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Title: Body identify its own tissue that isn't in blood flow? Post by: CarbonRobot on Mar 22, 2023 How does the body know that tissue that isn't connected via blood vessels isn't foreign and should be broken down? Like scar tissue, or the lens in the eye, or anything that develops then just breaks off from the body?
Title: Re: Body identify its own tissue that isn't in blood flow? Post by: bio_man on Mar 23, 2023 I thought scar tissue was highly vascularized - I'd double check that statement!
Further, you mentioned the lens; the fact that it is transparent definitely means it is avascular. However, that does not mean it has "immune privilege". Immune privilege is the idea that there are certain regions, the nervous system, cornea, retina, anterior chamber of the eye, testis, and liver for example, in which immune surveillance is reduced. Instead, according to the attached article, it should be considered immune quiescence instead (a state of low baseline immune activation). Let's assume your original assumption is true, that the lens has this "immune privilege". You're wondering what allows certain tissue to have lower security, for example. The theory of immune privilege is based on the idea that there is: 1) anatomic separation between blood and neural tissue (in the case of the lens), 2) molecules required for antigen presentation are absent under normal physiological conditions (which is what I was originally thinking), 3) absence of lymph drainage, and 4) decreased T-cell surveillance. Those are the four reasons why some tissue are more "privileged" than others. Interesting, the idea originated in 1948 when observations that homologous skin transplantations into the brain did not elicit the same degree of immune response as transplantations into other sites [1]. Title: Re: Body identify its own tissue that isn't in blood flow? Post by: CarbonRobot on Mar 24, 2023 "Because scar tissue does not have blood flow, cold is spreading as fast or faster through the scar tissue than the normal myocardium"
I found this at sciencedirect.com. Don't know if that is heart specific? Title: Re: Body identify its own tissue that isn't in blood flow? Post by: bio_man on Mar 24, 2023 According to this article:
Cardiac scars, often perceived as “dead” tissue, are very much alive, with heterocellular activity ensuring the maintenance of structural and mechanical integrity following heart injury. To form a scar, non-myocytes such as fibroblasts, proliferate and are recruited from intra- and extra-cardiac sources. Fibroblasts perform important autocrine and paracrine signalling functions. They also establish mechanical and, as is increasingly evident, electrical junctions with other cells. While fibroblasts were previously thought to act simply as electrical insulators, they may be electrically connected among themselves and, under certain circumstances, to other cells, including cardiomyocytes. A better understanding of these interactions will help target scar structure and function and facilitate the development of novel therapies aimed at modifying scar properties for patient benefit. Below, I have highlighted some more key parts in the article that say it much better than I do: Fibrotic scars, such as in skin, are generally acellular and predominantly composed of fibrillar collagen [11]. In the heart, however, scar tissue assumes a more proactive role than simply preserving ventricular integrity, facilitating force transmission, and preventing rupture. Nonetheless, myocardial scarring does share common mechanisms and morphological milestones with classic wound healing. Despite prevailing perceptions, cardiac scars are dynamic living structures [16, 17]. The abundantly present ECM is interlaced with phenotypically diverse groups of cells: interstitial fibroblast-like cells (both functionally and structurally heterogeneous, endothelial cells, vascular smooth muscle, surviving cardiomyocytes, immune cells, neurons, and adipocytes [18, 19] (Fig. 1B,C). The scar is a metabolically dynamic tissue which furthermore, exhibits non-linear passive and active mechanical properties (‘active’ force-generation by non-myocytes over time occurs at scales that are orders of magnitude longer than the heartbeat) [20]. Contractile properties of the scar rely on the presence of non-vascular, α-smooth muscle actin-expressing non-myocytes, which persist in cardiac scars for many years following injury, such as with myocardial infarction (MI) [21–23] (note that not all subsets of fibroblasts express contractile proteins [24]). They also depend on the presence of an extensive cytoplasmic fibrillar system of cell-to-cell and cell-to-ECM attachments [25]. Title: Re: Body identify its own tissue that isn't in blood flow? Post by: CarbonRobot on Mar 24, 2023 Do you know of other tissues that get no blood flow other than eye lens and vitreous gel?
And do you think we get cataracts because there is zero blood flow in the lens? I know images might appear more red, but with blood flow might proteins accumulating on the lens have a means to clean up? Title: Re: Body identify its own tissue that isn't in blood flow? Post by: bio_man on Mar 25, 2023 Quote Do you know of other tissues that get no blood flow other than eye lens and vitreous gel? Cartilage! That's why once cartilage is damaged, it does not get repaired as easily as other tissues might. It has repair mechanisms in place, but repair is typically slow and ineffective. Cataract forms when protein deposits build up on the lens of the eye. For example, a perforating wound to the capsule of the lens will cause leakage into their area, leading to opaque lens characteristic of cataracts. Thus, you could say that because it is NOT vascularized, there's really no mechanism to clean up the build up of proteins, or whatever is built up there. |