Elastic lymphatic vessels

Figure 9.17 Routes of parenteral medication, showing the tissues penetrated by intramuscular, intravenous, subcutaneous and intradermal injections the needles, with bevel up, penetrate the epidermis (cuticle) consisting of stratified epithelium with an outer horny layer, the corium (dermis or true skin) consisting of tough connective tissue, elastic fibres, lymphatic and blood vessels, and nerves, the subcutaneous tissue tela subcutanea) consisting of loose connective tissue containing blood and lymphatic vessels, nerves, and fat-forming cells, the fascia (a thin sheet of fibrous connective tissue), and the veins, arteries and muscle.

Subcutis (hypodermis) The subcutis is the lowest layer of skin consisting of fatty tissue, blood and lymphatic vessels, nerve fibers, and elastic fibers. 

Blood and lymphatic vessels are soft tissues with densities which exhibit nonlinear stress-strain relationships [1]. The walls of blood and lymphatic vessels show not only elastic [2, 3] or pseudoelastic [4] behavior, but also possess distinctive inelastic character [5, 6] as well, including viscosity, creep, stress relaxation and pressure-diameter hysteresis. The mechanical properties of these vessels depend largely on the constituents of their walls, especially the collagen, elastin, and vascular smooth muscle content. In general, the walls of blood and lymphatic vessels are anisotropic. Moreover, their properties are affected by age and disease state. This section presents the data concerning the characteristic dimensions of arterial tree and venous system the constituents and mechanical properties of the vessel walls. Water permeability or hydraulic conductivity of blood vessel walls have been also included, because this transport property of blood vessel wall is believed to be important both in nourishing the vessel walls and in affecting development of atherosclerosis [7-9]. 

Mechanical properties of the arteries from human and various animals have been extensively studied. However, literature on lymphatic vessels is very scarce. The data on the circumferential elastic modulus of the lymphatic vessels obtained by Ohhashi et al [53, 54] seem to be too low considering that the lymphatics are originating from the veins. 

The tunica media contains predominantly smooth muscle cells and elastin fibres that are much more highly organized in larger arteries due to the role required in the movement of large volumes of blood. Additional structural support is provided by an external elastic lamina. The remaining and outermost layer of the blood vessel is the tunic adventitia that is composed almost entirely of fibro-elastic connective tissue. Lymphatic and nerve plexi are found in the adventitia along with the vasa... 

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