Information

Digestion Enzymes in Carbohydrate Metabolism?

Digestion Enzymes in Carbohydrate Metabolism?



We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Digestion of carbohydrates is ending in small intestine with mainly disaccharidases. Isomaltose is broken down to 2 molecules of glucose by the enzyme called alpha dextrinase(oligo-1,6 glucosidase or isomaltase) which hydrloyze 1,6 linkage of isomaltose. In the case of glycogen metabolism there is debranching enzymes that are transferase and alpha 1,6 glucosidase. According to this informations can we say that alpha dextrinase (isomaltase) and alpha 1,6glucosidase are the same enzyme ?


1,6-glucosidases are a class of enzymes and not just one enzyme. It does not mean that all the members of this class are the same enzymes. They catalyse the same kind of reactions but their properties and substrate specificities differ. Check BRENDA for details.

BTW, dextrin-1,6-glucosidase is a synonym for amylo-alpha-1,6-glucosidase. Other 1,6-glucosidases are different enzymes with different EC numbers.


The Activity of Carbohydrate-Degrading Enzymes in the Development of Brood and Newly Emerged workers and Drones of the Carniolan Honeybee, Apis mellifera carnica

The activity of glycogen Phosphorylase and carbohydrate hydrolyzing enzymes α-amylase, glucoamylase, trehalase, and sucrase was studied in the development of the Carniolan honey bee, Apis mellifera carnica Pollman (Hymenoptera: Apidae), from newly hatched larva to freshly emerged imago of worker and drone. Phosphorolytic degradation of glycogen was significantly stronger than hydrolytic degradation in all developmental stages. Developmental profiles of hydrolase activity were similar in both sexes of brood high activity was found in unsealed larvae, the lowest in prepupae followed by an increase in enzymatic activity. Especially intensive increases in activity occurred in the last stage of pupae and newly emerged imago. Besides α-amylase, the activities of other enzymes were higher in drone than in worker broods. Among drones, activity of glucoamylase was particularly high, ranging from around three times higher in the youngest larvae to 13 times higher in the oldest pupae. This confirms earlier suggestions about higher rates of metabolism in drone broods than in worker broods.


What you'll learn:

The food that is consumed by the body, travels down the digestive tract, where it is acted upon by various enzymes and thus utilized by the body. The breakdown of carbohydrates begins in the mouth and ends at the colon. The undigested carbohydrates are then expelled out of the body. Several steps occur between the initiation and passage of carbohydrates.

The process of digestion begins as soon as the food enters the mouth. First of all, the chewing mechanism occurs. This is aided by the secretions of the secretory glands that moisten the food while it is being chewed. The secretion secreted from your secretion glands moistens food as it is chewed. The human saliva produces a substance that acts as a catalyst in the digestion process. It is referred to as an enzyme that begins the breakdown method of the sugars. The chewed food is swallowed into a small bolus-like form and passes through the abdominal cavity. The muscular tract that joins the mouth and the stomach provides this passage. Acidic juices are released in the abdomen that destroy the harmful microorganisms present in the food. From there, it further enters the next step of digestion. The food then moves from the abdomen into the small intestine. This causes the exocrine glands to unleash duct gland enzyme. This catalyst converts the food and releases dextrin and malt sugar. Next is the formation of maltase, disaccharidase, and sucrase. These enzymes provide an added advantage and break down the sugars into more monosaccharide units. These simple forms of sugars are directly absorbed by the small intestine. In the next step, there is the processing of the absorbing material by the liver. Polyose form remains in the liver while the aldohexose form is eliminated out from the body through blood. The unabsorbed material moves to the colon. Enteric microorganisms that inhabit the colon, counteract the undigested material. Most of the material has fiber content that cannot be digested by the body. Therefore, from the colon, it is moved out together with the stools.


Summary of Carbohydrate Digestion:

The primary goal of carbohydrate digestion is to break polysaccharides and disaccharides into monosaccharides, which can be absorbed into the bloodstream.

1. After eating, nothing needs to happen in the digestive tract to the monosaccharides in a food like grapes, because they are already small enough to be absorbed as is.

2. Disaccharides in that grape or in a food like milk are broken down (enzymatically digested) in the digestive tract to monosaccharides (glucose, galactose, and fructose).

3. Starch in food is broken down (enzymatically digested) in the digestive tract to glucose molecules.

4. Fiber in food is not enzymatically digested in the digestive tract, because humans don’t have enzymes to do this. However, some dietary fiber is fermented in the large intestine by gut microbes.

