Osmoregulation and Excretion

Abstract

The article discusses advances in osmoregulation and excretion with emphasis on how multicellular animals in different osmotic environments regulate their milieu intérieur. Mechanisms of energy transformations in animal osmoregulation are dealt with in biophysical terms with respect to water and ion exchange across biological membranes and coupling of ion and water fluxes across epithelia. The discussion of functions is based on a comparative approach analyzing mechanisms that have evolved in different taxonomic groups at biochemical, cellular and tissue levels and their integration in maintaining whole body water and ion homeostasis. The focus is on recent studies of adaptations and newly discovered mechanisms of acclimatization during transitions of animals between different osmotic environments. Special attention is paid to hypotheses about the diversity of cellular organization of osmoregulatory and excretory organs such as glomerular kidneys, antennal glands, Malpighian tubules and insect gut, gills, integument and intestine, with accounts on experimental approaches and methods applied in the studies. It is demonstrated how knowledge in these areas of comparative physiology has expanded considerably during the last two decades, bridging seminal classical works with studies based on new approaches at all levels of anatomical and functional organization. A number of as yet partially unanswered questions are emphasized, some of which are about how water and solute exchange mechanisms at lower levels are integrated for regulating whole body extracellular water volume and ion homeostasis of animals in their natural habitats. © 2014 American Physiological Society. Compr Physiol 4:405‐573, 2014.

Stressor- and tissue-specific regulation of the corticotropin-releasing factor system across epithelial tissues in rainbow trout

“…These contrasting responses between tissues likely reflect the different osmoregulatory role(s) of the gills versus the intestine in SW. Whereas the gills are responsible for exporting ions out of the body, ions are taken up across the intestine to maintain a favourable gradient facilitating water absorption (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014). However, it is not clear why greater CRF system activity in the intestine of SW-acclimated fish would be beneficial from an osmoregulatory standpoint since the CRF system generally promotes ion and/or water excretion (or reduces absorption) across taxa and epithelium types (Cannell et al, 2016;Marshall and Bern, 1981;Stengel and Taché, 2009).…”

“…Therefore, we set out to compare whether transcriptional regulation of the CRF system varies between immune and osmotic stressors. We specifically focused on the gills and intestine because both tissues are key osmoregulatory organs (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014) and are important for the prevention of pathogen entry from the external environment (Koppang et al, 2015;Salinas and Parra, 2015).…”

Stressor- and tissue-specific regulation of the corticotropin-releasing factor system across epithelial tissues in rainbow trout

“…These contrasting responses between tissues likely reflect the different osmoregulatory role(s) of the gills versus the intestine in SW. Whereas the gills are responsible for exporting ions out of the body, ions are taken up across the intestine to maintain a favourable gradient facilitating water absorption (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014). However, it is not clear why greater CRF system activity in the intestine of SW-acclimated fish would be beneficial from an osmoregulatory standpoint since the CRF system generally promotes ion and/or water excretion (or reduces absorption) across taxa and epithelium types (Cannell et al, 2016;Marshall and Bern, 1981;Stengel and Taché, 2009).…”

“…Therefore, we set out to compare whether transcriptional regulation of the CRF system varies between immune and osmotic stressors. We specifically focused on the gills and intestine because both tissues are key osmoregulatory organs (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014) and are important for the prevention of pathogen entry from the external environment (Koppang et al, 2015;Salinas and Parra, 2015).…”

Stressor‐ and Tissue‐Specific Regulation of the Corticotropin‐Releasing Factor System Across Epithelial Tissues in Rainbow Trout

“…These contrasting responses between tissues likely reflect the different osmoregulatory role(s) of the gills versus the intestine in SW. Whereas the gills are responsible for exporting ions out of the body, ions are taken up across the intestine to maintain a favorable gradient facilitating water absorption [ 37 , 38 , 39 ]. However, it is not clear why greater transcription of CRF system components in the intestine of SW‐acclimated fish would be beneficial from an osmoregulatory standpoint since the CRF system generally promotes ion and/or water excretion (or reduces absorption) across taxa and epithelium types [ 25 , 36 , 68 ].…”

Structural Adaptations to Saline Stress: Histomorphological Changes in the Osmoregulatory and Metabolic Organs of Perca schrenkii Under Acute and Chronic Challenges

“…In contrast, the kidney maintained internal balance through more moderate but critical adjustments. Salinity-dependent reduction in glomerular number lowers glomerular filtration rate to conserve body water [ 31 , 32 ]. During chronic acclimation, significant tubular dilation at 5 ppt (with stable epithelial thickness) suggests targeted compensatory enhancement of ion reabsorption [ 33 , 34 ], shifting from “damage control” to “active adaptation”.…”

