what is the name given to the starch-digesting enzyme secreted by salivary glands?

Affiliate 15. Animal Diet and the Digestive Arrangement

15.3 Digestive System Processes

Learning Objectives

By the end of this section, yous will be able to:

• Describe the process of digestion
• Detail the steps involved in digestion and assimilation
• Define elimination
• Explicate the role of both the small and large intestines in assimilation

Obtaining nutrition and energy from nutrient is a multi-step process. For true animals, the starting time step is ingestion, the act of taking in food. This is followed by digestion, absorption, and elimination. In the following sections, each of these steps volition be discussed in particular.

Ingestion

The big molecules found in intact food cannot pass through the prison cell membranes. Nutrient needs to exist broken into smaller particles so that animals tin can harness the nutrients and organic molecules. The outset pace in this process is ingestion. Ingestion is the procedure of taking in food through the mouth. In vertebrates, the teeth, saliva, and tongue play important roles in mastication (preparing the food into bolus). While the food is beingness mechanically broken downwards, the enzymes in saliva begin to chemically process the food as well. The combined action of these processes modifies the food from large particles to a soft mass that can be swallowed and can travel the length of the esophagus.

Digestion and Absorption

Digestion is the mechanical and chemical break down of nutrient into small organic fragments. It is important to break downwards macromolecules into smaller fragments that are of suitable size for absorption across the digestive epithelium. Large, complex molecules of proteins, polysaccharides, and lipids must be reduced to simpler particles such equally unproblematic sugar before they can be absorbed by the digestive epithelial cells. Different organs play specific roles in the digestive process. The animal diet needs carbohydrates, poly peptide, and fat, every bit well as vitamins and inorganic components for nutritional balance. How each of these components is digested is discussed in the following sections.

Carbohydrates

The digestion of carbohydrates begins in the oral fissure. The salivary enzyme amylase begins the breakdown of nutrient starches into maltose, a disaccharide. As the bolus of nutrient travels through the esophagus to the stomach, no significant digestion of carbohydrates takes place. The esophagus produces no digestive enzymes but does produce mucous for lubrication. The acidic surroundings in the breadbasket stops the action of the amylase enzyme.

The adjacent step of carbohydrate digestion takes identify in the duodenum. Call up that the chyme from the stomach enters the duodenum and mixes with the digestive secretion from the pancreas, liver, and gallbladder. Pancreatic juices also incorporate amylase, which continues the breakup of starch and glycogen into maltose, a disaccharide. The disaccharides are broken down into monosaccharides past enzymes called maltases

, sucrases, and lactases, which are also present in the castor border of the minor intestinal wall. Maltase breaks down maltose into glucose. Other disaccharides, such as sucrose and lactose are cleaved down by sucrase and lactase, respectively. Sucrase breaks down sucrose (or "table carbohydrate") into glucose and fructose, and lactase breaks down lactose (or "milk sugar") into glucose and galactose. The monosaccharides (glucose) thus produced are absorbed then can be used in metabolic pathways to harness energy. The monosaccharides are transported across the abdominal epithelium into the bloodstream to be transported to the different cells in the body. The steps in carbohydrate digestion are summarized in Figure fifteen.16 and Table 15.v.

Figure 15.16.  Digestion of carbohydrates is performed past several enzymes. Starch and glycogen are broken down into glucose by amylase and maltase. Sucrose (tabular array sugar) and lactose (milk sugar) are cleaved down by sucrase and lactase, respectively.

Table15 .five Digestion of Carbohydrates

Enzyme	Produced By	Site of Action	Substrate Acting On	End Products
Salivary amylase	Salivary glands	Mouth	Polysaccharides (Starch)	Disaccharides (maltose), oligosaccharides
Pancreatic amylase	Pancreas	Small intestine	Polysaccharides (starch)	Disaccharides (maltose), monosaccharides
Oligosaccharidases	Lining of the intestine; brush border membrane	Small intestine	Disaccharides	Monosaccharides (e.thou., glucose, fructose, galactose)

Protein

A big function of protein digestion takes place in the stomach. The enzyme pepsin plays an important role in the digestion of proteins past breaking down the intact poly peptide to peptides, which are curt chains of iv to ix amino acids. In the duodenum, other enzymes— trypsin, elastase, and chymotrypsin—act on the peptides reducing them to smaller peptides. Trypsin elastase, carboxypeptidase, and chymotrypsin are produced past the pancreas and released into the duodenum where they human activity on the chyme. Further breakdown of peptides to single amino acids is aided by enzymes called peptidases (those that pause downwards peptides). Specifically, carboxypeptidase, dipeptidase, and aminopeptidase play important roles in reducing the peptides to free amino acids. The amino acids are absorbed into the bloodstream through the pocket-sized intestines. The steps in protein digestion are summarized in Figure 15.17 and Table fifteen.6.

