antagonist. 1. a muscle that counteracts the action of another muscle, its agonist. 2. a drug that binds to a cellular receptor for a hormone, neurotransmitter, or another drug blocking the action of that substance without producing any physiological effect itself.
in the body (Figure 20â1). In general, the more widely a cancer spreads, the harder it becomes to eradicate. It is generally metastases that kill the cancer patient. Cancers are traditionally classified according to the tissue and cell type from which they arise. Carcinomas are cancers arising from epithelial cells, and they
Tumors of the renal calyces, renal pelvis and ureters start in the layer of tissue that lines the bladder and the upper urinary tract, called the urothelium. Cancer that starts in the urothelium is called urothelial (or transitional cell) cancer. This is the most common type of cancer found in the bladder, as well. Because many of the organs in the urinary system share common cells, cancers found in these organs often look and act alike. Parts of the kidney. Image Â© 2003 Fairman Studios, LLC.