Macaulay, right, turns his attention from inanimate objects to human anatomy in his latest book, The Way We Work.

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To his many fans, David Macaulay is nothing less than America’s Explainer-in-Chief — the ultimate authority on everything from the fine points of building a pyramid to the inner workings of corkscrews, microwaves, zippers and other everyday contraptions.

Now the longtime Rhode Island School of Design professor and award-winning author of Cathedral, Pyramid and The Way Things Work, has tackled his most challenging subject yet: the human body.

The result, The Way We Work: Getting to Know the Amazing Human Body (Houghton Mifflin, $35 hardcover), is due in bookstores on Tuesday. Weighing in at more than 300 pages — and chock-full of illustrations covering everything from hip joints to hair follicles, lungs to lymph glands — the book is one of Macaulay’s longest to date.

It was also one of the most difficult.

“There were definitely times when I thought ‘Man, what have you gotten yourself into?’ ” Macaulay confessed during a recent phone interview. “At first, it was a little puzzling because I actually think of myself as a pretty good researcher. But the human body is so complicated — and everything about it is so interconnected — that it was often hard to know when to stop.”

Now that the book — his 23rd — is finally done, Macaulay is gearing up for a month-long book tour that will bring him to Boston this week and to Providence on Oct. 18 for the annual Rhode Island Festival of Children’s Books and Authors. He’s also the focus of “Building Books: The Art of David Macaulay,” a RISD Museum exhibit that includes some of the hundreds of colored-pencil drawings he made for The Way We Work.

For readers who fell in love with the spare black-and-white drawings Macaulay created for early books such as Castle and Pyramid, that may sound sacrilegious. But Macaulay, who’s used color for many of his more recent projects, said that choosing color for The Way We Work was easy.

“Actually, it was a no-brainer,” he said. “Black and white worked for a lot of the early books because what they were describing — building a cathedral, for example — was fairly straightforward. But the body is much more complicated. There’s no way you could differentiate between, say, a vein and a muscle without using color.”

Nevertheless, Macaulay is prepared for readers who still prefer his pen-and-ink drawings.

“Frankly, I’m glad they even remember my older books,” he said. “But it also reminds me of what people used to say about Woody Allen — you know, ‘I used to love his movies until he got serious.’ ”

“Serious,” at least in the sense of “heavy,” “obscure” and “hard to understand,” is not a word that one associates with Macaulay or his work. Indeed, he’s known for taking complicated subjects — medieval construction practices, for example, or the behavior of subatomic particles — and making them accessible to average readers.

He also has an impish sense of humor, a trait that shows up frequently in The Way We Work.

A drawing of the small intestine, for example, shows a family of four rafting past areas marked “bile,” “chyme” and “pancreatic juice.” (In a clever touch, everyone is wearing a safety vest.) A section on the circulatory system, meanwhile, shows a group of white and red blood cells splashing around a pool, complete with a diving board and lifeguard towers.

In the interview, Macaulay said that humor plays a key role in making The Way We Work work.

“One thing I really didn’t want to do was write an anatomy textbook,” he said. “Instead, the idea was to take readers on a quick tour of their own bodies, beginning with an explanation of the body’s basic cellular structure and including all the major physiological systems and processes.

“And just as a good tour guide knows when to crack a joke or tell an amusing anecdote, I tried to inject a little humor here and there. Granted, that may not be the way they do it at Harvard Medical School, but then The Way We Work isn’t intended as a how-to guide for doctors.”

At the same time, Macaulay wanted his drawings to be accurate.

To that end, he took an anatomy class at RISD, observed Boston medical students dissecting cadavers and sat in on surgical procedures, including one to remove a diseased pancreas. (Macaulay describes the experience as “Fascinating, but not something I’m never likely to do again.”)

A stickler for details, Macaulay also consulted with a wide array of experts, including specialists in internal medicine, infectious diseases, biochemistry and gerontology.

