Question

Which of the following is true of the large intestine? It contains microorganisms that may produce useful by-products that can be absorbed. b. It stores and concentrates fecal material. c. Its cells absorb ions and water that remain in chyme after it leaves the small intestine. d. It varies considerably in size and may even be absent in some vertebrates. e. All of the above are true of the large intestine.

Short answer

The correct answer is (e), all the statements are true for the large intestine.

Step-by-step solution

Identifying the roles of the large intestine

Firstly, review the literature or textbook related to the anatomy and function of the large intestine. It will provide a solid understanding that the large intestine indeed hosts microorganisms that produce useful by-products (choice a) and absorbs leftover water and ions from the chyme (choice c). It also stores and concentrates fecal material (choice b).

Considering the size variation

Next, evaluate the statement about the size variation of the large intestine among different vertebrates. It is known that the size and length of the large intestine may vary amongst organisms, and in some rare cases, it may even be absent. Hence, choice d is also correct.

Answer confirmation

Based on above analysis, all the options from a to d are accurate descriptions of the large intestine's functions and characteristics. Therefore, the correct answer is e. All of the above are true of the large intestine.

Key concepts

Anatomy of the Large Intestine

Understanding the anatomy of the large intestine is crucial to appreciating its role in the human body. This organ finalizes the digestive process by helping to absorb water and nutrients, and by preparing waste for excretion. It consists of several parts: the cecum, colon, rectum, and anal canal. The colon, which is further divided into ascending, transverse, descending, and sigmoid sections, is where most of the water and salt absorption takes place. The inner surface is lined with a mucus membrane that contains tiny pockets called crypts, which are lined with cells that produce mucus and absorb nutrients.

This intricate structure is crucial for its function, as the large intestine is responsible not only for absorption and secretion but also serves as a storage space for waste material. The large intestine's ability to store fecal matter is due to its wider diameter compared to the small intestine. This difference in size allows for a more significant accumulation of waste, which is eventually removed from the body through the process of defecation.

Intestinal Microorganisms

The large intestine is teeming with a diverse community of microorganisms, collectively known as the gut flora or microbiota. These microorganisms include bacteria, archaea, viruses, and eukaryotes, which play a crucial role in maintaining health. The symbiotic bacteria break down undigested carbohydrates, ferment dietary fibers, and produce essential vitamins like vitamin K and B vitamins. They can also metabolize bile acids, sterols, and xenobiotics, contributing to the overall metabolic functions in the body.

These microbial by-products can be absorbed by the body and provide additional nutritional benefits, such as short-chain fatty acids (SCFAs) that supply energy to colon cells and help regulate electrolyte and fluid balance. Understanding the delicate balance of these microorganisms is vital, as disturbances can lead to gastrointestinal disorders like irritable bowel syndrome or inflammatory bowel disease. The microbiota also plays a role in immune function, where it educates the immune system to distinguish between harmful and benign invaders and can even influence the body's response to certain medications.

Absorption in the Large Intestine

Absorption in the large intestine is primarily concerned with water and electrolytes like sodium and chloride. Since the small intestine has already absorbed most of the nutrients, the large intestine's main task is to absorb the remaining water and electrolytes from the chyme to prevent dehydration and maintain the body's electrolyte balance. This process turns the watery chyme into semi-solid feces.

Specialized cells within the intestinal wall, known as colonocytes, play a direct role in this absorption. These cells are adept at transporting ions across their membranes, thereby allowing the movement of water by osmosis. As water is absorbed, the volume of fecal matter decreases, and its consistency becomes firmer until it becomes stool. Insoluble fibers that reach the large intestine can serve as bulking agents, increasing the efficiency of the stool's movement toward the rectum. Regular bowel movements are crucial for overall digestive health, as they ensure the timely excretion of waste and prevent the buildup of toxic substances.