Answer
The correct answer is $c. haustra$.
Work Step by Step
The correct answer is $c. haustra$.
Haustra are pouches or sac-like structures that are found in the large intestine (specifically in the colon), not in the small intestine. They are formed by the contractions of the colon's longitudinal muscles, which give the colon its characteristic appearance of haustra separated by constrictions. Haustra allow for the segmentation and mixing of fecal material in the large intestine, aiding in water absorption and the formation of feces.
The other options mentioned contribute to the absorptive surface area of the small intestine:
$a. Length$ - The small intestine's length greatly increases its surface area, providing more space for absorption.
$b. Brush Border$ - The brush border refers to the microvilli-covered surface of the small intestine's absorptive cells, which significantly increases the absorptive surface area for nutrients.
$d. Circular Folds (Plicae Circulares)$ - These are permanent ridges of the mucosa and submucosa layers that run perpendicular to the length of the small intestine. They help increase the surface area and slow down the passage of chyme, enhancing nutrient absorption.
$e. Villi$ - Villi are finger-like projections on the inner lining of the small intestine. Each villus is covered in absorptive cells and contains a network of blood vessels and a lacteal, all of which work to absorb nutrients.
So, $haustra$ do not contribute to the absorptive surface area of the small intestine; they are characteristic structures of the large intestine.
