Blood flow veins

Long-lasting vasoconstriction is produced by the ETs in almost all arteries and veins and several studies have shown that ET-1 causes a reduction in renal blood flow and urinary sodium excretion. ET-1 has been reported to be a potent mitogen in fibroblasts and aortic smooth muscle cells and to cause contraction of rat stomach strips, rat colon and guinea pig ileum. In the central nervous system, ETs have been shown to modulate neurotransmitter release. 

FIGURE 5.38 Pictorial presentation of the microscopic structure of the liver. The picture shows the classical liver lobulus. The functional acinus and its three zones are at the left. The acinal zones are marked by numbering them 1-3. These zones correspond to the direction of blood flow from the portal arteries (PA) to the terminal veins (TV). Zone I corresponds to the periportal area in classical liver pathology, zone 2, the interlobular region (midzone), and zone 3, centrelobular region. ... 

Which difference could account for the fact that a diver is much less likely to suffer from the bends if he breathes a mixture of 80% helium and 20% oxygen than if he breathes air (The bends is a painful, sometimes fatal, disease caused by the formation of gas bubbles in the veins and consequent interruption of blood flow. The bubbles form from gas dissolved in the blood at high pressure.)... 

In general, arterial thrombi are platelet-rich ( white clots ) and form at ruptured atherosclerotic plaques, leading to intraluminal occlusion of arteries that can result in end-organ injury (e.g., myocardial infarction, stroke). In contrast, venous thrombi consist mainly of fibrin and red blood cells ( red clots ), and usually form in low-flow veins of the limbs, producing deep vein thrombosis (DVT) the major threat to life results when lower extremity (and, occasionally, upper extremity) venous thrombi embolize via the right heart chambers into the pulmonary arteries, i.e., pulmonary embolism (PE). 

When administering a drug into a vein by a venipuncture, tiie nurse should place a tourniquet above the selected vein. It is important to tighten the tourniquet so that venous blood flow is blocked but arterial blood flow is not. The nurse should allow the veins to fill (distend) and then should pull tiie skin taut (to anchor the vein and the skin) and insert tiie needle into tiie vein, bevel up, and at a short angle to tiie skin. Blood should immediately flow into the syringe if tiie needle is properly inserted into the vein. 

Thrombosis is the formation of a clot. A thrombus may form in any vessel, artery, or vein when blood flow is impeded. For example, a venous thrombus can... 

The red thrombus consists primarily of red cells and fibrin. It morphologically resembles the clot formed in a test tube and may form in vivo in areas of retarded blood flow or stasis (eg, veins) with or without vascular injury, or it may form at a site of injury or in an abnormal vessel in conjunction with an initiating platelet plug. 

Linner, E. (1952). Eflfect of unilateral hyation of the common carolid artery on the blood flow through the uveal trait as measured directly in a vortex vein. Acta Physiol. Scand. 26, 70-78. 

Iturriage, H., Ugarte, H. and Israel, Y, (1980). Hepatic vein oxygenation, liver blood flow and the rate of ethanol metabolism in recently abstinent alcoholic patients. Eur. J. Clin. Invest. 10, 211-218. 

Duplex ultrasonography is the most commonly used test to diagnosis DVT. It is a non-invasive test that can measure the rate and direction of blood flow and visualize clot formation in proximal veins of the legs. It cannot reliably detect small blood clots in distal veins. Coupled with a careful clinical assessment, it can rule in or out (include or exclude) the diagnosis in the majority of cases. 

The portal vein is the primary vessel leading into the liver it receives deoxygenated venous blood flow from the small intestine, stomach, pancreas, and spleen (Fig. 19-1). The inflow from these organ systems accounts for approximately 75% of... 

Portal hypertension is a consequence of increased resistance to blood flow through the portal vein. Increased resistance is usually due to restructuring of intrahepatic tissue (sinusoidal damage) but may also be caused by presinusoidal damage such as portal vein occlusion from trauma, malignancy, or thrombosis. A third (and the least common) mechanism is outflow obstruction of the hepatic vein. This latter damage is posthepatic, and normal liver structure is maintained. This chapter will focus on portal hypertension caused by intrahepatic damage from cirrhosis. 

Central PN refers to the administration of PN via a large central vein, and the catheter tip must be positioned in the vena cava. Central PN allows the infusion of a highly concentrated, hypertonic nutrient admixture. The typical osmolarity of a central PN admixture is about 1500 to 2000 mOsm/L. Central veins have much higher blood flow, and the PN admixture is diluted rapidly on infusion, so phlebitis is usually not a concern. Patients who require PN administration for longer periods of time (greater than 7 days) should receive central PN. One limitation of central PN is the need for placement of a central venous catheter and an x-ray to confirm placement of the catheter tip. Central venous catheter placement may be associated with complications, including pneumothorax, arterial injury, air embolus, venous thrombosis, infection, chylothorax, and brachial plexus injury.1,20... 

Coronary artery bypass graft surgery Thoracic surgery whereby parts of a saphenous vein from a leg or internal mammary artery from the arm are placed as conduits to restore blood flow between the aorta and one or more coronary arteries to bypass the coronary artery stenosis (occlusion). 