Carbohydrates in food

Is this carbohydrate enzymatically digested? (enzyme name)


Pancreatic Amylase and Maltase

As the combination of gastric juices and partially digested food enters the small intestine, the pancreas secretes pancreatic juices, which contain the enzyme pancreatic amylase. This enzyme acts on the remaining polysaccharides and breaks them into disaccharide units of maltose. In the final step of complex carbohydrate digestion, the enzyme maltase present in the lining of the small intestine breaks maltose into two units of glucose. Glucose is then absorbed and enters the bloodstream.


17 Chapter 17: Digestive System

All living organisms need nutrients to survive. While plants can obtain nutrients from their roots and the energy molecules required for cellular function through the process of photosynthesis, animals obtain their nutrients by the consumption of other organisms. At the cellular level, the biological molecules necessary for animal function are amino acids, lipid molecules, nucleotides, and simple sugars. However, the food consumed consists of protein, fat, and complex carbohydrates. Animals must convert these macromolecules into the simple molecules required for maintaining cellular function. The conversion of the food consumed to the nutrients required is a multistep process involving digestion and absorption. During digestion, food particles are broken down to smaller components, which are later absorbed by the body. This happens by both physical means, such as chewing, and by chemical means, via enzyme-catalyzed reactions.

One of the challenges in human nutrition is maintaining a balance between food intake, storage, and energy expenditure. Taking in more food energy than is used in activity leads to storage of the excess in the form of fat deposits. The rise in obesity and the resulting diseases like type 2 diabetes makes understanding the role of diet and nutrition in maintaining good health all the more important.

After studying this chapter, you should be able to:

  • With regards to the anatomy of the digestive system
    • a. Locate and recognize the basic function of G.I. tract organs and accessory organs.
    • b. Diagram the path of food as it passes through the digestive system.

    The Digestive System

    The process of digestion begins in the mouth (oral cavity) with the intake of food (Figure). The teeth play an important role in masticating (chewing) or physically breaking food into smaller particles. This action not only decreases the size of the food particles to facilitate swallowing, but also increases surface area for chemical digestion. The enzymes present in saliva (amylase and lipase) also begin to chemically break down food (starch and fats, respectively). The food is then swallowed and enters the esophagus —a long tube that connects the mouth to the stomach. Using peristalsis , or wave-like smooth-muscle contractions, the muscles of the esophagus push the food toward the stomach. The stomach contents are extremely acidic, with a pH between 1.5 and 2.5. This acidity kills microorganisms, breaks down food tissues, and activates digestive enzymes. Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion. The smaller molecules are absorbed into the blood stream through the epithelial cells lining the walls of the small intestine. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces it is stored in the rectum until it is excreted through the anus.

    The components of the human digestive system are shown. The GI tract is the tube that includes the oral cavity, esophagus, stomach, small intestine, large intestine, and rectum. The accessory organs are those that indirectly join to this tube via ducts and include the salivary glands, liver, gall bladder, and pancreas.

    Oral Cavity

    Both physical and chemical digestion begin in the mouth or oral cavity , which is the point of entry of food into the digestive system. The food is broken into smaller particles by mastication, the chewing action of the teeth. All mammals have teeth and can chew their food to begin the process of physically breaking it down into smaller particles.

    The chemical process of digestion begins during chewing as food mixes with saliva, produced by the salivary glands (Figure). Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains lysozyme, which has antibacterial action. It also contains an enzyme called salivary amylase that begins the process of converting starches in the food into a disaccharide called maltose. Another enzyme called lipase is produced by cells in the tongue to break down fats. The chewing and wetting action provided by the teeth and saliva prepare the food into a mass called the bolus for swallowing. The tongue helps in swallowing—moving the bolus from the mouth into the pharynx. The pharynx opens to two passageways: the esophagus and the trachea. The esophagus leads to the stomach and the trachea leads to the lungs. The epiglottis is a flap of tissue that covers the tracheal opening during swallowing to prevent food from entering the lungs.

    (a) Digestion of food begins in the mouth. (b) Food is masticated by teeth and moistened by saliva secreted from the salivary glands. Enzymes in the saliva begin to digest starches and fats. With the help of the tongue, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of work by Mariana Ruiz Villareal)

    Esophagus

    The esophagus is a tubular organ that connects the mouth to the stomach. The chewed and softened food (i.e. the bolus) passes through the esophagus after being swallowed. The smooth muscles of the esophagus undergo peristalsis (contractions) that pushes the food toward the stomach. The peristaltic wave is unidirectional—it moves food from the mouth the stomach, and reverse movement is not possible, except in the case of the vomit reflex. The peristaltic movement of the esophagus is an involuntary reflex it takes place in response to the act of swallowing and you don’t exert conscious control over it.

