39
Respiratory Turbinates
Albatrosses, petrels, fulmars and shearwaters possess large external nostrils and are
related to the group of seabirds called “tubenoses”. These specifi cally structured
nostrils help them to fi nd good feeding areas, other birds, breeding areas and nest
sites by smell (see for review Nunn and Stanley 1998 ; Brooke 2004 ; Onley and
Scofi eld 2007 ). Intriguingly, some representatives of “tubenoses” can smell food up
to 30 km away!
Thus, seabirds possess cartilaginous, epithelially covered projections within
their nasal cavity known as conchae, or turbinates. Respiratory turbinates of seabirds
are situated directly in the path of respiratory airfl ow, greatly increasing the surface
area of the nasal epithelial mucosa and simultaneously reducing the effective
distance of respiratory air from the mucosal surfaces. As inspired air passes through
the nasal cavities and over the moist surfaces of the respiratory turbinates, heat
and water are exchanged, warming and humidifying the air while simultaneously
cooling the epithelium of the turbinates. The effi ciency of this evaporative exchange
is such that the temperature of the nasal surfaces may occasionally drop below the
temperature of the ambient air (Geist 2000 ).
Physiology of the respiratory turbinates is a very interesting scientifi c fi eld because
of a strong functional association with endothermy (Scholander et al. 1950 ; Hillenius
1994 ; Ruben 1995 ). It is well established that high levels of oxygen consumption and
concomitant elevated rates of lung ventilation are tightly linked to endothermy in both
mammals and birds. As written by Ruben and Jones ( 2000 ), “respiratory turbinates,
which occur in greater than 99 % of all extant birds and mammals, facilitate an intermittent countercurrent exchange of respiratory heat and water between respired air
and the moist, epithelial linings of the turbinates. In doing so, they signifi cantly reduce
respiratory water and heat loss that would otherwise be linked to the high rates of lung
ventilation associated with mammalian and avian endothermy” (Ruben and Jones
2000 ). Interestingly, some kind of vascular shunts exists between respiratory turbinates and the brain. It has long been suggested that respiratory turbinates may be
utilized as brain “coolers” in birds and mammals (Baker 1982 ).
Salt Gland
Feeding in saline environments can be dangerous for animals which have no
physiological mechanisms for removing of NaCl and which are able to prevent the
blood from becoming too salty. Birds which habituate in marine areas ingest much
more salt than their kidneys can process. Correspondingly, they use special salt or
nasal glands (Marples 1932 ; Schmidt–Nielsen and Sladen 1958 ; McFarland 1959 ;
Schmidt–Neilsen et al. 1970 ; Ellis and Goertemiller 1977 ). These structures are
located above the eye and can excrete a strong salty liquid. The bird kidney is able to
excrete salts at concentrations of about one-half that found in sea water!
Why is it principally possible that seabirds can drink seawater? Because their
cephalic salt glands secrete a NaCl solution more concentrated than seawater!
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview
Respiratory Turbinates
Albatrosses, petrels, fulmars and shearwaters possess large external nostrils and are
related to the group of seabirds called “tubenoses”. These specifi cally structured
nostrils help them to fi nd good feeding areas, other birds, breeding areas and nest
sites by smell (see for review Nunn and Stanley 1998 ; Brooke 2004 ; Onley and
Scofi eld 2007 ). Intriguingly, some representatives of “tubenoses” can smell food up
to 30 km away!
Thus, seabirds possess cartilaginous, epithelially covered projections within
their nasal cavity known as conchae, or turbinates. Respiratory turbinates of seabirds
are situated directly in the path of respiratory airfl ow, greatly increasing the surface
area of the nasal epithelial mucosa and simultaneously reducing the effective
distance of respiratory air from the mucosal surfaces. As inspired air passes through
the nasal cavities and over the moist surfaces of the respiratory turbinates, heat
and water are exchanged, warming and humidifying the air while simultaneously
cooling the epithelium of the turbinates. The effi ciency of this evaporative exchange
is such that the temperature of the nasal surfaces may occasionally drop below the
temperature of the ambient air (Geist 2000 ).
Physiology of the respiratory turbinates is a very interesting scientifi c fi eld because
of a strong functional association with endothermy (Scholander et al. 1950 ; Hillenius
1994 ; Ruben 1995 ). It is well established that high levels of oxygen consumption and
concomitant elevated rates of lung ventilation are tightly linked to endothermy in both
mammals and birds. As written by Ruben and Jones ( 2000 ), “respiratory turbinates,
which occur in greater than 99 % of all extant birds and mammals, facilitate an intermittent countercurrent exchange of respiratory heat and water between respired air
and the moist, epithelial linings of the turbinates. In doing so, they signifi cantly reduce
respiratory water and heat loss that would otherwise be linked to the high rates of lung
ventilation associated with mammalian and avian endothermy” (Ruben and Jones
2000 ). Interestingly, some kind of vascular shunts exists between respiratory turbinates and the brain. It has long been suggested that respiratory turbinates may be
utilized as brain “coolers” in birds and mammals (Baker 1982 ).
Salt Gland
Feeding in saline environments can be dangerous for animals which have no
physiological mechanisms for removing of NaCl and which are able to prevent the
blood from becoming too salty. Birds which habituate in marine areas ingest much
more salt than their kidneys can process. Correspondingly, they use special salt or
nasal glands (Marples 1932 ; Schmidt–Nielsen and Sladen 1958 ; McFarland 1959 ;
Schmidt–Neilsen et al. 1970 ; Ellis and Goertemiller 1977 ). These structures are
located above the eye and can excrete a strong salty liquid. The bird kidney is able to
excrete salts at concentrations of about one-half that found in sea water!
Why is it principally possible that seabirds can drink seawater? Because their
cephalic salt glands secrete a NaCl solution more concentrated than seawater!
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview