Integration
Something that we’ve found helpful is looking at how a challenge or problem that occurs within the system (i.e. disease) impacts the system as a whole. This level of thinking is beyond course level but it might be helpful when learning how to approach potential test questions.
Learning Outcomes
In this section, you will learn…
- How to integrate various content through various situations similar to case studies.
- Many real-life examples and how they apply to content you have learned thus far.
Disease-Related Example: Gastroparesis
When you study disease-related examples and compare them to normal functioning, you can further see the functions of each component in the GIT. You don’t need to know what gastroparesis is and the associated clinical symptoms, but you should be able to recognize how these clinical abnormalities impact GIT function and further absorption and digestion (not for testing, it’s just a good practice to be able to apply your knowledge of the GIT to other topics).
Gastroparesis occurs due to vagus nerve damage. The vagus nerve innervates the GIT and helps promote the movement of the chyme to the small intestine through contractions. Let’s break down what this means, why this is problematic and how we can connect it to the material learned throughout the semester.
The vagus nerve is damaged and that means that it won’t be able to depolarize, sending an action potential from neuron to neuron — the result is reduced/lack of contraction of the muscles lining the stomach. As such, the stomach will fill during feeding, but it is less efficient at emptying. So food lasts longer in the stomach than it should. In addition to creating problems within the stomach (since food should not sit dormant in the stomach for too long!), we know that this would be particularly problematic from an absorption stance. Less chyme leaving the stomach means fewer food constituents to be digested by pancreatic enzymes and less nutrient absorption, leading to weight loss.
Tips From Past Students
Case Study: Eating a Sandwich
So we’ve talked about what’s happening at certain points in your digestive tract when food is consumed, but we haven’t really pieced it all together. In this following case study, we will examine what happens when your classmate, Sam, eats a sandwich. Sam just left his HK*2810 final exam and is famished. He heads to the Bullring to grab a sandwich. Upon entry into the Bullring, he is welcomed by a pleasant aroma of food. Even before Sam orders and starts eating his food, saliva production increases in his mouth.
Salivary production is all thanks to the salivary glands which contain parotid, submandibular and sublingual cells. Digestive enzymes that can be found in saliva include alpha-amylase and lingual lipase. Mucin is another secretion to provide lubrication. Sam takes a bite of the sandwich and begins chewing.
The bolus is propelled into Sam’s pharynx and from there, the esophagus. Striated muscle makes up the upper region of the esophagus and is under voluntary control whereas the lower esophageal region is composed of smooth muscle and is under involuntary control.
Sam is loving his sandwich and he is vibing to the live music in the Bullring. While swallowing the piece of sandwich he does a handstand. The bolus isn’t regurgitated but rather continues down the esophagus. This is due to unidirectional propulsion down the GIT via peristalsis.
The bolus is propelled into the acidic stomach environment. Lots of things are going on here so let’s break it down. Gastric juices and churning motions help mix and digest food to create chyme, chemical breakdown of protein commences, mucosal lining provides a protective barrier between the stomach and highly acidic stomach environment. When food enters the stomach, this is the beginning of the gastric phase. Cells types in the gastric glands and their functions are important to note.
Hydrochloric acid is one of the main gastric secretions that denatures protein in foodstuffs. The acidic environment and the churning movements in the stomach help mix and liquefy foodstuffs into acidic chyme that will be moved into the small intestine. Only “liquid food” (aka chyme) can pass through the pyloric sphincter to reach the small intestine. Any solid matter remains in the stomach until it can be further digested.
Did you know that there is a Centre for Bariatric Excellence at the Guelph General Hospital that is committed to providing patients with quality care? It is known as bariatric surgery. For many of you, bariatric surgery may be a reoccurring topic covered in many upper-year classes! Bariatric surgery is weight loss surgery for severely obese individuals that are unsuccessful in losing weight via non-surgical methods. There are three types: restrictive, malabsorptive and combined, which is a mix of the two. We will talk about combined gastric bypass, the most common type of bariatric surgery is called Roux-en-Y Gastric Bypass which is a type of combined. There are two parts to this surgery, the restrictive portion that makes the stomach smaller and the malabsorptive portion that shortens the digestive tube and bypasses the majority of the absorption sites in the small intestine. One of the main problems with gastric bypass surgery is that patients often have micronutrient deficiencies following surgery because of the restrictive/malabsorptive nature of this surgery. This includes iron deficiencies are common because the surgery bypasses the main site of absorption. There’s also decreased secretion of gastric acid due to a decreased stomach capacity and so this reduces the ability for ferric iron to be reduced to ferrous iron for absorption.
You may find the effects of this surgery intuitive considering your knowledge of the GIT. When there is less space in the stomach, less food can be eaten during meals and the stomach isn’t as efficient at secreting gastric acid to partially digest the food. And the shortened digestive tract bypasses a large portion of the absorption site in the small intestine and as such, fewer nutrients can be absorbed by the body.
