Yasmin

Sheng-Fu Larry Lo, M.D., M.H.S.

• Co-Director, Spinal Oncology
• Assistant Professor of Neurosurgery

https://www.hopkinsmedicine.org/profiles/results/directory/profile/10004080/larry-lo

Hemodynamics of the maternal venous compartment: a new area to explore in obstetric ultrasound imaging birth control pills 9 order yasmin with mastercard. Maternal Cardiac Deceleration Capacity: a novel way to explore maternal autonomic function in pregnancies complicated by hypertensive disorders and intrauterine growth restriction birth control pills prevent pregnancy by order 3.03 mg yasmin mastercard. Bedside diagnosis of two major clinical phenotypes of hypertensive disorders of pregnancy. Low molecular weight heparin: does it represent a clinical opportunity for preventing preeclampsia associated with fetal growth restriction Introduction the problem of cardiovascular problems in pregnancy due to chemotherapy exposure is rather rare. Nevertheless, situations of chemotherapy administration for cancer diagnosed during pregnancy and pregnancies after cancer treatment have occurred in increasing numbers over recent years. Treatment of (childhood) cancer has improved, resulting in more cancer survivors that reach reproductive life and become pregnant. Most frequently seen tumors in children and young women are hematological malignancies, tumors of the central nervous system and breast cancer. For breast and hematological malignancies the standard chemotherapy schedules contain anthracyclines. Chemotherapy-induced cardiotoxicity is a serious complication that poses a grave threat to life and limits the clinical use of various chemotherapeutic agents, particularly anthracyclines. This cardiotoxicity can present shortly after chemotherapy exposure, but might also become clear only decennia after the cancer treatment. As extensively discussed in other chapters of this volume, pregnancy is a specific physiologic state associated with significant cardiovascular changes and adaptations resulting in increased cardiac output and workload, and a reduced peripheral vascular resistance. These circulatory adaptations could result in increased sensitivity to cardiovascular side effects of cancer treatments. Apart from the effect on the maternal heart, chemotherapy exposure during pregnancy can also influence the development of the fetal heart. Cytotoxic treatment is given with the aim of killing tumor cells by interfering with the process of cell division. Since embryological and fetal development is characterized by highly proliferating cells, fetal tissues are more vulnerable to toxic effects of chemotherapy than adult tissues with a low proliferating index. Best known are the anthracyclines, but antimetabolites, antimicrotubule agents and targeted therapy agents are also known to cause cardiac damage (Table 21. The cardiovascular complications that have been described are heart failure, hypertension, arrhythmia, (myo) pericarditis, ischemic lesions and thrombo-embolic complications (Table 21. Since anthracyclines are widely used and are clearly associated with cardiac side effects, the cardiac effects of this drug group have been examined extensively. Anthracycline-induced Cardiotoxicity Anthracycline exposure has been associated with both acute and chronic cardiotoxicity [2]. Of all patients receiving anthracycline-containing chemotherapy, 3% will develop acute cardiotoxic effects, consisting of left ventricular systolic and/or diastolic dysfunction, arrhythmias, pericarditis/myocarditis syndrome and myocardial necrosis leading to dilated cardiomyopathy and acute heart failure. The chronic cardiotoxicity which has been described after anthracycline exposure consists of two groups. First, patients with subclinical cardiac abnormalities including reduced left ventricular mass and contractility; thirty years after chemotherapy exposure, this is seen in 50% of the patients. The second group reveals progressive myofibrillar loss and degeneration of the left ventricular cardiomyocytes leading to congestive heart failure. Chapter 21: Chemotherapy and Cardiovascular Function in Pregnancy 221 Thirty years after chemotherapy exposure, this complication is seen in 7. Main outcome measures were the incidence of and risk factors for congestive heart failure, myocardial infarction, pericardial disease and valvular abnormalities in survivors of cancer compared with siblings. The data were collected based on a questionnaire that was completed by the patients or their parents. Exposure to 250 mg/m2 or more of anthracyclines increased the relative hazard of congestive heart failure, pericardial disease and valvular abnormalities by two to five times compared with survivors who had not been exposed to anthracyclines. The cumulative incidence of adverse cardiac outcomes in cancer survivors continued to increase up to 30 years after