Cholecystokinin (CCK or CCK-PZ; from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac (

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...

)'') is a

peptide hormone Peptide hormones or protein hormones are hormones whose molecules are peptide, or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine system of animals, including h ...

of the

gastrointestinal system The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...

responsible for stimulating the

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...

and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

. Cholecystokinin, formerly called pancreozymin, is synthesized and secreted by

enteroendocrine cell Enteroendocrine cells are specialized cells of the gastrointestinal tract and pancreas with endocrine function. They produce gastrointestinal hormones or peptides in response to various stimuli and release them into the bloodstream for systemic ef ...

s in the

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 m ...

, the first segment of the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

. Its presence causes the release of

digestive enzymes Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption into the cells of the body. Digestive enzymes are found in the digestive tracts of anim ...

and

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile ...

from the

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...

and

, respectively, and also acts as a hunger suppressant.

History

Evidence that the small intestine controls the release of bile was uncovered as early as 1856, when French physiologist

Claude Bernard Claude Bernard (; 12 July 1813 – 10 February 1878) was a French physiologist. Historian I. Bernard Cohen of Harvard University called Bernard "one of the greatest of all men of science". He originated the term ''milieu intérieur'', and the a ...

showed that when dilute acetic acid was applied to the orifice of the bile duct, the duct released bile into the duodenum. In 1903 the French physiologist showed that this reflex was not mediated by the nervous system. In 1904 the French physiologist Charles Fleig showed that the discharge of bile was mediated by a substance that was conveyed by the blood. There remained the possibility that the increased flow of bile in response to the presence of acid in the duodenum might be due to

secretin Secretin is a hormone that regulates water homeostasis throughout the body and influences the environment of the duodenum by regulating secretions in the stomach, pancreas, and liver. It is a peptide hormone produced in the S cells of the duode ...

, which had been discovered in 1902. The problem was finally resolved in 1928 by

Andrew Conway Ivy Andrew Conway Ivy (February 25, 1893 – February 7, 1978) was an American physician. He was appointed by the American Medical Association as its representative at the 1946 Nuremberg Medical Trial for Nazi doctors, but later fell into disrepute for ...

and his colleague Eric Oldberg of the

Northwestern University Medical School Northwestern or North-western or North western may refer to: * Northwest, a direction * Northwestern University, a private research university in Evanston, Illinois ** The Northwestern Wildcats, this school's intercollegiate athletic program ** No ...

, who found a new hormone that caused contraction of the gall bladder and that they called "cholecystokinin". In 1943, Alan A. Harper and Henry S. Raper of the

University of Manchester , mottoeng = Knowledge, Wisdom, Humanity , established = 2004 – University of Manchester Predecessor institutions: 1956 – UMIST (as university college; university 1994) 1904 – Victoria University of Manchester 1880 – Victoria Univer ...

discovered a hormone that stimulated pancreatic

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

secretion and that they named "pancreozymin"; however, pancreozymin was subsequently found to be cholecystokinin. Swedish biochemists Johannes Erik Jorpes and Viktor Mutt undertook the monumental task of isolating and purifying porcine cholecystokinin and then determining its

amino acid sequence Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthes ...

. They finally presented porcine cholecystokinin's amino acid sequence in 1968.

Structure

Cholecystokinin is a member of the gastrin/cholecystokinin family of peptide hormones and is very similar in structure to

gastrin Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas. Gastrin ...

, another

gastrointestinal hormone The gastrointestinal hormones (or gut hormones) constitute a group of hormones secreted by enteroendocrine cells in the stomach, pancreas, and small intestine that control various functions of the digestive organs. Later studies showed that most of ...

