Snorkel breathing in the elephant explains the unique anatomy of its pleura

Human larynx motor cortices coordinate respiration for vocal-motor control

Vocal flexibility is a hallmark of the human species, most particularly the capacity to speak and sing. This ability is supported in part by the evolution of a direct neural pathway linking the motor cortex to the brainstem nucleus that controls the larynx the primary sound source for communication. Early brain imaging studies demonstrated that larynx motor cortex at the dorsal end of the orofacial division of motor cortex (dLMC) integrated laryngeal and respiratory control, thereby coordinating two major muscular systems that are necessary for vocalization. Neurosurgical studies have since demonstrated the existence of a second larynx motor area at the ventral extent of the orofacial motor division (vLMC) of motor cortex. The vLMC has been presumed to be less relevant to speech motor control, but its functional role remains unknown. We employed a novel ultra-high field (7T) magnetic resonance imaging paradigm that combined singing and whistling simple melodies to localise the larynx motor cortices and test their involvement in respiratory motor control. Surprisingly, whistling activated both 'larynx areas' more strongly than singing despite the reduced involvement of the larynx during whistling. We provide further evidence for the existence of two larynx motor areas in the human brain, and the first evidence that laryngeal-respiratory integration is a shared property of both larynx motor areas. We outline explicit predictions about the descending motor pathways that give these cortical areas access to both the laryngeal and respiratory systems and discuss the implications for the evolution of speech.

Suction feeding by elephants

Despite having a trunk that weighs over 100 kg, elephants mainly feed on lightweight vegetation. How do elephants manipulate such small items? In this experimental and theoretical investigation, we filmed elephants at Zoo Atlanta showing that they can use suction to grab food, performing a behaviour that was previously thought to be restricted to fishes. We use a mathematical model to show that an elephant's nostril size and lung capacity enables them to grab items using comparable pressures as the human lung. Ultrasonographic imaging of the elephant sucking viscous fluids show that the elephant's nostrils dilate up to [Formula: see text] in radius, which increases the nasal volume by [Formula: see text]. Based on the pressures applied, we estimate that the elephants can inhale at speeds of over 150 m s^-1, nearly 30 times the speed of a human sneeze. These high air speeds enable the elephant to vacuum up piles of rutabaga cubes as well as fragile tortilla chips. We hope these findings inspire further work in suction-based manipulation in both animals and robots.

Histology of 24 organs from Asian elephant calves (Elephas maximus)

Background

Elephants are the largest and heaviest living terrestrial animals, but information on their histology is still lacking. This study provides a unique insight into the elephant's organs and also provides a comparison between juvenile Asian elephants and adult Asian elephants or other species. Here we report on the histological structure of 24 organs, including the skin, brain (cerebrum, cerebellar hemisphere, vermis, thalamus, midbrain), spinal cord, sciatic nerve, striated skeletal muscle, cardiac muscle, bone (flat bone and long bone), cartilage (hyaline cartilage and fibrocartilage), heart (right atrium, right ventricle), blood vessels (aorta, pulmonary artery and caudal vena cava), trunk, trachea, lung, tongue, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum, colon, rectum), liver and pancreas, kidney, ovary, uterus (body and horn) and spleen of two juvenile Asian elephants.

Methods

Tissue sections were stained with Harris's hematoxylin and eosin Y.

Results

While almost all structures were similar to those of other species or adult elephants, some structures were different from other mammalian species, such as: plexiform bone was found in flat bone only; a thin trachealismuscle was observed in the trachea; and no serous or mucinous glands were found in the submucosa of the trachea.

Discussion

Histological information from various organs can serve as an important foundation of basal data for future microanatomical studies, and help in the diagnosis and pathogenesis in sick elephants or those with an unknown cause of death.

