Spinal Cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. Neural tissue can generate oscillatory activity in many ways, driven either by mechanisms within individual neurons or by interactions between neurons. Dr Gonzalez was truly brilliant. Share your thoughts with other customers. The myelin sheath is a multi-layered membrane, unique to the nervous system, that functions as an insulator to greatly increase the velocity of axonal impulse conduction. Peripheral Neuropathy is damage to or disease affecting nerves, which may impair sensation, movement, gland or organ function, or other aspects of health, depending on the type of nerve affected. The opposite of a black box is a system where the inner components or logic are available for inspection , which is most commonly referred to as a white box sometimes also known as a "clear box" or a "glass box".
Vitamin B1: Thiamine
Another source of ocean pollution by sewage-related waste is the disposal of biosolids, a semisolid byproduct of the sewage treatment process, often called sludge. Historically, sludge in developed nations was disposed in coastal waters: New York's twenty sewage treatment plants, for example, once disposed their sludge offshore in a region known as the New York Bight.
Although today's environmental regulations in the United States prohibit this practice, sewage sludge is still disposed at sea in some countries.
Disease-causing microbes are the primary human health risk in sewage-contaminated waters, and the main cause of recreational beach closures. Here a sign warns San Diego beachgoers of sewage in the waters. Animal wastes often reach waterbodies via runoff across the land surface, or by seepage through the surface soil layers.
Hence, agricultural runoff containing animal wastes does not receive any "treatment" except what is naturally afforded by microbial activity during its transit to a waterbody. In coastal watersheds, these wastes can flow through river networks that eventually empty into the sea. Nutrients and organic materials from plants, animals, and humans that enter coastal waters, either directly or indirectly, can stimulate a biological, chemical, and physical progression known as eutrophication.
Coastal eutrophication is commonly observed in estuaries , bays, and marginal seas. In a broad sense, coastal eutrophication mirrors the eutrophication of lakes. For example, as increased nutrients stimulate algal and other plant growth, light transmission decreases. The eventual bacterial decay of algae and other plants lowers the dissolved oxygen level in the water.
In extreme cases, all of the oxygen can be removed. Human-accelerated eutrophication known as cultural eutrophication can be triggered by inputs of sewage, sludge, fertilizers, or other wastes containing nutrients such as nitrogen and phosphorus. As recently as the s, for example, the New York Bight was essentially lifeless due to oxygen depletion, caused largely by decades of sewage and sludge disposal. As of , Halifax Harbor was still receiving a daily influx of raw sewage, creating serious ecological and public health concerns.
Nutrient-enriched runoff from agricultural land in the midwestern United States is the primary cause of the well-known Gulf of Mexico "Dead Zone. Much of the nitrogen reaching the gulf is from agricultural fertilizers, with lesser amounts from residential fertilizers and other sources.
The water of the 20,kilometer 7,square-mile Dead Zone, extending from the mouth of the Mississippi River Basin to beyond the Texas border, has so little oxygen that essentially no marine life exists. If human-accelerated eutrophication is not reversed, the entire coastal ecosystem ultimately may be changed. Sensitive species may be replaced by more tolerant and resilient species, and biologically diverse communities may be replaced by less diverse ones.
Further, nutrient enrichment and the associated eutrophication in coastal waters is implicated in some harmful algal blooms, in which certain species of algae produce biotoxins natural poisons that can be transferred through the food web, potentially harming higher-order consumers such as marine mammals and humans.
Sewage, particularly if partially treated or untreated, brings high microbe concentrations into the ocean. Human diseases can be caused by waterborne pathogens that contact the skin or eyes; waterborne pathogens that are accidentally ingested when water is swallowed; or foodborne pathogens found in the tissues of fish and shellfish consumed as seafood. Beach pollution consequently is a persistent public health problem. Annually, thousands of swimming advisories and beach closings are experienced because high levels of disease-causing microbes are found in the water.
Sewage often is responsible for the harmful microbial levels. Seafood contaminated by sewage-related pathogens sickens untold numbers of people worldwide. Regulatory agencies will close a fishery when contamination is detected.
However, many countries lack regulatory oversight or the resources to adequately monitor their fisheries. Industrial wastes primarily enter coastal waters from terrestrial land-based activities. Industries, like municipalities and other entities that generate wastes, dispose of many liquid wastes through wastewater systems and ultimately to waterbodies , whereas they dispose of their solid wastes in landfills. The quantity and characteristics of industrial wastewater depends on the type of industry, its water and wastewater management, and its type of waste pretreatment if any before delivery to a wastewater sewage treatment plant.
