In humans, melanin is the primary determinant of skin color. It is also found in hair, the pigmented tissue underlying the iris of the eye, and the stria vascularis of the inner ear. In the brain, tissues with melanin include the medulla and pigment-bearing neurons within areas of the brainstem, such as the locus coeruleus and the substantia nigra.

It also occurs in the zona reticularis of the adrenal gland. The melanin in the skin is produced by melanocytes, which are found in the basal layer of the epidermis. Although, in general, human beings possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and ethnic groups more frequently or less frequently express the melanin-producing genes, thereby conferring a greater or lesser concentration of skin melanin.

Some individual animals and humans have very little or no melanin synthesis in their bodies, a condition known as albinism. Because melanin is an aggregate of smaller component molecules, there are many different types of melanin with differing proportions and bonding patterns of these component molecules. Both pheomelanin and eumelanin are found in human skin and hair, but eumelanin is the most abundant melanin in humans, as well as the form most likely to be deficient in albinism.

Melanins have very diverse roles and functions in various organisms. A form of melanin makes up the ink used by many cephalopods (see cephalopod ink) as a defense mechanism against predators. Melanins also protect microorganisms, such as bacteria and fungi, against stresses that involve cell damage such as UV radiation from the sun and reactive oxygen species.

Melanin also protects against damage from high temperatures, chemical stresses (such as heavy metals and oxidizing agents), and biochemical threats (such as host defenses against invading microbes). Therefore, in many pathogenic microbes (for example, in Cryptococcus neoformans, a fungus) melanins appear to play important roles in virulence and pathogenicity by protecting the microbe against immune responses of its host.

 In invertebrates, a major aspect of the innate immune defense system against invading pathogens involves melanin. Within minutes after infection, the microbe is encapsulated within melanin (melanization), and the generation of free radical byproducts during the formation of this capsule is thought to aid in killing them.

Some types of fungi, called radiotrophic fungi, appear to be able to use melanin as a photosynthetic pigment that enables them to capture gamma rays. The black feathers of birds owe their color to melanin; they are much more readily degraded by bacteria than white feathers, or those containing other pigments such as carotenes.

In some mice, melanin is used slightly differently. For instance, in Agouti mice, the hair appears brown because of alternation between black eumelanin production and a yellow variety of pheomelanin. The hairs are actually banded black and yellow, and the net effect is the brown color of most mice. Some genetic irregularities can produce either fully black or fully yellow mice.
Catechol melanins are plant melanins.(


UVA, UVB, and UVC can all damage collagen fibers and, therefore, accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage. In the past, UVA was considered not harmful or less harmful, but today it is known it can contribute to skin cancer via indirect DNA damage (free radicals and reactive oxygen species).

It penetrates deeply, but it does not cause sunburn. UVA does not damage DNA directly like UVB and UVC, but it can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA.

Accordingly the DNA damage caused indirectly to skin by UVA consists mostly of single-strand breaks in DNA, while the damage caused by UVB includes direct formation of thymine dimers or other pyrimidine dimers, and double-strand DNA breakage.

UVA is immunosuppressive for the entire body (accounting for a large part of the immunosuppressive effects of sunlight exposure), and UVA is mutagenic for basal cell keratinocytes in skin.

Because UVA does not cause reddening of the skin (erythema), it is not measured in the usual types of There is no good clinical measurement for blockage of UVA radiation, but it is important for sunscreen to block both UVA and UVB. Some scientists blame the absence of UVA filters in sunscreens for the higher melanoma risk found for sunscreen users.

UVB light can cause direct DNA damage. As noted above UVB radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent Pyrimidine bases, producing a dimer. Most UV-induced pyrimidine dimers in DNA are removed by the process known as nucleotide excision repair that employs about 30 different proteins.

Those pyrimidine dimers that escape this repair process can induce a form of programmed cell death called apoptosis or can cause DNA replication errors leading to mutation. When DNA polymerase comes along to replicate a strand of DNA with an unrepaired pyrimidine dimer, it reads a CC dimer as AA and not the original CC. This causes the DNA replication mechanism to add a TT on the growing strand. This mutation can result in cancerous growths, and is known as a "classical C-T mutation".

