry to hear that.

5. Waiter : What can I do for you, sir?
Guest : …
Waiter : Yes, certainly.
A. Can I see the menu, please?
B. Would you like the menu?
C. May 1 borrow-the menu?
D. Will you write the menu? .


6. Rina : Hi, Jane. I hear that your sister gave birth to a son ...
Jane : Three and a half kilos.
Rina : Really? He must be a healthy baby.

A. How much does he weigh?
B. How old is he?
C. How cut is he?
D. How tall is he?

7. Rita : Where did you go for your holiday?
Tuti : I went to Bali.
Rita : How was ... there?
Tuti : It was hot and dry

A. the season
B. the climate
C. the weather
D. the temperature

8. Ziky : What about the hotel?
Ilham : Don't worry. There'll be enough rooms for the guests.
Widuri : ... because it's a public holiday.

A. I think so.
B. What a nice day
C. I'm pleased with it
D. lam doubtful about that.

9. What do you know about a zebra?
A Zebra is ... a horse but has black and white stripes

A. like
B. not the same as
C. different from
D. not similar to

10. X : Get up, please. Riko.
Y : In a minute, Mom. I'm still sleepy.
X : Come on. Have a shower right now, or you'll be late for school.
Where does the dialogue take place?

A. In the office
B. At home
C. In class
D. In the library

11. Dony : ... do you go fishing?
Deni : Once a week.
A. How far
B. How long
C. How often
D. How many

12. Mr. Wilman : Mr. Enoch, do you mind having dinnerat my house this evening?
Mr. Enoch : That sounds good.
Mr. Wilman : Are you sure?
Mr. Enoch : …
A. I'm positive
B. Fine, go ahead
C. I'm afraid I can't
D. No, I can't

13. This notice means ...



a. Throw your rubbish here
b. Bring your own rubbish
c. Do not throw rubbish here
d. Do not pick up the rubbish
For questions 30 to 32 choose the best words to complete the text
Here are some ... (14) on how to be a successful English learner. First, don't be ... (15) of making mistakes. Second, use every opportunity to practice your English. At last, be an optimistic person

14. A. tips 15. A. afraid
B. clues B. proud
C. plans C. brave
D. rules D. shy

Read the following text and answer questions 15 to 17

The Lamb and the Wolf
One day the wolf was slaking his thirst at a stream when he chanced to see a lamb, also drinking, at some distance down the stream. Outraged, he growled, "You are muddying my drinking water, now I shall eat you."
The lamb protested, "But, Sir, how can I be muddying your drinking water? I am farther down stream than you are. The water is flowing from your part of the stream to where I am."
"Upstream or downstream, your drinking is muddying my water, and I shall eat you." So saying, the wolf leaped upon the lamb and devoured him.

14. Where did the story happen?
a. On the river.
b. In the forest
c. In the jungle
d. At the zoo.

15. The following facts made the wolf get angry with the lamb, except ...
A. the lamb muddied the water
B. the wolf wanted to eat the lamb
C. the lamb drank at the same stream
D. the lamb protested him

16. We can learn from the story that …
A. Never drink the river water,
B. Never clean our body on the stream.
C. The bad will always beat the good.
D. The strong will always rule the weak.

Definition of a translation

Translation, as process, is always uni-directional, namely, it is always performed in a given direction from a source language into a target language. Different writers define translation in different ways. Here are some translation definitions.

• Translation is the replacement of textual material in one language ( source language) by equivalent textual material in another language (target language). (catford, 1969)
• Translation is made possible by an equivalent thought that lies behind its different verbal expression.(Savory, 1969)
• Translation consists in reproducing in the receptor language the closest natural equivalent of source languge message, first in terms of meaning and secondly in terms of style (Nida, 1969)
• Translation is aproses of finding a target language equivalent for an source language utterance. (Pinchuck, 1977)
• Translation is the rendering of a source language text into the target language so as to ensure that : 1. The surface meaning of the two will approximately similar and the structure of the source language will be preserved as closely as possible but not so closely that the target language structures will be seriously distorted. (Mc Guire, 1980)
• Translation is a craft consisting in the attempt to replace a written message and or by statement in one language by the same message and or statement in another language. (Newmark, 1981)

from some translation definition above, we may focus that:

• The word equivalent is used by Catford, Savory, Nida, and Pinchuck. While Mc GUire uses the word similar which is synonymous to the word equivalent.
• Textual material(Catford), source language (McGuire), written message (Newmark), and Source Language message (Nida) are synonymous to indicate something to be translated into target language.
• Replacement (catford) and reproducing (Nida) derive from replace and reproduce which are synonymous. The word replace is used by Newmark.

