Ch 3 - Diets
Why is celiac disease awareness on the rise?
Celiac disease is also attracting attention because, as researchers have recently discovered, some people with the condition don't exhibit the typical symptoms of diarrhea or weight loss, which makes it even harder to identify and diagnose. One other symptom of celiac disease usually not associated with the condition can be a specific type of skin rash. When patients with the rash cut gluten out of their diets, the rash disappears. In addition, individuals with celiac disease have a higher risk of thyroid disease, and they may also be at higher risk of experiencing various neurological problems. - Once Murray and others began to spread the news that celiac disease could manifest itself in unsuspected ways and that untreated celiac disease could increase the risks of all sorts of health problems, people started paying much more attention to gluten.
Hemorrhoids
Consuming sufficient fiber along with adequate fluid intake softens stools because it holds water, thus decreasing the risk of both constipation and painful inflamed veins in the lower rectum or anus, a condition called hemorrhoids.
what are the 2 processes of digestion?
Digestion is comprised of two processes: mechanical digestion and chemical digestion. Working together, these two processes break down the nutrients in food into smaller and smaller components so that the nutrients can be absorbed and utilized by our bodies, but each process has its own unique spin.
Effect of Celiac Disease on the last few steps of nutrient circulation
For people with untreated celiac disease, however, the last few steps of nutrient circulation may not progress properly, and the intricate and essential process of absorption becomes disrupted. The gluten found in the wheat-based hamburger bun sparks an immune reaction that triggers the person's immune cells to attack other body cells. These so-called autoimmune cells begin destroying the villi of the small intestine. This leaves a flattened and reduced surface on the small intestine that compromises digestion and absorption of nutrients. Over time, this damage to the intestinal tract increases the risk of certain types of intestinal cancers, including intestinal lymphomas (cancers involving cells of the immune system), which could help explain the higher mortality rate among people suffering from celiac disease.
Role of Hormones in Digestion
Hormones are your body's chemical messengers. Together with the nervous system, hormones regulate motility, appetite, and the release of secretions into the GI tract.
What are the effects of inflamatory bowel disease?
Individuals with IBDs are at risk for serious or even life-threatening complications. These include bowel obstruction (caused by the narrowing of the intestinal wall); ulcers in the digestive track, including the mouth and anus; fistulas (an abnormal connection between the intestine and skin or other organs); malnutrition because of poor absorption; colon cancer; and problems in parts of the body outside the GI tract, such as kidney stones or arthritis. A person with IBD needs a nourishing diet to deal with potential nutrient deficiencies brought about by absorption issues, as well as assistance when significant weight loss occurs. People suffering with IBDs are treated with anti-inflammatory drugs and often require surgical procedures to deal with medical complications.
Probiotics
One of the means by which diet influences the gut microbiota is through the ingestion of live, beneficial microbes found in some foods and in dietary supplements. These helpful microbes are known as probiotics—a word you may have seen on food, beverage, or supplement labels. The World Health Organization defines probiotics as "live microorganisms, which when consumed in adequate amounts confer health benefits on the host." Although there is little evidence that probiotics become permanent members of the gut microbial community, their temporary residence causes healthy shifts in the microbial population to help maintain or restore a healthy balance of "friendly" bacteria and other microbes. The most compelling evidence for probiotic effectiveness appears to be limited to alleviating symptoms of both diarrhea and constipation. Although some manufacturers add probiotics to their products, probiotics are found naturally in fermented foods (for example, dairy products such as yogurt, buttermilk, and kefir). Other fermented sources of probiotics include soy sauce (if unpasteurized), tempeh (soybean cake), miso (soybean paste), and kombucha (tea).
Celiac Disease and Prebiotics
Scanning the prebiotic list, you'll notice that some of those foods—rye, wheat, and barley—are damaging for people with celiac disease because they contain gluten. Not surprisingly, then, people with celiac disease consume fewer prebiotics and therefore tend to have a significantly different mix of bacterial species in their guts than people who can eat gluten-containing prebiotics without problems
Role of Secretions in Digestion
Secretions from accessory organs such as the pancreas and gallbladder play an important role in the digestion of the hamburger in the lumen of the small intestine. Chyme that enters the small intestine from the stomach is very acidic, and if it doesn't get neutralized, it denatures and inactivates the enzymes required for digestion. The pancreas releases pancreatic juice that contains bicarbonate akin to baking soda that neutralizes the gastric acids in chyme.
What is the digestive system made up of?
