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You can cut a planarian into Intrigued by the potential hundreds of pieces buy cheap betapace 40 mg on-line, and each piece will grow of these masterful cells order betapace 40 mg otc, into a complete worm safe betapace 40 mg. Scientists have discovered The New Genetics I Life’s Genetic Tree 53 If people have a gene that inﬂuences their risk cytochrome P450 family betapace 40mg low cost, abbreviated 3A4 and for a disease, and mice have the gene too, you 3A5, encode proteins that process more than half could study some aspect of the disease in mice, of all of the medicines that are sold today. You could even study the disease exposed vary so widely, a scientist might pre in yeast, if it has the gene, as well. Using comparative genomics, If toxins from the environment get into our researchers such as Anna Di Rienzo of the bodies, they don’t always make us sick. That’s University of Chicago have shown that this is because liver enzymes come to our rescue to indeed the case. The genes that sequence differences within these genes in people encode those enzymes are under constant evolu living throughout the world. It turns out that one variant of the gene that For example, certain liver enzymes called encodes the cytochrome P450 3A5 protein makes cytochrome P450 proteins metabolize, or break this enzyme very efﬁcient at breaking down down, hormones that our bodies make as well as cortisol, a hormone that raises salt levels in the many of the foreign substances that we encounter. In fact, just two genes within the that planarians can perform the amazing act Although humans are only distantly related of regeneration due to the presence of, yes, to planarians, we have many of the same genes, specialized stem cells in their bodies. He and his team hope to ﬁgure out how cells could generate any type of cell and be used these genes allow the specialized stem cells to treat diseases. But to realize this potential, we to travel to a wounded site and “turn into” any need a much better understanding of the proper of the 30 or so cell types needed to recreate a ties of these cells and how to efﬁciently produce mature worm. However, there seems to be a cost associated with that beneﬁt—the 3A5 gene variant raises the risk for some types of high blood pressure. That means that in environments in which retaining salt is not beneﬁcial, evolution selects against this gene variant. Another scientist who studies interactions between genes and the environment is Serrine Lau of the University of Arizona in Tucson. She studies a class of harmful molecules called polyphenols, present in cigarette smoke and car exhaust, that cause kidney cancer in rats, and perhaps, in people. Scientists have discovered that some African popu lations near the equator have a high frequency of a their risk of developing cancer. In people and rats with the genetic was amazed to ﬁnd a striking link between the signature, she reasons, the tumor suppressor existence of the gene variant and the geographic doesn’t work right, so tumors grow. She suggests that this is could identify those at risk, Lau says, such people because this gene variant provides a health could be forewarned to avoid contact with spe ciﬁc chemicals to protect their health. The New Genetics I Life’s Genetic Tree 55 However, think about this scenario: Who should make those decisions? For example, would it be ethical for an employer to refuse to hire somebody because the person has a genetic signature that makes him or her more likely to The liver and kidneys are susceptible to damage from get cancer if exposed to a chemical used in the toxins since these body organs process chemicals. These are all it’s a tiny sliver of tissue about the size of a examples of nature’s amazing sense of grain of rice, located behind the eyes. These aren’t But did you know that certain forms actually clocks, but rather are ensembles of of insomnia and manicdepressive illness genes inside clusters of cells that switch on are associated with biological clocks and off in a regular, 24hour cycle—our not working properly? Many physiology behavior researchers working with insect and other model systems have identiﬁed genes that are critical for keeping biological time. Some people, The New Genetics I Life’s Genetic Tree 57 however, routinely get by with only 3 to Although the shaker ﬂies don’t 4 hours of sleep. Researchers have noted appear sleepdeprived, Cirelli found that that this trait seems to run in families, they have a different problem: They suggesting a genetic link. Chiara Cirelli of the University of Her work may also pave the way for WisconsinMadison did a genetic search improved sleep aids and effective for fruit fly mutants that don’t sleep remedies for jet lag. Next in deafness, mental retardation, heart disease and line are dozens of additional species, including the way in which bacterial toxins cause illness. This means that common with other species are as important as when scientists read the sequence of another the genes we share. For example, consider the fact species’ genome, they’re likely to discover that the that humans and chimpanzees have remarkably organism has many of the genes that, in humans, different abilities and physical features. My Collaborator Is a Computer We’ve made the case that comparing genomes can offer fresh insight on the basic genetic ingre dients for health and the causes of disease. Does this mean staring at thousands of pages of genetic letters, looking for those