Interplay between intestinal permeability and metabolic dysfunction-associated steatotic liver disease: Could there be a role for extra virgin olive oil consumption?

Table 1 Types of intestinal barriers, roles, and examples for each category

Type of barrier	Description	Examples and functions
Mechanical barrier	Physical structures that prevent the entry of pathogens and unwanted substances	Intestinal epithelium: A layer of cells that lines the intestine; tight junctions: Connections between epithelial cells that prevent the passage of substances; mucosa: Production of mucus that traps pathogens and foreign particles
Vascular barrier	A vascular network that provides nutrients and oxygen and removes waste	Capillaries, lymphatics; a barrier that opposes the entry of bacteria from the intestinal lumen into the circulatory system; maintains the proper functioning of intestinal cells and the immune system
Chemical barrier	Chemical substances that inhibit the growth of pathogenic microbes and protect the intestine	Digestive enzymes, such as pepsin and lipase, which break down nutrients; gastric acid: Its low pH kills many pathogens; natural antibiotics, such as defensin, which acts against bacteria
Immunological barrier	Components of the immune system that monitor and defend the intestine from pathogens	Immune cells: Such as T and B lymphocytes, macrophages, and dendritic cells; immunoglobulins: In particular, IgA, which neutralize pathogens and toxins; gut-associated lymphoid tissue (GALT): Lymphoid structures that play a key role in intestinal immune response
Microbial barrier	Microbes that colonize the intestine and compete with pathogens for resources (microbiome)	Intestinal flora: Beneficial bacteria such as Lactobacillus and Bifidobacterium that maintain balance and inhibit the growth of pathogens; nutritional competition: Beneficial bacteria occupy ecological niches and resources, making it difficult for pathogens to colonize; production of antimicrobial substances: Some bacteria produce substances that inhibit the growth of other microorganisms

GALT: Gut-associated lymphoid tissue.