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Troubleshooting And Repair Of Consumer Electronic Equipment - Back to Troubleshooting Table of Contents. Va office inspector general office audits , Va office of inspector general office of audits and evaluations veterans benefits administration review of alleged inappropriate prioritization of appeals at. Cat 2015 - khel khel mein - gp ka funda, mba blog cat, Sir i am cl classroom student and i bought smart cat cracker videos package primarily for va as my va is weak but the biggest issue i am facing is in para jumbles. Beneficiary financial counseling service online , Beneficiary financial counseling service online preparation. Arteries and veins transport blood in two distinct circuits: the systemic circuit and the pulmonary circuit ([link]). Different types of blood vessels vary slightly in their structures, but they share the same general features. By the time blood has passed through capillaries and entered venules, the pressure initially exerted upon it by heart contractions has diminished. The walls of arteries and veins are largely composed of living cells and their products (including collagenous and elastic fibers); the cells require nourishment and produce waste. Both arteries and veins have the same three distinct tissue layers, called tunics (from the Latin term tunica), for the garments first worn by ancient Romans; the term tunic is also used for some modern garments. The tunica intima (also called the tunica interna) is composed of epithelial and connective tissue layers. Next to the endothelium is the basement membrane, or basal lamina, that effectively binds the endothelium to the connective tissue. In larger arteries, there is also a thick, distinct layer of elastic fibers known as the internal elastic membrane (also called the internal elastic lamina) at the boundary with the tunica media.
Under the microscope, the lumen and the entire tunica intima of a vein will appear smooth, whereas those of an artery will normally appear wavy because of the partial constriction of the smooth muscle in the tunica media, the next layer of blood vessel walls. The smooth muscle layers of the tunica media are supported by a framework of collagenous fibers that also binds the tunica media to the inner and outer tunics. The outer tunic, the tunica externa (also called the tunica adventitia), is a substantial sheath of connective tissue composed primarily of collagenous fibers.
Farther from the heart, where the surge of blood has dampened, the percentage of elastic fibers in an artery’s tunica intima decreases and the amount of smooth muscle in its tunica media increases. Notice that although the distinctions between elastic and muscular arteries are important, there is no “line of demarcation” where an elastic artery suddenly becomes muscular. With a lumen averaging 30 micrometers or less in diameter, arterioles are critical in slowing down—or resisting—blood flow and, thus, causing a substantial drop in blood pressure. A capillary is a microscopic channel that supplies blood to the tissues themselves, a process called perfusion. The wall of a capillary consists of the endothelial layer surrounded by a basement membrane with occasional smooth muscle fibers. For capillaries to function, their walls must be leaky, allowing substances to pass through. The most common type of capillary, the continuous capillary, is found in almost all vascularized tissues.
A fenestrated capillary is one that has pores (or fenestrations) in addition to tight junctions in the endothelial lining.
A metarteriole is a type of vessel that has structural characteristics of both an arteriole and a capillary. The precapillary sphincters, circular smooth muscle cells that surround the capillary at its origin with the metarteriole, tightly regulate the flow of blood from a metarteriole to the capillaries it supplies. Although you might expect blood flow through a capillary bed to be smooth, in reality, it moves with an irregular, pulsating flow.
Cardiovascular System: Edema and Varicose Veins Despite the presence of valves and the contributions of other anatomical and physiological adaptations we will cover shortly, over the course of a day, some blood will inevitably pool, especially in the lower limbs, due to the pull of gravity.
Most people experience a daily accumulation of tissue fluid, especially if they spend much of their work life on their feet (like most health professionals).
Edema may be accompanied by varicose veins, especially in the superficial veins of the legs ([link]).
