Review the Section Entitled Pharynx and Esophagus in Chapter 17 of the Textbook

Chapter 11: Introduction to the Body'due south Systems

11.two Digestive System

Learning Objectives

Past the cease of this section, y'all volition be able to:

• Explain the processes of digestion and absorption
• Explain the specialized functions of the organs involved in processing nutrient in the torso
• Describe the ways in which organs work together to assimilate nutrient and absorb nutrients
• Draw the essential nutrients required for cellular role that cannot be synthesized by the animate being torso
• Describe how excess carbohydrates and energy are stored in the body

All living organisms need nutrients to survive. While plants can obtain nutrients from their roots and the energy molecules required for cellular office through the procedure of photosynthesis, animals obtain their nutrients past the consumption of other organisms. At the cellular level, the biological molecules necessary for fauna part are amino acids, lipid molecules, nucleotides, and simple sugars. Nevertheless, the food consumed consists of poly peptide, fat, and complex carbohydrates. Animals must convert these macromolecules into the unproblematic molecules required for maintaining cellular office. The conversion of the nutrient consumed to the nutrients required is a multistep procedure involving digestion and absorption. During digestion, food particles are broken down to smaller components, which are later on absorbed by the body. This happens past both physical ways, such as chewing, and by chemical means.

One of the challenges in man diet is maintaining a remainder between food intake, storage, and free energy expenditure. Taking in more food energy than is used in activeness leads to storage of the excess in the course of fat deposits. The rise in obesity and the resulting diseases similar type ii diabetes makes understanding the role of diet and nutrition in maintaining good health all the more important.

The Human Digestive Organization

The process of digestion begins in the oral cavity with the intake of food. The teeth play an important function in masticating (chewing) or physically breaking food into smaller particles. The enzymes present in saliva also brainstorm to chemically suspension down food. The food is and so swallowed and enters the esophagus—a long tube that connects the mouth to the tummy. Using peristalsis, or wave-like smooth-musculus 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 ii.5. This acidity kills microorganisms, breaks down nutrient tissues, and activates digestive enzymes. Further breakdown of nutrient takes place in the small intestine where bile produced by the liver, and enzymes produced past the pocket-size intestine and the pancreas, continue the process of digestion. The smaller molecules are captivated into the blood stream through the epithelial cells lining the walls of the small intestine. The waste product textile travels on to the big intestine where water is absorbed and the drier waste cloth is compacted into feces; information technology is stored until information technology is excreted through the anus.

Effigy 11.iv The components of the homo digestive system are shown.

Oral Crenel

Both physical and chemical digestion begin in the rima oris or mouth, which is the bespeak of entry of food into the digestive arrangement. The food is cleaved into smaller particles past mastication, the chewing activity of the teeth. All mammals take teeth and tin chew their food to begin the process of physically breaking information technology down into smaller particles.

The chemical process of digestion begins during chewing as food mixes with saliva, produced past the salivary glands (Figure eleven.5). Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains lysozyme, which has antibacterial action. Information technology likewise contains an enzyme called salivary amylase that begins the process of converting starches in the nutrient into a disaccharide called maltose. Another enzyme called lipase is produced by cells in the tongue to break downward fats. The chewing and wetting action provided by the teeth and saliva prepare the nutrient into a mass called the bolus for swallowing. The natural language helps in swallowing—moving the bolus from the mouth into the throat. The throat 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 forbid food from entering the lungs.

Figure xi.5 (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 brainstorm to digest starches and fats. With the help of the natural language, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of piece of work past Mariana Ruiz Villareal)

Esophagus

The esophagus is a tubular organ that connects the rima oris to the tummy. 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—information technology moves food from the mouth to the stomach, and reverse motility is non possible, except in the case of the vomit reflex. The peristaltic motion of the esophagus is an involuntary reflex; information technology takes place in response to the act of swallowing.

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

Tum

A big part of protein digestion occurs in the tum (Figure eleven.seven). 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 nutrient. Chemical digestion is facilitated by the churning action of the stomach caused by wrinkle and relaxation of smooth muscles. The partially digested food and gastric juice mixture is called chyme. Gastric emptying occurs within two to six hours afterwards a repast. Merely a pocket-sized corporeality of chyme is released into the small intestine at a fourth dimension. The movement of chyme from the stomach into the small intestine is regulated by hormones, tum distension and muscular reflexes that influence the pyloric sphincter.

