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.

Wednesday, March 25, 2009 Lecture

Wednesday’s lecture covered the cardiovascular system. We discussed the elements that blood is comprised of, covering the structure of an erythrocyte (red blood cell) and the various leukocytes (white blood cells) (i.e. neutrophil, eosinophil, basophil, lymphocytes, and monocytes). We also covered how to identify different leukocytes from one another and the functions of several of them. Red Blood Cells and White Blood Cells are both formed in the red bone marrow of the proximal epiphysis of long bones in adults. The structure of a RBC and the recycling of its parts were also covered. The process of blood clotting was overviewed, including the importance of clotting factor X and fibrinogen, which turns into solid fibrin and makes a web-like mesh to trap elements that form a clot. We covered the various blood types, the compatibility of blood types, and the anti-bodies each blood type has. The Rh factor was discussed as well as the importance of Rhogam shots for pregnant women. Finally, we studied heart models to determine the flow of blood in and out of the human heart.

Blood, a liquid connective tissue, is not only the most critical fluid in our body, but can also reveal disorders our body may have. The study and counting of different blood elements can indicate several disorders. A hematocrit shows the percentage of red blood cells in the blood, a low hematocrit can indicate anemia, while a high hematocrit can indicate dehydration or polycthemia (a bone marrow disorder). A high white blood cell count could indicate infection, inflammation, allergy, or stress. A low white blood cell count (leucopenia) could indicate infection or even cancer. A CBC, or complete blood count, performed by a medical specialist can evaluate both your white blood count (WBC) and red blood count (RBC) to determine and bodily disorders.

Wednesday, March 11, 2009

Wednesday’s class covered the material that will be on our next quiz—information over the endocrine system and autonomic nervous systems. We discussed the Adrenal glands, the medulla and cortex, as well as the hormones each releases and the location from which they’re released. We also covered the thyroid glands and how follicular, parafollicular, and colloid cells come into play. The follicular cells produce T3 and T4 (Thyroxine) from molecules of “DIT” and “MIT.” Thyroxine affects our BMR, or, basal metabolic rate. We also discussed the different tracts that luteinizing hormone takes in males versus females, starting from the hypothalamus. Our discussion also covered the parasympathetic and sympathetic nervous systems. We talked about the cranial nerves that have parasympathetic fibers and also discussed the pre/post-ganglionic fibers of the sympathetic nervous system and the different neurotransmitters that can be released. Lastly, we discussed the pathway of the cAMP/PKA secondary messenger system pathway.

Thyroxine, which is released by the thyroid gland, plays a major role in the regulation of your metabolism. Too much thyroxine (hyperthyroidism) can result in weight loss, nervousness, and/or anxiety and too little thyroxine (hypothyroidism) can result in sluggishness and weight gain. In order to treat both disorders doctors use prescribed medication. In the case of hyperthyroidism, too much T3/T4 is being produced, thus, a medication called an anti-thyroid drug is taken, which blocks the release of some thyroxine. Smaller amounts of thyroxine are still produced, but in much smaller quantities than before. In hypothyroidism, individuals are prescribed synthetic, man-made thyroxine, which mimics the effects of the natural hormone. In both cases it is common for the individual to be on these medications for life (in some hypothyroidism cases, however, individuals can regain thyroid function).

Wednesday, March 4, 2009

During Wednesday’s class we learnt about the endocrine system. We discussed the endocrine glands that release hormones into our blood streams, alter bodily functions and maintain homeostasis. The glands that create hormones include the pineal, hypothalamus, anterior pituitary, thyroid gland, parathyroid glands, thymus, and pancreas. We learnt about the anterior and posterior pituitary and how releasing hormones from the hypothalamus allow the release of anterior pituitary hormones through the hypothalamo-hypophyseal portal system. Oxytocin and Anti-Diuretic Hormone are two hormones made in nuclei in the hypothalamus and are transported into the posterior pituitary for storage via the hypothamo-hypophyseal tract. The two major types of hormones are protein hormones and steroid hormones. Although steroid hormones are slower to affect their target organs they have longer-lasting effects. Protein steroids, however, are more easily maneuvered.

As can be imagined, hormones play a critical role in the development of our bodies. Growth hormone, released by the anterior pituitary, is a hormone that allows our bodies to grow—especially during puberty. In class we discussed how dwarfism can be caused by a growth hormone deficiency. However, aside from synthetic growth hormone, what other methods can be performed to aid in the lives of dwarfs? The child of one of my parent’s relatives is a dwarf and is about 18 years old now. A year or so after I met him (which was about 5 years ago) he was to undergo surgery on his spine to increase his height and prevent scoliosis or kyphosis (abnormal curvatures of the spine). I researched the surgery and found that many dwarfs have problems with their spines that can become crippling. In order to prevent this from happening doctors fuse certain vertebrae of the spine together and place metal rods along the spine for stability. This straightens the spine during the healing process. After the vertebrae are fused the spine can no longer bend (or is limited in its bending ability). This prevents scoliosis or kyphosis from developing. During the healing process they must also wear a “halo” around their heads to prevent their necks from moving before the spine is healed. Not only does the surgery prevent the crippling of the spine, but it can also add a few inches to the individual’s height, as it did with the person I know.

Wednesday, February 25, 2009 Lecture

The lecture focused mainly on the autonomic nervous system and touched upon other topics such as secondary messenger systems and the major anatomical landmarks of the eye and ear. All impulses of the autonomic nervous system are efferent impulses. The two major divisions of the autonomic nervous system are the parasympathetic (cranio-sacral) and the sympathetic (thoraco-lumbar) systems. The parasympathetic system is responsible for the “Rest and Digest” reflex and is the restorer of homeostasis. The sympathetic nervous system is responsible for the “Fight or Flight” response. Both systems target smooth muscle, cardiac muscle, and glands. There are two neurons involved in the parasympathetic and sympathetic nervous systems: the pre-ganglionic neuron and post-ganglionic neuron. They are named this because they are before or after a ganglion, or bundle or nerve fibers. The pre-ganglionic neuron always releases Ach and excites the second neuron. The receptors that lie in the post-ganglionic neuron and target cell are cholinergic receptors. Cholinergic receptors include muscarinic (excitatory or inhibitory) and nicotinic (excitatory) and bind to acetylcholine. Another type of receptors is Adrenergic Receptors, which include Alpha 1, Alpha 2, Beta 1, and Beta 2 receptors, each affecting their target organs in different ways. Adrenergic receptors bind to epinephrine and norepinephrine. Secondary Messenger pathways utilize G-proteins to “carry” their message from the receptor to the channels located elsewhere in the cell. There are two different pathways in secondary messenger systems: pKA and pKC.

We also studied the major landmarks of the external, middle, and inner ear.

I’m sure all of us have either had an ear infection or known someone who has had one. If you’ve experienced one yourself you know that it causes a dull pain and can last several days or weeks. I researched exactly what causes an ear infection and found out that it is typically an infection of the middle ear (where the malleus, incus, stapes, pharyngotympanic tube, and the tympanic membrane are located). Middle ear infections are caused by the swelling of the pharyngotympanic tube (which connects the pharynx and the middle ear). This swelling can lead to a blockage of the tube, which traps fluid inside your middle ear where germs and bacteria cause an infection. Ear infections are more typical amongst children because their Eustachian tube is smaller and more easily blocked. Antibiotics can treat the infection.