跟读练习: Stem Cells - 通过视频学习英语口语
加载中...
1
The human body contains organs such as bones, the brain, heart, and reproductive organs.
2
The basic cells that give rise to all of the different cells in these organs are called stem cells.
3
One type of stem cell is an egg cell from a woman that has been fertilized by a sperm from a man.
4
This single cell, called a zygote, is the first cell in a developing human being.
5
It's also called a totipotent stem cell because it can form any type of cell in the body,
6
as well as the umbilical cord and placenta.
7
After a zygote has divided a few times, it becomes an early-stage embryo called a blastocyst.
8
Embryonic stem cells come from the cells inside the blastocyst.
9
Embryonic stem cells are pluripotent.
10
This means they can form any cell in the body, but not the cells in the umbilical cord or placenta.
11
In the lab, embryonic stem cells are donated from leftover embryos created during in vitro fertilization.
12
In vitro fertilization is a procedure to help a woman become pregnant.
13
Another type of stem cell is an adult stem cell.
14
Small groups of these cells are found in some organs, such as the skin, after birth, and into adulthood.
15
Adult stem cells are multipodent.
16
This means they can only become a few different cell types related to the organ where they're found.
17
For example, the skin contains a small number of adult stem cells that can divide to create new skin adult stem cells.
18
Or, they can become more specialized skin cells to replace those that are lost due to cell aging or damage.
19
In the lab, scientists can now induce or cause a regular body cell, such as a skin cell,
20
to change into a pluripotent stem cell.
21
Like embryonic stem cells, these induced pluripotent stem cells can become any type of cell in the body.
22
Scientists study stem cells to learn how and why they become many different types of cells.
23
In the future, these cells may be used to regrow tissues and organs that have been damaged by injury or disease.
24
Stem cell therapy is a procedure that uses stem cells to treat a disease or condition.
25
Currently, stem cell therapy only treats diseases and cancers of the blood.
26
In leukemia, for example, the patient's bone marrow makes many abnormal white blood cells that can't do their job to fight infection.
27
Over time, these abnormal cells crowd out the production of healthy white blood cells.
28
In stem cell therapy for leukemia, called hematopoietic stem cell transplantation,
29
a a doctor will take a sample of blood or bone marrow from the patient or a donor.
30
In some cases, donor blood may come from a baby's umbilical cord after it's born.
31
These tissue samples contain healthy hematopoietic or blood-forming stem cells.
32
Then, doctors will give the patient chemotherapy drugs or use radiation to kill the abnormal white blood cells and their stem cells.
33
Once the abnormal cells are gone, the doctor will transplant the healthy hematopoietic stem cells from the tissue samples into the patient.
34
These healthy stem cells will make new blood cells, including normal white blood cells, which will allow the body to fight off infections.
关于本课
您正在使用跟读技巧通过视频"Stem Cells"练习英语口语和发音。
每天练习15到30分钟，将显著提高您的英语流利度和发音准确度。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。