THE DIGESTIVE SYSTEM
This is the system responsible for changing the food into substances suitable for absorption. The body needs material for growth, repair, heat and energy.
Digestive juices contain enzymes, which break down the food. The digestive tract starts at the mouth passing through the pharynx, the oesophagus, the stomach the small and large intestine and ending with the rectum and the anus.
Starting with the teeth:
There are 32 permanent teeth. The tongue consists of striated voluntary muscles and is attached to the mandible and hydroid bones.
The upper surface of it covered with papillae of which there are three forms:
The fill form papillae, the fungi form and the valuate.
Taste buds are resident in the walls of the valuate papillae.
There are 3 pairs of salivary glands: The carotid glands in the front of and below the ears, the sub lingual glands below the tongue and the sub-
The salivary glands produce secretions containing the enzyme, ptyalin, which helps the digestion, cooked starches. From the mouth the food passes into the pharynx (a muscular tube that has 7 openings into it, the mouth, the oesophagus, the larynx, two posterior apertures of the nose and two auditory tubes from the ears.) From the pharynx food passes into the oesophagus (A muscular tube with a mucus membrane covered with fibrous tissue.) From there, it passes into the stomach.
The stomach presents two curvatures, the greater and the lesser curvature and is divided into three parts. The cardiac portion, the body and the pyloric.
The openings into the stomach are guarded by circular bands of muscle, the cardiac sphincter muscle at one end and the pyloric sphincter muscle at the other.
The stomach has three coverings the outer coat of serious membrane, the middle muscular coat and the inner mucus membrane.
The membrane is lined with the glands, which produce gastric juice, containing enzymes pepsin and rennin and also hydrochloric acid.
From here the food passes into the smaller intestine, the first part being the duodenum the remainder consists of the duodenum and ileum.
The inner coat of the small intestine is comprised of mucus membrane arranged in folds known as vabulae connivents. The mucous membrane is covered with minute projections known as villi, each villus contains a lacteal for the absorption of fat and a capillary loop for the absorption of sugar and protein.
This membrane also contains intestinal glands, which produce a secretion known as succus entericus, which contains enzymes for the digestion of sugars and protein.
The mucus membrane is studded with lymphatic nodules and in the latter part of the small intestine that is ileum, groups of these nodules are found and are known as peyer’s patches, there function is to fight infection. The small intestine then merges with the large intestine.
This can be divided into nine parts. It starts with the cecum into which the ileum opens. This opening is guarded by the ileocaceal valve, which allows onward flow and prevents backward flow of contents. The vermiform appendix is attached to the blind end of the cecum.
The ascending colon passes upwards from the cecum along the right side of abdomen and bends left at the right hepatic flexure to become the transverse colon. This passes across the abdominal cavity and turns downwards at the splenetic flexure to continue as the descending colon. This goes down the left side of the abdomen to the sigmoid colon in the pubic cavity and the rectum, which has two sphincter muscles at the exit.
Supporting organs to the digestive system:
The Liver: Situated just below the diaphragm on the right side of the body it is really a gland and is the largest organ in the body, weighing approximately 1.5kg. It is divided into 2 lobes, the larger right lobe and the smaller left lobe.
The right lobe is subdivided into the quad rate and the caudate lobes. The liver has many functions one of which is the formation and storage of bile and to concentrate it by eight to ten times; When required the bile passes out of the gallbladder into the duodenum.
The Pancreas: This also is a gland. It is divided into head, neck and tail. A duct running the length of organ collects pancreatic juice and passes it to the duodenum at the same point that the common bile duct passes in bile. There are some specialised cells in the pancreas, which produce insulin these are called islets. The insulin is passed into the general circulation and controls carbohydrate metabolism.
