The human body can survive the complete removal of more than a dozen organs and the partial removal of several others, though “survival” and “no consequences” are very different things. Some organs, like the gallbladder and appendix, leave relatively subtle traces when they’re gone. Others, like the thyroid or both kidneys, require lifelong medical management. And a few removals reveal surprising facts about how the body compensates, rewires, or fails to fully adjust. The picture is more nuanced than most people assume, and the trade-offs vary enormously depending on which organ is taken out and how much of it remains.
The Gallbladder
Gallbladder removal, or cholecystectomy, is one of the most common surgeries worldwide, performed hundreds of thousands of times each year in the United States alone. The gallbladder stores and concentrates bile produced by the liver. Without it, bile drips continuously into the small intestine rather than being released in controlled bursts after meals. Most people adapt well, but the adjustment is not biologically silent. Research in animal models shows that gallbladder removal reshapes the liver’s gene expression and metabolism, with cholesterol processing emerging as the pathway most disrupted in the weeks following surgery.1PubMed Central. Gallbladder removal induces hepatic transcriptional and metabolic shifts with cholesterol dysregulation as a key feature
There are metabolic ripple effects too. Studies in mice found that gallbladder removal worsened insulin resistance and lipid profiles, especially when combined with a high-fat diet.2PubMed Central. Effects of Bile Acid Modulation by Dietary Fat, Cholecystectomy, and Bile Acid Sequestrant on Energy, Glucose, and Lipid Metabolism and Gut Microbiota in Mice Separate research found that people who had undergone cholecystectomy burned more fat during rest and had higher energy expenditure during sleep compared to those who still had their gallbladders.3PubMed Central. Cholecystectomy Is Linked With Lower Respiratory Exchange Ratio and Higher Lipid Oxidation and Sleep Energy Expenditure The practical upshot: most people do fine after gallbladder removal, but the body’s handling of fats and cholesterol shifts in ways that may matter over years, particularly for people already at metabolic risk.
The Appendix
The appendix was long dismissed as a vestigial organ with no real function. That view has changed substantially. The appendix appears to serve as a reservoir for beneficial gut bacteria, sheltering them behind protective biofilms so they can repopulate the intestines after disruptions like infections or antibiotic treatment.4PubMed Central. The functional landscape of the appendix microbiome under conditions of health and disease It also plays an active role in local immune function.
Removing the appendix does leave a mark on gut ecology. People who have had an appendectomy tend to have less diverse gut bacteria, including lower levels of microbes that produce short-chain fatty acids, which are important for colon health.5PubMed Central. Appendectomy Is Associated With Alteration of Human Gut Bacterial and Fungal Communities That said, appendicitis is a genuine emergency, and the trade-off between a ruptured appendix and slightly less bacterial diversity is not remotely close. The interesting question is whether we should be more cautious about incidental appendectomies performed during other abdominal surgeries when the appendix is perfectly healthy.
The Spleen
The spleen filters blood, recycles old red blood cells, and houses immune cells that are critical for fighting certain types of bacteria. You can live without it, but you become permanently more vulnerable to infections, particularly from encapsulated bacteria like the ones that cause pneumococcal pneumonia, meningitis, and sepsis. A large cohort study following over 8,000 American veterans for up to 27 years found that people who had their spleens removed had roughly double the risk of pneumonia, about two and a half times the risk of meningitis, and more than three times the risk of septicemia compared to matched controls. The elevated infection risk persisted more than a decade after surgery.6Haematologica. Long-term risks after splenectomy among 8,149 cancer-free American veterans: a cohort study with up to 27 years follow-up
The most feared complication is overwhelming post-splenectomy infection, a rare but rapidly fatal condition that can strike at any time after the surgery. Case reports document it occurring 26 and even 30 years after splenectomy.7PubMed Central. Fatal Delayed-Onset Overwhelming Post-splenectomy Infection 26 Years After Splenectomy for Immune Thrombocytopenic Purpura8PubMed. Overwhelming post-splenectomy infection caused by Streptococcus agalactiae, sequence type 10 with capsular serotype Ib encapsulating ST10/1b occurring 30 years after splenectomy: a case report This is why people without spleens are advised to stay current on pneumococcal and meningococcal vaccines and to carry antibiotics for emergency use. The vulnerability never goes away.
