The aged human appendix: its structure and iron content

Phylogeny and herbivory are related to avian cecal size

Avian ceca, a pair of blind sacs arising from the junction of the ileum and colon, are homologous to the cecum in mammals. Cecal size is hypothesized to depend on dietary proclivities and pressures, with faunivorous species having short ceca, whereas herbivorous species have long ceca. Previous tests of this hypothesis, however, did not account for phylogenetic pseudoreplication among closely related taxa. We collated published data on cecal length, dietary category, flying ability, and body mass from 155 avian taxa. Character states were mapped onto a phylogenetic framework, and the permutation tail probability test was used to detect phylogenetic signal in each character. Phylogenetic signal is significant among the characters. As with the cecoappendicular complex in mammals, closely-related birds tend to have similar cecal length. To account for phylogenetic pseudoreplication, we performed phylogenetic generalized least squares regression on cecal length and body mass with dietary category, superordinal-level clade, and flying ability as cofactors. The best-fitting regression model supports the dietary hypothesis for the avian cecum. Among sampled birds of comparable body mass, mean cecal length is significantly longer in herbivorous species than in carnivorous ones (p = 0.008), presumably allowing the extraction of nutrients without the burden of fermenting bulky masses of dietary fiber. Exceptions to this trend, however, suggest that avian ceca are functionally complex and may have additional roles in water balance and nitrogen recycling.

The primate appendix: a reassessment

The presence of a vermiform appendix is often cited as a shared, derived character uniting the Hominoidea (apes and humans). However, appendix-like structures have been reported for many other primate taxa. A review of the literature reveals that the confusion arises because several different, and sometimes contradictory, criteria are enlisted to distinguish an appendix. The measures most frequently used to define this structure are gross shape and certain aspects of histology (e.g., lymphoid concentration). Unfortunately, descriptions of shape lack quantification, and histological thin-sections have not been studied for many primate taxa. In addition, although lymphoid concentration in the human appendix is known to vary considerably with age, this information is rarely reported in the primate literature. Given these complications, additional studies on the morphology and ontogeny of this region are warranted. This research will lead to a more accurate definition of the vermiform appendix. Most authors currently describe this feature as a narrow diverticulum of the cecum with thick walls and concentrated lymphoid tissue. However, the presence of thick mucosal layers and appreciable lymphoid tissue in taxa lacking appendices (e. g., Saguinus, Cercocebus) suggests that these features may be primitive primate traits. If so, wall thickness and lymphoid concentration cannot be used to define the vermiform appendix. These results suggest that a more rigorous definition of the appendix is requisite for this feature to be used in primate systematics.

Non-heme (Fe3+) in the lung increases with age in both humans and rats

Increasing non-heme iron concentrations in host tissues are potentially significant, because they can be associated with an increased risk of injury including infections, fibrosis, and neoplasms. We tested the hypothesis that non-heme (Fe3+) in the lung increases with age in both humans and rats. Human tissue was collected at autopsy before fixation occurred. The total number of specimens was 131 with 78 nonsmokers and 53 smokers. Tissue was hydrolyzed in 3 N hydrochloric acid and 10% trichloroacetic acid. Supernatant (Fe3+) was measured with a thiocyanate assay. Non-heme (Fe3+) increased with age in nonsmokers. The correlation coefficient between lung (Fe3+) and age in the nonsmokers was 0.58 (p < 0.0001). Iron stains were negative, whereas those for ferritin demonstrated increased uptake with aging. Smokers had significantly greater non-heme (Fe3+) relative to nonsmokers (101.1 and 46.0 micromol/L respectively; T = 11.44, p < 0.0001). Lung non-heme (Fe3+) in smokers also increased with age (r = 0.75; p < 0.0001). Iron stains demonstrated uptake in the proximity of retained pigmented material. Ferritin stains demonstrated intense uptake in both the macrophages and the airway and alveolar epithelium of smokers. An animal model was also analyzed for an effect of aging on lung non-heme (Fe3+). At specified times between 30 and 186 days of age, rats (n = 48) were anesthetized and exsanguinated, and the lungs were excised. In rats, similar to humans, a positive correlation was seen between lung non-heme (Fe3+) and age (r = 0.73; p = 0.007). Stains for iron in rat lung were uniformly negative, whereas those for ferritin demonstrated increased uptake by airway and alveolar epithelium in older rats. We conclude that non-heme (Fe3+) in lung tissue increases with age in both humans and rats. Elevations in lung non-heme (Fe3+) could contribute to an increased incidence of pneumonias, pulmonary fibrosis, and bronchogenic carcinoma observed among older individuals.