The Federal Reserve's balance sheet got a lot bigger last year .... and so did its profits.

According to figures released Friday, the Fed reported net income of $101.3 billion. That's an increase of nearly 30% from 2013.

But the Fed sends nearly all of its profits to the Treasury. Last year, that amounted to $96.9 billion. The Fed said this was a record.

The Fed also ended 2014 with nearly $4.5 trillion in assets -- up from about $4 trillion in 2013.

The central bank has been criticized by some economists and politicians for the size of its balance sheet, which ballooned during the financial crisis as the Fed bought billions of dollars of bonds and other securities each month to try and boost the economy.

The concern is that the Fed may be helping blow up bubbles in the stock and bond markets because it has injected so much money into the markets through its purchases. Stocks are near all-time highs and investors continue to also plow money into long-term U.S. Treasuries.

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But this bond buying program, known as quantitative easing or QE, is now over.

Still, the Fed's balance sheet may not shrink too dramatically just yet. That's because the central bank has said that it will continue to reinvest the principal payments from all of its holdings for awhile.

The Fed hinted earlier this week that it will probably begin to raise interest rates later this summer.

During a press conference, Fed chair Janet Yellen said that the central bank will eventually end its investments in bonds once it starts raising rates "as a way of gradually reducing the size of our portfolio over time."

But she added that the Fed had not decided how long it will wait to finally slow the pace of those investments. She reiterated that the Fed won't do so until "economic conditions were appropriate after we begin raising rates."

She noted that about $800 billion worth of Treasuries on the Fed's books are due to mature over the next two years.

Still, the Fed has a long way to go before the size of its balance sheet is back to where it was at the start of the Great Recession. It had about $850 billion in assets in 2008.

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The size of the Fed's balance sheet is not the only thing the Fed has come under fire for, however.

Some Republicans in Congress -- most notably Senator Rand Paul -- have also argued that the Fed needs to share more about its finances and inner workings with the public.

Fed chair Janet Yellen fought back against those complaints in Wednesday's press conference.

"I believe the Federal Reserve is already one of the most transparent central banks of any around the globe" she said. "We provide an immense amount of information both financial about our balance sheet and our monetary policy operations. We have audited financial statements. We published our balance sheet every week."