The digestive system includes the organs of the GI tract and accessory organs: the salivary glands, liver, gallbladder, and pancreas, all of which secrete fluids containing a variety of agents, such as enzymes and acids, that aid in digestion.
How many Americans are affected by celiac diseases?
The hype surrounding gluten doesn't really apply to the vast majority of people—studies show that celiac disease may affect only approximately 1% of Americans. Other individuals may have GI-related or other symptoms when they consume gluten and experience what has been termed non-celiac gluten sensitivity, a real but poorly understood condition that at present is primarily self-diagnosed. The actual incidence rate is unclear, but a recent study confirmed the condition in fewer than 10% of individuals who reported gluten sensitivity. Thus, many people appear to be avoiding gluten unnecessarily, with any perceived benefits coming from heightened awareness of their overall food choices and a lower intake of refined and processed foods.
Segmentation vs. Peristalsis
There are two fundamental patterns of these muscle contractions: peristalsis and segmentation. Peristalsis creates propulsive muscle contractions to move food forward through the complete length of the GI tract, from the esophagus to the anus. Segmentation, in contrast, occurs when circular muscles in the small intestine contract in an uncoordinated fashion so that fluid contents gently slosh back and forth between the segments. These contractions serve to mix intestinal contents with digestive fluids and bring nutrients in the intestinal fluid in contact with the small intestine's absorptive surface. Similar segmentation contractions also occur in the large intestine.
Transport of Nutrients Across the Cell Membrane
To enter the mucosal cells lining the GI tract, water and small amounts of a few other nutrients can pass directly through the cell membrane by simple diffusion. The cell membrane serves as the boundary that holds the content of the body's cells in place and keeps their internal structures safe so that cells function properly. The membrane also serves as a semipermeable filter through which nutrients can enter and wastes can be excreted. Many nutrients enter the cells by facilitated diffusion, which requires a specific transport protein to help each of these nutrients move through the cell membrane. Simple diffusion and facilitated diffusion depend on the cell's concentration gradient, which moves molecules across the cell membrane from an area of high concentration to an area of low concentration. The entry of other nutrients into cells depends on active transport, which requires both a transport protein and energy to bring them across a membrane.
Role of Enzymes in Digestion
Without the work of enzymes, digestion (and many other body processes) could not occur. An enzyme is a protein molecule that functions to catalyze, or speed up, the rate at which a chemical reaction produces new compounds with altered chemical structures. These reactions may subtly alter the chemical structure, or they may produce dramatically larger or smaller molecules. Enzymes have a specific shape that will fit only molecules that have a coordinating shape, like matching pieces of a puzzle. As facilitators, the enzymes bind to their coordinating molecule, initiate a chemical reaction, and move on. Thus, enzymes can participate in these chemical reactions many times without being altered themselves. The salivary glands, stomach, pancreas, and small intestine produce enzymes to break down the chemical compounds in food into units that are small enough to be absorbed. You can recognize enzymes by their names: They end in the suffix "-ase," with the first portion of the enzyme's name identifying the type of molecule they digest. For example, the enzyme "protease" digests protein.
Chemical Digestion
breaks chemical bonds to cleave large molecules into smaller ones. - Chemical digestion is the form of digestion that involves enzymes and other substances released from salivary glands, as well as from the stomach, small intestine, and pancreas. It takes place in the mouth, small intestine, and stomach.
Acid Reflux
is a condition in which the sphincter muscles separating the stomach and the esophagus relax, so food and stomach acid are occasionally regurgitated back into the esophagus. The stomach acid can cause a burning feeling called heartburn.
Motility
is a term used to describe the contractions of the GI tract's smooth muscles that mix food with digestive fluids and propel food along the length of the tract.
Gastroesophageal reflux disease (GERD)
s a recurrent and more serious form of acid reflux that is accompanied by inflammation and/or erosion of the esophageal lining along with pain and gastrointestinal issues. Individuals with untreated GERD can be at risk of certain cancers or other complications. Fortunately, over-the-counter and prescription drugs can treat GERD, and sufferers can control symptoms by avoiding foods that cause discomfort, including alcohol, onions, chocolate, citrus fruits, and large or fatty meals.
Vomiting
the forceful movement of stomach contents from the stomach through the mouth and out of the body—can be caused by many things, including emotional stress, motion sickness, viruses, or foodborne bacteria.
4 Basic Stages of Digestion
- First, food is ingested through the mouth and enters the tubular channel called the alimentary canal, also called the gastrointestinal tract (GI tract). The GI tract extends from the mouth to the anus and includes the mouth, esophagus, stomach, small intestine, and large intestine. Second, as food passes through the GI tract, it is digested, or broken down into smaller units. Third, these smaller units of nutrients then undergo absorption, meaning that they pass into the bloodstream or lymphatic system, which transports them throughout the body. Finally, anything not absorbed is excreted as waste through the opening (the anus) at the other end.
