Tow it’s time to put all of the digestive anatomy and physiology rogether to get a “big picture” view of the digestive system. In this exercise you will trace the pathway that three different nutrients take from their ingestion at the mouth to their arrival at the heart. You will trace a cookie (primarily carbohydrates), an egg (primarily protein), and MATERIALS greasy fried food (primarily lipids). Laminated outline of the human body Water-soluble marking pens Along the way, detail the following for each 1. The anatomical pathway that each takes, from ingestion, through in passage through the alimentary canal, to its absorption into the blood, and finally to its passage through the blood until it reaches the heart. 2. The physical and chemical processes that break down each substance, including enzyme-catalyzed chemical Some hints: Don’t forget that carbohydrates and amino acids travel through the hepatic portal system before they enter the general circulation. Remember that digestion and absorption are quite different for lipids. For example, fats are not absorbed into the intestinal blood capillaries. Use the text in Exercise 24-3 (p. 649) and your list of enzymes that you completed in Pre-Lab Exercise 24-3 (p. 628) for reference. Refer to the tracing exercises from Unit 18 (p. 486) and Unit 21 (p. 553) to review the pathway of blood and lymph flow through the body. You may find it helpful to physically trace the pathway on a laminated outline of the human body to better visualize the processes. Tracing Steps 1 Cookie: Start: mouth Digestive System heart Er UN 24
The Correct Answer and Explanation is :
The digestive system processes nutrients—carbohydrates, proteins, and lipids—through distinct pathways, each involving specific anatomical structures and physiological processes. Here’s an overview of how a cookie (primarily carbohydrates), an egg (primarily protein), and greasy fried food (primarily lipids) are digested and absorbed, ultimately reaching the heart.
1. Cookie (Carbohydrates):
- Ingestion and Digestion: The process begins in the mouth, where salivary amylase starts breaking down complex carbohydrates into simpler sugars. The food then moves through the esophagus to the stomach, where mechanical churning continues the breakdown. In the small intestine, pancreatic amylase further digests carbohydrates into monosaccharides. These monosaccharides are absorbed through the intestinal lining into the bloodstream.
- Absorption and Transport: Once absorbed, monosaccharides enter the hepatic portal vein, which directs them to the liver for processing. After liver processing, glucose is released into the general circulation, eventually reaching the heart.
2. Egg (Proteins):
- Ingestion and Digestion: In the mouth, mechanical chewing breaks the egg into smaller pieces. In the stomach, pepsinogen is activated to pepsin, initiating protein digestion. The partially digested proteins move to the small intestine, where pancreatic enzymes like trypsin and chymotrypsin further break them down into amino acids.
- Absorption and Transport: Amino acids are absorbed through the small intestine’s lining into the bloodstream. They enter the hepatic portal vein, travel to the liver for processing, and then are released into the general circulation, reaching the heart.
3. Greasy Fried Food (Lipids):
- Ingestion and Digestion: In the mouth, mechanical chewing breaks the food into smaller pieces. In the stomach, lingual lipase begins the digestion of lipids. The food then moves to the small intestine, where bile emulsifies fats, increasing the surface area for pancreatic lipase to act. Pancreatic lipase breaks down triglycerides into fatty acids and monoglycerides.
- Absorption and Transport: These components form micelles, which facilitate their absorption into the intestinal lining. Inside the enterocytes, they are reassembled into triglycerides and packaged into chylomicrons. Chylomicrons enter the lymphatic system via lacteals and eventually enter the bloodstream through the thoracic duct. They circulate through the body, delivering lipids to various tissues, including the heart.
Understanding these pathways highlights the complexity of nutrient digestion and absorption, emphasizing the body’s intricate mechanisms for processing and utilizing different types of nutrients.