studies in medicine but turned to zoology, an early
childhood interest.
In1897 he began work for Christian Bohr at the
laboratory of medical physiology and later became his
assistant. In 1916 he became chair of the zoophysiolo-
gy department at the University of Copenhagen, a posi-
tion he held until he retired in 1945.
In 1904 he constructed a microtonometer, making
it possible to determine the gas content of blood with
great precision. He established that the movement of
gases between the alveoli and the blood occurs through
passive diffusion. With exercise physiologist Johannes
Lindhard, Krogh began the field of exercise physiology
in Scandinavia between 1910 and 1915. He developed
an automatically controlled bicycle ergometer
(1910–11) that is still in use today for exercise. He also
demonstrated that muscles burn fat during exercise,
and included in his inventions was a climate chamber
that could be carried to measure continuous tempera-
tureand humidity over a 24-hour period. For his work
on capillaries, discovering capillary-motor-regulating
mechanisms, he received the Nobel Prize in physiology
or medicine in 1920. Some of his important writings
include The Anatomy and Physiology of Capillaries192 Krogh, Schack August Steenberg
An example of the scrubby condition of trees at the tree line, known as krummholz, in the White Mountains of New Hampshire.
(Courtesy of Tim McCabe)
H 20In the Krebs cycle acetyl (from
pyruvate) is broken down to CO 2
and H. The H is held in NADH (from
reduction of NAD). The NADH then
is reoxidized in an electron transport
chain, with production of ATP.pyruvateacetyl CoA
CoA
citrateisocitratesuccinyl
CoAADPATPsuccinate2Hfumaratemalate2H oxaloacetateglycolysisC0 2 +2HC0 2 +2H-oxoglutarateThe Krebs cycle is a biochemical cycle in the second stage of
cellular respiration, involving eight steps, that completes the
metabolic breakdown of glucose molecules to carbon dioxide.