Nicotine also counteracts anticholinergics by activating nicotinic acetylcholine receptors. Progesterone is a hormone in the endometrium that counteracts estrogen driven growth. It counteracts the poisonous effects of acetaldehyde. Recombination counteracts physical linkage between adjacent genes, thereby reducing genetic hitchhiking. The force backwards directly counteracts gravity, and slows the skier. REM sleep apparently counteracts attempts to suppress certain thoughts. As such, the sloshing water contained in this central opening counteracts the swell-induced floater oscillations. Protein phosphatase 1 counteracts phosphorylation of S695. The buffer counteracts the alkalinity of soap. TMAO also counteracts the protein-destabilizing tendencies of urea and of deep-water pressure. For example, DGLA yields PGE, which powerfully counteracts PGE. The latter exercise thus counteracts the "stiffening, shrinking aspects of aging". This negative pressure counteracts the mass the star gains, avoiding a singularity. White Tara counteracts illness and thereby helps to bring about a long life. It appears that inclusion of the photos counteracts the dehumanization of the medical process.