Describe the processes of digestion,
absorption, and metabolism.
The gastrointestinal tract, or alimentary canal, is a hollow tube that begins at the mouth and ends
at the anus. The specific parts of the tract include the mouth, esophagus, stomach, small/ large
intestine, and the anus. Other organs that lie outside the tract but support it work by secretion of
important enzymes and digestive fluids are the pancreas, gallbladder, and liver.
- Receives Food – The mouth
- Releases Nutrients – The digestion and separation of components takes place in
the stomach and small intestine
- Delivers Nutrients – Microvilli, absorbing structures, are located in the small intestine
and transfer nutrients into the portal blood (amino acids or glucose).
- Excretes Non-Digestible Waste - Fecal matter moves from the colon down to the rectum
Digestion is the complicated process by which food is broken down and nutrients are released. It
is the step that helps to prepare food for body use. Digestion involves two types of actions:
- Chemical breakdown of food into its constituent parts through the action of enzymes and
other specialized fluids. Each chemical agent acts on a particular macronutrient in a
specific region of the gastrointestinal tract.
- Muscular, or mechanical, includes mechanical mixing and propulsive movements
controlled by neuromuscular, self-regulating systems. These notions work together
to move the food mass along the alimentary canal at the best rate for digestion and
absorption.
Food is digested chemically through the combined action of various secretions of the
following four types:
- Enzymes attack designated chemical bonds within the structure of nutrient compounds,
freeing their component parts.
- Hydrochloric Acid and Buffer Ions are secretions that produce the pH necessary for the
activity of certain enzymes.
- Mucus is a sticky, slippery fluid that lubricates and protects the inner lining of
the gastrointestinal tract and eases the passage of the food mass.
- Water and electrolytes are agents that provide the appropriate solutions in the
amounts needed to circulate substances released in digestion.
*Organized muscle layers in the gastrointestinal wall provide the motility needed for digestion,
and the coordinated interaction of four smooth-muscle layers make it possible for four
different types of movement.
*Movement of Food Through the Digestive Tract
,1. The first steps in digestion begin at the mouth, where salivary enzymes act on
carbohydrates and all foods are broken down into smaller particles to facilitate the later
action of digestive juices. The esophagus will deliver the food mass to the stomach.
Mastication is when food is broken down into smaller particles by chewing or
biting. Food is broken down through the salivary amylase, which is secreted by salivary
glands. Mucus is also secreted to lubricate and bind food particles together. Salivary
secretions also help to moisten food particles so they can easily move down the
esophagus.
2. The esophagus is a muscular tube that connects the mouth and throat with the stomach
and serves as a channel to carry the food mass into the body after swallowing. Two
key components to the esophagus are the Upper Esophageal Sphincter and the Lower
Esophageal Sphincter.
The Upper Esophageal Sphincter: Controls the entry of the food into the
esophagus. Between swallows, the UES is closed. It is located in the pharyngeal
area.
The Lower Esophageal Sphincter: Controls the movement of the food into the
stomach. It prevents the acidic chemical action in the stomach from back flowing
into the esophagus. Prevents the reflux of acid into the esophagus.
3. As food moves into the stomach, it will rest against the stomachs wall, and the stomach
will increase its kneading and mixing actions to move the mass of food. This moves
food down to the distal end of the stomach. The contractions will reduce the food mass
to a semifluid chyme. The highly acidic chyme must be released slowly enough to
allow it to be buffered by the alkaline secretions of the small intestine.
*The caloric density of a meal, along with its volume and composition,
influences the rate of stomach empting.
*The speed at which food moves from the gastroesophageal sphincter to the distal
end of the stomach and into the small intestine influence food intake, as messages
to the brain are signaling the arrival of food in the SI, which brings about the
release of gastrointestinal hormones that induce feeling of satiety.
Secretions produces in the stomach include the following:
*Hydrochloric Acid creates the acidic environment needed for digestive enzymes
to work.
*Mucus is a viscous secretion that protects the stomach lining from the eroding
effect of the acid, and it also binds and mixes the food mass and helps to move
it along
*Enzymes: The major enzyme in the stomach is pepsin, which begins the
breakdown of protein and is activated by hydrochloric acid. The stomach also
produces a small amount of gastric lipase, and rennin in children.
Absorption of some nutrients and vitamins, such as vitamin B, begin in the stomach.
4. In comparison to the other sections of the gastrointestinal tract, the small intestine carries
the major burden of chemical digestion. It secretes several enzymes that are specific to
, each carbohydrate, fat, or protein, and is assisted by other enzymes entering from the
pancreas. The small intestine acts as regulatory center, sensing the nutrient content, ph.,
osmolality of its contents, and controls enzyme secretion. The majority of nutrient
absorption occurs in the small intestine.