    Ring-like muscles called sphincters form valves in the digestive system. The gastro-esophageal sphincter (a.k.a. lower esophageal or cardiac sphincter) is located at the stomach end of the esophagus. In response to swallowing and the pressure exerted by the bolus of food, this sphincter opens, and the bolus enters the stomach. When there is no swallowing action, this sphincter is shut and prevents the contents of the stomach from traveling up the esophagus. Acid reflux or “heartburn” occurs when the acidic digestive juices escape back into the esophagus and the low pH irritates the unprotected surface. Prolonged and repeated exposure of the esophagus to this acidity can cause physical damage.

    Stomach

    A large part of protein digestion occurs in the stomach (Figure). The stomach is a saclike organ that secretes gastric digestive juices.

    Protein digestion is carried out by an enzyme called pepsin in the stomach chamber. The highly acidic environment kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the catabolism of protein in the food. Chemical digestion is facilitated by the churning action of the stomach caused by contraction and relaxation of smooth muscles. The partially digested food and gastric juice mixture is called chyme . Gastric emptying occurs within two to six hours after a meal. Only a small amount of chyme is released into the small intestine at a time. The movement of chyme from the stomach into the small intestine is regulated by hormones, stomach distension and muscular reflexes that influence the pyloric sphincter. The low pH of the stomach will denature the amylase and lipase that were secreted in the mouth. Therefore, over time, chemical digestion of starches and fats will decrease in the stomach.

    The stomach lining is unaffected by pepsin and the acidity because pepsin is released in an inactive form (pepsinogen) that is activated by the low pH. The stomach also has a thick mucus lining that protects the underlying tissue.

    Small Intestine

    Chyme moves from the stomach to the small intestine. The small intestine is the organ where the digestion of protein, fats, and carbohydrates is completed. The small intestine is a long tube-like organ with a highly folded surface containing finger-like projections called the villi. The top surface of each villus has many microscopic projections called microvilli. The epithelial cells at the surface of these structures absorb nutrients from the digested food and release them to the bloodstream on the other side. Methods of transport previously discussed (e.g.active transport)are used during this movement. The villi and microvilli, with their many folds, increase the surface area of the small intestine and increase absorption efficiency of the nutrients.

    The human small intestine is over 6 m (19.6 ft) long and is divided into three parts: the duodenum, the jejunum and the ileum. The duodenum is separated from the stomach by the pyloric sphincter. The chyme is mixed with pancreatic juices, an alkaline/basic solution rich in bicarbonate that neutralizes the acidity of chyme from the stomach. This result raises the pH and creates an environment that is appropriate for enzymes. Pancreatic juices contain several digestive enzymes (amylase, trypsin, and lipase) that break down starches, proteins, and fats, respectively. Bile is produced in the liver and stored and concentrated in the gallbladder it enters the duodenum through the bile duct. Bile contains bile salts, which make lipids accessible to the water-soluble enzymes. This is accomplished via a process called emulsification, a type of physical digestion. Bile keeps fat droplets from coming back together again, thus increasing the surface area available to lipase. The wall of the small intestines secrete disaccharidases, which faciltate digestion of disaccharides (e.g. maltose, sucrose, and lactose) into their respective monosaccharides. The monosaccharides, amino acids, bile salts, vitamins, and other nutrients are absorbed by the cells of the intestinal lining.

    The undigested food is sent to the colon from the ileum via peristaltic movements. The ileum ends and the large intestine begins at the ileocecal valve. The vermiform, “worm-like,” appendix is located at the ileocecal valve. The appendix of humans has a minor role in immunity.

    Large Intestine

    The large intestine reabsorbs the water from indigestible food material and processes the waste material (Figure). The human large intestine is much smaller in length compared to the small intestine but larger in diameter. It has three parts: the cecum, the colon, and the rectum. The cecum joins the ileum to the colon and is the receiving pouch for the waste matter. The colon is home to many bacteria or “intestinal flora” that aid in the digestive processes. The colon has four regions, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. The main functions of the colon are to extract the water and mineral salts from undigested food, and to store waste material.

    The large intestine reabsorbs water from undigested food and stores waste until it is eliminated. (credit: modification of work by Mariana Ruiz Villareal)

    The rectum (Figure) stores feces until defecation. The feces are propelled using peristaltic movements during elimination. The anus is an opening at the far-end of the digestive tract and is the exit point for the waste material. Two sphincters regulate the exit of feces, the inner sphincter is involuntary and the outer sphincter is voluntary.

    Accessory Organs

    The organs discussed above are the organs of the digestive tract through which food passes. Accessory organs add secretions and enzymes that break down food into nutrients. Accessory organs include the salivary glands, the liver, the pancreas, and the gall bladder. The secretions of the liver, pancreas, and gallbladder are regulated by hormones in response to food consumption.