Familial pneumothorax: towards precision medicine

One in 10 patients suffering from primary spontaneous pneumothoraces has a family history of the disorder. Such familial pneumothoraces can occur in isolation, but can also be the presentation of serious genetic disorders with life-threatening vascular or cancerous complications. As the pneumothorax frequently precedes the more dangerous complications by many years, it provides an opportunity to intervene in a focused manner, permitting the practice of precision medicine. In this review, we will discuss the clinical manifestations and underlying biology of the genetic causes of familial pneumothorax.

Serum osmolality and effects of water deprivation in captive Asian elephants (Elephas maximus)

Serum from 21 healthy, captive Asian elephants (Elephas maximus) was evaluated by measured and calculated osmolality. Serum osmolality results for this population of Asian elephants had a median of 261 mOsm/kg and an interquartile interval of 258-269 mOsm/kg when measured by freezing point osmometry and a median of 264 mOsm/kg and an interquartile interval of 257-269 mOsm/kg when measured by vapor pressure osmometry. These values are significantly lower than values reported in other mammalian species and have important diagnostic and therapeutic implications. Calculated osmolality produced unreliable results and needs further study to determine an appropriate formula and its clinical application in this species. A 16-hr water deprivation test in 16 Asian elephants induced a small, subclinical, but statistically significant increase in measured serum osmolality. Serum osmolality, blood urea nitrogen, and total protein by refractometer were sensitive indicators of hydration status. Serum osmolality measurement by freezing point or vapor pressure osmometry is a useful adjunct to routine clinical tests in the diagnostic evaluation of elephants.

Pulmonary circulation in extreme environments

The pulmonary circulation is subject to direct challenge from both altered pressure and altered gravity. To efficiently exchange gas, the pulmonary capillaries must be extremely thin-walled and directly exposed to the alveolar space. Thus, alterations in ambient pressure are directly transmitted to the capillaries with the potential to alter pulmonary blood flow. To produce ventilation, the mammalian lung must expand and contract, and so it is a highly compliant structure. Thus, because the capillaries are contained in the alveolar walls, alterations in the apparent gravitational force deform the lung and directly affect pulmonary blood flow both through lung deformation and through changes in the hydrostatic pressure distribution in the lung. High gravitational forces are encountered in the aviation environment, while gravity is absent in spaceflight. Diving subjects the lung to large increases in ambient pressure, while large reductions in pressure occur, often associated with alterations in oxygen level and airway pressure, in aviation. This article reviews the effects of alterations in both gravity and ambient pressure on the pulmonary circulation.

Implications of an avian-style respiratory system for gigantism in sauropod dinosaurs

In light of evidence for avian-like lungs in saurischian dinosaurs, the physiological implications of cross-current gas exchange and voluminous, highly heterogeneous lungs for sauropod gigantism are critically examined. At 12 ton the predicted body temperature and metabolic rate of a growing sauropod would be similar to that of a bird scaled to the same body weight, but would increase exponentially as body mass increases. Although avian-like lung structure would be consistent with either a tachymetabolic-endothermic or a bradymetabolic-gigantothermic model, increasing body temperature requires adjustments to avoid overheating. We suggest that a unique sauropod structure/function unit facilitated the evolution of gigantism. This unit consisted of (1) a reduction in metabolic rate below that predicted by the body temperature, akin to thermal adaptation as seen in extant squamates, (2) presence of air-filled diverticula in the long neck and in the visceral cavity, and (3) low activity of respiratory muscles coupled with the high efficiency of cross-current gas exchange.

Foetal age determination and development in elephants

Elephants have the longest pregnancy of all mammals, with an average gestation of around 660 days, so their embryonic and foetal development have always been of special interest. Hitherto, it has only been possible to estimate foetal ages from theoretical calculations based on foetal mass. The recent development of sophisticated ultrasound procedures for elephants has now made it possible to monitor the growth and development of foetuses of known gestational age conceived in captivity from natural matings or artificial insemination. We have studied the early stages of pregnancy in 10 captive Asian and 9 African elephants by transrectal ultrasound. Measurements of foetal crown-rump lengths have provided the first accurate growth curves, which differ significantly from the previous theoretical estimates based on the cube root of foetal mass. We have used these to age 22 African elephant foetuses collected during culling operations. Pregnancy can be first recognized ultrasonographically by day 50, the presumptive yolk sac by about day 75 and the zonary placenta by about day 85. The trunk is first recognizable by days 85-90 and is distinct by day 104, while the first heartbeats are evident from around day 80. By combining ultrasonography and morphology, we have been able to produce the first reliable criteria for estimating gestational age and ontological development of Asian and African elephant foetuses during the first third of gestation.

