Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Anatomy and Physiology of the Digestive System
The Role of Digestive Tract Microflora. Dysbiosis

Various microorganisms inhabit numerous structures of The Human Body. The Human digestive tract is likewise "colonized" by them. However, while some sections contain few or virtually no microorganisms, others host them in massive quantities.

Despite the bactericidal properties of saliva, the Oral Cavity contains a remarkably high concentration of microbes: 10⁷—10⁸ per 1 mL of oral fluid.

Due to the bactericidal action of gastric juice, the contents of a healthy human Stomach are sterile at the peak of Digestion; nonetheless, the initial phase of digestion reveals a relatively high number of microorganisms (up to 10³ per 1 mL of contents) swallowed along with saliva. Approximately the same quantity is found in the duodenum and the initial section of the jejunum. Microorganisms are regularly detected in the Contents of the ileum, averaging 10⁶ per 1 mL. The bacterial count reaches its maximum in the contents of the Large Intestine.

Digestive secretions play a major role in shaping the microflora of the digestive tract. For instance, saliva contains Lysozyme, which exerts a bactericidal effect on the oral microflora.

Owing to Hydrochloric acid and other factors, gastric juice also possesses bactericidal properties, which significantly affects the number and COMPOSITION OF THE microflora in both The Stomach and the intestines. In the Small Intestine, the quantity and Properties of the microflora depend on the inflow of Pancreatic and Intestinal juices, as well as Bile. The ileocecal valve prevents the retrograde movement of microorganisms from the large intestine into the small intestine.

It is worth noting that the nutrient content of the chyme also influences the quantity of microflora. These substances are essential for the vital activity of the microorganisms themselves. Therefore, a balanced and adequate diet is vital, among other things, for maintaining a stable population of normal microflora.

Normal microflora—eubiosis—performs A number of crucial Functions in the body:

1) it participates in shaping the immunobiological reactivity of the body and protects it against the invasion and proliferation of pathogenic (disease-causing) microorganisms;

2) it facilitates the utilization of certain undigested nutrients, which are subsequently absorbed from the intestine and integrated into the human body's METABOLISM;

3) it takes part in The breakdown of bile acids and various organic substances, contributing to The formation of organic acids, their ammonium salts, amines, etc.;

4) it is involved in the inactivation of certain digestive Enzymes;

5) it participates in the synthesis of vitamin K and B-group Vitamins, as well as a number of Amino Acids and CARBOHYDRATES;

6) it helps maintain normal intestinal motility;

7) it contributes to the formation of fecal masses.

Additionally, enzymes produced by large intestine Bacteria break down Cellulose, Pectins, and several other substances that were not digested in the small intestine.

Intestinal microflora is categorized into three groups:

1) principal group—bifidobacteria and bacteroides—accounting for about 90% of all microbes;

2) concomitant group—lactobacilli, escherichia, enterococci—making up 10% of the total number;

3) residual group—enterobacter, proteus, Yeasts, clostridia, staphylococci, aerobic bacilli—representing less than 1%.

Microorganisms in the intestine can exist in two forms: within the mucous membrane (M-microflora) and in the intestinal lumen (L-microflora). M-microflora is more resistant to external influences than L-microflora. Furthermore, the number of L-microorganisms increases more sharply from the stomach to the large intestine than that of M-microflora, while anaerobic microflora predominates over aerobic microflora.

The human macroorganism and its microflora, including that of the digestive tract, constitute a unified dynamic system. The dynamism of the digestive tract's microbial biocenosis is determined by the influx of microorganisms (about 1 billion per day), The rate of their reproduction and death within the digestive tract, and their elimination via feces (normally, 10¹²—10¹⁴ microorganisms are excreted daily).

The composition and quantity of microorganisms in the digestive tract depend on endogenous and exogenous factors. The former include the Influence of the mucous membrane of the digestive canal (its secretions and motility) and, naturally, the mutual interactions among the microorganisms themselves. The latter encompass diet, environmental factors, and The Use of medications, particularly Antibiotics. Under The Influence of these factors, especially the excessive use of antibiotics and other drugs, the population of microorganisms changes.

Pathogenic microflora is generally more resistant to both exogenous and endogenous factors, which leads to the disruption of eubiosis. This alters the characteristic balance among different species of the digestive tract's microflora, leading to a condition known as dysbiosis. In dysbiosis, the microflora fails to fully perform its proper functions, which negatively impacts the vital activity of the human body as a whole.

To restore normal intestinal microflora, a range of pharmaceutical preparations—known as eubiotics (such as bifidumbacterin and lactobacterin)—is utilized; however, the most critical measure is the Prevention of dysbiosis, which is achieved by maintaining a proper diet (incorporating fermented dairy products into the menu) and the rational use of medications.

Review Questions

1. List the Functions of the Digestive System.

2. Describe the Structural Features of hollow and parenchymatous Organs.

3. Classify the Teeth and characterize their Structure.

4. Outline the differences between children's and adult dental formulas.

5. List the papillae of the Tongue and indicate their functions.

6. What is The Role of saliva?

7. Characterize the processes that take place in the oral cavity.

8. What was I. P. Pavlov's contribution to The Study of DIGESTION IN THE oral cavity?

9. Name the PARTS OF THE Pharynx and the phases of swallowing.

10. Describe the structural Features of the esophageal wall.

11. What are the anatomical parts of the stomach?

12. List the functions of the stomach.

13. Which phases of gastric juice secretion did I. P. Pavlov identify?

14. Name the parts of the small intestine.

15. Describe the structural features of the small intestine wall.

16. What processes occur in the small intestine?

17. Name the lobes, surfaces, and borders of the Liver.

18. What is the "wonderful net" (rete mirabile) of the liver?

19. List the biliary tract components and the parts of the Gallbladder.

20. List the functions of the liver.

21. Which enzymes are present in pancreatic juice? What is their significance?

22. List the segments of the large intestine.

23. What functions does the large intestine perform?

24. How are the organs positioned relative to the Peritoneum? Provide Examples of extra-, meso-, and intraperitoneal positions of abdominal organs.

25. List the derivatives of the peritoneum.

26. What is the role of the feeding center?

27. Define The concepts of "eubiosis" and "dysbiosis".