L10: sexual function and fertilisation Flashcards
Describe the functions of different constituents of seminal plasma
Seminal vesicles – 60% of volume
-alkaline fluid = neutralises the acid in male urethra & female reproductive tract
-fructose, prostaglandins, clotting factors
Prostate gland – 25% of volume
-proteolytic enzymes = breakdown clotting proteins, re-liquefying semen
-citric acid, acid phosphatase
Bulbourethral glands – very small volume
-alkaline fluid = a mucous that lubricates the end of the penis and urethral lining
List the stages of the human sexual response
Excitement phase
Plateau phase
Orgasm phase
Resolution phase – return to haemodynamic norm followed by refractory period in males
Describe the excitement phase in men
Occurs due to psychogenic stimuli, which are centrally controlled as well as tactile sensory afferents
Parasympathetic efferents that dominant via the pelvic nerve
Somatic efferents from the pudendal nerve
Both together result in erection
Describe the physiology of erection
Sinusoids within the corpora cavernosa need to relax and arterial dilation needs to occur - both happen due to neuronal input
Venous dilatation is required – increased blood flow against the tough tunica albuginea surrounding the corpora cavernosa, which compresses the venous drainage within the tunica albuginea
Sympathetic tone needs to be inhibited while the parasympathetic innervation is stimulated via the pelvic and cavernous nerve
Nitric oxide – causes vascular smooth muscle relaxation via M3 receptors
Describe the causes and management of erectile dysfunction
Can arise due to many different causes – psychological input, vascular disorders, anti-hypertensives, neurological disorders & trauma of fibrous tissues of the corpora cavernosa
Management – correct underlying disorders, or improve erection by increasing amounts of NO and cGMP
Describe emission and ejaculation in men
Emission – semen is moved into the prostatic urethra -> requires smooth muscle contraction from the prostate, vas deferens & seminal vesicles
Ejaculation – expulsion of semen -> requires contraction of glands, ducts & internal sphincter to prevent retrograde ejaculation
Both are under sympathetic control (somatic involvement of the muscles of the pelvic floor & perineum also contribute to ejaculation)
What is the capacitation reaction?
Sperm are deposited in the female reproductive tract at the cervix
Requires an additional process to become fully mature = CAPACITATION
Sperm cell membrane changes to allow fertilisation to occur & tail movement changes
Describe fertilisation
Enzymes in the acrosome are released to remove the outer granulosa cells surrounding the ovum
Sperm then interacts with the zona pellucida -> triggers the acrosome reaction -> consequent loss of the outer membrane of the sperm -> allows the head of a single sperm to penetrate the ovum & fuse with the membrane
Cortical reaction – prevents further sperm from entering & triggers meiosis II to finish
Morula produced & then blastocyst hatches so that it can implant itself in the endometrial lining
Describe implantation
Cells of the outer cell mass (trophoblast) interact with the endometrial lining
Implants within the stroma of the endometrium, where secretory glands and increased vasculature have formed during the menstrual cycle
What is the fertile window?
Sperm can survive for up to 72 hours, ovum for 24 hours
Window of fertility = sperm can be deposited three days before ovulation for fertilisation to be successful
Describe the sexual response in females
Excitement phase – vaginal lubrication appears, clitoris enlarges & labia swells
Plateau phase – vagina expands, uterus elevates & colour change in labia
Orgasm phase – contractions in uterus, anal sphincter contracts & rhythmic contractions in orgasmic platform
Resolution phase – uterus lowers, vaginal returns to normal & orgasmic platform disappears
