Module 3: Conception and Implantation Flashcards
Four phase model components
-phase 1
-phase 2
-phase 3
-phase 4
Phase 1
-excitement
-increase in arousal that results as a response to sexual stimuli, characterized by increased heart rate, and blood pressure, and increase of blood flow to the genitals etc
Phase 2
-plateau
-characterized by continuation or intensification of responses in phase 1
Phase 3
-orgasm
-conclusion of plateau phase, lasts only a few seconds
-involuntary muscle contractions, peak in heart rate, blood pressure and breathing, and release of muscle tension
Phase 4
-resolution
-body returns to normal state, swelled/erect body parts return to previous size and colour
How is sexual response mediated
-by coordinated activity of autonomic and somatic innervation
Where does innervation for reproductive organs originate from
-sacral (parasympathetic) and lumbar nerve roots (sympathetic) in spine
Vascular dilation
-part of the sex response, causes this of genital organs
Stimulation of secretions
-either prostatic or vaginal secretions
Smooth muscle contractions
-of vas deferens during ejaculation in males
-rhythmic vaginal contractions during orgasm in females
Contractions of the somatic pelvic muscles
-accompany orgasm in both sexes
Phase 1 in males
-erectile reflex caused by stimulation of parasympathetic nerves that supply arterioles of penis
Phase 1 in males molecules
-nitric oxide
-guanylyl cyclase
Nitric oxide
-main molecule responsible for inducing relaxation of smooth muscles of the penile arterioles
Guanylyl cyclase
-activated by nitric oxide
-increases cellular concentration of cGMP to cause a reduction in intracellular ion concentration
Phase 2 in males
-erection continues
-urethral sphincter contracts to prevent retrograde ejactulation
-bulborethral glands produce mucus
-scrotum becomes tightened causing testicles to rise to body
Phase 3 in males components
-emission
-expulsion
-emission continued
-expulsion continues
Phase 3 in males emission
-bladder neck closes to prevent retrograde ejaculation
Phase 3 in males expulsion
-semen is propelled outward via muscular contractions
Phase 3 in males emission continued
-sperm cells are mized with prostatic fluid as they are ejected into prostatic section of urethra, followed by seminal vesicle fluid
Phase 3 in males expulsion continued
-rhythmic contractions are generated by bulbospongiosus and ischiocavernosus modules
Phase 4 in males
-the release of oxytocin is believed to be chiefly responsible for the male refractory period
Erectile disorders
-ischemic priapism
-erectile dysfunction
Ischemic priapism
-condition where the penis remains erect for hours due to inadequate draining of blood from penis
-occurs when there are problems in the resolution phase
NO pathway and erectile dysfunction
-PDE-5 rapidly metabolizes cGMP to GMP
-blocking this enxyme would allow cGMP concentrations to increase which would led to increased vasodilation
Phase 1 in females components
-swelling of external genitalia
-elevation of uterus
-increased vaginal lubrication
-swelling of breasts
Phase 1 in females swelling of external genitalia innervation
-innervated by parasympathetic nerve fibres
Phase 1 in females elevation of the uterus
-uterus raises upward, known as uterine tenting
-causing internal enlargement of vaginal canal
Phase 1 in females increased vaginal lubrication
-production of vaginal lubrication
Phase 1 in females swelling of the breasts
-increased blood pressure causes swelling and enlargement of breasts
Phase 2 in females
-swelling of clitoris, labia minora, and vagina increases
-uterus elevated further
-near orgasm the pubococcygeus muscle tightens, reducing diameter of vaginal opening
Orgasmic platform
-tissues near vaginal opening swell significantly
Phase 3 in females
-orgasm leads to involuntary, rhythmic contractions of the uterus and vaginal muscles, followed by release of muscle tension
Phase 4 in females
-a refractory period occurs but is not as pronounced as in males
-some women can experience multiple orgasms before or after entering refractory period
Persistent genital arousal disorder
-women
-spontanoeus, unwanted and uncontrollable genital arousal experienced by patients is often very painful and significantly disrupts functioning
