Renal anatomy of the manatee, Trichechus manatus, Linnaeus

Histological study of seventeen organs from dugong (Dugong dugon)

Background

Dugongs are marine mammals with a crescent-shaped tail fluke and a concave trailing margin that belong to the family Dugongidae., They are distributed widely in the warm coastal waters of the Indo-Pacific region. Importantly, the population of dugongs has decreased over the past decades as they have been classified as rare marine mammals. Previous studies have investigated the habitat and genetic diversity of dugongs. However, a comprehensive histological investigation of their tissue has not yet been conducted. This study provides unique insight into the organs of dugongs and compares them with other mammal species.

Methods

Tissue sections were stained with Harris's hematoxylin and eosin Y. The histological structure of 17 organ tissues obtained from eight systems was included in this study. Tissue sections were obtained from the urinary system (kidney), muscular system (striated skeletal muscle and smooth muscle), cardiovascular system (cardiac muscle (ventricle), coronary artery, and coronary vein), respiratory system (trachea and lung), gastrointestinal system (esophagus, stomach, small intestine, liver, and pancreas), reproductive system (testis), lymphatic system (spleen and thymus), and endocrine system (pancreas).

Results

While most structures were similar to those of other mammal species, there were some differences in the tissue sections of dugongs when compared with other mammalian species and manatees. These include the kidneys of dugongs, which were non-lobular and had a smooth, elongated exterior resulting in a long medullary crest, whereas the dugong pyloric epithelium did not have overlying stratified squamous cells and was noticably different from the Florida manatee.

Discussion

Histological information obtained from various organs of the dugong can serve as an essential foundation of basal data for future microanatomical studies. This information can also be used as high-value data in the diagnosis and pathogenesis of sick dugongs or those with an unknown cause of death.

Baseline urinalysis results in 32 healthy Antillean manatees (Trichechus manatus manatus)

OBJECTIVE

To describe results of analysis of free-catch urine samples collected from Antillean manatees (Trichechus manatus manatus) under human care in the Caribbean.

ANIMALS

32 Antillean manatees in 5 Caribbean oceanaria and rescue centers.

PROCEDURES

Urine samples were obtained by opportunistic free catch during physical examination or through the use of operant conditioning procedures. Urinalyses consisted of macro- and microscopic evaluations, biochemical analyses with test strips, and refractometry. Results were compared for manatees grouped on the basis of age, sex, and habitat.

RESULTS

Urine samples were typically clear, straw colored, and alkaline (mean pH, 8.0); had a urinoid odor and low specific gravity (mean, 1.010); and had results on qualitative test strips that were consistently negative for the presence of glucose, bilirubin, ketones, proteins, nitrites, RBCs, and WBCs. Microscopically, the mean ± SD number of RBCs and WBCs/hpf was 0.5 ± 0.3 RBCs/hpf and 1.1 ± 1.5 WBCs/hpf. The presence of some epithelial cells and crystals was typical. Spermatozoa were found in urine from 1 of 15 sexually mature males, and parasite larvae and eggs were found in urine from 2 manatees.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of the present study yielded the first compilation of baseline urinalysis values in healthy Antillean manatees under human care, which, when combined with physical examination and other diagnostic procedures, can help in monitoring the health of these animals. We encourage the use of free-catch urine collection methods, as used in the present study, for routine urinalyses of manatees under human care in zoos, aquaria, or rescue centers.

Osmoregulation and electrolyte balance in a fully marine mammal, the dugong (Dugong dugon)