Figure fifteen.17
Poly peptide digestion is a multistep process that begins in the stomach and continues through the intestines.

Table 15.6. Digestion of Poly peptide

Enzyme	Produced By	Site of Activeness	Substrate Acting On	Cease Products
Pepsin	Stomach chief cells	Stomach	Proteins	Peptides
Trypsin Elastase Chymotrypsin	Pancreas	Small intestine	Proteins	Peptides
Carboxypeptidase	Pancreas	Minor intestine	Peptides	Amino acids and peptides
Aminopeptidase Dipeptidase	Lining of intestine	Minor intestine	Peptides	Amino acids

Lipids

Lipid digestion begins in the tum with the help of lingual lipase and gastric lipase. However, the bulk of lipid digestion occurs in the small intestine due to pancreatic lipase. When chyme enters the duodenum, the hormonal responses trigger the release of bile, which is produced in the liver and stored in the gallbladder. Bile aids in the digestion of lipids, primarily triglycerides past emulsification. Emulsification is a procedure in which large lipid globules are broken downward into several small lipid globules. These minor globules are more than widely distributed in the chyme rather than forming large aggregates. Lipids are hydrophobic substances: in the presence of water, they will amass to form globules to minimize exposure to water. Bile contains bile salts, which are amphipathic, meaning they contain hydrophobic and hydrophilic parts. Thus, the bile salts hydrophilic side can interface with water on one side and the hydrophobic side interfaces with lipids on the other. By doing so, bile salts emulsify large lipid globules into small lipid globules.

Why is emulsification of import for digestion of lipids? Pancreatic juices contain enzymes called lipases (enzymes that pause down lipids). If the lipid in the chyme aggregates into big globules, very little area of the lipids is bachelor for the lipases to act on, leaving lipid digestion incomplete. By forming an emulsion, bile salts increment the available surface area of the lipids many fold. The pancreatic lipases tin then human action on the lipids more than efficiently and assimilate them, every bit detailed in Effigy fifteen.18. Lipases break down the lipids into fatty acids and glycerides. These molecules tin can pass through the plasma membrane of the cell and enter the epithelial cells of the abdominal lining. The bile salts surround long-chain fat acids and monoglycerides forming tiny spheres called micelles. The micelles move into the brush edge of the pocket-size intestine absorbent cells where the long-chain fat acids and monoglycerides lengthened out of the micelles into the absorptive cells leaving the micelles behind in the chyme. The long-concatenation fat acids and monoglycerides recombine in the absorptive cells to class triglycerides, which aggregate into globules and go coated with proteins. These large spheres are called chylomicrons. Chylomicrons comprise triglycerides, cholesterol, and other lipids and accept proteins on their surface. The surface is as well composed of the hydrophilic phosphate "heads" of phospholipids. Together, they enable the chylomicron to movement in an aqueous environment without exposing the lipids to water. Chylomicrons leave the absorbent cells via exocytosis. Chylomicrons enter the lymphatic vessels, and then enter the claret in the subclavian vein.

Effigy xv.18.
Lipids are digested and captivated in the modest intestine.

Vitamins

Vitamins can exist either water-soluble or lipid-soluble. Fat soluble vitamins are absorbed in the same manner every bit lipids. It is of import to consume some amount of dietary lipid to help the absorption of lipid-soluble vitamins. Water-soluble vitamins tin be directly captivated into the bloodstream from the intestine.

Concept in Action

This website has an overview of the digestion of poly peptide, fat, and carbohydrates.

Figure 15.xix.  Mechanical and chemical digestion of nutrient takes place in many steps, commencement in the rima oris and ending in the rectum.

Which of the following statements about digestive processes is truthful?

1. Amylase, maltase, and lactase in the mouth digest carbohydrates.
2. Trypsin and lipase in the tummy digest protein.
3. Bile emulsifies lipids in the pocket-sized intestine.
4. No food is absorbed until the small intestine.

