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10

First, I think it worthwhile considering 'Why would internal symmetry be beneficial?' Developmental simplicity jumps to mind immediately. You can also consider relationship to external organs; the stomach and esophagus are lined up with the mouth which is symmetrical about the sagittal plane. Or maybe even balance; the lungs are large organs and if put to ...


6

Smith et al. (2009) provide a survey of the morphology of the cecal appendix. One current hypothesis is that the appendix provides "safe harbor" for symbiotic gut bacteria. Among mammals, there is a vast array of cecal appendices: In summary: A comparative anatomical approach reveals three apparent morphotypes of the cecal appendix, as well as ...


6

Building on the answer given by Sean Connolly above, it would be very easy to imagine evolutionary scenarios where organs are more likely to develop asymmetrically than symmetrically. For instance, imagine an organism that has a simple digestive system that consists only of a single undifferentiated intestine that runs directly from mouth to anus in a ...


5

The number of mammary glands a species has is related to litter size. The relationship generally follows the "one-half rule," which states that the average litter size is equal to half the number of mammaries. The number of mammaries also tends to put an upper limit on litter size. It's not necessarily a hard limit, but survival tends to drop noticeably when ...


5

Aside from humans, it is largely rodents and most notably rabbits that have an appendix. Therefore, using rabbits as my example: In rabbits, the appendix is thought to have a key role in the development of the immune system. Specifically it has been shown experimentally that when neonatal rabbits are given an appendectomy levels of Immunoglobulin A and G ...


5

Yes. Blood will continue to circulate (as long as you're alive and your heart is beating), so will eventually come in contact with your lungs. Once there, the gasses (O2, CO2) will cross out into the lung and be exhaled. All diffusion is driven down a concentration gradient.


5

The problem is that real organs are just damn complex - yes the kidney's prime role is just to be a filter, but in order to do so it must be plugged in to a dozen regulation mechanisms - osmotic balance, ion management, protein management and a plethora of more subtle ones. Moreover it is a part of body, so it must also follow all the standard protocols to ...


4

I was told in my undergraduate degree that males produce sperm all the time, and that under conditions of no sexual stimulation, that sperm is excreted involuntarily every 15-16 days, at night, while dreaming. I was also told that the renewal rate of sperm is higher under regular sexual stimulation, which increases the fertility of the sperm that is ...


4

The appendix was thought to be vestigial in humans until recently. Now it appears that, like rabbits, it is a safe harbour for symbiotic bacteria in the intestines. Source: Bollinger, Barbas, Bush, et al. J Theor Biol. 2007 Dec 21;249(4):826-31. Epub 2007 Sep 7.


3

Maybe it is due to two factors: 1) The liver is one of the few solid non-tubular organs. If a tubular organ is damaged, all the layers that composes it must regenrate. This layers usually have different cell types, wich is always nasty for regneration since some of them may be formed by specilized tissue(For instance, myocites are very difficult to ...


3

It's old and I can't get access to this issue of the Annals of the New York Academy of Science, but it looks like it has some relevant information. Sifting through the abstracts it seems the vasculature of the fetal liver is completed at around 8 weeks although is still different to the adult vasculature because of the umbilical vein. The growth of the organ ...


2

Not entirely on your question but I think sufficiently relevant: This paper (freely available) identified a non-causal link between ejaculatory frequency and incidence of prostate cancer. Men were asked their age at first ejaculation, the maximum number of ejaculations ever experienced in 24 h, and to estimate the average number of times that they had ...


2

As an addition to the excellent post by Erin. As a name-giving key feature,mammals have mammary glands. "Animals that are bilaterally symmetric have mirror symmetry in the sagittal plane", which includes Chordates such as mammals. Some have seen this iconic picture, showing the bilateral symmetry in chordates: It is easy to see why most commonly even ...


2

Perhaps you can infer relative lifespan from the age at which organs start declining in someone of average health. Skin, muscles, bones, eyes, and ears start to visibly decline around age 40. Kidneys become smaller and their ability to filter blood starts to decline around age 30. Brain function begins to decline around 70, even in the absence of ...


2

It is, indeed, the alimentary canal. It is actually this canal that it's important for one to remove when "de-veining" shrimp, rather than the vein itself, which lies immediately dorsal to the digestive tract. In the future, I might suggest doing a little more research prior to asking the stack exchange, as frequent users of the site do like to see ...


2

Quoting a great biologist Peter Medawar : It is by no means difficult to imagine a genetic endowment which can favor young animals only at the expense of their elders; or rather at their own expense when they, themselves, grow old. A gene or combination of genes that promotes this state of affairs will, under certain numerically definable ...


1

Depends what you consider an organ. Typically though it's the cells which require the most metabolic activity which have the shortest life span. The kidney is the most of the major internal organs with up to 36 hours with liver coming second at up to 16 hours.


1

Since cells are the origin of every life, any tissue must at least be based on cells. Some tissue matter is outside the cells (plant cell walls), some apparently non-cellular tissue is really a bloated organelle. Both happens. As to your theses, yes, an example are oil reservoirs in plants no, these are just big cells. A striking example is spinal cord ...


1

I found that a search through Google Books was helpful... While without the excretion of feces, it might seem as if the liver would not be active, but the liver tissue is not only active in development and tissue generation but serves direct physiological function as well. After initial phases of development, the liver produces fetal red blood cells which ...


1

On the question "would this possible?", my answer is yes. It is not unimaginable that organs could be grown without MHC proteins, although, as you mentioned, there's no guarantee that essential functions of the organ wouldn't be affected as well. This is not science-fiction at all. The question deserves a good answer by someone who works in the field!



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