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And within just a few weeks there will be nothing left but a skeleton! 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. They are long-lived, depend on mitochondria for energy, and are best at attacking dead cells and pathogens capable of living within cells. Nutrient artery Arteriole Metarteriole Elastic artery. The production of milk begins prior to birth under the control of the hormone prolactin. Wikipedia articles incorporating text from the 20th edition of Gray's Anatomy Lymphatics of the torso.
Low Red Blood Cell Count Causes
Inside the mouth are many accessory organs that aid in the digestion of food—the tongue, teeth, and salivary glands. Teeth chop food into small pieces, which are moistened by saliva before the tongue and other muscles push the food into the pharynx.
The pharynx, or throat, is a funnel-shaped tube connected to the posterior end of the mouth. The pharynx is responsible for the passing of masses of chewed food from the mouth to the esophagus.
The pharynx also plays an important role in the respiratory system, as air from the nasal cavity passes through the pharynx on its way to the larynx and eventually the lungs. Because the pharynx serves two different functions, it contains a flap of tissue known as the epiglottis that acts as a switch to route food to the esophagus and air to the larynx.
It carries swallowed masses of chewed food along its length. At the inferior end of the esophagus is a muscular ring called the lower esophageal sphincter or cardiac sphincter. The function of this sphincter is to close of the end of the esophagus and trap food in the stomach.
The stomach is a muscular sac that is located on the left side of the abdominal cavity, just inferior to the diaphragm. In an average person, the stomach is about the size of their two fists placed next to each other. This major organ acts as a storage tank for food so that the body has time to digest large meals properly. The stomach also contains hydrochloric acid and digestive enzymes that continue the digestion of food that began in the mouth.
It is located just inferior to the stomach and takes up most of the space in the abdominal cavity. The entire small intestine is coiled like a hose and the inside surface is full of many ridges and folds. These folds are used to maximize the digestion of food and absorption of nutrients. The liver is a roughly triangular accessory organ of the digestive system located to the right of the stomach, just inferior to the diaphragm and superior to the small intestine.
The liver weighs about 3 pounds and is the second largest organ in the body. The liver has many different functions in the body, but the main function of the liver in digestion is the production of bile and its secretion into the small intestine. The gallbladder is a small, pear-shaped organ located just posterior to the liver.
The gallbladder is used to store and recycle excess bile from the small intestine so that it can be reused for the digestion of subsequent meals. The pancreas is a large gland located just inferior and posterior to the stomach. The pancreas secretes digestive enzymes into the small intestine to complete the chemical digestion of foods.
The large intestine is a long, thick tube about 2. It is located just inferior to the stomach and wraps around the superior and lateral border of the small intestine. The large intestine absorbs water and contains many symbiotic bacteria that aid in the breaking down of wastes to extract some small amounts of nutrients.
Feces in the large intestine exit the body through the anal canal. The digestive system is responsible for taking whole foods and turning them into energy and nutrients to allow the body to function, grow, and repair itself.
The six primary processes of the digestive system include:. The first function of the digestive system is ingestion, or the intake of food. The mouth is responsible for this function, as it is the orifice through which all food enters the body. The mouth and stomach are also responsible for the storage of food as it is waiting to be digested. This storage capacity allows the body to eat only a few times each day and to ingest more food than it can process at one time. In the course of a day, the digestive system secretes around 7 liters of fluids.
These fluids include saliva, mucus, hydrochloric acid, enzymes, and bile. 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.
So it seems that Galen may actually have been sort of on the right track when he wrote about fluid rushing through the brain when sleep came on. Our own research, now it's 2, years later, suggests that what's happening is that when the brain is awake and is at its most busy, it puts off clearing away the waste from the spaces between its cells until later, and then, when it goes to sleep and doesn't have to be as busy, it shifts into a kind of cleaning mode to clear away the waste from the spaces between its cells, the waste that's accumulated throughout the day.
So it's actually a little bit like how you or I, we put off our household chores during the work week when we don't have time to get to it, and then we play catch up on all the cleaning that we have to do when the weekend rolls around. Now, I've just talked a lot about waste clearance, but I haven't been very specific about the kinds of waste that the brain needs to be clearing during sleep in order to stay healthy. 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.
My brain's making amyloid-beta right now, and so is yours. But in patients with Alzheimer's disease, amyloid-beta builds up and aggregates in the spaces between the brain's cells, instead of being cleared away like it's supposed to be, and it's this buildup of amyloid-beta that's thought to be one of the key steps in the development of that terrible disease. So we measured how fast amyloid-beta is cleared from the brain when it's awake versus when it's asleep, and we found that indeed, the clearance of amyloid-beta is much more rapid from the sleeping brain.
So if sleep, then, is part of the brain's solution to the problem of waste clearance, then this may dramatically change how we think about the relationship between sleep, amyloid-beta, and Alzheimer's disease.
A series of recent clinical studies suggest that among patients who haven't yet developed Alzheimer's disease, worsening sleep quality and sleep duration are associated with a greater amount of amyloid-beta building up in the brain, and while it's important to point out that these studies don't prove that lack of sleep or poor sleep cause Alzheimer's disease, they do suggest that the failure of the brain to keep its house clean by clearing away waste like amyloid-beta may contribute to the development of conditions like Alzheimer's.
So what this new research tells us, then, is that the one thing that all of you already knew about sleep, that even Galen understood about sleep, that it refreshes and clears the mind, may actually be a big part of what sleep is all about. See, you and I, we go to sleep every single night, but our brains, they never rest. While our body is still and our mind is off walking in dreams somewhere, the elegant machinery of the brain is quietly hard at work cleaning and maintaining this unimaginably complex machine.
Like our housework, it's a dirty and a thankless job, but it's also important. In your house, if you stop cleaning your kitchen for a month, your home will become completely unlivable very quickly. But in the brain, the consequences of falling behind may be much greater than the embarrassment of dirty countertops, because when it comes to cleaning the brain, it is the very health and function of the mind and the body that's at stake, which is why understanding these very basic housekeeping functions of the brain today may be critical for preventing and treating diseases of the mind tomorrow.