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 pancreas.

Secretin is produced in the S cells of the duodenum, which are located in the crypts of Lieberkuhn. Secretin helps regulate the pH of the duodenum by inhibiting the secretion of gastric acid from the parietal cells of the stomach and stimulating the production of bicarbonate from the pancreas. 

Secretin helps in regulating the $pH$ of the duodenum by

• Watery diarrhoea, hypokalemia, achlorhydria, is caused by overproduction of vasoactive intestinal peptide (VIP) which stimulates fluid and electrolyte secretion in the intestinal epithelium via activation of the cyclic adenosine monophosphate pathway. Hence, Hypokalemia is caused by the overproduction of VIP.

Answer is option A i.e. "Gastrin"
Stimuli in the stomach and small intestine activate or induce gastric juice production. The gastrin in digestive acid secretion is induced by the mechanical and chemical stimulation of stomach.

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 gastric cells in the pyloric antrum of the stomach, duodenum, and the pancreas. Gastrin is directly responsible for the release of gastric acid, which breaks down the proteins in the food you eat.

•  Vasoactive intestinal peptide, also known as vasoactive intestinal polypeptide or VIP, is a peptide hormone that is vasoactive in the intestine. VIP is produced in many tissues of vertebrates including the gut, pancreas, intestine and suprachiasmatic nuclei of the hypothalamus in the brain. Hence, VIP hormone is produced in Pancreas and Intestine. 

Answer is option A i.e. "Duodenum and pancreas"
Secretin is a hormone that regulates water homeostasis throughout the body. Duodenum and pancreas are associated with secretion and stimulation of secretin hormone in following way: when hydrochloric acid passes from the stomach into the duodenum, secretin is released into the bloodstream and stimulates the duct cells of the pancreas to secrete water and bicarbonate.

• Vasoactive intestinal polypeptide (VIP), a 28-amino-acid polypeptide secreted by cells throughout the intestinal tract. 
• It stimulates the secretion of electrolytes and water by the intestinal mucosa.
• Some pancreatic islet-cell tumours secrete excessive amounts of VIP (a condition called Verner-Morrison syndrome, or pancreatic cholera). VIP-secreting tumours cause severe, intractable, debilitating watery diarrhoea and an associated loss of large quantities of potassium. The resulting dehydration may be life-threatening. Hence, VIP hormone stimulates the Intestinal secretion of water and electrolyte.
So, the correct answer is 'Intestinal secretion of water and electrolyte'.

• Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. 
• Cholecystokinin, officially called pancreozymin, is synthesized and secreted by enteroendocrine cells in the duodenum, the first segment of the small intestine. 
• Cholecystokinin also increases the release of fluid and enzymes from the pancreas to break down fats, proteins and carbohydrates.
•  Cholecystokinin seems to be involved with appetite by increasing the sensation of fullness in the short-term, that is, during a meal rather than between mealsHence, Cholecystokinin involves in Controlling appetite.
So, the correct answer is 'Controlling appetite'.

• Cholecystokinin, officially called pancreozymin, is synthesized and secreted by enteroendocrine cells or I-cell in the duodenum, the first segment of the small intestine.
•  Its presence causes the release of digestive enzymes and bile from the pancreas and gallbladder, respectively, and also acts as a hunger suppressant. Hence, I cell secretes cholecystokinin hormone.

Gastric inhibitory peptide inhibits gastric acid secretion in the stomach.
Cholecystokinin is a  small intestinal hormone that stimulates the secretion of pancreatic enzymes and bile. Secretin is a small intestinal hormone secreted by epithelial cells od small intestine epithelial cells; stimulates secretion of bicarbonate-rich fluids from the pancreas and liver. Hence Gastric inhibitory peptide, Cholecystokinin, and Secretin hormones regulate the secretion of digestive juices and help indigestion
So, the correct option is 'All of the above'.

