The process of absorption mainly occurs in the small intestine.

Question

i. The critical factor in absorption is surface area. In your own
words, explain four aspects of the small intestine that allow it to
have such an extensive surface area and be so efficient at
absorbing nutrients.
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g. The large intestine, also called the _____________, receives the remnants
of the chyme from the small intestine. Describe what it must absorb from
this mostly indigestible material.
i. The final remnants, the feces, then enter the final portion of the large
intestine called the __________________________.
ii. Water absorption is one of the critical functions of the large
intestine. Explain what happens if too much water is absorbed
and then if too little water is absorbed.
● Too much water absorption:
● Too little water absorption:
iii. How does fiber impact this process?2

Answer 1

The small intestine is highly specialized to maximize nutrient absorption through several key adaptations that increase its surface area:

1. Villi: The inner lining of the small intestine is covered with tiny finger-like projections called villi. These structures increase the surface area significantly and allow for greater exposure of the intestinal wall to the nutrients present in the chyme.

2. Microvilli: Each villus is further covered by even smaller hair-like structures called microvilli. This creates a brush border effect, vastly increasing the surface area available for absorption and enhancing the efficiency of nutrient uptake.

3. Folds (Plicae Circulares): The lining of the small intestine also contains large circular folds known as plicae circulares. These folds help slow down the passage of chyme, allowing more time for nutrients to be absorbed. They also contribute to the overall surface area of the intestine.

4. Length: The small intestine is very long, averaging around 6 meters (20 feet) in adults. This extended length allows for more time and area for absorption to occur as the chyme moves through the digestive tract.

g. The large intestine, also called the colon, receives the remnants of the chyme from the small intestine. It must absorb water, electrolytes (such as sodium and potassium), and any remaining nutrients, as well as vitamins produced by gut bacteria (like vitamin K) from this mostly indigestible material.

i. The final remnants, the feces, then enter the final portion of the large intestine called the rectum.

ii. Water absorption is one of the critical functions of the large intestine. Here's what happens in different scenarios:

• Too much water absorption: If the large intestine absorbs too much water, this can lead to constipation, where stools become hard and difficult to pass. This can result in discomfort and potential complications such as hemorrhoids or anal fissures.

• Too little water absorption: Conversely, if too little water is absorbed, it can result in diarrhea. This causes stools to become watery and loose, potentially leading to dehydration and electrolyte imbalance, which can be serious if it persists.

iii. Fiber impacts this process by increasing the bulk of the stool and promoting regular bowel movements. Soluble fiber can help regulate water absorption, leading to softer stools, while insoluble fiber adds bulk that aids in moving waste through the intestines. Adequate fiber intake can help prevent both constipation and diarrhea by helping to normalize bowel function.