The Thymus
The thymus sits behind the breastbone and is sometimes removed during cardiac surgery simply because it is in the way. For decades, this was considered harmless because the thymus shrinks with age and was assumed to be largely inactive in adults. A study published in the New England Journal of Medicine upended that assumption. Researchers found that adults who had their thymus removed during cardiac surgery had nearly triple the all-cause mortality and double the cancer risk at five years compared to matched controls who had the same cardiac surgery without thymectomy. People who had undergone thymectomy also produced fewer new T cells and had higher levels of inflammatory markers in their blood.9N Engl J Med. Health Consequences of Thymus Removal in Adults The findings suggest the thymus continues contributing to immune health well into adulthood, and surgeons have become more cautious about removing it incidentally.
The Stomach
Partial gastrectomy, where a portion of the stomach is removed, is common in cancer treatment and weight-loss surgery. Total gastrectomy, where the entire stomach is removed, is rarer but performed when cancer demands it. Without a stomach, the esophagus is connected directly to the small intestine. People can eat and digest food, but meals must be much smaller and more frequent because there is no reservoir to hold food.
The most medically consequential long-term effect of total gastrectomy is vitamin B12 deficiency. The stomach produces intrinsic factor, a protein essential for absorbing the tiny amounts of B12 present in food. Without the stomach, almost none of that dietary B12 gets absorbed, and patients eventually develop deficiency that can lead to a type of anemia and nerve damage if untreated.10JAMA Internal Medicine. Vitamin B12 Deficiency Following Total Gastrectomy Lifelong B12 injections solve the problem, but the requirement never ends.
Large Portions of the Intestines
The small intestine is where most nutrient absorption happens, and the body can tolerate losing modest segments of it. But when resection is extensive, the result is short bowel syndrome, a condition where the remaining intestine cannot absorb enough nutrients and fluids to sustain health without medical support. Depending on which segments are removed and how much remains, patients may need intravenous nutrition for months, years, or permanently.
The good news is that the intestine can adapt. Over time, the remaining bowel undergoes structural and functional changes that improve absorption. Intestinal villi grow longer, the intestinal wall thickens, and nutrient uptake per unit of remaining bowel increases.11PubMed. Intestinal adaptation following resection Medications that mimic gut hormones can accelerate this process, and rehabilitation protocols now focus on maximizing adaptation so patients can wean off intravenous feeding over time.12PubMed. Anatomical and physiological considerations in short bowel syndrome: Emphasis on intestinal adaptation and the role of enterohormones The colon can also be removed entirely, which is done for conditions like ulcerative colitis. An internal pouch fashioned from the small intestine can take over some of the colon’s water-absorbing role, though bowel habits never fully return to normal.
The Liver, Partially
The liver is the body’s most regenerative major organ. Surgeons can remove up to about two-thirds of it, and the remaining tissue will regrow to nearly the original mass within weeks to months. This is what makes living-donor liver transplantation possible: a healthy person donates a portion of their liver, and both the donor’s remnant and the transplanted piece regenerate.
How the liver rebuilds depends on how much was taken. After a large resection, the remaining liver cells divide rapidly, with nearly all hepatocytes entering the cell cycle. After a smaller resection, the liver recovers its mass primarily by having each cell grow larger rather than by producing new cells.13The American Journal of Pathology. Understanding Liver Regeneration: From Mechanisms to Regenerative Medicine Both pathways are triggered largely by changes in blood flow through the remaining tissue, as increased portal pressure and shear stress signal the liver that it needs to get bigger.14PubMed Central. Liver regeneration after partial hepatectomy: Triggers and mechanisms What the liver cannot do is regenerate if the entire organ is removed. Total hepatectomy is fatal without transplantation.
