Unit 5 Reflection

In Unit 5, we started off by talking a lot about the digestive system. Here's a sneak peak at what I knew prior to the unit, what I wanted to know, and what I've learned in terms of digestion:

The main functions of our digestive system include ingestion or good, secretion, propulsion of food through the body, digestion/breaking down of the food, absorption of nutrients from the food, and defecation or removal of feces. When food enters the body through the mouth, it is chewed up by the teeth in our mouth and saliva, forming a bolus (mass of broken down food) with the help of the hard palate - the roof of the mouth. This bolus then travels through the pharynx (throat) and to the esophagus, which uses peristalsis to move food into the stomach. The stomach is where physical change (the mashing of the food by the contraction of the stomach walls) and chemical change (the breakdown of food by gastric juices and acids) take place. The broken down food, now called chyme, then travels through the duodenum, jejunum, and ileum of the small intestine in that order. Accessory organs like the liver (which produces bile to break down large fats), the gallbladder (which stores the bile for the liver), and the pancreas (which produces enzymes) aid the small intestine. The small intestine is also lined with microvilli to increase absorption. Finally, the food enters the large intestine, where more absorption takes place, and then it is excreted through the anus as waste. This continuous flow of food through the digestive system is described in the diagram below, with all the main organs and their functions labelled. 

To better visualize the various organs that work together in our digestive system and how long the digestive system really is, we did a pretty interesting Digestive System Lab, which also allowed us to understand how it is the many intricate folds of the digestive system that allow it to fit in our abdomen. 

To build off of what we learned about the digestive system, we also discussed metabolism and the three states: fed state, fasting state, and starvation state. The three stages of energy extraction that the body goes through when food enters the body are large molecules get broken down into smaller monomers, those small molecules are then turned into Acetyl CoA, and the Krebs Cycle and Oxidative Phosphorylation are used in oxidation of the molecules to make ATP. The Fed State (absorptive state) occurs directly after a meal. During this state, sugars absorbed by the intestines travel directly to the liver and the pancreas releases insulin, which stops the release of glucagon. Excess amino acids are sent to the liver for processing and excess glucose and fatty acids are made into triglycerides and stored in the adipose tissue. The Fasting State (postabsorptive state) occurs within one hour of the meal and is when glycogen in the liver is converted to glucose and gluconeogenesis (the synthesis of glucose by the liver) occurs. The body begins to use fats for energy in order to conserve glucose (it is conserved for the brain and red blood cells). The liver also converts excess Acetyl CoA into ketone bodies. Lastly, during the Starvation State which occurs 4-5 days after fasting, the muscles start relying on adipose tissue for energy. The graph below depicts how the glucose and insulin levels in the body vary throughout the course of a normal day. Various organs like the brain, muscles, liver, adipose tissue, and heart, all also have specialized roles in our metabolism. Hormones like insulin, glucagon, adrenaline, and cortisol also coordinate with the body's metabolic processes to ensure that the body consistently has good nutrition. 

One of the main hormones that controls fuel metabolism is insulin. Insulin, a hormone produced by the beta cells of our pancreas, allows glucose to be taken up by liver cells and stimulates the synthesis of glycogen. It's like a "key" that unlocks cells by attaching to the "lock" (GLUT-4 receptors of the cell) and opening the door that allows glucose to enter the cell. In a normal cell, the main function of insulin as described above is shown in the diagram:

Now that we had discussed fuel metabolism and how it works in our bodies, we learned about disruptions that can occur, for example, diabetes - which occurs when the body cannot properly regulate the blood glucose levels. Essentially, the body has trouble regulating the insulin and glucagon in the blood, so the person's blood sugar levels get too high. Type 1 diabetes, an autoimmune disorder destroys pancreatic beta cells so that the body can no longer make insulin. In this type of diabetes, the GLUT-4 receptors stay trapped inside the cell and cannot go to the surface to allow glucose in (as it does in the picture above), so the glucose accumulates outside the cell, increasing the person's blood glucose levels. Type 2 diabetes, on the other hand, begins as insulin resistance. Because both types of diabetes can have extremely detrimental health effects, it is important to be aware of the symptoms (shown in the cartoon below) and be aware of your blood glucose levels, diet, and exercise to make sure you do not become diabetic. 

