cortisol, a steroid hormone that increases the availability of glucose
to cells, as well as having numerous other complex effects throughout
the body. Cortisol is part of our body’s response to perceived threat
and other kinds of stress.
Other neurons in the hypothalamus produce the neuropeptides
oxytocin (Fig. 21.3) and vasopressin. These two molecules are close
chemical relatives, each consisting of a polypeptide chain of nine
amino acids:
Oxytocin: Cys-Tyr—Ile-Gln-Asn-Cys-Pro-Leu-Gly
Vasopression: Cys-Tyr-Phe-Gln-Asn-Cys-—Pro-Arg-GlyIn these primary amino acid sequences of human oxytocin and va-
sopressin, amino acids are represented by three-letter abbreviations.
The molecules are the same except for the two amino acids shown in
boldface.
Oxytocin and vasopressin produced by neurons in the hypothal-
amus are released as hormones via the adjacent pituitary gland into
the blood circulation. As systemic hormones they have effects that
give rise to their names. Oxytocin acts on the female uterus during
childbirth to induce contractions and facilitate birth. It also simu-
lates the production and release of milk from the mammary glands.
Vasopressin acts on the kidneys to slow the transfer of water from the
blood to the urine (in this context, it is also called an antidiuretic hor-
mone) and also acts systemically to constrict blood vessels.
Oxytocin, from Greek oxy = acute, quick, sharp, from Oxus, ancient
Greek name for the Amu Darya River, flowing across Central Asia,
from the Himalayas to the Aral Sea; and tokos = birth.