In addition to their primary function of returning blood to the heart, veins may be considered blood reservoirs, since systemic veins contain approximately 64 percent of the blood volume at any given time ([link]). When blood flow needs to be redistributed to other portions of the body, the vasomotor center located in the medulla oblongata sends sympathetic stimulation to the smooth muscles in the walls of the veins, causing constriction—or in this case, venoconstriction. Vascular Surgeons and Technicians Vascular surgery is a specialty in which the physician deals primarily with diseases of the vascular portion of the cardiovascular system. Vascular technicians are specialists in imaging technologies that provide information on the health of the vascular system. Blood pumped by the heart flows through a series of vessels known as arteries, arterioles, capillaries, venules, and veins before returning to the heart. The arterial system is a relatively high-pressure system, so arteries have thick walls that appear round in cross section. An especially leaky type of capillary found in the liver and certain other tissues is called a ________. A blood vessel with a few smooth muscle fibers and connective tissue, and only a very thin tunica externa conducts blood toward the heart. Soldering and Desoldering Equipment and Techniques Solder is Not Glue The ease and quality of your work will depend both on .
UpdateStar has been tested to meet all of the technical requirements to be compatible with Windows 10, 8.1, Windows 8 . An artery is a blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels. Arteries and arterioles have thicker walls than veins and venules because they are closer to the heart and receive blood that is surging at a far greater pressure ([link]).
In other words, in comparison to arteries, venules and veins withstand a much lower pressure from the blood that flows through them. Since blood passes through the larger vessels relatively quickly, there is limited opportunity for blood in the lumen of the vessel to provide nourishment to or remove waste from the vessel’s cells.
From the most interior layer to the outer, these tunics are the tunica intima, the tunica media, and the tunica externa (see [link]).
Lining the tunica intima is the specialized simple squamous epithelium called the endothelium, which is continuous throughout the entire vascular system, including the lining of the chambers of the heart. The basement membrane provides strength while maintaining flexibility, and it is permeable, allowing materials to pass through it.
Like the other components of the tunica intima, the internal elastic membrane provides structure while allowing the vessel to stretch. It is generally the thickest layer in arteries, and it is much thicker in arteries than it is in veins. Along with the collagenous fibers are large numbers of elastic fibers that appear as wavy lines in prepared slides. All arteries have relatively thick walls that can withstand the high pressure of blood ejected from the heart. Arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished.
Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). There are three major types of capillaries, which differ according to their degree of “leakiness:” continuous, fenestrated, and sinusoid capillaries ([link]).
Continuous capillaries are characterized by a complete endothelial lining with tight junctions between endothelial cells.
Sinusoid capillaries are flattened, and they have extensive intercellular gaps and incomplete basement membranes, in addition to intercellular clefts and fenestrations.


Slightly larger than the typical capillary, the smooth muscle of the tunica media of the metarteriole is not continuous but forms rings of smooth muscle (sphincters) prior to the entrance to the capillaries. Their function is critical: If all of the capillary beds in the body were to open simultaneously, they would collectively hold every drop of blood in the body and there would be none in the arteries, arterioles, venules, veins, or the heart itself.
This pattern is called vasomotion and is regulated by chemical signals that are triggered in response to changes in internal conditions, such as oxygen, carbon dioxide, hydrogen ion, and lactic acid levels. Compared to arteries, veins are thin-walled vessels with large and irregular lumens (see [link]). Any blood that accumulates in a vein will increase the pressure within it, which can then be reflected back into the smaller veins, venules, and eventually even the capillaries. This disorder arises when defective valves allow blood to accumulate within the veins, causing them to distend, twist, and become visible on the surface of the integument. Their ability to hold this much blood is due to their high capacitance, that is, their capacity to distend (expand) readily to store a high volume of blood, even at a low pressure.