The endocrine system controls the processes involved in movement and physiological equilibrium, and includes all of the hormones, tissues, and glands. There are two types of hormones: steroid hormones and nonsteroid hormones. Steroid hormones are lipid soluble and diffuse through cell membranes, while nonsteroid hormones are not lipid soluble and are reveived by receptors external to the cell membrane. Both are regulated by negative feedback loops, by which the secretion of a specific hormone is turned on or off by physiological changes. Each of the glands in the endocrine system (depicted in the picture below) secretes specific hormones that are regulated in their own unique ways.

Lastly, we discussed the lymphatic system and how it functions in immunity by having immune cells on standby ready to respond to foreign cells, lipid absorption by having lacteals in the small intestine that absorb dietary lipids, and fluid recovery by absorbing plasma proteins and fluids from the tissues and returns it to the bloodstream. Lymph, a clear colorless, fluid flows through lymphatic capillaries, to lymphatic vessels, and to lymph nodes. Four mechanisms that enable lymph flow are rhythmic contractions, the skeletal muscle pump, a thoracic pump, and the rapid flow of blood in subclavian veins which draws lymph into it. Lymphocytes (B cells, T cells, and natural killer cells), which although are part of the lymphatic system, play a huge role in our immune system - see my Unit 4 Reflection for more information on the immune system. The lymph nodes, thymus, tonsils, and spleen also each play a key role in the lymphatic system.  

This unit went by pretty quickly and covered a lot of interesting topics. One thing that really helped me more fully understand the various topics were the articles we read. For example, "Stress, Metabolism, and Liquidating Your Assets" - a chapter from the book, Why Zebras Don't Get Ulcers - compared the digestive system to banks. The author discusses how surplus money is kept in mutual funds, tax-free bonds, etc. in much the same way that surplus energy is stored in triglycerides, glycogen and proteins. In addition, the article entitled "Does Your Metabolism Need an Overhaul?" discussed how even people with normal weight can be prediabetic. The article talks about how the speed and efficiency of metabolism depends on the amount of muscle a person has because muscles are the primary place where sugar is burned. Although it was a lot of material this unit, these additional readings provided analogies and alternative explanations that really helped me understand the material. Some unanswered questions I have are how the lymphatic system works together with the circulatory system to circulate lymph, how the lymphatic system works to fight against cancers, and what kinds of negative feedbacks help to regulate the endocrine system.

Reflecting on my Goals from the beginning of this semester, I'm happy to say that I've been improving a lot on my confidence. I've had a couple of college interviews in the past couple weeks, and made a point to have firm handshakes and catch myself if I started slouching during the interview. I also made sure to enunciate while talking (no mumbling), and ask a lot of well thought out questions. I think I'm getting a lot better at this goal and being critical of myself when I don't raise my hand in class enough or start to mumble when I'm talking to someone. 

I'm still working on my second goal - sleeping earlier - because it's hard not to procrastinate as a second semester senior. It's really good that I looked back at my goals, because now I know that is one I need to work on. I get home at 2:30pm every day and no longer have an endless list of college applications to work on, so there is no need for me to be sleeping so late. I generally have a biphasic sleeping cycle (where you nap once midday and then sleep for 5-6 hours), which had worked out brilliantly junior year and first semester of senior year because I had a lot of work and could generally concentrate better at night; however, this semester, I'm having trouble sleeping at night and do not have that much work, so there is no need for me to nap during the day. I'm really going to try harder to start and finish my homework as soon as I get home, so that I can get to bed by 11 as per my new year goals, and adopt a monophasic sleeping cycle.

School-wise, I can honestly say that the "second semester senior" feeling that everyone had been talking about has slowly but surely been kicking in. Nonetheless, I've been working on my studying habits a lot more, and can report that the VARK Questionnaire that I looked into in my Unit 4 Reflection from last semester has really helped me hone in on the studying strategies that work for me. From the VARK Questionnaire, I learned that visual aids, diagrams, and writing things down generally helps me study better. In AP Biology, we've been learning about DNA replication and Protein synthesis and in order to study for the test we had earlier this week, I hand-wrote my own notes as I read the textbook and consolidated my notes into diagrams where I drew out and labelled the DNA. In addition, in my AP Gov class, I've made sure to draw out flowcharts so I can keep a timeline of events in my head to make it easier to remember the material and the causes and effects of various events. I will also do this for the upcoming test in Anatomy, as drawing out the various body systems the way they are drawn out in the images in this post will really help me visualize how these systems work together to help our body maintain homeostasis.