What do pseudo-ruminant animals use to ferment and digest feed by bacterial action?

Affiliate 15. Fauna Nutrition and the Digestive System

15.one Digestive Systems

Learning Objectives

By the finish of this section, you will be able to:

• Explain the processes of digestion and absorption
• Compare and contrast dissimilar types of digestive systems
• Explicate the specialized functions of the organs involved in processing food in the torso
• Depict the ways in which organs work together to digest nutrient and absorb nutrients

Animals obtain their nutrition from the consumption of other organisms. Depending on their diet, animals can be classified into the following categories: plant eaters (herbivores), meat eaters (carnivores), and those that eat both plants and animals (omnivores). The nutrients and macromolecules present in nutrient are not immediately accessible to the cells. There are a number of processes that modify food inside the brute body in lodge to make the nutrients and organic molecules accessible for cellular office. Equally animals evolved in complexity of course and function, their digestive systems have also evolved to accommodate their various dietary needs.

Herbivores, Omnivores, and Carnivores

Herbivores are animals whose master food source is plant-based. Examples of herbivores, every bit shown in Figure 15.2 include vertebrates similar deer, koalas, and some bird species, as well as invertebrates such equally crickets and caterpillars. These animals accept evolved digestive systems capable of handling big amounts of plant material. Herbivores tin can be further classified into frugivores (fruit-eaters), granivores (seed eaters), nectivores (nectar feeders), and folivores (leaf eaters).

Effigy 15.2.  Herbivores, like this (a) mule deer and (b) monarch caterpillar, eat primarily plant material. (credit a: modification of work by Neb Ebbesen; credit b: modification of piece of work by Doug Bowman)

Carnivores are animals that eat other animals. The discussion carnivore is derived from Latin and literally means "meat eater." Wild cats such equally lions, shown in Figure 35.3 a and tigers are examples of vertebrate carnivores, equally are snakes and sharks, while invertebrate carnivores include sea stars, spiders, and ladybugs, shown in Figure 15.iii b . Obligate carnivores are those that rely entirely on animal flesh to obtain their nutrients; examples of obligate carnivores are members of the cat family, such as lions and cheetahs. Facultative carnivores are those that as well consume non-creature food in addition to animal nutrient. Note that there is no clear line that differentiates facultative carnivores from omnivores; dogs would be considered facultative carnivores.

Figure 15.3.  Carnivores similar the (a) lion eat primarily meat. The (b) ladybug is also a carnivore that consumes small insects chosen aphids. (credit a: modification of work by Kevin Pluck; credit b: modification of piece of work by Jon Sullivan)

Omnivores are animals that eat both plant- and animal-derived nutrient. In Latin, omnivore ways to eat everything. Humans, bears (shown in Effigy 15.4 a ), and chickens are example of vertebrate omnivores; invertebrate omnivores include cockroaches and crayfish (shown in Figure 15.4 b ).

Effigy 15.four.  Omnivores like the (a) bear and (b) crayfish eat both found and brute based nutrient. (credit a: modification of work by Dave Menke; credit b: modification of piece of work by Jon Sullivan)

Invertebrate Digestive Systems

Animals have evolved different types of digestive systems to aid in the digestion of the different foods they consume. The simplest example is that of a gastrovascular cavity and is plant in organisms with only ane opening for digestion. Platyhelminthes (flatworms), Ctenophora (comb jellies), and Cnidaria (coral, jelly fish, and sea anemones) use this type of digestion. Gastrovascular cavities, as shown in Effigy 15.5 a , are typically a blind tube or crenel with only one opening, the "mouth", which also serves every bit an "anus". Ingested material enters the mouth and passes through a hollow, tubular cavity. Cells within the cavity secrete digestive enzymes that break down the nutrient. The food particles are engulfed by the cells lining the gastrovascular cavity.

The alimentary canal, shown in Figure 15.five b , is a more than advanced arrangement: information technology consists of i tube with a mouth at ane end and an anus at the other. Earthworms are an example of an animal with an alimentary canal. Once the food is ingested through the mouth, it passes through the esophagus and is stored in an organ called the crop; and so it passes into the gizzard where it is churned and digested. From the gizzard, the nutrient passes through the intestine, the nutrients are absorbed, and the waste is eliminated every bit carrion, called castings, through the anus.

