Loose connective tissue

Synthesis. Histamine [51-45-6] 2-(4-imidazolyl)ethylarnine (1) is formed by decarboxylation of histidine by the enzyme L-histidine decarboxylase (Fig. 1). Most histamine is stored preformed in cytoplasmic granules of mast cells and basophils. In humans mast cells are found in the loose connective tissue of all organs, especially around blood and lymphatic vessels and nerves. These cells are most abundant in the organs expressing allergic diseases the skin, respiratory tract, and gastrointestinal tract. 

The basement membrane is a structure that supports overlying epithelial or endothelial cells. The primary fimction of the basement membrane is to anchor down the epithelium to its loose connective tissue underneath. This is achieved by cell-matrix adhesions through cell adhesion molecules. 

The innermost layer of an artery, which consists of loose connective tissue covered by a monolayer of endothelium that resides on a basement membrane. In human arteries, the intima often contains resident smooth muscle cells even early in life. Atherosclerotic plaques form in the intima. 

Hyaluronic acid consists of an unbranched chain of repeating disaccharide units containing GlcUA and GlcNAc. Hyaluronic acid is present in bacteria and is widely distributed among various animals and tissues, including synovial fluid, the vitreous body of the eye, cartilage, and loose connective tissues. 

HA GIcNAc, GlcUA Nil No firm evidence Synovial fluid, vitreous humor, loose connective tissue... 

KSII GIcNAc, Gal Same as KS 1 GalNAc-Thr Loose connective tissue... 

As shown in Figure 48-8, the keratan sulfates consist of repeating Gal-GlcNAc disaccharide units containing sulfate attached to the 6 position of GlcNAc or occasionally of Gal. Type 1 is abundant in cornea, and type II is found along with chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types I and II have different attachments to protein (Figure 48—8). 

Loose connective tissue An example is subcutaneous, in which the ground substance is gel like and the fibres are irregularly disposed in sheets and bundles. 

KSII is found in loose connective tissue proteoglycan aggregates with chondroitin sulfate. KS I is found in cornea. 

I a Found in synovial fluid of joints, vitreous humor of the eye, the umbilical cord, loose connective tissue and cartilage. 

Meyer, F.A. (1983) Macromolecular basis of globular protein exclusion and of swelling pressure in loose connective tissue (umbilical cord). Biochim. Biophys. Acta., 755, 388-399. 

Meyer, F.A., Koblentz, M. and Silberberg, A. (1977) Structural investigation of loose connective tissue by using a series of dextran fractions as non-interacting macromolecular probes. Biochem. J., 161, 285-291. 

During the days following the focal ischemic event, macrophages and glial cells infiltrate the lesion. After about 1-2 weeks, a loose connective tissue matrix is formed along the infarct borders. The necrotic cells have completely resolved 2 weeks later, with macrophages remaining in the tissue adjacent to the infarcted area (Clark et al. 1993). 

All of these structures have an epithelial lining that lies at the interface as well as extracellular matrix including basement membranes and loose connective tissue that supports the cellular layers (Table 3.2). These tissues are similar in their general structure they all have an inner cellular layer, supportive connective tissue, and an outer cellular layer. It is important to be familiar with the structure of these tissues to be able to analyze how external and internal mechanical forces are transduced at both the macroscopic and microscopic level into and out of cells. The effect of mechanical loading on these tissues is complex, but as discussed above, with increased frictional forces on the epidermis, the surface layer of skin actually increases the thickness of the epidermis. 

Fibroblasts Loose connective tissue Supports epithelium... 

Dermis Fibroblasts, histiocytes immune cells Epithelium of accessory Loose connective tissue Supports epidermis Contains accessory... 

Endometrium Columnar epithelium Fibroblasts and glandular cells Basal epithelium Endothelium Basement membrane Loose connective tissue Blood vessel walls Secretes substances... 

Myometrium Smooth muscle cells Fibroblasts Endothelium Loose connective tissue Smooth muscle fibers Blood vessel walls Supports endometrium... 

The mouth and esophagus are composed of two layers, the mucosa and submucosa (Figure 3.5). The mucosa is lined on its outer surface by a stratified squamous epithelium with layers of polyhedral cells of the intermediate layers and low columnar cells of the basal layer. Below the cellular layer is the lamina propria containing loose connective tissue with blood vessels and small aggregates of lymphocytes. Smooth muscle within the mucosa (muscularis mucosal layer) is seen as small bundles. The submucosa... 

This is a layer of loose connective tissue that supports the epithelium and also contains blood vessels, lymphatics and nerves. 

Deep to the reticular layer of the dermis is the hypodermis (subcutis) consisting of very loose connective tissue with adipose cells. This layer helps to anchor the dermis to the underlying muscle or bone. This thermal barrier and mechanical cushion is sometimes considered to be a site that acts as a depot or reservoir for certain toxic compounds. 

The sclera is an opaque vascular structure continuous with the cornea at the limbus.The loose connective tissue overlying the sclera—the conjunctiva—is also vascularized. The conjunctiva and sclera, as routes of drug penetration, are responsible for less than one-fifth of all drug absorption to the iris and ciliary body. This limited absorption is due to the extensive vascularization of these tissues, which results in removal of most dmgs. However, in recent years, the conjunctiva has been studied as a route of possible drug delivery because it contains a larger surface area than the cornea and possesses key transport processes that may allow fc>r penetration into intraocular tissues (Figure 2-4). 

Another possible function of L-ascorbic acid in the cuticle is to promote collagen formation. No evidence for this has been obtained using insects, but L-ascorbic acid deficiency disease in penaeid shrimp, termed black death, was related to collagen hypohydroxylation (39,40). Melanized lesions of loose connective tissue occurred in endocuticle at intersegmental spaces. Perhaps insects also underhydroxylate collagen when deficient in ascorbic acid. 

---