Circulatory system flow through

The adenohypophysis does not have a direct anatomical connection with the hypothalamus therefore, regulation of hormone secretion by way of neuronal signals is not possible. Instead, these two structures are associated by a specialized circulatory system and the secretion of hormones from the adenohypophysis is regulated by hormonal signals from the hypothalamus (see Figure 10.2). Systemic arterial blood is directed first to the hypothalamus. The exchange of materials between the blood and the interstitial fluid of the hypothalamus takes place at the primary capillary plexus. The blood then flows to the adenohypophysis through the hypothalamic-hypophyseal portal veins. Portal veins are blood vessels that connect two capillary beds. The second capillary bed in this system is the secondary capillary plexus located in the adenohypophysis. 

Describe how blood pressure changes as blood flows through the circulatory system... 

Gravitational forces may have a profound influence on blood flow through the circulatory system. As a result, VR and CO may be affected. Imagine that the circulatory system is a column of blood that extends from the heart to the feet. As in any column of fluid, the pressure at the surface is equal to zero. Due to the weight of the fluid, the pressure increases incrementally below the surface. This pressure is referred to as the hydrostatic pressure. 

The velocity of blood flow through capillaries is slow compared to the rest of the circulatory system because of the very large total cross-sectional surface area of the capillaries. Although each individual capillary has a diameter of... 

Amino acids, sugars, and minerals pass through the small intestine into the circulatory system, where they are mixed with blood. The primary reactor organs in processing blood are muscle and the kidneys. The fluid flows in nearly total recycle through arteries and veins, which are basically the pipes in the system, and capillaries, where most of the transfer to and from the reactors and separators occurs. 

SMAs are also used in another application related to cardiac health problems, as vena-cava filters. In some instances, it is desirable to protect a patient against the possibility that a blood clot formed elsewhere in the body will travel through the circulatory system into the heart, where it may cause a heart attack or stroke. Tiny, umbrella-shaped devices made of SMA materials have proven to he effective in such cases. In these devices, called vena-cava filters, the umbrella portion of the device consists of a mesh of tiny wires made of an SMA material. The device is inserted into the circulatory system in the form of a reduced-size (martensite phase), folded-up umbrella. Once in place, it is opened in such a way that the umbrella fills the vessel leading into the heart. The mesh design allows blood to flow through normally but filters out any blood clots that are carried along with the blood. 

Figure 4 Balloon angioplasty with and without stent deployment, (a) In balloon angioplasty, a thin catheter is threaded through the circulatory system until the uninflated balloon at its tip penetrates the diseased artery at the point of blockage, as shown in the top diagram. The balloon is then inflated to expand the artery, as shown in the middle, before being deflated and withdrawn to allow blood flow to resume (bottom panel). (b) An increasingly common feature of angioplasty involves deployment of an expandable wire structure to help keep the artery from collapsing after the balloon is withdrawn. The procedure is the same as in (a), except that a wire stent is placed over the balloon before insertion (top). The stent expands when the balloon is inflated (middle) and retains its expanded form after the balloon and catheter are withdrawn (bottom), remaining in place after the procedure is complete to provide a permanent structural support for the arterial wall.

The placenta keeps the maternal and fetal circulation systems separate, nourishes the fetus, eliminates fetal wastes, and produces hormones vital to pregnancy. It is composed of large collections of fetal vessels called villi, which are surrounded by intervillous spaces in which maternal blood flows. For substances to move from maternal circulation to fetal circulation, they must cross through the trophoblasts and several membranes. The transfer of any substance depends largely on the concentration gradient between the maternal and fetal circulatory systems, the presence or absence of circulating binding proteins, the hpid solubility of the substance, and the presence of facilitated transport, such as ion pumps or receptor-mediated endocytosis (Box 54-1). The placenta is an effective barrier to the movement... 

The properties of water are different from those of sodium chloride and carbon dioxide. Water is the only one of the three compounds that occurs in Earth s environment in aU three states of matter, as shown in Figure 4.7. At sea level, liquid water boils into gaseous water (steam) at 100°C and freezes to solid water (ice) at 0°C. Pure water does not conduct electricity in any of its states. Water is also excellent at dissolving other substances. It is often called the universal solvent in recognition of this valuable property. Water plays a vital role in the transport of dissolved materials, whether the aqueous solution is flowing down a river up the xylem in a tree or through the veins, capillaries, and arteries of your circulatory system. 

Cholesterol is probably the best-known lipid because of the correlation between cholesterol levels in the blood and heart disease. Cholesterol is synthesized in the hver and is also found in almost all body tissues. Cholesterol is also found in many foods, but we do not require it in our diet because the body can synthesize all we need. A diet high in cholesterol can lead to high levels of cholesterol in the bloodstream, and the excess can accumulate on the walls of arteries, restricting the flow of blood. This disease of the circulatory system is known as atherosclerosis and is a primary cause of heart disease. Cholesterol travels through the bloodstream packaged in particles that also contain cholesterol esters, phospholipids, and proteins. The... 

The animals used in these studies were conditioned male dogs of mixed breed. Access to the animals circulatory systems was accomplished via an acute shunt surgically implanted in the neck of the dog. The shunt was constructed of Vie in. Silastic tubing anastomosed to the carotid artery and jugular vein. Blood flow through the shunt was on the order of 1 L/min. 

Flow through the vessels of the circulatory system is driven by the hydrostatic pressure created in the ventricles. The flow rate through a cyhndrical vessel of radius R can be estimated from the equations for conservation of momentum (see [4]) ... 

Figure 6.3 Geometry of cylindrical vessel. Many of the important characteristics of the flow of blood through the circulatory system can be modeled by a simple cylindrical geometry.

The circulatory systems in plants and animals conform to physical principles. Each system has a means to propel the fluid, because, from Newton s laws of motion, fluid will not move by itself. Power is required to move the fluid. In plants, this power is supplied by a combination of water evaporation in the leaves, an osmotic gradient from root to leaf, and capillary action. In animals, this power is usually supplied by one or more hearts through which the blood flows. 

Thus, resistance to flow through a tube correlates directly with catheter length and fluid viscosity and inversely with the fourth power of catheter diameter. For steady flow, the delivery system can be modeled as a series of resistors representing each component, including administration set, access catheter, and circulatory system. When dynamic aspects of the delivery system are considered, a more detailed model including catheter and venous compliance, fluid inertia, and turbulent flow is required. Flow resistance may be defined with units of mm Hg/(L/h), so that 1 fluid ohm = 4.8 x 10 " Pa s/m. Studies determining flow resistance for several catheter components with distilled water for flow rates of 100, 200, and 300 mL/h appear in Table 25.1. 

Output data from the mock circulatory system, during a cardiac cycle, are the aortic and ventricular pressure diagrams, the flow rate through the valve diagram and the average values of these variables. As an example. Fig. 2 shows the output data obtained while testing a tilting disc Hall Raster (HK) valve of 27 mm tissue anulus diameter (TAD). Nine different tests have been performed at three... 

Cardiac output and venous return are inextricably interdependent. Clearly, except for small, transient disparities, the heart will be unable to pump any more blood than is delivered to it through the venous system. Similarly, because the circulatory system is a closed circuit, the rate of venous return must equal the cardiac output under equilibrium conditions. The flow around the entire closed circuit depends upon the capability of the pump, the characteristics of the circuit, and the total volume of fluid in the system. Cardiac output and venous return are simply two terms for expressing the flow around the closed circuit. Cardiac output is the volume of blood being pumped by the heart per unit time. Venous return is the volume of blood returning to the heart per unit time. At equilibrium, these two flows are identical. 

---