Digestive Systems and Absorption of Food Nutrients

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Digestive Systems and Absorption of Food
Nutrients
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Digestion

• Is the process of breaking feed down into simple
  substances that can be absorbed by the body

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Absorption

• Refers to taking the digested parts of the feed
  into the bloodstream.

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Ruminants

• Are animals that have a stomach that is divided
  into several parts. Cattle, Sheep, and Goats are
  ruminants. Ruminants are cud-chewing animals.

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Non ruminants

• Are animals that have simple, one-compartment
  stomachs. Pigs, horses, and poultry are non
  ruminants.

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The Digestive System

• Consists of the parts of the body involved in
  chewing and digesting feed. This system also
  moves the digested feed through the animals body
  and absorbs the products of digestion.

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• There is a great deal of difference among animals
  in their ability to use various kinds of feed.
  This difference is mainly the result of
  differences in their digestive systems. Ruminant
  animals can digest large quantities of fibrous
  feeds, such as hay and pasture.

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• Non-ruminant animals need a high-energy,
  low-fiber ration, such as grain.
• Grains and protein supplements are called
  concentrates.

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Cont.

• Cattle and sheep can digest about 44 percent of
  the roughage they eat.

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Roughage

• Refers to high-fiber feeds, such as hay, silage,
  and pasture.
• Horses are able to digest about 39 percent of the
  roughage in their ration.
• Swine can digest only about 22 percent of the
  roughage they eat.

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• Ruminants can digest large quantities of roughage
  because of the bacteria present in their
  digestive systems.
• These bacteria can produce proteins, B-complex
  vitamins, and vitamin K.

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Parts of the digestive System

• The digestive system is made up of a number of
  parts of organs.
• The system begins at the mouth, which is where
  the food enters the animals body.
• The esophagus or gullet is a tube like passage
  from the mouth to the stomach.

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• The stomach receives the feed and adds chemicals
  that help in the digestive process.
• The food next enters the small intestine.
• The small intestine is a long folded tube
  attached to the lower end of the stomach.

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• From there, the digested material passes to the
  large intestine.
• The large intestine is larger in diameter but
  much shorter in length than the small intestine.
• The large intestine ends with the rectum.
• Undigested material, called feces, is passed from
  the body through the anus.

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Cont.

• The digestive system also includes a number
  accessory organs.
• Accessory organs are the teeth, tongue, salivary
  glands, liver, and pancreas.
• The first three are located in the mouth.
• The liver is the largest gland in the body. It is
  located along the small intestine just past the
  stomach.

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• The pancreas is located along the upper part of
  the small intestine.
• The digestive systems of most livestock are very
  similar in terms of the parts they contain.
• However, there are some differences in the
  poultry digestive system.
• Poultry have no teeth. They have a crop and
  gizzard.

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• They also have two blind pouches, called ceca,
  that are attached to the small intestine.

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Cont.

• The cloaca is an enlarged part connected to the
  large intestine. Elimination (passing of feces)
  in poultry is through the vent.

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The Digestive Process
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Mouth and Esophagus

• The chewing action of the mouth and teeth breaks,
  cuts, and tears up the feed.
• This increases the surface area of the feed
  particles which, in turn, helps the chewing and
  swallowing process.
• Saliva also stimulates the taste.

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• In ruminants, saliva is important in the chewing
  of the cud.
• In most animals, saliva contains the enzymes,
  salivary amylase and salivary maltase.
• Enzymes are substances called organic catalysts
  that speed up the digestive process.

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• Salivary amylase changes some starch to maltose
  or malt sugar.
• Salivary maltase changes maltose to glucose.

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Cont.

• Ruminants do not chew their food completely when
  they eat.
• Roughages, such as hay and silage, and coarse
  feeds, such as unbroken kernels of corn, are
  re-chewed later. These feeds from ball-like
  masses in the stomach.

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• The material is then forced back up the esophagus
  to be chewed again.
• This is called rumination or chewing the cud.
• The tongue helps direct the feed to the throat
  for swallowing.
• The chewed material enters the esophagus.

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• Food is carried down the esophagus by a series of
  muscle contractions.
• A valve called the cardia is located at the end
  of the esophagus.
• This valve prevents food in the stomach from
  coming back into the esophagus.

