Introduction into the male reproductive system
Ability to reproduce is a basic characteristic of living systems. Reproductive capabilities are endangered by a water estrogen pollution, chronic stress an inactive lifestyle. Reduced sperm count per 1 ml of ejaculate is more often found in centers of reproductive medicine. Even in healthy male population, the sperm count halved during last fifty years. From over a 30 million per 1 ml of ejaculate to just about 15 million. Morphological abnormalities, in particular altered sperm head count or volume, are seen commonly.
Because of these pathological findings, knowledge of basic male reproductive processes is of utmost importance.
Erection is a physiological state of temporal penis hyperemia, which is achieved through activation of visceral reflex. Centre of this reflex is located in sacral spine segments (S2-S4). It is also called an erectile centre. Afferent fibers originate from pseudounipolar neurons, whose dendrites create pudendal nerves. They innervate a mechanoreceptors of glans penis and adjacent tissues. Pseudounipolar neuron axons synapses with interneurons and preganglionic neurons in reflex centre. Efferent fibers form reflex center pas along with pelvic splanchnic nerves. They synapse in autonomic ganglion, where postganglionic neurons are localized. Postganglionic axons join with cavernous nerves of penis and prostatic plexus. These innervates proper penis tissue.
Postsynaptic parasympathetic axons branches nearby helicine artery, where they release acetylcholine. Acetylcholine stimulates endothelial cells to synthesize nitric oxide from the arginine. Nitric oxide diffuses to smooth muscles tissue of artery media, where it induces a dilatation. Dilated helicine arteries fill corpus cavernosum.
Ischiocavernosus and bulbospongiosus muscle are contracted during the filling phase. Thus reducing penis venous drainage.
Activity of erectile reflex is controlled by limbic system, which regulates ratio of sympathetic and parasympathetic tone. Its control function is so intense, that erection may occur without proper mechanoreceptor stimulation. This phenomena underlines erection achieved through erotic imaginations, pictures or movies depicting sexual acts. Reflex is induced by stimulation of reward centre, because of positive affective quality attached to such stimuli. Increased activity of hypothalamic reward centers is also presented in erection achieved through mechanical stimulation. Increased parasympathetic activity is a necessary condition for erection to occur.
Chronic stress distinguished by an increased sympathetic tone impede erection occurrence and its maintenance. On the other hand increased parasympathetic tone leads to priapism. A pathologic condition, where an erection is prolonged and can lead to necrosis of corpora cavernosa. Ejaculation impairment may also occur while the parasympathetic tone is increased.
Ejaculation is physiological process where an ejaculate is expelled out of penis. It is commonly accompanied by an orgasm (even in nocturnal emission).
Ejaculation is controlled by sympathetic nervous system. Sympathetic tone increases rapidly when a certain threshold of erotic stimulation is achieved. Ejaculatory centre in lumbar spine segments (L2-L3) is stimulated. Sympathetic neurons originating in ejaculatory centre innervate ductus deferens and urethra. Neurons surrounding ductus deferens release noradrenaline. Noradrenaline stimulates rhythmical contractions of smooth muscles in duct wall. Thus the fluid from the epididymis into the prostatic part of urethra. This phase is called emission. Seminal fluid mixes with products from prostate and Cowper’s gland in urethra. Thus a final fluid called ejaculate is formed. Its volume is about 0.1 – 10 ml. Smooth muscle of urethra contracts rhythmically, expelling its contents.
Subchapter Author: Patrik Maďa