1. The GI system

Pancreas: is a gland that is about 12-15cm long and 2.5 cm thick and is usually connected to the duodenum by two ducts. a healthy pancreas produces the pancreatic juice which contains the correct chemicals in order to digest the foods we eat. It produces enzymes that are important for digestion, including trypsin and chymotrypsin to digest proteins, amylase for carbohydrates and lipase for fats. When food enters the stomach, these pancreatic juices are released and cumulates at the pancreatic duct and it joins the common bile duct to form the ampulla of Vater which is located at the duodenum. They are then released to digest food.

Duodenum is the shortest and first segment of the small intestine. It receives partially digested food known as chyme from the stomach and plays a vital role in the chemical digestion of chyme is preparation for absorption into the small intestine. Many chemical secretions from the pancreas, liver and gall bladder mix with the chyme in the duodenum to facilitate chemical digestion. The duodenum is 25-30cm long, c shaped, hollow tube

Gallbladder: pear shaped hollow structure under the liver. It's primary function is to store and concentrate bile. It serves as a reservoir for bile while it's not being used for digestion, the gall ladders absorbent lining concentrates the stored bile. When food enters the small intestine, the hormone cholecystokinin is released, signalling the gallbladder to contract and secrete bile into the small intestine through the common bile duct. The bile helps the digestive process by breaking up food.

Small intestines: most digestion and absorption of food takes place in the small intestines. It is adapted for absorption by having a large surface area, further increased by villi and micro villi. food comes into the small intestines from the stomach. To further aid digestion and absorption, intestinal juice is produced to increase absorption. There are two types of movement in the small intestine. Segmentation are mixing contractions that occur in the small intestine which mix chyme with digestive juices and brings the food into contact with mucosa for absorption. Afterwards peristalsis occurs The small intestine has three parts; the duodenum breaks down food. The jejunum and ileum absorb nutrients and send them into the bloodstream. The inner lining of the small intestine is folded back and forth to increase surface area for nutrient absorption

The salivary glands: submandibular, sublingual and paratoid glands: Produce saliva which keeps the mouth and other digestive areas moist, salivary amylase helps break down carbohydrates, lubricates the passage of food down from pharynx to oesophagus

Pharynx: Located behind mouth and nose. When food moves towards throat the windpipe closes, forces food to move into the pharynx. Voluntary and involuntary muscles contract and road to swallow food, forcing it into the oesophagus Thick lining in the pharynx protects it from rough food particles and harsh chemical food components.

Two groups of organs compose the digestive system. GI tract and the accessory digestive organs. GI tract: mouth, pharynx, esophagus, stomach and the intestines. Accessory digestive organs: teeth, tongue, Salvador glands, liver, gall bladder and pancreas.

Processes: Ingestion: taking food and liquid into the mouth. Digestion: mechanical and chemical processes break down food into small molecules. Absorption: absorbed substances pass into blood or lymph to circulate cells throughout the body Defection: digested materials not absorbed leave the body through the anus.

Muscularis: consists of smooth muscle, found in two sheets; an inner layer of smooth circular muscle and outer layer of longitudinal smooth muscle Involuntary contractions of smooth muscle helps breakdown food, mix it with digestive enzymes Myenteric plexus:

Serosa: serous membrane composed of areoler connective tissue and simple squamous epithelium. Also contains serous fluid-

Mucosa: mucous membrane lined with mucous. Inner lining of the GI tract, composed of three layers- a layer of epithelium, a layer of connective tissue, layer of smooth muscle.

Submucosa: consists of areoles connective tissue that binds the mucosa to the muscularis. It contains many blood and lymphatic vessels that receive absorbed food molecules. Contains an extensive network of neurones known as the submucosal plexus Also contains glands and lymphatic tissue

Oesophagus: a tube that connects the pharynx to the stomach, 20cm long. It's made up of muscles that contract to move food into the stomach in a process called peristalsis The oesophagus has bands of muscles called the upper and lower oesophageal sphincter which relax when a person swallows food and contracts when they are not to prevent stomach acid from flowing up the oesophagus.

The liver: regulates most chemical levels in the blood and excrete a product called bile. Bile helps to break down fats, preparing them for further digestion and absorption. All th blood leaving the stomach and intestines passes through the lover and it processes this blood and breaks down, balances and creates nutrients for the body to use. It's other functions include: Producing bile which helps carry away waste and breaks down fats, store and release glucose as needed, regulating blood clotting, production of cholesterol and special proteins to help carry fats through the body