40
According to the modern view (Hughes 2003 ), “salt gland secretion generates
osmotically free water that sustains their other physiological processes. Acclimation
to saline induces interstitial water and Na move into cells. When the bird drinks
seawater, Na enters the plasma from the gut and plasma osmolality increases. This
induces water to move out of cells expanding the extracellular fl uid volume,”
(Hughes 2003 ). Increases in plasma osmolarity and extracellular fl uid volume
stimulate secretion using salt gland. The augmented intracellular fl uid content
should allow more rapid expansion of extracellular fl uid volume in response to
elevated plasma osmolarity. Of course, fi nally intestinally absorbed sodium chloride
must be reabsorbed by the kidneys.
The capillaries around salt glands are arranged so that the fl ow of blood is in the
direction opposite to the fl ow of secretory fl uid. This fl ow maintains a minimum
concentration gradient between blood and the tubular lumen along the entire length
of the tubule. The avian salt gland is a countercurrent system that concentrates the
secreted salt solution.
Intriguingly, the salt gland can be an example for microenvironments of some
halophilic microorganisms. For example, a suitable environment for the colonization of extreme halophilic prokaryotes like Halococcus morrhuae and Hcc.
Dombrowskii have been reported within the nostrils of the Cory’s Shearwater
( Calonectris diomedea ), which are endowed with a salt-excreting gland (Brito–
Echeverria et al. 2009 ). Because of migration routes of this seabird between
Mediterranean as the South Atlantic, it is suggested that dispersal mechanisms of
haloarchaea across the Earth’s surface can be determined by this phenomenon, too.
Uropygial (Preen) Glands
The preen gland, which is located above the base of the seabird tail, produce oil- based
substance. Seabirds use this liquid to keep their feathers clean, fl exible and waterproof
by constantly preening (see for review Hou 1928a , b ; Elder 1954 ; Jacob and Ziswiler
1982 ). The gland is diverse in size, shape and presence/absence of tufts of feathers. The
nipple- like protuberance of the gland exudes oil containing phospholipids, glycolipids,
neutral lipids as well as acidic mucins (see for review Salibian and Montalti 2009 ). The
bird uses the bill or the sides and back of the head to spread the oil throughout the
plumage when a bird preens. “Preen oil helps keep the plumage of waterfowl in good
condition. The oil maintains the fl exibility of feathers, and keeps feather barbules from
breaking,” (Moyer et al. 2003 ). Also antifungal as well as antibacterial properties of the
oil are known. This substance also preserves the feather keratin. Additionally, control of
plumage hygiene, thermal insulation, defense against predators, and pheromone production are examples of the physiological roles associated with the preen gland secretion (see for review Lequette et al. 1989 ; Nevitt and Bonadonna 2005 ; Nevitt 2008 ).
Waterproof Feathers
Sebum-like lipids are synthesized and secreted in the form of droplets by sebokeratinocytes, which are unique structural components of the avian epidermis. This epidermis also elaborates, but rarely secretes, the multigranular bodies (lipid—enriched
1 Introduction
According to the modern view (Hughes 2003 ), “salt gland secretion generates
osmotically free water that sustains their other physiological processes. Acclimation
to saline induces interstitial water and Na move into cells. When the bird drinks
seawater, Na enters the plasma from the gut and plasma osmolality increases. This
induces water to move out of cells expanding the extracellular fl uid volume,”
(Hughes 2003 ). Increases in plasma osmolarity and extracellular fl uid volume
stimulate secretion using salt gland. The augmented intracellular fl uid content
should allow more rapid expansion of extracellular fl uid volume in response to
elevated plasma osmolarity. Of course, fi nally intestinally absorbed sodium chloride
must be reabsorbed by the kidneys.
The capillaries around salt glands are arranged so that the fl ow of blood is in the
direction opposite to the fl ow of secretory fl uid. This fl ow maintains a minimum
concentration gradient between blood and the tubular lumen along the entire length
of the tubule. The avian salt gland is a countercurrent system that concentrates the
secreted salt solution.
Intriguingly, the salt gland can be an example for microenvironments of some
halophilic microorganisms. For example, a suitable environment for the colonization of extreme halophilic prokaryotes like Halococcus morrhuae and Hcc.
Dombrowskii have been reported within the nostrils of the Cory’s Shearwater
( Calonectris diomedea ), which are endowed with a salt-excreting gland (Brito–
Echeverria et al. 2009 ). Because of migration routes of this seabird between
Mediterranean as the South Atlantic, it is suggested that dispersal mechanisms of
haloarchaea across the Earth’s surface can be determined by this phenomenon, too.
Uropygial (Preen) Glands
The preen gland, which is located above the base of the seabird tail, produce oil- based
substance. Seabirds use this liquid to keep their feathers clean, fl exible and waterproof
by constantly preening (see for review Hou 1928a , b ; Elder 1954 ; Jacob and Ziswiler
1982 ). The gland is diverse in size, shape and presence/absence of tufts of feathers. The
nipple- like protuberance of the gland exudes oil containing phospholipids, glycolipids,
neutral lipids as well as acidic mucins (see for review Salibian and Montalti 2009 ). The
bird uses the bill or the sides and back of the head to spread the oil throughout the
plumage when a bird preens. “Preen oil helps keep the plumage of waterfowl in good
condition. The oil maintains the fl exibility of feathers, and keeps feather barbules from
breaking,” (Moyer et al. 2003 ). Also antifungal as well as antibacterial properties of the
oil are known. This substance also preserves the feather keratin. Additionally, control of
plumage hygiene, thermal insulation, defense against predators, and pheromone production are examples of the physiological roles associated with the preen gland secretion (see for review Lequette et al. 1989 ; Nevitt and Bonadonna 2005 ; Nevitt 2008 ).
Waterproof Feathers
Sebum-like lipids are synthesized and secreted in the form of droplets by sebokeratinocytes, which are unique structural components of the avian epidermis. This epidermis also elaborates, but rarely secretes, the multigranular bodies (lipid—enriched
1 Introduction