The human body is an astonishingly complex and fascinating marvel, a genuine “Body Odyssey” that continues to captivate and challenge our understanding. From the visible mechanics of digestion to the microscopic worlds within, there’s always something new to learn, even for those deeply immersed in medical studies.

Making Learning Fun (and Gross!)

Educational exhibitions and books are making the wonders of the human body accessible and engaging for all ages. One popular exhibit featured video footage of the digestive system with charming sound effects and a graphic explanation of what happens to a hamburger, much to children’s delight. Visitors could even climb into a model mouth, crawl down a throat, and choose a path to either the digestive system or the lungs, with computer screens providing information on each section. Another part of the exhibition allowed children to play in a giant model of skin, complete with pink foam for epidermis, black spikes for hair, and plastic spheres for sweat bubbles. It also showcased how much skin a person sheds monthly (a full rubbish bag!) and encouraged sun protection.

Beyond physical exhibits, books like the Gross and Ghastly: Human Body series offer answers to “burning questions” about the body’s more disgusting features, such as making a candle from earwax or why farts smell differently. These brightly colored guides, filled with pop-eyed characters and animated body parts, jump “gleefully from vomit to poop to blood and back to poop again”. Other books provide “weird but true” facts about the human body, covering everything from the speed of a sneeze to the high percentage of bones in hands and feet.

Even medical students are constantly surprised by discoveries. Two students gained viral fame on TikTok for sharing facts they learned in medical school, including that urine is blood filtered by the kidneys and is sterile, that bones produce blood, and that bone marrow is found in all bones, not just the spine. Perhaps most surprisingly, they discovered that there is more bacterial DNA inside our bodies than our DNA, and these bacteria help digest food and produce vitamins.

The Hidden World: Our Vast Virome

Beyond the macroscopic and familiar, the human body hosts an incredibly vast and diverse population of viruses, collectively known as the virome. While centuries of research linked specific viruses to diseases, the significance of entire viral populations was only truly appreciated with the development of advanced DNA sequencing methods in the early 2000s. It’s estimated that there are approximately 1013 viral particles per human individual, exhibiting immense heterogeneity.

The human virome comprises:

• Bacteriophages (phages): Viruses that infect bacteria.

• Viruses that infect other cellular microorganisms like archaea.

• Viruses that infect human cells.

• Transient viruses found in food.

Viral populations vary significantly across the human body, with the gastrointestinal tract containing the most abundant populations, often reaching around 10⁹ virus-like particles (VLPs) per gram of intestinal contents. Other sites like the oral cavity (~10⁸ VLPs per millilitre of saliva), blood (~10⁸ VLPs per millilitre), skin, urogenital system, and even the nervous system (~10⁴ VLPs per millilitre of cerebrospinal fluid) also host diverse viral communities. Most identifiable viruses in the gut are phages, particularly Caudovirales (tailed phages) and spherical Microviridae. Notably, the healthy human gut typically has low proportions of eukaryotic viruses, and most resident viruses are non-enveloped, which makes sense given the harsh conditions of the gut and the need for faecal-oral transmission.

The virome’s establishment is a stepwise process. Healthy neonates typically lack a detectable virome at birth but are rapidly colonised after delivery. The first detectable viruses are mainly phages from families like Siphoviridae, Podoviridae, and Myoviridae, often from pioneering bacteria in the infant gut. Later in life, lytic phages become more common, and viruses that replicate in human cells, which can cause gastroenteritis, also appear.

As pictured in The human virome: assembly, composition and host interactions by Guanxiang Liang and Frederic D. Bushman  (2021)

Numerous factors influence the virome’s structure, including diet, age, geographic location, and disease. Breastfeeding, for example, is linked to a lower accumulation of animal cell viruses in infants’ guts. While host genetics has a less clear influence on the virome in healthy individuals, they are well-established in inherited diseases like primary immunodeficiencies, where conditions like epidermodysplasia verruciformis allow viruses to replicate aggressively. Studies also show that geography strongly impacts human virome variation, with differences seen across regions and between Western and non-Western populations.

The virome isn’t just a collection of pathogens; it actively interacts with the human host, affecting health in various ways. Phages can influence bacterial communities, and there’s increasing interest in phage therapy to treat drug-resistant bacterial infections. Phages may also directly interact with the host immune system, triggering immune responses. Alterations in virome populations have been associated with diseases like inflammatory bowel disease, type 1 diabetes, hypertension, and even colorectal cancer.