The following all help in the absorption process:
Enzymes: Specific enzymes act on specific macronutrients to bring about their final
breakdown to forms the body can absorb and use.
Carbohydrates: In the mouth, Salivary amylase breaks down starch into dextrin.
In the small intestine, Pancreatic Amylase breaks down starch into disaccharides;
lactose, sucrose, and maltose. Disaccharides are broken down into
monosaccharides. Further breakdown is done, but the end products of
carbohydrates are fructose, glucose, galactose. Pancreatic Amylase and
Dextrin for carbohydrates
Protein: In the stomach, Pepsin and hydrochloric acid break down protein to
polypeptides. In the small intestine, trypsin breaks down protein and polypeptides
into dipeptides. Further breakdown is done, but the end products of proteins
are amino acids. Pepsin, hydrochloric acid, and trypsin for proteins.
Fat: In the mouth, Lingual Lipase plays a minor role in the start of fat digestion.
In the stomach, Tributyrinase breaks down tributyrin (butterfat)to glycerol and
fatty acids. In the small intestine, Bile emulsifies fat and the pancreatic lipase
breaks down fat into glycerol, diglycerides, monoglycerides, and fatty acids.
Lingual lipase and Tributyrinase.
Mucus: The glands located at the entrance of the duodenum secrete large amounts of
mucus. As in the stomach, mucus protects the intestinal mucosa from irritation and
digestion by the highly acidic chyme. Other cells along the wall of the intestinal wall will
secrete mucus when touched by the moving food mass, protecting the mucosal tissues
from abrasion.
Hormones: When signaled by the presence of acid in the food mass entering from the
stomach, the mucosal cells in the upper region of the small intestine produce the local
gastrointestinal hormone secretin 5. In turn, this secretion will stimulate the pancreas to
send alkaline pancreatic juices into the duodenum to buffer the acidic chyme.
Bile: Bile emulsifies fat and facilitates its digestion. Bile is produced in the liver as a
dilute watery solution and is then concentrated and stored by the gallbladder. When
fat enters the duodenum, the local gastrointestinal hormone cholecystokinin (CCK) is
secreted by glands in the intestinal mucosa and stimulates the gallbladder to contract and
release bile. By means of the enterohepatic circulation, molecules of bile are reabsorbed
and returned to the liver and gallbladder to be used over and over again. CCK also acts
absorption, and metabolism.
The gastrointestinal tract, or alimentary canal, is a hollow tube that begins at the mouth and ends
at the anus. The specific parts of the tract include the mouth, esophagus, stomach, small/ large
intestine, and the anus. Other organs that lie outside the tract but support it work by secretion of
important enzymes and digestive fluids are the pancreas, gallbladder, and liver.
- Receives Food – The mouth
- Releases Nutrients – The digestion and separation of components takes place in
the stomach and small intestine
- Delivers Nutrients – Microvilli, absorbing structures, are located in the small intestine
and transfer nutrients into the portal blood (amino acids or glucose).
- Excretes Non-Digestible Waste - Fecal matter moves from the colon down to the rectum
Digestion is the complicated process by which food is broken down and nutrients are released. It
is the step that helps to prepare food for body use. Digestion involves two types of actions:
- Chemical breakdown of food into its constituent parts through the action of enzymes and
other specialized fluids. Each chemical agent acts on a particular macronutrient in a
specific region of the gastrointestinal tract.
- Muscular, or mechanical, includes mechanical mixing and propulsive movements
controlled by neuromuscular, self-regulating systems. These notions work together
to move the food mass along the alimentary canal at the best rate for digestion and
absorption.
Food is digested chemically through the combined action of various secretions of the
following four types:
- Enzymes attack designated chemical bonds within the structure of nutrient compounds,
freeing their component parts.
- Hydrochloric Acid and Buffer Ions are secretions that produce the pH necessary for the
activity of certain enzymes.
- Mucus is a sticky, slippery fluid that lubricates and protects the inner lining of
the gastrointestinal tract and eases the passage of the food mass.
- Water and electrolytes are agents that provide the appropriate solutions in the
amounts needed to circulate substances released in digestion.
*Organized muscle layers in the gastrointestinal wall provide the motility needed for digestion,
and the coordinated interaction of four smooth-muscle layers make it possible for four
different types of movement.
*Movement of Food Through the Digestive Tract
,1. The first steps in digestion begin at the mouth, where salivary enzymes act on
carbohydrates and all foods are broken down into smaller particles to facilitate the later
action of digestive juices. The esophagus will deliver the food mass to the stomach.