Elimination

The final step in digestion is the elimination of undigested food content and waste products. The undigested nutrient material enters the colon, where near of the water is reabsorbed. Recall that the colon is likewise habitation to the microflora called "intestinal flora" that aid in the digestion procedure. The semi-solid waste is moved through the colon by peristaltic movements of the muscle and is stored in the rectum. As the rectum expands in response to storage of fecal thing, information technology triggers the neural signals required to set up the urge to eliminate. The solid waste is eliminated through the anus using peristaltic movements of the rectum.

Common Problems with Elimination

Diarrhea and constipation are some of the most common wellness concerns that affect digestion. Constipation is a condition where the feces are hardened because of excess h2o removal in the colon. In contrast, if enough h2o is not removed from the feces, it results in diarrhea. Many bacteria, including the ones that cause cholera, bear on the proteins involved in water reabsorption in the colon and event in excessive diarrhea.

Emesis

Emesis, or vomiting, is emptying of food by forceful expulsion through the mouth. It is frequently in response to an irritant that affects the digestive tract, including but not limited to viruses, bacteria, emotions, sights, and food poisoning. This forceful expulsion of the nutrient is due to the strong contractions produced past the breadbasket muscles. The procedure of emesis is regulated by the medulla.

Summary

Animal nutrition should exist counterbalanced and meet the needs of the torso. Carbohydrates, proteins, and fats are the primary components of food. Some essential nutrients are required for cellular function but cannot exist produced by the animal body. These include vitamins, minerals, some fatty acids, and some amino acids. Food intake in more than necessary amounts is stored equally glycogen in the liver and musculus cells, and in fat cells. Excess adipose storage tin lead to obesity and serious health problems. ATP is the energy currency of the cell and is obtained from the metabolic pathways. Excess carbohydrates and energy are stored as glycogen in the torso.

Exercises

1. Where does the majority of poly peptide digestion take place?
   1. stomach
   2. duodenum
   3. mouth
   4. jejunum
2. Lipases are enzymes that pause down ________.
   1. disaccharides
   2. lipids
   3. proteins
   4. cellulose
3. Explain why some dietary lipid is a necessary role of a balanced diet.

Answers

1. A
2. B
3. Lipids add flavor to food and promote a sense of satiety or fullness. Fatty foods are sources of high energy; one gram of lipid contains ix calories. Lipids are as well required in the diet to aid the assimilation of lipid-soluble vitamins and for the production of lipid-soluble hormones.

Glossary

aminopeptidase: protease that breaks downwards peptides to single amino acids; secreted by the brush border of pocket-size intestine
anus: go out point for waste material
bile: digestive juice produced by the liver; of import for digestion of lipids
bolus: mass of food resulting from chewing action and wetting past saliva
carboxypeptidase: protease that breaks down peptides to unmarried amino acids; secreted by the brush border of the minor intestine
chylomicron: pocket-size lipid globule
chyme: mixture of partially digested nutrient and tum juices
chymotrypsin: pancreatic protease
digestion: mechanical and chemical break down of food into minor organic fragments
dipeptidase: protease that breaks down peptides to single amino acids; secreted by the brush border of pocket-size intestine
duodenum: outset part of the small-scale intestine where a large role of digestion of carbohydrates and fats occurs
elastase: pancreatic protease
esophagus: tubular organ that connects the rima oris to the stomach
essential nutrient: nutrient that cannot be synthesized past the trunk; it must be obtained from food
gallbladder: organ that stores and concentrates bile
ingestion: human activity of taking in nutrient
jejunum: second part of the modest intestine
lactase: enzyme that breaks downward lactose into glucose and galactose
large intestine: digestive system organ that reabsorbs water from undigested material and processes waste affair
lipase: enzyme that chemically breaks downwardly lipids
liver: organ that produces bile for digestion and processes vitamins and lipids
maltase: enzyme that breaks down maltose into glucose
mineral: inorganic, elemental molecule that carries out important roles in the body
pancreas: gland that secretes digestive juices
pepsin: enzyme found in the tummy whose main role is protein digestion
rectum: area of the trunk where carrion is stored until emptying
small intestine: organ where digestion of protein, fats, and carbohydrates is completed
breadbasket: sac-similar organ containing acidic digestive juices
sucrase: enzyme that breaks downwardly sucrose into glucose and fructose
trypsin: pancreatic protease that breaks down poly peptide
vitamin: organic substance necessary in minor amounts to sustain life

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Source: https://opentextbc.ca/biology/chapter/15-3-digestive-system-processes/

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