The breadbasket 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-similar organ with a highly folded surface containing finger-like projections called the villi. The peak surface of each villus has many microscopic projections called microvilli. The epithelial cells of these structures blot 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 minor intestine and increase absorption efficiency of the nutrients.

The human modest intestine is over six m (19.six 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 intermission downwardly starches, disaccharides, proteins, and fats. Bile is produced in the liver and stored and full-bodied in the gallbladder; it enters the duodenum through the bile duct. Bile contains bile salts, which make lipids attainable to the water-soluble enzymes. The monosaccharides, amino acids, bile salts, vitamins, and other nutrients are captivated 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 big intestine begins at the ileocecal valve. The vermiform, "worm-like," appendix is located at the ileocecal valve. The appendix of humans has a pocket-size role in immunity.

Large Intestine

The large intestine reabsorbs the water from indigestible nutrient material and processes the waste material material (Figure 11.6). The human large intestine is much smaller in length compared to the pocket-size intestine but larger in diameter. Information technology 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 thing. 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 principal functions of the colon are to extract the h2o and mineral salts from undigested food, and to store waste product.

Figure 11.six The big intestine reabsorbs water from undigested food and stores waste until it is eliminated. (credit: modification of work past Mariana Ruiz Villareal)

The rectum (Figure 11.6) stores feces until defecation. The carrion are propelled using peristaltic movements during elimination. The anus is an opening at the far-terminate of the digestive tract and is the exit point for the waste product fabric. Two sphincters regulate the exit of feces, the inner sphincter is involuntary and the outer sphincter is voluntary.

Accessory Organs

The organs discussed to a higher place are the organs of the digestive tract through which food passes. Accessory organs add together secretions and enzymes that break downward nutrient into nutrients. Accompaniment organs include the salivary glands, the liver, the pancreas, and the gall bladder. The secretions of the liver, pancreas, and gallbladder are regulated past hormones in response to nutrient consumption.

The liver is the largest internal organ in humans and information technology plays an important role in digestion of fats and detoxifying claret. The liver produces bile, a digestive juice that is required for the breakup of fats in the duodenum. The liver likewise processes the absorbed vitamins and fatty acids and synthesizes many plasma proteins. The gallbladder is a modest 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.

Figure 11.7 The stomach has an extremely acidic surroundings where most of the protein gets digested. (credit: modification of work by Mariana Ruiz Villareal)

Nutrition

The post-obit video is primarily about water soluble vitamins such as vitamin B and C their roles, especially in energy metabolism. Some of the more than common and obscure minerals found in vitamins are too identified.

Vitamin Types

And the next video is an introduction to another category of vitamins, the fat soluble group such as vitamin E, D and K.

Fatty Soluble Vitamins

The human being diet should be well balanced to provide nutrients required for actual function and the minerals and vitamins required for maintaining structure and regulation necessary for good health and reproductive adequacy (Figure xi.8).

Effigy 11.8 For humans, a balanced diet includes fruits, vegetables, grains, protein, and dairy. (credit: USDA)

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 downwards into glucose through biochemical modification; still, humans do non produce the enzyme necessary to assimilate cellulose (fiber). The abdominal flora in the human gut are able to excerpt some nutrition from these plant fibers. These institute fibers are known as dietary cobweb and are an important component of the diet. The excess sugars in the body are converted into glycogen and stored for later utilise in the liver and muscle tissue. Glycogen stores are used to fuel prolonged exertions, such as long-distance running, and to provide free energy during food shortage. Fats are stored under the peel of mammals for insulation and energy reserves.

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

Fats add flavor to nutrient and promote a sense of satiety or fullness. Fat foods are too 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 fatty-soluble vitamins and the product of fat-soluble hormones.

While the animate being torso 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 trunk cannot produce them.

