Reproductive Endocrinology II Flashcards
4 stages of sexual arousal
- excitement (psychogenic and/or somatogenic, individualised)
- plateau
- orgasm
- resolution
Male excitement
- heightened sexual awareness
- testicular vasocongestion
- engorgement of penis
Female excitement
- heightened sexual awareness
- vasodilation of vagina and external genitalia
- erection of clitoris
- lubrication of vagina
- enlargement of breasts
- flush to skin
Male plateau
- intensification of excitement
- increase HR, BP, resp rate, muscle tension
Female plateau
- as male
- vasodilation of lower 1/3 of vagina causing tightening around penis
- “tenting effect”
- uterus raises
- lifts cervix
- enlarges upper 1/2 of vagina to make room for ejaculate
Male orgasm
- intense physical pleasure
- ejaculation
- rhythmic contractions of pelvic muscles every 0.8 seconds
- increase HR, BP, resp rate, muscle tension
Female orgasm
- intense physical pleasure
- rhythmic contractions of pelvic muscles every 0.8 sec
- increase HR, BP, resp rate, muscle tension
- no ejaculation
- no refractory period so can have another orgasm immediately
Emission of ejaculation
- stimulation of mechanoreceptors in glands of penis
- synthetic response
- contraction of smooth muscle in Prostate -> prostatic fluid, reproductive ducts -> sperm, seminal vesicles -> s.v. fluid
- semen secreted into prostatic urethra
Expulsion of ejaculation
- motor neurone induced rhythmic contraction (0.8/sec) of skeletal muscle at base of penis
- semen forced out through urethra
How is male erection accomplished
engorgement of the penis erectile tissue with blood as a result of marked parasympathetically induced vasodilation of the penile arterioles and mechanical compression of the veins
Male resolution
- temporal refractory period
- relaxation
- return of body to pre excitement state
- slowing of blood flow to penis
Female resolution
- no refractory period
- relaxation
- return of body to pre excitement stage
Capacitation
- freshly ejaculated sperm are incapable of fertilisation and must undergo capacitation
- surface of sperm is altered by removal of glycoprotein coat
- tail movements become whip like
- cAMP levels rise to promote acrosomal reaction
Describe the process of fertilisation
1) sperm penetrates radiata via membrane-bound enzymes in plasma membrane of its head and binds to ZP3 receptors on the zona pellucida
2) binding of sperm to these receptors triggers acrosome reaction -> hydrolytic enzymes in acrosome are released onto the zona pellucida
3) acrosomal enzymes digest zona pellucida, creating pathway to plasma membrane of the ovum
4) sperm fuses and nucleus enters the ovum cytoplasm
5) sperm stimulates release of calcium stored in cortical granules in the ovum, which activates ZP3 receptors, leading to the block polyspermy
Penetration of egg by sperm
- Allurin -> released by mature ovum to attract sperm, sperm smell this chemical using olfactory receptor
- Fertilin binds to inregrin
- Acrosomal reaction
- Final meiotic division of secondary oocyte triggered
- sperm and egg nuclei fuse
Acrosomal reaction
- enzymes in the acrosomal tip allow a sperm to “burrow “ through the outer layers of ovum and enter cytoplasm
- block to polyspermy membrane changes triggered
- tail of sperm probably lost
Early stages of development from fertilisation to implantation
fertilised ovum progressively divides and differentiates into a blastocyst as it moves from site of fertilisation in upper oviduct to site of implantation in the uterus
Implantation 1
- initial contact with the epithelium of uterus -> blastocyst is sticky
- proteases released from trophoblast
- pathways created allowing trophoblast cells to grow into endometrium
- trophoblast releases nutrients for embryo
Implantation 2
- trophoblast cells tunnel into the endometrial lining
- boundaries between trophoblast cells disintegrate “syncytiotrophoblast” will become foetal placenta
- trophoblast induces “decidualization” od endometrium - increased local vascularisation and nutrient storage
- formation of blood vessels in local area by implantation site
- blastocyst becomes buried in uterine lining by day 12
Development of the placenta
- placenta derived from both trophoblast and decidual tissue
- trophoblast cells differentiate into multinucleat “syncytiotrophoblasts” which invade decidua and break down capillaries to form cavities filled with maternal blood
- developing embryo sends capillaries into the syncytiotrophoblast projections to form “placental villi”
- each villus contains foetal capillaries separated form maternal blood by a thin layer of tissue
- 2 way exchange of respiratory gases, nutrients, metabolites, etc. between mother and foetus, largely down diffusion gradient
Hormonal maintenance of pregnancy during 1st trimester
- hCG produced by blastocyst prolongs life of corpus luteum -> for 10 weeks, CL grows and produces increasing concentrations of progesterone and oestrogen, after 10 weeks the placenta produces these hormones
- hCG detected in urine throughout pregnancy
- hCG may trigger vomiting centre