In addition to serving as blood reservoirs, veins help to regulate cardiac output (CO) by way of changes in venous return (VR). Venous return is defined as the volume of blood that flows from the systemic veins into the right atrium per minute. As discussed in Chapter 14 (cardiac output), a healthy heart pumps all of the blood returned to it. Therefore, CO is equal to VR ... 

The pressure gradient, or the inflow pressure minus the outflow pressure, is determined by the pressure at the beginning of the venous system (Pv) and right atrial pressure (Prblood flow the slightly stiffer large veins offer a small degree of resistance (Rv). 

The effect of sympathetic stimulation on venous resistance is minimal. As previously stated, it is the larger, less flexible veins that provide resistance to blood flow. However, these blood vessels are sparsely innervated therefore, little change takes place in vessel radius and physiological effect on blood flow is relatively insignificant. 

Blood tends to pool in the highly distensible veins. Furthermore, the excessive filtration of fluid out of the capillaries and into the tissues that occurs causes edema or swelling of the ankles and feet. As a result, VR and therefore CO are decreased, leading to a decrease in MAP. This fall in MAP can cause a decrease in cerebral blood flow and, possibly, syncope (fainting). 

Baroreceptors are sensitive to changes in MAP. As VR, CO, and MAP decrease, baroreceptor excitation is diminished. Consequently, the frequency of nerve impulses transmitted from these receptors to the vasomotor center in the brainstem is reduced. This elicits a reflex that will increase HR, increase contractility of the heart, and cause vasoconstriction of arterioles and veins. The increase in CO and TPR effectively increases MAP and therefore cerebral blood flow. Constriction of the veins assists in forcing blood toward the heart and enhances venous return. Skeletal muscle activity associated with simply walking decreases venous pressure in the lower extremities significantly. Contraction of the skeletal muscles in the legs compresses the veins and blood is forced toward the heart. 

The hepatic artery supplies the liver with 300 ml/min of oxygenated blood from the aorta. The remaining 1050 ml/min of blood flow is delivered by the hepatic portal vein. This blood comes directly from the digestive tract. It is low in oxygen but contains a high concentration of nutrients absorbed from the intestines. 

Blood flowing from the intestines to the liver through the hepatic portal vein often contains bacteria. Filtration of this blood is a protective function provided by the liver. Large phagocytic macrophages, referred to as Kupffer cells, line the hepatic venous sinuses. As the blood flows through these sinuses, bacteria are rapidly taken up and digested by the Kupffer cells. This system is very efficient and removes more than 99% of the bacteria from the hepatic portal blood. 

The answer is a. (Hardman, pp 762-764.) Experimentally, nitrates dilate coronary vessels. This occurs in normal subjects, resulting in an overall increase in coronary blood flow. In arteriosclerotic coronaries, the ability to dilate is lost, and the ischemic area may actually have less blood flow under the influence of nitrates. Improvement in the ischemic conditions is the result of decreased myocardial oxygen demand because of a reduction of preload and afterload. Nitrates dilate both arteries and veins and thereby reduce the work of the heart. Should systemic blood pressure fall, a reflex tachycardia will occur. In pure coronary spasm, such as Prinzmetal s angina, the effect of increased coronary blood flow is relevant, while in severe left ventricular hypertrophy with minimal obstruction, the effect on preload and afterload becomes important. 

The more recent thoracic pump theory is based on the belief that blood flow during CPR results from intrathoracic pressure alterations induced by chest compressions. During compression (systole), a pressure gradient develops between the intrathoracic arteries and extrathoracic veins, causing forward blood flow from the lungs into the systemic circulation. After compression ends (diastole), intrathoracic pressure declines and blood flow returns to the lungs. 

Venous thromboembolism (VTE) results from clot formation in the venous circulation and is manifested as deep vein thrombosis (DVT) and pulmonary embolism (PE). A DVT is a thrombus composed of cellular material (red and white blood cells, platelets) bound together with fibrin strands. A PE is a thrombus that arises from the systemic circulation and lodges in the pulmonary artery or one of its branches, causing complete or partial obstruction of pulmonary blood flow. 

Venous stasis is slowed blood flow in the deep veins of the legs resulting from damage to venous valves, vessel obstruction, prolonged periods of immobility, or increased blood viscosity. Conditions associated with venous stasis include major medical illness (e.g., heart failure, myocardial infarction), major surgery, paralysis (e.g., stroke, spinal cord injury), polycythemia vera, obesity, or varicose veins. 

To study the effect of PGDN on cerebral blood flow, Godin et al. (1995) injected male Sprague-Dawley rats (through a jugular vein cannula) with PGDN at 0.1 to 30 mg/ kg and measured cerebral blood flow with a fiberoptic laser-Doppler flow probe in contact with the brain. Following a small initial drop in cerebral perfusion that lasted 1 min, blood flow rapidly increased and reached a maximum 2 min after injection. The increase in perfusion was correlated with dose, but due to the small number of animals and individual variability, a clear dose-response relationship was not obtained. 

Nuclear A test of the structure, blood flow, and function of the kidneys. The doctor injects a mildly radioactive solution into an arm vein and uses x-rays to monitor its progress through the kidneys. [NIH]... 

---