Dugongs (Dugong dugon) are fully marine mammals that live independently of fresh water so must balance water and electrolytes in a hyperosmotic environment. To investigate osmoregulation, matched plasma and urine from 51 live wild dugongs were analysed for osmolality, major electrolytes (Na⁺, Cl^-, K⁺), urea, creatinine, and glucose. Maximum urine osmolality (1468 mOsm kg ^-1) and Na⁺, K⁺, and Cl^- concentrations (757, 131.3, 677 mmol L^-1, respectively) indicate that dugongs are capable of concentrating urine above seawater and could potentially realise a net gain of free water from drinking seawater. However, mean urine osmolality of 925.4 (± 46.6) mOsm kg^-1 suggests that mariposia is unlikely to be an important osmoregulatory mechanism. Dugongs may obtain enough preformed water from their seagrass diet and metabolic oxidation to maintain homeostasis. Mean plasma osmolality of 339.6 (± 1.8) mOsm kg^-1 is higher than in the related manatees but within the range for fully marine cetaceans. Relatively high mean plasma Na⁺ (175.5 ± 1.7 mmol L^-1) and K⁺ (6.9 ± 0.1 mmol L^-1), as well as mean urinary Na⁺ (469.6 ± 22.5 mmol L^-1) and K⁺ levels (32.5 ± 4.5 mmol L^-1) may reflect a salt-rich seagrass diet. Pregnant females had higher mean plasma osmolality (355.3 ± 4.9 mmol L^-1) than non-pregnant females and males (337.9 ± 1.7 mOsm kg^-1), suggesting that fluid retention was not a feature of pregnancy. Further research on water intake and endocrinology will enhance our understanding of osmoregulation in dugongs.

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.

Stress physiology in marine mammals: how well do they fit the terrestrial model?

Stressors are commonly accepted as the causal factors, either internal or external, that evoke physiological responses to mediate the impact of the stressor. The majority of research on the physiological stress response, and costs incurred to an animal, has focused on terrestrial species. This review presents current knowledge on the physiology of the stress response in a lesser studied group of mammals, the marine mammals. Marine mammals are an artificial or pseudo grouping from a taxonomical perspective, as this group represents several distinct and diverse orders of mammals. However, they all are fully or semi-aquatic animals and have experienced selective pressures that have shaped their physiology in a manner that differs from terrestrial relatives. What these differences are and how they relate to the stress response is an efflorescent topic of study. The identification of the many facets of the stress response is critical to marine mammal management and conservation efforts. Anthropogenic stressors in marine ecosystems, including ocean noise, pollution, and fisheries interactions, are increasing and the dramatic responses of some marine mammals to these stressors have elevated concerns over the impact of human-related activities on a diverse group of animals that are difficult to monitor. This review covers the physiology of the stress response in marine mammals and places it in context of what is known from research on terrestrial mammals, particularly with respect to mediator activity that diverges from generalized terrestrial models. Challenges in conducting research on stress physiology in marine mammals are discussed and ways to overcome these challenges in the future are suggested.

METHODS USED DURING GROSS NECROPSY TO DETERMINE WATERCRAFT-RELATED MORTALITY IN THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

Between 1993 and 2003, 713 (24%) of 2,940 dead Florida manatees (Trichechus manatus latirostris) recovered from Florida waters and examined were killed by watercraft-induced trauma. It was determined that this mortality was the result of watercraft trauma because the external wound patterns and the internal lesions seen during gross necropsy are recognizable and diagnostic. This study documents the methods used in determining watercraft-related mortality during gross necropsy and explains why these findings are diagnostic. Watercraft can inflict sharp- and blunt-force trauma to manatees, and both types of trauma can lead to mortality. This mortality may be a direct result of the sharp and blunt forces or from the chronic effects resulting from either force. In cases in which death is caused by a chronic wound-related complication, the original incident is usually considered to be the cause of death. Once a cause of death is determined, it is recorded in an extensive database and is used by Federal and state managers in developing strategies for the conservation of the manatee. Common sequelae to watercraft-induced trauma include skin lesions, torn muscles, fractured and luxated bones, lacerated internal organs, hemothorax, pneumothorax, pyothorax, hydrothorax, abdominal hemorrhage and ascites, and pyoperitoneum.

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.

Kidney of giraffes

This study focuses on certain aspects of the renal structure of the giraffe, with some implications as to its function. About 4,000 collecting ducts open at the truncated end of a curved crest that juts into the renal pelvis as the inner medulla (IM). Extensions of the pelvis pass between the medullary (MP) and vascular (VP) processes almost to the corticomedullary border. The MPs contain an IM and an outer medulla (OM) containing clusters of capillaries (vascular bundles). The VPs contain the interlobar arteries and veins. All of the IM and almost all of the OM, with its vascular bundles, are bathed with pelvic urine. The cortex comprises 63% of the parenchyma. The OM has nine times the mass of the IM. The IM comprises 4% of the parenchyma. The ratio of mass of the adult cortex to the medulla is 1.7:1.0, and the number of glomeruli per kidney is 6.6 x 10(6). Glomerular mass is 6.2-6.7% of renal mass in the adult and 5.2% in the 6-month-old calf. The dimensions of the glomerular capsules are the same across the thickness of the cortex. Every terminal collecting duct drains an estimated 1,650 nephrons. In the adult giraffe the ratio of thickness of the muscularis of the main renal artery (RA) to its diameter is 0.117 (right RA) and 0.132 (left RA). These ratios are close to those in rhinoceros and ox but greater than in man. The visceral arteries (celiac, anterior mesenteric, and renal) have about the same muscularis : diameter ratio. Giraffes have arterial hypertension, but atherosclerosis is apparently absent and serum lipid fractions are low.

