Week 7.0 - Coitis and fertilisation Flashcards
How long does it take for spermatogonia to mature into spermatozoa?
-upto 74 days (50 in testis 12-24 in epididymis)
When does spermatogenesis begin/end?
-From puberty until death
How many of the sperm produced per day become viable sperm?
-50%
Does production of sperm stay the same throughout life?
-Decreases in quantity and quality with age
Which hormone acts on the leydig cells? What is the result of this?
- LH
- Production of testosterone
Which hormone acts on the sertoli cells? What is the result of this?
- FSH
- Antigen binding protein production leading to the concentration of testosterone in luminal fluid enabling spermatogenesis
If the pituitary gland is removed, how is spermatogenesis stimulated?
-FSH and testosterone
What is the function of oestrogen in the testis?
-Increase sperm viability
What is nuclear condensation and when does it happen?
-Extrusion of the cytoplasm and condensation of the nucleus from spermatid to spermatozoon
What does the acrosome contain? Why?
-Golgi apparatus and hydrolytic enzymes to enable sperm to penetrate ovum
Identify the main feature of the midpiece of a spermatozoon
Why is this needed?
- Mitochondria packed around either side
- Motility is a highly energy dependant process
What is the tail of a sperm made from?
-Flagellum produced by microtubules
What signals for the cytoplasm and organelles to be stripped from the permatid?
-Testosterone
What is different between the mature spermatozoa in the seminiferous tubules and the mature spermatozoa in the epididymis?
-Lack motility in the seminiferous tubules
What is spermiation?
-Release of spermatozoa from sertoli cells into seminiferous lumen
How are spermatozoa transported from seminiferous lumen to epididymis?
-Testicular fluid (produced by sertoli cells) and peristaltic contraction
How long can mature spermatozoa stay in the epididymis?
-Several months, eventually phagocytosed
How do the spermatozoa get into ductus deferens?
-Upon sexual arousal the epididymal wall contracts and expels the sperm into the ductus deferens
What are the phases of coitus?
- Excitement phase
- Plateau phase
- Orgasmic phase
- Resolution phase
What is the refractory period in males?
-After ejaculation it is not possible to ejaculate again upon further stimulation
Describe the excitement phase of the male sexual response
- Sensory and psychological stimulation
- Inhibition of sympathetic outflow (thoracolumbar)
- Activation of parasympathetic outflow (sacral)
- Ach-> M3 on endothelial cells of penile bvs -> increased Ca-> activation of eNOS -> NO production
- Arterial vasodilation in corpora cavernosa
- Increased penile blood flow
- Penile filling (full of blood but not erect)
- Penile tumescence (erection)
What happens to the testes and scrotum upon sexual arousal?
-Testes elevate and engorge and scrotal skin thickens and tenses
Describe the plateau phase of male sexual response
- Activation of sacrospinous reflex
- Contraction of ishiocavernosus -> compresses crus of penis and impedes venous return -> venous engorgement
- Rise in intracavernosus pressure higher than systolic pressure -> decreased arterial inflow
- Stimulation of secretion from accessory glands
- Loss of erection unlikely
Which accessory glands are stimulated in the plateau phase of male sexual response?
- Cowpers glands
- Littre’s glands
What are the two stages of orgasmic phase in male sexual arousal?
- Emission
- Ejactulation
Describe the emission stage of orgasmic phase in male sexual response
- Stimulation of sympathetic reflex
- Contraction of smooth muscle in ductus deferens, seminal vesicle and prostate
- Internal and external urethra contracts
- Semen becomes pooled in urethral bulb
Describe the ejaculation stage of orgasmic phase of male sexual response
- Sympathetic spinal reflex with cortical control
- Further contraction of glands and ducts and sphincters
- Filling of urethra stimulates pudendal nerve-> contractions of the genital organs, ischiocavernosus and bulbocavernosus -> expulsion of semen
Describe the resolution phase of the male sexual response
- Activation of sympathetic outflow
- Contraction of arteriolar smooth muscle in corpora cavernosa
- Increased venous return
- Detumescence and flaccidity
- Testes descend and scrotum thins and relaxes
- Refractory period entered
Describe the excitement phase of the female sexual response
- Sensory and psychological stimulation
- Activation of parasympathertic outflow; inhibition of sympathetic outflow
- Vasocongestion causes vaginal lubrication to begin
- Clitoris becomes engorged with blood
- Uterus elevates, inner 2/3 of vagina lengthens and expands
- Increased muscle tone, HR and BP
Describe the plateau phase of female sexual response
- Further increase in muscle tone, HR and BP
- Labia minora deepen in colour
- Clitoris withdraws under its hood
- Barthlin glands secretions lubticates vestibule for entry of penis
- Orgasmic platform forms in lower 1/3 of vagina, upper 2/3 fully distended and uterus is fully elevated
Describe the orgasmic phase of the female sexual response
- Orgasmic platform contracts rhythmically 3-15 times
- Uterus contracts, anal sphincter contracts
- Clitoris remains retracted under its hood
- No refractory period - multiple orgasms possible
In which direction does the uterus contract during a female orgasm?
-From fundus down to cervix
Describe the resolution phase of the female sexual response
- Clitoris descends and engorgement subsides
- Labia returned to unaroused colour and size
- Uterus descends
- Vagina shortens and narrows back to unaroused state
What happens to the breasts during female sexual response?
- Breasts increase in size
- Nipples become erect
- Areola increases in size
- Sex flush
What is ‘the G spot’?