Mastication is when food is broken down into smaller particles by chewing or
biting. Food is broken down through the salivary amylase, which is secreted by salivary
glands. Mucus is also secreted to lubricate and bind food particles together. Salivary
secretions also help to moisten food particles so they can easily move down the
esophagus.
2. The esophagus is a muscular tube that connects the mouth and throat with the stomach
and serves as a channel to carry the food mass into the body after swallowing. Two
key components to the esophagus are the Upper Esophageal Sphincter and the Lower
Esophageal Sphincter.
The Upper Esophageal Sphincter: Controls the entry of the food into the
esophagus. Between swallows, the UES is closed. It is located in the pharyngeal
area.
The Lower Esophageal Sphincter: Controls the movement of the food into the
stomach. It prevents the acidic chemical action in the stomach from back flowing
into the esophagus. Prevents the reflux of acid into the esophagus.
3. As food moves into the stomach, it will rest against the stomachs wall, and the stomach
will increase its kneading and mixing actions to move the mass of food. This moves
food down to the distal end of the stomach. The contractions will reduce the food mass
to a semifluid chyme. The highly acidic chyme must be released slowly enough to
allow it to be buffered by the alkaline secretions of the small intestine.
*The caloric density of a meal, along with its volume and composition,
influences the rate of stomach empting.
*The speed at which food moves from the gastroesophageal sphincter to the distal
end of the stomach and into the small intestine influence food intake, as messages
to the brain are signaling the arrival of food in the SI, which brings about the
release of gastrointestinal hormones that induce feeling of satiety.
Secretions produces in the stomach include the following:
*Hydrochloric Acid creates the acidic environment needed for digestive enzymes
to work.
*Mucus is a viscous secretion that protects the stomach lining from the eroding
effect of the acid, and it also binds and mixes the food mass and helps to move
it along
*Enzymes: The major enzyme in the stomach is pepsin, which begins the
breakdown of protein and is activated by hydrochloric acid. The stomach also
produces a small amount of gastric lipase, and rennin in children.
Absorption of some nutrients and vitamins, such as vitamin B, begin in the stomach.
4. In comparison to the other sections of the gastrointestinal tract, the small intestine carries
the major burden of chemical digestion. It secretes several enzymes that are specific to
, each carbohydrate, fat, or protein, and is assisted by other enzymes entering from the
pancreas. The small intestine acts as regulatory center, sensing the nutrient content, ph.,
osmolality of its contents, and controls enzyme secretion. The majority of nutrient
absorption occurs in the small intestine.
The following all help in the absorption process:
Enzymes: Specific enzymes act on specific macronutrients to bring about their final
breakdown to forms the body can absorb and use.
Carbohydrates: In the mouth, Salivary amylase breaks down starch into dextrin.
In the small intestine, Pancreatic Amylase breaks down starch into disaccharides;
lactose, sucrose, and maltose. Disaccharides are broken down into
monosaccharides. Further breakdown is done, but the end products of
carbohydrates are fructose, glucose, galactose. Pancreatic Amylase and
Dextrin for carbohydrates
Protein: In the stomach, Pepsin and hydrochloric acid break down protein to
polypeptides. In the small intestine, trypsin breaks down protein and polypeptides
into dipeptides. Further breakdown is done, but the end products of proteins
are amino acids. Pepsin, hydrochloric acid, and trypsin for proteins.
Fat: In the mouth, Lingual Lipase plays a minor role in the start of fat digestion.
In the stomach, Tributyrinase breaks down tributyrin (butterfat)to glycerol and
fatty acids. In the small intestine, Bile emulsifies fat and the pancreatic lipase
breaks down fat into glycerol, diglycerides, monoglycerides, and fatty acids.
Lingual lipase and Tributyrinase.
Mucus: The glands located at the entrance of the duodenum secrete large amounts of
mucus. As in the stomach, mucus protects the intestinal mucosa from irritation and
digestion by the highly acidic chyme. Other cells along the wall of the intestinal wall will
secrete mucus when touched by the moving food mass, protecting the mucosal tissues
from abrasion.
Hormones: When signaled by the presence of acid in the food mass entering from the
stomach, the mucosal cells in the upper region of the small intestine produce the local
gastrointestinal hormone secretin 5. In turn, this secretion will stimulate the pancreas to
send alkaline pancreatic juices into the duodenum to buffer the acidic chyme.
Bile: Bile emulsifies fat and facilitates its digestion. Bile is produced in the liver as a
dilute watery solution and is then concentrated and stored by the gallbladder. When
fat enters the duodenum, the local gastrointestinal hormone cholecystokinin (CCK) is
secreted by glands in the intestinal mucosa and stimulates the gallbladder to contract and
release bile. By means of the enterohepatic circulation, molecules of bile are reabsorbed
and returned to the liver and gallbladder to be used over and over again. CCK also acts
