Solving a longstanding mystery, scientists have found that the human heart continues to generate new cardiac cells throughout the life span, although the rate of new cell production slows with age.
The finding, published in the April 3 issue of Science, could open a new path for the treatment of heart diseases such as heart failure and heart attack, experts say.
"We find that the beating cells in the heart, cardiomyocytes, are renewed," said lead researcher Dr. Jonas Frisen, a professor of stem cell research at the Karolinska Institute in Stockholm, Sweden. "It has previously not been known whether we were limited to the cardiomyocytes we are born with or if they could be renewed," he said.
The process of renewing these cells changes over time, Frisen added. In a 20-year-old, about 1 percent of cardiomyocytes are exchanged each year, but the turnover rate decreases with age to only 0.45 percent by age 75.
"If we can understand how the generation of new cardiomyocytes is regulated, it may be potentially possible to develop pharmaceuticals that promote this process to stimulate regeneration after for example, a heart attack, "Frisen said.
That could lead to treatment that helps restore damaged hearts.
"A lot of people suffer from chronic heart failure," noted co-author Dr. Ratan Bhardwaj.
Ratan Bhardwaj, also from the Karolinska Institute. "Chronic heart failure arises from heart cells dying," he said.
With this finding, scientists are "opening the door to potential therapies to having ourselves heal ourselves," Bhardwaj said. "Maybe one could devise a pharmaceutical agent that would make heart cells make new and more cells to overcome the problem they are facing."
But barriers remain. According to Bhardwaj, scientists do not yet know how to increase heart cell production to a rate that would replace cells faster than they are dying off, especially in older patients with heart failure. In addition, the number of new cells the heart produces was estimated using healthy hearts-whether the rate of cell turnover in diseased hearts is the same remains unknown.
The human heart stops producing cardiac cells______.

A:when a person becomes old B:as soon as a person gets sick C:immediately after a person is born D:once a person dies

给出下列的不完整的类代码，则下列的( )语句可以加到横线处。
class Person
String name，department；
int age
public Person(String n)name=n；
public Person(String n，int a)name=n；age=a；
pubilc Person(String n，String d，int a)
_______________
department=d；

A:Person(n，a)； B:this(Person(n，a))； C:this(n，a)； D:this(name，age)；

给出下列的不完整的类代码，则下列的( )语句可以加到横线处。 class Person{ String name，department； int age public Person(String n){name=n；} public Person(String n，int a){name=n；age=a；} pubilc Person(String n，String d，int a) { _______________ department=d； } }

A:Person(n，； B:this(Person(n，)； C:this(n，； D:this(name，ag；

给出下列的不完整的类代码，则下列的哪个语句可以加到横线处 class Person { String name，department； int age； public Person( String n ){ name = n；} public Person( String n，int a ) { name = n；age = a；} public Person( String n，String d，int a ) { _____________ department = d； } }

A:Person(n，a)； B:this(Person(n，a) )； C:this(n，a)； D:this(name，age)；

给出下列的不完整的类代码，则下列的哪个语句可以加到横线处 class Person { String name，department； int age； public Person( String n ){ name = n；} public Person( String n，int a ) { name = n；age = a；} public Person( String n，String d，int a ) { _____________ department = d； } }

A:Person(n，； B:this(Person(n， )； C:this(n，； D:this(name，ag；

给出下面不完整的类代码，则横线处的语句应该为( )。 class Person { String name，department； int age； public Person (Strings) {name=s；} public Person (String s，int a) {name=s；age=a;} public Person (String n，String d，int a){ __________ department=d； } }

A:Person (n，； B:this (Person(n，)； C:this(n，； D:this(name，ag；

给出下列的不完整的类代码，则哪个语句可以被加到横线处 ( ) class Person{ String name,department; int age； public Person(String n){name=n;} public Person(String n，int s){name=n; age=a；} public Person(String n，String d，int a){ department=d；______ } }

A:Person(n,； B:this(Person(n,)； C:this(n,； D:this(name,ag；