Objective 78: Distinguish among the different parts (gross and histological) of the alimentary canal in terms of structure and function

Again, the Interactive Physiology section of our textbook's website is absolutely amazing! This animated review not only goes over the structure of the alimentary canal, but it goes over the functions as well. This review allowed me to interact with the alimentary canal because I could click my mouse over certain organs and the review goes into detail about the functions of it and shows its internal structures. I don't know how many times I referred to this site to help me on my quest of completing these objectives, but I'm glad that our textbook provided it. I would have been so lost without this site, but the textbook and class lectures were also very helpful in my understanding of this important body system.

The histology portion is something that I still can't wrap my head around. Hopefully one day the information will just make sense, but as of now I'm totally clueless in front of the microscope. For some reason I can't tell one thing from another and it is very frustrating. The same Histology site that I used for respiratory system was great in helping me understand the alimentary canal as well.

Objective 57: Justify the role of lacteals in transporting products of digestion

Lacteals are highly specialized lymphatic capillaries that are located in the crypts of the villi of the intestinal mucosa. But since they are located in the villi, how do they transport products of digestion? I referred to both the lymphatic and digestive chapters for my answer (page 657 and 767) and it helped me understand these important capillaries. The lacteals play a huge role in absorbing digestive fats (chyle) from the intestine and then leads it to the thoracic duct, which ultimately sends it to the left subclavian vein. Being able to review the diagram from chapter 22 page 768 gave me a better insight on the structure of the lacteal and how it plays a role in absorbing chyle. I also reviewed the histology of the lacteal, and with both these diagrams and the information from the book I was really able to have a light bulb click on for me.

Objective 68 & 70: Chemical buffer system

Objective 68: Recognize how chemical buffers interact to protect the body against lethal changes of pH
Objective 70: Recognize how the lungs and kidneys interact to protect the body against lethal changes of pH

Wow, if only you know how long it actually took me to figure this objective out. I put it off as long as I could because I try to stay as far away from anything remotely chemistry related as possible. I finally decided to be brave and take a stab at it, and I realized that the lecture outline and textbook gave some quite handy information on the chemical buffer system. Mind you, this topic is still very confusing for me. Still, the lecture outline and book helped me a great deal in trying to sort this information out in my head. Are you ready? Here's what I learned from the textbooks information.

Our body chemical buffer is a system of one or more compounds that act to resist changes in pH when a strong acid or base is added. They do this by either binding to hydrogen whenever the pH drops or releasing hydrogen whenever the pH rises. The chemical buffer system is composed of bicarbonate, phosphate, and protein buffer systems. These buffer systems are so closely related which allows any drifts in pH to be resisted by the entire buffer system. The bicarbonate buffer system buffers both ICF and ECF, but it is the only important ECF buffer. The phosphate buffer system is a very effecient buffer in urine and in ICF. Proteins in plasma and cells are the body's most powerful source of buffers.

The kidneys and lungs play an important part in protecting the body against lethal changes of pH as well. Chemical buffers cannot remove excess acids or bases from the body, and thats where the kidneys and lungs come into play. I kind of see them as the football players on the bench waiting for their turn to get into the game. Kidneys adjust bicarbonates, eliminate fixed metabolic acids (phosphoric, uric, lactic acids, and ketones), and prevent metabolic acidosis. The lungs eliminate carbonic acid by expelling carbon dioxide. It is amazing how different systems of our body work together to maintain homeostasis.

I know I'm teaching the topic again to you it seems, but being able to write out a summary of how the chemical buffer system is important really does help me grasp the information better. I guess since i'm writing it out, it's sticks easier to my brain.