- end of 1st trimester, hCG stimulates male foetal gonads to produce steroid hormones -> genitalia differentiation
Why oestrogen does not initially come from placenta
- placenta does not possess all enzymes needed for oestrogen synthesis in 1st trimester
- placenta requires dehydroepiandosterone (DHEA) from foetal adrenal cortex, which takes time to develop
- “foetoplacental unit” is used
Roles of oestrogens and progesterone in pregnancy
- secreted by CL in 1st trimester and placenta in 2nd and 3rd trimesters
- oestrogens stimulate growth of myometrium musculature and stimulate development of mammary gland ducts
- progesterone suppresses contractions of uterine myometrium, promotes formation of mucus plug, and stimulates development of mammary milk glands
Gestation
- approx 38 weeks from conception, approx 40 weeks from last period
- embryo/foetus grows and develops
Changes mothers undergo during gestation
- enlargement of uterus
- enlargement of breasts which become able to produce milk
- increased blood volume
- weight gain
- increased pulmonary ventilation
- increased urine
- increased nutritional requirements
Endocrine secretions of the placenta during gestation
- hCG
- oestrogens and progesterone
- hCS
- PTHrp
- relaxin
- CRH
Function of hCG
- maintains CL
- stimulates secretion of testosterone by developing testes in the XY embryos
Function oestrogen
- stimulates growth of the myometrium
- helps prepare the mammary glands for lactation
Functions of progesterone
- suppresses uterine contractions to provide a quiet environment for the foetus
- promotes formation of a cervical mucus plug to prevent uterine contamination
- helps prepare the mammary glands for lactation
Functions of human chorionic somatomammotropin (hCS)
- reduces maternal use of glucose and promotes the breakdown of stored fat so that greater quantities of glucose and free fatty acids may be shunted to the foetus
- helps prepare the mammary glands for lactation
Functions of relaxin
- softens the cervix in preparation for cervical dilation at parturition
- loosens the connective tissue between the pelvic bones in preparation for parturition
Functions of placental PTHrp
- increases maternal plasma calcium level for use in calcifying foetal bones; if necessary, promotes localised dissolution of maternal bones, mobilising their calcium stores for use of the developing foetus
Parturition
- labour, delivery or birth
- requires dilation of the cervical canal and contractions of uterine myometrium
Preparation for parturition
- Braxton-Hicks contractions (“false labour” increased uterine sensitivity)
- softening of cervix caused by relaxin and prostaglandins
- relaxation of pelvic bones caused by relaxin
- foetal drop so that head is in contact with cervix
Labour initiation
- increased CRH secretion into foetal circulation
- increased ACTH increases cortisol and DHEA release from the foetal adrenal cortex
1st stage of labour
- cervical dilation stage
- takes many hours
- rupture of amniotic sac
- cervix dilates to 10cm to accommodate the baby’s head
2nd stage of labour
- delivery of baby
- usually takes 30-90 minutes
- baby moves through cervix to vagina
- stretch receptors in vagina trigger contraction of abdominal wall to augment uterine contractions
- mother can voluntarily contract abs
- after birth, baby is freed from placenta by cutting umbilical cord
3rd stage of labour
- delivery of placenta
- takes 15-30 minutes
- placenta separates from myometrium and uterine contractions cause it to be expelled after birth
- myometrium contracts and prevents haemorrhage by constricting uterine blood vessels at site of placental attachment
Involution
- shrinkage of uterus to pre pregnancy size
- takes 4-6 weeks
- induced by fall in oestrogen and progesterone levels after loss of placenta, oxytocin
Development of the breast
- in non-pregnant state, mostly adipose and rudimentary ducts
- breast does not fully develop until pregnancy
What triggers the development of the breast
- increase of oestrogen causes duct development
- increase of progesterone causes lobule formation
- prolactin and hCS causes synthesis of enzymes for milk production
- breasts are mature by month 4 of gestation
- prolactin also stimulates milk production after partutition
Prolactin action on stimulating milk production
- stimulatory action of prolactin is blocked in later stages of pregnancy by high levels of oestrogen and progesterone
- immediately after parturition oestrogen and progesterone levels fall, allowing prolactin to induce milk production
Suckling
- triggers neuroendocrine reflex
- secretion of prolactin (milk production) and oxytocin (milk ejection)
Function of oxytocin
- stimulates contraction of myoepithelial cells
- hastens involution
- suppresses LH and FSH secretion - suppresses menstrual cycle
Components of breast milk
- more than 100 constituents
- elmusion of particles isotonic with plasma
- water
- lactose about 7% but lower in colostrum
- lipids 3-5%
- vitamins
- minerals
- immunoprotective agents
- colostrum = milk produced in first 5 days after birth
