Lymphatic systems

The fats are essential constituents of the food of animals, although conversion of carbohydrates to fats in the animal body does occur. They are partially absorbed from the gut as fats to the lymphatic system and par-... 

Vinyl chloride Liver - angiosarcoma Brain Lung - carcinoma Lymphatic system - lymphoma... 

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.)... 

By definition, chylomicrons are found in chyle formed only by the lymphatic system draining the intestine. They are responsible for the transport of all dietary lipids into the circulation. Small quantities of VLDL... 

Figure 25-2. The formation and secretion of (A) chylomicrons by an intestinal cell and (B) very low density lipoproteins by a hepatic cell. (RER, rough endoplasmic reticulum SER, smooth endoplasmic reticulum G, Golgi apparatus N, nucleus C, chylomicrons VLDL, very low density lipoproteins E, endothelium SD, space of Disse, containing blood plasma.) Apolipoprotein B, synthesized in the RER, is incorporated into lipoproteins in the SER, the main site of synthesis of triacylglycerol. After addition of carbohydrate residues in G, they are released from the cell by reverse pinocytosis. Chylomicrons pass into the lymphatic system. VLDL are secreted into the space of Disse and then into the hepatic sinusoids through fenestrae in the endothelial lining.

Both intact carotenoids and their apolar metabolites (retinyl esters) are secreted into the lymphatic system associated with CMs. In the blood circulation, CM particles undergo lipolysis, catalyzed by a lipoprotein lipase, resulting in the formation of CM remnants that are quickly taken up by the liver. In the liver, the remnant-associated carotenoid can be either (1) metabolized into vitamin A and other metabolites, (2) stored, (3) secreted with the bile, or (4) repackaged and released with VLDL particles. In the bloodstream, VLDLs are transformed to LDLs, and then HDLs by delipidation and the carotenoids associated with the lipoprotein particles are finally distributed to extrahepatic tissues (Figure 3.2.2). Time-course studies focusing on carotenoid appearances in different lipoprotein fractions after ingestion showed that CM carotenoid levels peak early (4 to 8 hr) whereas LDL and HDL carotenoid levels reach peaks later (16 to 24 hr). 

The lymphatic system, also known as the secondary circulatory system, connects the bladder to the kidney and may represent a way for bacteria to be transported and subsequently cause... 

Lymphatic system The tissues and organs that produce, store, and carry white blood cells that fight infection and disease. This system includes the bone marrow, spleen, thymus, and lymph nodes and a network of thin tubes that carry lymph and white blood cells. 

The ICRP deposition model estimates the fraction of inhaled material initially retained in each compartment (see Figure 3-2). The model was developed with five compartments (1) the anterior nasal passages (ET,) (2) all other extrathoracic airways (ET2) (posterior nasal passages, the naso- and oropharynx, and the larynx) (3) the bronchi (BB) (4) the bronchioles (bb) and (5) the alveolar interstitium (AI). Particles deposited in each of the regions may be removed and redistributed either upward into the respiratory tree or to the lymphatic system and blood by different particle removal mechanisms. 

A highly complex network of arteries, arterioles, and capillaries penetrates the dermis from below and extends up to the surface of, but not actually into, the epidermis. A matching venous system siphons the blood and returns it to the central circulation. Blood flow through the vasculature is linked to the production and movement of lymph through a complementary dermal lymphatic system. The dermis is laced with tactile, thermal, and pain sensors. 

The lymphatic system of the skin extends up and into the papillary layers of the dermis. A dense, flat meshwork of lymphatic capillaries is found here [11]. Lymph passes into a deeper network at the lower boundary of the dermis. Serum, macrophages, and lymphocytes readily negotiate through the skin s lymphatic and vascular networks. 

Factors known to influence the clearance of drugs from interstitial sites, following extravasation or parenteral interstitial or transepithelial administration, include size and surface characteristics of particles, formulation medium, the composition and pH of the interstitial fluid, and disease within the interstitium. Studies indicate that soluble macromolecules smaller than 30 nm can enter the lymphatic system, whereas particulate materials larger than 50 nm are retained in the interstitial sites and serve as a sustained-release depot. The use of lipids or an oil in a formulation and the presence of a negative surface charge all appear to... 

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)... 

J. G. Hall, The lymphatic system in drug targeting An overview, in Targeting of Drugs. Anatomical and Physiological Considerations (G. Gregoriadis and G. Poste, eds.), Plenum Press, New York, 1985, p. 15. 

With disruption of this barrier, molecules such as albumin freely enter the brain and ions and water follow. Because the brain lacks a well-developed lymphatic system, clearance of plasma constituents is slow, edema occurs, and intracranial pressure rises. At lower levels of exposure, subtle dysfunction of the blood-brain barrier may contribute to neurobehavioral deficits in children (Bressler and Goldstein 1991 Goldstein 1993). The particular vulnerability of the fetus and infant to the neurotoxicity of lead may be due in part to immaturity of the blood-brain barrier and to the lack of the high-affinity leadbinding protein in astroglia, which is discussed later in this section. Results of measurements of transendothelial electrical resistance across the blood-brain barrier from mice of various ages showed that lead potentiates cytokines-induced increase in ion permeability of the blood-brain barrier (Dyatlov et al. 

Over the course of a day, approximately 20 1 of fluid are filtered from the capillaries and about 171 of fluid are reabsorbed into the capillaries. The remaining 31 is returned to the vascular compartment by way of the lymphatic system. 

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... 

Cells in vivo exist either attached to a surface or free in suspension. Adherent cell lines originate from cells of solid tissue. Breast carcinoma cell lines (such as MCF7, T47D, and SK-BR-3) are adherent cultures, and these cells are grown on the surface of plastic flasks that have been treated to facilitate adhesion (see Fig. 6.2). Suspension culture cell lines originate from cells that exist in suspension, such as those cells present in the blood and the lymphatic system (see Fig. 6.3). 

Benjamin, S. A., Jones, R. K., Snipes, M. B. and Lustgarten, C. S. (1975c). Comparative effects of inhaled relatively insoluble forms of "Y, l44Ce, and "Sr on canine peripheral lymphocyte function, page 90 in Radiation and the Lymphatic System, USAEC Report No. CONF-740930 (National Technical Information Service, Springfield, Virginia). 

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