Thus equivalent, source language text and replacement are the three important elements in translation. Some other element include meaning, style, craft and process.
Translation equivalence could be in the rank of word for word, phrase for phrase, sentence for sentence and so on.
It seems easier to get the equivalent of English words in isolation, but when it comes to phrases and sentences then the knowledge of grammar plays an important role.
Since word sometimes have more than one meaning, their translation equivalent could be a problem unless they are used in context (Phrase, sentence, or paragraph).

The Angiosperms Question and Answer

1. What are angiosperms, the flowering plants? What is the main feature that distinguishes them from the gymnosperms?
Flowering plants have flowers and seeds (phanerogamic plants). They differ from gymnosperms by having their seeds within fruits.

2. What are the two main groups into which flowering plants are divided?
Angiosperm plants are divided into monocotyledonous (monocots) and dicotyledonous (dicots).

3. What are the main morphological differences between monocot plants and dicot plants?
The main differentiation criteria between monocots and dicots are: number of cotyledons (seed leaf) in seeds, one in monocots and two in dicots; pattern of leaf veins, parallel in monocots, reticulated in dicots; multiplicity of petal number, multiples of three in monocots, multiples of four or five in dicots; position of vascular bundles in the stem, scattered in monocots, concentrically ringed in dicots.
Grasses, banana tree, sugar cane, orchids are examples of monocots. Sunflowers, oaks and waterlilies are examples of dicots.

4. What are the androecium and the gynoecium? What are the other structures of flowers?
Androecium is the set of male reproductive structures of flowers. It comprehends the stamens formed of filament and anther; one flower has one androecium that may have one or several stamens. Gynoecium is the set of female reproductive structures of flowers. It generally is composed of a single pistil that includes the stigma, the style and the ovary. The androecium usually surrounds the central gynoecium.
Besides the androecium and the gynoecium typical flowers are also made of peduncle, sepals and petals.

5. What is pollination? What are the main forms of pollination?
The process in which pollen grains (the male gametophytes of phanerogamic plants) reach the female gametophyte is called pollination.
The main forms of pollination are: anemophily, in which pollen is carried by wind. Hydrophily, pollination helped by water; entomophily, pollen carried by insects; ornitophily, pollination by birds; chiropterophily, pollen dissemination by bats.

Characteristics of the flowers of each plant species relate to the type of pollination used by the plant. Colored flowers are specialized in bird and insect attraction; nocturnal flowers generally are white and perfumed, many specialized in pollination by bats; the nectar is also a specialization to attract pollinator animals; flowers that produce an exaggerated amount of pollen often use the wind as pollinator; the position of anthers more external or internal next to the nectar is a way to facilitate the pollen dissemination respectively by the wind or by animals.

6. How are the male gametophytes and the male gametes formed in angiosperms?
In the anthers of each stamen there are pollen sacs. Within the pollen sacs there are microspore mother cells, or microsporocytes. These cells undergo meiosis forming microspores. Each microspore by mitosis forms a pollen grain containing one generative cell and one tube cell. The pollen grain is the male gametophyte.
When pollination occurs and the pollen grain makes contact with the stigma (the apex of the pistil) the tube cell elongates its cytoplasm forming the pollen tube that grows towards the ovary. The generative cell divides forming two sperm nuclei (male gametes) that migrate through the pollen tube.

7. How many cellular nuclei does the pollen tube of angiosperms have? What is the ploidy of each of these nuclei?
The pollen tube that is the mature male gametophyte of angiosperms has three cellular nuclei: two sperm nuclei and one tube cell nucleus.
All those nuclei are part of the male gametophyte of the plant and thus each of them is haploid (n).

8. How is the female gametophyte formed in angiosperms?
In the flower ovary there are megasporangia enclosed by a tegument having a small opening, the micropyle. Within the megasporangium there is a megasporocyte, or megaspore mother cell, that undergoes meiosis forming four megaspores of which three regress and only one is functional. The functional megaspore undergoes (three) mitosis generating eight cells that as a whole form the embryonic sac.

