Reproductive System Week 7 Flashcards
What is coitus?
The act of sexual intercourse that results in the deposition of sperms inside the vagina at the level of the cervix
What happens to the sperm after ejaculation at the cervix?
A proportion of sperm enters the uterus and reaches the uterine tubes where they may encounter an ovum released from the ovary
What is conception?
Fertilisation of the ovum by a sperm and the subsequent establishment of pregnancy
What are the stages of sexual excitement?
Excitement phase, plateau phase, orgasmic phase and resolution phase
What happens during sexual excitement (broadly)?
Genital and systemic changes in both sexes
Describe the male sexual response
Excitement phase -
- sensory and psychological stimulation–> limbic system
- activation of sacral parasympathetic neurones
- inhibition of thoracolumbar sympathetic neurones
- ACh -> M3 receptors on endothelial cells –> more intracellular Calcium –> activation of eNOS –> NO production (vasodilator)
- Arteriolar vasodilation in corpus cavernosa
- increased penile blood flow
- penile filling (latency)
- penile tumescence (erection - reversible) -
- testes begin to elevate and engorge
- scrotal skin thickens and tenses
Plateau phase
Activation of sacrospinous reflex
Contraction of bulbospongiosus ischiocavernosus (compresses crus penis and
impedes venous return) → venous engorgement
Rise in intracavernosus pressure → decreased arterial inflow Stimulation of secretionfrom accessory glands:
Cowper’s and Littre’s glands
• Lubricate distal urethra
• Neutralise acidic urine in urethra
• 5% of ejaculate
Corona may become further engorged
Testes become completely engorged and elevated
Loss of erection unlikely
Orgasm:
Emission:
Simulation of thoracolumbar sympathetic reflex
Contraction of smooth muscle in ductus deferens, ampulla, seminal
vesicle and prostate
Internal and external urethral sphincters contract - prevents retrograde ejaculation
Semen is pooled in urethral bulb
Contractions of ampulla of vas deferens
Ejaculation:
Spinal reflex (with cortical control)
Sympathetic Nervous System (L1, L2)
Contraction of glands and ducts (smooth muscle)
Internal urethral sphincter contracts
Filling of the internal urethra stimulates pudendal nerve
–>contractions of the genital organs, the ischiocavernosus and bulbocavernosus muscles –>expulsion of semen
External urethral sphincter relaxes
Contractions of penile urethra
Contraction of anal sphincter
Resolution:
Activation of thoracolumbar sympathetic pathway
Contraction of arteriolar smooth muscle in corpora cavernosa Increased venous return
Detumescence and flaccidity - erection loss
Refractory period
Testes descend and return to unstimulated size
Scrotum thins and resumes wrinkled appearance
Describe the female sexual response
Excitement:
Same neuronal responses as male - parasympathetic from sacral plexus
Vaginal lubrication begins (due to vasocongestion)
Inner 2/3 of vagina lengthen and expand
Clitoris engorges with blood
Uterus elevates
Increase in muscle tone, heart rate, and BP
Breast size increases
Nipple becomes erect
Veins become more distinct
Plateau:
Further increase in muscle tone, heart rate and BP
Labia minora deepen in color
Clitoris withdraws under its hood
Bartholin’s gland secretion lubricates vestibule for entry of penis
Orgasmic platform forms in lower 1/3 of vagina - rhythmic contractions
Inner 2/3 of vagina fully extended
Breast same as orgasm phase
Orgasm:
Orgasmic platform (outer 1/3 of vagina) contracts rhythmically 3-15
times
Uterus contracts starting at fundus and moving down, anal sphincter contracts
Clitoris remains retracted under hood
No refractory period - multiple orgasms possible
Greater size increase of breast
Areola increases in size and causes nipple to seem less erect
Sex flush may appear on breasts and upper abdomen
Resolution:
Clitoris descends and engorgement subsides
Labia return to unaroused size and color
Uterus descends to unaroused position
Vagina shortens and narrows back to unaroused state
Breast - areola detumescence nipple appears more erect - disappearance of sex flush, return to unaroused size of breast
What is the G spot?
Grafenberg spot (Ernest Grafenberg, a
gynaecologist who first publicised G spot in
1950s)
Area of erotic sensitivity located along the
anterior wall of the vagina.
Some women are able to experience orgasm and possibly ejaculation from G spot stimulation.
– G spot tissue is similar to male prostate;
therefore, fluid may be similar to prostatic
component of semen.
Supported by research that showed
presence of enzyme in female ejaculate
characteristic of prostate secretions
Orgasm from G spot stimulation is same as
orgasm from clitoral stimulation, though intensity
may vary depending on the method of
stimulation.
What happens to the female sexual response with age?
Some women report reduced desire
Reduced vasocongestion response, causing reduced
vaginal lubrication
Vaginal and urethral tissue lose elasticity
Length and width of vagina decrease; reduced expansile
ability of inner vagina during arousal
Number of orgasmic contractions is often reduced
More rapid resolution
What is a normal amount to be having sex?
Normal varies from person to person
10-20% of married couples report engaging in sexual activity a couple of times per year
30% report engaging in sexual activity 2-3 times per week
What is the most common type of sexual dysfunction?