The Body Ages: The Aorta Story

As we age, the human body undergoes progressive changes, some of which are visible, while others occur at a microscopic level. The aorta, the largest artery in the human body, is a prime example of an organ that undergoes significant age-related changes. Its primary function is to transport oxygenated blood from the heart to all organs and cells.

With advancing age, the aorta’s morphology changes:

• The luminal diameter and overall length of the aorta progressively increase in both sexes.

• The thickness of the aortic wall, specifically the tunica intima and tunica media, increases. The tunica intima, the innermost layer, thickens with age due to the accumulation of myointimal cells that store lipids.

• The microstructural components of the aortic wall also change. There’s a decrease in elastic fibres and smooth muscle cells in the tunica media, while the amount of collagen fibres tends to increase. This leads to elastin fragmentation and fibrosis.

• These changes can result in increased blood pressure and reduced elasticity of the vessel.

Age is a significant risk factor for degenerative changes and diseases affecting the aorta, such as atherosclerosis. Atherosclerosis is characterised by the accumulation of plaque (fats, cholesterol, fibres, cells) in the intima layer, leading to conditions like thrombosis and lumen obstruction. Understanding these age-associated changes in the aorta is crucial for future clinical therapies and can even be applied for age determination.

Broader Health Context: From Local to Global

Beyond individual anatomical and physiological changes, public health initiatives play a vital role in human well-being. Exhibitions also address topics like immunisation, explaining it through cartoons and video games like “Champion Game: Your Body Against the Germs!”. The exhibit even featured equipment from the 1950s polio epidemic, including a modified tricycle used to help children maintain muscle strength. Health camps, some of which still operate in New Zealand, teach children life skills, personal hygiene, and self-care. The “Body Odyssey” exhibition also focused on local health issues like skin cancer and asthma, exploring allergic reactions and different treatment types, and even featuring a look at a smoker’s lung.

On a global scale, tackling health issues requires concerted efforts. In Nigeria, for instance, despite a sound education system and strong media networks, discussions around HIV/AIDS remain taboo, and misinformation is widespread due to government inaction. Against this backdrop, groups like Nigerian Journalists Against AIDS (JAAIDS) are tackling the issue with energy. Their website aims to educate Nigerian journalists on HIV/AIDS, enabling them to inform the public. The site is interactive, featuring an excellent AIDS e-forum where hundreds of members, not just journalists, exchange vital information and discuss health issues. JAAIDS founder Omolulu Falobi won an award for innovative internet use, and the site’s homepage provides hourly updates on new HIV cases and AIDS deaths in Nigeria, underscoring the urgency of information dissemination. As one source states, in the fight against AIDS, “information is everything”.

Finally, global health concerns like landmines also highlight the body’s vulnerability and the need for support. A benefit concert for the Campaign for a Landmine Free World brought together leading musicians like Emmylou Harris, Steve Earle, John Prine, and Elvis Costello to raise funds. Bobby Muller, president of Vietnam Veterans of America Foundation (VVAF), noted how crucial such support is for their work. The concert raised significant funds, with Harris and Nancy Griffith auctioning scarves made in a VVAF-sponsored rehabilitation centre, enough to clear landmines from about eight football pitches.

In conclusion, from the intricate workings of our cells and organs to the broad challenges of public health, the human body remains a source of endless discovery and a central focus of scientific and societal endeavour.

References

1. Archer, K. (2002) ‘Burps, scabs, sunburn, and other pressing issues are examined in Body Odyssey, an exhibition that aims to explain to children the wonders of the human body’, The Lancet, 359(9303), pp. 364–365.

2. Archer, K. (2002) ‘Immunisation is well explained in a cartoon and video game, Champion Game: Your Body Against the Germs!’, The Lancet, 359(9303), pp. 364–365.

3. Archer, K. (2002) ‘Burps, scabs, sunburn, and other pressing issues are examined in Body Odyssey, an exhibition that aims to explain to children the wonders of the human body’, The Lancet, 359(9303), pp. 364.

4. Archer, K. (2002) ‘The first exhibit looks at skin, and children can play in a giant model of skin, with pink pieces of foam to represent the epidermis, black spikes as hair, and plastic spheres for bubbles of sweat’, The Lancet, 359(9303), pp. 364.

5. Archer, K. (2002) ‘Only since the death from AIDS in 1997 of Fela Kuti, the popular Nigerian musician, did the issue of HIV/AIDS become a reality for many Nigerians’, The Lancet, 359(9303), pp. 364.

