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Retrieved from " https: It's part of the digestive tract, but it doesn't seem to do anything, though it can cause big problems because it sometimes gets infected and needs to be removed. For instance, more connections to metabolic control largely the glucose-insulin system have been uncovered in recent years. Have fun with hands-on learning about the digestive system! The esophagus remains as a simple, straight tube. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.
Goblet cells secrete mucus lining that protect the stomach from the acid and self-digestion. Stomach produces pepsin, which digests proteins secreted in an inactive form, gets activated in acidic environment Pepsin is special in that it works best at very acid pH. Liver production of bile: Gluconeogenesis from glycerol and amino acids deamination. Breaks down fats, makes cholesterol, makes lipoproteins used to transport fats. Stores vitamins A, D and B12 and iron. Blood sugar too low: Blood sugar too high: Ducts draining to duodenum and gall bladder.
Bile storage in gall bladder Gall bladder stores excess, unused bile, and concentrates it. Secretes it when needed. Bile breaks down large fat droplets into smaller microscopic droplets by forming micelles. This increases the total surface area of the fat for lipase action. Pancreas production of enzymes, bicarbonate Pancreas is the major source for all the digestive enzymes. Amylase - digests starch. Lipase - digests fat. Ribonuclease - digests nucleic acids.
Small intestine absorption of food molecules and water Small intestine is the major place for digestion and absorption. The sensitivity of the periodontal membrane that surrounds and supports the teeth, rather than the power of the muscles of mastication, determines the force of the bite.
Mastication is not essential for adequate digestion. Chewing does aid digestion, however, by reducing food to small particles and mixing it with the saliva secreted by the salivary glands.
The saliva lubricates and moistens dry food, while chewing distributes the saliva throughout the food mass. The movement of the tongue against the hard palate and the cheeks helps to form a rounded mass, or bolus , of food. The lips, two fleshy folds that surround the mouth, are composed externally of skin and internally of mucous membrane , or mucosa. The mucosa is rich in mucus-secreting glands, which together with saliva ensure adequate lubrication for the purposes of speech and mastication.
The cheeks, the sides of the mouth, are continuous with the lips and have a similar structure. A distinct fat pad is found in the subcutaneous tissue the tissue beneath the skin of the cheek; this pad is especially large in infants and is known as the sucking pad.
On the inner surface of each cheek, opposite the second upper molar tooth, is a slight elevation that marks the opening of the parotid duct, leading from the parotid salivary gland , which is located in front of the ear.
Just behind this gland are four to five mucus-secreting glands, the ducts of which open opposite the last molar tooth. The roof of the mouth is concave and is formed by the hard and soft palate.
The hard palate is formed by the horizontal portions of the two palatine bones and the palatine portions of the maxillae, or upper jaws. The hard palate is covered by a thick, somewhat pale mucous membrane that is continuous with that of the gums and is bound to the upper jaw and palate bones by firm fibrous tissue.
The soft palate is continuous with the hard palate in front. Posteriorly it is continuous with the mucous membrane covering the floor of the nasal cavity. The soft palate is composed of a strong, thin, fibrous sheet, the palatine aponeurosis, and the glossopalatine and pharyngopalatine muscles.
A small projection called the uvula hangs free from the posterior of the soft palate. The floor of the mouth can be seen only when the tongue is raised. In the midline is a prominent, elevated fold of mucous membrane frenulum linguae that binds each lip to the gums, and on each side of this is a slight fold called a sublingual papilla , from which the ducts of the submandibular salivary glands open.
Running outward and backward from each sublingual papilla is a ridge the plica sublingualis that marks the upper edge of the sublingual under the tongue salivary gland and onto which most of the ducts of that gland open. The gums consist of mucous membranes connected by thick fibrous tissue to the membrane surrounding the bones of the jaw.
The gum membrane rises to form a collar around the base of the crown exposed portion of each tooth. Rich in blood vessels, the gum tissues receive branches from the alveolar arteries; these vessels, called alveolar because of their relationship to the alveoli dentales, or tooth sockets, also supply the teeth and the spongy bone of the upper and lower jaws, in which the teeth are lodged.
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Nicholas Carr Hightower Harvey J. Read More on This Topic. Page 1 of Next page The teeth. Learn More in these related Britannica articles: As the embryo folds off, the endoderm is rolled in as the foregut and hindgut. Continued growth progressively closes both the midbody and the midgut. The esophagus remains as a simple, straight tube. The stomach grows faster on its dorsal side, thereby forming….