Objective 60 & 61: Pancreatic juices and chemical forms

Objective 60: Describe enzymatic and bicarbonate content of pancreatic juices
Objective 61: State the chemical forms in which the major food classes are absorbed

Reading up on these two topics was a lot easier than I had originally thought. For some reason, I thought that the pancreatic juices were going to be this complicated mix of enzymes and electrolytes. I also believed that the chemical forms of the food classes were going to have a very long process to being absorbed. Well, I was in for a pleasant shock. I was able to located the information in the text book and lecture outlines, and they both did a great job in helping me understand the two. Pancreatic juice consists primarily of water, electrolytes (mainly bicarbonate), and enzymes (amylase, lipases, nucleases). The acinar cells produce the enzyme-rich component of pancreatic juice. Along with the lecture outline slides, I also referred to chapter 22 page 775 to help me understand the make up of the juice.

I copied this chart from chapter 22 lecture outline, but it can also be found on page 785. It really does a great job in outlining the chemical forms that each type of food gets broken down into. It then tells you the path of absorption that these chemicals forms travel within the body. I don't know how I would have figured out this objective without this chart. Its extremely detailed, and informative and it really made that light bulb go off for me. So what I learned is that carbohydrates are broken down into oligosaccharides and disaccharides; protein is broken down into amino acids; fats are broken down into monoglycerides, glycerol and fatty acids; and nucleic acids are broken down into pentose sugars, N-containing bases, and phosphate ions. After the major food classes are broken down into their chemical forms, it is from there that they are absorbed into different parts of the body. The last column of the chart describes in detail where they are shipped off too. Isn't the digestive system spectacular?

Objective 58: Relate structure and function of the endocrine system to digestion

This is a very broad topic, which means there could be a variaty of answers to cover this topic. I actually am still having a hard time figuring out the best way to answer this question correctly, but I'm going to give it my best shot. So, here it goes. The endocrine system is the second great control system of the body. It is made up of a serious of glands that produce a variaty of hormones. These hormones act as "chemical" messengers and help regulate a majority of the body's basic functions. There is a passage from the textbook that really helps me understand, in short, what the endocrine hormones are responsible for. In chapter 15, the passage on page 519 states "The major processes controlled and integrated by these "mighty molecules" are reproduction; growth and development; maintenance of electrolyte, water, and nutrient balance of the blood; regulation of cellular metabolism and energy balance; and mobilization of body defenses." This really helps me see how the endocrine affects the other systems more clearly. The digestion system is composed of a system of organs that helps break down food into nutrients, absorbs the nutrients into the bloodstream, and then gets rid of the wastes. So in short, the endocrine system produces important hormones (for example -gastrin, cholecystokinin, secretin) that allow the digestive function to take place. Without these hormones, our bodies could not digest the food we take in.

I know that we are not suppose to "teach" the information, but I couldn't find anything in the textbook or online that really gave me an "aha" moment. There was a small article called Enteric Endocrine System that provided a few small pieces of information that guided me, but for the most part I was on my own. Being able to write this information out on this blog really gave me a clearer understanding on how the endocrine system was related to the digestion process. The lecture in class was the only helpful thing to help me understand this information, since we discuss certain topics in depth.

Objective 59: Appreciate the microscopic anatomy of the liver

During lab, our class was asked to look at different slides of tissues and organs for each chapter. So when we get to the Digestive system, our class was asked to look at the slide of the liver during lab and this is where I was able to view and appreciate the microscopic anatomy of the liver. During lab, I was able to view the slide of the liver under 100X and 400X and examine the different parts and structures that the liver had. It is always a little difficult for me to find out exactly where each important part is when looking at the slide, so it was extremely helpful to have the Practice Anatomy Lab which is included in the books website. So along with viewing the slides in lab, the Practive Anatomy Lab online was very helpful when i was trying to understand the microscopic parts of the liver. When you put your mouse of the parts of the liver, the online lab shows you what the part is called (for example each lobe is called the liver lobule and the circle in the middle of each lobe is the central vein) and even highlights it for you which really contributed to my understanding of the microscopic liver. The Practice Anatomy Labs were really a lifesafer for me when it came to lab slides.

An example of a liver slide