How has the pelvis changed over time
-relative position shifted downwards
-wider pelvic and vaginal canal to fir bigger heads
How has the penis changed over time
-had to grow larger to maintain compulsory fit necessary to stimulate both partners toward sexual intercourse
Egg transport
-refers to the movement of oocyte from moment of expulsion from ovarian follicle to entry into the distal segment of fallopian tube
Cumulus-oocyte complex
-oocyte is released within this thick layer, and produces large amounts of hyaluronan, which forms an expanded extracellular matrix
Cumulus-oocyte complex function
-aiding of picking up the oocyte by the oviduct
-release of sperm-attracting molecules that increase chances of an encounter
Egg sweeping
-the oocyte does not immediately land in the fallopian tube it must find its way
-it is believed that periodic sweeping of ovarian surface by fimbriae allows egg to attach
Oocyte transfer to ampulla
-the beating of ciliated cells of the oviductal epithelium and peristaltic movements of oviduct help with transport
Activation of the oocyte
-final step that occurs at fertilization, where it completes meiosis II and fusion with the sperm
Capacitation
-process by which sperm acquire the capacity to fertilize
When does capacitation begin
-when sperm come in contact with the cervical mucus
Decapacitation factors
-inhibitory factors that aim to delay activation and increase chances of reaching oocyte in optimal state
-seminal fluids coat them with these factors
Main decapacitation factor
-cholesterol
Cholesterol
-powerful decapacitation factor that serves to stabilize plasma membrane of spermatozoa during transit
Albumin
-from female secretions
-binds cholesterol causing the outer membrane to have increase permeability and fluidity
What does a more permeable sperm plasma membrane cause
-allows for influx of calcium and bicarbonate resulting in activation of second messengers and initiation of signaling events that will later facilitate the acrosome reaction
Flagellar wave pattern of sperm
-changes to asymmetrical and faster thrashing of the sperm tail
-propels sperm forward and to penetrate the outer layer of the oocyte
Catsper sperm hyperactivation
-calcium ion channel
Catsper function
-binding of progesterone activates calcium channel and stimulated hypermobility of tail towards the oocyte
Acrosome reaction
-exocytotic process occuring in the sperm head that is essential or penetration of the zona pellucida and fertilization of the oocyte
Role of seminal fluid in fertilization
-has an alkaline pH and other factors to protect sperm from natural acidity of vaginal canal which is toxic to sperm
What happens to most of the sperm relesed during ejaculation
-they are eliminated through the same mechanisms designed to defend female tract from pathogens
Mechanisms to facilitate transfer of sperm
-cervical mucus and muscle contraction
-oviductal fluid
Cervical mucus and muscle contraction
-cervical mucus becomes thinner due to high levels of estrogen, which helps the sperm swim towards oocyte
Oviductal fluid
-produced by oviductal epithelium and always flows in the direction of the uterus
-both egg and chemoattractant molecules that indicate the position of the egg are pushed towards incoming sperm
Cervical mucus in the follicular phase
-prior
Cervical mucus around time of ovulation
-trigger opening of the cervix and thinning of cervical mucus to help sperm swim towards egg
Cervical mucus during the luteal phase
-secretions form a thick plug and the cervix tightens in order to block sperm penetration
How long is oocyte available for
-24-48 hours
How long can sperm survive for
-3-5 days
Where is the site of fertilization
-oviduct
-specifically the ampulla of fallopian tube
Steps of fertilization
-binding and penetration of cumulus matrix
-adhesion and penetration of zona pellucida
-plasma membrane fusion
-oocyte activation and nuclear fusion
Binding and penetration of cumulus matrix
-sperm makes contact with outer layer of cumulus cells, a protein that is present in the sperm head comes in contact with hyaluronan molecules in extracellular matrix and begins to degrade them to reach zona pellucida
Adhesion and penetration of zona pellucida