Secretin is a hormone that regulates water homeostasis. It is secreted by the duodenum. When hydrochloric acid passes from the stomach into the duodenum, secretin is released. It stimulates the acinar cells of the pancreas to secrete water and bicarbonate into the pancreatic duct. This water and bicarbonate is then drained into the duodenum.

• Gastric inhibitory polypeptide (GIP) or gastro inhibitory peptide, also known as the glucose-dependent insulinotropic peptide, is an inhibiting hormone of the secretin family of hormones. 
• While it is a weak inhibitor of gastric acid secretion, its main role is to stimulate insulin secretion.  
• It is synthesized by K cells, which are found in the mucosa of the duodenum and the jejunum of the gastrointestinal tract. Hence, the GIP  hormone stimulates the lipase activity

• Duocrinin is a postulated gastrointestinal hormone that is liberated by the contact of gastric contents with the intestine and that stimulates the secretory activity of the duodenal glands (Brunner glands). Hence, Duocrinin  the hormone whose secretion is stimulated by the acidic chyme in intestine.

• Secretin stimulates the secretion of a bicarbonate-rich pancreatic fluid. Secretin enters the bloodstream or intestinal lumen and stimulates bicarbonate secretion (by interacting with pancreatic ductal cells), which neutralizes the pH of the gastric chyme upon entering the small intestine.

• GIP  stimulates insulin secretion in response to a meal.
• Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility.
• Fatty acids in the lumen of the duodenum stimulate endocrine cells to release the hormone cholecystokinin (CCK). CCK stimulates contractions in the smooth muscle of the gallbladder.
  

CCK is cholecystokinin and secretin are released by duodenum cells and CCK acts upon gallbladder for the secretion of bile while secretin stimulates stomach and they both stimulate the pancreas to secrete enzymes and hydrogen bicarbonate that neutralize acidic chyme.

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 duodenum, which are located in the intestinal glands. Secretin primarily functions to neutralize the pH in the duodenum, allowing digestive enzymes from the pancreas (e.g., pancreatic amylase and pancreatic lipase) to function optimally. Secretin targets the pancreas; pancreatic centroacinar cells have secretin receptors in their plasma membrane.

Hormones are the chemicals which transfer signal from one part to the other. There are several hormones which have an effect on the stomach, pancreas as well as liver, these hormones are as follows:

Cholecystokinin is a peptide hormone of the gastrointestinal system, responsible for stimulating the digestion of fat and protein. Cholecystokinin, previously called pancreozymin, is secreted in the duodenum and causes the release of digestive enzymes and bile from the pancreas and gallbladder, respectively. 

The secretion of pancreatic juice is stimulated by secretin and CCK, produced by endocrine cells in the walls of the duodenum. The presence in the duodenum of acid material from the stomach stimulates the production of these hormones.

Cholecystokinin, previously called pancreozymin, is synthesized by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum, and causes the release of digestive enzymes and bile from the pancreas and gallbladder, respectively. 

Contraction of the muscle wall in the gallbladder is stimulated by the vagus nerve of the parasympathetic system and by the hormone cholecystokinin, which is produced in the upper portions of the intestine. The contractions result in the discharge of bile through the bile duct into the duodenum of the small intestine. 

Enterogastrone is a hormone, whereas amylase, trypsin and enterokinase are enzymes. Amylase is starch splitting enzyme, while trypsin is a proteolytic enzyme. Enterokinase is a proteolytic enzyme, which acts on trypsinogen and converts it to active trypsin. Enterogastrone, is a hormone secreted by the duodenal mucosa, when fatty food is in the stomach or small intestine; it is also thought to be released, when sugars and proteins are in the intestine. Enterogastrone is transported by the bloodstream to the glands and muscles of the stomach, where it inhibits gastric movements and secretions, possibly by blocking the production or activity of gastrin, the hormone that initially causes these functions.

Secretin is the most important hormone of digestive tract and also first hormone discovered in digestive tract. This hormone stimulates pancreas for synthesis and secretion of non enzymatic part of pancreatic juice. It also stimulates liver for secretion of bile juice and inhibit the gastric acid secretion in stomach and reduce rate of contraction of stomach.