The mutations caused by the direct DNA damage carry a UV signature mutation that is commonly seen in skin cancers. The mutagenicity of UV radiation can be easily observed in bacterial cultures. This cancer connection is one reason for concern about ozone depletion and the ozone hole.

Individuals with an inherited defect in one of the proteins necessary for nucleotide excision repair may suffer from a condition called xeroderma pigmentosum that is characterized by extreme sun-sensitivity and by a high incidence of skin cancers.

(Also see DNA repair-deficiency disorder. As a defense against UV radiation, the type and amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue.

UVA gives a quick tan that lasts for days by oxidizing melanin that was already present, and it triggers the release of the melanin from melanocytes. However, because this process does not increase the total amount of melanin, a UVA-produced tan is largely cosmetic and does not protect against either sun burn or UVB-produced DNA damage or cancer.

By contrast, UVB yields a slower tan that requires roughly two days to develop, because the mechanism of UVB tanning is to stimulate the body to produce more melanin. However, the production of melanin by UV, called melanogenesis, requires direct DNA damage by UVB to initiate.

The photochemical properties of melanin make it an excellent photoprotectant from both UVA and UVB. Older and more widespread sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin, and, therefore, the penetration of these sunscreen ingredients into the lower layers of the skin may increase the amount of free radicals and reactive oxygen species (ROS).

In recent years, improved filtering substances have come into use in commercial sunscreen lotions that do not significantly degrade or lose their capacity to protect the skin as the exposure time increases (photostable substances).(


Buah naga (Inggris: pitaya) adalah buah dari beberapa jenis kaktus dari marga Hylocereus dan Selenicereus. Buah ini berasal dari Meksiko, Amerika Tengah dan Amerika Selatan.

Namun sekarang juga dibudidayakan di negara-negara Asia seperti Taiwan, Vietnam, Filipina, Indonesia dan Malaysia. Buah ini juga dapat ditemui di Okinawa, Israel, Australia utara dan Tiongkok selatan. Hylocereus hanya mekar pada malam hari.

Pada tahun 1870 tanaman ini dibawa orang Perancis dari Guyana ke Vietnam sebagai tanaman hias. Oleh orang Vietnam dan orang Cina buahnya dianggap membawa berkah. Oleh sebab itu, buah ini selalu diletakkan di antara dua ekor patung naga berwarna hijau di atas meja altar.

Warna merah buah terlihat mencolok di antara warna naga-naga yang hijau. Dari kebiasaan inilah buah itu di kalangan orang Vietnam yang sangat terpengaruh budaya Cina dikenal sebagai thang loy (buah naga). Istilah Thang loy kemudian diterjemahkan di Eropa dan negara lain yang berbahasa Inggris sebagai dragon fruit (buah naga).

Morfologi tanaman buah naga terdiri dari akar, batang, duri, bunga, dan buah. Akar buah naga hanyalah akar serabut yang berkembang dalam tanah pada batang atas sebagai akar gantung. Akar tumbuh di sepanjang batang pada bagian punggung sirip di sudut batang. Pada bagian duri, akan tumbuh bunga yang bentuknya mirip bunga Wijayakusuma.

Bunga yang tidak rontok berkembang menjadi buah. Buah naga bentuknya bulat agak lonjong seukuran dengan buah alpukat. Kulit buahnya berwarna merah menyala untuk jenis buah naga putih dan merah, berwarna merah gelap untuk buah naga hitam, dan berwarna kuning untuk buah naga kuning. Di sekujur kulit dipenuhi dengan jumbai-jumbai yang dianalogikan dengan sisik naga. Oleh sebab itu, buah ini disebut buah naga.
Batangnya berbentuk segitiga, durinya sangat pendek dan tidak mencolok, sehingga sering dianggap "kaktus tak berduri". Bunganya mekar pada awal senja jika kuncup bunga sudah berukuran sekitar 30 cm.

Mahkota bunga bagian luar yang berwarna krem, mekar sekitar pukul sembilan malam, lalu disusul mahkota bagian dalam yang putih bersih, meliputi sejumlah benang sari yang berwarna kuning. Bunga seperti corong itu akhirnya terbuka penuh pada tengah malam, karena itu buah naga dikenal sebagai night blooming cereus.