. CCK and gastrin share the same five C-terminal amino acids. CCK is composed of varying numbers of

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s depending on

post-translational modification Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribosome ...

of the 150-amino acid precursor, preprocholecystokinin. Thus, the CCK peptide hormone exists in several forms, each identified by the number of amino acids it contains, e.g., CCK-58, CCK-33, CCK-22 and CCK-8. CCK58 assumes a

helix-turn-helix Helix-turn-helix is a DNA-binding protein (DBP). The helix-turn-helix (HTH) is a major structural motif capable of binding DNA. Each monomer incorporates two α helices, joined by a short strand of amino acids, that bind to the major groove of D ...

configuration. Biological activity resides in the C-terminus of the peptide. Most CCK peptides have a

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ar ...

group attached to a

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...

located seven residues from the C-terminus (see

tyrosine sulfation Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated. ...

). This modification is crucial for the ability of CCK to activate the

cholecystokinin A receptor The Cholecystokinin A receptor is a human protein, also known as CCKAR or CCK1, with CCK1 now being the IUPHAR-recommended name. Function This gene encodes a G-protein coupled receptor that binds sulfated members of the cholecystokinin (CCK) ...

. Nonsulfated CCK peptides also occur, which consequently cannot activate the CCK-A receptor, but their biological role remains unclear.

Function

CCK plays important

physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

roles both as a

neuropeptide Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

and as a

in the gut. It is the most abundant neuropeptide in the central nervous system. CCK has been researched thoroughly for its role in digestion and it participates in a number of processes such as

satiety Satiety ( ) is a state or condition of fullness gratified beyond the point of satisfaction, the opposite of hunger. It is a state which induces meal termination.Hetherington, M.Sensory-specific satiety and its importance in meal termination ''Neuro ...

and

anxiety Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...

Gastrointestinal

CCK is synthesized and released by enteroendocrine cells in the mucosal lining of the small intestine (mostly in the duodenum and jejunum), called I cells, neurons of the

enteric nervous system The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract. It is capable of ...

, and neurons in the brain. It is released rapidly into the circulation in response to a meal. The greatest stimulator of CCK release is the presence of

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

s and/or certain in the

s in the

chyme Chyme or chymus (; from Greek χυμός ''khymos'', "juice") is the semi-fluid mass of partly digested food that is expelled by a person's stomach, through the pyloric valve, into 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 m ...

. In addition, release of CCK is stimulated by monitor peptide (released by pancreatic

acinar cells Centroacinar cells are spindle-shaped cells in the exocrine pancreas. They represent an extension of the intercalated duct into each pancreatic acinus. These cells are commonly known as duct cells, and secrete an aqueous bicarbonate solution unde ...

), CCK-releasing protein (via

paracrine signalling Paracrine signaling is a form of cell signaling, a type of cellular communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. Signaling molecules known as paracrine factors diffuse over ...

mediated by

enterocyte Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase its ...

s in the

gastric The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

and

intestinal mucosa The gastrointestinal wall of the gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut (the lumen) outwards, these are: # Mucosa # Submucosa # Muscular layer # Serosa or adventitia The mucosa is ...

), and

acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Part ...

(released by the

parasympathetic nerve The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of t ...

fibers of the

vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right ...

). Once in the circulatory system, CCK has a relatively short half-life.

Digestion

CCK mediates digestion in the small intestine by inhibiting gastric emptying. It stimulates the

of the

to release a juice rich in pancreatic

(hence an alternate name, ''pancreozymin'') that catalyze the digestion of fat, protein, and carbohydrates. Thus, as the levels of the substances that stimulated the release of CCK drop, the concentration of the hormone drops as well. The release of CCK is also inhibited by

somatostatin Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-couple ...

and pancreatic peptide. Trypsin, a protease released by pancreatic acinar cells, hydrolyzes CCK-releasing peptide and monitor peptide, in effect turning off the additional signals to secrete CCK. CCK also causes the increased production of hepatic bile, and stimulates the contraction of the

gall bladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, althoug ...

and the relaxation of the

sphincter of Oddi The sphincter of Oddi (also hepatopancreatic sphincter or Glisson's sphincter), abbreviated as SO, is a muscular valve that in some animals, including humans, controls the flow of digestive juices (bile and pancreatic juice) out of the pancreas t ...