Less dramatic than the vasoconstriction seen in smaller arteries and arterioles, venoconstriction may be likened to a “stiffening” of the vessel wall. This includes repair and replacement of diseased or damaged vessels, removal of plaque from vessels, minimally invasive procedures including the insertion of venous catheters, and traditional surgery. Arteries transport blood away from the heart and branch into smaller vessels, forming arterioles. The venous system is a lower-pressure system, containing veins that have larger lumens and thinner walls. As their own lumen averages just 30 micrometers or less, arterioles are critical in slowing down—or resisting—blood flow. Eventually, the smallest arteries, vessels called arterioles, further branch into tiny capillaries, where nutrients and wastes are exchanged, and then combine with other vessels that exit capillaries to form venules, small blood vessels that carry blood to a vein, a larger blood vessel that returns blood to the heart. The blood returned to the heart through systemic veins has less oxygen, since much of the oxygen carried by the arteries has been delivered to the cells. Their walls are considerably thinner and their lumens are correspondingly larger in diameter, allowing more blood to flow with less vessel resistance. Further, the walls of the larger vessels are too thick for nutrients to diffuse through to all of the cells. Damage to this endothelial lining and exposure of blood to the collagenous fibers beneath is one of the primary causes of clot formation.
The thin outer layer of the tunica intima contains a small amount of areolar connective tissue that consists primarily of elastic fibers to provide the vessel with additional flexibility; it also contains some collagenous fibers to provide additional strength.
The tunica media consists of layers of smooth muscle supported by connective tissue that is primarily made up of elastic fibers, most of which are arranged in circular sheets.
Separating the tunica media from the outer tunica externa in larger arteries is the external elastic membrane (also called the external elastic lamina), which also appears wavy in slides. However, those close to the heart have the thickest walls, containing a high percentage of elastic fibers in all three of their tunics.
The muscle fibers in arterioles are normally slightly contracted, causing arterioles to maintain a consistent muscle tone—in this case referred to as vascular tone—in a similar manner to the muscular tone of skeletal muscle. The diameter of a capillary lumen ranges from 5–10 micrometers; the smallest are just barely wide enough for an erythrocyte to squeeze through. Although a tight junction is usually impermeable and only allows for the passage of water and ions, they are often incomplete in capillaries, leaving intercellular clefts that allow for exchange of water and other very small molecules between the blood plasma and the interstitial fluid. The number of fenestrations and their degree of permeability vary, however, according to their location. Each metarteriole arises from a terminal arteriole and branches to supply blood to a capillary bed that may consist of 10–100 capillaries. For example, during strenuous exercise when oxygen levels decrease and carbon dioxide, hydrogen ion, and lactic acid levels all increase, the capillary beds in skeletal muscle are open, as they would be in the digestive system when nutrients are present in the digestive tract.
Because they are low-pressure vessels, larger veins are commonly equipped with valves that promote the unidirectional flow of blood toward the heart and prevent backflow toward the capillaries caused by the inherent low blood pressure in veins as well as the pull of gravity.
Increased pressure will promote the flow of fluids out of the capillaries and into the interstitial fluid. Edema has many potential causes, including hypertension and heart failure, severe protein deficiency, renal failure, and many others. Varicose veins may occur in both sexes, but are more common in women and are often related to pregnancy. The large lumens and relatively thin walls of veins make them far more distensible than arteries; thus, they are said to be capacitance vessels.
Following completion of medical school, the physician generally completes a 5-year surgical residency followed by an additional 1 to 2 years of vascular specialty training.
This profession often overlaps with cardiovascular technology, which would also include treatments involving the heart. Arterioles distribute blood to capillary beds, the sites of exchange with the body tissues. The arterioles can also constrict or dilate, which varies their resistance, to help distribute blood flow to the tissues. In contrast, in the pulmonary circuit, arteries carry blood low in oxygen exclusively to the lungs for gas exchange.
Arteries have smaller lumens than veins, a characteristic that helps to maintain the pressure of blood moving through the system. In addition, many veins of the body, particularly those of the limbs, contain valves that assist the unidirectional flow of blood toward the heart.
Larger arteries and veins contain small blood vessels within their walls known as the vasa vasorum—literally “vessels of the vessel”—to provide them with this critical exchange. Until recently, the endothelium was viewed simply as the boundary between the blood in the lumen and the walls of the vessels. This is normally the thickest tunic in veins and may be thicker than the tunica media in some larger arteries.
Their thick tunica media allows muscular arteries to play a leading role in vasoconstriction.
In reality, all blood vessels exhibit vascular tone due to the partial contraction of smooth muscle.
