A Complete Guide to Your Villi

Villi are tiny, hair-like projections and tissues composed of the cells lining your small intestine's inside walls. They serve a critical role in digestion, absorbing nutrients from food and helping to deliver these nutrients to the blood.

Damage to these structures may cause malabsorption, making it difficult for your body to get the energy it needs. Following a nutritious diet, staying hydrated, and regularly exercising can keep your villi healthy.

Anatomy of the Villi

The villi reach out from the inner walls of the small intestine—the 20+ foot tube that connects the stomach and large intestine, twisting along its course through your abdomen. Your villi form on the walls of the small intestine and can mimic the appearance of a brush.

Structure

The walls of the intestine are made up of layers of smooth muscle and tissue. Villi are found in the innermost layer of your intestine, known as the mucosa. Epithelial cells make up the villi, and several types of these cells exist. These include:

• Enterocytes: About 80% of epithelial cells are enterocytes, which are column-shaped cells that absorb nutrients
• Enteroendocrine cells: Produce peptide hormones, which regulate cell growth and development
• Goblet cells: Secrete mucus, forming a protective layer around the villi and small intestine walls
• Tuft cells: Sense what's in the small intestines and secrete proteins to communicate with cells and trigger an immune response

Villi are extremely tiny structures. These finger-like projections are 0.4-1 millimeter in length. To understand how small that is, 1 millimeter is the width of a line drawn by a sharpened pencil. Villi typically become shorter and broader as you move down the small intestine.

Each villus (individual villi) also has tiny microvilli, which are even smaller projections that also aid digestion. Tiny depressions called "crypts" separate the villi. This is where enterocytes and other epithelial cells develop before migrating to the tips of the villi, where they are shed.

Anatomical Variations

Diseases and inflammatory medical conditions like celiac disease can cause villous atrophy, where villi shorten or even flatten entirely. Their appearance may also change, which can cause clover, leaf-like, or pencil-tip shapes.

What Do the Villi Do?

As food and digestive juices, known as "chyme," pass from the stomach, the small intestine digests the food, filters waste, and absorbs nutrients. Along its course, bile from the liver and fluid from the pancreas mix with the chyme, neutralizing the stomach acids and helping to digest food. Alongside aiding digestion, your villi also help recycle cells and assist with immune function.

Digestive System Function

The main job of the villi is to absorb necessary nutrients from the lumen (cavity) of the small intestine and transfer them to the bloodstream. Since the enterocytes in villi compose a single-cell outer layer, this nutrient extraction process is very efficient. The finger-like shape makes villi especially effective. Compared to a flat surface of the same size, villi and their microvilli provide 60-100 times more absorptive surface area, making digestion easier.

Villi absorb a range of minerals and nutrients, including:

• Iron
• Lipids and fats
• Water
• Carbohydrates
• Salt
• Amino acids and fatty acids from protein
• Most vitamins, including B12, A, D, and E

The goblet cells in villi produce mucus that protects the small intestine from digestive juices and provides lubrication, allowing food and waste to pass to the large intestine more easily.

Cell Regeneration

Another critical job of the villi is assisting in the epithelial cell recycling process. These cells have a quick lifespan and must be replaced every 3-5 days. Epithelial cells form in the crypts of villi and migrate to the tips of the villi, where they are shed. This process is critical for maintaining the structure and function of the small intestine.

Immune System Function

Along with digestion, the villi also help protect the small intestine and play a role in immune system function. Most of the body's immune cells are found in the connective tissues of the small intestines, just beneath the epithelium. Tuft cells and receptors in the villi trigger an immune response to infection.

The tips of villi also contain collections of immune cells, such as dendrites (spindly cells), leukocytes, and lymphocytes. This collection, known as the immune regulatory hub, protects from infection or damage and breaks down dead cells. 

Associated Health Conditions

Damage to the villi, or villous atrophy, affects your body's ability to get energy and nutrition from food. This causes malnutrition, which can lead to severe consequences like organ damage, starvation, and sometimes fatal complications like cardiac arrest. Several health conditions can increase your risk of villous atrophy.

Celiac Disease

Celiac disease is an autoimmune disorder that causes inflammation that damages the villi. This reaction is triggered by eating gluten, found in wheat, rye, barley, and many other food products. This condition is the most common cause of villous atrophy, and common signs of celiac disease include:

• Abdominal pain
• Bloating and gas
• Constipation
• Loss of appetite
• Lactose intolerance
• Nausea and vomiting
• Oily, foul-smelling, or sticky stools

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) refers to diseases that cause chronic inflammation in the intestines. The symptoms occur due to an immune reaction to gut microbiota—bacteria in the intestines that assist digestion.

There are two types of IBD that can cause villous atrophy: Crohn's disease and ulcerative colitis. Crohn's disease causes symptoms like diarrhea and abdominal pain, while ulcerative colitis can cause bloody diarrhea and constipation.

Lymphoma

Lymphoma is a type of cancer that develops in the lymph nodes, which play an important role in your immune system. There are two types of lymphoma: Hodgkin lymphoma (which is less severe) and non-Hodgkin lymphoma. Typical signs of this cancer include:

• Painless, swollen lymph nodes in the groin, neck, or underarm
• Unintended weight loss
• Fever
• Night sweats
• Itchy skin
• Fatigue

Medications

Damage to the villi can also be a side effect of several medications, such as:

• Advil (ibuprofen), a nonsteroidal anti-inflammatory drug
• CellCept (mycophenolate mofetil), which prevents organ rejection after a transplant
• Azasan (azathioprine), which helps treat rheumatoid arthritis
• Xatmep (methotrexate), a chemotherapy drug

Infections

Intestinal infections can also harm your villi and increase your risk of atrophy. These infections include:

• Giardia infection: Giardia are tiny parasites found in soil, water, and food. This infection can cause diarrhea, foul-smelling stools, stomach pain, nausea, and fatigue.
• infectionH. pylori : A common cause of food poisoning, Helicobacter pylori (H. pylori) bacteria infect the stomach and intestines, leading to symptoms like diarrhea, bloating, belching, and other digestive concerns.

Human Immunodeficiency Virus (HIV)

HIV is a sexually transmitted infection (STI) that progressively weakens the immune system. Complications can lead to small intestine damage, and the virus can directly lead to villous atrophy.

Diagnostic Testing

If you're noticing changes to your digestive health or have a condition that can cause villous atrophy, seek care from a healthcare provider. They can help you identify the cause through various assessments, such as:

• Physical exam: Feels for lumps or abnormalities in the abdomen
• Blood test: Detects antibodies that can be a sign of celiac disease, IBD, infections, and cancer, and assesses cholesterol levels and potential vitamin deficiencies
• Biopsy: Collects a small tissue sample from your small intestine to check for signs of villi damage or flattening under a microscope
• Genetic tests: Determines whether you're at risk for celiac disease, which can contribute to villous atrophy

Tips for Keeping Your Villi Healthy

Keeping your villi healthy means making lifestyle changes to promote overall gut health. Several changes may help:

• Avoid foods high in sugar and saturated fats
• Incorporate fruits, vegetables, lean proteins, and high-fiber options in your diet
• Adopt a gluten-free diet if you have celiac disease
• Drink water to help food move through your digestive system
• Boost physical activity to prevent IBD and other intestinal conditions
  

A Quick Review 

Villi are tiny, finger-like tissues inside the walls of the small intestine. They play an important role in digestion and help your body absorb nutrients from food.

Some health conditions can damage your villi, making it difficult for your body to get the nutrition it needs. Following a nutritious diet, staying hydrated, moving your body, and getting treatment for underlying conditions can improve the function of your villi and your overall gut health.