In the small intestine is the site of further digestion and absorption. Digestive juices are produced by the accessory organs (i.e. pancreas, liver, and gallbladder). Mechanical digestion is occurring due to segmentation and peristalsis. There is an abundance of villi and microvilli which increase the surface area of the GIT to aid in absorption. The intestinal phase of digestion starts when chyme arrives in the small intestine.
The pancreas is also the production site for many digestive enzymes. Secretions consist of an aqueous component from the pancreatic duct cells and an enzymatic component from the acinar cells. The aqueous component will neutralize the acidic chyme and the enzymatic component contains digestive enzymes.
The liver produces bile acids and these are stored in the gallbladder until they need to be released into the small intestine. Bile acids are able to be recycled. Hepatocytes take up the bile acids and these are then re-secreted. This is called enterohepatic circulation — only a few bile acids are lost (those lost, need to be accounted for so the liver with synthesizing more).
Ever wonder why the bag of Quaker oats has a health claim on their packaging saying that oats help to lower cholesterol? Well, it’s very much correlated with oats’ ability to increase bile acid excretion. When we eat fibrous food like oats there is an increase in bile acid excretion along with this indigestible fiber that passes through the digestive tract unabsorbed. Increased excretion of bile acids means that less is reabsorbed and recycled so the liver needs to produce more new bile acids using hepatic cholesterol. After time hepatic cholesterol will be depleted and the liver takes cholesterol from the blood to use to make new bile. This will decrease total cholesterol levels in the blood!
In the large intestine, this is the last chance for the absorption of water, vitamins, and electrolytes to be absorbed before waste products are excreted from the GIT. The GIT is highly innervated — if it wasn’t, there would be no communication between the digestive organs, food presence, stimulation telling organs to secrete digestive enzymes, etc. Sam is able to digest his sandwich due to neural inputs.
The local nervous system, aka the “second brain,” is called the enteric nervous system which is located in the myenteric and submucosal plexuses. The neurons in the enteric nervous system do not differ from those learned in other units in that they all depolarize due to a stimulus — depolarization causes an action potential which is propagated to other neurons resulting in a change in AP frequency and pattern to the coordinating center. Enteric nervous systems and central nervous systems BOTH have sensory, motor and interneurons. The enteric nervous system receives inputs from the central nervous system. Afferent and efferent signals are through vagus nerves which maintain that communication between your brain and your GIT.
Let’s think about what might happen if this neural connection was severed (during gastric bypass surgeries, one of the main effects is vagal manipulation — the alteration of vagus nerve signaling). Using your knowledge of the course content regarding the enteric nervous system, it might be easy to see how neural inputs relate to overall GIT functioning. Brain to GIT communication normally regulates the release of gastric acid and digestive enzyme secretions and the GIT to brain communication emits hunger signals. So, if an individual had impaired vagus nerve signaling, there would be impaired digestive enzyme secretion and they may not be able to get receive hunger signals telling them it’s time to eat. This often decreases food intake and subsequently leads to weight loss.
Tips From Past Students
There’s a lot of information in this textbook and we know it gets stressful and overwhelming to look at. When we were creating and refining this unit we wanted to make it as interactive as possible and as conversational as possible.
You’ve reached the end of the content for HK*2810. Yay! It’s been a journey, but we hope you learned lots along the way and will take this knowledge with you as you move onto your future classes and even after your undergrad. Learning is dynamic and doesn’t stop here.
In this class and in any other classes you have, think of the broader picture when reviewing this content. ZOOM OUT. Really. Stop looking at your notes as if you’re looking at them under a microscope. Believe me when I say it’s the best thing you can do for yourself. Not only will it help you grasp the content better but it will allow you to think more critically.
Gone are the days when memorization is what profs want you to focus on. Integration is key.
Here are some tips that we have found incredibly helpful.
- Create a mind map or a concept list. What are the main terms that you think are the MOST important? Going through the process of creating your own mind map will allow you to better understand the content and how it all fits together.
- Teach someone else the content. Odds are your roommate, friend, pet, family member or a stranger you talked to in the grocery line won’t understand what you’re talking about, but teaching someone else the content can help you to gauge your understanding of things that you may need to brush up on. Don’t feel comfortable doing this? Record yourself and play it back.
- Create a case study or find a case study relating to this course content. Identity how this problem would change normal body function and how does the body respond to this challenge?
You got this!
Sincerely,
Past HK*2810 Students
Test Your Knowledge
Thinking Beyond:
- Provide an example of how the concept of integration relates to this unit.
- Explain how vagus nerve damage can cause issues regarding absorption. How is signaling affected? What happens to the action potentials meant to be signaling muscle contraction?
- From start to finish, explain how a bite of food is digested. Be sure to include the anatomy of the digestive system, the importance of AP generation, and ion movement that allows the proper breakdown of food.
Subchapter Quiz
The questions below can be used to assess your knowledge within this chapter. There are multiple-choice questions that you should attempt without referring to your notes. The questions will provide you with responses to your answers to guide your studying but should not be used as your only resource.
