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We’ve already talked about the ASVAB cardiovascular system. Take a few minutes to review that topic before commencing.

Done?

Great! Now we can proceed to learn more about the digestive system. We review other body systems in future ASVAB blog articles.

• Digestive system(below)
• Immune system
• Reproductive system
• Cardiovascular system
• Nervous system
• Endocrine system
• Integumentary system
• Respiratory system

The digestive system is that part of the body responsible for digestion. Digestion is the process by which we metabolise food and drink and, in that process, we extract nutritional value from those foods, whilst eliminating undigestible and waste products through the urine and feces.

Organs and body parts that play a role in digestion include:

• Oral cavity – including teeth, saliva and taste
• Esophagus – the tract that connects the oral cavity to the stomach
• Stomach – hydrochloric acid (also known as ‘gastric acid’) product breaks down food into chyme. The more that food is broken down, the easier those nutrients are absorbed from the small intestinal wall into the blood. When the stomach produces too much acid, we experience this pain/discomfort as indigestion and need to take supplements that contain calcium or magnesium ions. These ions are capable of ‘chelating’ acid, converting the acid to a form that is more ‘basic’ (less acidic).
• Pancreas – produces enzymes that further break down fats, carbohydrates and proteins. The pancreas also produces a hormone called insulin, which works to monitor and regulate blood glucose to safe levels.
• Small intestine – most nutrients are absorbed through the wall of the small intestine, particularly the first part of the small intestine – the duodenum.
• Large intestine – undigestible matter cannot be absorbed by the body and so, once all nutrients have been extracted, the waste products pass into the large intestine. As the waste moves slowly through the intestine (via a process known as peristalsis), more and more water is absorbed from the waste back into the body. As a result, the waste matter becomes more and more solid and, from there, ejected out of the body in a process known scientifically as defecation.
• Liver – an organ with a multi-functional dimension. It is used to detoxify waste products. The liver is also used as a processing center; taking in nutrients from the body and either storing them or converting them to active forms for use around the body.
• Gallbladder – produces enzymes which are released into the digestive tract to facilitate the digestion and absorption of fats (lipids).

We mentioned enzymes above. Enzymes are very important mediators of digestion in the body. Enzymes always end in the suffix -ase. You can tell what the enzyme does based on the name. For example – lipase is an enzyme that breaks down lipids, or fats. Proteases are enzymes that break down proteins.

From the saliva in our oral cavity, through to our stomach and pancreas and small intestine, we produce these enzymes to break down food into their constituent components. Effective absorption of nutrients cannot take place unless food is broken down to its most fundamental constituents.

Otherwise, nutrients – such as proteins and fats – are unable to pass through the filtering system of the small intestine and into the blood; where the nutrients can pass to sites where they are needed and to other body parts, such as the liver, where those nutrients may be stored for future use.

Let’s take a closer look at the bio-constituents of food.

Food contains nutrients. These nutrients are used by the body for energy sustenance, maintenance and cell repair, and to prevent ill-health via a strong and secure immune system.

Nutrients are classified as either:

• Macronutrients– carbohydrates, fats and proteins
• Micronutrients – vitamins and minerals

Macronutrients include carbohydrates, fats and proteins. Carbohydrate are sugar-based nutrients that sustain energy levels. Some carbohydrates provide immediate energy sustenance, whereas other “carbs” provide more long-term sustenance.

Fats are also known as lipids.

Lipids – like carbohydrates – are also an energy source. Lipids are also converted by the body into hormones. Cholesterol, too, is produced from lipids. Not all cholesterol is bad. There are two main types – HDL and LDL cholesterol.

HDL cholesterol is high-density lipoprotein cholesterol – known colloquially as “good cholesterol”. We need HDL cholesterol for maintenance, hormone production and sustenance for cell membrane repair and other important functions.

LDL cholesterol is low-density lipoprotein cholesterol – known colloquially as “bad cholesterol”. Elevated levels of LDL cholesterol can be dangerous, increasing the probability that arteries become clogged with a thick cholesterol plug. Sometimes, that plug bursts and comes loose, traversing through blood vessels until it finds a blood vessel to clog.

That is what happens during a heart attack, known medically as a myocardial infarction.

To maintain a healthy lipid profile, then, we need to consume foods high in HDL cholesterol whilst minimizing our consumption of foods packed with LDL cholesterol. We all know what these foods are. For example – processed foods, red meats, burgers and other forms of fried food, are all high in LDL cholesterol. Many foods – particularly eggs – are beneficial to maintain healthy HDL cholesterol levels.

As part of your ASVAB science test prep, you must have a thorough knowledge of the digestive system.

Here, we’ve done precisely that. We’ve put together a comprehensive blueprint of the topics you must know. This ASVAB test guide is by no means exhaustive, but it does touch upon the essential topics.

Registered members already have access to our ASVAB science test questions. If you haven’t yet registered, take a few seconds to complete the process now. It gives you instant online access to an amazing range of exam-like questions you can expect to see on the day of your ASVAB exam.

In the meantime, though, check back to our ASVAB blog as we continue to pump out even more great content to help improve your knowledge of the digestive system and every other aspect of the human body you need to know!