Role of the tongue and saliva in mechanical digestion
As you chew your mouthful of hamburger, the teeth tear and crush the bread and meat, thus beginning mechanical digestion, which increases the surface area available for the enzymes to begin their work of chemical digestion. While we chew, the salivary glands near the jaw and under the tongue release saliva, which both lubricates the mouth and esophagus and contains salivary amylase, an enzyme that starts digesting the carbohydrates in the bun, as well as a lipase, which begins digesting fats in the meat. The tongue mixes saliva with the foods in the mouth and pushes the food to the back of the mouth to initiate swallowing.
Role of Large Intestine in Digestion
From the small intestine, any undigested nutrients that remain in the chyme are passed into the large intestine, which consists of the cecum, colon, and rectum. Here, little digestion or absorption take place; there are no villi. Secreted mucus protects and lubricates the smoother lining of the large intestine, making it easier for everything that's left over to be excreted as feces - But before that happens, the large intestine will extract electrolytes (sodium, chloride, and potassium), some fatty acids, vitamins (K, biotin, and folate), and water. In addition, the large intestine contains hundreds of different types of bacteria that feed on undigested fiber and starch; because humans have no enzymes that digest dietary fiber, these bacteria perform some of that function, producing gas and short-chain fatty acids in the process. Some bacteria play a role in preventing disease, reducing the activity of other bacteria that may cause it. When microbes, including bacteria, cause disease, they are known as pathogens.
How quickly does the stomach empty food into the small intestine?
How quickly the stomach empties into the small intestine depends on the composition and quantity of the foods and fluids you consume. A hamburger typically spends 24-72 hours going from the mouth to the anus, but this transit time can change because of illness, medication, your level of activity, and even your emotional state. Food with more fiber, for instance, slows emptying from the stomach, helping you feel full, or satiated. But as fiber passes into the large intestine, it can also stimulate propulsive contractions, which speeds up the transit of the intestinal contents through the rest of the digestive system, which helps promote regular bowel movements. These combined effects of fiber are important and help explain why nutrition professionals recommend healthy amounts of vegetables, fruits, whole grains, and other high-fiber foods in the diet.
Metabolism
Metabolism includes all of the chemical reactions that occur within the human body that convert one molecule into another molecule to provide energy or to synthesize substances that are required to sustain life.
Circulation of Nutrients in Blood and Lymph
Once inside the cells of the brush border of the small intestine, nutrients must reach the areas of the body where they are needed. The circulatory system, which includes both blood vessels and the lymphatic system, distributes vital nutrients to tissues and organs. For example, carbohydrates, amino acids, minerals, and water-soluble vitamins enter directly into blood vessels, where they are transported in blood to the liver before reaching other organs. Most fats (and some vitamins) enter lymph (a watery fluid surrounding tissue) and travel through the lymphatic system before they find their way into the blood. As a result, they reach the liver only after circulating throughout the rest of the body. (INFOGRAPHIC 3.9) Some nutrients as well as many of the toxins we ingest are largely removed from the blood by the liver, where they are then metabolized.
The Role of the Esophagus in Bolus Transport to The Stomach
Once the hamburger has been chewed and coated in saliva, it becomes a soft, moist lump of food known as a bolus, which is swallowed and passed through the throat. It then enters the esophagus, a roughly 10-inch-long muscular tube that transports the bolus of burger from the mouth to the stomach, relying on gravity and peristalsis. Positioned at the junction of the esophagus and the stomach is a circular muscle ( sphincter) that normally functions as a one-way valve (as do other sphincters in the body). As food nears the lower-esophageal sphincter, that sphincter relaxes to let food pass into the stomach; otherwise, the sphincter stays tightly closed to prevent foods and secretions in the stomach from moving backward into the esophagus.
Gallstones
Painful gallstones can develop when substances in bile crystallize into small pebbles within the gallbladder. With gallstones, the gallbladder may not be able to empty properly, causing pain in the upper abdomen. Recurrent gallstones generally require the surgical removal of the gallbladder.