that are the same or different? The New Genetics I Life’s Genetic Tree 59 Computers are an essential tool for scientists who store and analyze huge amounts of genomic data. Other researchers who work in the ﬁeld of Rather, the gigantic task of comparing the bioinformatics mine genomic information hid nucleotides that make up the genomes of two or den in the masses of data. They are looking for more species is the perfect job for a computer, a scientiﬁc treasure in the form of new biological natural multitasker. These experiments can zero in on pre human genome contains 3 billion nucleotides, viously hidden patterns and reveal links between you can easily see why this is work well suited to different ﬁelds of research. Bioinformaticists and computational biolo Researchers called computational biologists gists are in high demand because they play a very help analyze genomic data. Conversely, it has pro Humans and mice share over pinpointing mutations in genes, so it is the vided scientiﬁc evidence that helped convict 80 percent of the same basis for much of the research discussed in criminals. Can you think of an experi ment using fruit ﬂies that could help researchers better understand jet lag? C H A P T E R 4 Genes Are Us or science, the sequencing of the human changes create words with new meanings— F genome was a groundbreaking achievement, genes that code for different proteins. Will any of this information make whatsoever, at least not ones that today’s scien a difference in your life? A genome is all of the genetic material that an Researchers are beginning to use knowledge individual (or a species) has. The human genome learned from genome sequencing research to differs from the gorilla genome, which differs ﬁgure out how being healthy and being sick are from the rice genome, and so on. And doctors person has a “human genome,” it is not exactly are starting to use genetic information to make the same in all people. In some cases, the spelling people, Herceptin is a miracle drug because it Reading the Book of Human Genes In April 2003, researchers across the world cele brated a milestone and an anniversary. They wanted to map the location Cambridge, Massachusetts, are working to better of every gene within chromosomes and decipher understand the human genome and to sequence the complete, letterbyletter sequence of the the genomes of other organisms. The New Genetics I Genes Are Us 63 reduces the risk that their breast cancer will come though, so it shouldn’t be prescribed. Research is back, and it also decreases their odds of dying proceeding quickly to develop other genetic tests from the disease. Researchers can were new tools and technologies that made the link these variations to dis work go faster and helped the researchers man ease risk and healthrelated age and analyze the ﬂood of data. The unsettling truth is that how the cytochrome P450 proteins (and many medicines work as expected in fewer than half of other types of proteins) work on drugs.
These glands are found all over the skin’s surface cheap betapace 40 mg overnight delivery, but are especially abundant on the palms of the hand generic 40 mg betapace fast delivery, the soles of the feet buy 40 mg betapace with amex, and the forehead (Figure 5 buy betapace 40 mg without prescription. They are coiled glands lying deep in the dermis, with the duct rising up to a pore on the skin surface, where the sweat is released. This type of sweat, released by exocytosis, is hypotonic and composed mostly of water, with some salt, antibodies, traces of metabolic waste, and dermicidin, an antimicrobial peptide. Eccrine glands are a primary component of thermoregulation in humans and thus help to maintain homeostasis. An apocrine sweat gland is usually associated with hair follicles in densely hairy areas, such as armpits and genital regions. Apocrine sweat glands are larger than eccrine sweat glands and lie deeper in the dermis, sometimes even reaching the hypodermis, with the duct normally emptying into the hair follicle. In addition to water and salts, apocrine sweat includes organic compounds that make the sweat thicker and subject to bacterial decomposition and subsequent smell. The release of this sweat is under both nervous and hormonal control, and plays a role in the poorly understood human pheromone response. Most commercial antiperspirants use an aluminum-based compound as their primary active ingredient to stop sweat. When the antiperspirant enters the sweat gland duct, the aluminum-based compounds precipitate due to a change in pH and form a physical block in the duct, which prevents sweat from coming out of the pore. Sebaceous Glands A sebaceous gland is a type of oil gland that is found all over the body and helps to lubricate and waterproof the skin and hair. They generate and excrete sebum, a mixture of lipids, onto the skin surface, thereby naturally lubricating the dry and dead layer of keratinized cells of the stratum corneum, keeping it pliable. The fatty acids of sebum also have antibacterial properties, and prevent water loss from the skin in low-humidity environments. The underlying hypodermis has important roles in storing fats, forming a “cushion” over underlying structures, and providing insulation from cold temperatures. It acts as a protective barrier against water loss, due to the presence of layers of keratin and glycolipids in the stratum corneum. It also is the first line of defense against abrasive activity due to contact with grit, microbes, or harmful chemicals. Sweat