Facebook is headed back to Capitol Hill for another grilling from lawmakers.

Antigone Davis, Facebook’s global head of safety, is expected to face harsh questioning from senators on Thursday morning about Instagram’s effect on teenagers, addressing accusations that Facebook has known for years that its photo-sharing app has caused mental and emotional harm.

The hearing, which starts at 10, is the first of two that the Senate’s consumer protection subcommittee will hold on the effect that Facebook has on young people. The second, on Tuesday, will be with a whistle-blower who has shared information about Facebook’s research on teenagers.

The hearings were called after The Wall Street Journal published a series of articles this month about internal research at Facebook. One of the articles reported that, according to Facebook’s findings, one in three teenagers said Instagram made his or her body image issues worse. Among teenagers who had suicidal thoughts, 13 percent of British users and 6 percent of American users said they could trace those thoughts to Instagram.

On Wednesday evening, Facebook released two slide decks from the research cited by The Journal. The company heavily annotated the slides, at times disputing or reframing the accuracy and intention of the research report. The company said in its slides that many teenagers reported positive experiences on Instagram, including that the app at times helped with mental health.

Lawmakers have criticized the company and its executives for hiding the research, which appeared to contradict public statements by Facebook’s chief executive, Mark Zuckerberg, and the executive in charge of Instagram, Adam Mosseri. Both have long downplayed warnings that Instagram — through filters that can enhance images and a “like” button that can be used as a gauge of popularity — created a fraught environment for young users and made many teenagers feel worse about themselves.

This week, Mr. Mosseri announced that Facebook would pause plans to release a version of Instagram aimed at children in elementary and middle school.

Mr. Mosseri has argued that The Journal’s article on Instagram took research out of context, and said the number of teenagers in the study was “quite small.” He has said many teenagers report positive experiences on Instagram.

Ms. Davis, who has led safety at Facebook for seven years, is expected to reiterate that message in the hearing. The company has defended the idea of an app for children, like YouTube Kids, saying it could provide stronger safety and privacy features for young children than the main Instagram app.

Senator Marsha Blackburn of Tennessee, the ranking Republican on the consumer protection subcommittee, said in a statement, “From turning a blind eye to the negative impacts of its platforms on teens’ mental health to its inability to police for trafficking, domestic servitude and other harmful content, Facebook has a lot to account for.”