Prebiotics
Prebiotics are primarily undigested carbohydrates that healthy bacteria use to boost their growth in the large intestine. (You can think of prebiotics as substances that "feed" or nourish good bacteria.) Eating prebiotics may prevent and treat diarrhea and colon cancer, boost the absorption of minerals, reduce levels of fat in the blood, and help control blood glucose. Some of these benefits may result from the short-chain fatty acids that are produced as bacteria use the prebiotics. These short-chain fatty acids, which are only three or four carbons in length, are then absorbed and provide us with a little energy as well. Prebiotics can also reduce the risk of gastrointestinal infections, because in order to establish infections, "bad" bacteria must adhere to the lining of the gut. As "good" bacteria increase in the gut in response to the ingestion of prebiotics (or in response to probiotics), they take up more and more real estate, making it difficult for the bad bacteria to find a home. In addition, as the number of good bacteria increases, they grab the majority of the available nutrients, leaving little for the unwanted microbes. Sources of prebiotics include chicory, Jerusalem artichokes, whole-grain rye, oats, wheat, and barley, leeks, garlic, and onion.
Gut Microbiota in the GI Tract
The bacteria that inhabit our GI tract are the dominant component of our gut microbiota—the complex community of all microorganisms (such as bacteria and even fungi) that live there. (INFOGRAPHIC 3.11) A healthy gut microbiota contains a diverse and well-balanced array of hundreds of different types of bacteria that have an intricate and interactive relationship with each other and their human host. The significance of this relationship is demonstrated by recent observations that there is communication between microbes in our gut and the brain. It is then perhaps of little surprise that disruptions to the balance of microbes inhabiting our gut, and/or a decrease in their diversity, is linked to a number of human maladies, including inflammatory bowel diseases, allergies, autoimmune diseases (such as celiac disease), diabetes, cancer, obesity, depression and anxiety, and perhaps even autism. Consequently, maintaining an appropriate gut microbial balance is critically important to our overall health. Although many factors affect the intestinal microbial population (for example, geography, genetics, age, medications, and stress), diet has a potent influence on its composition.
The Role of the Stomach in Digestion of a Bolus
The bolus then enters the stomach, a muscular, J-shaped sack that can accommodate up to 4 cups of food and generally takes about two to four hours to empty. The stomach secretes gastric juices that contain hydrochloric acid (HCL), which help to unfold the proteins in the food through chemical digestion. The gastric juices also contain enzymes such as proteases that digest proteins and lipase that digests fat. Importantly, the gastric juices also contain mucus that lubricates the food and protects the stomach lining from acidity. The particularly forceful peristaltic contractions of the stomach vigorously churn the hamburger bolus, fragmenting it into fine particles that are dispersed throughout the gastric fluid. This essentially grinds the food into a semiliquid mass called chyme. A few teaspoons at a time, chyme is passed along to the small intestine, moving through the partially relaxed pyloric sphincter that functions as a sieve, allowing only small food particles (generally smaller than 1 millimeter, or about the size of the tip of a sharpened pencil) to pass through
Role of lumen and mucus (mucosal cells)
The inside space of the GI tract is called the lumen, which is lined with a layer of mucosal cells called the mucosa, so named because it is protected by a layer of thick fluid called mucus. Mucosal cells allow our body to absorb nutrients so that they can be transported by the blood or lymph to where they are needed.
The Role of the Liver in Digestion
The liver and the gallbladder also help to digest the many lipids found in the hamburger. The liver produces bile—which is stored in the gallbladder, a small, pear-shaped sac below the liver in the right upper abdomen—that contains substances critical for effective lipid digestion. The hormone cholecystokinin (CCK) is released from the small intestine in response to the hamburger's fats and protein in the small intestine; CCK stimulates the gallbladder to release bile and the pancreas to secrete juice into the lumen of the small intestine. In addition to bicarbonate, pancreatic juice contains enzymes—lipases, proteases, and amylase—that further break down the hamburger's large fat, protein, and carbohydrate molecules into smaller ones. Enzymes located in the brush border complete the digestion of the burger's carbohydrates and proteins.
The Beginning Processes of Digestion
The object of digestion is to break down large molecules into smaller units, and the first stop is the mouth. Picture a hamburger poised to enter your mouth, or oral cavity. The first bite, or even the mouth-watering anticipation of the first bite, initiates the mechanical and chemical processes of digestion.
What is the primary function of the digestive system?
The primary function of the digestive system is to digest, or progressively break down, the nutrients in our foods into compounds that are small enough to be taken up into our body.