Osmoregulation in Marine Mammals

Osmoregulation in marine mammals has been investigated for over a century; however, a review of recent advances in our understanding of water and electrolyte balance and of renal function in marine mammals is warranted. The following topics are discussed: (i) kidney structure and urine concentrating ability, (ii) sources of water, (iii) the effects of feeding, fasting and diving, (iv) the renal responses to infusions of varying salinity and (v) hormonal regulation. The kidneys of pinnipeds and cetaceans are reniculate in structure, unlike those of terrestrial mammals (except bears), but this difference does not confer any greater concentrating ability. Pinnipeds, cetaceans, manatees and sea otters can concentrate their urine above the concentration of sea water, but only pinnipeds and otters have been shown to produce urine concentrations of Na+ and Cl−1 that are similar to those in sea water. This could afford them the capacity to drink sea water and not lose fresh water. However, with few exceptions, drinking is not a common behavior in pinnipeds and cetaceans. Water balance is maintained in these animals via metabolic and dietary water, while incidental ingestion and dietary salt may help maintain electrolyte homeostasis. Unlike most other aquatic mammals, sea otters commonly drink sea water and manatees frequently drink fresh water. Among the various taxonomic groups of marine mammals, the sensitivity of the renin–angiotensin–aldosterone system appears to be influenced by the availability of Na+. The antidiuretic role of vasopressin remains inconclusive in marine mammals, while the natriuretic function of atrial natriuretic peptide has yet to be examined. Ideas on the direction of future studies are presented.

Estimation of water turnover rates of captive West Indian manatees (Trichechus manatus) held in fresh and salt water

The ability of West Indian manatees (Trichechus manatus) to move between fresh and salt water raises the question of whether manatees drink salt water. Water turnover rates were estimated in captive West Indian manatees using the deuterium oxide dilution technique. Rates were quantified in animals using four experimental treatments: (1) held in fresh water and fed lettuce (N=4), (2) held in salt water and fed lettuce (N=2), (3) acutely exposed to salt water and fed lettuce (N=4), and (4) chronically exposed to salt water with limited access to fresh water and fed sea grass (N=5). Animals held in fresh water had the highest turnover rates (145+/−12 ml kg-1 day-1) (mean +/− s.e.m.). Animals acutely exposed to salt water decreased their turnover rate significantly when moved into salt water (from 124+/−15 to 65+/−15 ml kg-1 day-1) and subsequently increased their turnover rate upon re-entry to fresh water (146+/−19 ml kg-1 day-1). Manatees chronically exposed to salt water had significantly lower turnover rates (21+/−3 ml kg-1 day-1) compared with animals held in salt water and fed lettuce (45+/−3 ml kg-1 day-1). Manatees chronically exposed to salt water and fed sea grass had very low turnover rates compared with manatees held in salt water and fed lettuce, which is consistent with a lack of mariposia. Manatees in fresh water drank large volumes of water, which may make them susceptible to hyponatremia if access to a source of Na+ is not provided.

Kidneys of the killerwhale and significance of reniculism

BACKGROUND

The kidneys of all Cetacea are composed of many small relatively independent kidneys (renicules) containing considerable interrenicular tissue. Although reniculism is not entirely confined to the Cetacea, it is desirable to consider the possible advantage of reniculism to mammals of gigantic size. The kidneys of the killerwhale, Orcinus orca, are compared from this standpoint to the kidneys of diverse mammals.

METHODS

The specific renal parenchymal mass, glomerular counts, glomerular size, and specific glomerular mass of the killerwhale are measured and compared quantitatively (statistically) with similar data from numerous diverse mammals. Simultaneously, a method is described for enumerating the renicules of a cetacean kidney.

