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Views Read Edit View history. The most common cause is infection but lymph nodes can also become swollen because of cancer. Mechanical digestion is the physical breakdown of large pieces of food into smaller pieces. The red blood cells perform the important function of supplying oxygen to different tissues of the body. It carries swallowed masses of chewed food along its length. The entire reproductive cycle takes about 28 days on average, but may be as short as 24 days or as long as 36 days for some women. The waste product that these recent studies focused most on is amyloid-beta, which is a protein that's made in the brain all the time.
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There are several hundred of these receptors and they recognize patterns of bacterial lipopolysaccharide, peptidoglycan, bacterial DNA, dsRNA, and other substances. Clearly, they are set to target both Gram-negative and Gram-positive bacteria. Lymphocytes come in two major types: B cells and T cells. Their total mass is about the same as that of the brain or liver. B cells are produced in the stem cells of the bone marrow; they produce antibody and oversee humoral immunity.
T cells are nonantibody-producing lymphocytes which are also produced in the bone marrow but sensitized in the thymus and constitute the basis of cell-mediated immunity.
The production of these cells is diagrammed below. Parts of the immune system are changeable and can adapt to better attack the invading antigen. There are two fundamental adaptive mechanisms: Macrophages engulf antigens, process them internally, then display parts of them on their surface together with some of their own proteins. This sensitizes the T cells to recognize these antigens.
All cells are coated with various substances. CD stands for cluster of differentiation and there are more than one hundred and sixty clusters, each of which is a different chemical molecule that coats the surface.
The large number of molecules on the surfaces of lymphocytes allows huge variability in the forms of the receptors. They are produced with random configurations on their surfaces. There are some 10 18 different structurally different receptors. Essentially, an antigen may find a near-perfect fit with a very small number of lymphocytes, perhaps as few as one.
T cells are primed in the thymus, where they undergo two selection processes. The first positive selection process weeds out only those T cells with the correct set of receptors that can recognize the MHC molecules responsible for self-recognition. Then a negative selection process begins whereby T cells that can recognize MHC molecules complexed with foreign peptides are allowed to pass out of the thymus.
They secrete chemicals called lymphokines that stimulate cytotoxic T cells and B cells to grow and divide, attract neutrophils, and enhance the ability of macrophages to engulf and destroy microbes. Suppressor T cells inhibit the production of cytotoxic T cells once they are unneeded, lest they cause more damage than necessary. Memory T cells are programmed to recognize and respond to a pathogen once it has invaded and been repelled. An immunocompetent but as yet immature B-lymphocyte is stimulated to maturity when an antigen binds to its surface receptors and there is a T helper cell nearby to release a cytokine.
This sensitizes or primes the B cell and it undergoes clonal selection , which means it reproduces asexually by mitosis. Most of the family of clones become plasma cells. These cells, after an initial lag, produce highly specific antibodies at a rate of as many as molecules per second for four to five days.
The other B cells become long-lived memory cells. Antibodies , also called immunoglobulins or Igs [with molecular weights of — Md] , constitute the gamma globulin part of the blood proteins.
They are soluble proteins secreted by the plasma offspring clones of primed B cells. The antibodies inactivate antigens by, a complement fixation proteins attach to antigen surface and cause holes to form, i. Constituents of gamma globulin are: IgG is the only antibody that can cross the placental barrier to the fetus and it is responsible for the 3 to 6 month immune protection of newborns that is conferred by the mother.
IgM is the dominant antibody produced in primary immune responses, while IgG dominates in secondary immune responses. IgM is physically much larger than the other immunoglobulins. Notice the many degrees of flexibility of the antibody molecule. This freedom of movement allows it to more easily conform to the nooks and crannies on an antigen.
The upper part or Fab a ntigen b inding portion of the antibody molecule physically and not necessarily chemically attaches to specific proteins [called epitopes] on the antigen. Thus antibody recognizes the epitope and not the entire antigen.
The Fc region is crystallizable and is responsible for effector functions, i. Lest you think that these are the only forms of antibody produced, you should realize that the B cells can produce as many as 10 14 conformationally different forms. The process by which T cells and B cells interact with antigens is summarized in the diagram below.