diagnosis [2]. Risk factors for developing cardiac problems after anthracycline exposure are a higher cumulative dose, a higher Cmax, concomitant radiation therapy involving heart region (vascular injury, endothelial dysfunction), female sex, younger age at diagnosis, longer time of follow up, black ethnicity, Trisomy 21, pre-existing cardiac risk factors (diabetes, obesity, renal failure, congenital heart disease) and additional treatment with amasacrine, trastuzumab, cyclophosphamide, bleomycin, vincristine or different anthracycline derivates [2, 3]. For example, the risk of developing heart failure and asymptomatic decline in systolic function after exposure to trastuzumab is around 4% [4], but increases to up to 25% when trastuzumab is administered concurrently with or shortly after anthracycline treatment [5]. Studies have shown that multiple mechanisms are involved in anthracycline-induced cardiotoxicity, including oxidative damage, changes in calcium metabolism and activation of apoptotic pathways [3, 6]. Cell death results in a decreased number of myocardial cells and an increased loading on surviving muscle cells. Also, the normal cardiac repair mechanisms are affected by anthracycline exposure and there is a depletion of cardiac stem cells. These effects influence the function of the surviving cells and can cause a progressive deterioration in cardiac function. Moreover, patients treated with chemotherapy also receive co-medication, such as steroids and erythropoietin, that are also associated with induction of hypertension [7]. Pregnancy is a specific physiologic state associated with major hemodynamic adaptations resulting in increased cardiac output and workload, and therefore requires some cardiac reserve capacity. Echocardiographic measurements show an important increase in 222 Section 5: Controversies Table 21. These circulatory changes require a cardiac reserve capacity before getting pregnant and could result in increased sensitivity to cardiovascular side effects of cancer treatments administered during pregnancy. When chemotherapy is administered in pregnancy several aspects need to be considered, namely pharmacokinetics of chemotherapeutic agents in pregnant women, and maternal and fetal cardiovascular effects of chemotherapy exposure in pregnancy. Pharmacokinetics of Chemotherapy in Pregnant Women Apart from the cardiac adaptations mentioned before, during pregnancy the total body water and plasma volume increases with 50%, glomerular filtration rate increases by 40%, hepatic metabolism changes and the body fat mass increases till 30% [8, 9]. This finding would suggest that higher drug dosages should be prescribed to pregnant women than to nonpregnant women. Maternal Cardiovascular Effects of Chemotherapy Administered During Pregnancy In women with established cardiac disease, the physiologic changes associated with late pregnancy and labor may cause cardiac decompensation. Even so, the impact of chemotherapy in pregnancy might be higher, seen increased hemodynamic loading in pregnancy. Nevertheless, in the current literature there is no mention of an increased frequency of heart failure, left ventricular dysfunction or hypertensive complications when chemotherapy is administered during pregnancy [1, 13, 17, 18]. The data are, however, very limited and different monitoring strategies have been used in different centers. Fetal Cardiovascular Effects of Prenatal Exposure to Chemotherapy Maternal illness and cancer treatment during pregnancy can affect fetal development. Current data show an increased risk of congenital malformations after exposure to chemotherapy in the first gestational trimester [18]. When chemotherapy is administered in the second and third trimester, there is an increased risk of fetal growth restriction and preterm birth [17]. These complications have been linked to cardiovascular problems later in life, such as hypertension, higher body fat percentages, waist circumferences, plasma uric acid levels, alanine aminotransferase levels and aspartate transaminase levels [19, 20]. Since anthracyclines are known to induce a dose-related cardiotoxicity in children and adults, the fetal heart could be affected. Fetal myocardium differs from adult myocardium because fetal myocytes are smaller, and typically have a single nucleus compared with the multinuclear cells prevalent after birth. The myocytes also contain fewer sarcomeres per mass unit, and different isoforms of contractile proteins are expressed [21, 22]. The myocytes contain lower numbers of mitochondria and the antioxidant pathways are still underdeveloped. All these factors might make the fetal myocardium more vulnerable to damage by chemotherapeutic agents. There might also be an effect on the fetal stem cell population that might influence cardiac repair mechanisms, but no data are currently available.