A tribute to John Burnard West

John West is well known to the "Hypoxia" community for his many contributions to the physiology and Pathophysiology of high altitude and for his leadership of the 1981 American Medical Research Expedition to Everest. He is known to the wider medical world for his researches into respiratory physiology especially gas exchange in the lung and perhaps even more for his numerous books on these topics. His publication list numbers over 400 original papers. His research career started in the UK but since 1969 he has been Professor of Medicine at UCSD, leading a very productive team at La Jolla. He has been honoured by numerous prizes and named lectureships, the latest honour being to be elected to the Institute of Medicine, National Academies (USA).

Morphological evidence of marine adaptations in human kidneys

Amongst primates, kidneys normally exhibiting lobulated, multipyramidal, medullas is a unique attribute of the human species. Although, kidneys naturally multipyramidal in their medullary morphology are rare in terrestrial mammals, kidneys with lobulated medullas do occur in: elephants, bears, rhinoceroses, bison, cattle, pigs, and the okapi. However, kidneys characterized with multipyramidal medullas are common in aquatic mammals and are nearly universal in marine mammals. To avoid the deleterious effects of saline water dehydration, marine mammals have adaptively thickened the medullas of their kidneys--which enhances their ability to concentrate excretory salts in the urine. However, the lobulation of the kidney's medullary region in marine mammals appears to be an adaptation to expand the surface area between the medulla and the enveloping outer cortex in order to increase the volume of marine dietary induced hypertonic plasma that can be immediately processed for the excretion of excess salts and nitrogenous waste. A phylogenetic review of freshwater aquatic mammals suggest that most, if not all, nonmarine aquatic mammals inherited the medullary pyramids of their kidneys from ancestors who originally inhabited, or frequented, marine environments. So this suggest that most, if not all, aquatic mammals exhibiting kidneys with lobulated medullas are either marine adapted--or are descended from marine antecedents. Additionally, a phylogenetic review of nonhuman terrestrial mammals possessing kidneys with multipyramidal medullas suggest that bears, elephants and possibly rhinoceroses, also, inherited their lobulated medullas from semiaquatic marine ancestors. The fact that several terrestrial mammalian species of semiaquatic marine ancestry exhibit kidneys with multipyramidal medullas, may suggest that humans could have, also, inherited the lobulated medullas of their kidneys from coastal marine ancestors. And a specialized marine diet in ancient human ancestry could, also, explain the reactivation and enumeration of corporeal eccrine sweat glands and the copious secretion of salt tears. The substantial loss of genetic variation in humans relative to other hominoid primates, combined with the apparent isolation of early Pliocene human ancestors from particular retroviruses that infected all other African primate species, may suggest that such a semiaquatic marine phase, during the emergence of Homo, may have occurred on an island off the coast of Africa during the early Pliocene.

Pleural mechanics and fluid exchange

The pleural space separating the lung and chest wall of mammals contains a small amount of liquid that lubricates the pleural surfaces during breathing. Recent studies have pointed to a conceptual understanding of the pleural space that is different from the one advocated some 30 years ago in this journal. The fundamental concept is that pleural surface pressure, the result of the opposing recoils of the lung and chest wall, is the major determinant of the pressure in the pleural liquid. Pleural liquid is not in hydrostatic equilibrium because the vertical gradient in pleural liquid pressure, determined by the vertical gradient in pleural surface pressure, does not equal the hydrostatic gradient. As a result, a viscous flow of pleural liquid occurs in the pleural space. Ventilatory and cardiogenic motions serve to redistribute pleural liquid and minimize contact between the pleural surfaces. Pleural liquid is a microvascular filtrate from parietal pleural capillaries in the chest wall. Homeostasis in pleural liquid volume is achieved by an adjustment of the pleural liquid thickness to the filtration rate that is matched by an outflow via lymphatic stomata.

