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Penulis Topik: Urat nadi kok warna biru?  (Dibaca 18272 kali)

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Offline reborn

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Urat nadi kok warna biru?
« pada: Juli 21, 2008, 01:25:13 PM »
Halo lagi  ;D

Kita kan tau kalo darah warnanya merah. Trus kenapa kok pembuluh darah vena (urat nadi) kita warnanya biru? Coba cek deh, bener kan biru? Apalagi kalo yang kulitnya putih, pasti jelas keliatan tuh warnanya biru.

Offline milmi

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Re: Urat nadi kok warna biru?
« Jawab #1 pada: Juli 22, 2008, 01:30:14 AM »
Bos Admin, piye toh? Kan pernah nyicipin FK, kok masih tanya juga. Salah pula pertanyaanya :P
Yg sering terlihat berwarna biru itu bukan nadi, tetapi vena. Sedangkan yg sering disebut nadi adalah arteri, letaknya lebih ke dalam dan sulit terlihat, namun dapat dirasakan denyutannya (karena itu ada istilah denyut nadi). Saya sudah mencari jawabannya dan ketemu penjelasan yg cukup memuaskan, tapi berhubung lg males ngetik, saya copy paste aja ya :P

From http://www.madsci.org/posts/archives/1996-12/840084221.An.r.html
Why blue veins? Here are my thoughts.

1) This may seem obvious, but the color of your 'superficial veins' (the ones you can see) is clearly due to the blood that is in them. You can prove this to yourself by finding an obvious vein, say on the back of your hand, and stripping the blood out of it by pressing on it and pushing toward your finger tips. The vein disappears, but will reappear as soon as you lift the pressure and the blood is allowed to re-enter. Cool, huh?

2) It is further clear that the oxygen content of the blood in the vein is a big player, since whole parts of your body can turn blue that are normally pink (at least in a caucasian). Doctors call this cyanosis. For example, kids with heart defects can turn their whole body blue, and people with certain "rheumatologic" disease can have periodic episodes where their normally pink fingertips turn blue. In general, these things happen because the amount of oxygen in the blood in the capillary beds drops below the normal level. By inference, then, the blue color of veins that you see is due to the low amount of oxygen *normally* in that blood.

3) HOWEVER, oxygen poor blood is most definitely NOT blue. As you point out, it is a sort of purplish/maroon color at best. I work in the clinical labs, and have seen countless tubes of blood drawn from oxygen poor veins into vacuum tubes (i.e. never exposed to air), and it has never looked like the color of your veins!

4) Your thought experiment about the appearance of veins in surgery is a very good one. Basically, no, veins do not appear blue in surgery. But understand that the types of veins you see through your skin are never really dissected in surgery, they're too small and thin. Nonetheless, many veins do get dissected, and they typically have a reddish appearance. But paradoxically, they often keep that appearance even after the blood is washed from them, since they are inevitably coated with amounts of loose connective tissue called fascia which has blood in it and is thus red. So in the end this question is confounded, but again, they never appear truly blue.

5) So we seem to be narrowing it down. Skin must be having an effect. Can we find more evidence for this? I think that varicose veins are a help here. We have all seen people with 'spider looking' dilated veins in their legs. While their appearance is a certainly variable, not infrequently they are sort of a maroon color, much like the blood appears. These veins are dilated and have stretched their walls and the overlying skin, and as a result are very close to the surface. And they are no longer blue!!

So, what all these little bits of evidence say is that both the oxygen content of the blood AND the overlying skin affect the apparent color of the veins you see. Realize that to see the vein at all, light has to go THROUGH the skin and hit the blood in the vein. The blood absorbs certain colors of light, and reflects others back through the skin. In the skin, it is potentially subject to all sorts of effects, including scatter by the 'stratified' layers, and absorption by the pigmented layers (i.e. melanin). For some reason, the combination of these effects (absorption by oxygen poor blood and absorption/deflection in the skin) gives a blue color. I'm not sure if anyone could say in absolutely precise terms why blue, but there it is.

A long-winded answer, but hopefully enough to satisfy even a true 'blue-blood.'

Thanks for the question.

Tom Wilson, MD PhD
...setetes air di samudera luas...