RESULTS

Specific parenchymal mass of a killerwhale adult's two kidneys (0.33%) is close to the expected value for mammals of its adult body mass (2,087 kg). The diameter of the adult's glomerular capsules (153 microm) is strikingly less than that expected from its body mass (regression equation and graph for mammals in general). However, the number of glomeruli per kidney (approximately 100 x 10[6]) is markedly greater than that for mammals of its body mass (regression equation and graph for mammals in general) and is the first such count for a cetacean. The total glomerular mass relative to parenchymal renal mass of the O. orca infant and adult is, nevertheless, 5.5% and 6.0%, respectively, and is thus close to the general mammalian value of approximately 5%.

CONCLUSIONS

Organization of a cetacean kidney into numerous renicules does not increase specific renal parenchymal mass or specific glomerular mass. The apparent advantage of numerous independent renicules is the limit that is afforded for length of tubules in the necessarily large kidneys of gigantic mammals.

Kidney of elephants

BACKGROUND

Elephants are an important and isolated order. Their kidneys need substantial investigation and hitherto have not been portrayed even by a pyelogram.

METHODS

Pyelograms and injection of vessels with colored acrylic emulsions were done initially. Dissection was under fiberoptics using a dissecting microscope with frequent measurements. Special areas were cut for microscopy (light and electron) and photography. Glomerular counts were done by macerating weighted pieces of cortex and later finding the cortical fraction of the renal parenchyma.

RESULTS

The elephant kidney is devoid of dorsoventral symmetry. It is composed of 8 +/- 2 lobes separated by fine interlobar septa. There is no reduction of lobes with maturity. The pelvis bifurcates at the sinus into primary branches or infundibula which dispatch a secondary branch or infundibulum into every lobe. Interlobar arteries and veins, nerves, fat, and connective tissue generally accompany every secondary infundibulum into its lobe. A major branch of the renal artery may perforate the renal capsule and course to the cortico-medullary (C-M) border independently of the secondary infundibulum to that lobe. The number of glomeruli per kidney is approximately 15 x 10(6). In adults the glomerular mass is 4.9 +/- 0.5% of the renal parenchyma and 6.7 +/- 0.3% of the cortex. Areae cribrosae occur generally at low papillae. They are the outlets of numerous terminal collecting ducts which may be accompanied by a tubus maximus (T.M.) A T.M. of diameter 1.6 mm and length 10 mm may act as the only substitute for an area cribrosa. Wide anastomoses between the two main renal veins occur within the renal sinus. Intralobar arteries and veins often course right through the outer medulla to and from, respectively, the C-M border.

CONCLUSIONS

Anatomically, an elephant's kidneys appear to be able to concentrate urine only moderately. Their kidneys tend to resemble those of the manatee but not of the dugong.

Renal anatomy of the pigmy hippopotamus (Choeropsis liberiensis): an overview

The adult kidney of Choeropsis liberiensis is 74.8% cortex and 22.9% medulla. The neonatal cortex is relatively less. A single kidney has about 3 x 10(6) glomeruli. These form 5% of renal mass in the adult but more so in neonates. The primary tubus maximus, TM1, follows the lateral curvature of the kidney. It gives off, toward the hilum, dorso-ventrally paired secondary tubi maximi, TM2. The tubi are a single layer of high cuboidal epithelium from which terminal collecting ducts arise throughout the surrounding inner medulla. The cranial and caudal limbs of TM1 open at a diminutive pelvis which receives a small papilla in continuity with TM1. The medulla is continuous although variably distorted by folds of cortex at the lateral curvature of the kidney. The renal lobes project toward the medial border and consist of cortex, medulla and TM2. The lobar cortex is continuous with the common cortex of the lateral curvature. The kidney, although strongly lobed, has no infundibula or rencules. A main peripheral vein courses medial and parallel to TM1. It is apparently a modified large arcuate vein and receives arcuate and interlobar tributaries. At the level of the papilla it joins the main renal vein. The arterial supply is mainly by interlobar arteries but there are also sizeable external perforator arteries which branch from the main renal artery and perforate the cortex of lobes about the hilum. The source of the arteries is illustrated.