List the main genera of normal biota presently known to occupy the respiratory tract birth control 3 weeks cheap 3.03 mg yasmin visa. The common cold is often called rhinitis birth control exam yasmin 3.03mg line, from the Latin word rhin, meaning "nose," and the suffix -itis, meaning "inflammation. People can acquire some degree of immunity to a cold virus that they have encountered before, but because there are more than 200 viruses, this immunity does not provide much overall protection. Prevention Agents the common cold is caused by one of over 200 different kinds of viruses. The particular virus is almost never identified, and the symptoms and handling of the infection are the same no matter which of the viruses is responsible. The most common type of virus leading to the common cold is the group called rhinoviruses, of which there are 99 serotypes. Most viruses causing the common cold never lead to any serious consequences, but some of them can be serious for some patients. In this section, we consider all cold-causing viruses together as a group because they are treated similarly. Viral infection of the upper respiratory tract can predispose a patient to secondary infections by other microorganisms, such as bacteria. Secondary infections may explain why some people report that their colds improved when they were given antibiotics. A virus originally caused the cold, but a bacterial infection might have followed. A traditional vaccine would need to contain antigens from about 200 viruses to provide complete protection. Because most of the viruses causing the common cold use only a few different chemicals on host epithelium for their attachment site, some scientists have proposed developing a vaccine that would stimulate antibody to the docking site on the host. Other approaches include inducing antibody to the sites of action for the inflammatory mediators. The best way to prevent transmission is frequent hand washing, followed closely by stopping droplets from traveling away from the mouth and nose by covering them when sneezing or coughing. It is better to do this by covering the face with the crook of the arm rather than the hand, because subsequent contact with surfaces is less likely. A wide variety of over-the-counter agents, such as antihistamines and decongestants, improve symptoms by blocking inflammatory mediators and their action. The use of these agents may also cut down on transmission to new hosts, because fewer virus-loaded secretions are produced. Zinc appears to block the replication of rhinovirus; however, it appears to only reduce the duration of the common cold and not prevent the disease. They must penetrate the mucus that coats the respiratory tract and then find firm attachment points. The symptoms we experience as the common cold are mainly the result of our body fighting back against the viral invaders. Virusinfected cells in the upper respiratory tract release chemicals that attract certain types of white blood cells to the site, and these cells release cytokines and other inflammatory mediators, as described in chapters 14 and 16. These mediators generate a localized inflammatory reaction, characterized by swelling and inflammation of the nasal mucosa, leakage of fluid from capillaries and lymphatic vessels, and increased production of mucus. Transmission the Common Cold Approximately 200 viruses (rhinoviruses, adenoviruses, and coronaviruses) Indirect contact, droplet contact Attachment proteins; most symptoms induced by host response Not necessary Hygiene practices For symptoms only Highest incidence among preschool and elementary schoolchildren, with average of three to eight colds per year; adults and adolescents: two to four colds per year and Epidemiology Cold viruses are transmitted by droplet contact, but indirect transmission may be more common, such as when a healthy person touches a fomite and then touches one of his or her own vulnerable surfaces, such as the mouth, nose, or an eye. In some cases, the viruses can remain airborne in droplet nuclei and aerosols and can be transmitted via the respiratory route. The epidemiology of the common cold is fairly simple: Practically everybody gets colds-and fairly frequently. Children have more frequent infections than adults, probably because nearly every virus they encounter is a new one and they have no secondary immunity to 21. The infectious agents that may be responsible for the condition include a variety of viruses or bacteria and, less commonly, fungi. The inflammatory symptoms of a cold produce a large amount of fluid and mucus, and when trapped in the sinuses, these secretions provide an excellent growth medium for bacteria or fungi. This is why it is common for patients suffering from the common cold to then develop sinusitis caused by bacteria or fungi. Signs lasting for longer than 12 weeks are termed chronic sinusitis, and such cases are often difficult to treat due to loss of mucociliary defenses and bacterial biofilm formation in the sinuses. Broad-spectrum antibiotics may be prescribed when the physician feels that the sinusitis is bacterial in