Unit 5 Reflection

In this unit, we began by talking about the digestive system. We did a lab showing the length of our digestive tract, and the total length I ended up with was quite surprising. The digestive system has two main purposes: digestion and absorption. Food starts in the mouth, where it is broken down by saliva and teeth. It then goes down the esophagus into the stomach, where it is further digested using both contraction and gastric juices. The food goes into the small intestine, where absorption starts. The small intestine is composed of the duodenum, jejunum, and ileum. In the duodenum, more chemical digestion occurs, while the jejunum and ileum are primarily involved in absorption, and use microvilli to do so. Finally, the remaining indigestible food goes into the large intestine, where it is dried out and then excreted through the rectum.

Next, we talked about metabolism, or where nutrients go after they are absorbed by the small intestine. It turns out that there are actually three states of metabolism- the fed state, the fasting state, and the starving state. In the fed state, the body releases insulin, prompting the liver to store glucose, while amino and fatty acids are sent to the cells. About an hour after a meal, the body goes into the fasting state. Glucagon levels rise, and glucose stored in the liver is used. The body begins to rely more on fatty acids and ketone bodies. Finally, after four to five days of not eating, the body goes into the starvation state, where the body relies almost exclusively on ketone bodies for fuel.

In the next lesson, we learned about diabetes. Type one is an autoimmune disorder in which the body attacks the insulin-producing cells in the pancreas, leading the body to become insulin dependent, or unable to produce insulin, so they must inject it into themselves. This often begins in children, and it has a relatively quick onset. Type two diabetes is far more common. It usually appears in adults, and is caused by insulin resistance, meaning the cells no longer respond to insulin, either because excess fats in the blood block insulin receptors or because their fat is secreting a hormone preventing insulin from binding to its receptors. Both types of diabetes have terrible consequences if they are not managed properly.

The endocrine system also plays an important role in metabolism. This system consists of glands which secrete hormones of two types: steroid and nonsteroid. Steroid hormones are lipid soluble, and can therefore pass through cell membranes, binding to receptors inside the cell and affecting DNA. Nonsteroid hormones, however, react with receptors outside the cell, triggering a reaction and ultimately influencing functions inside the cell. Hormones are controlled through negative feedback- meaning they are turned on and off based on physical changes. The pituitary gland, which acts as the middle man between the hypothalamus and the rest of the body, consists of the posterior lobe, which produces ADH and oxytocin, and the anterior lobe, which produces  ACTH, GH, FSH, lutenizing hormone, and prolactin. The thyroid gland is in the middle of the neck, and it secretes T3, T4, and calcitonin, regulating metabolism and promoting glycolysis and gluconeogenesis. The parathyroid gland secretes PTH, which regulates phosphate levels and plasma calcium. The adrenal medulla secretes epinephrine and norepinephrine, which controls the fight or flight response, while the adrenal cortex secretes mineral corticoids, glucocorticoids, and gonadocorticoids. The pancreas produces insulin and glucagon to help with metabolism, and the kidneys regulate red blood cell production. Gonads control sex characteristics.

Finally, we learned about the lymphatic system, which helps with immunity, lipid absorption, and fluid recovery. Lymph vessels, which are filled with lymph,  travel through the body beside blood vessels. Lymph capillaries clean out the spaces between cells, then flow into the lymph vessels and eventually the lymph nodes, which filter the lymph. Lymph is pumped through vessels by rhythmic contractions. There are different types of lymphocytes in lymph nodes which fight pathogens- the T cells, which fight previously identified pathogens, B cells, which produce antibodies, and NK cells, which watch for pathogens. Some important lymph nodes are the thymus, which produces T cells; the tonsils, which fight inhaled pathogens; and the spleen, which regulates red blood cells and responds to pathogens in the blood.

This unit was a bit difficult because I had just transferred into this class, so I wasn't sure exactly what was expected of me, especially  with the journals, but I think I figured that out fairly quickly. Another difficulty I had was in not planning far enough in advance for this test. I did well at engaging in class and contributing to groups even though I was new to the class. 

I would still like to know what the difference between the lymphatic system and the immune system is, if there is any, as well as how the human digestive system has evolved to become what it is in our species, and what gut bacteria really do for you, other than make you fart. I would also like to know more about the circulatory system, as it seems very important to all of the systems we just learned about.

I think I have done pretty well on my New Year's Goals. I have been participating in class frequently, both in group and lecture settings, and paying attention. I did have a bit of trouble with planning out my assignments- I was a bit rushed on my elevator pitch, and I definitely should have started studying for this test earlier- but I think that I have been doing pretty well with my goals this unit. I will try to look on Canvas more frequently, though.