Further studies on the kidney of the hook-lipped African rhinoceros, Diceros bicornis

A healthy, pregnant Diceros bicornis (No. 29455), with histologically normal but relatively large kidneys containing a correspondingly large number of nephrons, died suddenly from an injury. Renal lobation was studied partly from serial transverse cuts across the kidney. The fibromuscular pelvic conduits, which are a craniocaudal bifurcation of the ureter, are associated with prominent longitudinally disposed paraconduital veins which anastomose with the interlobar veins. The arcuate veins open widely into the paraconduital veins. The latter drain into the major tributaries of the renal vein at the renal sinus. The interlobar arteries enter the parenchyma through the interlobar septa. These arteries release internal perforator branches, through the septa, which pass to the corticomedullary border, branch along that border as arcuate arteries, and release cortical branches centrifugally. All these branches give off twigs to the glomeruli. Relative renal mass of mammals is inversely proportional to their adult body mass. This is indicated by a regression line which includes rhinoceroses. D. bicornis No. 29455, accordingly, has exceptionally large kidneys. The mesonephros of the 75 mm fetus of D. bicornis has mature glomeruli and tubules. The metanephros has pelvic conduits, paraconduital veins, but, as yet, no medullary loops.

The kidney of tapirs: a macroscopical study

The renal cortex of tapirs, water-loving primordial ungulates, was continuous, nonlobed, and about 80% of renal mass in adult and 71% in term-neonate. In the neonates even the peripheral glomeruli were moderately mature. Tapirus bairdi had about 4 million glomeruli per kidney and T. pinchaque about 3 million smaller glomeruli. Number of glomeruli per gm of cortex was 12,444 in T. bairdi and 13,400 in T. pinchaque. Cortical loops were common in the medullary rays. The medulla was the simple crest-type. The terminal collecting ducts (T.C.D.) opened separately at the crest and not into a tubus maximus. The "outer stripe" of the outer medulla apparently was telescoped into the deep cortex. The medullary loops turned at a thick portion and at nearly all levels of the medulla. The medullary crest was lined by urothelium which extended into the ends of the T.C.D. Otherwise the T.C.D. were made of columnar epithelium. The pelvic urothelium was continuous with that of the medullary crest at the dorsal and ventral fornices. The fornices were well within the inner medulla. Hence only inner medulla could be exposed to pelvic urine. The hilar arteries, unlike the other two perissodactyl families (rhinoceri and equids), passed through the cortico-medullary (C-M) border and some large arteries and veins passed through the outer medulla to and from the C-M border without branches or tributaries. Unlike kidneys with a medullary crest in diverse eutherian mammals, tapirs lacked pelvic extensions along the major intrarenal blood vessels and thus lacked pelvic intervascular eminences.

Renal morphology of the hook-lipped African rhinoceros, Diceros bicornis, Linnaeus

The kidney of Diceros bicornis has about 60 lobes, all appearing peripherally. These are separated by interlobar septa, except for small septal defects through which tubules pass. Renal capsule and interlobar septa are fibromuscular and contain small blood vessels. The kidney is about 65% cortex. It contains about 12.5 x 10(6) glomeruli, which form about 7% of the cortical mass and 4.6% of the renal mass. Diameter of a glomerular capsule is about 244 microns, there being no difference in size across the cortex in these adults. The ureter bifurcates into a cephalic and a caudal, fibromuscular, urothelial-lined conduit, into which open about 23 urothelial-lined infundibula. The common large collecting duct, or tubus maximus, of every lobe opens at the apex of its infundibulum. Two tubi may join into one infundibulum. The tubi and their terminal collecting ducts (of Bellini) are part of the inner medulla. Musculature of conduits and infundibula is largely longitudinal. The calyx may be represented by a circular muscle bundle near the apex of every infundibulum. The large intralobar veins are partly adherent to their infundibulum and calyx and receive arcuate veins via valved orifices. Most branches of the renal artery enter via the interlobar septa. Within a septum they branch again and also supply numerous perforators, which thence enter the cortex. Remaining branches of the renal artery enter cortex directly from without. A fibromuscular scaffolding lies deep to arcuate veins where they contact medulla. Where these veins contact cortical tubules; however, their walls become merely endothelium, like the walls of the interlobular veins.