    The liver is the largest internal organ in humans and it plays an important role in digestion of fats and detoxifying blood. The liver produces bile, a digestive juice that is required for the breakdown of fats in the duodenum. The liver also processes the absorbed vitamins and fatty acids and synthesizes many plasma proteins. The gallbladder is a small organ that aids the liver by storing bile and concentrating bile salts.

    The pancreas secretes bicarbonate that neutralizes the acidic chyme and a variety of enzymes (trypsin, amylase, and lipase) for the digestion of proteins, carbohydrates, and fats, respectively.

    The stomach has an extremely acidic environment where most of the protein gets digested. (credit: modification of work by Mariana Ruiz Villareal)

    Nutrition

    The human diet should be well balanced to provide nutrients required for bodily function and the minerals and vitamins required for maintaining structure and regulation necessary for good health and reproductive capability (Figure).

    For humans, a balanced diet includes fruits, vegetables, grains, protein, and dairy. (credit: USDA)

    Explore this interactive United States Department of Agriculture website to learn more about each food group and the recommended daily amounts.

    The organic molecules required for building cellular material and tissues must come from food. During digestion, digestible carbohydrates are ultimately broken down into glucose and used to provide energy within the cells of the body. Complex carbohydrates, including polysaccharides, can be broken down into glucose through biochemical modification however, humans do not produce the enzyme necessary to digest cellulose (fiber). The intestinal flora in the human gut are able to extract some nutrition from these plant fibers. These plant fibers are known as dietary fiber and are an important component of the diet. The excess sugars in the body are converted into glycogen and stored for later use in the liver and muscle tissue. Glycogen stores are used to fuel prolonged exertions, such as long-distance running, and to provide energy during food shortage. Fats are stored under the skin of mammals for insulation and energy reserves.

    Proteins in food are broken down during digestion and the resulting amino acids are absorbed. All of the proteins in the body must be formed from these amino-acid constituents no proteins are obtained directly from food.

    Fats add flavor to food and promote a sense of satiety or fullness. Fatty foods are also significant sources of energy, and fatty acids are required for the construction of lipid membranes. Fats are also required in the diet to aid the absorption of fat-soluble vitamins and the production of fat-soluble hormones.

    While the animal body can synthesize many of the molecules required for function from precursors, there are some nutrients that must be obtained from food. These nutrients are termed essential nutrients , meaning they must be eaten, because the body cannot produce them. Essential nutrients include some fatty acids, some amino acids, vitamins, and minerals.

    Section Summary

    There are many organs that work together to digest food and absorb nutrients. The mouth is the point of ingestion and the location where both mechanical and chemical breakdown of food begins. Saliva contains an enzyme called amylase that breaks down carbohydrates and an enxyme lipase that breaks down triglycerides. The food bolus travels through the esophagus by peristaltic movements to the stomach. The stomach has an extremely acidic environment. The enzyme pepsin digests protein in the stomach. Further digestion and absorption take place in the small intestine. The large intestine reabsorbs water from the undigested food and stores waste until elimination.

    Carbohydrates, proteins, and fats are the primary components of food. Some essential nutrients are required for cellular function but cannot be produced by the animal body. These include vitamins (both fat and water soluble) , minerals, some fatty acids, and some amino acids. Food intake in more than necessary amounts is stored as glycogen in the liver and muscle cells, and in adipose tissue. Excess adipose storage can lead to obesity and serious health problems.

    Adapted from Openstax Human Biology


    Vitamins

    Vitamins can be either water-soluble or lipid-soluble. Fat-soluble vitamins are absorbed in the same manner as lipids. It is important to consume some amount of dietary lipid to aid the absorption of lipid-soluble vitamins. Water-soluble vitamins can be directly absorbed into the bloodstream from the intestine.

    Review Figure 5.22 on your own. You can also use this website, which is an overview of the digestion of protein, fat, and carbohydrates.

    Figure 5.22. Mechanical and chemical digestion of food takes place in many steps, beginning in the mouth and ending in the rectum.


    The Human Digestive System

    The process of digestion begins in the mouth with the intake of food (Figure 1). The teeth play an important role in masticating (chewing) or physically breaking food into smaller particles. The enzymes present in saliva also begin to chemically break down food. The food is then swallowed and enters the esophagus—a long tube that connects the mouth to the stomach. Using peristalsis, or wave-like smooth-muscle contractions, the muscles of the esophagus push the food toward the stomach. The stomach contents are extremely acidic, with a pH between 1.5 and 2.5. This acidity kills microorganisms, breaks down food tissues, and activates digestive enzymes. Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion. The smaller molecules are absorbed into the blood stream through the epithelial cells lining the walls of the small intestine. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces it is stored until it is excreted through the anus.

