關於消化系統

Salivary Glands
The mouth contains the salivary glands which are accessory digestive glands that produce a fluid secretion called saliva.

The Tooth
The tooth can be broken down by acids produced by the mouth for digestive purposes. This process is called "decay". To prevent decay, good oral hygiene, consisting of daily brushing and flossing, is necessary.

The Esophagus
The esophagus is a muscular tube which carries food and liquids from the throat to the stomach for digestion after it has been chewed and chemically softened in the mouth.

Stomach
The stomach consists of layers of muscle and nerves that continue the breakdown of food which begins in the mouth.The stomach has several functions: (1) as a storage bin, holding a meal in the upper portion and releasing it a little at a time into the lower portion for processing; (2) as a food mixer, the strong muscles contract and mash the food into a sticky, slushy mass; (3) as a sterilizing system, where the cells in the stomach produce an acid which kills germs in "bad" food; (4) as a digestive tub, the stomach produces digestive fluid which splits and cracks the chemicals in food to be distributed as fuel for the body.

Liver
The liver cleanses the blood and processes nutritional molecules, which are distributed to the tissues. When we eat, more blood is diverted to the intestines to deal with digestive processes; when not eating, three-fourths of the blood supply to the liver comes from the intestines.

Spleen
The spleen is the largest of the lymphoid tissues. It is a valuable organ which produces some of the white blood cells, filters the blood, destroys old, worn-out red blood cells and returns needed iron to the blood, disposing of the rest as waste. The spleen also stores excess blood for emergencies; for example, when oxygen in the circulatory system is short.

Small Intestine
It is divided into three sections: (1) the duodenum, a receiving area for chemicals and partially digested food from the stomach; (2) the jejunum, where most of the nutrients are absorbed into the blood and (3) the ileum, where the remaining nutrients are absorbed before moving into the large intestine. The intestines process about 2.5 gallons of food, liquids and bodily waste every day. The small intestine also makes waves which move the food forward, but these are usually weak and infrequent to allow the food to stay in one place until the nutrients can be absorbed. If a toxic substance enters the small intestine, these movements may be strong and rapid to expel the poisons quickly.

Large Intestine
The large intestine, or colon, consists of ascending, transverse, descending, and sigmoid portions. Substances which have not been absorbed in the small intestine enter the large intestine in the form of liquid and fiber. The large intestine or "bowel" is sometimes called the "garbage dump" of the body, because the materials that reach it are of very small use to the body and are sent on to be disposed of. The first half of the colon absorbs fluids and recycles them into the blood stream. The second half compacts the wastes into feces, secretes mucus which binds the substances, and lubricates it to protect the colon and ease its passage.

Rectum
The rectum is a short, muscular tube that forms the lowest portion of the large intestine and connects it to the anus. Feces collects here until pressure on the rectal walls cause nerve impulses to pass to the brain, which then sends messages to the voluntary muscles in the anus to relax, permitting expulsion.

Site of action: mouth
Source: salivary gland
Secretion: saliva
Constituents and consequence:
amylase: starch-->maltose
lysozyme: attack bacterial cell wall
mucus: lubrication of food mass
hydrogencarbonate: buffer action provides almost neutral medium for the action of amylase; maintain correct pH

Site of action: esophagus
Source: wall of esophagus
Secretion: mucus (lubrication)
Function of esophagus: move food to stomach by peristaltic waves

Site of action: stomach
Source: gastric gland
Secretion: gastric juice
Constituents and consequence:
HCl: provides acidic medium for the activites of protease; kill germs; stops the action of salivary amylase; activate protease
mucus: protection of stomach lining against the action of protease
protease: protein-->peptides+amino acids

Site of action: duodenum
Source: liver and pancreas
Secretion: bile and pancreatic juice respectively
Constituents and consequence:
For bile:
sodium bicarbonate: neutralization of stomach acid
bile salts: emulsification, formation of micelles
bile pigments: breakdown product of haemoglobin for excretion
For pancreatic juice:
amylase: starch-->maltose
protease: protein-->peptides+amino acid
peptidase: peptides-->amino acids
lipase: fat-->fatty acids+monoglycerides

