6.1 Sexual Function And Fertilisation Flashcards
Where is the majority of semen produced?
The accessory glands
What is the function of accessory glands secretion?
- transport medium for sperm
- neutralises acidic environment of vagina ( buffering capability )
- nutrition source for spermatozoa
- Prostaglandins in the secretion stimulate muscular activity in the female tract
Why does semen initially clot?
Due to clotting factors provided by the seminal vesicles.
How is semen unclotted?
By the substance from the prostate that contains specific enzymes to break down the coagulation
What factors of sperm are considered when looking at issues with infertility?
Time taken to breakdown coagulation of semen
Amount, morphology and motility of sperm
What are the 4 phases in the human sexual response?
Excitement phase
Plateau phase
Orgasm phase
Resolution phase
What are the 2 main stimuli for the excitement phase?
Psychogenic
Somatic
What is the refractory phase?
A phase after the orgasm phase where the individual returns to haemodynamic norm
How does the resolution phase vary between males and females?
Men have a refractory period whilst women do not.
In the excitement phase in men, what neurones result in an erection?
Parasympathetic efferent from the pelvic nerve
Somatic efferents from the pudendal nerve
Describe the physiology of an erection
- Parasympathetic in the pelvic nerve stimulate smooth muscle relaxation
- Sinusoids in the corpus cavernous relax
- Arterial dilation
- Increased blood flow against the though tunica albuginea surrounding the corpus cavernosa
- Compression of venous drainage
- Blood is prevented from leaving the penis, engorgement of the arteries causes erection.
Why is it important the the corpus spongiosum does not become completely compressed by the erection?
As the urethra runs in the corpus spongiosum. Urethra needs to remain open to allow the semen to leave
Describe the neurotransmitters involved in maintaining an erection
Parasympathetic neurones from the pelvic and cavernous nerve secrete ACh.
ACh acts on M3 receptor to increase calcium intracellular levels.
Calcium activates NO synthase, producing citrulline and NO in the breakdown of arginine.
No is the key intracellular transmitter stimulation vasodilation via guanylyl cyclase using GTP to form Cyclic GMP. This pathway continues and results in smooth muscle relaxation.
Disruption to which factors can call erectile dysfunction?
Psychological input Vascular disorder Anti-hypertensives Neurological disorders Trauma of the fibrous tissue of the corpus cavernosa
How does viagra work to help patients with erectile dysfunction?
Increases the amount of cGMP in the cells by stopping the breakdown of cGMP by phosphodiesterase
What occurs in the emission stage in men?
Semen moves into the prostate urethra. This occurs due to smooth muscle contraction from the prostate, vas deferents and seminal vesicles.
What is ejaculation?
The expulsion of semen
What structures contract during ejaculation?
The glands
Ducts
Bladder Internal sphincter
Rhythmic striatal contractions
Why does the internal sphincter contract during ejaculation?
To avoid retrograde ejaculation and sperm entering the bladder
What’s the nervous supply that controls emission and ejaculation of semen?
Sympathetic control
What is capacitation?
The final step of sperm to become fully mature.Occurs in the female reproductive tract at the cervix.
Sperm cell membrane changes to allow fertilisation, tail movement changes.
Describe how a sermon fertilises an oocyte
Enzymes in the across membrane released to remove outer granuloma cells that are still surrounding the ovum as the corona radiata.
Sperm interacts with zona pellucida causing acrosome reaction.
Single head of sperm will penetrate ovum and fuse with the membrane
What does the cortical reaction do?
Prevents further sperm from entering
Trigger meiosis II of the ovum to complete.
What’s special about the cells of the morula?
Totipotent
What is hatching?
When the zona pellucida degenerates, allowing the morula to continue dividing. The blastocyst can then implant into the endometrial lining.
Where does the embryo implant?
In the postero-superior surface of the uterine cavity. In the stroma of the endometrium
What structural adaptations does the stroma undergo in preparation for implantation ?
Increased secretory glands
Increased vasculature
What is the window of fertility?
