Capitulo III: Metodología
3.6. Procedimientos de Análisis de datos
3.6.1. Análisis de Granulometría de los Agregados:
THE PHYSIOLOGY OF COITUS
Normal sexual arousal has been described in four levels in both the male and the female. These levels consist of excitement, plateau, orgasmic and resolution phases. In the male, theexcitement phase results in compression of the venous channels of the penis, resulting in erection. This is mediated through the parasympathetic plexus through S2
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Chapter
| 22 | is a marked sweating reaction in some 30–40% of viduals. During this phase, the male becomes refractory to further stimulation. The plateau phase may be prolonged if ejaculation does not occur.In the female, the excitement phase involves nipple and clitoral erection, vaginal lubrication, resulting partly from vaginal transudation and partly from secretions from Bar-tholin’s glands, thickening and congestion of the labia majora and the labia minora and engorgement of the uterus. Stimulation of the clitoris and the labia results in progression to the orgasmic platform, with narrowing of the outer third of the vagina and ballooning of the vaginal vault. The vaginal walls become congested and purplish in colour and there is a marked increase in vaginal blood flow. During orgasm, the clitoris retracts below the pubic symphysis and a succession of contractions occurs in the vaginal walls and pelvic floor approximately every second for several seconds. At the same time, there is an increase in pulse rate, hyperventilation and specific skeletal muscu-lar contractions. Blood pressure rises and there is some diminution in the level of awareness. Both intravaginal and intrauterine pressures rise during orgasm.
The plateau phase may be sustained in the female and result in multiple orgasm. Following orgasm, resolution of the congestion of the pelvic organs occurs rapidly, although the tachycardia and hypertension accompanied by a sweating reaction may persist.
Factors that determine human sexuality are far more complex than the simple process of arousal by clitoral or penile stimulation. Although the frequency of intercourse and orgasm declines with age, this is in part mediated by loss of interest by the partners. The female remains capable of orgasm until late in life but her behaviour is substan-tially determined by the interest of the male partner.
Sexual interest and performance also decline with age in the male and the older male requires more time to achieve excitement and erection. Ejaculation may become less fre-quent and forceful.
Common sexual problems are discussed inChapter 19.
and S3. During the plateau phase, the penis remains engorged and the testes increase in size, with elevation of the testes and scrotum. Secretion from the bulbourethral glands results in the appearance of a clear fluid at the urethral meatus. These changes are accompanied by general systemic features including increased skeletal muscle tension, hyperventilation and tachycardia.
Erectile dysfunction may result from neurological damage to the spinal cord or the brain and is seen as a result of spina bifida, multiple sclerosis and diabetic neuropathy. However, there are over 200 prescription drugs that are known to cause impotence and these account for some 25% of all cases.
Recreational drugs such as alcohol, nicotine, cocaine, marijuana and LSD may also cause impotence; however this can usually be improved by the male taking the pharmacologic preparation sildenafil citrate (Viagra®).
Seminal emission depends on the sympathetic nervous system. Expulsion of semen is brought about by contraction of smooth muscle within the seminal vesicles, ejaculatory ducts and prostate.
The orgasmic phase is induced by stimulation of the glans penis and by movement of penile skin on the penile shaft.
There are reflex contractions of the bulbocavernosus and ischiocavernosus muscles and ejaculation of semen in a series of spurts. Specific musculoskeletal activity occurs that is characterized by penile thrusting. The systemic changes of hyperventilation and rapid respiration persist.
During the resolution phase, penile erection rapidly sub-sides, as does the hyperventilation and tachycardia. There
Essential reproductive science
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Section
Essential information Essential information
Oogenesis Oogenesis
• Primordial germ cells appear in the yolk sac
• By 20 weeks, there are 7 million oogonia
• Number of oocytes falls to 1 million by birth
• Number falls to about 0.4 million by puberty
• Chromosome number in gametes is half that of normal cells
• Primary oocyte remains in suspended prophase for 10–50 years
• The second meiotic division commences as the ovum enters the tube
Follicular development in the ovary Follicular development in the ovary
• Most ova never reach advanced maturity, and about 800 are lost each month
• Aggregation of stromal cells around follicles become thecal cells
• Innermost layers of granulosa cells form the corona radiata
• After ovulation, the corpus luteum is formed Hormonal events and ovulation Hormonal events and ovulation
• FSH stimulates follicular growth
• FSH stimulates LH receptor development
• LH stimulates ovulation and stimulates and sustains development of the corpus luteum
• Follicles produce oestrogen
• Corpus luteum produces oestrogen and progesterone The endometrial cycle
The endometrial cycle
• Menstrual phase – shedding of functional layer of endometrium
• Phase of repair – day 4–7 of cycle
• Follicular phase – maximum period of growth of endometrial glands, due to oestrogen
• Luteal phase – ‘saw-toothed’ glands, pseudodecidual reaction in stroma
Spermatogenesis Spermatogenesis
• Full maturation takes 64–70 days
• Mature sperm arise from haploid spermatids Structure of spermatozoon
Structure of spermatozoon
• Head is covered by acrosomal cap
• Body contains helix of mitochondria
• Tail consists of two longitudinal fibres and nine pairs of fibres
Seminal plasma Seminal plasma
• Originates from the prostate, seminal vesicles and bulbourethral glands
• High concentration of fructose provides energy for sperm motility
• High concentration of prostaglandins Sperm transport
Sperm transport
• Rapid migration into receptive cervical mucus
• Sperm migrate at 6 mm/min
• Only motile sperm reach the fimbriated ends of the tubes
Capacitation Capacitation
• Final sperm maturation occurs during passage through the oviduct
• Inhibitory substances produced in caudo-epididymis and in seminal plasma
Fertilization Fertilization
• Small number of sperm reach oocyte
• Adherence of sperm initiates the acrosome reaction
• Sperm head fuses with oocyte plasma membrane
• Sperm head and midpiece engulfed into oocyte
• Fusion of male and female chromosomes is known as syngamy
• 36 hours after fertilization, the morula is formed
• 6 days after fertilization, implantation occurs Physiology of coitus
Physiology of coitus
• Penile erection results from compression of venous channels
• Ejaculation mediated by contractions of bulbo- and ischiocavernosus
• Female excitation results in nipple and clitoral erection
• Lubrication comes from vaginal transudation, Bartholin’s glands secretions
• Orgasm results in clitoral retraction and contractions of pelvic floor muscles
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