origin. Most uncomplicated cases may be best treated by having the patient "wait it out" while his or her own immune system clears the infection. Discharge from the nose and mouth appears opaque and may have a green or yellow color in the case of bacterial infections. Discharge caused by an allergy is usually clear, and the symptoms may be accompanied by itchy, watery eyes. Causative Fungi Fungal sinusitis is rare, but it is often recognized when antibacterial drugs fail to alleviate symptoms. Simple fungal infections may normally be found in the maxillary sinuses and are noninvasive in nature. These colonies are generally not treated with antifungal agents but instead are simply mechanically removed by a physician. Aspergillus fumigatus is a common fungus involved in this type of infection, but Bipolaris species are an emerging cause of fungal sinusitis today. The growth of fungi in this type of sinusitis may be encouraged by trauma to the area. More serious invasive fungal infections of the sinuses may be found in severely immunocompromised patients. Fungi such as Aspergillus and Mucor species may invade the bony structures in the sinuses and even travel to the brain or eye. These infections are treated aggressively with a combination of surgical removal of the fungus and intravenous antifungal therapy (Disease Table 21. Agents Viruses Viral infection is probably the most common cause of mild sinusitis. Bacteria Any number of bacteria that are normal biota in the upper respiratory tract may cause sinus infections. Many cases are caused by Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Corynebacterium tuberculostearicum, and Haemophilus influenzae. The causative organism is usually not identified, but treatment is begun empirically, based on the symptoms. The bacteria that cause these infections are most often normal biota in the host and do not have an arsenal of virulence factors that lead to their ability to cause disease. The pathogenesis of this condition is brought about by the confluence of several factors: predisposition to infection because of underlying infection; buildup of fluids, providing a rich environment for bacterial multiplication; and sometimes the anatomy of the sinuses, which can contribute to entrapment of mucus and bacterial growth. Of course, the virus causing a preceding cold is transmissible, but the host takes it from there by creating the conditions favorable for respiratory tract microorganisms to multiply in the sinus spaces. A large proportion of these cases are allergic sinusitis episodes, but approximately 30% of them are caused by bacterial overgrowth in the sinuses. As with many upper respiratory tract infections, smokers have higher rates of infection than nonsmokers. Children who are exposed to large amounts of secondhand smoke are also more susceptible. Infections Acute Otitis Media (Ear Infection) this condition is another common sequela of the common cold- for reasons similar to the ones described for sinusitis. Viral infections of the upper respiratory tract lead to inflammation of the eustachian tubes and the buildup of fluid in the middle ear, which can lead to bacterial multiplication in those fluids. Bacteria can migrate along the eustachian tube from the upper respiratory tract (figure 21. When bacteria encounter mucus and fluid buildup in the middle ear, they multiply rapidly.

Aortic Valve Stenosis Aortic valve stenosis is the most frequent valve abnormality birth control for women does size buy yasmin 3.03 mg low cost. For those born in the early- and mid20th century birth control pills 21 day cycle purchase yasmin 3.03 mg on line, rheumatic fever was a common cause but now accounts for <10% of cases of aortic stenosis. The great majority of aortic stenoses is a result of degenerative calcification and comes to clinical attention in the sixth decade of life or later. Aortic stenosis causes extra work for the heart, resulting in left ventricular hypertrophy. Aortic Valve Insufficiency Insufficiency of the aortic valve results in aortic regurgitation (backrush of blood into the left ventricle), producing a heart murmur and a collapsing pulse (forcible impulse that rapidly diminishes). This technique may detect as little as 20 mL of fluid in the pericardial cavity, such as that resulting from pericardial effusion. Doppler echocardiography is a technique that demonstrates and records the flow of blood through the heart and great vessels by Doppler ultrasonography, making it especially useful in the diagnosis and analysis of problems with blood flow through the heart, such as septal defects, and in delineating valvular stenosis and regurgitation, especially on the left side of the heart. Sonographer placing transducer in a left intercostal space in the parasternal line, overlying the heart. A long, narrow catheter is passed into the ascending aorta via the femoral artery in the inguinal region. Under fluoroscopic control, the tip of the catheter is placed just inside the opening of a coronary artery. A small injection of radiopaque contrast material 904 is made, and cineradiographs are taken to show