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The Ruminant stomach

• The four parts of the ruminant stomach are rumen,
  reticulum, omasum, and abomasum.
• Because of this four-part stomach, digestion in
  ruminants differs from that in non ruminants.
• Ruminants eat rapidly.

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• They do not chew much of their feed before they
  swallow it.
• The solid part of the feed goes into the rumen.
• The liquid part goes into the reticulum, then to
  the omasum, and on into the abomasum.

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• In the rumen, the feed is mixed and partially
  broken down by bacteria. A slow churning and
  mixing action takes place.

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Cont.

• When the rumen is full, the animal lies down. The
  feed is then forced back into the mouth and
  rumination occurs.
• Cattle chew their cud about six to eight times
  per day.
• A total of five to seven hours each day is spent
  in ruminant.

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• There is no division between the rumen and the
  reticulum.
• Together, they make up about 85 percent of the
  stomach.
• They are located on the left side of the middle
  of the animal.
• The rumen and reticulum contain millions of
  micro-organisms called bacteria and protozoa.

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Cont.

• Bacteria and protozoa are one-celled animals.
  Muscles in the rumen and reticulum help break the
  food into smaller particles. This makes it easier
  for the bacteria to act in the digestive process.
  Saliva and water are added to the feed to aid in
  digestion.

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Amino acids

• Are compounds that contain carbon, hydrogen,
  oxygen, and nitrogen.
• They are essential for growth and maintenance of
  cells.
• Bacteria also produce many of the vitamins needed
  by the animal.
• As the bacteria die, the animal digests them.
• This process makes protein and vitamins available
  to the animal.

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The non ruminant stomach

• When feed enters either the stomach of the non
  ruminant or the abomasum of the ruminant, gastric
  juice begins to flow.
• This fluid comes from glands in the wall of the
  stomach. The gastric juice contains 0.2 to 0.5
  percent hydrochloric acid.
• It stops all action of amylase when it mixes with
  the feed.

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• The gastric juice contains additional enzymes
  called pepsin, rennin, and gastric lipase.

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Cont.

• These enzymes act on the fed in the following
  ways.
• Pepsin breaks the proteins in the feed into
  proteoses and peptones.
• The casein of the milk is curdled by the rennin.
• Emulsified fats are split by the gastric lipase
  into glycerol and fatty acids

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• However, most of the fat entering the stomach is
  not emulsified. Thu, gastric lipase has little to
  do in the digestion process.

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Small intestine

• When the partly digested feed leaves the stomach,
  it is an acid, semi-fluid, gray, pulpy mass.
• This material is called chyme.
• In the small intestine, the chyme is mixed with
  three digestive juices pancreatic juice, bile,
  and intestinal juice.

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Pancreatic juice

• Is secreted (formed and given off) by the
  pancreatic lipase, and maltase.

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Trypsin

• Breaks down proteins not broken down by pepsin.
• Some of the proteosoes and peptones are broken
  down by trypsin to peptides.
• Proteoses, peptones, and peptides are
  combinations of amino acids. Proteoses are the
  most complex compounds, with peptides being the
  simplest.

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Pancreatic amylase

• Changes starch in the feed into maltose.
• Pancreatic amylase is more active in this process
  than salivary amylase because it is found in
  greater quantities and has a longer time to work
  on the feed.
• Sugar and maltose are broken down into even
  simpler substances.
• When acted on by maltase, they are changed into a
  simple sugar called glucose.

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Lipase

• Works on fats in the feed. It changes them into
  fatty acids and glycerol.

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Bile

• The liver produces a yellowish-green, alkaline,
  bitter liquid called bile.
• Bile is stored in the gall bladder in all animals
  except the horse.
• Bile aids in the digestion of fats and fatty
  acids. It also helps in the action of the enzyme,
  lipase. In a final step, fatty acids combine with
  bile to form soluble bile salts.

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Intestinal juice

• Glands in the walls of the small intestine
  produce intestinal juice.
• This fluid contains peptidase, sucrase, maltase,
  and lactase, which help in the digestion process.
  
• Proteoses and peptones are broken down by
  peptides into amino acids.

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• Starches and sugars are broken down by sucrase,
  maltase, and lactase into the simple sugars,
  glucose, fructose, and galactose.