Effigy fifteen.v.  (a) A gastrovascular cavity has a unmarried opening through which food is ingested and waste product is excreted, as shown in this hydra and in this jellyfish medusa. (b) An alimentary culvert has two openings: a mouth for ingesting food, and an anus for eliminating waste product, as shown in this nematode.

Vertebrate Digestive Systems

Vertebrates have evolved more complex digestive systems to adapt to their dietary needs. Some animals have a single stomach, while others have multi-chambered stomachs. Birds have developed a digestive organisation adapted to eating unmasticated nutrient.

Monogastric: Single-chambered Breadbasket

Every bit the discussion monogastric suggests, this type of digestive arrangement consists of one ("mono") breadbasket chamber ("gastric"). Humans and many animals have a monogastric digestive system as illustrated in Figure 15.6 ab . The process of digestion begins with the rima oris and the intake of nutrient. The teeth play an important role in masticating (chewing) or physically breaking downward food into smaller particles. The enzymes nowadays in saliva as well begin to chemically break down food. The esophagus is a long tube that connects the rima oris to the stomach. Using peristalsis, or wave-like shine muscle contractions, the muscles of the esophagus push the food towards the stomach. In order to speed up the actions of enzymes in the stomach, the tummy is an extremely acidic environment, with a pH between 1.5 and 2.5. The gastric juices, which include enzymes in the tum, act on the food particles and continue the process of digestion. Further breakdown of food takes identify in the pocket-size intestine where enzymes produced by the liver, the small intestine, and the pancreas continue the procedure of digestion. The nutrients are captivated into the claret stream across the epithelial cells lining the walls of the small-scale intestines. The waste material material travels on to the large intestine where h2o is absorbed and the drier waste product material is compacted into carrion; it is stored until it is excreted through the rectum.

Figure 15.vi.
(a) Humans and herbivores, such equally the (b) rabbit, have a monogastric digestive organisation. Notwithstanding, in the rabbit the pocket-size intestine and cecum are enlarged to allow more time to assimilate constitute fabric. The enlarged organ provides more surface area for absorption of nutrients. Rabbits digest their nutrient twice: the kickoff time nutrient passes through the digestive system, it collects in the cecum, and then information technology passes as soft carrion called cecotrophes. The rabbit re-ingests these cecotrophes to further digest them.

Avian

Birds confront special challenges when it comes to obtaining nutrition from food. They do not have teeth and so their digestive organization, shown in Figure 15.7, must be able to procedure un-masticated food. Birds have evolved a variety of beak types that reflect the vast variety in their diet, ranging from seeds and insects to fruits and nuts. Because virtually birds fly, their metabolic rates are loftier in order to efficiently procedure food and keep their torso weight low. The tum of birds has 2 chambers: the proventriculus, where gastric juices are produced to digest the food earlier it enters the stomach, and the gizzard, where the food is stored, soaked, and mechanically ground. The undigested material forms food pellets that are sometimes regurgitated. Most of the chemical digestion and assimilation happens in the intestine and the waste is excreted through the cloaca.

Figure fifteen.7.  The avian esophagus has a pouch, called a crop, which stores food. Nutrient passes from the ingather to the first of ii stomachs, called the proventriculus, which contains digestive juices that intermission down food. From the proventriculus, the food enters the second tummy, called the gizzard, which grinds food. Some birds swallow stones or grit, which are stored in the gizzard, to aid the grinding process. Birds do not take split up openings to excrete urine and feces. Instead, uric acid from the kidneys is secreted into the large intestine and combined with waste from the digestive procedure. This waste is excreted through an opening called the cloaca.

Parts of the Digestive System

The vertebrate digestive organisation is designed to facilitate the transformation of food matter into the food components that sustain organisms.

Oral Cavity

The oral cavity, or rima oris, is the bespeak of entry of food into the digestive organisation, illustrated in Figure 15.9. The nutrient consumed is broken into smaller particles by mastication, the chewing activeness of the teeth. All mammals take teeth and tin chew their food.