Substances that can pass between cells include metabolic products, such as glucose, water, and small hydrophobic molecules like gases and hormones, as well as various leukocytes.
Fenestrated capillaries are common in the small intestine, which is the primary site of nutrient absorption, as well as in the kidneys, which filter the blood.
These very large openings allow for the passage of the largest molecules, including plasma proteins and even cells. When the surrounding tissues need oxygen and have excess waste products, the precapillary sphincters open, allowing blood to flow through and exchange to occur before closing once more ([link]).
During sleep or rest periods, vessels in both areas are largely closed; they open only occasionally to allow oxygen and nutrient supplies to travel to the tissues to maintain basic life processes. The walls of venules consist of endothelium, a thin middle layer with a few muscle cells and elastic fibers, plus an outer layer of connective tissue fibers that constitute a very thin tunica externa ([link]).
In order to treat edema, which is a sign rather than a discrete disorder, the underlying cause must be diagnosed and alleviated. More than simple cosmetic blemishes, varicose veins are often painful and sometimes itchy or throbbing. As you will note in [link], approximately 21 percent of the venous blood is located in venous networks within the liver, bone marrow, and integument.
In the United States, most vascular surgeons are members of the Society of Vascular Surgery.
Although recognized by the American Medical Association, there are currently no licensing requirements for vascular technicians, and licensing is voluntary.
Capillaries lead back to small vessels known as venules that flow into the larger veins and eventually back to the heart.


Arteries, arterioles, venules, and veins are composed of three tunics known as the tunica intima, tunica media, and tunica externa.
Pulmonary veins then return freshly oxygenated blood from the lungs to the heart to be pumped back out into systemic circulation.
Together, their thicker walls and smaller diameters give arterial lumens a more rounded appearance in cross section than the lumens of veins. This is critical because blood flow becomes sluggish in the extremities, as a result of the lower pressure and the effects of gravity. Since the pressure within arteries is relatively high, the vasa vasorum must function in the outer layers of the vessel (see [link]) or the pressure exerted by the blood passing through the vessel would collapse it, preventing any exchange from occurring. Recent studies, however, have shown that it is physiologically critical to such activities as helping to regulate capillary exchange and altering blood flow. In addition, many veins, particularly in the lower limbs, contain valves formed by sections of thickened endothelium that are reinforced with connective tissue, extending into the lumen. Contraction and relaxation of the circular muscles decrease and increase the diameter of the vessel lumen, respectively. The outer layers of the tunica externa are not distinct but rather blend with the surrounding connective tissue outside the vessel, helping to hold the vessel in relative position. The importance of the arterioles is that they will be the primary site of both resistance and regulation of blood pressure. Continuous capillaries not associated with the brain are rich in transport vesicles, contributing to either endocytosis or exocytosis.
They are also found in the choroid plexus of the brain and many endocrine structures, including the hypothalamus, pituitary, pineal, and thyroid glands. Blood flow through sinusoids is very slow, allowing more time for exchange of gases, nutrients, and wastes.
If all of the precapillary sphincters in a capillary bed are closed, blood will flow from the metarteriole directly into a thoroughfare channel and then into the venous circulation, bypassing the capillary bed entirely. Venules as well as capillaries are the primary sites of emigration or diapedesis, in which the white blood cells adhere to the endothelial lining of the vessels and then squeeze through adjacent cells to enter the tissue fluid. Vascular technicians typically have an Associate’s degree or certificate, involving 18 months to 2 years of training. Although arteries and veins differ structurally and functionally, they share certain features.
The endothelium releases local chemicals called endothelins that can constrict the smooth muscle within the walls of the vessel to increase blood pressure. Specifically in arteries, vasoconstriction decreases blood flow as the smooth muscle in the walls of the tunica media contracts, making the lumen narrower and increasing blood pressure. If you are able to palpate some of the superficial veins on your upper limbs and try to move them, you will find that the tunica externa prevents this. Their abundant elastic fibers allow them to expand, as blood pumped from the ventricles passes through them, and then to recoil after the surge has passed. Fortunately, because the blood pressure has eased by the time it reaches these more distant vessels, elasticity has become less important.