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Absorption

• The wall of the small intestine is lined with
  many small fingerlike projections called villi.
• These increase the absorption area of the small
  intestine.
• Most food nutrients used by the animal are
  absorbed form the small intestine.

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The cecum

• Or blind gut is found where the small intestine
  joins the large intestine.
• The cecum is a small organ and has little
  function in most animals, except the horse.
• In the horse, roughage feeds are digested by
  bacterial action in the cecum, which explains why
  the horse can eat large amounts of roughage.

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Large Intestine

• The large intestine is larger in diameter but
  much shorter in length than the small intestine.
• The main function of the large intestine is to
  absorb water.
• Material that is not digested and absorbed in the
  small intestine passes into the large intestine.

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Development of the ruminant stomach

• The abomasum is the only part of the stomach of
  young ruminant animals that functions.
• Therefore, young ruminants cannot use roughages
  in their diet.
• Milk fed to the animal goes directly to to the
  abomasum.
• This action continues until the other parts of
  the stomach have developed.

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Digestion in poultry

• Poultry possess certain special digestive organs
  that are not found in other animals.
• Feed taken in by poultry first goes to the crop
  for storage.
• Here it is softened by saliva and secretions from
  the crop wall.
• The feed moves from the crop, through the
  glandular stomach into the muscular stomach.

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• The large red walls of the muscular stomach are
  thick, powerful muscles.

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Cont.

• Two blind pouches, or ceca, are found where the
  small intestine joins the large intestine. These
  are about 7 inches long. Their function is not
  known, but they are usually filled with soft,
  undigested feed. The cloaca is an enlarged part
  found where the large intestine joins the vent.

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Cont.

• Feces from the large intestine are passed out of
  the body through the vent. Eggs from the oviduct
  and urine from the kidneys also pass through the
  vent.

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Absorption of feed

• Digested feed is absorbed from the small
  intestine. Some feed is also absorbed from the
  large intestine. Feed is not broken down enough
  to be absorbed in the mouth or esophagus. In
  ruminants, some fatty acids are absorbed from the
  rumen. The stomach tissue of nonruminants is not
  suited for absorption.

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Cont.

• Villi, the millions of small finger-shaped
  projections on the wall of the intestine, are the
  key to absorption. Each villus ( singular of
  villi) has a network of blood capillaries and a
  lymph vessel through which nutrients enter the
  bloodstream. When absorbed, digested protein is
  in the form of amino acids.

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Cont.

• Starches and sugars are present as glucose,
  fructose, and galactose. Fiber is in the form of
  short-chained fatty acids. As the substances are
  absorbed by the blood capillaries in the villi,
  they pass through the liver and then into the
  blood.

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Cont.

• Digested fats, in the from of soaps and glycerol,
  undergo a slightly different process. They are
  formed again into fats and absorbed by the lymph
  vessel in the villi. They are then carried in the
  nick into the circulatory system.

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• Villi also absorb water and dissolved minerals
  into the bloodstream. The large intestine absorbs
  nutrients directly into the bloodstream. This is
  done through capillaries in the wall of the
  intestine.

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Cont.

• Most nutrients end their journey in the muscle
  cells. Some are deposited in the liver. The
  animal uses the nutrients to replace wornout
  cells and to build new ones. Some nutrients are
  used for energy others are stored in the form of
  fat for later use.

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Metabolism

• Is the sum of the processes, both chemical and
  physical, that are used by living organisms and
  cells to handle nutrients after they have been
  absorbed from the digestive system. The metabolic
  process include anabolism, catablism, and
  oxidation of nutrients.

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Anabolism

• Is the formation and repair of body tissues.
  Catabolism is the breakdown of body tissues into
  simpler substances and waste products. Oxidation
  of nutrients provides energy for the animal

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Summary

• Digestion is the breaking down of feeds into
  simple substances that can be absorbed into the
  bloodstream and used by the body cells. Enzymes
  do most of the job of digestion. Ruminant animals
  can use a lot of roughage in their rations. They
  have a four-part stomach in which bacteria break
  

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Cont.

• Down the roughage. Nonruminants must have more
  concentrates, such as grain, in their ration
  because they have a simple , one-part stomach.

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Cont.

• Most digested feed is absorbed from the small
  intestine of the animal. The small intestine has
  millions of tiny projections called villi through
  which nutrients are absorbed and enter the
  bloodstream.