Biological complexity: human male sex function (Introduction)

by David Turell , Wednesday, July 13, 2016, 19:50 (3055 days ago) @ David Turell

Another example of high complexity:-http://www.evolutionnews.org/2016/07/irreducible_com102983.html-"The first task, of producing enough sperm, relates to his fertility and is accomplished by the testes. This is dependent on having enough of the gonadotropins, Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH), producing enough testosterone and having enough properly functioning specific receptors. The sperm produced in the testes is combined with nutrient fluids from the seminal vesicles and the prostate gland to form semen. During sexual intercourse the semen is released from the erect penis into the woman's vagina. The normal amount of semen usually needed for adequate fertility is at least 2 milliliters and the concentration of sperm per milliliter should generally be greater than 20 million. In addition, the appearance of the sperm (morphology) and their ability to move well (motility) are very important factors that affect fertility as well.-***-"The second task, of being able to deposit the sperm inside the female, refers to his potency. This involves having a firm enough normally shaped erection to penetrate deep enough into the vagina and ejaculate semen which is dependent on having a normal penis and normal nerve and vascular function. A penile erection is achieved by hydraulic pressure. Running the length of the penis, surrounding the urethra, above and on each side, are the corpus spongiosa and the corpus cavernosa. These tube-shaped venous chambers are surrounded by strong fibrous tissue. Sex-related thoughts and sensory stimulation of the penis and pelvic region activates the parasympathetic nerves which signals them to send out a neurohormone called acetylcholine. The acetylcholine attaches to specific receptors on the blood vessels in the penis which causes an increase in arterial blood flow into these chambers while at the same time reducing the venous outflow. This combination results in blood collecting within these chambers resulting in penile erection. After erection takes place, with continued stimulation the sympathetic nervous system swings into action and sends out a neurohormone called norepinephrine. The norepinephrine attaches to specific receptors on the associated pelvic muscles causing coordinated contraction and ejaculation of the semen from the penis, which is usually accompanied by the pleasurable sensation of orgasm. As sympathetic nerve stimulation brings on climax and ejaculation to complete the sexual act, the parasympathetic stimulation that caused the erection in the first place turns off and the penis becomes flaccid soon afterwards. -***-"In summary, the two main tasks of male fertility (producing enough sperm and depositing them inside the female) require much more than just having male sexual organs. He must be able to produce enough healthy and vigorous sperm which is dependent on having, not only properly working testes, but the right amount of hormones and properly working receptors as well. In addition, it isn't enough that he has a properly built male internal genital duct system and external genitalia. He must also have proper neurovascular function in the pelvis, which involves the neurohormones acetylcholine and norepinephrine and their specific receptors, to achieve enough of an erection to penetrate deep into the vagina and deposit his semen."-Comment: As usual this human function is highly complex and raises the issue of how it developed during evolution. It involves the coordination of the circulation of the penis, hormones, sperm production, prostatic fluids, nervous controls, and sexual thoughts hat stimulate the process.