(Glisson's sphincter), resulting in the delivery of

into the duodenal part of the small intestine.

Bile salt Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Prima ...

s form

amphipathic An amphiphile (from the Greek αμφις amphis, both, and φιλíα philia, love, friendship), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'') properties. Such a compoun ...

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

micelle A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated collo ...

s that

emulsify An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Altho ...

fats, aiding in their digestion and absorption. Effects of CCK on the gastrointestinal tract

Satiety

As a peptide hormone, CCK mediates satiety by acting on the

CCK receptor Cholecystokinin receptors or CCK receptors are a group of G-protein coupled receptors which bind the peptide hormones cholecystokinin (CCK) and gastrin. There are two different subtypes CCKA and CCKB which are ~50% homologous: Various cholecys ...

s distributed widely throughout the

. The mechanism for hunger suppression is thought to be a decrease in the rate of gastric emptying. CCK also has stimulatory effects on the

, effects that can be inhibited by

capsaicin Capsaicin (8-methyl-''N''-vanillyl-6-nonenamide) ( or ) is an active component of chili peppers, which are plants belonging to the genus ''Capsicum''. It is a chemical irritant for mammals, including humans, and produces a sensation of burning ...

. The stimulatory effects of CCK oppose those of

ghrelin Ghrelin (; or lenomorelin, INN) is a hormone produced by enteroendocrine cells of the gastrointestinal tract, especially the stomach, and is often called a "hunger hormone" because it increases the drive to eat. Blood levels of ghrelin are highe ...

, which has been shown to inhibit the vagus nerve. The effects of CCK vary between individuals. For example, in

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...

s, CCK administration significantly reduces hunger in adult males, but is slightly less effective in younger subjects, and even slightly less effective in females. The hunger-suppressive effects of CCK also are reduced in obese rats.

Neurological

CCK is found extensively throughout the

, with high concentrations found in the

limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''Ps ...

. CCK is synthesized as a 115 amino acid

preprohormone A preprohormone is the precursor protein to one or more prohormones, which are in turn precursors to peptide hormones. In general, the protein consists of the amino acid chain that is created by the hormone-secreting cell, before any changes have ...

, that is then converted into multiple

isoforms A protein isoform, or "protein variant", is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences. While many perform the same or similar biological roles, some isof ...

. The predominant form of CCK in the central nervous system is the

sulfated Sulfation is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the ...

octapeptide, CCK-8S.

Anxiogenic

In both humans and rodents, studies clearly indicate that elevated CCK levels causes increased

. The site of the anxiety-inducing effects of CCK seems to be central with specific targets being the

basolateral amygdala The basolateral amygdala, or basolateral complex, consists of the lateral, basal and accessory-basal nuclei of the amygdala. The lateral nuclei receives the majority of sensory information, which arrives directly from the temporal lobe structures, ...

hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...

, peraqueductal grey, and cortical regions.

Panicogenic

The CCK tetrapeptide fragment

CCK-4 Cholecystokinin tetrapeptide (CCK-4, Trp- Met- Asp- Phe-NH2) is a peptide fragment derived from the larger peptide hormone cholecystokinin. Unlike cholecystokin which has a variety of roles in the gastrointestinal system as well as central nervou ...

( Trp- Met-

Asp Asp may refer to: Places * Asp, part of Densbüren, Aargau, Switzerland * Aspe (''Asp'' in Valencian), Alicante, Spain * Asp Lake, a lake in Minnesota Animals * Asp (fish) * Asp (snake), in antiquity, one of several venomous snakes ** ''Cera ...

