A variant source of arterial supply to the ascending, transverse and descending colon.

Anatomic variations involving arterial supply of the large intestines are of clinical significance. Variations range from the pattern of origin, branching and territorial supply. The colon, the part of the large intestine, usually receives its arterial blood supply from branches of the superior and inferior mesenteric arteries. However, anatomic variation in this vascular arrangement has been reported, with vascular anatomy of the right colon being described as complex and more variable compared with the left colon. During routine cadaveric dissection of the supracolic and infracolic viscera, we encountered an additional mesenteric artery originating directly from the anterior surface of the abdominal aorta between the origins of the superior and inferior mesenteric arteries. This additional "inferior mesenteric artery" ran obliquely superiorly toward the left colon giving rise to two branches supplying the distal part of the ascending colon, the transverse colon and the proximal part of the descending colon. Awareness and knowledge of this anatomic variation are important for radiologists and surgeons to improve the quality of surgery and avoid both intra- and postoperative complications during surgical procedures of the colon.

Evolutionary explanations in medical and health profession courses: are you answering your students' "why" questions?

BACKGROUND: Medical and pre-professional health students ask questions about human health that can be answered in two ways, by giving proximate and evolutionary explanations. Proximate explanations, most common in textbooks and classes, describe the immediate scientifically known biological mechanisms of anatomical characteristics or physiological processes. These explanations are necessary but insufficient. They can be complemented with evolutionary explanations that describe the evolutionary processes and principles that have resulted in human biology we study today. The main goal of the science of Darwinian Medicine is to investigate human disease, disorders, and medical complications from an evolutionary perspective. DISCUSSION: This paper contrasts the differences between these two types of explanations by describing principles of natural selection that underlie medical questions. Thus, why is human birth complicated? Why does sickle cell anemia exist? Why do we show symptoms like fever, diarrhea, and coughing when we have infection? Why do we suffer from ubiquitous age-related diseases like arteriosclerosis, Alzheimer's and others? Why are chronic diseases like type II diabetes and obesity so prevalent in modern society? Why hasn't natural selection eliminated the genes that cause common genetic diseases like hemochromatosis, cystic fibrosis, Tay sachs, PKU and others? SUMMARY: In giving students evolutionary explanations professors should underscore principles of natural selection, since these can be generalized for the analysis of many medical questions. From a research perspective, natural selection seems central to leading hypotheses of obesity and type II diabetes and might very well explain the occurrence of certain common genetic diseases like cystic fibrosis, hemochromatosis, Tay sachs, Fragile X syndrome, G6PD and others because of their compensating advantages. Furthermore, armed with evolutionary explanations, health care professionals can bring practical benefits to patients by treating their symptoms of infection more specifically and judiciously. They might also help curtail the evolutionary arms race between pathogens and antibiotic defenses.