9. What is the embryonic sac? Which are the cells that form the embryonic sac? What are their ploidies?
The embryonic sac is the female gametophyte of angiosperms.
The embryonic sac is composed of three cells that remain next to the micropyle, two lateral synergids and the central oosphere (egg); one binucleated cell, the polar nuclei, is placed in the central region; three antipodal cells stay in the opposite side to the micropyle.
Since all these cells come by mitosis from the functional megaspore they are haploid (n).

10. After pollination how does fecundation occur in angiosperms? In these plants is fecundation dependent on water?
After pollination one of the sperm nuclei from the pollen tube unites with the oosphere of the embryonic sac forming the diploid (2n) zygote. The other sperm nucleus fuses with the polar nuclei of the embryonic sac originating a triploid (3n) cell that by mitosis will turn into the secondary endosperm of the seed. The synergids and the antipodal cells degenerate after the fecundation process.
Fecundation in these plants is independent from water.

11. What is the difference between self pollination and cross pollination? Which of these two modes of pollination contributes more to the plant diversity?
Self pollination occurs when pollen grains from a flowering plant fall into the pistils of the same plant and thus gametes from the same individual unite to form a zygote. Cross pollination occurs when pollinators carry pollen grains from a plant to reach other individual plants of the same species thus gametes of different individuals form the zygote.
Since it promotes formation of zygotes containing genes from different individuals (new gene combinations) cross pollination contributes more to biological diversity.

12. What is dichogamy?
Dichogamy is the phenomenon of the maturation of female reproductive structures of the plant in a different period to the maturation of the male reproductive structures. Dichogamy prevents self pollination and makes cross pollination almost obligatory so assisting in an evolutionary strategy to promote genetic recombination.

13. What are the typical structures of the seed? What is endosperm?
A typical seed is composed of the embryo, endosperm and shell. Within seeds of angiosperms there are one or two cotyledons (seed leaf, one in monocots, two in dicots).
The endosperm is the tissue within the seed that has the function of nourishing the embryo.

14. How different are the endosperm of gymnosperms and the endosperm of angiosperms?
In gymnosperms the endosperm is haploid (n), it is called primary endosperm. In angiosperm the endosperm is triploid (3n), it is called secondary endosperm.

15. What are cotyledons?
Cotyledons, or seed leaves, are structures formed by the embryo of angiosperms to absorb nutrients from the endosperm and to store and transfer these nutrients to the embryo. (Cotyledons are auxiliary embryonic structures).
Seeds of monocots have a single cotyledon. Seeds of dicots have two cotyledons.

16. What are the main functions of fruits?
The main functions of fruits are the protection and spreading of seeds.

17. From which floral structure do fruits come?
Fruits are modified ovaries of the flowers.

18. How are fruits formed?
The fecundation in angiosperms triggers the release of hormones that act upon the ovaries. The ovary wall then develops into a fruit that contains the seeds.

19. Are fruits always the flesh part of the “fruits”? Is the edible part of the onion a fruit?
In some so-called fruits the actual fruit is not the flesh part. For example, the flesh part of the strawberry is not the fruit. The fruits are the small hard dots on the surface of the strawberry. Another example: the flesh part of the cashew is not the fruit. The fruit is the nut.
The edible part of the onion is the stem of the plant and not the fruit.

20. Why are there plants having single-seeded fruits and plants having fruits with more than one seed?
Plants that produce single-seeded fruits, for example, mango and avocado, often have ovaries with only one egg inside. Fruits with more than one seed are originated from plants whose ovaries have more than one egg.

21. What are infructescences, pseudofruits and parthenocarpic fruits?
Infructescences are aggregated fruits formed from inflorescences, aggregated flowers. Grape clusters are examples of infructescences. Pseudofruits are “fruits” not made in the ovaries and in general their true fruits lack development and are found within the flesh, like in apples and pears. Parthenocarpic fruits are those made without fecundation, by means of hormonal stimuli, like bananas.

22. What is the evolutionary importance of the fruits for the angiosperms?
The fruits contain seeds and they can detach from the plant falling on the ground or can serve as food for animals. Therefore with the emergence of fruits the seeds of angiosperms could be transported across long distances contributing to the propagation of the species.