the lumen of the artery and its branches, as well as any stenotic areas that may be present. It has many causes, all of which result in a reduced blood supply to the vital 905 myocardial tissue. The most common cause of ischemic heart disease is coronary artery insufficiency resulting from atherosclerosis. As coronary atherosclerosis progresses, the collateral channels connecting one coronary artery with the other expand, which may initially permit adequate perfusion of the heart during relative inactivity. Despite this compensatory mechanism, the myocardium may not receive enough oxygen when the heart needs to perform increased amounts of work. Slowly Progressive Coronary Artery Disease In slow occlusion of a coronary artery, the collateral circulation has time to increase so that adequate perfusion of the myocardium can occur when a 907 potentially ischemic event occurs. On sudden blockage of a large coronary branch, some infarction is probably inevitable, but the extent of the area damaged depends on the degree of development of collateral anastomotic channels. If large branches of both coronary arteries are partially obstructed, an extracardiac collateral circulation may be used to supply blood to the heart. These collaterals connect the coronary arteries with the vasa vasorum (small arteries) in the tunica adventitia of the aorta and pulmonary arteries and with branches of the internal thoracic, bronchial, and phrenic arteries. Clinical studies show that anastomoses cannot provide collateral routes quickly enough to prevent the effects of sudden coronary artery occlusion. Angina Pectoris Pain that originates in the heart is called angina or angina pectoris (L. Individuals with angina commonly describe the transient (15 seconds to 15 minutes) but moderately severe constricting pain as tightness in the thorax, deep to the sternum. The pain is the result of ischemia of the myocardium that falls short of inducing the cellular necrosis that defines infarction. The reduced blood flow results in less oxygen being delivered to the cardiac striated muscle cells. As a result of the limited anaerobic metabolism of the myocytes, lactic acid accumulates and the pH is reduced in affected areas of the heart. Strenuous exercise (especially after a heavy meal), sudden exposure to cold, and stress all require increased activity on the part of the heart, but the occluded vessels cannot provide it. When food enters the stomach, blood flow to it and other parts of the digestive tract is increased. Sublingual nitroglycerin (medication placed or sprayed under the tongue for absorption through the oral mucosa) may be administered because it dilates the coronary (and other) arteries. Furthermore, the dilated vessels accommodate more of the blood volume, so less blood arrives in the heart, relieving heart congestion. Such angina provides a warning that the coronary arteries are compromised and that there is a need for a change of lifestyle, a health care intervention, or both. Coronary Bypass Graft Patients with obstruction of their coronary circulation and severe angina may undergo a coronary bypass graft operation. The great saphenous vein is commonly harvested for coronary bypass surgery because it (1) has a diameter equal to or greater than that of the coronary arteries, (2) can be easily dissected from the lower limb, and (3) and offers relatively lengthy portions with a minimum occurrence of valves or branching. Reversal of the implanted segment of vein can negate the effect of a valve if a valved segment must be used. A coronary bypass graft shunts blood from the aorta to a stenotic coronary artery to increase the flow distal to the obstruction. Simply stated, it provides a detour around the stenotic area (arterial stenosis) or blockage (arterial atresia). Revascularization of the myocardium may also be achieved by surgically anastomosing an internal thoracic artery with a coronary artery. Hearts with coronary bypass grafts are commonly found during dissections in the gross anatomy laboratory. The vessel is stretched to increase the size of the lumen, thus improving blood flow. In other cases, 910 thrombokinase is injected through the catheter; this enzyme dissolves the blood clot. After dilation of the vessel, an intravascular stent may be introduced to maintain the dilation. Intravascular stents are composed of rigid or semirigid tubular meshes, collapsed during introduction. Once in place, they expand or are expanded with a balloon catheter, to maintain luminal patency. Functional testing of the heart includes exercise tolerance tests (treadmill stress tests), primarily to check the consequences of possible coronary artery disease. Exercise tolerance tests are of considerable importance in detecting the cause of heartbeat irregularities. Coronary Occlusion and Conducting System of Heart Damage to the conducting system of the heart, often resulting from ischemia caused by coronary artery disease, produces disturbances of cardiac muscle contraction. Damage to one of the bundle branches results in a bundle-branch block, in which excitation passes along the