    Figure 1. The components of the human digestive system are shown.

    Oral Cavity

    Both physical and chemical digestion begin in the mouth or oral cavity, which is the point of entry of food into the digestive system. The food is broken into smaller particles by mastication, the chewing action of the teeth. All mammals have teeth and can chew their food to begin the process of physically breaking it down into smaller particles.

    The chemical process of digestion begins during chewing as food mixes with saliva, produced by the salivary glands (Figure 2). Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains lysozyme, which has antibacterial action. It also contains an enzyme called salivary amylase that begins the process of converting starches in the food into a disaccharide called maltose. Another enzyme called lipase is produced by cells in the tongue to break down fats. The chewing and wetting action provided by the teeth and saliva prepare the food into a mass called the bolus for swallowing. The tongue helps in swallowing—moving the bolus from the mouth into the pharynx. The pharynx opens to two passageways: the esophagus and the trachea. The esophagus leads to the stomach and the trachea leads to the lungs. The epiglottis is a flap of tissue that covers the tracheal opening during swallowing to prevent food from entering the lungs.

    Figure 2. (a) Digestion of food begins in the mouth. (b) Food is masticated by teeth and moistened by saliva secreted from the salivary glands. Enzymes in the saliva begin to digest starches and fats. With the help of the tongue, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of work by Mariana Ruiz Villareal)

    Esophagus

    The esophagus is a tubular organ that connects the mouth to the stomach. The chewed and softened food passes through the esophagus after being swallowed. The smooth muscles of the esophagus undergo peristalsis that pushes the food toward the stomach. The peristaltic wave is unidirectional—it moves food from the mouth the stomach, and reverse movement is not possible, except in the case of the vomit reflex. The peristaltic movement of the esophagus is an involuntary reflex it takes place in response to the act of swallowing.

    Ring-like muscles called sphincters form valves in the digestive system. The gastro-esophageal sphincter (or cardiac sphincter) is located at the stomach end of the esophagus. In response to swallowing and the pressure exerted by the bolus of food, this sphincter opens, and the bolus enters the stomach. When there is no swallowing action, this sphincter is shut and prevents the contents of the stomach from traveling up the esophagus. Acid reflux or “heartburn” occurs when the acidic digestive juices escape into the esophagus.

    Stomach

    A large part of protein digestion occurs in the stomach (Figure 4). The stomach is a saclike organ that secretes gastric digestive juices.

    Protein digestion is carried out by an enzyme called pepsin in the stomach chamber. The highly acidic environment kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the catabolism of protein in the food. Chemical digestion is facilitated by the churning action of the stomach caused by contraction and relaxation of smooth muscles. The partially digested food and gastric juice mixture is called chyme. Gastric emptying occurs within two to six hours after a meal. Only a small amount of chyme is released into the small intestine at a time. The movement of chyme from the stomach into the small intestine is regulated by hormones, stomach distension and muscular reflexes that influence the pyloric sphincter.

    The stomach lining is unaffected by pepsin and the acidity because pepsin is released in an inactive form and the stomach has a thick mucus lining that protects the underlying tissue.

    Small Intestine

    Chyme moves from the stomach to the small intestine. The small intestine is the organ where the digestion of protein, fats, and carbohydrates is completed. The small intestine is a long tube-like organ with a highly folded surface containing finger-like projections called the villi. The top surface of each villus has many microscopic projections called microvilli. The epithelial cells of these structures absorb nutrients from the digested food and release them to the bloodstream on the other side. The villi and microvilli, with their many folds, increase the surface area of the small intestine and increase absorption efficiency of the nutrients.

    The human small intestine is over 6 m (19.6 ft) long and is divided into three parts: the duodenum, the jejunum and the ileum. The duodenum is separated from the stomach by the pyloric sphincter. The chyme is mixed with pancreatic juices, an alkaline solution rich in bicarbonate that neutralizes the acidity of chyme from the stomach. Pancreatic juices contain several digestive enzymes that break down starches, disaccharides, proteins, and fats. Bile is produced in the liver and stored and concentrated in the gallbladder it enters the duodenum through the bile duct. Bile contains bile salts, which make lipids accessible to the water-soluble enzymes. The monosaccharides, amino acids, bile salts, vitamins, and other nutrients are absorbed by the cells of the intestinal lining.

    The undigested food is sent to the colon from the ileum via peristaltic movements. The ileum ends and the large intestine begins at the ileocecal valve. The vermiform, “worm-like,” appendix is located at the ileocecal valve. The appendix of humans has a minor role in immunity.

