Digestão e absorção de carboidratos | MK Fisiologia
Digestion and Absorption of Carbohydrates
In this video, the focus is on discussing the digestion and absorption processes of carbohydrates as a macronutrient in the diet. The speaker highlights the importance of motor functions and secretory functions in gastrointestinal digestion.
Digestion Processes of Carbohydrates
- Digestion relies on both motor functions (e.g., chewing) and secretory functions (e.g., enzyme secretion) in the gastrointestinal tract.
- Carbohydrates in food are mainly in the form of monosaccharide polymers or polysaccharides.
- Polysaccharides like starch (plant origin) and glycogen (animal origin) need hydrolysis for absorption through chemical reactions catalyzed by digestive enzymes.
Types of Polysaccharides
- Starch and glycogen have different glucose linkages, affecting their branching structures.
- Other polysaccharides like cellulose with beta 1-4 linkages are classified as fibers, passing through the small intestine undigested but may be digested by intestinal bacteria.
Disaccharides in Diet
- Common disaccharides like sucrose (glucose + fructose) and lactose (glucose + galactose) are found in various foods.
- Digestion starts with alpha-amylase in saliva breaking down carbohydrates into oligosaccharides due to limited time in the mouth.
Digestion Continues
- Gastric acid halts carbohydrate digestion until reaching the duodenum where pancreatic enzymes neutralize acidity for further breakdown.
- Pancreatic alpha-amylase continues digesting starches into maltose, maltotriose, and dextrins upon entering the alkaline environment of the small intestine.
Absorption Process
- Enzymes at microvilli surfaces of enterocytes break down oligosaccharides into monosaccharides for absorption.
Digestion of Carbohydrates in the Small Intestine
This section discusses the process of carbohydrate digestion in the small intestine, focusing on the absorption of glucose, galactose, and fructose by specific transporters present in enterocytes.
Absorption Mechanisms in the Small Intestine
- Glucose and galactose are transported into enterocytes by the SGLT1 cotransporter, which utilizes the sodium gradient for active secondary transport.
- Fructose is passively transported via diffusion facilitated by a specific transporter called GLUT 5. Despite its name suggesting glucose transport, GLUT 5 exclusively transports fructose.
Absorption into Circulation
- In the basolateral membrane facing capillaries, glucose, galactose, and fructose can exit enterocytes through GLUT 2 transporters. There may be unidentified transporters for fructose absorption as well.
Metabolism and Utilization
- Once absorbed, monosaccharides like glucose, galactose, and fructose can be taken up by cells throughout the body for metabolism to provide energy.
Key Takeaways
- Carbohydrate digestion initiates in the mouth and concludes in the small intestine with various endoenzymes and exoenzymes facilitating breakdown.