Site of action: small intestine
Source: wall of small intestine
Secretion: intestinal juice
Constituents and consequence:
carbohydrases:
-maltase: maltase-->glucose
-sucrase: sucrase-->glucose
-lactase: lactase-->glucose
aminopeptidase: peptides-->amino acids
lipase: fat-->fatty acids+monoglycerides
mucus: lubrication of food mass; protection of intestinal lining aganist the action of enzymes

Site of action: large intestine
Source: wall of large intestine
Secretion: mucus(lubrication)
Functions of large intestine: storage and concentration of undigested matter; absorption of salt and water; mixing and propulsion of contents; defecation

中文 消化系統的主要功能是消化食物，吸收營養，排出消化吸收後的食物殘渣，人體的消化系統主要由消化道和消化腺組成。
消化道包括口腔、咽、食管、胃、小腸、大腸、肛管、組成
消化腺又分為小消化腺和大消化腺兩種。
小消化腺是散在於消化管各部的管壁內的小腺體。這類腺體數量甚多，如胃腺、腸腺等：
大消化腺位於消化道外，它們主要通過導管淨分泌物排入消化管內。大消化腺主要有：三對唾液腺（腮腺、下頜下腺、舌下腺）、肝臟和胰臟。
消化系統是一個與生物相關的小作品。你可以通過編輯或修訂擴充其內容。


消化系統
人體：口腔 - 咽 - 食道 - 胃 - 胰腺 - 膽囊 - 肝 - 小腸（十二指腸、空腸、迴腸） - 盲腸 - 結腸 - 直腸 - 肛門
其他動物：嗉囊
英文
Salivary Glands
The mouth contains the salivary glands which are accessory digestive glands that produce a fluid secretion called saliva.
The Tooth
The tooth can be broken down by acids produced by the mouth for digestive purposes. This process is called "decay". To prevent decay, good oral hygiene, consisting of daily brushing and flossing, is necessary.
The Eso*****us
The eso*****us is a muscular tube which carries food and liquids from the throat to the stomach for digestion after it has been chewed and chemically softened in the mouth.
Stomach
The stomach consists of layers of muscle and nerves that continue the breakdown of food which begins in the mouth.The stomach has several functions: (1) as a storage bin, holding a meal in the upper portion and releasing it a little at a time into the lower portion for processing; (2) as a food mixer, the strong muscles contract and mash the food into a sticky, slushy mass; (3) as a sterilizing system, where the cells in the stomach produce an acid which kills germs in "bad" food; (4) as a digestive tub, the stomach produces digestive fluid which splits and cracks the chemicals in food to be distributed as fuel for the body.
Liver
The liver cleanses the blood and processes nutritional molecules, which are distributed to the tissues. When we eat, more blood is diverted to the intestines to deal with digestive processes; when not eating, three-fourths of the blood supply to the liver comes from the intestines.
Spleen
The spleen is the largest of the lymphoid tissues. It is a valuable organ which produces some of the white blood cells, filters the blood, destroys old, worn-out red blood cells and returns needed iron to the blood, disposing of the rest as waste. The spleen also stores excess blood for emergencies; for example, when oxygen in the circulatory system is short.
Small Intestine
It is divided into three sections: (1) the duodenum, a receiving area for chemicals and partially digested food from the stomach; (2) the jejunum, where most of the nutrients are absorbed into the blood and (3) the ileum, where the remaining nutrients are absorbed before moving into the large intestine. The intestines process about 2.5 gallons of food, liquids and bodily waste every day. The small intestine also makes waves which move the food forward, but these are usually weak and infrequent to allow the food to stay in one place until the nutrients can be absorbed. If a toxic substance enters the small intestine, these movements may be strong and rapid to expel the poisons quickly.
Large Intestine
The large intestine, or colon, consists of ascending, transverse, descending, and sigmoid portions. Substances which have not been absorbed in the small intestine enter the large intestine in the form of liquid and fiber. The large intestine or "bowel" is sometimes called the "garbage dump" of the body, because the materials that reach it are of very small use to the body and are sent on to be disposed of. The first half of the colon absorbs fluids and recycles them into the blood stream. The second half compacts the wastes into feces, secretes mucus which binds the substances, and lubricates it to protect the colon and ease its passage.
Rectum
The rectum is a short, muscular tube that forms the lowest portion of the large intestine and connects it to the anus. Feces collects here until pressure on the rectal walls cause nerve impulses to pass to the brain, which then sends messages to the voluntary muscles in the anus to relax, permitting expulsion.