excreted from sweat glands deters microbes from over-colonizing the skin surface by generating dermicidin, which has antibiotic properties. It provides a barrier between your vital, life-sustaining organs and the influence of outside elements that could potentially damage them. The skin can be breached when a child skins a knee or an adult has blood drawn—one is accidental and the other medically necessary. However, you also breach this barrier when you choose to “accessorize” your skin with a tattoo or body piercing. Because the needles involved in producing body art and piercings must penetrate the skin, there are dangers associated with the practice. These include allergic reactions; skin infections; blood-borne diseases, such as tetanus, hepatitis C, and hepatitis D; and the growth of scar tissue. Despite the risk, the practice of piercing the skin for decorative purposes has become increasingly popular. According to the American Academy of Dermatology, 24 percent of people from ages 18 to 50 have a tattoo. Sensory Function The fact that you can feel an ant crawling on your skin, allowing you to flick it off before it bites, is because the skin, and especially the hairs projecting from hair follicles in the skin, can sense changes in the environment. The hair root plexus surrounding the base of the hair follicle senses a disturbance, and then transmits the information to the central nervous system (brain and spinal cord), which can then respond by activating the skeletal muscles of your eyes to see the ant and the skeletal muscles of the body to act against the ant. The skin acts as a sense organ because the epidermis, dermis, and the hypodermis contain specialized sensory nerve structures that detect touch, surface temperature, and pain. These receptors are more concentrated on the tips of the fingers, which are most sensitive to touch, especially the Meissner corpuscle (tactile corpuscle) (Figure 5. In addition to these specialized receptors, there are sensory nerves connected to each hair follicle, pain and temperature receptors scattered throughout the skin, and motor nerves innervate the arrector pili muscles and glands. The sympathetic nervous system is continuously monitoring body temperature and initiating appropriate motor responses. Recall that sweat glands, accessory structures to the skin, secrete water, salt, and other substances to cool the body when it becomes warm. Even when the body does not appear to be noticeably sweating, approximately 500 mL of sweat (insensible perspiration) are secreted a day. In addition to sweating, arterioles in the dermis dilate so that excess heat carried by the blood can dissipate through the skin and into the surrounding environment (Figure 5. In contrast, the dermal blood vessels constrict to minimize heat loss in response to low temperatures (b). Although the temperature of the skin drops as a result, passive heat loss is prevented, and internal organs and structures remain warm. If the temperature of the skin drops too much (such as environmental temperatures below freezing), the conservation of body core heat can result in the skin actually freezing, a condition called frostbite. Among these changes are reductions in cell division, metabolic activity, blood circulation, hormonal levels, and muscle strength (Figure 5. In the skin, these changes are reflected in decreased mitosis in the stratum basale, leading to a thinner epidermis. The dermis, which is responsible for the elasticity and resilience of the skin, exhibits a reduced ability to regenerate, which leads to slower wound healing. The hypodermis, with its fat stores, loses structure due to the reduction and redistribution of fat, which in turn contributes to the thinning and sagging of skin. Other cells in the skin, such as melanocytes and dendritic cells, also become less active, leading to a paler skin tone and lowered immunity. Wrinkling of the skin occurs due to breakdown of its structure, which results from decreased collagen and elastin production in the dermis, weakening of muscles lying under the skin, and the inability of the skin to retain adequate moisture. In general, these products try to rehydrate the skin and thereby fill out the wrinkles, and some stimulate skin growth using hormones and growth factors. In the presence of sunlight, a form of vitamin D called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver3 converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin) in the kidneys. Vitamin D is essential for normal absorption of calcium and phosphorous, which are required for healthy bones. The absence of sun exposure can lead to a lack of vitamin D in the body, leading to a condition called rickets, a painful condition in children where the bones are misshapen due to a lack of calcium, causing bowleggedness. Elderly individuals who suffer from vitamin D deficiency can develop a condition called osteomalacia, a softening of the bones. In present day society, vitamin D is added as a supplement to many foods, including milk and orange juice, compensating for the need for sun exposure. These range from annoying but relatively benign bacterial or fungal infections that are categorized as disorders, to skin cancer and severe burns, which can be fatal. Cancer is a broad term that describes diseases caused by abnormal cells in the body dividing uncontrollably. The Skin Cancer Foundation reports that one in five Americans will experience some type of skin cancer in their lifetime.
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