Stressor- and tissue-specific regulation of the corticotropin-releasing factor system across epithelial tissues in rainbow trout

“…These contrasting responses between tissues likely reflect the different osmoregulatory role(s) of the gills versus the intestine in SW. Whereas the gills are responsible for exporting ions out of the body, ions are taken up across the intestine to maintain a favourable gradient facilitating water absorption (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014). However, it is not clear why greater CRF system activity in the intestine of SW-acclimated fish would be beneficial from an osmoregulatory standpoint since the CRF system generally promotes ion and/or water excretion (or reduces absorption) across taxa and epithelium types (Cannell et al, 2016;Marshall and Bern, 1981;Stengel and Taché, 2009).…”

“…Therefore, we set out to compare whether transcriptional regulation of the CRF system varies between immune and osmotic stressors. We specifically focused on the gills and intestine because both tissues are key osmoregulatory organs (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014) and are important for the prevention of pathogen entry from the external environment (Koppang et al, 2015;Salinas and Parra, 2015).…”

Stressor‐ and Tissue‐Specific Regulation of the Corticotropin‐Releasing Factor System Across Epithelial Tissues in Rainbow Trout

“…These contrasting responses between tissues likely reflect the different osmoregulatory role(s) of the gills versus the intestine in SW. Whereas the gills are responsible for exporting ions out of the body, ions are taken up across the intestine to maintain a favorable gradient facilitating water absorption [ 37 , 38 , 39 ]. However, it is not clear why greater transcription of CRF system components in the intestine of SW‐acclimated fish would be beneficial from an osmoregulatory standpoint since the CRF system generally promotes ion and/or water excretion (or reduces absorption) across taxa and epithelium types [ 25 , 36 , 68 ].…”

Structural Adaptations to Saline Stress: Histomorphological Changes in the Osmoregulatory and Metabolic Organs of Perca schrenkii Under Acute and Chronic Challenges

“…In contrast, the kidney maintained internal balance through more moderate but critical adjustments. Salinity-dependent reduction in glomerular number lowers glomerular filtration rate to conserve body water [ 31 , 32 ]. During chronic acclimation, significant tubular dilation at 5 ppt (with stable epithelial thickness) suggests targeted compensatory enhancement of ion reabsorption [ 33 , 34 ], shifting from “damage control” to “active adaptation”.…”

Stressor- and tissue-specific regulation of the corticotropin-releasing factor system across epithelial tissues in rainbow trout

“…These contrasting responses between tissues likely reflect the different osmoregulatory role(s) of the gills versus the intestine in SW. Whereas the gills are responsible for exporting ions out of the body, ions are taken up across the intestine to maintain a favourable gradient facilitating water absorption (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014). However, it is not clear why greater CRF system activity in the intestine of SW-acclimated fish would be beneficial from an osmoregulatory standpoint since the CRF system generally promotes ion and/or water excretion (or reduces absorption) across taxa and epithelium types (Cannell et al, 2016;Marshall and Bern, 1981;Stengel and Taché, 2009).…”

“…Therefore, we set out to compare whether transcriptional regulation of the CRF system varies between immune and osmotic stressors. We specifically focused on the gills and intestine because both tissues are key osmoregulatory organs (Evans et al, 2005;Grosell, 2010;Larsen et al, 2014) and are important for the prevention of pathogen entry from the external environment (Koppang et al, 2015;Salinas and Parra, 2015).…”

Stressor‐ and Tissue‐Specific Regulation of the Corticotropin‐Releasing Factor System Across Epithelial Tissues in Rainbow Trout

“…These contrasting responses between tissues likely reflect the different osmoregulatory role(s) of the gills versus the intestine in SW. Whereas the gills are responsible for exporting ions out of the body, ions are taken up across the intestine to maintain a favorable gradient facilitating water absorption [ 37 , 38 , 39 ]. However, it is not clear why greater transcription of CRF system components in the intestine of SW‐acclimated fish would be beneficial from an osmoregulatory standpoint since the CRF system generally promotes ion and/or water excretion (or reduces absorption) across taxa and epithelium types [ 25 , 36 , 68 ].…”

Structural Adaptations to Saline Stress: Histomorphological Changes in the Osmoregulatory and Metabolic Organs of Perca schrenkii Under Acute and Chronic Challenges

“…In contrast, the kidney maintained internal balance through more moderate but critical adjustments. Salinity-dependent reduction in glomerular number lowers glomerular filtration rate to conserve body water [ 31 , 32 ]. During chronic acclimation, significant tubular dilation at 5 ppt (with stable epithelial thickness) suggests targeted compensatory enhancement of ion reabsorption [ 33 , 34 ], shifting from “damage control” to “active adaptation”.…”