6. Archer, K. (2002) ‘Although the government now finally acknowledges that Nigeria has an HIV problem, critics would say their attempts to address the issues are too late and mostly, so far, incomplete’, The Lancet, 359(9303), pp. 364.

7. Archer, K. (2002) ‘Against this backdrop, it is inspirational to see groups such as Nigerian Journalists Against AIDS tackling this momentous task with so much energy and positivity’, The Lancet, 359(9303), pp. 364.

8. Archer, K. (2002) ‘The site is interactive and comprehensive’, The Lancet, 359(9303), pp. 364.

9. Archer, K. (2002) ‘In the fight against AIDS, information is everything’, The Lancet, 359(9303), pp. 364.

10. Hargreaves, S. (2002) ‘Leading American alt country musicians joined with the more traditional John Prine and the UK player and songwriter, Elvis Costello, for a benefit concert in aid of the Campaign for a Landmine Free World’, The Lancet, 359(9303), pp. 364.

11. Hargreaves, S. (2002) ‘Bobby Muller, president of VVAF (see page 273), spoke from the stage: “Nothing has enabled me to garner more support for our work than Emmylou Harris and her friends”’, The Lancet, 359(9303), pp. 365.

12. Archer, K. (2002) ‘The asthma exhibit explores allergic reactions with models of healthy and asthmatic airways and a Vaudeville-style cartoon, Pollen vs Asthma: an Allergic Drama’, The Lancet, 359(9303), pp. 364.

13. Archer, K. (2002) ‘A model of a blood vessel entered down a slide and complete with cushions for red and white blood cells attracted plenty of interest from toddlers’, The Lancet, 359(9303), pp. 365.

14. Archer, K. (2002) ‘Children can also have a play with “Dexter”, the Endoscope Dexterity Trainer’, The Lancet, 359(9303), pp. 365.

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16. Liang, G. and Bushman, F.D. (2021) ‘Abstract | The human body hosts vast microbial communities, termed the microbiome’, Nature Reviews Microbiology, 19, pp. 415–425.

17. Liang, G. and Bushman, F.D. (2021) ‘Viral populations vary greatly across the human body’, Nature Reviews Microbiology, 19, pp. 415–425.

18. Liang, G. and Bushman, F.D. (2021) ‘Recent studies have uncovered numerous factors that show associations with virome structure in addition to anatomical location, such as diet, age, and geographic location of the individual sampled’, Nature Reviews Microbiology, 19, pp. 415–425.

19. Liang, G. and Bushman, F.D. (2021) ‘Viruses that are found in humans can be categorised by various features’, Nature Reviews Microbiology, 19, pp. 415–425.

20. Liang, G. and Bushman, F.D. (2021) ‘Most constituents of the human virome are inferred to be phages’, Nature Reviews Microbiology, 19, pp. 415–425.

21. Liang, G. and Bushman, F.D. (2021) ‘Table 1 | Examples of viral population alterations in human disorders’, Nature Reviews Microbiology, 19, pp. 415–425.

22. Liang, G. and Bushman, F.D. (2021) ‘Viruses that infect human cells are also an important part of the human virome’, Nature Reviews Microbiology, 19, pp. 415–425.

23. Liang, G. and Bushman, F.D. (2021) ‘Virome of different body sites Numerous recent studies have characterized the human virome at different body sites, revealing rich populations at numerous locations (fig. 2)’, Nature Reviews Microbiology, 19, pp. 415–425.

24. Liang, G. and Bushman, F.D. (2021) ‘Metagenomic sequencing of the human gut virome also indicated that Caudovirales is commonly predominant, along with the spherical Microviridae (reviewed in refs9,10,35–38)’, Nature Reviews Microbiology, 19, pp. 415–425.

25. Liang, G. and Bushman, F.D. (2021) ‘A notable pattern in viruses of the gut is that most residents, including both phages and human viruses, are not enveloped’, Nature Reviews Microbiology, 19, pp. 415–425.

26. Liang, G. and Bushman, F.D. (2021) ‘Oral cavity ~10^8 VLPs per millilitre of saliva’, Nature Reviews Microbiology, 19, pp. 415–425.

27. Liang, G. and Bushman, F.D. (2021) ‘Gastrointestinal tract ~10^9 VLPs per gram of faeces’, Nature Reviews Microbiology, 19, pp. 415–425.

