Wednesday, April 22

Wednesday’s lecture covered topics of the digestive system. We learned the layers of the gastrointestinal tract and the various cells of the gastric glands, the substances they secrete, and how these substances aid in digestion. The muscularis layer of the tract is innervated by the parasympathetic nervous system, specifically the vagus nerve (cranial nerve X). This layer is comprised of smooth muscle and plays an important role in moving food along the digestive tract. The stomach plays an important role in the mechanical breakdown of food into chyme. The pancreas not only secretes important hormones for the endocrine system but also secretes important chemicals for digestion. The pancreatic acinar cells secrete digestive enzymes into the pancreatic duct, which meets the common bile duct from the liver at the hepatopancreatic ampulla, before they are released into the duodenum. The liver uses nutrients to create proteins and bile (which is secreted through the common bile duct and meets the pancreatic digestive enzymes at the hepatopancreatic ampulla). The small intestine contains folds of villi, each one which contains microvilli (“brush border”). We also discussed the difference between High density, low density, and very-low density lipoproteins.

As with any cranial nerve, the vagus nerve (X) plays a vital role in digestion. Not only does it keep your heart at a normal rate but it also aids in the release of digestive enzymes and smooth muscle contractions along your GI tract. I wonder then, what would happen if there was trauma to the vagus nerve and how this would affect your health (since its functions are so vital). I read online how some people’s vagus nerves were severed during surgery and now they are required to take medications to help with such things as a normal heart beat and digestive enzyme release. We definitely take for granted the role of our parasympathetic system (probably because we aren’t consciously aware of its functions!) but we would certainly realize how different life would be if our nerves did not work properly!

Wednesday, April 15 Lecture

Wednesday’s lecture covered the last topic of the cardiovascular system (how fetal blood circulation differs from that of an adult, and the changes in a fetal heart after birth) as well as part of the lymphatic and immune system.  Lymph fluid is created from the blood plasma that leaks out of blood capillaries into tissues to become interstitial fluid.  The lymph moves through capillaries (which are single layers of simple squamous epithelium and fenestrated for the movement of small particles) then into lymphatic vessels (which are larger in size).  The lymph is filtered through lymph nodes that lie along lymph vessels.  There are three major clusters of lymph nodes in the cervical, axillary, and inguinal regions (where pathogens can more easily enter the body).  The lymph is then dumped into the venous blood via the thoracic and lymphatic ducts through the left and right subclavian veins, respectively. 

Lymph nodes house attacking “units” for the immune system.  Just under the outer capsule, the subcapsular sinus is filled with lymph fluid and contains resident macrophages, which are APC’s or antigen-presenting cells.  They identify self from non-self cells in order to determine an immune response.  Self proteins contain MHC-1, or a major histocompatibility complex (which is also used to determine tissue compatibility in organ donations).  MHC-II’s are released when a macrophage, B-cell, or eosinophil undergoes phagocytocis.  Transient macrophages move throughout the lymph fluid and are specialized in determining if anything is foreign.

There are specific steps that occur in response to the invasion of a foreign cell:

1)      Chemotaxis—chemicals are released the attract WBC’s (especially macrophages) to the damaged tissue.  (example: prostaglandins, histamine, bradykinin, collectively known as chemokines that induce vasodilation)

2)      Adhesion—margination is when ICAM’s, or intercellular adhesion molecules, are formed on a WBC, and pavementing is the tethering of the matching ICAM’s to the vessel wall to slow down the WBC and allow it to move out of the blood vessel.

3)      Diapedesis—WBC’s move through the blood vessel wall and extend “arms” to create a pseudopod.  They then ingest the microbe and fuse with other pseudopods to make a phagosome.  The phagosome fuses with already present lysosomes to create a phagolysosome in which oxygen free radicals destroy the microbe.

Lastly, we covered the topic of complement protein activation, the activation sequence to activate a MAC (membrane attack complex) and the by-products that become potent vasodilators.

 

One topic that was peculiar to me was the drainage of lymph fluid into the venous blood.  The right lymphatic duct drains lymph from the upper right quadrant of the body into the right subclavian vein and the thoracic duct is responsible for the remaining 75 % of the lymph fluid.  I wonder what the anatomical significance of this unbalance is.  I thought it could be because of vital organs that lie in the 75 % of the body drained by the thoracic duct.  Although there would be more lymph fluid that could be “infiltrated by a microbe,” there would also be more WBC’s available to attack the pathogens.  The right lymphatic duct doesn’t seem to be as important, considering that the only vital organ it drains is the right half of the brain.  In fact, some individuals do not even have a right lymphatic duct and instead the lymph fluid is drained directly into the veins of the neck.  I could not find a valid explanation for the disparity between the two draining ducts so if anyone has any information it would be appreciated!

Wednesday, April 8 Lecture

Wednesday’s lecture covered several topics of the cardiovascular system. We covered arteries (which carry blood away from the heart) and veins (which carry blood towards heart). Capillaries exchange carbon dioxide and oxygen and wastes and nutrients. Portal systems are two capillary networks, in which the first exchanges substances and the second exchanges wastes and gases. We also discussed the layers of blood vessels such as the tunica externa, tunica media, and tunica interna. The remainder of the class comprised of learning the locations of various important blood vessels. We covered such topics as the blood flow to and from the brain, the coronary circuit, the pulmonary circuit, the blood vessels of the thorax, the branches of the abdominal aorta, and the blood flow to the lower extremities.

The topic of anatomical redundancy explains how there are multiple blood routes to major organs. This allows for blood to remain flowing to the specific organ in case there is a blockage in one of the routes. For example blood to the brain is delivered via the vertebral arteries through the subclavian arteries as well as the internal carotid artery from the common carotid arteries. I wondered if, because of this dual-pathway of blood to the brain, if a slight blockage could occur in one of the pathways and a person could continue living as normal. Also, if a slight blockage would occur, could the other path have more blood pumped through it to make up the difference? With the help of Ms. Peterson and a few web sources I found that this in fact could happen. As we know there are two routes leading into the Circle of Willis. In fact, “as long as the Circle of Willis can maintain blood pressure at fifty percent of normal, no infarction or death of tissue will occur in an area where a blockage exists.” “Sometimes, an adjustment time is required before collateral circulation can reach a level that supports normal functioning; the communicating arteries will enlarge as blood flow through them increases. In such cases, a transient ischemic attack may occur, meaning that parts of the brain are temporarily deprived of oxygen.” I found it quite interesting that the body can make such adjustments, even in such a critical area such as the brain.