23. What are the trends of the gametophyte in the evolution of plants?
A tendency of the gametophyte evolution in plants has been towards the formation of gametes that are independent from water. In bryophytes and in pteridophytes the fecundation is totally dependent on water. In phanerogamic plants such dependency does not exist.
Another tendency is the reduction in the size and duration of the gametophyte. In bryophytes the gametophyte is indeed the lasting stage. In pteridophytes, gymnosperms and angiosperms it became the temporary stage and its relative size was successively reduced.
A third evolutionary trend relates to the interdependency between gametophytes and sporophytes. In bryophytes the sporophyte is entirely dependent on the gametophyte to survive. In the remaining plants the sporophyte is the independent stage and the once autotrophic gametophyte in bryophytes and pteridophytes became dependent upon the sporophyte in the phanerogamic plants.

Definition of a culture

The culture is a people refers to all aspect of shared life in a community. Children who grow up in a social group learn ways of doing things, ways of expressing themselves, ways of looking things, what things they should value and what things they should avoid or despise, what is expected from them and what they may expect from others.
Yet culturally determined features may be seen in their action, social relationships, moral convictions, attractions and revulsions. These features can also be seen through the institutions their social group establishes and converses. They can also be seen in the art and literature which the members of the two group produce and appreciate.
A language is learned and used within such a context, drawing from the culture distinctive meanings and function which language learner must assimilate, if they want to control the language as the native speakers of the language control it. There are of course, variations, certain pattern of behavior and value system maybe discerned which integral parts of culture whole are.
It is necessary to see how such patterns function in relation to each other and to appreciate their place within the cultural system. Language learners who want to communicate with individuals from other cultural background should understand the cultural behavior of others and at the same time recognize their influence of their culture, over their thoughts, their activities and their and their forms of linguistic expression.
When the students meet, a difference set of behavior pattern or difference set of values they may be socked and embarrassed. They may consider the speakers of the language they are learning as strange, stupid, not well manner etc.
In a society where individuals must never admit that what they are wearing is valuable or in good taste, will not say “thank you” to a complement on their appearance, because they consider it an indication of lack of breeding, where as it is the normal response of an American. In this situation, the simple remark or question is only comprehensible within the structure of relationship and social education in the society.

Blood Question and Answer

Here some basic question and answer about Blood, I hope you can use it for your exam preparation.
Blood Questions