- Phe-NH₂) reliably causes anxiety and

panic attack Panic attacks are sudden periods of intense fear and discomfort that may include palpitations, sweating, chest pain or chest discomfort, shortness of breath, trembling, dizziness, numbness, confusion, or a feeling of impending doom or of losing ...

s (panicogenic effect) when administered to humans and is commonly used in scientific research for this purpose of in order to test new

anxiolytic An anxiolytic (; also antipanic or antianxiety agent) is a medication or other intervention that reduces anxiety. This effect is in contrast to anxiogenic agents which increase anxiety. Anxiolytic medications are used for the treatment of anxi ...

drugs.

Positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including bl ...

visualization of regional cerebral blood flow in patients undergoing CCK-4 induced panic attacks show changes in the

anterior cingulate gyrus In the human brain, the anterior cingulate cortex (ACC) is the frontal part of the cingulate cortex that resembles a "collar" surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24, 32, and 33. It is involved i ...

, the

claustrum The claustrum (Latin, meaning "to close" or "to shut") is a thin, bilateral collection of neurons and supporting glial cells, that connects to cortical (e.g., the pre-frontal cortex) and subcortical regions (e.g., the thalamus) of the brain. It ...

- insular-

amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...

region, and

cerebellar vermis The cerebellar vermis (from Latin ''vermis,'' "worm") is located in the medial, cortico-nuclear zone of the cerebellum, which is in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior ...

Hallucinogenic

Several studies have implicated CCK as a cause of

visual hallucinations A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinatio ...

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

. Mutations in CCK receptors in combination with mutated CCK genes potentiate this association. These studies also uncovered potential racial/ethnic differences in the distribution of mutated CCK genes.

Interactions

CCK has been shown to

interact Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...

with the Cholecystokinin A receptor located mainly on pancreatic acinar cells and

Cholecystokinin B receptor The cholecystokinin B receptor also known as CCKBR or CCK2 is a protein that in humans is encoded by the ''CCKBR'' gene. This gene encodes a G protein-coupled receptor for gastrin and cholecystokinin (CCK), regulatory peptides of the brain and ga ...

mostly in the brain and stomach. CCK_B receptor also binds gastrin, a gastrointestinal hormone involved in stimulating gastric acid release and growth of the gastric mucosa. CCK has also been shown to interact with

calcineurin Calcineurin (CaN) is a calcium and calmodulin dependent serine/threonine protein phosphatase (also known as protein phosphatase 3, and calcium-dependent serine-threonine phosphatase). It activates the T cells of the immune system and can be bloc ...

in the pancreas. Calcineurin will go on to activate the transcription factors

NFAT Nuclear factor of activated T-cells (NFAT) is a family of transcription factors shown to be important in immune response. One or more members of the NFAT family is expressed in most cells of the immune system. NFAT is also involved in the developme ...

1–3, which will stimulate

hypertrophy Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J ...

and growth of the pancreas. CCK can be stimulated by a diet high in protein, or by

protease inhibitors Protease inhibitors (PIs) are medications that act by interfering with enzymes that cleave proteins. Some of the most well known are antiviral drugs widely used to treat HIV/AIDS and hepatitis C. These protease inhibitors prevent viral replicat ...

. CCK has been shown to interact with

orexin Orexin (), also known as hypocretin, is a neuropeptide that regulates arousal, wakefulness, and appetite. The most common form of narcolepsy, type 1, in which the individual experiences brief losses of muscle tone ("drop attacks" or cataplexy), ...

neurons, which control appetite and wakefulness (

sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...

). CCK can have indirect effects on sleep regulation. CCK in the body cannot cross the

blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of ...

, but certain parts of the

and brainstem are not protected by the barrier.

References

External links

* * {{Gastrointestinal hormones Anxiogenics Hepatology Intestinal hormones Neuropeptides Cholecystokinin agonists

History

Structure

Function

Gastrointestinal

Digestion

Satiety

Neurological

Anxiogenic

Panicogenic

Hallucinogenic

Interactions

See also

References

External links