As food enters the confined space of the stomach, it starts applying pressure to the stomach wall. As food enters the stomach, the food bangs against the stomach wall, distending it. This distention causes the stomach to release gastrin. Gastrin stimulates the gastric glands to secrete more gastric juice. 

Fatty acids in the lumen of the duodenum stimulate endocrine cells to release the hormone cholecystokinin (CCK). CCK stimulates contractions in the smooth muscle of the gallbladder. CCK causes relaxation of the sphincter of Oddi, allowing bile release into the duodenum.

Fatty acids in the lumen of the duodenum stimulate endocrine cells to release the hormone cholecystokinin (CCK). CCK stimulates contractions in the smooth muscle of the gallbladder. CCK causes relaxation of the sphincter of Oddi, allowing bile release into the duodenum.

When food leaves the stomach through its pyloric end and enters the duodenum it is called chyme (acidic). The $HCI$ of chyme stimulates the wall of duodenum to secrete hormones. It secretes various hormones, example secretin, which is the most important hormone of digestive tract and is released by duodenum. This hormone stimulates pancreas for synthesis and secretion of non enzymatic part of pancreatic juice. It also stimulates liver for secretion of bile juice and inhibit the gastric acid secretion in stomach and reduces rate of contraction of stomach.

Secretin is the most important hormone of digestive tract. This hormone stimulates pancreas for synthesis and secretion of non enzymatic part of pancreatic juice. It also stimulates liver for secretion of bile juice and inhibit the gastric acid secretion in stomach and reduce rate of contraction of stomach.

Enterogastrone is a hormone secreted by the duodenal mucosa, when fatty food is in the stomach or small intestine; it is also released, when sugars and proteins are in the intestine. Enterogastrone is transported by the bloodstream to the glands and muscles of the stomach, where it inhibits gastric movements and secretions, by blocking the production or activity of gastrin.

Wm. M. Bayliss and Ernest H. Starling  discovered  secretin, the first hormone, in 1902. They discovered this hormone when they were studying the pancreatic secretion. Secretin hormone stimulates the pancreas to secrete digestive fluid.

Secretin is the most important hormone of digestive tract. This hormone stimulates pancreas for synthesis and secretion of non enzymatic part of pancreatic juice, while pancreozymin promotes the secretion of enzymatic part of the pancreatic juice. Secretin also stimulates liver for secretion of bile juice and inhibit the gastric acid secretion in stomach and reduces rate of contraction of stomach.

Secretin is a peptide hormone produced in the S cells intestinal gland of the duodenum. It inhibits the secretion of gastric acid from the parietal cells of the stomach thereby helps in regulating the pH of duodenum. Hence option A is correct.

Enterogastrone is a hormone secreted by the duodenal mucosa, when fatty food is in the stomach or small intestine. It is also thought to be released, when sugars and proteins are in the intestine. Enterogastrone is transported by the bloodstream to the glands and muscles of the stomach, where it inhibits gastric movements and secretions, possibly by blocking the production or activity of gastrin, the hormone that initially causes these functions. Enterogastrone may slow down stomach emptying by reducing the amount of acid produced. High acid content causes the valve between the stomach and intestine to relax, allowing food passage.

• Cholecystokinin is secreted by cells of the upper small intestine. 
• Its secretion is stimulated by the introduction of hydrochloric acid, amino acids, or fatty acids into the stomach or duodenum. 
• Cholecystokinin stimulates the gallbladder to contract and release stored bile into the intestine. Hence, Cholecystokinin stimulates Gall's bladder.

• VIP in the pituitary helps to regulate prolactin secretion; it stimulates prolactin release in the domestic turkey. Additionally, the growth-hormone-releasing hormone (GH-RH) is a member of the VIP family and stimulates growth hormone secretion in the anterior pituitary gland. Hence, VIP  regulates the secretion of prolactin in turkey.