1. What are the main functions of the blood?The blood is a means of substance transportation throughout the body. The blood distributes nutrients, oxygen, hormones, antibodies and cells specialized in defense to the tissues and collects residuals like nitrogen wastes and carbon dioxide from them.
2. What are the constituent elements of the blood? The blood is made of a liquid and a cellular part. The fluid part is called plasma and in it there are several substances, like proteins, lipids, carbohydrates and mineral salts. The cellular constituents of the blood are also known as blood corpuscles and they comprise the erythrocytes (red blood cells), leukocytes and platelets.
3. What is hematopoiesis? Hematopoiesis is the formation of blood cells and other constituent elements of the blood.
4. Where does hematopoiesis occur? Hematopoiesis occurs in the bone marrow (mainly within flat bones), where erythrocytes, leukocytes and platelets are made, and in the lymphoid tissue, responsible for the maturation of leukocytes and found in the thymus, spleen and lymphnodes.
5. In which bones can bone marrow chiefly be found? Is the bone marrow made of osseous tissue?Bone marrow can mainly be found in the internal cavities of flat bones, like the vertebrae, the ribs, the scapulae, the sternum and the hips. The bone marrow is not made of osseous tissue, although it is a connective tissue as bone tissue is.
6. What are blood stem cells? Stem cells are undifferentiated cells able to differentiate into other types of specialized cells. The stem cells of the bone marrow originate the differentiated blood cells. According to stimulus from specific growth factors the stem cells are turned into red blood cells, leukocytes and megakaryocytes (cells that form platelets). Research shows that stem cells of the bone marrow can also differentiate into muscle, nervous and hepatic cells.
7. What are the other names by which erythrocytes are known? What is the function of these cells? Erythrocytes are also known as red blood cells (RBCs), or red corpuscles. Red blood cells are responsible for oxygen transport from the lungs to the tissues.
8. What is the name of the molecule that transports oxygen in red blood cells? The respiratory pigment of the red blood cells is hemoglobin.
9. What is the molecular composition of hemoglobin? Does the functionality of hemoglobin as a protein depend upon its tertiary or upon its quaternary structure? Hemoglobin is a molecule made of four polypeptide chains, each bound to a iron-containing molecular group called a heme group. So the molecule contains four polypeptide chains and four heme groups. As a protein composed of association of polypeptide chains, the functionality of hemoglobin depends upon the integrity of its quaternary structure.
10. On average what is the life duration of the red blood cells? Where are they destroyed? What is the destination of the heme groups after the destruction of hemoglobin molecules? On average red blood cells live around 120 days. The spleen is the main organ where old red blood cells are destroyed. During the red blood cell destruction the heme groups turn into bilirubin and this substance is then captured by the liver and later excreted in the bowels as part of the bile.
11. What are the functions of the spleen? Why is a total splenectomy (surgical removal of the spleen) compatible with life? The spleen has many functions: it participates in the destruction of old red blood cells; in it specialized leukocytes are matured; it helps the renewal of the hematopoietic tissue of the bone marrow when necessary; it can act as a spongelike organ to retain or liberate blood from or for the circulation. Total splenectomy is not incompatible with life as none of the functions of the spleen are vital and at the same time exclusive of this organ.
12. What is anemia? What are the four main types of anemia? Anemia is low concentration of hemoglobin in the blood. The four main types of anemia are the nutrient-deficiency anemia, anemia caused by blood loss, hemolytic anemia and aplastic anemia. Nutrient-deficiency anemia is caused by dietary deficiency of fundamental nutrients for the production or functioning of the red blood cells, like iron (iron deficiency anemia), vitamin B12 and folic acid. Anemia caused by blood loss occurs in hemorrhagic conditions or in diseases like peptic ulcerations and hookworm disease. Hemolytic anemia is caused by excessive destruction of red blood cells, for example, in diseases like malaria or in hypervolemic conditions (excessive water in blood that causes lysis of red blood cells). Aplastic anemia occurs from deficiencies of the hematopoiesis and it happens when the bone marrow is injured by cancers from other tissues (metastasis), by autoimmune diseases and by intoxication from drugs (like sulfas and anticonvulsants) or by chemical substances (like benzene, insecticides, paints, herbicides and solvents in general). Some genetic diseases also affect the bone marrow causing aplastic anemia.
13. What is the difference between white and red blood cells? What are leukocytes? Red blood cells are erythrocytes and white blood cells are the leukocytes. Leukocytes are cells specialized in the defense of the body against strange agents and they are part of the immune system.
14. What are the types of leukocytes and how are they classified into granulocytes and agranulocytes? The types of leukocytes are lymphocytes, monocytes, neutrophils, eosinophils and basophils. Granulocytes are those in whose cytoplasm there are granules (when viewed under electronic microscopy): neutrophils, eosinophils and basophils are granulocytes. Agranulocytes are the other leukocytes: lymphocytes and monocytes.
15. What is the generic function of leukocytes? What are leukocytosis and leukopenia? The generic function of leukocytes is to participate in the defense of the body against strange agents that penetrate it or are made inside the body. Leukocytosis and leukopenia are clinical conditions in which the count of leukocytes in a blood sample is abnormal. When the leukocyte count in a blood sample is above the normal level for the individual leukocytosis is defined. When the leukocyte count is lower than the expected normal level leukopenia is defined. The multiplication of these defense cells, leukocytosis, generally takes place when the body is suffering infections or in cancers of these cells. The lowering of these defense cells, or leukopenia, occurs when some diseases attack the cells, like in AIDS, or when immunosuppressor drugs are used. In general the body creates leukocytosis as a defense reaction when it is facing infectious or pathogenic agents. The clinical condition of leukocytosis is thus a sign of infection. Leukopenia occurs when there is a deficiency in the production (for example, in bone marrow diseases) or excessive destruction of leukocytes (for example, in case of HIV infection).