One Kidney
People are born with two kidneys but need only one to live a healthy life. Kidney donation is the most common context for voluntary single-kidney living, and the outcomes are generally reassuring. After one kidney is removed, the remaining kidney compensates by filtering more blood. This compensatory increase in filtration happens quickly and, when it is robust in the early period after donation, predicts better long-term kidney function.15PubMed. Early increase in single-kidney glomerular filtration rate after living kidney donation predicts long-term kidney function
The concern with a single kidney is that the same compensatory hyperfiltration that keeps things working in the short term can, over decades, contribute to protein leaking into the urine, high blood pressure, and gradual decline in kidney function. Genetic factors and other health conditions like diabetes or obesity influence how well the remaining kidney holds up.16PubMed Central. Hyperfiltration-mediated Injury in the Remaining Kidney of a Transplant Donor For healthy donors without those risk factors, the absolute risk of eventually needing dialysis remains low, but it is not zero, which is why donor screening is so rigorous.
The Bladder
Radical cystectomy, or complete bladder removal, is a standard treatment for muscle-invasive bladder cancer. Without a bladder, urine still needs somewhere to go. The two main options are an external stoma, where urine drains into a bag worn outside the body, or a neobladder, where a surgeon fashions a new internal reservoir from a segment of the patient’s own small intestine. The neobladder connects to the urethra, allowing the person to urinate in something close to the normal way, though the process requires retraining because the new reservoir lacks the nerve signals of a natural bladder.17PubMed Central. Neobladder “Function”: Tips and Tricks for Surgery and Postoperative Management Continence is achievable for many patients, though nighttime leakage is common, and the learning curve is real.
Lungs, Fully or Partially
A single lobe of the lung can be removed (lobectomy), or an entire lung can be removed (pneumonectomy). The functional difference between these two operations is stark. Six months after lobectomy, lung capacity drops by roughly 7 to 10 percent, and exercise capacity barely changes. After pneumonectomy, lung capacity drops by about a third, and peak exercise capacity falls by around 20 percent, with many patients finding that breathlessness replaces leg fatigue as the main barrier during exertion.18PubMed. Pulmonary function and exercise capacity after lung resection
The remaining lung does compensate to some degree. Animal studies show that after one lung is removed, the other hyperinflates, alveoli enlarge, and the tissue barrier between air and blood thins, all of which help improve gas exchange in the single remaining lung.19PubMed Central. Structural changes underlying compensatory increase of diffusing capacity after left pneumonectomy in adult dogs Still, a person living with one lung will always have less respiratory reserve, and strenuous activities will be harder. Both lungs cannot be removed without a lung transplant, as there is no equivalent of dialysis for breathing.
The Thyroid
Total thyroidectomy is performed for thyroid cancer, severe hyperthyroidism, and large goiters. The thyroid produces hormones that regulate metabolism, heart rate, body temperature, and much else, so removing it entirely means committing to lifelong synthetic hormone replacement. In practice, levothyroxine replaces the thyroid’s main hormone output effectively. A study of patients one year after total thyroidectomy found that replacement therapy kept overall thyroid hormone levels in the normal range, though the balance shifted: one hormone fraction ran higher than before surgery while another ran lower.20Journal of Basic and Clinical Health Sciences. Thyroid Hormone Replacement in Total Thyroidectomized Patients: Symptomatic and Metabolic Effects of Levothyroxine Monotherapy Some patients report persistent symptoms like fatigue and weight changes even when blood tests look normal, which has driven interest in combination hormone therapy, though the evidence on whether adding a second thyroid hormone truly helps remains mixed.
