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the digestive system.

2020-02-03 来源: 51Due教员组 类别: Essay范文

今天给大家带来一篇优秀的范文,是一篇关于介绍消化系统的演讲稿。文章通过对消化系统的系统的主要两个部分,消化系统的主要消化过程等来介绍。再通过有趣的内容:当他们点披萨的时候,他们更喜欢把披萨切成8块而不是12块,因为12块对他们的消化系统来说太多了。来激发读者的阅读兴趣。

1. Hello, everyone. I’m XXX from Group X. Today we will present about the digestive system. Some of you might have such friends: when they order a pizza, they prefer to have it cut into 8 pieces instead of 12, as 12 pieces are too much for their digestive systems. But will their digestive systems agree with the statement? Let’s go on and find out.

2. Our digestive system includes two sections: the organs of the digestive tract and the accessory digestive organs.

3. The digestive tract consists of organs labelled in this picture: mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

4. And the accessory organs in our digestive system include pancreas, liver, and gall bladder.

5. The whole system performs a range of duties, which can be summarized into 4 major ones: food ingesting, digesting it to nutrients, absorbing nutrients, and eliminating indigestible remains.

6. Based on these functions, digesting process can be classified into mechanical digestion and chemical digestion. Mechanical digestion acts as chewing, stomach churning and segmentation that happen in the small intestine, whereas chemical Digestion is mainly conducted by Enzymes.

7. Now let’s look at the system from the beginning. Mouth is the entrance of food. What’s more, it also helps with tasting, moistening food and mechanical digestion.

8. Apart from teeth that grind up food and tongue that blends food up with saliva as well as further generates bolus, there are also 3 couples of salivary glands that can secrete salivary amylase, which is the start point of starch digestion.

9. Further inside the mouth is the Pharynx. It is a passageway for air and nutrition, located behind the uvula. It is the start point of wallowing reflex. Epiglottis is the structure that covers opening of the trachea when swallowing, stopping us from getting choke.

10. Esophagus is further down, which goes through the diaphragm and connects the pharynx and the stomach together. It moves food along the esophagus to the stomach by Peristalsis, a series of rhythmic contractions. The circular muscles around Esophagus are called Sphincters, which are in charge of whether to allow substances moving in and out the stomach.

11. Stomach is at the end of esophagus. The strong, crescent organ has a thick wall. Gastric glands can secrete gastric juice, in which the pepsin starts the process of protein digestion. Partially digested food become chyme here, mixed up with HCl. This kind of strong acid can effectively kill bacteria and further dissolve minerals as well as stimulate pepsin. Stomach is highly extendable, who can enlarge to accommodate lots of food and can shrink without enough food.

12. Next is the small intestine. It is around 6 meters in length, with a diameter of 2.5 cm, well protected in our abdominal cavity. The first 25 cm of it is called duodenum. Chyme from the stomach arrives in here, mixed with bile that can emulsify fats, pancreatic fluid that neutralizes the acid in chyme as well as brings enzymes, and intestinal fluid. The functions of these 3 are shown in this graph.

13. In the inner surface of the small intestine are finger-like projections that greatly increase the absorption area, known as Villi. Inside villi lay lacteals that absorb fatty acids and blood capillaries that absorb glucose and amino acids.

14. As you can see in the picture, the section outside is the large intestine. It is also known as the colon. It is 6.5 cm in diameter. It mainly absorbs H2O, salts and vitamins. Vermiform appendix is the part hanging outside, which may be associated to immune reaction, but can easily become inflamed and rupture causing peritonitis. Rectum temporarily hosts feces, further leads into the anus, which is a structure made up with sphincter muscles that are in charge of reflex action. Escherichia coli (coliforms) play an important role in indigestible material producing B complex vitamins as well as major vitamin Ks.

Now I will pass the next section to my groupmate, XXX. Thank you.


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