The extensive chemical process of digestion begins in the mouth. As food is being chewed, saliva, produced by the salivary glands, mixes with the nutrient. Saliva is a watery substance produced in the mouths of many animals. At that place are three major glands that secrete saliva—the parotid, the submandibular, and the sublingual. Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains immunoglobulins and lysozymes, which have antibacterial action to reduce tooth decay by inhibiting growth of some leaner. Saliva likewise contains an enzyme chosen salivary amylase that begins the procedure of converting starches in the food into a disaccharide called maltose. Some other enzyme called lipase is produced by the cells in the tongue. Lipases are a class of enzymes that can break down triglycerides. The lingual lipase begins the breakdown of fat components in the food. The chewing and wetting action provided by the teeth and saliva prepare the nutrient 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 trachea, which leads to the lungs, and the esophagus, which leads to the breadbasket. The trachea has an opening chosen the glottis, which is covered past a cartilaginous flap called the epiglottis. When swallowing, the epiglottis closes the glottis and food passes into the esophagus and non the trachea. This arrangement allows food to exist kept out of the trachea.

Figure 15.9.
Digestion of food begins in the (a) oral cavity. Nutrient is masticated by teeth and moistened by saliva secreted from the (b) salivary glands. Enzymes in the saliva brainstorm to assimilate starches and fats. With the help of the tongue, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of work past the National Cancer Plant)

Esophagus

The esophagus is a tubular organ that connects the mouth to the tummy. The chewed and softened food passes through the esophagus after existence swallowed. The smooth muscles of the esophagus undergo a serial of wave like movements called peristalsis that push button the food toward the stomach, as illustrated in Figure fifteen.ten. The peristalsis wave is unidirectional—it moves nutrient from the mouth to the stomach, and opposite movement is not possible. The peristaltic movement of the esophagus is an involuntary reflex; it takes place in response to the human action of swallowing.

Figure 15.10.  The esophagus transfers nutrient from the mouth to the stomach through peristaltic movements.

A band-like musculus called a sphincter forms valves in the digestive arrangement. The gastro-esophageal sphincter is located at the tum terminate of the esophagus. In response to swallowing and the force per unit area exerted by the bolus of food, this sphincter opens, and the bolus enters the stomach. When there is no swallowing activeness, this sphincter is shut and prevents the contents of the tum from traveling upwards the esophagus. Many animals take a truthful sphincter; however, in humans, at that place is no true sphincter, but the esophagus remains airtight when at that place is no swallowing action. Acid reflux or "heartburn" occurs when the acidic digestive juices escape into the esophagus.

Breadbasket

A large part of digestion occurs in the tum, shown in Figure 15.xi. The stomach is a saclike organ that secretes gastric digestive juices. The pH in the stomach is betwixt ane.5 and two.5. This highly acidic environment is required for the chemical breakdown of food and the extraction of nutrients. When empty, the breadbasket is a rather small organ; nonetheless, information technology tin expand to up to 20 times its resting size when filled with food. This characteristic is particularly useful for animals that need to consume when food is available.

Figure 15.11.  The human stomach has an extremely acidic environment where most of the protein gets digested. (credit: modification of work by Mariana Ruiz Villareal)

Which of the following statements about the digestive system is false?

1. Chyme is a mixture of nutrient and digestive juices that is produced in the stomach.
2. Food enters the big intestine before the pocket-size intestine.
3. In the small intestine, chyme mixes with bile, which emulsifies fats.
4. The stomach is separated from the small-scale intestine past the pyloric sphincter.

The breadbasket is also the major site for protein digestion in animals other than ruminants. Protein digestion is mediated by an enzyme called pepsin in the stomach chamber. Pepsin is secreted past the chief cells in the breadbasket in an inactive form called pepsinogen. Pepsin breaks peptide bonds and cleaves proteins into smaller polypeptides; it also helps actuate more pepsinogen, starting a positive feedback mechanism that generates more than pepsin. Another cell type—parietal cells—secrete hydrogen and chloride ions, which combine in the lumen to form hydrochloric acid, the primary acidic component of the stomach juices. Hydrochloric acid helps to catechumen the inactive pepsinogen to pepsin. The highly acidic environment too kills many microorganisms in the food and, combined with the action of the enzyme pepsin, results in the hydrolysis of protein in the food. Chemical digestion is facilitated by the churning action of the tum. Wrinkle and relaxation of polish muscles mixes the tummy contents about every xx minutes. The partially digested food and gastric juice mixture is chosen chyme. Chyme passes from the tummy to the small intestine. Further protein digestion takes place in the small intestine. Gastric emptying occurs inside two to six hours after a meal. Only a small-scale amount of chyme is released into the small intestine at a time. The motility of chyme from the tum into the small intestine is regulated by the pyloric sphincter.

