Blood capillaries types

Hollow-fiber (capillary)-type membrane oxygenators are the most widely used today, and comprise two main types (i) those where blood flow occurs inside the capillaries and (ii) those where there is a cross-flow of blood outside the capillaries. Although in the first type the blood flow is always laminar, the second type has been used more extensively in recent times, as the mass transfer coefficients are higher due to blood turbulence outside capillaries and hence the membrane area can be smaller. Figure 15.3 shows an example of the cross-flow type membrane oxygenator, with a built-in heat exchanger for controlling the blood temperature. 

Capillaries are the exchange vessels of the body. They have structural variations to allow different levels of metabolic exchange (of exogenous and endogenous substances) between blood and the surrounding tissues. The structure of the walls varies depending on their resident tissue. There are three major types of blood capillaries continuous fenestrated and sinusoidal (discontinuous) [1] ... 

Capillary endothelial cells comprise 30-42% of cells in the alveolar region and comprise the walls of the extensive network of blood capillaries in the lung parenchyma. The endothelium forms a continuous, attenuated cell layer that transports respiratory gases, water, and solutes. However, it also forms a barrier to the leakage of excess water and macromolecules into the pulmonary interstitial space. Pulmonary endothelial cells, like type I cells, are vulnerable to injury from inhaled substances and substances in the systemic circulation. Injury to the endothelium results in fluid and protein leakage into the pulmonary interstitium and alveolar spaces, resulting in pulmonary edema. 

A number of factors determine whether tissue in the lung parenchyma is successfully repaired after injury or whether an inflammatory response progresses to a pathologic outcome. As mentioned previously, the alveolar region is especially vulnerable to damage due to the delicate architecture of the type I epithelium and blood capillary endothelial membranes. An appropriate balance of catabolic and... 

Bone is synthesized by osteoblasts which transport calcium ions from blood into a secreted, uncalcified osteoid matrix composed mostly of type I collagen. During calcification, monocyte-like cells are attracted out of the adjacent blood capillaries and adhere to irregularities in the calcifying bone surface and eventually become osteoclasts. These cells, which resorb the bone, develop according to genetic and environmental stimuli that determine bone shape and response to stress. 

A remarkable new product is the FreeStyle glucose measuring system from TheraSense Inc. Because of the capillary-type sensor and coulometric measuring principle a 300 nl drop of whole blood is sufficient for one test. Even less painful is the ionophoretic detection with the GlucoWatch ... 

Capillary Electrophoresis Slab-gel techniques were used in forensic serology until the late 1980s to separate and detect polymorphic serum proteins found in blood and body fluids. Around the time that DNA began to supplant traditional blood group typing in forensic serology, capillary electrophoresis (CE) was introduced to separate small molecules. Ironically, by the turn of the century, CE-based instruments dominated DNA typing. 

Convection is a process by which a substance is dragged along by the flow of fluid hence the term solvent drag is used to describe this type of transport. The flow is powered by osmotic or hydrostatic pressure gradients which exist across tissue boundaries. The kidney is an example of an organ which depends on hydrostatic pressure-driven convection for filtration of substances by the glomerulus and osmotic-pressure driven convection for solute reabsorption in the proximal tubule. Filtration and reabsorption by blood capillaries depends on Starling s relationship ... 

Another illnstration of snrface tension is the meniscus, the curved surface of a liquid contained in a narrow tnbe. Fignre 12.8(a) shows the concave surface of water in a graduated cylinder. (You probably know from your laboratory class that you are to read the volume level with the bottom of the meniscus.) This is caused by a thin film of water adhering to the wall of the glass cylinder. The snrface tension of water causes this film to contract, and as it does, it pulls the water up the cylinder. This effect, known as capillary action, is more pronounced in a cylinder with a very small diameter, such as a capillary tube used to draw a small amount of blood. Two types of forces bring about capil-... 

Immersion electrodes are the most common glass electrodes. These are roughly cylindrical and consist of a barrel or stem of inert glass that is sealed at the lower end to a tip, which is often hemispherical, of special pH-responsive glass. The tip is completely immersed in the solution during measurements. Miniature and microelectrodes are also used widely, particularly in physiological studies. Capillary electrodes permit the use of small samples and provide protection from exposure to air during the measurements, eg, for the determination of blood pH. This type of electrode may be provided with a water jacket for temperature control. 

Histamine is a substance present in various tissues of die body, such as die heart, lungs, gastric mucosa, and skin (Pig. 36-1). The highest concentration of histamine is found in die basophil (a type of white blood cell) and mast cells diat are found near capillaries. Histamine is produced in response to injury. It acts on areas such as die vascular system and smooth muscle, producing dilatation of arterioles and an increased permeability of capillaries and venules. Dilatation of die arterioles results in localized redness. An increase in die permeability of... 

A third type is a disseminated fibrin deposit in very small blood vessels or capillaries. 

Bone is a porous tissue composite material containing a fluid phase, a calcified bone mineral, hydroxyapatite (HA), and organic components (mainly, collagen type). The variety of cellular and noncellular components consist of approximately 69% organic and 22% inorganic material and 9% water. The principal constiments of bone tissue are calcium (Ca ), phosphate (PO ), and hydroxyl (OH ) ions and calcium carbonate. There are smaller quantities of sodium, magnesium, and fluoride. The major compound, HA, has the formula Caio(P04)g(OH)2 in its unit cell. The porosity of bone includes membrane-lined capillary blood vessels, which function to transport nutrients and ions in bone, canaliculi, and the lacunae occupied in vivo by bone cells (osteoblasts), and the micropores present in the matrix. 

It is essentially a 2-stage process, as shown in Figure 3-5. First, there is a dissociation (dissolution) of particles then the dissolved molecules or ions diffuse across capillary walls and are taken up by the blood. Immediately following dissolution, rapid absorption is observed. For some elements, rapid absorption does not occur because of binding to respiratory-tract components. In the absence of specific data for specific compounds, the model uses the following default absorption rate values for those specific compounds that are classified as Types F (fast), M (medium), S (slow), and V (instantaneous) ... 

Located in close proximity to the primary capillary plexus in the hypothalamus are specialized neurosecretory cells. In fact, the axons of these cells terminate on the capillaries. The neurosecretory cells synthesize two types of hormones releasing hormones and inhibiting hormones (see Table 10.2). Each of these hormones helps to regulate the release of a particular hormone from the adenohypophysis. For example, thyrotropin-releasing hormone produced by the neurosecretory cells of the hypothalamus stimulates secretion of thyrotropin from the thyrotrope cells of the adenohypophysis. The hypo-thalamic-releasing hormone is picked up by the primary capillary plexus travels through the hypothalamic-hypophyseal portal veins to the anterior pituitary leaves the blood by way of the secondary capillary plexus and exerts its effect on the appropriate cells of the adenohypophysis. The hypophyseal hormone, in this case, thyrotropin, is then picked up by the secondary capillary plexus, removed from the pituitary by the venous blood, and delivered to its target tissue. 

The sympathetic system also innervates vascular smooth muscle and regulates the radius of the blood vessels. All types of blood vessels except capillaries are innervated however, the most densely innervated vessels include arterioles and veins. An increase in sympathetic stimulation of vascular smooth muscle causes vasoconstriction and a decrease in stimulation causes vasodilation. Constriction of arterioles causes an increase in TPR and therefore MAP. Constriction of veins causes an increase in venous return (VR) which increases end-diastolic volume (EDV), SV (Frank-Starling law of the heart), CO, and MAP. 

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