Sexual response cycle: occurs with physical and psychological stimulation that causes parasympathetic nerve stimulation which leads to arterial dilation and venous constriction in the genital area. In women, this vasocongestion causes the clitoris to increase in size and mucoid fluid to appear on vaginal walls as lubrication. The vagina widens in diameter and increases in length. The nipples become erect. In men, penile erection occurs, as well as scrotal thickening and elevation of the testes. In both sexes, there is an increase in heart and respiratory rates and blood pressure.