Saat mekar penuh, buah naga menyebar bau yang harum. Aroma ini untuk memikat kelelawar, agar menyerbuki bunga buah naga.(


Aluminium ialah unsur kimia. Lambang aluminium ialah Al, dan nomor atomnya 13. Aluminium ialah logam paling berlimpah.

Aluminium bukan merupakan jenis logam berat, namun merupakan elemen yang berjumlah sekitar 8% dari permukaan bumi dan paling berlimpah ketiga.

Aluminium terdapat dalam penggunaan aditif makanan, antasida, buffered aspirin, astringents, semprotan hidung, antiperspirant, air minum, knalpot mobil, asap tembakau, penggunaan aluminium foil, peralatan masak, kaleng, keramik , dan kembang api.

Aluminium merupakan konduktor listrik yang baik. Terang dan kuat. Merupakan konduktor yang baik juga buat panas. Dapat ditempa menjadi lembaran, ditarik menjadi kawat dan diekstrusi menjadi batangan dengan bermacam-macam penampang. Tahan korosi.

Aluminium digunakan dalam banyak hal. Kebanyakan darinya digunakan dalam kabel bertegangan tinggi. Juga secara luas digunakan dalam bingkai jendela dan badan pesawat terbang.

Ditemukan di rumah sebagai panci, botol minuman ringan, tutup botol susu dsb. Aluminium juga digunakan untuk melapisi lampu mobil dan compact disks.(


Kista adalah tumor jinak di yang paling sering ditemui. Bentuknya kistik, berisi cairan kental, dan ada pula yang berbentuk anggur. Kista juga ada yang berisi udara, cairan, nanah, ataupun bahan-bahan lainnya.

Kista termasuk tumor jinak yang terbungkus selaput semacam jaringan. Kumpulan sel-sel tumor itu terpisah dengan jaringan normal di sekitarnya dan tidak dapat menyebar ke bagian tubuh lain.

Itulah sebabnya tumor jinak relatif mudah diangkat dengan jalan pembedahan, dan tidak membahayakan kesehatan penderitanya.

Berdasarkan tingkat keganasannya, kista terbagi dua, yaitu non-neoplastik dan neoplastik. Kista non-neoplastik sifatnya jinak dan biasanya akan mengempis sendiri setelah 2 hingga 3 bulan. Sementara kista neoplastik umumnya harus dioperasi, namun hal itu pun tergantung pada ukuran dan sifatnya.

Selain pada ovarium kista juga dapat tumbuh di vagina dan di daerah vulva (bagian luar alat kelamin perempuan). Kista yang tumbuh di daerah vagina, antara lain inklusi, duktus gartner, endometriosis, dan adenosis.

Sedangkan kista yang tumbuh di daerah vulva, antara lain pada kelenjar bartholini, kelenjar sebasea serta inklusi epidermal.(


Satu lagi varian smartphone Windows Phone Lumia milik Nokia yang hadir di tahan air. Smartphone tersebut adalah Lumia 925 yang kini sudah bisa dipesan secara langsung di beberapa toko online terkemuka tanah air.

Smartphone ini telah secara resmi mulai dijual di Indonesia pada 1 November 2013 kemarin. Beberapa toko online yang sudah menjual smartphone ini di antaranya adalah Erafone, Lazada, Blibli ataupun

Selain itu, smartphone ini juga tersedia di Nokia Store, Sentraponsel serta Oke Shop. Mengenai harganya, smartphone ini dipatok dengan harga sebesar 6.2 juta Rupiah.

Lumia 925 ini hadir dengan layar AMOLED berukuran 4.5 inci yang memiliki resolusi 1280 x 768 piksel. Di dalamnya terdapat prosesor dual core Snapdragon dengan kecepatan 1.5GHz yang ditunjang oleh RAM sebesar 1GB dan memori internal 16GB.

Smartphone ini juga memiliki baterai berkapasitas 2000 mAh di bagian belakang dan mendukung teknologi wireless charging dengan cover tambahan.

Smartphone ini mempunyai keunggulan pada desainnya yang terbuat dari bahan metal yang dikombinasikan dengan polikarbonat. Smartphone ini juga memiliki kamera 8.7MP yang dilengkapi fitur OIS dan teknologi PureView.(