are polypeptides similar to insulin); somatomedins,
polypeptides made by the liver and fibroblasts that,
when released into the blood (stimulated by soma-
totropin), help cell division and growth by incorporat-
ing sulfates into collagen, RNA, and DNA synthesis;
HGH (human growth hormone), also called soma-
totropin, a proteinlike hormone from the pituitary
gland that stimulates the liver to produce somato-
medins that stimulate growth of bone and muscle;
platelet-derived growth factor (PDGF), a glycoprotein
that stimulates cell proliferation and chemotaxis in car-
tilage, bone, and other cell types; fibroblast growth fac-
tor, which promotes the proliferation of cells of
mesodermal, neuroectodermal, epithelial, or endothe-
lial origin; epidermal growth factor (EGF), important
for cell development as it binds to receptors on cell sur-
face to create a growth signal; and granulocyte colony-
stimulating factor (G-CSF), a growth factor that
promotes production of granulocytes, a type of white
blood cell.
guanylate cyclase An ENZYME catalyzing the con-
version of guanosine 5’-triphosphate to cyclic guano-
sine 3’,5’-monophosphate, which is involved in cellular
REGULATIONprocesses. One member of this class is a
HEME-containing enzyme involved in processes regulat-
ed by nitrogen monoxide.
guardcell Specialized epidermal cells; two crescent-
shaped cells on either side of the pore of a stoma in the
stem or leaf epidermis. By changing shape, i.e., by
opening and closing via changes in turgor, they regulate
gas exchange and water loss by covering or uncovering
the pore, which lets oxygen out and carbon dioxide in.
Gullstrand, Allvar (1862–1930) SwedishOphthal-
mologist Allvar Gullstrand was born on June 5,
1862, in Landskrona and was the eldest son of Dr. Pehr
Alfred Gullstrand, principal municipal medical officer,
and his wife Sofia Mathilda Korsell. He was educated
at schools in Landskrona and Jönköping, and he
attended Uppsala University, but left in 1885 to spend
a year at Vienna. He then continued his medical studies
at Stockholm and presented his doctorate thesis in
- He was appointed lecturer in ophthalmology in
1891 and was appointed the first professor of ophthal-
mology at Uppsala University in 1894. He stayed in
that position until 1914, when he was given a personal
professorship in physical and physiological optics at
Uppsala University, becoming an emeritus professor in
1927.
Gullstrand contributed a great deal to the knowl-
edge of clinical and surgical ophthalmology and of the
structure and function of the cornea of the eye, as well
as research on astigmatism, and was self-taught in this
area. He laid out his ideas in his doctoral thesis in
1890, Bidrag till astigmatismens teori(Contribution
to the theory of astigmatism) and further refined them
in Allgemeine Theorie der monochromatischen Aber-
rationen und ihre nächsten Ergebnisse für die Oph-
thalmologie (General theory of monochromatic
aberrations and their immediate significance for oph-
thalmology), 1900; Die reelle optische Abbildung
(The true optical image), 1906; and Die optische
Abbildung in heterogenen Medien und die Dioptrik
der Kristallinse des Menschen (The optical image in
heterogeneous media and the dioptrics of the human
crystalline lens), 1908. Further important works
included Tatsachen und Fiktionen in der Lehre von
der optischen Abbildung(Facts and fictions in the the-
oryof the optical image), 1907; and Einführung in die
Methoden der Dioptrik der Augen des Menschen
(Introduction to the methods of the dioptrics of the
human eyes), 1911.
In 1911 he invented the slit lamp and the reflex-
free ophthalmoscope to help study the eye. He intro-
duced a surgical technique for the treatment of
symblepharon (a fibrous tract that connects the bulba
conjunctiva to conjunctiva on the eyelid) and redefined
the theory of accommodation. In 1911 he received the
Nobel Prize for his research on dioptrics of the eye,
although at first he declined it. Gullstrand died in
Stockholm on July 28, 1930. Gullstrand is seen as one
of the founders of modern ophthalmology.guttation A way for plants to expel water in excess
of transpiration—principally through hydathodes, a
special epidermal structure at the terminations of veins
around the margins of the leaves—and especially under
conditions of relatively high humidity. The expelled
water appears on the ends of leaves mostly on moist
cool nights and resembles dew.guttation 153