Question

Microvilli ________ . a. increase the surface area of the stomach b. are the main type of cell in the lining of the small intestine c. project from the surface of cells in the small intestine d. produce bile

Short answer

c. Project from the surface of cells in the small intestine.

Step-by-step solution

Understand the Biological Term

Microvilli are tiny, finger-like projections from the surface of certain cells. They are designed to increase the surface area, allowing for more efficient absorption or secretion, commonly associated with cells in the small intestine.

Identify Relevant Options

Look for options that correctly describe the function or location of microvilli. Based on the definition, microvilli primarily increase a cell's surface area and are commonly found lining the cell surfaces of the small intestine.

Evaluate Each Option

a. Increase the surface area of the stomach: While microvilli increase surface area, they are not primarily found in the stomach, but in the small intestine, so this is incorrect. b. Are the main type of cell in the lining of the small intestine: Microvilli are not cells themselves; they are structures extending from cells, so this is incorrect. c. Project from the surface of cells in the small intestine: This correctly describes microvilli, as they are indeed projections from the surface of cells in the small intestine to increase absorption. d. Produce bile: Microvilli do not produce bile; bile is produced by the liver and stored in the gallbladder, so this is incorrect.

Select the Correct Answer

Based on the evaluation, option c: 'project from the surface of cells in the small intestine' correctly describes the role and location of microvilli.

Key concepts

The Small Intestine

The small intestine is a long, coiled tube that plays a crucial role in digestion and nutrient absorption. Nestled between the stomach and the large intestine, it stretches about 20 feet in length in adults. Despite its name, it is not small in length; the term "small" refers to its diameter compared to the large intestine.
In the small intestine, food undergoes further breakdown after partially digesting in the stomach. Here, several essential processes occur:

• Digestive enzymes and bile work together to further break down food particles.
• Nutrients are absorbed into the bloodstream through the intestinal walls.
• Waste products are moved toward the large intestine for eventual excretion.

The small intestine is divided into three parts: the duodenum, jejunum, and ileum. Each section has distinct functions but collectively, they work to ensure that the body receives the nutrients it needs to function properly.

Absorption

Absorption in the small intestine is a fundamental process for nutrient uptake. This is primarily where the magic of digestion happens, where nutrients from food pass into the bloodstream.
The interior of the small intestine is specially adapted for this function. Its lining is covered with tiny projections known as villi, each of which is covered in even smaller structures called microvilli. Microvilli play a pivotal role in absorption because they substantially increase the surface area available for nutrient uptake.
Imagine a sponge with its many holes and intricate structure: the more the holes, the better it can absorb liquid. Similarly, microvilli enhance the absorptive efficiency of the intestine. Nutrients absorbed in the small intestine include:

• Amino acids from proteins
• Simple sugars from carbohydrates
• Fatty acids and glycerol from fats
• Vitamins and minerals

These nutrients then enter the bloodstream and are transported to cells throughout the body to be used as energy, building materials, and for various other essential functions.

Cell Surface Projections

Cell surface projections, such as microvilli, are small extensions from the cell membrane. They are primarily involved in increasing the surface area of a cell, which is particularly important in the small intestine.
Microvilli are densely packed on the surface of intestinal cells and are one of the most significant adaptations for effective absorption.

Function of Microvilli

Microvilli enhance the cell's ability to absorb nutrients, allowing more efficient uptake of food particles. They work in concert with villi, the larger projections lining the intestinal wall.

Characteristics of Microvilli

• They are extremely small, measuring only about 1 micron in length.
• Microvilli are covered in enzymes that further aid in the digestion of nutrients.
• Their dense presence on intestinal cells is sometimes referred to as the "brush border" due to their microscopic appearance.

Overall, these projections are essential for maximizing the small intestine's ability to absorb essential nutrients efficiently and effectively, making them key players in the digestive system.