1. Mouth: This is where the digestion process starts off at. Mechanical digestion and chemical digestion. The difference between them is that mechanical digestion is where the food is actually physically being torn apart. And chemical digestion breaks down the food by using enzymes.
2.Teeth: take in the food and start to mechanically digesting it by breaking food into smaller pieces.
3. Tongue: Contains taste buds. They tastes sweet/salty at the top of the tongue, sour on the sides of the tongue and bitter at the back. Tasting bitterness can save our lives because poisons most often taste bitter. The tongue also moves the food around the mouth and towards the teeth to mix the food and the saliva.
The final job of the tongue is that it pushes the bolus of the food to the back of the throat to the 'swallow reflex center'.
4. Salivary Glands: are ducted glands that produce saliva. The saliva liquefied food, contains amylase and begins to chemical digest, lubricates and softens the bolus of food and it also has an enzyme (lyric enzyme) in saliva kill bacteria.
5. Pharynx: is located at the back of the throat, which opens to both the respiratory and digestive systems. When food is places on the 'reflex center' by the tongue three things happens. The soft palate covers the opening to the noes, the epiglottis covers the trachea and peristalsis of the esophagus begins.
6. Epiglottis: is a flap that covers the trachea tube so that food does not go down the trachea.
7. Esophagus: is a 30 cm long tube that connect the pharynx to the stomach. No digestion occurs here. Food moves through the esophagus (and the rest of the digestive tract) by a process called peristalsis, which is a slow, rhythmic contraction that pushes the bolus along.
8. Cardiac Sphincter: is a ring of muscle located at the beginning of the stomach which stops food from re-entering the esophagus.
9. Stomach: is a J shaped organ that can hold 23 liters of food. It also contains the circular and longitudinal smooth muscle layers, but also has a third muscle layer in the transfers. It churns food and liquefied it which is mechanical digestion. This process is helped by the ridges in the mucosa layer of the stomach. It has gastric juices which are pepsinogen (inactive), hydrochloride acid (acid) and mucus (protects). HCl is release when protein enter the stomach, it transforms pepsinogen into and active hydrolytic enzyme pepsin. Pepsin then digests proteins into smaller polypeptides.
10. Pyloric Sphincter: is located at the base of the stomach and it will meter out the chyme into the duodenum at a slow, constant rate.
11. Duodenum: is the beginning of the small intestine. The walls of the duodenum release intestinal juices (pancreatic juices are released before) which are peptidases, nucleases, maltase, lactase and sucrase. Peptidases breaks di/tri peptides into amino acids. Nucleases breaks nucleic acid into nucleotides. Maltase digests maltose into glucose and glucose. Lactase digests lactose into glucose and galactose. Sucrase digests sucrose into glucose and fructose.
12. Liver: Has over 500 functions. It destroys old red blood cells ( convert hemoglobin to bile), produce bile, detoxifies blood, deamination of amino acids (gluconeogenesis)(birth of sugar), makes blood clotting proteins, makes urea and regulates the blood glucose level at ~0.1% of plasma.
13. Gall Bladder: Stores bile that the liver made. When the gall bladder receives a message from the hormone CCK, it releases bile into the common bile duct, which dumps into the duodenum. The purpose of the bile is it emulsifies fats in the duodenum.
14. Pancreas: is both an endocrine gland and a exocrine gland. This means that it produces hormones and digestive juices. The hormones the pancreas makes are insulin and glucagon. These hormones are made in the specialized cells of the pancreas called 'the islets of Langerhans'. Insulin is used when there is more than 0.1% glucose in the blood, the pancreas releases the insulin and it will cause the liver to convert the glucose to glycogen for storage, it promotes the formation of fats and causes the protein in cell membranes to open and allow the entrance of glucose into cells. This results in lower blood sugar levels. Glucagon is used when there is less than 0.1% glucose in the blood, the pancreas releases the hormone glucagon and it will cause the liver to convert glycogen into glucose to be released into the blood. This will result in higher blood sugar levels. The pancreatic juices that the pancreas releases are sodium bicarbonate, pancreatic amylase, lipase, trypsin and nucleases. Sodium Bicarbonate is released to neutralize the stomach acid(pH of 2.5) to a pH of 8.5. Amylase converts uncooked starch to maltose. Lipase converts lipids to fatty acids and glycerol. Trypsin converts small polypeptides into di/tri peptides. Nucleases converts nucleic acids into nucleotides. The pancreatic juices are released into the duodenum where they are then used to break down the chyme.
15. Small intestine: has three parts: duodenum(starts chemical digestion), jejunum(finishes digestion and begins absorption) and the ileum(absorbs all of the nutrients into the circulatory and lymphatic systems). The small intestine has an increased rate of absorption due to its highly convoluted walls with very large surface area. There are fold in the mucosa layer called villi which increase the surface area for absorption. The villi also has smaller folds called micro villi. The absorption of nutrients takes place through the columnar cells of the micro villi which involves active transport and requires a lot of energy. Sugar and amino acids are absorbed by the mesenteric capillaries (blood stream) and glycerol and fatty acids are absorbed by the lacteal ( lymphatic system).
16. Appendix: sits at the junction of the small intestine and large intestine. It’s a thin tube about four inches long. The function of the appendix is not known.
17. Large Intestine(colon): it is larger in diameter but is much shorter in length than the small intestine. It has 4 main parts which are the ascending colon, transverse colon, descending colon and sigmoid colon(rectum). The large intestine absorbs water and salts that were used in the digestive process. It also has E.Coli bacteria that live in it. The E.Coli has four things that they do which are, slow the movement through the colon which allows time for water to be reabsorbed, they eat the wastes and produce useful things that we new to survive like vitamin K and amino acids, they also produce growth factor and the produce waste of there own (methane gas). By the end of the large intestines the waste are transformed into feces. If the waste move through the intestine too quickly it cannot absorb enough water resulting in diarrhea, if it goes to slow it will absorbed too much water resulting in constipation.
18. Rectum: Is the terminal portion of the large intestine, extending from the sigmoid colon to the anal canal. It acts as a temporary storage site for feces.
19. Anus: is the last part of the digestive tract. The anus is where the feces leaves the body.
The 3 Hormones that control digestion!
Gastrin: when food is present in the stomach gastrin is released and this causes the cells of the stomach mucosa to release gastric juices.
Secretin: is released when there is acidic chyme in the duodenum, this hormone causes the pancreatic juices to be released.
Cholecystokinin (CCK): is released when fats and proteins enter the duodenum, it is released into the blood stream and I causes the gall bladder to secrete bile and the pancreas to release it's pancreatic juices with digestive enzymes. These juices are sent to the duodenum where the enzymes can begin the digestion of lipids and proteins.
And that is everything I know about the digestive system!
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