International Journal of Clinical Case Reports 2024, Vol.14, No.1, 31-39 http://medscipublisher.com/index.php/ijccr 32 host, it reveals the role of the intestinal microbiome in maintaining intestinal homeostasis. It plays a role in improving digestion and absorption of nutrients, regulating intestinal immunity, etc. This study will also focus on the relationship between intestinal microbiome imbalance and intestinal diseases, with a view to discovering new disease markers and therapeutic targets, and providing new ideas and methods for the diagnosis and treatment of intestinal diseases. 1 Overview of the Human Microbiome 1.1 Composition and diversity of human microbiome The human microbiome is a complex ecosystem composed of trillions of microbial cells, which far exceed the number of cells in the human body itself (Hills et al., 2019). These microorganisms include bacteria, viruses, fungi, archaea, etc. They are widely and complexly distributed in the human body, ranging from the skin, mouth to intestines and other parts of the body. The types and quantities of these microorganisms vary significantly between different parts and individuals, and this variability constitutes the diversity of the human microbiome. Gupta et al. (2017) explored the variation in human microbial composition and diversity among different geographical locations, ethnic groups, or lifestyles, providing a global perspective on factors influencing health and disease. The diversity of the human microbiome is not only reflected in species composition, but also in genetic composition. The microorganisms in the microbiome carry a large amount of genetic information, which constitutes the gene pool of the microbiome. Rothschild et al. (2018) showed that environmental factors play a more important role in shaping the human intestinal microbiome than host genetic factors, emphasizing the importance of diet and lifestyle in maintaining intestinal health. The number of genes in the human microbiome far exceeds the number of genes in the human body itself. These genes play an important role in human metabolism, immunity, nutrition and other aspects. Cai et al. (2020) research showed that there are significant differences in the types and quantities of human MSM in different organs or parts. The intestines are colonized by more than 1 000 species of microorganisms. Among the six phyla of intestinal commensal bacteria, Firmicutes and Bacteroidetes account for 90% of the total number of intestinal commensal bacteria. Most of the obligate anaerobes include The genera Bacteroidetes, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus and Bifidobacterium are also colonized by bacteria of the genera Escherichia and Lactobacillus. 1.2 Interactions between the microbiome and the host The interaction between the microbiome and the host is a two-way process, with both the influence of microorganisms on the host and the influence of the host on the microorganisms. The microbiome helps the host digest food, synthesize vitamins, etc. by participating in the host's metabolic process. The microbiome participates in the host's metabolic process, not only helping the host digest food, but also participating in the production of short-chain fatty acids (such as butyric acid , propionic acid, and acetic acid). These substances play an important role in maintaining the integrity of the intestinal wall, regulating immune responses, and affecting the host's energy balance (Belkaid and Hand, 2014). Selber-Hnatiw et al. (2017) examined the relationship between the microbiome and host health from the perspective of microbial community dynamics. Research highlights how microbial populations communicate with their hosts through biochemical signals, coordinating nutrient exchange and appropriate immune function. This study reveals that imbalances (dysbiosis) in microbial composition are often associated with human disease, suggesting that balanced microbial communities are critical to human health. Milani et al. (2017) collected information and reviewed the literature and found that the composition, activity and impact of the infant intestinal microbiome on health, as well as how microorganisms colonize the
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