The fatty acids omega-3 blastoff-linolenic acid and omega-6 linoleic acid are essential fatty acids needed to make some membrane phospholipids. Vitamins are some other course of essential organic molecules that are required in small quantities. Many of these assistance enzymes in their office and, for this reason, are called coenzymes. Absence or low levels of vitamins tin have a dramatic effect on health. Minerals are another set of inorganic essential nutrients that must be obtained from nutrient. Minerals perform many functions, from muscle and nerve role, to acting equally enzyme cofactors. Certain amino acids also must exist procured from food and cannot exist synthesized by the body. These amino acids are the "essential" amino acids. The man body can synthesize only 11 of the xx required amino acids; the balance must be obtained from nutrient.

Obesity

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 nutrient consumed contribute to obesity?

Fatty foods are calorie-dense, meaning that they accept more calories per unit of measurement mass than carbohydrates or proteins. 1 gram of carbohydrates has four calories, ane gram of protein has iv calories, and one gram of fat has 9 calories. Animals tend to seek lipid-rich food for their higher energy content. Greater amounts of food energy taken in than the trunk'southward requirements volition result in storage of the excess in fat deposits.

Backlog 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 part is to store fat for later utilise.

The charge per unit of obesity among children is rapidly rising in the United States. To combat childhood obesity and ensure that children get a healthy commencement in life, in 2010 Get-go Lady Michelle Obama launched the Permit's Move! campaign. The goal of this campaign is to brainwash parents and caregivers on providing healthy nutrition and encouraging agile lifestyles in futurity generations. This program aims to involve the entire customs, including parents, teachers, and healthcare providers to ensure that children have admission to good for you foods—more fruits, vegetables, and whole grains—and eat fewer calories from candy foods. Some other goal is to ensure that children get concrete activity. With the increase in telly viewing and stationary pursuits such every bit video games, sedentary lifestyles have get the norm. Visit world wide web.letsmove.gov to larn more than.

Section Summary

At that place are many organs that work together to assimilate nutrient and absorb nutrients. The mouth is the indicate of ingestion and the location where both mechanical and chemic breakdown of nutrient begins. Saliva contains an enzyme called amylase that breaks downwardly carbohydrates. The food bolus travels through the esophagus by peristaltic movements to the stomach. The tum has an extremely acidic surroundings. The enzyme pepsin digests protein in the stomach. Farther digestion and assimilation accept identify in the small intestine. The large intestine reabsorbs water from the undigested food and stores waste matter 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 torso. These include vitamins, minerals, some fatty acids, and some amino acids. Nutrient intake in more than necessary amounts is stored every bit glycogen in the liver and muscle cells, and in adipose tissue. Excess adipose storage tin lead to obesity and serious health problems.

Glossary

amylase: an enzyme establish in saliva and secreted by the pancreas that converts carbohydrates to maltose

anus: the exit point of the digestive system for waste matter material

bile: a digestive juice produced by the liver; important for digestion of lipids

bolus: a mass of food resulting from chewing action and wetting by saliva

colon: the largest portion of the large intestine consisting of the ascending colon, transverse colon, and descending colon

chyme: a mixture of partially digested food and stomach juices

esophagus: a tubular organ that connects the mouth to the tum

essential nutrient: a nutrient that cannot be synthesized past the torso; information technology must be obtained from nutrient

gallbladder: the organ that stores and concentrates bile

big intestine: a digestive organisation organ that reabsorbs water from undigested cloth and processes waste product matter

liver: an organ that produces bile for digestion and processes vitamins and lipids

mineral: an inorganic, elemental molecule that carries out of import roles in the body

oral crenel: the point of entry of food into the digestive system

pancreas: a gland that secretes digestive juices

pepsin: an enzyme found in the stomach whose main office is protein digestion

peristalsis: moving ridge-like movements of muscle tissue

rectum: the surface area of the body where feces is stored until elimination

salivary gland: one of three pairs of exocrine glands in the mammalian mouth that secretes saliva, a mix of watery mucus and enzymes

small intestine: the organ where digestion of protein, fats, and carbohydrates is completed

tummy: a saclike organ containing acidic digestive juices

vitamin: an organic substance necessary in small-scale amounts to sustain life

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Source: https://opentextbc.ca/biology/chapter/11-2-digestive-system/

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