Question

Questions 1. Explain the digestive system and all the hormones associated with the digestive system.

Include all of the GI hormones; CCK, Gastrin etc.

Answer 1

Digestive system is made up of gastrointestinal tract (GI tract) or alimentary canal and accessory organs, which help in the process of digestion and absorption . GI tract is a tubular structure extending from the mouth up to anus, with a length of about 30 feet. It opens to the external environment on both ends.
GI tract is formed by two types of organs:
1. Primary digestive organs.
2. Accessory digestive organs.
1. Primary Digestive Organs
Primary digestive organs are the organs where actual digestion takes place.
Primary digestive organs are:
i. Mouth
ii. Pharynx
iii. Esophagus
iv. Stomach.
v. Small intestine vi. Large intestine.
2. Accessory Digestive Organs
Accessory digestive organs are those which help prim- ary digestive organs in the process of digestion.
Accessory digestive organs are: i. Teeth
ii. Tongue
iii. Salivary glands
iv. Exocrine part of pancreas
v. Liver
vi. Gallbladder.
WALL OF GASTROINTESTINAL TRACT
In general, wall of the GI tract is formed by four layers which are from inside out:
1. Mucus layer
2. Submucus layer
3. Muscular layer
4. Serous or fibrous layer.

Gastrointestinal (GI) hormones are the hormones secreted in GI tract. These hormones are polypeptides in nature and belong to the family of local hormones . Major function of these hormones is to regulate the secretory activities and motility of the GI tract.

Gastrin
Source: G cells in stomach, TG cells in GI tract, Islets in fetal pancreas ,Anterior pituitary, Brain.
Functions-Stimulates gastric secretion and motility, Promotes growth of gastric mucosa,
Stimulates release of pancreatic hormones ,   
Stimulates secretion of pancreatic juice ,
Stimulates secretion of pancreatic hormones..

Secretin
Source:S cells of small intestine.
Functions-Stimulates secretion of watery and alkaline pancreatic secretion,
Inhibits gastric secretion and motility Constricts pyloric sphincter,
Increases potency of cholecystokinin action.

Cholecystokinin
Source: I cells of small intestine.
Functions-Contracts gallbladder,
Stimulates pancreatic secretion with enzymes , Accelerates secretin activity,
Increases enterokinase secretion,
Inhibits gastric motility,
Increases intestinal motility,
Augments contraction of pyloric sphincter Suppresses hunger,
Induces drug tolerance to opioids.

Gastric inhibitory peptide (GIP)
Source: K cells in duodenum and jejunum Antrum of stomach.
Functions-Stimulates insulin secretion,
Inhibits gastric secretion and motility.

Vasoactive intestinal polypeptide (VIP)
Source: Stomach,Small and large intestines.
Functions-Dilates splanchnic (peripheral) blood vessels, Inhibits Hcl secretion in gastric juice,
Stimulates secretion of succus entericus,
Relaxes smooth muscles of intestine,
Augments acetylcholine action on salivary glands,
Stimulates insulin secretion.

Glucagon
Source: α-cells in pancreas ,A cells in stomach, L cells in intestine.
Functions-Increases blood sugar level.