When digesting poly peptide and some fats, the stomach lining must exist protected from getting digested by pepsin. There are two points to consider when describing how the stomach lining is protected. First, as previously mentioned, the enzyme pepsin is synthesized in the inactive form. This protects the principal cells, because pepsinogen does non have the same enzyme functionality of pepsin. 2nd, the stomach has a thick mucus lining that protects the underlying tissue from the action of the digestive juices. When this mucus lining is ruptured, ulcers can form in the stomach. Ulcers are open wounds in or on an organ caused past bacteria (Helicobacter pylori) when the fungus lining is ruptured and fails to reform.

Small Intestine

Chyme moves from the stomach to the small intestine. The modest intestine is the organ where the digestion of protein, fats, and carbohydrates is completed. The minor intestine is a long tube-like organ with a highly folded surface containing finger-like projections called the villi. The apical surface of each villus has many microscopic projections called microvilli. These structures, illustrated in Figure 15.12, are lined with epithelial cells on the luminal side and allow for the nutrients to exist absorbed from the digested food and absorbed into the blood stream on the other side. The villi and microvilli, with their many folds, increment the surface area of the intestine and increase absorption efficiency of the nutrients. Absorbed nutrients in the blood are carried into the hepatic portal vein, which leads to the liver. There, the liver regulates the distribution of nutrients to the balance of the body and removes toxic substances, including drugs, alcohol, and some pathogens.

Figure xv.12.  Villi are folds on the pocket-sized intestine lining that increase the surface area to facilitate the absorption of nutrients.

Which of the post-obit statements almost the pocket-sized intestine is false?

1. Absorptive cells that line the small intestine have microvilli, small projections that increase surface area and aid in the absorption of nutrient.
2. The inside of the small-scale intestine has many folds, called villi.
3. Microvilli are lined with blood vessels as well as lymphatic vessels.
4. The inside of the small intestine is called the lumen.

The human being small intestine is over 6m long and is divided into 3 parts: the duodenum, the jejunum, and the ileum. The "C-shaped," stock-still part of the small intestine is called the duodenum and is shown in Figure xv.11. The duodenum is separated from the stomach by the pyloric sphincter which opens to let chyme to motion from the stomach to the duodenum. In the duodenum, chyme is mixed with pancreatic juices in an alkaline solution rich in bicarbonate that neutralizes the acidity of chyme and acts as a buffer. Pancreatic juices also comprise several digestive enzymes. Digestive juices from the pancreas, liver, and gallbladder, besides as from gland cells of the intestinal wall itself, enter the duodenum. Bile is produced in the liver and stored and concentrated in the gallbladder. Bile contains bile salts which emulsify lipids while the pancreas produces enzymes that catabolize starches, disaccharides, proteins, and fats. These digestive juices suspension down the nutrient particles in the chyme into glucose, triglycerides, and amino acids. Some chemical digestion of nutrient takes place in the duodenum. Absorption of fatty acids also takes identify in the duodenum.

The second function of the small intestine is called the jejunum, shown in Figure 15.11. Here, hydrolysis of nutrients is connected while well-nigh of the carbohydrates and amino acids are captivated through the abdominal lining. The majority of chemical digestion and nutrient absorption occurs in the jejunum.

The ileum, too illustrated in Figure fifteen.11 is the terminal role of the minor intestine and here the bile salts and vitamins are absorbed into blood stream. The undigested nutrient is sent to the colon from the ileum via peristaltic movements of the muscle. The ileum ends and the large intestine begins at the ileocecal valve. The vermiform, "worm-similar," appendix is located at the ileocecal valve. The appendix of humans secretes no enzymes and has an insignificant role in immunity.

