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The Digestive System (Pathway through the Digestive Tract (Mixing and…
The Digestive System
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Small Intestine
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Duodenum- receives the acid chyme from the stomach. Most of the enzymatic action of food is done here.
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Plicae circularis- deep folds of the mucosal and submucosal layers that force the liquid chyme to spiral through the intestine
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Stomach
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Pylorus- narrow portion at the lower end of the stomach and contains the pyloric sphincter. This sphincter regulates passage from the stomach to small intestine.
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Stomach Gastric Juice
Parietal cells- produces intrinsic factor and hydrochloric acid. Intrinsic factor binds to B12 in the stomach allowing B12 to be absorbed by the small intestine
Chief cells- they produce the enzymes pepsinogen and gastric lipase. Pepsinogen is activated by pepsin by the action of HCl which then breaks down proteins. Gastric lipase breaks down fats.
Mucous cells- mucus is needed to coat the stomach to protect it from the high acid content and enzymes
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Gastric juice is made up of mucus, hydrolytic enzymes, and hydrochloric acid (HCl)
Digestion
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Chemical: Uses chemicals to break down large macromolecules into smaller molecules for absorption. Begins in the mouth with saliva, continues to the stomach with HCl and enzymes, then most of the chemical digestion occurs in the small intestines.
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Gallbladder- Concentrated Bile: during storage of bile, it concentrates it
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Layers
Submucosa- contains blood vessels, nerve fibers, lymphatic vessels, and lymph nodes
Muscularis externa- helps move food along the digestive tract and helps mix digestive contents into smaller pieces
Mucosa-absorption of digestive foods, and protection against foreign invaders
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Mouth
Salivary glands- secrete saliva. One of the first enzymes that starts the breakdown of food is produced here.
3 salivary glands- parotids, submandibulars, sublinguals
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Teeth- consists of 3 layers (crown, dentin, pulp). The teeth are responsible for cutting and tearing food.
Accessory Organs
Gallbladder- secretes bile into a duct. It is stored until stimulated by a hormone to release it into the duodenum.
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Liver- ability to regenerate dead or damaged tissues.Cells in liver produce bile. Bile salts break down fats we eat into the size needed for absorption.
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Functions
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Absorption- movement of small, diffusible molecules into the bloodstream so they can enter cells
Mechanical breakdown of food- where food is moved around by the tongue and broken up into smaller pieces by the teeth
Large Intestine
Cecum-first sac like structure from the small intestine and has the vermiform appendix hanging off of it. The large intestine contains bacteria that are good for us. The bacteria produces Vitamin B12 and Vitamin K.
The colon circles the small intestine and starts with the ascending colon on the right side. Then goes through the splenic flexure to the descending colon, then sigmoid colon, then rectum, then anus.
Once food has reached the large intestine it is mostly unabsorbable, useless material as most of the nutrients have been taken out in the small intestine.
Hormones
Cholecystokinin: produced by the enteroendocrine cells. Stimulates the pancreas to secrete enzymes into the duodenum and stimulates the gallbladder to empty
Secretin: produced by enteroendocrine cells. Stimulates the pancreas to release digestive juice that is rich in bicarbonate
Gastrin: hormone produced in the stomach by G cells. Stimulates acid secretion which helps to move things along
Esophagus
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It moves food by peristalsis, which is a series of wave-like contractions