Capillary blood

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 13 presents a schematic diagram for drug absorption from the peritoneal cavity. As mentioned above, particles (e.g., erythrocytes, bacteria, colloidal gold, and liposomes) which are not able to pass capillary membranes are removed from the peritoneal cavity via the lymphatic system (Fig. 13, I and II). Relatively low molecular weight compounds (e.g., drugs) are exclusively absorbed via splenic blood capillaries into the portal vein (Fig. 13, III).

FIGURE 13 Schematic diagram for drug absorption fi om the peritoneal cavity. I and II represent the lymphatic system and III represents splenic blood capillaries. (Adapted from Hirano and Hunt, 1985.)... 

Signs of vitamin C deficiency in scurvy include skin changes, fragifity of blood capillaries, gum decay, tooth loss, and bone fracmre, many of which can be attributed to deficient collagen synthesis. 

The structure of the blood capillary wall is complex and varies in different organs and tissues. It consists of a single layer of endothelial cells joined together by intercellular junctions. Each endothelial cell, on an average, is 20-40 pm long, 10-15 pm wide, and 0.1-0.5 pm thick, and contains 10,000-15,000 uniform, spherical vesicles called plasmalemmal vesicles. These vesicles range in size between 60 and 80 nm in diameter. About 70% of these vesicles open on the luminal side of the endothelial surface, and the remaining open within the cytoplasm. Plasmalemmal vesicles are believed to be involved in the pinocytic transport of substances across the endothelium. The transition time of pinocytic vesicles across the cell is... 

Similar to blood capillaries, the lymphatic capillaries consist of a single layer of endothelial cells joined together by intercellular junctions. The diameter of small pores is 12 nm, whereas large pores range between 50 and 70 nm. The rate of formation of lymph depends on the hydrostatic pressure of blood and the... 

LPL found on the endothelial surfaces of the blood capillaries) to produce chylomicron remnants, which are then removed from the circulation by specific remnant receptors located on parenchymal liver cells. VLDLs are secreted by the liver. Following their secretion in blood, VLDLs undergo metabolism in a way... 

Although most drugs are absorbed from the intestine by the blood capillary network in the villi, they can also be taken up by the lymphatic system (an integral and necessary part of the vascular system, the function of which is to collect extra tissue fluid and return it to the vascular compartment), particularly by M cells that reside in the Peyer s patch regions of the intestine. Peyer s patches have also been implicated in the regulation of the secretory immune response. Wachsmann et al. [277] reported that an antigenic material encapsulated within a liposome, when administered perorally, is taken up by these M cells and exhibited better saliva and serum IgA (primary and secondary)... 

Figure 2.4 Schematic of the villi fingers covered by a monolayer of epithelial cells, separating the lumen from the blood capillary network [63,69]. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]...

The lymphatic capillaries are close-ended vessels in close proximity to blood capillaries and, like blood capillaries, lymphatic capillaries are composed of a single layer of endothelial cells. However, large gaps in between these cells allow not only fluid, but also proteins and particulate matter to enter the lymphatic capillaries quite readily. Once the fluid has entered these capillaries, it is referred to as lymph. Not surprisingly, the composition of this fluid is similar to that of the interstitial fluid. 

Glucose and galactose enter the absorptive cells by way of secondary active transport. Cotransport carrier molecules associated with the disaccharidases in the brush border transport the monosaccharide and a Na+ ion from the lumen of the small intestine into the absorptive cell. This process is referred to as "secondary" because the cotransport carriers operate passively and do not require energy. However, they do require a concentration gradient for the transport of Na+ ions into the cell. This gradient is established by the active transport of Na+ ions out of the absorptive cell at the basolateral surface. Fructose enters the absorptive cells by way of facilitated diffusion. All monosaccharide molecules exit the absorptive cells by way of facilitated diffusion and enter the blood capillaries. 

Dipeptides and tripeptides are also presented to the brush border of the absorptive cells. As the nutrient molecules are absorbed, aminopeptidases split them into their constituent amino acids. The activity of aminopeptidases accounts for approximately 60% of protein digestion. The amino acid molecules then exit the absorptive cells by way of facilitated diffusion and enter the blood capillaries. 

Chylomicrons leave the absorptive cell by way of exocytosis. Because they are unable to cross the basement membrane of the blood capillaries, the chylomicrons enter the lacteals, which are part of the lymphatic system. The vessels of the lymphatic system converge to form the thoracic duct that drains into the venous system near the heart. Therefore, unlike products of carbohydrate and protein digestion that are transported directly to the liver by way of the hepatic portal vein, absorbed lipids are diluted in the blood... 

Nasal (NS) Through the nose. Cocaine is snorted up the nose and then absorbed through blood capillaries in the thin nasal membrane. 

The naturally occurring substance histamine causes blood capillaries to dilate and smooth muscle to contract. Most cells release it in response to wounding, allergies, and most inflammatory conditions. Antihistamines block the production of this substance, thereby combating a painful swelling. 

Figure 8.1 (A) Cross-sectional view of the organization of the small intestine, illustrating the serosa, the longitudinal and circular muscle layers (=muscularis externa), the submucosa, and the intestinal mucosa. The intestinal mucosa consists of four layers, the inner surface cell monolayer of enterocytes, the basal membrane, the lamina propria (connective tissue, blood capillaries), and the muscularis mucosae, (B) Schematic representation of an enterocyte (small intestinal epithehal cell) (according to Tso and Crissinger [151], with permission).

G. E. Palade. Fine structure of blood capillaries. J. Appl. Phys. 24 1424-1436 (1953). 

Palade GE. Fine structures of blood capillaries. J Appl Phys 1953 24 1424. 

Fig. 3.4 The structure of the pulmonary pleura 1, mesothelial layer 2, submesothelial layer 3, external elastic layer 4, interstitial layer 5, internal elastic layer B, blood capillary net E, elastic fiber net L, lymph vessel net. 

As precursors for the biosynthesis of fats (lipogenesis), the adipocytes use triacylglycerols from lipoproteins (VLDLs and chylomicrons see p. 278), which are formed in the liver and intestines and delivered by the blood. Lipoprotein lipase [1], which is located on the inner surface of the blood capillaries, cleaves these triacylglycerols into glycerol and fatty acids, which are taken up by the adipocytes and converted back into fats. 

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 entry of toxins into the brain and central nervous system (CNS) is frequently more difficnlt than into other tissues. The function of this blood-brain barrier is related to impaired permeability of the blood capillaries in brain tissne, the necessity for toxins to penetrate glial cells, and the low protein content of the CNS interstitial flnid (Klaassen, 1986). Lipid solnbihty of a toxin is an important factor in the penetration of the blood-brain barrier. 

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.

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