Big Intestine

The large intestine, illustrated in Effigy 15.thirteen, reabsorbs the water from the undigested nutrient material and processes the waste product. The human large intestine is much smaller in length compared to the pocket-size 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 thing. The colon is domicile to many leaner or "intestinal flora" that aid in the digestive processes. The colon can be divided into four regions, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. The main functions of the colon are to excerpt the h2o and mineral salts from undigested food, and to store waste material. Carnivorous mammals have a shorter large intestine compared to herbivorous mammals due to their diet.

Rectum and Anus

The rectum is the final finish of the large intestine, as shown in Effigy fifteen.13. The primary role of the rectum is to store the feces until defecation. The feces are propelled using peristaltic movements during emptying. The anus is an opening at the far-end of the digestive tract and is the leave point for the waste textile. Two sphincters between the rectum and anus control elimination: the inner sphincter is involuntary and the outer sphincter is voluntary.

Accessory Organs

The organs discussed higher up are the organs of the digestive tract through which food passes. Accessory organs are organs that add secretions (enzymes) that catabolize food into nutrients. Accessory organs include salivary glands, the liver, the pancreas, and the gallbladder. The liver, pancreas, and gallbladder are regulated by hormones in response to the nutrient consumed.

The liver is the largest internal organ in humans and information technology plays a very important role in digestion of fats and detoxifying claret. The liver produces bile, a digestive juice that is required for the breakup of fat components of the food in the duodenum. The liver also processes the vitamins and fats and synthesizes many plasma proteins.

The pancreas is another important gland that secretes digestive juices. The chyme produced from the stomach is highly acidic in nature; the pancreatic juices comprise high levels of bicarbonate, an brine that neutralizes the acidic chyme. Additionally, the pancreatic juices contain a large diverseness of enzymes that are required for the digestion of poly peptide and carbohydrates.

The gallbladder is a small-scale organ that aids the liver by storing bile and concentrating bile salts. When chyme containing fatty acids enters the duodenum, the bile is secreted from the gallbladder into the duodenum.

Summary

Different animals have evolved unlike types of digestive systems specialized to come across their dietary needs. Humans and many other animals take monogastric digestive systems with a unmarried-chambered stomach. Birds have evolved a digestive organization that includes a gizzard where the food is crushed into smaller pieces. This compensates for their inability to masticate. Ruminants that consume large amounts of plant fabric have a multi-chambered stomach that digests roughage. Pseudo-ruminants have similar digestive processes equally ruminants but practice not have the four-compartment tum. Processing nutrient involves ingestion (eating), digestion (mechanical and enzymatic breakdown of big molecules), absorption (cellular uptake of nutrients), and elimination (removal of undigested waste product as feces).

Many organs work together to digest food and absorb nutrients. The oral cavity 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. The food bolus travels through the esophagus by peristaltic movements to the breadbasket. The stomach has an extremely acidic environs. An enzyme chosen pepsin digests poly peptide in the breadbasket. Farther digestion and absorption take place in the small intestine. The large intestine reabsorbs h2o from the undigested nutrient and stores waste until elimination.

Exercises

1. Which of the post-obit statements nigh the digestive system is simulated?
   1. Chyme is a mixture of nutrient and digestive juices that is produced in the tummy.
   2. Food enters the large intestine before the small intestine.
   3. In the small intestine, chyme mixes with bile, which emulsifies fats.
   4. The stomach is separated from the modest intestine by the pyloric sphincter.
2. Which of the post-obit statements about the pocket-size intestine is false?
   1. Absorptive cells that line the small intestine have microvilli, minor projections that increase surface area and aid in the absorption of food.
   2. The inside of the minor intestine has many folds, called villi.
   3. Microvilli are lined with blood vessels as well as lymphatic vessels.
   4. The inside of the small intestine is called the lumen.
3. Which of the following is a pseudo-ruminant?
   1. cow
   2. hog
   3. crow
   4. horse
4. Which of the following statements is untrue?
   1. Roughage takes a long time to assimilate.
   2. Birds eat big quantities at 1 fourth dimension so that they tin fly long distances.
   3. Cows practise non have upper teeth.
   4. In pseudo-ruminants, roughage is digested in the cecum.
5. The acidic nature of chyme is neutralized past ________.
   1. potassium hydroxide
   2. sodium hydroxide
   3. bicarbonates
   4. vinegar
6. The digestive juices from the liver are delivered to the ________.
   1. tum
   2. liver
   3. duodenum
   4. colon
7. How does the polygastric digestive system assistance in digesting roughage?
8. How do birds digest their food in the absence of teeth?
9. What is the function of the accompaniment organs in digestion?
10. Explain how the villi and microvilli aid in assimilation.