3 days before ovulation
Ovum has a maximum life span of 24 hours, Sperm can survive 72 hours in the female reproductive tract
What maintains the endometrium in the waiting phase after ovulation?
The corpus luteum
What is the lifespan of the corpus luteum?
14 days
How many sperm are produced a day?
100 million
What are the 2 specialised cells in the testis?
Leydig cells
Sertoli cells
What are the 3 components of the accessory glands?
Seminal Vesicles
Prostate gland
Bulbourethral glands
Describe the fraction of the seminal plasma produced at the accessory glands?
Seminal vesicle - 60%
Prostate gland - 25%
Bulbourethral glands - V. Small volume
What is the function of secretions of the seminal vesicles?
- alkaline , neutralises acid in the male urethra and female reproductive tract.
- fructose, prostaglandins and clotting factors
What is the function of the secretions of the prostate gland?
- acidic, buffering
- proteolytic enzymes (breakdown clotting proteins)
- citric acid, acid phosphatase
Describe the secretions of the bulbourethral glands?
- alkaline fluid
- a mucous that lubricates the end of the penis and urethral lining
What’s the normal volume of ejaculation?
2 - 6ml
What’s the usual pH of semen?
7 - 8
Where is the normal fertilisation site of the ovum?
Ampulla
Which nerves release Ach in the stimulation of an erection?
Parasympathetic post ganglionic neurones
What GPCR is responsible for the initiation of an erection?
M3 receptor on endothelial cells.
How does NO enter vascular smooth muscle?
2 ways
- released directly from nerves (cavernous nerve )
- rise in intracellular calcium vie activation of M3 receptor triggers formation of intracellular NO
What is sildenafil?
A.k.a viagra. It is a PDE V inhibitor. Frequently used to treat erectile dysfunction
What spinal level does the stimulation of an erection stem from?
Point = parasympathetic
Reflexogenic pathway = S2 - S4
At what spinal level does the innervation for ejaculation stem from?
Shoot = Sympathetic
Psychogenic pathway T10 to L2
What action does oestrogen have on the mucus of the cervix?
Just oestrogen = thin stretchy mucus
During the lateral phase, when oestrogen and progesterone are being released, how does the composition of the cervical fluid vary?
Previously thin and stretchy -> now thick and sticky to prevent further sperm entering.
What is a fern test?
Detection of a fern like pattern of vaginal secretions when a specimen is allowed to dry on a glass slide and viewed under a microscope. Used to provide evidence for the presence of amniotic fluid
What is Spinnbarkeit mucus?
Cervical mucus at the time of ovulation. Cervical fluid is abundant clear and strechable
Describe the change in female physiology during sex
- Excitement = labia swell, clitoris enlarges, vaginal lubrication, flexes posteriorly
- Plateau = Vagina expands, uterus elevates, orgasmic platform
- Orgasm = Contractions in uterus, rhythmic contractions in orgasmic platform
- Resolution = uterus lowers, orgasmic platform disappears.
Where is the semen deposited after sex?
At the entry of the cervix
What is the fertile period?
Sperm deposition up to 3 days prior to ovulation or day of ovulation
How are gametes transported?
Oocyte : cilia beating and peristalsis of uterine tube
Sperm : own propulsion
How is the acrosome reaction triggered?
Sperm pushes through the corona radiata
Binds to the sperm surface receptor on the zona pellucida (ZP3 glycoprotein)
Triggers autosome reaction
What reaction takes place to block polyspermy?
Cortical reaction.
What occurs on fertilisation?
Series of calcium waves are activated following fusion of the oocyte and sperm membranes. Completion of meiosis II of the female gamete.
What happens in assisted reproductive technology?
Oocytes fertilised in vitro, allowed to divide to the 4-8 cell stage. Morula transferred into the uterus.
What happens in pre-implantation genetic diagnosis?
A single cell is removed from the morula and tested for serious heritable conditions before transferring the embryo into the mother
After hatching, what occurs next?
Implantation
Where does the uterus implant in placenta praevia?
Into the lower uterine segment
What part of the embryo interacts with the endometrium?
The synctiotrophoblast
