Anatomy and pysiology

Anatomy & Physiology

We begin a fantastic voyage through the body of a healthy female adult. Our starting point is the femoral vein, which is the largest vein in the groin. The femoral vein is a continuation of the popliteal vein, which is formed in the lower leg from the union of the front and back tibial veins (MedicineNet.com). As we take our voyage through the cardiovascular system, the veins and arteries become magically transparent so that we can see inside the body as we pass through it inside our microscopic craft. Our mission is to investigate the bacterium that is invading the lower lobe of the right lung. We will journey to that destination for further study; when we have the information we are looking for, we will continue on, eventually crossing the alveolar membrane and routing out of the body through the nose.

The femoral vein ends at the inferior margin of the inguinal ligament, where it becomes the external iliac vein. As we travel towards the heart along the upper leg, the femoral vein branches off into the superficial external pubic vein, the superficial internal circumflex, the superficial iliac circumflex, and the superficial epigastric. We are now in the trunk of the body. We pass the umbilicus. We move through the external iliac, which becomes the common iliac -- that also branches off into the internal iliac. The common iliac becomes the inferior vena cava. The inferior vena cava (also called the posterior vena cava) brings deoxygenated blood to the right atrium of the heart. We travel through the tricuspid valve into the right ventricle. The right ventricle contracts, forcing the blood past the pulmonary semilunar (crescent-shaped) valve, We then go into the pulmonary trunk.

The pulmonary trunk divides in two. The blood is still lacking oxygen, and the two pulmonary arteries, left and right, take us to the lungs. The blood becomes enriched with oxygen and travels back toward the heart. With the blood, we enter the heart through the right pulmonary vein (there is also a left pulmonary vein) that comes directly from the lungs. We then enter the left atrium. The bicuspid valve opens up and the blood fills the left ventricle. The ventricle contracts and the blood is forced past the aortic semilunar valve. The blood goes into the aorta -- the largest artery in the body -- and brings the oxygen-rich blood back through the body.

Rather than follow the blood's entire path, however, we chose to stop and investigate the lower lobe of the right lung. We chose the right lung because it is a bit more spacious. The left lung is slightly smaller to leave room for the heart.

The inside of the lung looks like a tree. The right bronchus, which branches from the trachea, branches further and further into tiny tubes. We see about thirty thousand bronchioles in the right lung; there are about the same number in the left lung, each one the thickness of a human hair. At the end of each bronchiole is a cluster of tiny air sacs, called alveoli. Each one of these has a mesh-like covering of capillaries. These are so narrow that blood cells can only go through them one at a time. The oxygen attaches to the blood cells and this is the means by which oxygenated blood returns to the body.

We are investigating the lower lobe of the right lung. This part of the lung is generally free from bacteria and that is the case here; our human is healthy. Nonspecific immunity refers to the mechanisms the body uses collaboratively with other systems. In the lower lobe, the spongy outside provides a physical barrier to the entry of bacterium. Inside, the lungs are made up of epithelium, cells that line cavities and surfaces of structures throughout the body. The honeycombed formation of epithelium gives the inside of the lungs much more surface area than on the outside.

According to Science News (2009), it is not uncommon for people to die from lung complications of a disease rather than the disease itself. Epithelial cells in the airway signal the immune system when bacteria are inhaled. Before bacteria reach us in the lungs, the immune system calls for white blood cells to move into the bloodstream to fight potential infection. Epithelial cells also have been shown to detect allergens.

T cells, short for T. lymphocytes, are white blood cells derived from the thymus gland. They play a key role in fighting infections such as tuberculosis and pneumonia. These cells secrete a type of protein, cytokines, which regulate or aid in the immune response.

Now that we have assurance that the lungs are clear and free of bacteria, we are ready to bring our fantastic voyage to a close. When the blood first came to the lungs through the pulmonary capillaries, there is very little oxygen. The hemoglobin in the red blood cells has carbon dioxide bound to it; the carbon dioxide leaves the blood and passes through the alveolar membrane into the air sac. The alveolar membrane is a thin tissue barrier made up of three major types of alveolar cells. Type I, squamous alveolar cells, form the structure of the alveolar wall. Great alveolar cells secrete pulmonary surfactant to lower surface tension, thus increasing the membranes capacity to exchange gases. Finally, there are macrophages. They destroy foreign matter, such as bacteria.