The precise diameter of the lumen of an arteriole at any given moment is determined by neural and chemical controls, and vasoconstriction and vasodilation in the arterioles are the primary mechanisms for distribution of blood flow. Sinusoids are found in the liver and spleen, bone marrow, lymph nodes (where they carry lymph, not blood), and many endocrine glands including the pituitary and adrenal glands.
The use of support hose, as well as elevating the feet and legs whenever possible, may be helpful in alleviating this condition.
Through venoconstriction, this “reserve” volume of blood can get back to the heart more quickly for redistribution to other parts of the circulation. The United States Bureau of Labor projects this profession to grow by 29 percent from 2010 to 2020.
The tunica intima is a thin layer composed of a simple squamous epithelium known as endothelium and a small amount of connective tissue. The restriction of the vasa vasorum to the outer layers of arteries is thought to be one reason that arterial diseases are more common than venous diseases, since its location makes it more difficult to nourish the cells of the arteries and remove waste products. Uncompensated overproduction of endothelins may contribute to hypertension (high blood pressure) and cardiovascular disease. Similarly, vasodilation increases blood flow as the smooth muscle relaxes, allowing the lumen to widen and blood pressure to drop. If the tunica externa did not hold the vessel in place, any movement would likely result in disruption of blood flow.
If artery walls were rigid and unable to expand and recoil, their resistance to blood flow would greatly increase and blood pressure would rise to even higher levels, which would in turn require the heart to pump harder to increase the volume of blood expelled by each pump (the stroke volume) and maintain adequate pressure and flow.
Here, there are tight junctions and no intercellular clefts, plus a thick basement membrane and astrocyte extensions called end feet; these structures combine to prevent the movement of nearly all substances.
Without these specialized capillaries, these organs would not be able to provide their myriad of functions. In addition, an arteriovenous anastomosis may bypass the capillary bed and lead directly to the venous system. Laser surgery and interventional radiologic procedures can reduce the size and severity of varicose veins. The tunica media is a thicker area composed of variable amounts of smooth muscle and connective tissue. There are also minute nerves within the walls of both types of vessels that control the contraction and dilation of smooth muscle. Both vasoconstriction and vasodilation are regulated in part by small vascular nerves, known as nervi vasorum, or “nerves of the vessel,” that run within the walls of blood vessels. For example, when bone marrow forms new blood cells, the cells must enter the blood supply and can only do so through the large openings of a sinusoid capillary; they cannot pass through the small openings of continuous or fenestrated capillaries.
These are generally all sympathetic fibers, although some trigger vasodilation and others induce vasoconstriction, depending upon the nature of the neurotransmitter and receptors located on the target cell. The elastic recoil of the vascular wall helps to maintain the pressure gradient that drives the blood through the arterial system. The liver also requires extensive specialized sinusoid capillaries in order to process the materials brought to it by the hepatic portal vein from both the digestive tract and spleen, and to release plasma proteins into circulation. As there are typically redundant circulation patterns, that is, anastomoses, for the smaller and more superficial veins, removal does not typically impair the circulation. The tunica externa is primarily a layer of connective tissue, although in veins, it also contains some smooth muscle.
Parasympathetic stimulation does trigger vasodilation as well as erection during sexual arousal in the external genitalia of both sexes. An elastic artery is also known as a conducting artery, because the large diameter of the lumen enables it to accept a large volume of blood from the heart and conduct it to smaller branches. There is evidence that patients with varicose veins suffer a greater risk of developing a thrombus or clot. Blood flow through vessels can be dramatically influenced by vasoconstriction and vasodilation in their walls. Nervous control over vessels tends to be more generalized than the specific targeting of individual blood vessels. Together, these neural and chemical mechanisms reduce or increase blood flow in response to changing body conditions, from exercise to hydration.
Regulation of both blood flow and blood pressure is discussed in detail later in this chapter.



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