unaffected branch and causes a normally timed systole of that ventricle only. The impulse then spreads to the other ventricle via myogenic (muscle propagated) conduction, producing a late asynchronous contraction. Obviously, this vital part of the conducting system must be preserved during surgical repair of the defect. Artificial Cardiac Pacemaker In some people with a heart block, an artificial cardiac pacemaker (approximately the size of a pocket watch) is inserted subcutaneously. The pacemaker consists of a pulse generator or battery pack, a wire (lead), and an electrode. Pacemakers produce electrical impulses that initiate ventricular contractions at a predetermined rate. An electrode with a catheter connected to it is inserted into a vein and its progression through the venous pathway is followed with a fluoroscope, a device for examining deep structures in real time (as motion occurs) by means of radiographs. Here, the electrode is firmly fixed to the trabeculae carneae in the ventricular wall and placed in contact with the endocardium. The increased intrathoracic pressure forces blood out of the heart into the great arteries. When the external pressure is released and the intrathoracic pressure falls, the heart again fills with blood. If the heart stops beating (cardiac arrest) during heart surgery, the surgeon attempts to restart it using internal or openchest heart massage. In atrial fibrillation, the normal regular rhythmical contractions of the atria are replaced by rapid irregular and uncoordinated twitchings of different parts of the atrial walls. The ventricles respond at irregular intervals to the dysrhythmic impulses received from the atria, but usually, circulation remains satisfactory.

Patients remain asymptomatic or experience recurrent "surface" infections indefinitely birth control pills free purchase yasmin 3.03 mg with amex. Wart diseases Human papillomaviruses: the causative agents of genital warts are human papillomaviruses birth control pills cost cvs generic 3.03mg yasmin with amex. Certain types infect cells on the female cervix that eventually result in malignancies of the cervix. Molluscum contagiosum: Caused by a virus in the family Poxviridae, molluscum contagiosum can take the form of wartlike growths in the membranes of the genitalia, and it can be transmitted sexually. Group B Streptococcus "colonization"-neonatal disease: Asymptomatic colonization of women by a beta-hemolytic Streptococcus in Lancefield group B is very common. High Impact Study these terms and concepts are most critical for your understanding of this chapter-and may be the most difficult. Concepts Defenses of genitourinary system Normal microbiota of genitourinary system Community-acquired vs. Genital herpes transmission can be reduced or prevented by all of the following, except a. Within a few days, he developed flulike symptoms, but these symptoms rapidly cleared on their own. Several weeks later, however, he developed a painful headache and jaundice; at this point, he immediately sought medical attention. Urinalysis revealed the signs of a distinct pathogen, and serology showed he had increasing levels of IgM antibody. Explain what disease you think this man was suffering from, and describe the causative agent. Summarize how a laboratory technologist would identify a case of vaginosis versus a case of vaginitis from a vaginal swab specimen. Explain why microscopic analysis of a urine specimen is more accurate for Chlamydia screening in males than in females. A young man presents to his primary care physician with genital lesions and is told that he has herpes. He refuses to believe this diagnosis because he is in a long-standing relationship with a woman who clearly has never shown signs of vaginal herpes lesions. Construct an informative response to this patient based upon the information in this chapter. Thinking about part (a) of this question, explain why the number of people in the United States who have genital herpes may be a lot higher than official statistics depict. Using the words that follow, please create a concept map illustrating the relationships among these key terms from chapter 23. This case focuses on the 2015 Quanta Magazine article, "Scientists Map 5,000 New Ocean Viruses. Well, since there are about 5 milliliters in a teaspoon and about 10 million viruses in a milliliter, you are swallowing tens of thousands of viruses. But there is no reason to panic: Unless you are swimming in polluted waters, these are not human viruses-they are bacteriophages, for the most part. This article told us that more than 5,000 types of viruses were identified for the first time in some groundbreaking studies using metagenomics to sample the contents of the sea that would pass through the smallest filters-filters that stopped bacteria, for example. But they were unable to cultivate the viruses in the lab, not knowing what their hosts were. With a metagenomic approach, viral sequences can be mapped from the seemingly clear water, and distinct viral genomes can be identified. The researchers estimate that the total number of new and different