Sex And Fertilisayion Flashcards
Outline the epididymal maturation of sperm
• On entry, spermatozoa not capable of movement
• Once at the tail of the epididymis they are capable of movement and have the potential to fertilise (capable of interacting with oocyte to begin fertilisation)
• Addition of secretory products to
surface of sperm
• Maturation
– Dependent on support of the epididymis by androgens
What are the functions of semen
- Spermatozoa
- Seminal plasma - derived from accessory glands of the male reproductive tract
• Function: – Transport medium – Nutrition – Buffering capacity – ? Role for prostaglandins in stimulating muscular activity in the female tract
What are the phases in the huma sexual response
• Excitement phase
– Psychogenic and / or somatogenic stimuli
• Plateau phase
• Orgasm phase
• Resolution phase
– Return to haemodynamic norm followed by a refractory period in males
Explain male sexual response i - erection
Stimulants
Psychogenic
Tactile (sensory afferents of penis and perineum)
Efferents
Somatic and autonomic efferents
•Pelvic nerve (PNS)
•Pudendal nerve (somatic)
Result = haemodynamic changes
Describe teh anatomical changes in erection
• Tunica albuginea • Erection requires – Sinusoidal relaxation – Arterial dilation – Venous compression Tunica albuginea gives counter pressure to engorgement of corpus spongiosum. This contributes to venous compression
Describe the innervation and neurophysiology of erection
• Fibres – Lumbar and sacral spinal levels • Pelvic nerve and pelvic plexus • Cavernous nerve to corpora and vasculature • Inhibition of sympathetic arterial vasoconstrictor nerves • Activation of PNS • Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries, releasing Nitric Oxide (NO)
What are the roles of NO in erection
• Post-ganglionic fibres release ACh • ACh bonds to M3 receptor on endothelial cells • A rise in [Ca2+]i , activation of NO Synthase and formation of NO • NO diffuses into vascular smooth muscle and causes relaxation (vasodilation) • NO also released directly from nerves
What are the causes of erectile dysfunction
• Psychological (descending inhibition of spinal reflexes) - psychogenic smulation may bot be possible/may be interrupted • Tears in fibrous tissue of corpora cavernosa • Vascular (arterial and venous) • Drugs
Therapy to treat: Viagra™ slows rate at which cGMP is degraded - cGMP rapports erection
Descrime emmission
• Under sympathetic auto control
• Emission
– Movement of semen into prostatic urethra
– Contraction of SM in prostate, vas deferens and seminal vesicles - tubular structures with outer covering of SM - propel glandular secretions along duct system
• Ejaculation
– Expulsion of semen
What happens in ejactulation
• Contraction of glands and ducts (smooth muscle)
• Bladder internal sphincter contracts
– Preventing retrograde ejaculation
• Rhythmic striatal muscle contractions (pelvic floor, and perineal muscles ischiocavernosus, bulbospongiosus)
Give a summary of the autonomic control of male sexual function
Erection • Sympathetic – Inhibition (reduction of tone at arterioles) • Parasympathetic – Active
Ejaculation
• Sympathetic
– Active
• ducts
Describe the changes to cervical mucus over the menstrual cycle
• The character of cervical mucus changes over the course of the menstrual cycle
• Oestrogen
– Thin, stretchy - supports movement of male gamete through tract
• Oestrogen and progesterone
– Thick, sticky; forms a plug - inhospitable to sperm, forms a mechanical barrier
What is capacitation
- further maturation of sperm in female reproductive tract (6-8 hours)
- sperm cell membrane changes to allow fusion with oocyte cell surface
- tail movement changes from beat to whip-like action (fig B)
- now capable of undergoing the acrosome reaction (fig C)
What is the fertile window
- Spermatozoa 48 -72hr
- Oocytes 6 – 24 hr (max)
- Fertile period: sperm deposition up to 3 days prior to ovulation or day of ovulation
Give an overview o events in fertilisation
- Occurs normally in the ampulla of the uterine tubes
- requires loss of sperm outer shell (acrosome)
- penetration of ovum membrane, fusion of ova and sperm membrane
- eventual formation and fusion of pronuclei
What is teh acrosome ad acrosome reaction
• Derived from golgi region of developing spermatid
• Contains enzymes
• Necessary for fertilisation
Acrosome reaction:
• Sperm pushes through corona radiata (granulose cells)
• Binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida
• Triggers acrosome reaction - release enzymes in acrosome - digest glycoprotein wall
• Digestion of zona pellucida
What happens during and just after fertilisation
• One sperm penetrates leading to fusion of plasma membranes • Cortical reaction - complex pathway, calcium wave - change in plasma membrane of oocyte to make any other sperm fusion impossible – Blocks polyspermy • Series of calcium waves are activated following fusion of oocyte and sperm membranes • Resumption of meiosis II occurs (c) • Pronuclei move together • Mitotic spindle forms leading to cleavage
What is the morula
Small bundle of cells
• each cell at this stage of development is
TOTIPOTENT
• i.e. has the capacity to become any cell type
Describe assisted reproductiove technology
• Oocytes are fertilised in vitro and allowed to divide to the 4- or 8- cell stage
• The morula is then transferred into the uterus
• PGD
– Pre-implantation Genetic Diagnosis
– a cell can be safely removed from the morula and tested for serious heritable
conditions prior to transfer of the embryo into the mother
Describe the blastocyst and hatching
• First differentiation
– Inner and outer cell masses - one gives embryo, one gives placenta
• Formation of the blastocyst
• blastocyst hatches from zona pellucida
• no longer constrained - now free to enlarge
• can now interact with uterine surface to implant
Describe implantation
• Outer cell mass (trophoblast) interacts with endometrium - at about time to next expected period
• Endometrium controls degree of invasion
• Ectopic implantation
– At sites other than endometrium
lined uterine cavity
– Invasion not controlled - runs unchecked
• Implantation in lower uterine segment can cause placenta praevia
