Digestive system

1. Digestive system • Helen Li, Natalie Wong, Chih-Yee Cheng, Rachel Kua

2. Esophagus- The esophagus is located in your throat near the windpipe. It’s purpose is to deliver food to your stomach by the muscle contractions called peristalsis. • Mouth- Beginning of the digestive system. The food is broken down into smaller pieces that are easier to digest while the saliva mixes with the food, breaking it down so the body can absorb it. • Cells in stomach: • Mucus cells- resisting attack by digestive acid and enzymes • parietal cells- secrete acid by pumping hydrogen ions across the cell membrane • chief cells- secrete the digestive enzymes (pepsins) Stomach- A hollow organ that holds food while it is being mixed with enzymes. This continues the process of breaking down food. Cells in the lining secretes strong acid and powerful enzymes which are responsible for the breakdown process. When the contents of the stomach are processed enough, it is released into the small intestine.

3. Small intestine- It is a 22 foot long muscular tube which breaks down food using enzymes released by the pancreas and bile from the liver. The small intestine consists of three segments, the duodenum, jejunum, and ileum. The duodenum plays a big role in the continuous process of breaking down food while the jejunum and ileum are responsible for the absorbtion of nutrients into the bloodstream. Cells Villi cell: These cells lining the inner surface of the small intestine are adapted to absorb the nutrients and chemicals which we ate or drank. Epithelial cells: The surface these cells contains various carrier molecules, which are used to absorb specific chemicals and nutrients as they pass through.

4. Pancreas- it secretes digestive enzymes into the duodenum and is both an endocrine and exocrine gland. These enzymes break down protein, fats, and carbohydrates. The pancreas also makes insulin. • Cells The endocrine function of the pancreas consists mainly of the secretion of the two major hormones, insulin and glucagon. Four cell types have been identified in the islets each producing a different hormone: A cells which produce glucagon, B cells that produce insulin, D cells, producing somatostatin, and F or D1 cells which produce pancreatic polypeptide.

5. Liver- Main function within the digestive system is to process the nutrients absorbed from the small intestines. Bile from the liver secreted into the small intestine also plays an important role in digesting fats. The liver is the body’s chemical factory. It takes raw materials that were absorbed by the intestines and makes all the various chemicals the body needs to function. The liver detoxifies potentially harmful chemicals. • Cells: • Hepatocytes cells- form and secrete bile, detoxify substances • Kupffer cells- clearing bacteria out of the portal blood steam, removing worn-out red blood cells • fenestrated endothelial cells- secrete substances • Ito cells - storage fat and vitamin A • Gallbladder- The gallbladder is not a vital organ and the body is able to cope without it, many people don't pay that attention to it until they start having problems with it. The gallbladder's function isn't well known and most people don't understand its importance. • The gallbladder is about 3 to 4 inches and is connected to the liver by the hepatic duct. Its function is to store bile for the liver and deliver it to the small intestine when it needed. The gallbladder also concentrates the bile so that it is ready to use.

6. Large intestine(colon)- The large intestine is a 6-foot long muscular tube that connects the small intestine to the rectum. It reabsorbs water and maintains the fluid balance of the body, absorbs certain vitamins, processes undigested material (fibre) and stores waste before it is eliminated.

7. Rectum- The rectum is an 8-inch chamber that connects the large intestine to the anus. It’s job is to receive waste from the large intestine, to let the person know that there is waste to be excreted, and to hold the waste until excretion happens. Cells • Intestinal rectal valve cells- virL and virR • Rectal gland-A ring of three large rectal gland cells, rect D, rect VL, rect VR. • They are rectal epithelial cells, adjacent to intestino-rectal valve and have microvilli. • Epithelial cells- • K’ and Ka • B, Y, U, K and P cell: postembryonic blast cell in male • Y cell:Rectal cell at hatching, becomes PDA in hermaphrodite, postembryonic blast cell in male

8. Anus- The anus is the last part of the digestive tract. It’s main function is to dispose of waste products out of the body. It excretes the undigested food from our body in the form of liquid or solid body waste. It also notifies you whether the content that needed to be excreted is solid, liquid or gas. Cells: Enteric muscles • Stomatointestinal muscles: mu intL - left intestinal muscle cell, attach to intestine and body wall anterior to anus. mu intR - right intestinal muscle cell, attach to intestine and body wall anterior to anus. • Anal Sphincter muscle: mu sph - a saddle-shaped muscle cell that encircles the intestinal-rectal valve. • Anal depressor muscle: mu anal - a single, H-shaped cell which lies just above the anus and connects the roof of the anal canal to the dorsal bodywall; its contractions act to increase the size of the anal opening by lifting the roof of the rectum and hence facilitate expulsion of intestinal contents.