-plasma membrane of sperm head bond to ZP3 which triggers acrosome reaction
Acrosome reaction
-involves fusion of plasma membrane with outer acrosomal membrane of sperm, which causes release of enzymes which allow sperm to reach vitelline membrane
Plasma membrane fusion
-sperm penetrate the zona and enter perivitelline space, inner acrosomal membrane binds to oocyte membrane via ZP2 receptor which mediates fusion of plasma membranes and sperm loses tail
Mechanisms of preventing double fertilization
-fast block
-cortical reaction (slow block)
Fast block
-near instantaneous change in sodium ion permeability upon binding of the first sperm
-depolarizes oocyte plasma membrane and prevents fusion of additional sperm cells
Cortical reaction (slow block)
-cortical granules sitting immediately below the oocyte plasma membrane fuse with the membrane and release zonal inhibiting proteins and glyocosaminoglycans into the perivitelline space
-causing release of any other attached sperm and detroying oocytes glycoproteins, preventing any other sperm from binding
Oocyte activation and nuclear fusion
-egg resumes and completes meiosis II and pronuclei of oocyte and sperm fuse to create a zygote
Zinc
-an element involved in egg activation, required for high levels for meiotic progression of the egg
What must happen to zinc levels after fertilization
-must decrease to allow for cell cycle resumption
Oocyte to embryo transition
-when parental genomes fuse, the genome is reprogrammed to switch from a highly specialized cell to a totipotent cell
Preimplantation period
-period of time between fertilization and the moment the embryo attaches
How long is the preimplantation period
-8-10 days
Cleavage
-rapid cell divisions that lead to tissue differentiation
When does cleavage occur
-day 0-8
Blastomeres
-resulting cells of cleavage
Day 1 of implantation process
-first cleavage
-will divide into 2 cells
-known as 2-cell stage
Day 2-4 of implantation process
-further cleavages, will divide into 4, 8, and 16 cells
What is a 16 cell mass called
-morula
Day 4 of implantation process
-compaction
-the morula cells will begin to exert pressure on each other and become deformed and flattened
Day 6-7 of implantation process
-zona hatching
-blastocyst breaks our of zona pellucida and this allows trophoblast cells to come in direct contact with uterine epithelium and begin process of implantation
Day 7-10 of implantation process
-implantation
-attaches itself to uterine cavity
Implantation steps
-apposition
-adhesion
-invasion
Implantation apposition
-connection with uterine wall is formed
-microvilli on surface of trophoblast interdigitate with microprotrusions on uterine epithelium known as pinopodes to make a weak connection
Implantation adhesion
-day 6-7
-combination of inhibitory signals and adhesive signals from endometrial surface help embryo avoid areas with poor chances of implantation, and adheres to an appropriate spot on endometrium
Implantation invasion
-trophoblast cells begin to penetrate and effectively invade endometrium by day 9-10
-uterine epithelium grows over to cover site of implantation
Ectopic implantation
-abnormal implantation of the blastocyst
Where might ectopic implantation occur
-ovary
-cervix
-abdominal cavity
Window of implantation
-endometrium is typically not receptive to implantation except around this window
Decidualization of the uterine lining
-a receptive endometrium will have increased vascularization and enhances secretory activity in uterine glands
What hormone helps with decidualization of uterine lining
-progesterone
What happens to uterus during decisualization
-uterine glands increase in size
-stromal cells turn into large swollen cells containing extra quantities of glycogen, proteins, and lipids for development of embryo
Decidua
-after decidualization the uterine lining is called this
-only during pregnancy
Histiotrophic nutrition
-embryo is unable to connect to maternal circulation early on and therefore receives nutrients provided by decidua
Hemotrophic nutrition
-after around day 16 the embryo will have access to maternal blood and will be able to receive nutrition in this way
Reccurent implantation failure
-cause of female infertility
-may be caused by inadequate uterus receptivity or problems with uterus itself
