Blood capillaries endothelial lining

Figure 2. (1) Neutrophils circulating passively in blood capillary. (2) Chemoattractants may be detected by the circulating neutrophils, by the endothelial cells lining the lumen, or both in order that the neutrophils become adhesive. This adhesion is mediated by selectins, a group of cell surface proteins. Neutrophils roll on the surface of the endothelial cells and then actively locomote seeking out spaces between the endothelial cells. (3) The adhesive neutrophils begin to squeeze between endothelial cells. (4) Cells move through the extracellular matrix towards the site of infection. Here adhesion is low and may not be necessary for locomotion. (5) At the site of infection, neutrophils become trapped by increased adhesion where they phagocytose bacteria and liberate the contents of their granules. After Lackie (1982,1986).

Figure 14.2 Phase contrast microscopic images of conditionally immortalized cells forming the inner blood-retinal barrier (A) and time-course of [3H] adenosine uptake by TR-iBRB cells (B). A Conditionally immortalized rat retinal capillary endothelial cell line TR-iBRB, retinal pericyte cell line TR-rPCT and Muller cell line TR-MUL. B The [ H]adenosine (14 nM) uptake was performed at 37°C in the presence (closed circle) or absence (open circle) of Na+.

Omidi Y, Campbell L, Barar J, Connell D, Akhtar S, Gumbleton M (2003) Evaluation of the immortalised mouse brain capillary endothelial cell line, b.End3, as an in vitro blood-brain barrier model for drug uptake and transport studies. Brain Res 990 95-112... 

The BBB separates cerebral capillary blood from brain parenchymal tissue. The B B B is formed by endothelial cells lining the blood capillaries in the brain. Unlike the intestinal membrane, BBB has little UWL. The paracellular pathway is negligible for most compounds under physiological conditions. 

The capillary endothelial cells in the brain, small extracellular space, sheet of glial cells lining the capillaries and the myelin sheath together constitute the barrier, so called blood-brain barrier. There is another... 

Figure 10.4. Schematic representation of antibody distribution into extravascular space across endothelial cells lining blood capillaries and into the tumor mass. Some of these antibody molecules may be further distributed into lymphatic capillaries.

The mechanism appears to involve a change in permeability of the endothelial lining of capillaries, which leads to tissue edema and further reduction of blood flow. 

The main permeability barrier in the airways to blood pathway lies with the epithelium of the lung airway rather than the intersitium or endothelial lining of the capillaries. The epithelial permeability towards hydrophilic solutes is at least 10-fold lower than that of the endothelium. The epithelium of the lung is much more permeable than that of other mucosal routes. For example, less than 3% of an oral dose of sodium cromoglycate reaches the circulation whereas more than 70% is absorbed from the lung into the bloodstream after inhalation. 

Bioavailabiity has not been well studied because of the lack of intravenous formulations. Mst first-generation histamine Hi-receptor antagonists readily cross the blood-brain barrier, vdiich consists of the endothelial lining of the capillaries of the CNS. The first-generation antihistamines listed in Section 2.1.5 are used as sedative-hypnotics. 

Boveri M, Berezowski V, Price A, Slupek S, Lenfant AM, Benaud C, Hartung T, Cecchelli R, Prieto P, Dehouck MP (2005) Induction of blood-brain barrier properties in cultured brain capillary endothelial cells comparison between primary glial cells and C6 cell line. Glia 51(3) 187-198... 

The mechanism of fever induction has been studied most extensively. The brain is protected from the potentially harmful effects of biologically active substances or cells in the circulation by the blood-brain barrier, which is manifested by the extremely tight junctions between the endothelial cells lining blood capillaries,48 which prevent circulating substances of a particular size and chemical property (as well as cells) from entering the brain. Proinflammatory cytokines are of a sufficiently large size that makes it unlikely that they can pass the blood-brain barrier. However, numerous pathways to explain how cytokines produced in the periphery can influence central nervous system events have been studied. For example, highly localized... 

The use of SLNs is one of the potential drug delivery methods for targeted brain drug delivery. Tighmess of the endothelial vascular lining, referred to as the blood-brain barrier (BBB), provides a challenge to development of brain drug delivery. In the BBB, capillary endothelial cells protect the... 

Another barrier of interest for drug delivery studies is the blood-brain barrier (BBB). The BBB is formed by the endothelial cells of brain capillaries. The primary characteristics of the BBB are its high resistance to chemical diffusion and transport due to the presence of complex tight junctions that inhibit paracellular transport and its low endocytic activity. Several in vitro models of the BBB have been developed, and several authors have reviewed the models and their possible uses as permeability and toxicity screens (Reinhardt and Gloor, 1997 Gumbkton and Audus, 2001 Lundquist and Renftel, 2002). The most common in vitro BBB model consists of a monolayer of primary isolated brain capillary endothelial cells, primary isolated endothelial cells from elsewhere in the body, or an endothelial cell line cultured on a membrane insert. The endothelial cells are often cocultured with astrocytes or astroglial cells. In cocultures, the barrier properties of the BBB model increase. 

It is known that the endothelial cells lining the capillary bed are markedly damaged during hyperoxic exposure. However, it is not at present known whether this damage is due to free-radical-induced injury of the endothelial cells or whether endothelial cells are simply responding to the diminished blood flow produced by the severe vasoconstriction. The theoretical basis for free-radical involvement is sound and it has been proposed that low oxygen tensions (hypoxia) followed by periods of reoxygenation are the most likely explanation for the disorder (Kelly, 1993). 

Blood is pumped away from the heart through arteries it permeates the tissues through networks of very small capillaries where nutrient delivery, gas exchange and waste removal occur and is finally returned to the heart via the veins. The structures of the arteries and veins differ in important ways. First, the veins have one-way valves which prevent the back-flow of blood and second, the walls of the arteries are much thicker, due largely to the layer of smooth muscle cells. Both types of vessel are lined on their inner surface with endothelial cells. Refer to Figure 5.2. 

Fig. 3.6 Sketch of an alveolar-capillary unit showing alveolar spaces, cells, and a blood vessel. AM — alveolar macrophage, PMN = polymorphic nucleosite. Other cells indicated Type I and II intraalveolus, a fibroblast in the interstitium, and endothelial cells lining the adjacent capillary. ChTV = chemotaxin.

A. The site of the blood-brain barrier was hotly debated for many years until electron micrographs clearly showed that endothelial cells lining brain capillaries are so closely joined to each other that passages of substances cannot readily occur through the intercellular clefts located between adjacent cells and that this constitutes a barrier to the passage of many substances from the blood to the parenchyma of the brain. 

There are differences in the ease of extravasation of macromolecules from the bloodstream into different tissues [14, 104, 105]. Capillaries in the liver, spleen, and bone marrow have incomplete basal membranes and are lined with endothelial cells which are not continuously arranged. Capillaries in the muscle have a somewhat tighter arrangement, and there is an almost impermeable barrier which isolates the central nervous system from circulating blood. The rate of glomerular filtration of macromolecules depends on their hydrodynamic radius, the threshold being approx. 45 A [106]. Structure of the macromolecule is of utmost importance, since shape, flexibility, and charge influence the penetration and possible readsorption in the tubular epithelia [100]. 

---