The small intestine absorbs nutrients through the intestinal wall through various means and processes. Drag each nutrient or
component to the appropriate classification necessary for its absorption.
Glucose
Amino acids
Water
Immune substances
from human milk
Fructose
Fat
Passive diffusion
Facilitated
diffusion
Active absorption
Phagocytosis
The Correct answer and Explanation is:
Nutrients are absorbed in the small intestine through different mechanisms depending on the nutrient’s structure, size, and the presence of transport proteins or energy-dependent processes. Here’s how these nutrients and components are absorbed:
Passive Diffusion:
- Fat: Fats are non-polar molecules, which means they can move through the lipid-rich cell membrane without the need for energy or carrier proteins. They diffuse passively from the lumen of the small intestine into the cells.
Facilitated Diffusion:
- Fructose: Fructose is absorbed via facilitated diffusion, where it requires a specific transporter protein (GLUT5) to move down its concentration gradient from the intestinal lumen into the epithelial cells, but it doesn’t require energy.
Active Absorption:
- Glucose: Glucose is absorbed actively through the sodium-glucose cotransporter (SGLT1). This process requires energy in the form of ATP to pump sodium out of the cell via the Na+/K+ ATPase pump, creating a gradient that allows glucose to enter the cell alongside sodium ions.
- Amino acids: Amino acids are absorbed actively using transporters that move these molecules into the intestinal cells. This process, like glucose absorption, is sodium-dependent and requires energy to maintain the sodium gradient that drives the movement of amino acids into the cells.
Phagocytosis:
- Immune substances from human milk: Large immune substances, like antibodies (e.g., IgA) from breast milk, are absorbed by a process known as phagocytosis. In this process, the cells of the intestinal lining engulf these large molecules and internalize them within vesicles, allowing them to be used by the infant’s immune system.
Water:
- Water: Water is primarily absorbed through passive osmosis. As nutrients like glucose and sodium are absorbed, water follows the solutes through osmotic gradients from the lumen into the bloodstream.
Explanation (300 words):
The small intestine is the primary site for nutrient absorption, and this process occurs through various mechanisms. Nutrients like glucose and amino acids, which are essential for cellular energy and protein synthesis, require active transport. This process demands energy because these nutrients often move against their concentration gradient. In glucose’s case, the sodium-glucose cotransporter facilitates its absorption in conjunction with sodium, which is pumped out of the cell using energy provided by ATP. Amino acids are absorbed in a similar sodium-dependent manner, allowing the body to acquire building blocks for proteins.
On the other hand, fructose, a simple sugar found in fruits, doesn’t need energy for absorption but requires a transporter protein (GLUT5) to assist in its movement from the intestinal lumen into cells, utilizing facilitated diffusion. Passive diffusion, which occurs without any energy or protein assistance, allows non-polar molecules like fats to easily pass through the lipid-rich cell membrane.
Water absorption is driven by osmotic gradients created as other solutes are absorbed. This allows water to passively move into the bloodstream, ensuring hydration and maintaining electrolyte balance.
Finally, phagocytosis is a unique process in which large immune molecules, such as antibodies from breast milk, are engulfed by intestinal cells. This process enables infants to acquire protective antibodies directly from their mother’s milk, boosting their immune system during early development.