An increase in the number of receptors on the surface of target cells, making the cells more sensitive to a hormone or another agent. For example, there is an increase in uterine oxytocin receptors in the third trimester of pregnancy, promoting the contraction of the smooth muscle of the uterus.
A canal that connects the urinary bladder to the umbilicus (bellybutton) during fetal development. The urachus is normally obliterated, so it is usually a solid cord. Failure for the urachus to fill in leaves it open. The telltale sign of an open urachus is leakage of urine through the umbilicus. An open urachus is a […]
- Uracil (U)
A nucleotide base and one member of the A-U (adenine-uracil) base pair in RNA. The other base pair in RNA is G-C (guanine-cytosine). Uracil takes the place in RNA that thymine (T) occupies in DNA.
A metallic element that is used as nuclear fuel and is highly toxic and radioactive. Exposure to radiation from uranium can occur in various ways. The breakdown of uranium products creates radon daughters. These can attach to dust particles and, if workers inhale the dust, the particles lodge in their lungs, where they release high […]
A salt derived from uric acid. When the body cannot metabolize uric acid properly, urates can build up in body tissues or crystallize within the joints. See also gout, uric acid.
- Urban typhus of Malaya
Murine typhus, an acute infectious disease with fever, headache, and rash, all quite similar to, but milder than, epidemic typhus. It is caused by a related microorganism, Rickettsia typhi (R. mooseri), transmitted to humans by rat fleas (Xenopsylla cheopis). The animal reservoir includes rats, mice and other rodents. Murine typhus occurs sporadically worldwide but is […]