From our anonymous insider…
One week before exams; my classmates are nervous.
Lectures introduced the immune system, both the innate and the marvelous adaptive immune system. All of our immune cells start their lives as bone marrow stem cells. These stem cells undergo education, either in the thymus or bone, to ensure they do not attack healthy cells yet can potentially attack foreign antigens. I had always thought during an infection our adaptive immune system would create a new immune cell against this foreign structure. Instead, the diversity of potential antigens to which our body can respond is determined within the first few years of life by a process of “student” immune cells randomly self-mutating their antigen receptors (see VDJ recombination). Only about 1-2 percent of the total cells graduate from self-mutation school; the remainder kill themselves. The textbook says that our immune system ends up with roughly 1,000 billion cells that can recognize 10 million different antigens. When an unknown invader arrives, if it is among the 10 million antigens that we’ve prepared to fight since early childhood, we’re in great shape. Otherwise we will need antibiotics or a trip to the hospital.
A doctor from the world’s only hospital that does thymus transplantation came in. As mentioned above, the thymus is the schoolhouse of the immune system, educating immune cells to not attack self. Transplanting a donor thymus, typically obtained from a young child whose thymus got in the way of cardiac surgery, could theoretically eliminate the issue of organ transplant rejection. If a diabetic needed a new kidney, immunosuppressors would be used to destroy the patient’s immune system and then the donor kidney and a donor-matched thymus would be transplanted. The regenerating immune system would be educated to not attack the patient nor the matched donor organ — thymus education is additive! The challenge is to generate a comprehensive thymus donor database or even engineer a biosynthetic thymus.
We dissected the arm from the shoulder to the elbow joint. I was amazed by the vasculature (arteries and veins) as it branches from the major vessels in the thorax and the interweaving nerve structures (see brachial plexus). We saw the funny bone, a.k.a. the ulnar nerve, as it passes between the medial epicondyle of the humerus and the olecranon, or elbow bump, of the ulna. I also discovered my favorite joint: the radiohumeral joint with the annular ligament of the radius. The radial humeral joint allows rotation of the forearm (supination, palm up, and pronation, palm down). The radial head, a spherical protrusion at the proximal end of the radius, is encapsulated in a sheath that allows it to rotate around a fixed point. Listening to the PhD medical researchers who come in as lecturers, I am coming to appreciate the amazing opportunity of anatomy lab. The researchers are experts on test tube experiments, but haven’t had time to look at the circulatory system or liver anatomy, for example.
Statistics for the week… Study: 18 hours; Sleep: 6 hours/night; Fun: 2 nights out. Example Fun: Friday after-class soccer followed by a repeat of the Week 4 jam session. More than half the class showed up and most of them sang along, despite any lack of formal musical training.
The Whole Book: http://tinyurl.com/MedicalSchool2020