    Large Intestine

    The large intestine reabsorbs the water from indigestible food material and processes the waste material (Figure 3). The human large intestine is much smaller in length compared to the small intestine but larger in diameter. It has three parts: the cecum, the colon, and the rectum. The cecum joins the ileum to the colon and is the receiving pouch for the waste matter. The colon is home to many bacteria or “intestinal flora” that aid in the digestive processes. The colon has four regions, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. The main functions of the colon are to extract the water and mineral salts from undigested food, and to store waste material.

    Figure 3. The large intestine reabsorbs water from undigested food and stores waste until it is eliminated. (credit: modification of work by Mariana Ruiz Villareal)

    The rectum (Figure 3) stores feces until defecation. The feces are propelled using peristaltic movements during elimination. The anus is an opening at the far-end of the digestive tract and is the exit point for the waste material. Two sphincters regulate the exit of feces, the inner sphincter is involuntary and the outer sphincter is voluntary.

    Accessory Organs

    The organs discussed above are the organs of the digestive tract through which food passes. Accessory organs add secretions and enzymes that break down food into nutrients. Accessory organs include the salivary glands, the liver, the pancreas, and the gall bladder. The secretions of the liver, pancreas, and gallbladder are regulated by hormones in response to food consumption.

    The liver is the largest internal organ in humans and it plays an important role in digestion of fats and detoxifying blood. The liver produces bile, a digestive juice that is required for the breakdown of fats in the duodenum. The liver also processes the absorbed vitamins and fatty acids and synthesizes many plasma proteins. The gallbladder is a small organ that aids the liver by storing bile and concentrating bile salts.

    The pancreas secretes bicarbonate that neutralizes the acidic chyme and a variety of enzymes for the digestion of protein and carbohydrates.

    ART CONNECTION Figure 4. The stomach has an extremely acidic environment where most of the protein gets digested. (credit: modification of work by Mariana Ruiz Villareal)

    With obesity at high rates in the United States, there is a public health focus on reducing obesity and associated health risks, which include diabetes, colon and breast cancer, and cardiovascular disease. How does the food consumed contribute to obesity?

    Fatty foods are calorie-dense, meaning that they have more calories per unit mass than carbohydrates or proteins. One gram of carbohydrates has four calories, one gram of protein has four calories, and one gram of fat has nine calories. Animals tend to seek lipid-rich food for their higher energy content. Greater amounts of food energy taken in than the body’s requirements will result in storage of the excess in fat deposits.

    Excess carbohydrate is used by the liver to synthesize glycogen. When glycogen stores are full, additional glucose is converted into fatty acids. These fatty acids are stored in adipose tissue cells—the fat cells in the mammalian body whose primary role is to store fat for later use.

    The rate of obesity among children is rapidly rising in the United States. To combat childhood obesity and ensure that children get a healthy start in life, in 2010 First Lady Michelle Obama launched the Let’s Move! campaign. The goal of this campaign is to educate parents and caregivers on providing healthy nutrition and encouraging active lifestyles in future generations. This program aims to involve the entire community, including parents, teachers, and healthcare providers to ensure that children have access to healthy foods—more fruits, vegetables, and whole grains—and consume fewer calories from processed foods. Another goal is to ensure that children get physical activity. With the increase in television viewing and stationary pursuits such as video games, sedentary lifestyles have become the norm. Visit www.letsmove.gov to learn more.


    Digestion Enzymes in Carbohydrate Metabolism? - Biology

    In this chapter, we have reviewed a lot of information about the digestive system that we can use to our advantage on Test Day. We began with an overview of the anatomy, keeping in mind that the system is designed to carry out extracellular digestion. Considering that all our foodstuffs are made up of fats, proteins, and carbohydrates, these compounds have to be broken down to their simplest molecular forms before they can be absorbed and distributed to the tissues and cells of the body. As we moved through the gastrointestinal tract, we discussed whether each organ was a site of absorption, digestion, or both. We spent a good bit of time discussing each of the enzymes involved in digestion and their specific purposes. While digestion occurs primarily in the oral cavity, stomach, and duodenum, absorption occurs primarily in the jejunum and ileum, where the method of transport into the circulatory system is slightly different depending on the compound. Finally, we discussed the three segments of the large intestine and their roles in water and salt absorption, as well as the temporary storage of waste products. Although the amount of information about the digestive system may seem overwhelming, the underlying concepts are relatively straightforward, and a systematic approach (like charts, tables, or flashcards) will help you manage this content.