Desire - increasing incidence
Name some sexual dysfunctions to do with desire
Hypoactivity
Aversion - revulsion or fear of one or more aspects of sex - often a result of assault or abuse
Hyperactive
Nymphomaniac
Kluver Bucci syndrome - bilateral medial temporal lobe lesions from cerebral metastases or head injury etc. –> hyperphagia, hypersexuality, hyperorality, visual agnosia and docility
Describe sexual dysfunctions involving arousal
Female - persistent, recurrent inability to attain or maintain lubrication-swelling response - -> lack of lubrication (especially in menopause)
Male - impotence - psychological (descending inhibition of spinal reflexes), tears in fibrous tissue of corpora cavernosa, vascular (atherosclerosis, diabetes), drugs (alcohol, antihypertensives - B blockers and diuretics)
Describe the mechanism of action of viagra
Inhibits cGMP breakdown in corpus cavernosum
Increases NO stimulated vasodilation
Increases penile blood flow –> erection
What is an alternative treatment to viagra?
Penile implant - reservoir of fluid - pump up by squeezing bulb in scrotum
Describe the properties of normal semen
2-4ml 20-200x10^6 sperm per ml Total sperm per ejaculate >40 X10^6 >60% sperm swimming forward vigorously <30% abnormal morphology Liquefaction within 1 hour
When is semen described as abnormal?
< 20x10^6 sperm per ml (oligozoospermia)
Or doesnt meet the other criteria for ‘normal’
What are some sperm morphological defects?
Giant Micro sperm Double head Double body Long head Rough head Abnormal middle piece
Describe the glandular components of semen
Bulbourethral glands - 5% volume
- alkaline fluid
- mucous lubricants the tip of the penis and urethral lining
Seminal vesicles - 60% of volume
- alkaline fluid - neutralises the acid in male urethra and female reproductive tract
- fructose (ATP production), prostaglandins (increase sperm motility, increase female genital smooth muscle contractions), clotting factors (semenogelin)
Prostate- 25% volume
- milky, slightly acidic fluid
- proteolytic enzymes (PSA, pepsinogen - breakdown clotting factors from seminal vesicles, reliquify semen in 10-20 mins)
- citric acid (ATP production), acid phosphatase
When is the female reproductive tract a hospitable environment for fertilisation and implantation?
Days 14-28 - uterine secretory phase - oestrogen and progesterone
How does the female reproductive tract aid in getting the semen to the site of fertilisation?
Site of fertilisation - ampulla
Site of deposition - cervix
Oxytocin stimulates uterine contractions
Describe how the cervical mucous changes over the uterine cycle
Days 7-14 - oestrogen only - abundant, clear non-viscous cervical mucous
Days 14-28 - oestrogen and progesterone - thick, sticky mucous plug - prevents infection from reaching uterus
Describe the nuclear maturation of the oocyte
Oocyte undergoes meiosis I
Nuclear membrane of oocyte disappears
First polar body separates and enters the perivitelline space
Second meiotic division takes place - stops in metaphase II
Describe the cytoplasmic maturation of the oocyte
Mitochondria dispersed throughout the cytoplasm
Endoplasmic reticulum - accumulates in oocyte cortex, protein and lipid synthesis creates cortical granules
The granules are initially dispersed throughout the cytoplasm but become cortical as the oocyte matures
Lipid droplets provide energy for meiosis, maturation, fertilisation and early embryo development
Cytoskeleton microfilaments migrate towards oocyte cortex
How many sperm are required to get pregnant?
Average 200-300 million per ejaculate
300 reach fertilisation site
299+ sacrificed to disperse the zona pellucida
1 sperm required for fertilisation
How long do sperm survive in the female genital tract?
Up to 5 days
How long do oocytes survive?
6-24 hours before phagocytosis
When is the fertile period?
Sperm deposition can be up to 3 days prior to ovulation or on the day of ovulation
The oocyte takes 3-4 days to travel from the ovary to the body of the uterus (cilia and Fallopian tube peristalsis)
Fertilisation is in the Fallopian tube
How long does it take the oocyte to travel to the uterus?
The oocyte takes 3-4 days to travel from the ovary to the body of the uterus (cilia and Fallopian tube peristalsis)
Describe how sperm further mature in the female genital tract before fertilisation can occur
Sperm undergo further maturation for 6-8 hours after deposition in the female genital tract (capacitation)
Sperm cell membrane changes in the female genital tract environment to allow fusion with the oocyte cell surface - removal of protein coat and acrosomal enzymes are exposed which can digest through the zona pellucida
Tail movement changes from beat to whip-like action (3mm/hour)
Sperm need to penetrate corona radiata (follicular cells)
And zona pellucida (glycoprotein membrane) of the ovum
Describe how the acrosome reaction begins and what it involves
When sperm contacts the corona radiata has an intact acrosome
Pushes through the corona radiata using the force produced by the tail
Proteins on sperm head bind to ZP3 proteins of zona pellucida
Triggers acrosome reaction:
Key signalling mechanism nvolves intracellular calcium
Acrosomal enzymes digest path through ZP
One sperm penetrates –> fusion of plasma membranes of oocyte and sperm
Sperm moves into cytoplasm –> zygote
Cortical reaction prevents polyspermy
Describe the plasma membrane of the oocyte
Can be divided into two major regions:
- the part that directly overlies the metaphase chromosomes is smooth and devoid of microvilli
- the rest is rich in micro villas protrusions - where sperm bind and fuse
Describe the fast block and slow block to polyspermy
Fast block:
Electrical change in oocyte membrane
Na channels open (resting potential is -75mV, fertilisation potential is +20mV)
Wave of depolarisation starts at point of entry of sperm and propagates across the cytoplasm
Slow block:
Calcium released from endoplasmic reticulum induces local exocytosis of cortical granules
Granules release enzymes to stimulate adjacent cortical granules to undergo exocytosis
Wave of exocytosis occurs around oocyte in 3 dimensions from original point of entry of sperm
What is syngamy?
The union of male and female pronuclei to form a diploid zygote nucleus (46 chromosomes)
Oocyte completes meiosis II, expels second polar body, and the male and female pronuclei migrate towards each other to fuse
