Learning Objectives
By the end of this section, you will be able to:
- Explain how bipotential tissues are directed to develop into male or female sex organs
- Name the rudimentary duct systems in the embryo that are precursors to male or female internal sex organs
- Describe the hormonal changes that bring about puberty, and the secondary sex characteristics of men and women
Introduction:
The following chapter will discuss the physiology of arousal and orgasm. Arousal includes the physiology of erection and increased lubrication production due to a combination of mental and physical stimuli. Orgasm typically includes the release of ejaculate and involuntary muscle contractions accompanied by feelings of euphoria. Immediately following orgasm there is resolution of vasocongestion in erectile tissue followed by feelings of contentment and relaxation.
Arousal:
The physiological process of arousal can begin due to sexual thoughts or from physical stimulation. Mostly commonly, the combination of mental and physical input together – synapsing with the sacral nerves roots – leads to reflexive patterns of physiologic arousal. Due to the reflexive nature of the response, positive mental stimulation is it not a requirement for physical signs of arousal to occur. Also, in the case of spinal cord injury, the location of the injury relative to the sacral nerve roots will dictate whether input from the brain, or from physical stimulation, will lead to physical signs of arousal. Sexual sensations are typically most intense due to physical stimulation of the glans of the clitoris or penis, although arousal can also occur due to stimulation of the nipples, all portions of the clitoris and penis, the vulva and perineal region, prostate, urethra, bladder, anal epithelium, scrotum, testes and vas deferens. Efferent and afferent signals related to sexual arousal travel along many nerves including the pudendal, pelvic splanchnic, hypogastric, vagus, ilioinguinal, posterior femoral cutaneous and genital branch of the genitofemoral nerve.
Erections are the result of vasocongestion, or engorgement of the tissues because of more arterial blood flowing into the erectile structure than is leaving in the veins. During sexual arousal, nitric oxide (NO) is released from parasympathetic nerve endings near blood vessels within the corpora cavernosa and spongiosum. Release of NO activates a signaling pathway that results in relaxation of the smooth muscles that surround the arteries, causing them to dilate. This dilation increases the amount of blood that can enter the erectile structures and induces the endothelial cells in the arterial walls to also secrete NO and perpetuate the vasodilation. The rapid increase in blood volume fills the erectile chambers, and the increased pressure of the filled chambers compresses the thin-walled venules, preventing venous drainage. The result of this increased blood flow to the erectile structures, and reduced blood returning from the struc