Offline reborn

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Re: Urat nadi kok warna biru?
« Jawab #2 pada: Juli 22, 2008, 03:00:09 PM »
Yg sering terlihat berwarna biru itu bukan nadi, tetapi vena. Sedangkan yg sering disebut nadi adalah arteri, letaknya lebih ke dalam dan sulit terlihat, namun dapat dirasakan denyutannya (karena itu ada istilah denyut nadi).

waduh, bener2 kritis semua di sini ya, mantap ;D Di post awal kan dah ditulis juga

Kita kan tau kalo darah warnanya merah. Trus kenapa kok pembuluh darah vena (urat nadi) kita warnanya biru?

tuh kan, emang pertanyaannya vena :P Tapi karena kebanyakan nyebutnya urat nadi, jadi begitu nulisnya biar nyambung. Duh, kudu hati2 nih kalo nulis di sini, bahaya  :o

Terjawab dengan penjelasan ini ya :

So, what all these little bits of evidence say is that both the oxygen content of the blood AND the overlying skin affect the apparent color of the veins you see. Realize that to see the vein at all, light has to go THROUGH the skin and hit the blood in the vein. The blood absorbs certain colors of light, and reflects others back through the skin. In the skin, it is potentially subject to all sorts of effects, including scatter by the 'stratified' layers, and absorption by the pigmented layers (i.e. melanin).

Walau pada akhirnya dia pake kata "for some reason" dan juga "not sure"

Kutip
For some reason, the combination of these effects (absorption by oxygen poor blood and absorption/deflection in the skin) gives a blue color. I'm not sure if anyone could say in absolutely precise terms why blue, but there it is.

Ada jawaban lain?

Offline milmi

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Re: Urat nadi kok warna biru?
« Jawab #3 pada: Juli 22, 2008, 11:27:01 PM »
waduh, bener2 kritis semua di sini ya, mantap ;D

Kita kan ingin mengajarkan yg benar kepada orang lain, karena itu harus membiasakan menggunakan istilah yg benar.

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Re: Urat nadi kok warna biru?
« Jawab #4 pada: Juli 22, 2008, 11:28:50 PM »
ada hubungannya dengan rayleigh-scattering? itu tuh yg bikin langit tampak biru...
RAYLEIGH-scattering in a very simple experiment

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Re: Urat nadi kok warna biru?
« Jawab #5 pada: Juli 26, 2008, 03:04:21 PM »
darah dalam arteri itu darah yang "penuh" oksigen terus dia muter-muter di seluruh tubuh kemudian kembali lagi menuju jantung dan paru untuk dapetin oksigen lagi. Nah, kedua darah ini, darah dalam arteri yang penuh oksigen dan darah dalam vena yang miskin oksigen, sama-sama berwarna merah. Bedanya hanya darah di arteri lebih cerah dibanding darah di vena.

Yang bisa kita lihat itu darah di vena, karena ada di deket permukaan kulit. Kalau memang kedua darah ini (dengan dan tanpa oksigen) warnanya merah, tulisan mas milmi juga sependapat, kenapa pada kulit terlihat warna biru?

Offline syx

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Re: Urat nadi kok warna biru?
« Jawab #6 pada: Juli 28, 2008, 10:29:03 PM »
coba deh cari-cari aja hubungannya dengan rayleigh-scattering.

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Re: Urat nadi kok warna biru?
« Jawab #7 pada: Juli 29, 2008, 01:33:20 AM »
Ah, jadi males jawab. Make bahasa Inggris sih..
Hehheehehehee :D :D

Offline eky

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Re: Urat nadi kok warna biru?
« Jawab #8 pada: Juli 29, 2008, 04:24:41 AM »
oh gitu toh ..
berarti yang selama ini gw salah sebut "nadi" dong ..
jadi malu .. haha :(

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Re: Urat nadi kok warna biru?
« Jawab #9 pada: Agustus 03, 2008, 09:50:16 AM »
Aku coba jawab ya...

Warna darah tergantung pada pigmen pembawa oksigennya. Pada darah manusia dan mammalia, pigmen pembawa oksigen adalah hemoglobin. Pada darah arteria (kecuali a.pulmonalis), hemoglobin mengikat banyak oksigen, menyebabkan warna sel darah merah menjadi merah cerah (oxygenated blood). Pada darah vena (kecuali v.pulmonalis), hemoglobin mengikat banyak karbondioksida, menyebabkan warna sel darah merah menjadi kebiruan (deoxygenated blood)

Contoh lain pada darah dengan pigmen klorokruorin, akan berwarna hijau bila teroksigneasi dan berwarna metalik bila deoksigenasi. Pigmen hemeritrin = violet (oksigenasi) dan menjadi tak berwarna bila deoksigenasi. Pigmen hemosianin   = biru (oksigenasi) dan menjadi tak berwarna bila deoksigenasi.

Itu yang aku tahu...
omne vivum ex vivo, so viva!

Offline syx

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Re: Urat nadi kok warna biru?
« Jawab #10 pada: Agustus 04, 2008, 11:13:41 PM »
ini dalam kondisi normal... jadi vena di bawah kulit terlihat berwarna biru. efek ini timbul karena rayleigh-scattering oleh lapisan lemak bawah kulit.

 

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