    In the end, the digestive system’s main purpose is to break down energy-containing compounds and get them into the circulation so they can be used by the rest of the body. Equally as important are the systems the body has for getting rid of compounds from the blood. Buildup of waste products like ammonia, urea, potassium, and hydrogen ions can lead to serious pathology. For instance, hyperammonemia (buildup of ammonia in the blood) can lead to severe, permanent neurological damage. Hyperkalemia (buildup of potassium in the blood) can quickly cause a fatal heart attack. Temperature regulation is similarly important both hyperthermia and hypothermia can lead to organ dysfunction and, ultimately, death. In the next chapter, we turn our attention to these regulatory systems: the renal system and the skin.

    Concept Summary

    Anatomy of the Digestive System

    ·&emspIntracellular digestion involves the oxidation of glucose and fatty acids to make energy. Extracellular digestion occurs in the lumen of the alimentary canal.

    o Mechanical digestion is the physical breakdown of large food particles into smaller food particles.

    o Chemical digestion is the enzymatic cleavage of chemical bonds, such as the peptide bonds of proteins or the glycosidic bonds of starches.

    ·&emspThe pathway of the digestive tract is: oral cavity &rarr pharynx &rarr esophagus &rarr stomach &rarr small intestine &rarr large intestine &rarr rectum

    ·&emspThe accessory organs of digestion are the salivary glands, pancreas, liver, and gallbladder.

    ·&emspThe enteric nervous system is in the wall of the alimentary canal and controls peristalsis. Its activity is upregulated by the parasympathetic nervous system and downregulated by the sympathetic nervous system.

    Ingestion and Digestion

    ·&emspMultiple hormones regulate feeding behavior, including antidiuretic hormone (ADH or vasopressin) and aldosterone, which promote thirst glucagon and ghrelin, which promote hunger and leptin and cholecystokinin, which promote satiety.

    ·&emspIn the oral cavity, mastication starts the mechanical digestion of food, while salivary amylase and lipase start the chemical digestion of food. Food is formed into a bolus and swallowed.

    ·&emspThe pharynx connects the mouth and posterior nasal cavity to the esophagus.

    ·&emspThe esophagus propels food to the stomach using peristalsis. Food enters the stomach through the lower esophageal (cardiac) sphincter.

    ·&emspThe stomach has four parts: fundus, body, antrum, and pylorus. The stomach has a lesser and greater curvature and is thrown into folds called rugae. Numerous secretory cells line the stomach.

    o Mucous cells produce bicarbonate-rich mucus to protect the stomach.

    o Chief cells secrete pepsinogen, a protease activated by the acidic environment of the stomach.

    o Parietal cells secrete hydrochloric acid and intrinsic factor, which is needed for vitamin B12 absorption.

    o G cells secrete gastrin, a peptide hormone that increases HCl secretion and gastric motility.

    ·&emspAfter mechanical and chemical digestion in the stomach, the food particles are now called chyme. Food passes into the duodenum through the pyloric sphincter.

    ·&emspThe duodenum is the first part of the small intestine and is primarily involved in chemical digestion.

    o Disaccharidases are brush-border enzymes that break down maltose, isomaltose, lactose, and sucrose into monosaccharides.

    o Brush-border peptidases include aminopeptidase and dipeptidases.

    o Enteropeptidase activates trypsinogen and procarboxypeptidases, initiating an activation cascade.

    o Secretin stimulates the release of pancreatic juices into the digestive tract and slows motility.

    o Cholecystokinin stimulates bile release from the gallbladder, release of pancreatic juices, and satiety.

    Accessory Organs of Digestion

    ·&emspAcinar cells in the pancreas produce pancreatic juices that contain bicarbonate, pancreatic amylase, pancreatic peptidases (trypsinogen, chymotrypsinogen, carboxypeptidases A and B), and pancreatic lipase.

    ·&emspThe liver synthesizes bile, which can be stored in the gallbladder or secreted into the duodenum directly.

    o Bile emulsifies fats, making them soluble and increasing their surface area.

    o The main components of bile are bile salts, pigments (especially bilirubin from the breakdown of hemoglobin), and cholesterol.

    ·&emspThe liver also processes nutrients (through glycogenesis and glycogenolysis, storage and mobilization of fats, and gluconeogenesis), produces urea, detoxifies chemicals, activates or inactivates medications, produces bile, and synthesizes albumin and clotting factors.

    ·&emspThe gallbladder stores and concentrates bile.

    Absorption and Defecation

    ·&emspThe jejunum and ileum of the small intestine are primarily involved in absorption.

    o The small intestine is lined with villi, which are covered with microvilli, increasing the surface area available for absorption.

    o Villi contain a capillary bed and a lacteal, a vessel of the lymphatic system.

    o Water-soluble compounds, such as monosaccharides, amino acids, water-soluble vitamins, small fatty acids, and water, enter the capillary bed.

    o Fat-soluble compounds, such as fats, cholesterol, and fat-soluble vitamins, enter the lacteal.

