29 topics with concise summaries: definitions, key facts, and classroom questions.
The "Digestion" section covers the entire journey of nutrients in the body: from mechanical and chemical processing in the oral cavity to the act of defecation. Here, we examine in detail how complex macronutrients are converted by enzymes into cell-accessible monomers.
The material is structured by GI tract segments and physiological processes. You will study gastric digestion (including hydrochloric acid secretion and its inhibition), duodenal function, liver functions, and bile formation. Separate articles cover motility, hydrolysis, and the absorption of proteins, fats, carbohydrates, as well as water and electrolytes. In addition, modern methods of tract examination and the significance of the intestinal microflora are reviewed.
In seminars and exams, instructors most frequently ask about the mechanisms of neurohumoral regulation of digestive functions. Pay special attention to the phases of gastric secretion, the regulation of pancreatic juice secretion, and the enterohepatic circulation of bile acids—these are classic questions requiring a clear understanding of physiological interrelationships.
What is the fundamental difference between luminal and membrane (mural) digestion?
Cavitary digestion occurs in the lumen of the gastrointestinal tract under the action of enzymes located away from their site of secretion. Surface digestion takes place on the microvilli surface with the participation of enzymes firmly anchored to the cell membrane and within the glycocalyx.
What is the essence of the GI regulation gradient?
This is a shift in the dominant type of control along the tract: neural reflexes predominate in the upper parts, the role of humoral factors increases in the middle parts, and local mechanisms prevail in the intestines.
Why are acute methods considered less reliable?
Acute experiments (vivisection) use anesthesia, which depresses the nervous system. In addition, severe surgical trauma and unnatural direct stimulation of nerve trunks distort the normal physiological reactions of the digestive tract.
Why might the composition of saliva change in renal failure?
The salivary glands possess an excretory function. In renal impairment, the concentration of urea, ammonia, uric acid, and creatinine in saliva increases compensatorily.
How does the swallowing center interact with the respiratory center?
These two centers are located close to each other in the medulla oblongata and are in a reciprocal (mutually inhibitory) relationship. Activation of the swallowing center automatically suppresses the activity of the respiratory center.
Does carbohydrate digestion occur in the stomach?
Yes, but exclusively through salivary enzymes (carbohydrases). Gastric juice contains no intrinsic amylolytic enzymes. Hydrolysis proceeds within the bulk of the food bolus until acidic juice penetrates it.
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