Chyme
Encyclopedia
Chyme is the semifluid mass of partly digested food expelled by the stomach into the duodenum
.
Also known as chymus, it is the liquid substance found in the stomach
before passing through the pyloric valve and entering the duodenum
. It results from the mechanical and chemical breakdown of a bolus
and consists of partially digested food, water, hydrochloric acid
, and various digestive
enzyme
s. Chyme slowly passes through the pyloric sphincter
and into the duodenum, where the extraction of nutrient
s begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme anywhere between 40 minutes to a few hours.
With a pH
of around 2, chyme emerging from the stomach is very acidic. To raise its pH, the duodenum
secretes a hormone
, cholecystokinin
(CCK), which causes the gall bladder to contract, releasing alkaline bile
into the duodenum. The duodenum also produces the hormone secretin
to stimulate the pancreatic secretion of large amounts of sodium bicarbonate
, which raises the chyme's pH to 7 before it reaches the jejunum
. As it is protected by a thick layer of mucus
and utilizes the neutralizing actions of the sodium bicarbonate and bile, the duodenum is not as sensitive to highly acidic chyme as the rest of the small intestine.
At a pH of 7, the enzymes that were present from the stomach are no longer active. This then leads into the further breakdown of the nutrients still present by anaerobic bacteria which at the same time help to package the remains. These bacteria also help synthesize vitamin B and vitamin K
.
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
.
Also known as chymus, it is the liquid substance found in the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
before passing through the pyloric valve and entering the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
. It results from the mechanical and chemical breakdown of a bolus
Bolus (digestion)
In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....
and consists of partially digested food, water, hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
, and various digestive
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s. Chyme slowly passes through the pyloric sphincter
Sphincter
A sphincter is an anatomical structure, or a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning...
and into the duodenum, where the extraction of nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
s begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme anywhere between 40 minutes to a few hours.
With a pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of around 2, chyme emerging from the stomach is very acidic. To raise its pH, the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
secretes a hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
, cholecystokinin
Cholecystokinin
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein...
(CCK), which causes the gall bladder to contract, releasing alkaline bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
into the duodenum. The duodenum also produces the hormone secretin
Secretin
Secretin is a hormone that controls the secretions into the duodenum, and also separately, water homeostasis throughout the body. It is produced in the S cells of the duodenum in the crypts of Lieberkühn...
to stimulate the pancreatic secretion of large amounts of sodium bicarbonate
Sodium bicarbonate
Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda . The natural mineral form is...
, which raises the chyme's pH to 7 before it reaches the jejunum
Jejunum
The jejunum is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
. As it is protected by a thick layer of mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
and utilizes the neutralizing actions of the sodium bicarbonate and bile, the duodenum is not as sensitive to highly acidic chyme as the rest of the small intestine.
At a pH of 7, the enzymes that were present from the stomach are no longer active. This then leads into the further breakdown of the nutrients still present by anaerobic bacteria which at the same time help to package the remains. These bacteria also help synthesize vitamin B and vitamin K
Vitamin K
Vitamin K is a group of structurally similar, fat soluble vitamins that are needed for the posttranslational modification of certain proteins required for blood coagulation and in metabolic pathways in bone and other tissue. They are 2-methyl-1,4-naphthoquinone derivatives...
.