    ·&emspThe large intestine absorbs water and salts, forming semisolid feces.

    o The cecum is an outpocketing that accepts fluid from the small intestine through the ileocecal valve and is the site of the appendix.

    o The colon is divided into ascending, transverse, descending, and sigmoid portions.

    o The rectum stores feces, which are then excreted through the anus.

    o Gut bacteria produce vitamin K and biotin (vitamin B7).

    Answers to Concept Checks

    1. Mechanical digestion, such as chewing, physically breaks food into smaller pieces. Chemical digestion involves hydrolysis of bonds and breakdown of food into smaller biomolecules.

    2. Oral cavity (mouth) &rarr pharynx &rarr esophagus &rarr stomach &rarr small intestine &rarr large intestine &rarr rectum &rarr anus

    3. The parasympathetic nervous system increases secretions from all of the glands of the digestive system and promotes peristalsis. The sympathetic nervous system slows peristalsis.

    1. Saliva contains salivary amylase (ptyalin), which digests starch into smaller sugars (maltose and dextrin), and lipase, which digests fats.

    Mucous cell

    Protect lining of stomach, increase pH (bicarbonate)

    Pepsinogen Digest proteins, once activated by H +

    Parietal cell

    HCl: decrease pH, kill microbes, denature proteins, some chemical digestion intrinsic factor: absorption of vitamin B12

    Increase HCl production, increase gastric motility

    Enzyme or Hormone?

    Brush-border enzyme break down sucrose into monosaccharides

    Increase pancreatic secretions, especially bicarbonate, reduce HCl secretion, decrease motility

    Dipeptidase

    Brush-border enzyme break dipeptides into free amino acids

    Cholecystokinin

    Recruit secretions from gallbladder and pancreas promote satiety

    Enteropeptidase

    Activate trypsinogen, which initiates an activation cascade

    4. Bile accomplishes mechanical digestion of fats, emulsifying them and increasing their surface area. Pancreatic lipase accomplishes chemical digestion of fats, breaking their ester bonds.

    1. Carbohydrates: pancreatic amylase proteins: trypsin, chymotrypsin, carboxy-peptidases A and B fats: pancreatic lipase

    2. Bile is composed of bile salts (amphipathic molecules derived from cholesterol that emulsify fats), pigments (especially bilirubin from the breakdown of hemoglobin), and cholesterol.

    3. Bile is synthesized in the liver, stored in the gallbladder, and serves its function in the duodenum.

    4. The liver processes nutrients (through glycogenesis and glycogenolysis, storage and mobilization of fats, and gluconeogenesis), produces urea, detoxifies chemicals, activates or inactivates medications, produces bile, and synthesizes albumin and clotting factors.

    5. As outgrowths of the gut tube, the accessory organs of digestion arise from embryonic endoderm.

    1. The two circulatory vessels are capillaries and lacteals. The capillary absorbs water-soluble nutrients, like monosaccharides, amino acids, small fatty acids, water-soluble vitamins, and water itself. The lacteal absorbs fat-soluble nutrients, like fats, cholesterol, and fat-soluble vitamins.

    2. The fat-soluble vitamins are A, D, E, and K.

    3. The small intestine consists of the duodenum, jejunum, and ileum. The large intestine consists of the cecum, colon, and rectum.

    4. While the large intestine’s main function is to absorb water, the small intestine actually absorbs a much larger volume of water. Thus, massive volumes of watery diarrhea are more likely to arise from infections in the small intestine than the large intestine.

    Shared Concepts

    ·&emspBiochemistry Chapter 2

    ·&emspBiochemistry Chapter 9

    o Carbohydrate Metabolism I

    ·&emspBiochemistry Chapter 11

    o Lipid and Amino Acid Metabolism

    ·&emspBiology Chapter 5

    ·&emspBiology Chapter 7

    o The Cardiovascular System

    ·&emspBiology Chapter 8

    If you are the copyright holder of any material contained on our site and intend to remove it, please contact our site administrator for approval.


    Weight Gain

    Excessive consumption of refined carbohydrates will tend to increase your fat mass, body weight and body mass index, or BMI, which is a measure of your fatness. Refined carbohydrate foods are rapidly digested and absorbed, and they tend to elevate your blood glucose level very quickly. This causes your pancreas to produce more insulin to prevent your blood glucose from getting too high, which sets up a scenario for your liver to secrete triglyceride-rich lipoproteins and subsequent triglyceride deposition in your fatty tissues. In turn, an increase in your fat mass will tend to lower your basal metabolic rate.


    Watch the video: Carbohydrate Digestion And Absorption - Carbohydrate Metabolism (August 2022).