28. Liang, G. and Bushman, F.D. (2021) ‘Vagina Eukaryotic viruses Anelloviridae Herpesviridae’, Nature Reviews Microbiology, 19, pp. 415–425.

29. Liang, G. and Bushman, F.D. (2021) ‘Urinary system ~10^7 VLPs per millilitre of urine’, Nature Reviews Microbiology, 19, pp. 415–425.

30. Liang, G. and Bushman, F.D. (2021) ‘Oral cavity. The human oral cavity contains diverse viral communities as well as complex microbial populations’, Nature Reviews Microbiology, 19, pp. 415–425.

31. Liang, G. and Bushman, F.D. (2021) ‘Respiratory tract. Virome analyses have been performed on respiratory tract samples including sputum, nasopharyngeal swabs and bronchoalveolar lavage, showing that the healthy human lung and respiratory tract can be populated by large viral communities29,58–62’, Nature Reviews Microbiology, 19, pp. 415–425.

32. Liang, G. and Bushman, F.D. (2021) ‘Blood. Viruses of blood have been studied closely, to understand human health and also to assess the safety of donor blood supplies’, Nature Reviews Microbiology, 19, pp. 415–425.

33. Liang, G. and Bushman, F.D. (2021) ‘Skin. Compared with other body sites, the skin has a relatively low microbial biomass, which can, for some samples, make it difficult to distinguish the resident microbiome and virome from various forms of contamination’, Nature Reviews Microbiology, 19, pp. 415–425.

34. Liang, G. and Bushman, F.D. (2021) ‘Urogenital system. Urine samples from healthy humans have been reported to contain viruses in the region of 10^7 VLPs per millilitre72’, Nature Reviews Microbiology, 19, pp. 415–425.

35. Liang, G. and Bushman, F.D. (2021) ‘Nervous system. Little information is available on virome populations in the nervous system in healthy humans’, Nature Reviews Microbiology, 19, pp. 415–425.

36. Liang, G. and Bushman, F.D. (2021) ‘To summarize the virome over multiple human body sites, the human gut contains the most abundant viruses and has been the most frequently studied’, Nature Reviews Microbiology, 19, pp. 415–425.

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38. Liang, G. and Bushman, F.D. (2021) ‘The virome at delivery. An early study of virome colonization sampled meconium shortly after delivery, and failed to find VLPs using epifluorescent microscopy but did report ~108 VLPs per gram at 1 week of life, suggesting that the neonate lacked a virome at birth but was quickly colonized93’, Nature Reviews Microbiology, 19, pp. 415–425.

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40. Liang, G. and Bushman, F.D. (2021) ‘A recent study investigated the production of the virome in gut samples of infants at 1 month of life and concluded that lytic phages were relatively rare49’, Nature Reviews Microbiology, 19, pp. 415–425.

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43. Liang, G. and Bushman, F.D. (2021) ‘Thus, recent data suggest that healthy infants are colonized in a stepwise fashion’, Nature Reviews Microbiology, 19, pp. 415–425.

44. Liang, G. and Bushman, F.D. (2021) ‘Diet. The infant virome, including both phages and eukaryotic viruses, can be affected by diet’, Nature Reviews Microbiology, 19, pp. 415–425.

45. Liang, G. and Bushman, F.D. (2021) ‘Host genetics and immunity. Intense interest has focused on the potential influence of human genetics on the microbiome, raising the linked question of the role of human genetics in programming the virome’, Nature Reviews Microbiology, 19, pp. 415–425.

46. Liang, G. and Bushman, F.D. (2021) ‘However, in inherited diseases such as primary immunodeficiencies, the effects of genetics on the virome are well established’, Nature Reviews Microbiology, 19, pp. 415–425.

47. Liang, G. and Bushman, F.D. (2021) ‘Diet, Medication, Disease, Geography, Ageing, Genetics, Cohabitation, Fig. 4 | Factors that shape the human virome’, Nature Reviews Microbiology, 19, pp. 415–425.

48. Liang, G. and Bushman, F.D. (2021) ‘Geography and stochastics of colonization. Large-scale virome studies have provided evidence that geographic location and stochastics of colonization have strong impacts on human virome variation’, Nature Reviews Microbiology, 19, pp. 415–425.

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54. Liang, G. and Bushman, F.D. (2021) ‘Conclusions and perspectives The virome field has come a long way since the first paper in 2002 that reported metagenomic sequencing of a viral specimen’, Nature Reviews Microbiology, 19, pp. 415–425.

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