Meissner corpuscles and somatosensory acuity: The prehensile appendages of primates and elephants

Meissner corpuscles (MCs) are specialized mechanoreceptors located exclusively in the papillae of glabrous skin. They are confined largely to cutaneous pads of the extremities and respond to transient, phasic, or vibratory stimuli. Though absent in most eutherian taxa, MCs are reported in all primates studied, being most developed in modern humans. The location of MCs between the internal ridges of the epidermis indicates they are well situated to detect friction or deformation at the external surface. Accordingly, MCs are hypothesized to provide primates generally with an enhanced tactile perception. However, the selective pressures favoring greater somatosensory acuity in primates are seldom considered. Interestingly, primate digital dexterity varies greatly. In general, dexterity improves with the extent to which foraging requires food manipulation or textural evaluation. This observation implies that MC density could vary accordingly. Here we report on the density of MCs in five anthropoid taxa selected to represent diverse dietary regimes. Results show that greater MC density correlates with the extent to which primates are frugivorous; however, locomotor and/or phylogenetic effects cannot be discounted.

Fetal lung development in the elephant reflects the adaptations required for snorkeling in adult life

The adult elephant is unique among mammals in that the pleural membranes are thickened and the pleural cavity is obliterated by connective tissue. It has been suggested that this peculiar anatomy developed because the animal can snorkel at depth, and this behavior subjects the microvessels in the parietal pleura to a very large transmural pressure. To investigate the development of the parietal pleura, the thickness of the endothoracic fascia (ET) was measured in four fetal African elephants of approximate gestational age 111-130 days, and the appearances were compared with those in human, rabbit, rat and mouse fetuses of approximately the same stage of lung organogenesis. The mean thicknesses of ET in the elephant, human, rabbit, rat and mouse were 403, 53, 29, 27 and 37 microm, respectively. This very early development of a thick parietal pleura in the elephant fetus is consistent with the hypothesis of a long history of snorkeling in the elephant's putative aquatic ancestors.

Arterial blood gas control in the upright versus recumbent Asian elephant

In the elephant, there is concern that lateral recumbency (LR) impairs respiratory muscle and lung function resulting in clinically significant arterial hypoxemia. Using healthy adult female Asian elephants (Elephas maximus, n=6), the hypothesis was tested that, given the O(2) binding characteristics of elephant blood, substantial reductions in arterial O(2) pressure (Pa(O(2))) in LR could be tolerated without lowering arterial O(2) content appreciably. Fifteen minutes of LR decreased Pa(O(2)) from 103+/-2 (upright, U) to 77+/-4 mmHg (P<0.05) and hemoglobin O(2) saturation (U, 97.8+/-0.1, LR, 95.3+/-0.5%, P<0.05). However, due to a recumbency-induced hemoconcentration, arterial O(2) content was unchanged (U, 18.2+/-2.4, LR, 18.3+/-2.1 ml O(2) per 100 ml). In addition, there was a mild hyperventilation in LR that reduced arterial CO(2) pressure (P(CO(2))) from 39.4+/-0.3 to 37.1+/-1.0 mmHg (P<0.05). These data indicate that the Asian elephant can endure at least short periods of LR without lowering arterial O(2) content.

Why doesn't the elephant have a pleural space?

The elephant is the only mammal whose pleural space is obliterated by connective tissue. This has been known for 300 years but never explained. The elephant is also the only animal that can snorkel at depth. The resulting pressure differences require changes in the pleural membranes and pleural space.