Question

A bolus is (a) a mass of crushed food moistened with saliva (b) the semisolid material resulting from partial digestion in the stomach. (c) the milky emulsified fat absorbed from small intestine (d) indigestible materials that help in movement and absorption.

Short answer

(a) a mass of crushed food moistened with saliva.

Step-by-step solution

Understanding the Definitions

Understand the definitions of the terms related to the digestive process to determine which one describes a bolus. A bolus refers to the mass of food that is chewed and mixed with saliva, ready to be swallowed.

Eliminating Incorrect Options

Examine each option. (b) refers to chyme, not bolus. (c) is referring to chyle. (d) generally refers to dietary fiber or roughage. None of these are the correct description of a bolus.

Identifying the Correct Definition

Choose the option that best fits the description of a bolus. A mass of crushed food moistened with saliva that is ready to be swallowed fits the definition of a bolus.

Key concepts

Human Digestive System

The human digestive system is a complex network designed to convert food into the nutrients our body needs to function. This system begins in the mouth, where the process of chewing breaks down food into a manageable size. Here, saliva mixes with the food to create a soft mass known as a bolus, making it easier to swallow. The bolus then travels down the esophagus and into the stomach.

Inside the stomach, digestive enzymes and acids initiate the breakdown of food proteins and fats, turning the bolus into a semi-liquid substance called chyme. The chyme moves to the small intestine where it is mixed with bile and pancreatic juices to further digest carbohydrates, proteins, and fats. Nutrients are absorbed through the walls of the intestine into the bloodstream, leaving behind waste products to be excreted. This incredible system ensures that our bodies are nourished and maintained.

Chyme

As a bolus moves from the mouth to the stomach, it undergoes a significant transformation. Stomach acid and enzymes act on this mass, turning it into chyme, a thick, acidic, soupy mixture. It's the chyme's consistency and acidity that enable the further breakdown of food particles. As the stomach contracts, it helps to mix the contents, ensuring thorough enzymatic activity.

The slow release of chyme into the small intestine marks the next phase of digestion. The regulation of this release is crucial as it ensures the small intestine has ample time to digest the nutrients and absorb them into the bloodstream. Without the formation of chyme, the process of efficiently breaking down food and extracting vital nutrients would be disrupted.

Chyle

Once the digestion of food moves past the stomach and into the small intestine, the body begins to absorb fatty acids and glycerol from the digested food. These fats are initially not soluble in the watery environment of bodily fluids. To address this, fats are emulsified by bile salts, which makes them more accessible for digestion by lipase enzymes. After the breakdown, they are absorbed and converted into a milky, fatty lymph called chyle.

Chyle circulates through the lymphatic system before it drains into the bloodstream, by which time it has mixed with blood and is no longer milky. This specialized substance is an essential part of the digestive process as it transports fats and certain vitamins, helping in the distribution of vital nutrients to cells throughout the body.

Digestive Process

Digestion is a carefully orchestrated process that begins the moment food enters the mouth. Saliva starts the digestive process by breaking down complex carbohydrates into simpler sugars and lubricating the food to form a bolus. Once swallowed, the bolus travels down the esophagus and reaches the stomach, where acids and enzymes break it down into chyme.

The chyme moves into the small intestine, wherein most nutrient absorption occurs. Here, enzymes from the pancreas and bile from the liver continue to digest the food particles. The resulting simple sugars, amino acids, fatty acids, and glycerol are readily absorbed into the bloodstream. Unused residues then move to the large intestine, where water absorption occurs, and finally, the waste is excreted. Throughout this process, the harmony between different organs and secretions is essential to ensure that the body sufficiently extracts nutrients and energy from the food we eat.