In the ABO blood typing system, when an A antigen is present in a person of blood type A , the body produces an anti-B antibody, and similarly for a B antigen. The blood of someone of type AB, has both antigens, hence has neither antibody.
Thus that person can be transfused with any type of blood, since there is no antibody to attack foreign blood antigens. A person of blood type O has neither antigen but both antibodies and cannot receive AB, A, or B type blood, but they can donate blood for use by anybody.
If someone with blood type A received blood of type B, the body's anti-B antibodies would attack the new blood cells and death would be imminent. All of these of these mechanisms hinge on the attachment of antigen and cell receptors. Since there are many, many receptor shapes available, WBCs seek to optimize the degree of confluence between the two receptors.
The number of these "best fit" receptors may be quite small, even as few as a single cell. This attests to the specificity of the interaction. And within just a few weeks there will be nothing left but a skeleton! The lymphatic system is part of your immune system. The two work together to protect you from illness and disease. The lymph diagram below shows you the vast lymphatic network running throughout your body.
Lymph is a clear fluid that carries white blood cells through the lymph vessels all around your body to help fight infection and disease. The watery lymph fluid bathes your tissues and distributes nutrients to your cells. After nourishing cells, lymph collects waste and foreign materials and carries them to lymph nodes to filter out harmful microbes and toxins.
Lymph nodes are in the neck, armpit, groin, chest, abdomen and all around the body. Your immune system is made up of a complex army of soldiers.
They include lymph, spleen and thymus glands, prostaglandin and histamine, bone marrow and a trillion different cells, such as T cells. But your skin is the largest component of the immune system. All the components of your immune system act synergistically to protect your body from invasion.
Immune warriors are in combat fighting off vicious invaders trying to take over your body. It was ingenious, but it was also beautiful. Let me tell you about what we found. So the brain has this large pool of clean, clear fluid called cerebrospinal fluid. We call it the CSF. The CSF fills the space that surrounds the brain, and wastes from inside the brain make their way out to the CSF, which gets dumped, along with the waste, into the blood.
So in that way, it sounds a lot like the lymphatic system, doesn't it? But what's interesting is that the fluid and the waste from inside the brain, they don't just percolate their way randomly out to these pools of CSF.
Instead, there is a specialized network of plumbing that organizes and facilitates this process. You can see that in these videos. Here, we're again imaging into the brain of living mice. The frame on your left shows what's happening at the brain's surface, and the frame on your right shows what's happening down below the surface of the brain within the tissue itself.
We've labeled the blood vessels in red, and the CSF that's surrounding the brain will be in green. Now, what was surprising to us was that the fluid on the outside of the brain, it didn't stay on the outside.
Instead, the CSF was pumped back into and through the brain along the outsides of the blood vessels, and as it flushed down into the brain along the outsides of these vessels, it was actually helping to clear away, to clean the waste from the spaces between the brain's cells.
If you think about it, using the outsides of these blood vessels like this is a really clever design solution, because the brain is enclosed in a rigid skull and it's packed full of cells, so there is no extra space inside it for a whole second set of vessels like the lymphatic system.
Yet the blood vessels, they extend from the surface of the brain down to reach every single cell in the brain, which means that fluid that's traveling along the outsides of these vessels can gain easy access to the entire brain's volume, so it's actually this really clever way to repurpose one set of vessels, the blood vessels, to take over and replace the function of a second set of vessels, the lymphatic vessels, to make it so you don't need them.
And what's amazing is that no other organ takes quite this approach to clearing away the waste from between its cells. This is a solution that is entirely unique to the brain. But our most surprising finding was that all of this, everything I just told you about, with all this fluid rushing through the brain, it's only happening in the sleeping brain.
Here, the video on the left shows how much of the CSF is moving through the brain of a living mouse while it's awake. Yet in the same animal, if we wait just a little while until it's gone to sleep, what we see is that the CSF is rushing through the brain, and we discovered that at the same time when the brain goes to sleep, the brain cells themselves seem to shrink, opening up spaces in between them, allowing fluid to rush through and allowing waste to be cleared out.