Answers

1. B
2. C
3. D
4. B
5. C
6. C
7. Animals with a polygastric digestive arrangement take a multi-chambered tum. The four compartments of the breadbasket are called the rumen, reticulum, omasum, and abomasum. These chambers contain many microbes that break downwardly the cellulose and ferment the ingested food. The abomasum is the "truthful" stomach and is the equivalent of a monogastric breadbasket chamber where gastric juices are secreted. The four-compartment gastric chamber provides larger space and the microbial support necessary for ruminants to digest plant fabric.
8. Birds have a tum chamber called a gizzard. Here, the food is stored, soaked, and basis into finer particles, often using pebbles. Once this process is complete, the digestive juices take over in the proventriculus and continue the digestive process.
9. Accessory organs play an important role in producing and delivering digestive juices to the intestine during digestion and assimilation. Specifically, the salivary glands, liver, pancreas, and gallbladder play important roles. Malfunction of any of these organs can lead to disease states.
10. The villi and microvilli are folds on the surface of the pocket-size intestine. These folds increase the expanse of the intestine and provide more area for the absorption of nutrients.

Glossary

alimentary canal: tubular digestive system with a mouth and anus
anus: leave point for waste material
bile: digestive juice produced by the liver; important for digestion of lipids
bolus: mass of food resulting from chewing activity and wetting by saliva
carnivore: beast that consumes animal flesh
chyme: mixture of partially digested food and stomach juices
digestion: mechanical and chemical break down of food into small organic fragments
duodenum: first part of the minor intestine where a large role of digestion of carbohydrates and fats occurs
endocrine system: organization that controls the response of the various glands in the body and the release of hormones at the appropriate times
esophagus: tubular organ that connects the mouth to the breadbasket
essential food: nutrient that cannot be synthesized past the body; it must be obtained from nutrient
gallbladder: organ that stores and concentrates bile
gastric inhibitory peptide: hormone secreted by the pocket-size intestine in the presence of fatty acids and sugars; information technology also inhibits acid product and peristalsis in guild to slow downward the rate at which nutrient enters the pocket-sized intestine
gastrin: hormone which stimulates hydrochloric acid secretion in the stomach
gastrovascular crenel: digestive organization consisting of a single opening
gizzard: muscular organ that grinds food
herbivore: beast that consumes strictly plant diet
ileum: last part of the small intestine; connects the minor intestine to the large intestine; of import for absorption of B-12
ingestion: deed of taking in food
jejunum: second part of the minor intestine
lactase: enzyme that breaks down lactose into glucose and galactose
large intestine: digestive system organ that reabsorbs water from undigested cloth and processes waste thing
lipase: enzyme that chemically breaks down 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 of import roles in the body
monogastric: digestive arrangement that consists of a single-chambered stomach
omnivore: animal that consumes both plants and animals
pancreas: gland that secretes digestive juices
pepsinogen: inactive form of pepsin
pepsin: enzyme found in the stomach whose chief role is poly peptide digestion
peristalsis: wave-like movements of musculus tissue
proventriculus: glandular part of a bird's stomach
rectum: area of the body where feces is stored until emptying
roughage: component of food that is low in free energy and high in fiber
ruminant: animal with a breadbasket divided into iv compartments
salivary amylase: enzyme found in saliva, which converts carbohydrates to maltose
small intestine: organ where digestion of protein, fats, and carbohydrates is completed
somatostatin: hormone released to finish acid secretion when the stomach is empty
sphincter: band of muscle that controls movement of materials throughout the digestive tract
stomach: saclike organ containing acidic digestive juices
villi: folds on the inner surface of the pocket-size intestine whose part is to increase absorption expanse
vitamin: organic substance necessary in small-scale amounts to sustain life

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Source: https://opentextbc.ca/biology/chapter/15-1-digestive-systems/

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