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18

Blood is considered a type of connective tissue (sometimes). However, an organ is formed of multiple different tissues. Thus, blood is a tissue, not an organ.


9

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 ...


8

Usually,blood moves through the body by force from the contraction of ventricles, the contraction on muscles, gravity, or other forces. At death, the only force left is gravity, which is why we see lividity (or livor mortis -pooling of blood in dependent positions) after death. This continues for ~8-12 hours (depending in part on temperature). The blood in ...


7

I'll contradict the answer posted here (ages ago) and say no, it isn't possible. Growing an organ wthout MHC proteins might be achievable, but it would be rejected for not having MHC1. NK cells instruct all cells without MHC1 to perform apoptosis. In this case, MHC1 antigens are required on cells for proper self-identification. Keeping MHC1-less cells alive ...


6

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


6

First of all, it will be practically impossible to make an estimation of how long a transplanted organ will live and how many times it could be transplanted. However, it is relatively safe to say that it will not live forever. To be able to receive an organ transplantation, the HLA MHC-complexes of donor and receiver need to be matched very carefully, to ...


5

Anatomically speaking, the palate is the roof of the mouth, separating the oral cavity (mouth) from the nasal cavity (inner nose). While the palate may be sensitive to heat and spiciness (via the capsaicin receptor, for example), it does not contain any taste buds, which are located on the tongue, and are part of the taste-sensing system. The other part of ...


5

While organs are generally considered to have a single, specified function (or perhaps a group of closely-related functions), blood (the fluid inside the vessels, not the vessels themselves) has many different functions: deliver $O_2$ from lungs to cells remove waste $CO_2$ from cells to lungs respond to injury by clotting carry multiple different types of ...


5

DNA will be never replaced (unless you are speaking about something, where DNA might be only trash, like in the case of blood transplantation or in the case when "organ" would be slowly replaced itself by host regenerative power and "organ" transplantation would be only something temporary, but then we are probably speaking about wider definition of organs). ...


5

The median lifetime of an organ transplant is some 5 to 10 years mainly due to chronic rejection mediated by host-versus-graft immune responses. Hence long-term transplants definitely have a limited half life. However, this graft rejection is relatively slow and early explantation and re-implantation in a new host may actually "reset" this process? With re-...


5

As part of your question, you ask if other animals can create sound without continuous airflow. Many insects (e.g. cicadas and moths) do exactly this by using tymbals. A tymbal/timbal is an external membrane organ that is controlled by muscles or wing movements, that cause the membrane to flip back and forth, creating clicks or other sounds. So in many ways ...


4

You change one thing and you have to change everything else to compensate. Lets look at what organs are not symmetric in tetrapods, the heart and the digestive system, everything else is symmetric. Note these are symmetric in more basal vertebrates like fish. the heart starts symmetrical in vertebrates but that changes when animals evolve independent ...


4

Here is a list of woodwind instruments. Do you know of any (non-open) reed instrument that produces a note without anyone blowing air through them? Imagine a clarinet being played on someone's lap pouring out a melody. That would be very, very remarkable indeed. Our ability to produce sound from our throats is in theory like a reed instrument in music. Let'...


4

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 ...


4

Capillaries only transport blood for short distances, and within an organ. The blood supply to/from a major organ is generally carried over a few major blood vessels (usually one artery, one vein). Splicing such larger blood vessels are what surgeons earn their pay to do. In terms of nerves, most transplanted organs function fairly well without being ...


4

A swollen organ may be described as distended if the swelling is symptomatic of a medical disfunction. The purpose of most bladders is to collect and retain a fluid; if that fluid needs to be discharged periodically, and is not able to do so, then there is usually pain as a result of the distension. Inability to urinate is known as ischuria or urinary ...


3

As far as it can be deducted from the picture you ask about Appendix or just Coecum. This is a normal finding and not abnormal one. (You can see a terminal Ileum as well). If other pictures were provided it could be possible to give more exact answer.


3

There are no composite tests that measure all the clinically important hormone producing glands. There are too many hormones produced by too many hormone producing cells/tissues in the body to test for all of them all at once (i.e. in a panel). For illustrative purposes only... if you go to wikipedia they have a list of all hormones in the human body which ...


3

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 ...


3

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 ...


3

The answer to your question is not really know yet and there is whole scientific field dedicated to it: developmental biology. I'll try to explain the basics however: Like you described the identity of a cell (its cell type; which organ it belongs to) is dependent on which of (actually) ~30000 human genes are activated (or read) in that cell. There are two ...


3

Why can't eating citric acid be used as a temporary primary source of energy - in place of fat/carbohydrate/protein? No reason it can't. Citric Acid technically contains 2.5kcal/g -- which is almost half of protein/carbohydrates, almost a third of alcohol, and a fourth of fat. So if someone needed 2500kcal/day, they'd need 1kg of straight Citric Acid. ...


3

As Mowgli pointed out, a bone marrow transplant involves destroying the patient's own immune system with radiation and, essentially, replacing it with a new one from the bone marrow donor. If you did a double kidney/bone marrow transplant from Alice into Bob, then Bob's new immune system (which is the same as Alice's) would recognize the new kidney from ...


3

This is a VERY hard question to answer; I think mostly because it is very hard to think about how the DNA actually encodes information. The first important thing to note (and also the only direct answer I can give to your question), is that (Yes) the human genome does encode all information to make a human being, but only in the context of a cell/organism ...


2

It helps to think about why it's beneficial for an organ/tissue to regenerate. The liver is your main detoxifying organ. It does this by chemically modifying external (and internal) molecules to counter their possible bad effects or simply to be able to excrete them. This role brings liver cells in harms way. Take paracetamol for example. It is recognized as ...


2

As dd3 said the density of mechanoreceptors dictates skin sensitivity to touch (also look at penfield map. It is a nice illustration of how different senses are mapped to the brain and to what extent each region is sensitive to stimulus). Skin thickness is also different in different regions. This article says that Dikkopf1 (a Wnt pathway antagonist) ...


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 evidence ...


2

No, MHCII mismatch can also lead to transplant rejection, though through different mechanisms. CD8+ Tcells (that recognize class I) may become activated and directly kill donor cells*, and some NK subtypes can see the lack of self MHCI and also induce cell death. MHCII mismatch on antigen presenting cells (APCs) brought along in the tissue may activate CD4+ ...


2

@zeller The better answers are being sought in a field called Regenerative Medicine. A number of techniques have been tried, among them 3D printing of organs and dissolving the cells from a donor organ leaving the collagen scaffolding, then reseeding the organ with a patients stem cells in a bioreactor. Most of these technologies, unfortunately, are in ...


2

In a healthy body, cells travel. But this is very dependent of the cell type. Some cell type will travel in all the body (lymphocytes, plasmocytes, etc) while other do not have any migration capability. The concept of diffusion is wrong to apply here, indeed the scales at which you are looking are not molecular. Moreover, there are very active mechanism ...


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