viruses that will be found in the sea will be in the tens of thousands. They do not know what all of these (mostly) bacteriophages are doing, and what role they play in the biosphere, but now they have the initial information to help them go down that path. It is intriguing to know that something so fundamental is still unknown by science. Draw an example of an energy pyramid, labeling primary producers, consumers, and decomposers. Discuss how metagenomic sampling has changed our view of deep subsurface and oceanic microbiology. List the stratified regions of large bodies of standing water, and describe how microbes are affected by this layering. Provide one example in which human disease has been affected by changes in the environment. This article emphasizes microbial activities that help maintain, sustain, and control the life-support systems on the earth. This subject is explored from the standpoint of the natural roles of microorganisms in the environment and their contributions to the ecological balance, including soil, water, and mineral cycles. Although we have known for a long time that geologic features on the earth, including coal and limestone, are formed in small or large part by microbes, it is only recently that we have come to understand the sheer mass of microbial life present on our planet. With the development of genomic techniques that do not rely on cultivating bacteria, we have discovered abundant microbial life all over-and within and around-our planet (figure 24. The vent effluent is rich in sulfides, and it feeds chemolithotrophic bacteria in the vicinity. Abiotic factors include nonliving components such as atmospheric gases, minerals, water, temperature, and light. A collection of organisms together with its surrounding physical and chemical factors is called an ecosystem. Biosphere Lithosphere Hydrosphere Atmosphere Biomes the Organization of Ecosystems the earth initially may seem like a random, chaotic place, but it is actually an incredibly organized, fine-tuned machine. Ecological relationships exist at several levels, ranging from the entire earth all the way down to a single organism (figure 24. This global ecosystem comprises the hydrosphere (water), the lithosphere (a few miles into the soil), and the atmosphere (a few miles into the air). The biosphere maintains or creates the conditions of temperature, light, gases, moisture, and minerals required for life processes. The terrestrial realm is usually distributed into particular climatic regions called biomes (by-ohmz), each of which is characterized by a dominant plant form, temperature, and precipitation. Biomes and aquatic ecosystems are generally composed of mixed assemblages of organisms that live together at the same place and time and that usually exhibit well-defined nutritional or behavioral interrelationships. Although most communities are identified by their easily visualized dominant plants and animals, they also contain a complex assortment of bacteria, fungi, algae, protozoa, and viruses. The basic units of community structure are populations, groups of organisms of the same kind. The habitat is the physical location and environment to which an organism has adapted. In the case of microorganisms, the habitat is frequently a microenvironment, where particular qualities of oxygen, light, or nutrient content are suitable for that microorganism. The niche is the overall role that a species (or population) serves in a community. This includes such Tropical forests Temperate deciduous forests Taiga Tundra Ecosystem South Gradient in latitude North Community Population Chlamydomonas Individual Organism 1. A nonliving thing has never been alive, whereas a dead thing was once alive but no longer is. A niche can be broad (such as scavengers that feed on nearly any organic food source) or narrow (microbes that decompose cellulose in forest litter). Microbes in natural ecosystems exhibit an amazing tendency to adapt to extreme environments. In 2008, researchers found a bacterium living completely alone, with no other life forms in its ecosystem. It was found in a South African gold mine, in fluid collected in cracks in the rock 2 miles below the surface. Obviously, there is no light there, and there are also no photosynthetic organisms (such as plants) to offer the indirect benefits of photosynthesis for the bacterium to use. The bacterium, named Desulforudis audaxviator, has to extract everything it needs from an abiotic environment. Apparently, it garners energy from metabolizing the hydrogen and sulfate produced from the radioactive decay of uranium in the rocks, and it possesses genes that enable it to leach inorganic carbon and nitrogen from the environment. The interesting spin on this discovery is that it now suddenly makes the possibility of finding microbial life on other planets more plausible. As one researcher said of Desulforudis, "This is just the kind of organism that could survive on Mars. The energy and nutritional relationships in ecosystems can be described in a number of convenient ways.

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