16. What are the mechanisms of hemorrhage contention called? The physiological mechanisms of hemorrhage contention (one of them is blood clotting) are generically named hemostasis, or hemostatic processes.
17. How are platelets formed? What is the function of platelets? What consequences does the clinical condition known as thrombocytopenia yield? Platelets, also known as thrombocytes, are fragments of giant cells of the bone marrow called megakaryocytes. With their properties of aggregation and adhesiveness they play a direct role in blood clotting and they also liberate substances that activate other hemostatic processes. Thrombocytopenia is a clinical condition in which the platelet count of the blood is lower than normal. In this situation the person becomes susceptible to hemorrhages.
18. How does the organism understand that a clotting process must begin? When there is some tissue wound with injury of blood vessel the platelets and endothelial cells of the wall of the damaged vessel liberate substances (respectively platelet factors and tissue factors) that trigger the clotting process.
19. How can the blood coagulation (clotting) process be described? Blood clotting encompasses a sequence of chemical reactions whose respective products are enzymes that catalyze the following reactions (that is why the clotting reactions are called cascade reactions). In the plasma thromboplastinogen transforms into thromboplastin, a reaction triggered by tissue and platelet factors liberated after injury of the blood vessel. Thromboplastin then catalyzes along with calcium ions the transformation of prothrombin into thrombin. Thrombin then catalyzes a reaction that produces fibrin from fibrinogen. Fibrin, as an insoluble substance, precipitates to form a network that traps red blood cells and platelets forming the blood clot and containing the hemorrhage.
20. What are clotting factors? Clotting factors are substances (enzymes, coenzymes, reagents) necessary for the clotting stages to happen. Besides those triggering factors and reagents already described (tissue and platelet factors, thromplastinogen, prothrombin, fibrinogen, calcium ions), other substances participate in the blood clotting process as clotting factors, like factor VIII, whose deficiency causes hemophilia A, or the factor IX, whose deficiency causes hemophilia B.
21. What is the organ where most of the clotting factors are produced? What is the role of vitamin K in the blood coagulation? Most of the clotting factors are produced in the liver. Vitamin K participates in the activation of several clotting factors and it is fundamental for the well-functioning of the blood coagulation.
22. What is factor VIII? What is the genetic disease in which this factor is absent? Factor VIII has the function of activating factor X that in its turn is necessary for the transformation of prothrombin into thrombin in the clotting cascade. Hemophilia A is the X-linked genetic disease in which the individual does not produce factor VIII and so is more susceptible to severe hemorrhages.
23. How is hemophilia treated? Why is hemophilia rare in females? Hemophilia is medically treated with administration of factor VIII, in case of hemophilia A, or of factor IX, in case of hemophilia B, by means of blood or fresh frozen plasma transfusions. Hemophilia, A or B, is an X-linked recessive inheritance and for a girl to be hemophilic it is necessary for both of her X chromosomes to be affected while boys, that have only one X chromosome, are more easily affected. A girl with only one affected chromosome does not present the disease since the normal gene of the unaffected other X chromosome produces the clotting factor.
24. What is the epidemiological association between hemophilia and HIV infection? Since hemophilic patients need frequent transfusions of clotting factors (VIII or IX) they are more susceptible to contamination by infectious agents present in the blood from which the transfused elements come. In the past the blood banks did not usually perform HIV detection tests and many hemophilic patients have become infected with the virus.
25. What are anticoagulants? What are the practical applications of anticoagulants, like heparin, in Medicine? Anticoagulants are substances that block the clotting reactions and thus stop the coagulation process. Ordinarily there are anticoagulants circulating in the plasma since under normal conditions the blood must be kept fluid. In Medicine anticoagulants like heparin are used in surgeries in which tissue injuries made by the surgical act could trigger undesirable systemic blood clotting. They are also used to avoid the formation of thrombus inside blood vessels of patients facing increased thrombotic risk.
26. What is dicoumarol? How does this substance act in the clotting process and what are some examples of its toxicity? Dicoumarol is an anticoagulant drug. Due to its molecular structure dicoumarol competes with vitamin K for the binding to substrates blocking the formation of clotting factors and interrupting the making of prothrombin. Dicoumarol is found in some vegetables undergoing decomposition, and it can cause severe internal hemorrhages when those vegetables are accidentally ingested. Coumarinic anticoagulants cannot be administered during pregnancy since they pass the placental barrier and can cause fetal hemorrhages.
27. Streptokinase is a substance used in the treatment of acute myocardial infarction. How does this substance act? Substances known as fibrinolytics, like streptokinase and urokinase, can destroy thrombi (clots formed inside blood vessels, capillaries or within the heart chambers) and are used in the treatment of obstructions of the coronary arteries or other blood vessels. Streptokinase destroys the fibrin network and so it dissolves the thrombotic clot. Its name comes after the bacteria that produce it, the streptococci.