Reproductive Organs
The uterus is one of the most frequently removed organs. Hysterectomy ends menstruation and the ability to carry a pregnancy, but if the ovaries are preserved, it does not trigger menopause. The ovaries are a different matter. Removing both ovaries before natural menopause causes immediate surgical menopause due to the sudden loss of estrogen and other hormones. Long-term follow-up of women who underwent premenopausal oophorectomy found that, compared to women who had the surgery after menopause, those in the premenopausal group had lower bone mineral density and more vaginal dryness and sexual discomfort, though no differences were seen in heart disease markers, cognitive function, or overall quality of life.21PubMed. Long-term outcomes of surgical menopause after risk-reducing salpingo-oophorectomy: results of the HARMOny study
In men, removal of both testes (bilateral orchiectomy) eliminates the body’s primary source of testosterone. This is sometimes done as part of prostate cancer treatment. The metabolic consequences are significant: compared to drug-based hormone suppression, orchiectomy was associated with greater fat gain, higher body fat percentage, and more insulin resistance.22PubMed Central. Systematic Review Articles Examining Differences in Pathological Outcomes and Safety for Prostate Cancer Patients Undergoing Either Subcapsular Orchiectomy or Medical Androgen Deprivation Therapy: A Systematic Review Animal research suggests that estrogen treatment can mitigate some of the liver-related metabolic damage from testosterone loss, underscoring how deeply sex hormones are woven into metabolism beyond reproduction.23PubMed Central. Estradiol mitigates lipid accumulation, oxidative stress, apoptosis, and MAPKs activation in NASH rat model with bilateral orchidectomy
The Heart, With a Catch
The heart is obviously essential, and removing it without a replacement is fatal. But it can, in a narrow technical sense, be removed entirely and replaced with a total artificial heart. In this procedure, both ventricles and all four heart valves are cut away and replaced with a pneumatically powered mechanical pump. The device has been used as a bridge to keep patients alive while they wait for a donor heart for transplantation.24PubMed. Cardiac replacement with a total artificial heart as a bridge to transplantation Total artificial hearts can restore blood flow in people with end-stage biventricular failure, but truly durable long-term support remains elusive due to complications including blood clotting, infection, and the basic biological challenge of having foreign materials in continuous contact with blood.25PubMed Central. Why Total Artificial Hearts Fail: Hemocompatibility, Infection, and the Biological Limits of Durable Cardiac Replacement No one currently lives permanently without a biological heart, but people have survived months on these machines.
The Larynx
Total laryngectomy, the removal of the voice box, is performed for advanced laryngeal cancer. It permanently separates the airway from the throat, meaning the person breathes through a stoma in the neck rather than through the mouth and nose. Speech is obviously the major casualty. Without a larynx, there is no natural way to vibrate air into sound. Several workarounds exist: a handheld electrolarynx that vibrates against the throat, esophageal speech where the person learns to swallow and release air from the esophagus, and tracheoesophageal speech using a small valve placed between the windpipe and esophagus. Research on post-laryngectomy speakers found that the relationship between breathing and speaking changes fundamentally, with some methods of alaryngeal speech decoupling voice production from the respiratory system entirely.26PubMed Central. Post-laryngectomy speech respiration patterns
Half the Brain
Perhaps the most dramatic removal that a person can survive is hemispherectomy, the removal or disconnection of an entire cerebral hemisphere. This is performed almost exclusively in children with severe, drug-resistant epilepsy affecting one side of the brain, and the results can be remarkable. Motor recovery often occurs through alternative pathways and recruitment of brain regions on the remaining side. Language development can proceed surprisingly well, especially when the surgery is performed early in life, challenging the old idea that each hemisphere has a fixed, irreplaceable role.27PubMed. Functional recovery and neuroplasticity post-hemispherectomy in humans Children who undergo the procedure generally lose function on the opposite side of their body, particularly fine motor control in one hand, but many walk, talk, attend school, and lead active lives. The young brain’s ability to reorganize after such a massive loss remains one of the most striking examples of neural plasticity documented in medicine.28PubMed Central. Hemispheric functional organization, as revealed by naturalistic neuroimaging, in pediatric epilepsy patients with cortical resections
When an Eye Is Removed
Enucleation, the surgical removal of an eye, is performed for eye cancers, severe trauma, or intractable pain. The immediate consequence is loss of depth perception and peripheral vision on the affected side. Over time, though, the brain adapts. A neuroimaging study of people who lost an eye early in life found that their visual cortex, auditory regions, and areas involved in combining sensory information all showed increased surface area and folding compared to people with two eyes. These changes were most pronounced in the hemisphere opposite the remaining eye, suggesting the brain had reorganized to make the most of the visual input it still received.29PubMed Central. Increased cortical surface area and gyrification following long-term survival from early monocular enucleation People who lose an eye learn to use head movements and monocular depth cues effectively, and most return to driving and daily activities, though some tasks like threading a needle or catching a ball remain harder.