Small Intestine and Digestion
The small intestine is the primary site for the digestion of food and the absorption of nutrients, and as we shall see, it is where digestion can go awry in people with celiac disease. The small intestine has three sections: the duodenum, the first portion of the small intestine after the stomach; the jejunum, the middle portion; and the ileum, the last and longest portion. The small intestine isn't actually "small" at all; it is a coiled hollow tube approximately 20 feet long and 1 1/2 inches wide, and several structural features give it a surface area approximately equal to the size of a tennis court. For example, the internal circular folds of the small intestine carry fingerlike projections called villi that increase its surface area for absorption. These villi are densely covered with fine hairlike projections called microvilli that further increase surface area and the efficiency of absorption. Because these structures give the lining of the small intestine a brushlike appearance (when viewed with a microscope), the lining is often called the brush border
Taste Buds
The tongue does more than help mix and swallow food, although—it's also part of the reason we enjoy that savory, juicy burger. The tongue contains taste buds that identify or sense foods on the basis of specific flavors or tastes. Food is a combination of five primary tastes: sweet, sour, salty, bitter, and umami, a more recently recognized savory flavor that's harder to identify but may be an element of your burger, as it's found in meats, seafood, cheese, and some vegetables. The number of taste buds we have declines with age, which explains why children—whose tongues have abundant taste-sensing cells—are often averse to strong flavors and may prefer to eat their burgers plain (or with a little ketchup) than with spicy mayonnaise or hot sauce. Taste buds don't just tell us if something is too bitter or salty; they also create signals that tell the rest of the GI tract to prepare for the next steps of digestion.
Why is the incidence of celiac disease on the rise?
Unfortunately, no one yet knows exactly why the incidence of this immune condition is rising, says Murray, although there are many possibilities. Celiac disease tends to appear more commonly in people with other immune disorders, which suggests that something in the environment may be interacting with genetic factors to alter their immune response. In other words, the rising incidence of celiac disease may be a sign of the complex interplay between our environment, our diet, and our genetics. But the good news is that celiac disease is largely treatable. By avoiding gluten, people with celiac disease can not only avoid unpleasant GI-symptoms but also reduce the risk of other autoimmune issues and potentially certain cancers. And for the few people with celiac disease, not eating gluten will allow them to better absorb nutrients from their diet and enjoy good health
diarrhea
defined as frequent loose and watery bowel movements that occur more than three times a day.
Constipation
having a bowel movement fewer than three times per week, is another symptom common in digestive disorders. In otherwise healthy people, a low-fiber diet, certain medications, lack of physical activity, or dehydration may be contributors.
inflamatory bowel disease (IBD)
is a broad term that describes serious, chronic conditions that are caused by an abnormal response by the body's immune system, which causes inflammation of the GI tract. The most common IBDs are ulcerative colitis and Crohn's disease. In ulcerative colitis, the mucosa of the intestine becomes irritated and swollen and ulcers (open wounds) develop. Ulcerative colitis is often most severe in the lower colon (the rectum), which can cause diarrhea. Crohn's disease most often affects the lower portions of the small intestine and parts of the large intestine. However, it can attack any part of the digestive tract.
Diverticular disease
is a common condition characterized by pouches or pockets in the wall or lining of any portion of the digestive tract, which can develop when the inner layer of the digestive tract pushes through weak spots in the outer layer. Age is a primary risk factor for diverticular disease, with an estimated one-third of Americans developing the condition by 60 years of age and two-thirds by age 85. A diet rich in fiber along with an active lifestyle appear to have a significant protective effect.
irritable bowel syndrome (IBS)
is a group of symptoms, including abdominal pain, bloating, diarrhea, and other discomforts, caused by changes in how the GI works. This disorder affects the muscle contraction of the colon (large intestine). Although it can be very uncomfortable and inconvenient, IBS does not lead to serious disease such as cancer, and it does not permanently harm the large intestine. IBS is one of the most common disorders diagnosed by doctors; up to 20% of adults in the United States have symptoms of IBS. Certain foods may trigger IBS symptoms, so individuals with the condition must take note of the foods or beverages, such as caffeine, alcohol, fatty foods, and some non-nutritive sweeteners, that may cause difficulty. When diarrhea occurs, water consumption must be increased to avoid dehydration. An increase in dietary fiber can help deal with the symptom of constipation. Some medications are prescribed for individuals with IBS, and probiotics may be helpful for some people.
Mechanical Digestion
is the physical fragmentation of foods into small particles - Mechanical digestion begins in the mouth, where teeth crush and tear food into small bits. It continues in the stomach, as forceful contractions vigorously churn food. This churning action disperses the small food fragments and exposes large molecules to the digestive fluids that will chemically dismantle them. In many cases, mechanical digestion is all that is required to release many vitamins, minerals, and phytochemicals from foods that are then taken up by mucosal cells lining the small intestine