• In the digestive system, VIP seems to induce smooth muscle relaxation (lower oesophagal sphincter, stomach, gallbladder), stimulate secretion of water into pancreatic juice and bile, and cause inhibition of gastric acid secretion and absorption from the intestinal lumen.
•  Its role in the intestine is to greatly stimulate secretion of water and electrolytes, as well as relaxation of enteric smooth muscle, dilating peripheral blood vessels, stimulating pancreatic bicarbonate secretion, and inhibiting gastrin-stimulated gastric acid secretion. 
•  It also has the function of stimulating pepsinogen secretion by chief cells. VIP seems to be an important neuropeptide during inflammatory bowel diseases.Hence, VIP hormone stimulates the secretion of Pepsinogen.

So, the correct answer is 'Pepsinogen'.

Enterogasterone is secreted by the epithelium which inhibits gastric secretion and morality.

Secretin is a digestive hormone secreted by the wall of the duodenum. Secretin helps regulate the pH of the duodenum by inhibiting the secretion of gastric acid from the parietal cells of the stomach and stimulates the acinar cells of the pancreas to secrete water and bicarbonate into the pancreatic ducts that drain into the duodenum. 

Enterocrinin is a hormone secreted by the duodenum mucosa and is stimulated by hydrogen ions which stimulates the intestinal glands to increase succus entericus juice. This breaks down sucrase, maltase, lactase, erepsin and nuclease for the body to use as energy.

cholecystokinin or CCK is a hormone released by stimulating endocrine cells by the fatty acids in the lumen of the duodenum. CCK or cholecystokinin role is to stimulate in smooth muscles of gallbladder and release of pancreatic secretions.

• Secretin is a hormone secreted by the small intestine on being stimulated by low pH. It stimulates the pancreas to release water and bicarbonate ions. These are then drained into the pancreatic duct.

• Cholecystokinin is secreted from the duodenum and causes contraction of gall bladder and secretion of pancreatic juice into duodenum.
• Secretin is secreted from duodenum and stimulates the secretion of pancreatic juice but inhibits the secretion of gastric juices.

• Pancreas is a heterocrine gland as it acts both as endocrine and exocrine gland. It secretes insulin hormone into blood and act as endocrine gland and when it secretes digestive enzymes and juice through pancreatic duct, it acts as exocrine gland.
  
• Adrenal cortex is part of adrenal gland and secretes glucocorticoids (cortisol,) mineralocorticoids (aldosterone) and sexocorticoids (androgens).
• Thyroid gland is situated between the trachea and larynx in the neck and secretes thyroxine hormone which increases oxygen consumption by metabolically active tissues.
  

Secretin is secreted in duodenum and stimulates the secretion of pancreatic juice but inhibits the secretion of gastric juices. It is released in response to acid in the small intestine, and stimulates the pancreas and bile ducts to release a flood of bicarbonate base, which neutralizes the acid.
So, the correct answer is 'Duodenum - pancreas'.

The pH of succus entericus is 7.8.

The correct answer is (d).

Cholecystokinin, previously called pancreozymin, is synthesized by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum. It is responsible for stimulating the digestion of fat and protein. Secretin is a peptide hormone that regulates water homeostasis throughout the body, and influences the environment of the duodenum by regulating secretions in the stomach and pancreas. Secretin is produced in the S cells of the duodenum, which are located in the crypts of Lieberkuhn.

Cholecystokinin (CCK), formerly called pancreozymin, is a digestive hormone released with secretin, when food from the stomach reaches the duodenum. Cholecystokinin causes contraction of the gallbladder, which forces bile into the duodenum.

Secretin stimulates the release of a watery bicarbonate solution from the pancreatic and bile duct epithelium. Secretin increases water and bicarbonate secretion from duodenal Brunner's glands to buffer the incoming protons of the acidic chyme. It also enhances the effects of cholecystokinin to induce the secretion of digestive enzymes and bile from pancreas and gallbladder, respectively.