Blood vessels, structure detailed

The epithelial layer is in immediate contact with the lumen of the gastrointestinal tract. The lamina propria, which functions as a structural support for the epithelial layer, is situated on the basolateral side of the epithelial layer. The lamina propria contains lymph vessels, smooth muscle cells, nerves, and blood vessels, which nourish the epithelium. The muscularis mucosa makes up the deepest layer, which is thought to be involved in contractility.8 A more detailed description of the forces that hold together the epithelial layer is provided below. 

The skin is an excellent barrier to microbial and parasitic infections. The most superficial layer of the skin is composed of flattened squamous cells, which are highly keratinized. Beneath this is the epidermal layer composed of cells tightly interconnected by desmosomes and other intercellular structures. These, in turn, are attached to the basement membrane composed of covalently bound or interwoven macromolecules. Between the basement membrane and a target blood vessel is an extracellular matrix rich in type I collagen, elastin and proteoglycan. Elastin and type I collagen are both interwoven fibrillar molecules, whereas the carbohydrate-rich proteoglycan behaves like a hydrated gel. For details of these macromolecular interactions, the reader is referred to reviews on the structure of skin. 

The main limitations of the Weinbaum-Jiji equation are associated with the importance of the countercurrent heat exchange. It was derived to describe heat transfer in peripheral tissue only, where its fundamental assumptions are most applicable. In tissue area containing a big blood vessel (>200 /rm in diameter), the assumption that most of the heat leaving the artery is recaptured by its countercurrent vein could be violated, thus, it is not an accurate model to predict the temperature field. In addition, this theory was primarily developed for closely paired microvessels in muscle tissue, which may not always be the main vascular structure in other tissues, such as the renal cortex. Furthermore, unlike the Pennes equation, which requires only the value of blood perfusion, the estimation of the enhancement in thermal conductivity requires that detailed anatomical studies be performed to estimate the vessel number density, size, and artery-vein spacing for each vessel generation, as well as the blood perfusion rate (Zhu et al., 1995). These anatomic data are normally not available for most blood vessels in the thermally significant range. 

This chapter reviews the essential concepts of vascular mechanics and its methods of quantification. Some of the important controversies are discussed, and further research areas are pointed out. Detailed information is provided on the structural and mechanical changes of arteries with age. The effect of vascular disorders such as arterosclerosis and hypertension on the mechanical behavior of blood vessels is discussed as well. Extensive addition literature sources are provided. 

MPR and CPR, obtained in different sectional planes, have revealed to he fundamental in or-der to evaluate the relationships between pancreatic disease and peri-pancreatic structures, especially in the preoperative CT assessment of pancreatic carcinoma and mainly in the evaluation of loco-regional spreading, furnishing fine details in the visualisation of the relationship between tumour and blood vessels (Nino-Murcia et al. 2003) (Fig. 21.1). 

The details of the pathogenesis of the fetal death are not known, but at least two different concepts prevail. It has been suggested that the primary structural injury involves failure of the placental vessels to develop normally, so that the embryo is killed by anoxemia. Others have proposed that the first structural injury is observed in the embryo itself where blood vessels develop inadequately. 

Within the medicinal field, bacterial cellulose alone was shown to be a versatile material for the construction of artificial blood vessels, an application which clearly benefits from the structural features of cellulose in combination with its chemical stability under physiological conditions [52], Other applications use cellulose for the production of implantable capsules [53], and even sensors [54], Another interesting biomedical application is the use of cellulose in films supporting wound healing, due to the hydrating characteristics of these cellulose-containing films [55], Besides, cellulose and cellulose derivatives are used as haemostatic agents [56], The latter two fields of application for cellulose have just recently been reviewed in the cited literatiu-e, and are thus not discussed in detail here. 

Amfetamine (Fig. 10.15) has structural similarities to noradrenaline. In the form of the free base it is relatively volatile and was thus used as a nasal decongestant through promoting constriction of mucosal blood vessels. It also has appetite-suppressing effects which have been attributed to its ability to displace serotonin from synaptic vesides, but since noradrenaline increases blood sugar levels this may also be part of its action. It is not fre-quendy used because of it potential for being addictive since, because of its high lipophilidty, it can also enter the CNS. Its main indication in current practice is in the treatment of narcolepsy. Amfetamines are discussed in more detail in Chapter 18. 

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