- Area of erotic sensitivity located on the anterior wall of the vagina which can stimulate female ejaculation in some women
- Tissue similar to prostate
What happens to the female sexual response cycle with age?
- Reduced desire
- Reduced vasocongestion-> reduced vaginal lubrication
- Vaginal and urethral tissue loose elasticity
- Length and width of vagina decrease with reduced expansile capacity
- Number of orgasmic contractions reduced
What is the most common problem in sexual dysfunction? How can it manifest?
- Desire
- Hypoactive, aversion, hyperactive nymphomania/satyriasis
What is Kluver Bucci syndrome?
-Bilateral medial temporal lobe lesion causing hyperphagia, hypersexuality, hyperorality, visual agnosia and docility
What is arousal sexual dysfunction in females?
-Persistent, recurrent inability to attain or maintain lubrication-swelling response
What is arousal sexual dysfunction in males? Give some causes
- Impotence
- Psychological, tissue damage, vascular damage, drugs (alcohol/anti-hypertensives)
How does viagra work?
-Inhibits cGMP breakdown causing increased Ca and Increased NO production
How much semen is produced in one ejaculation?
-2-4 ml
How many sperm in one ejaculation?
-20-200x10^6/ml
How many sperm are viable per ejaculation?
-60% (at least 30% abnormal)
What is the definition of abnormal low sperm count?
-less than 20 million/ml
Describe the glandular secretions from the seminal vesicles
- Make up 60% of ejaculate
- Alkaline fluid to neutralise urethra, fructose for ATP production, prostaglandins and clotting factors (semenogelin)
Why does semen contains prostaglandins?
-Increases sperm motility and female genital smooth muscle contraction
Why does semen contain clotting factors?
-Liquefaction of semen in 1 hour
Describe the glandular secretions from the prostate
- 25% of ejaculate
- Milkym slightly acidic secretion containing proteolytic enzymes (PSA/pepsinogen) and citric acid
Why do prostate secretions contain proteolytic enzymes?
-Activate clotting factors
Describe the glandular secretions from the bulbourethral glands
- 5% of ejaculate
- Alkaline fluid to neutralise distal urethra
Where is semen depositied?
-High in the vagina near external os
During the secretory phase of the uterine cycle, describe the mucus at the cervix
Why?
-Thick, sticky, acidic mucus plug to prevent bacterial inflow
What is the function of oxytocin in sperm transport?
-Stimulates uterine contraction to propel sperm
Describe cytoplasmic maturation in the oocyte
-Organelles become arranged around the periphery, lipid and protein synthesis occurs
How many sperm does it take for fertilisation?
- Out of 200-300 million sperm, ~300 reach the fertilisation site
- 299+ sacrificed to disperse the zona pellucida -> 1 for fertilisation
How long can sperm survive in the female genital tract?
-upto 5 days
How long does the ovulated oocyte survive?
-6-24 hours before phagocytosis
When is the fertile period when sperm needs to be depositied?
-Upto 3 days prior to ovulation and on day of ovulation
How and how long does fertilised oocyte take to travel to uterus?
-3/4 days via peristalsis and cilia
What does the sperm need to penetrate on the oocyte for fertilisation?
- Corona radiata
- Zona pellucida
What is capacitation?
- The final stage of spermatozoa maturation which takes place in the female genital tract
- Cell membrane changes to allow fusion with oocyte surface by removal of protein coat of sperm, exposing the acrosomal enzymes
- Tail changes from beat to whip-like action
What is the acrosome reaction?
- When sperm pushes through granulosa cells of corona radiata it has intact acrosome
- Protein coat then binds to ZP3 proteins of zona pellucida triggering acrosome reaction
- Path digested through ZP and one sperm penetrates and fuses with oocyte forming zygote
Where abouts in meiosis II of the oocyte is it halted?
-Metaphase
Describe sperm-oolemma binding and fusion
The oocyte has two regions of its PM: that which directly overlies metaphase chromosomes and is devoid of microvilli and the rest is rich in microvilli protrusions. The sperm binds to the microvilli
What is the fast block to polyspermy?
-As soon as a sperm penetrates the zona pellucida there is an electrical change in the oocyte membrane -> Na channels open increasing the membrane potential to +25 mv. This causes a wave of depolarisation which starts at the site of sperm entry and propagates across the cytoplasm -> this prevents sperm from fusing
What is the slow block to polyspermy?
- Ca released from ER induces local exocytosis of cortical granules-> granules release enzymes to stimulate adjacent granules to undergo exocytosis
- Wave of exocytosis around the oocyte alters the zona pellucida in such a way that sperm can no longer penetrate
What is syngamy?
- Completion of meiosis II with extrusion of polar body
- Male and female pronuclei migrate towards each other and fuse to form diploid zygote
What is polyploidy?
-Embryos containing 3 or more pronuclei (polyspermy of failure of polar body extrusion
What is cleavage?
-A series of rapid mitotic divisions which increases zygote cell number but not size thus increasing the nucleus:cytoplasmic ratio
How do monozygotic twins occur as a result of cleavage?
-Totipotent cells become divided into 2 separate individual cell masses
How do you get non-identical twins?
-Two eggs ovulates, two eggs fertilised
What is compaction?
-At the 8 cell stage, blastomeres undergo compaction where cells become polarised and communicate by tight junctions
What is a morula?
-16 stage blastomere as embryo passes into uterus
What is hatching?
-Local digestion of zona pellucida by enzymes produced by trophoblast so it can begin implantation
Does the conceptus implant immediately after entered uterus?
-No, nourished in an intrauterine fluid for 2-3 days
Where are spermatozoa produced?
-Seminiferous tubules