Because industrial waste frequently goes down the same sewers as domestic and commercial nonindustrial waste, sewage often contains high levels of industrial chemicals and heavy metals e. Substances that are not removed by wastewater treatment processes are discharged via the treated effluent to a receiving stream, river, or coastal outlet. Inland waters ultimately reach the ocean, carrying with them some residual chemical that are not attenuated, stored, or degraded during their journey through the watershed.
Other land-based sources of industrial pollutants in the ocean are pipeline discharges and transportation accidents, leaking underground storage tanks, and activities at ports and harbors.
Intentional, illegal dumping in inland watersheds and in inland waterbodies also can deliver industrial wastes to drainageways, and ultimately to the ocean. In coastal watersheds, some industries discharge their wastes directly to the ocean. Like industries located inland, these industries must first obtain a permit under the Clean Water Act.
Industrial pollutants also can directly enter the ocean by accidental spills or intentional dumping at sea. Wet and dry deposition of airborne pollutants is a sometimes overlooked, yet significant, source of chemical pollution of the oceans.
For example, sulfur dioxide from a factory smokestack begins as air pollution. Capillaries connect to arterioles on one end and venules on the other. Capillaries carry blood very close to the cells of the tissues of the body in order to exchange gases, nutrients, and waste products.
The walls of capillaries consist of only a thin layer of endothelium so that there is the minimum amount of structure possible between the blood and the tissues. The endothelium acts as a filter to keep blood cells inside of the vessels while allowing liquids, dissolved gases, and other chemicals to diffuse along their concentration gradients into or out of tissues.
Precapillary sphincters are bands of smooth muscle found at the arteriole ends of capillaries. These sphincters regulate blood flow into the capillaries. Since there is a limited supply of blood, and not all tissues have the same energy and oxygen requirements, the precapillary sphincters reduce blood flow to inactive tissues and allow free flow into active tissues. Veins are the large return vessels of the body and act as the blood return counterparts of arteries.
This lack of pressure allows the walls of veins to be much thinner, less elastic, and less muscular than the walls of arteries. Veins rely on gravity, inertia, and the force of skeletal muscle contractions to help push blood back to the heart. To facilitate the movement of blood, some veins contain many one-way valves that prevent blood from flowing away from the heart. As skeletal muscles in the body contract, they squeeze nearby veins and push blood through valves closer to the heart.
When the muscle relaxes, the valve traps the blood until another contraction pushes the blood closer to the heart. Venules are similar to arterioles as they are small vessels that connect capillaries, but unlike arterioles, venules connect to veins instead of arteries. Venules pick up blood from many capillaries and deposit it into larger veins for transport back to the heart. The heart has its own set of blood vessels that provide the myocardium with the oxygen and nutrients necessary to pump blood throughout the body.
The left and right coronary arteries branch off from the aorta and provide blood to the left and right sides of the heart. The coronary sinus is a vein on the posterior side of the heart that returns deoxygenated blood from the myocardium to the vena cava. The veins of the stomach and intestines perform a unique function: Blood leaving the digestive organs is rich in nutrients and other chemicals absorbed from food. The liver removes toxins, stores sugars, and processes the products of digestion before they reach the other body tissues.
Blood from the liver then returns to the heart through the inferior vena cava. The average human body contains about 4 to 5 liters of blood. As a liquid connective tissue, it transports many substances through the body and helps to maintain homeostasis of nutrients, wastes, and gases. Blood is made up of red blood cells, white blood cells, platelets, and liquid plasma.
Erythrocytes are produced inside of red bone marrow from stem cells at the astonishing rate of about 2 million cells every second. The shape of erythrocytes is biconcave—disks with a concave curve on both sides of the disk so that the center of an erythrocyte is its thinnest part. The unique shape of erythrocytes gives these cells a high surface area to volume ratio and allows them to fold to fit into thin capillaries.
Immature erythrocytes have a nucleus that is ejected from the cell when it reaches maturity to provide it with its unique shape and flexibility. The lack of a nucleus means that red blood cells contain no DNA and are not able to repair themselves once damaged. Erythrocytes transport oxygen in the blood through the red pigment hemoglobin. Hemoglobin contains iron and proteins joined to greatly increase the oxygen carrying capacity of erythrocytes. Add all three to Cart Add all three to List.
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