Yet even after more than two years of research, Macaulay said he found it difficult to get started. “No matter how much you learn about the body, there’s always more,” he said. “And that’s especially true now, when medical discoveries are happening all the time.”

Even as the book began to take shape, Macaulay continued to struggle. Finding a narrative structure that made sense of all the material he had gathered was one problem. Another was creating visual equivalents for bodily processes as diverse as sleeping, sweating and getting sick.

“There were a lot of nights when I woke up and thought: ‘You’re never going to finish,’ ” he recalled. “There was so much stuff to work with that it was easy to get lost.”

Gradually, an outline emerged.

“Ultimately, I decided to start with the most basic building blocks — things like atoms, molecules and cells,” Macaulay explained. “From there, I moved on to genes, proteins and DNA. It was a little like starting Cathedral or Castle with a chapter on geology. Before you could get to the heart or the muscles or the brain, you needed to know some basic chemistry and biology.”

Macaulay also enlisted the help of Richard Walker, a British author and teacher who’s won several awards for science writing. That allowed Macaulay to concentrate on the illustrations.

“Working with Richard was terrific,” Macaulay says. “As someone who comes from a scientific background, he understood most of the material better than I ever could. And even though we were working on opposite sides of the Atlantic, we communicated very well.”

Asked what section of the book proved most difficult to illustrate, Macaulay didn’t miss a beat.

“Definitely the brain,” he said. “I mean, think about it. On a purely physical level, it’s not very interesting — just a big mass of gray matter. But of course this ‘mass of gray matter’ is responsible for almost everything that makes us who we are — our thoughts, emotions, memories, dreams. Finding a way to make these invisible processes visible was a challenge.”

Another human activity — sex — also posed a challenge.

Ultimately, Macaulay decided to provide a full account of human sexuality, including a discussion of the anatomical differences between men and women and a description of the reproductive process, rather than censor such a fundamental side of human behavior.

“One of the great things about science is how it’s so matter-of-fact about everything, including the body,” he said. “And that’s something I believe in. They may not like the results in Kansas [site of frequent censorship battles], but I think I can live with that.”

Like most of Macaulay’s books, The Way We Work is grounded in a childlike sense of curiosity — a need to know not just how things work but why they work and where they came from. It’s a trait that first surfaced in 1973’s Cathedral: A Story of Its Construction and has continued through more than 30 other books, including Pyramid (1975), Castle (1977) Mill (1983) and the mega-selling The Way Things Work (1983, with text by Neil Yardley).

But Macaulay, who turns 62 in December, said he had some extra motivation this time.

“Actually, my awareness of my own mortality was one of the biggest motivations,” he said. “The first time I thought of doing a book on the human body was back in the 1980s. Every now and then I’d come back to it, but there really wasn’t a sense of urgency.

Over the past few years, though, I’ve lost some good friends — people who were close to me and who I always assumed would be there. Meanwhile, my wife and I have two young children who are growing up right in front of me. As a result, I definitely have a deeper respect for the human body in general, and my own body in particular, than I may have had in the past.”

Looking ahead, Macaulay said that he’s considering a number of projects. That includes a series of books for David Macaulay Studio, a new Houghton Mifflin imprint created specifically for him.

Now based in Vermont, Macaulay also said he’s excited about his upcoming trip to Providence.

“I’m really looking forward to seeing the Chace Center,” he said, referring to RISD’s striking new campus center on North Main Street. “I hear it’s pretty cool.”Where to see Macaulay and his work

•David Macaulay is one of the featured artists at this year’s Rhode Island Festival of Children’s Books and Authors. The festival takes place Oct. 18 at the Lincoln School, 301 Butler Ave. in Providence. For more information, call (401) 331-9696, ext. 3135; see www.festivalofchildrensbooks.org.

•The art exhibit “Building Books: The Art of David Macaulay” continues through Feb. 11 at the RISD Museum, 224 Benefit St. in Providence.

bvansicl@projo.com