Pregnancy, Menstrual Cycle and Reproduction Flashcards
How is foetal sex determined by the Y chromosome?
SRY gene codes for TDF or SRY-protein which switches on testicular development. The Sertoli cells of the testes produce Mullerian-inhibiting substance, which prevents Mullerian duct development.
Where is testosterone produced?
Leydig cells
What is the effect of testosterone (Development)
Causes Wolffian duct to differentiate into the epididymis, vas deferens, ejaculatory ducts and seminal vesicles.
What is the next step in male sex development (post-W. duct differentiation)?
Externally under the influence of dihydrotestosterone (DHT) produced from testosterone in target tissue, the penis forms and the tissue near it fuses to form the scrotum.
The testes descend into the scrotum (stimulated by testosterone)
How is foetal sex determined by the XX chromosomes?
Absence of Y chromosome = absence of SRY gene = the female will not have testes and will not secrete MIF or testosterone.
Absence of MIF = Mullerian system does not degenerate and a vagina and female external genitalia develop
Summary of differentiation until 6 weeks
Primitive gonads are identical
Summary of differentiation after 6 weeks
- If Y chromosomes are present and thus SRY gene: testes form and Mullerian development is inhibitied
- If Y chromosome is absent: ovaries form and Mullerian development occurs
Where do both the male and female gonads derive embryologically?
the urogenital ridge
Until when are primordial gonads undifferentiated?
6 weeks
In the genetic male, the testes begin to develop during the –th week?
7th week
What are germ cells? Where do they develop?
- Cells that develop into sperm and ova
- Originate from the yolk sac of the hind gut
- Specialised cells which develop into gametes
Anomalies of primary sex development
- Gonadal dysgeneses
- Intersex - 4XY disorders of sex differentiation
- Intersex - 4XX disorders of sex differentiation
- Androgen insensitivity testosterone syndrome
Gonadal dysgeneses CAUSE
- Non-disjunction
- Sex chromosome deletion
Hypothalamic-pituitary-gonadal axis
- Normally, gonadotrophin releasing hormone (GnRH) secreting neuroendocrine cells of the hypothalamus fire a brief burst of action potentials approximately every 90 minutes, secreting GnRH at this time
- The GnRH travels to the anterior pituitary via the hypothalamal-hypophyseal portal vessels and triggers the release of both LH and FSH
- FSH primary acts on the Sertoli cells to stimulate the secretion of paracrine agents required to initiate spermatogenesis
- LH acts primarily on the Leydig cells to stimulate testosterone secretion. Testosterone acts locally by diffusing from the interstitial spaces into the seminiferous tubules and then enters the Sertoli cells where it is able to facilitate spermatogenesis
Hypothalamic-pituitary-gonadal axis - NEGATIVE FEEDBACK
- Testosterone inhibits LH secretion in 2 ways:
- Acts on the hypothalamus to decrease the amplitude of GnRH resulting in a decrease in its secretion
- Acts directly on the anterior pituitary gland to decrease LH response to GnRH
- Sertoli cells release INHIBIN which acts on the anterior pituitary to inhibit the release of FSH`
Hormonal control of puberty - before puberty
- Low pulsatility amplitude of GnRH and GHRH (growth hormone releasing hormone) secretion from hypothalamus
- Low levels of pituitary FSH, LH and gonadal sex steroids
Hormonal control of puberty - at pubertal age
- The trigger is not clearly understood
- Increased amplitude of GnRH and GHRH
- Increased levels of FSH, LH and sex steroids
- Increased levels of growth hormone
Normal puberty
- Centrally driven
- Depends on intact Hypothalamus-Pituitary-Gonadal axis
- Influenced by nutrition, leptin and insulin, socio-cultural, genetic and exercise factors
- Trigger is not well understood
Causes of precocious puberty
- Gonadotrophin dependent
- Gonadotrophin independent
- Other variants
Gonadotrophin dependent (precocious puberty) reasons
- Intracranial lesions
- Infections
- Encephalitis
- Gn secreting tumours
- Hypothyroidism
Gonadotrophin independent (precocious puberty) reasons
- CAH
- Sex hormone secreting tumours
- E2 ingestion
Other variants (precocious puberty) reasons
Premature thelarche or adrenarche
Treatment of premature adrenarche
androgen receptor blockage
Causes of delayed puberty
General
- Constitutional delay (most cases) - Malabsorption (coeliac disease, inflammatory bowel disease) - Chronic disease or underweight
Gonadal failure
- Turner’s syndrome autoimmune syndrome
Gonadotrophin deficiency
- Kallman's syndrome - Hypothalamic/pituitary lesions
What covers the testes anteriorly?
Sac-like extension of the peritoneum → tunica vaginalis
Name of white fibrous capsule?
Tunica albugenia
Septa divide the testes into compartments containing — — where sperm are produced
seminiferous tubules
What do seminiferous tubules drain into?
- A network called RETE TESTIS
- The sperm then travel through efferent ductules which leave the rete testis and pierce the tunica albuginea and empty into a single duct within the epididymis
- The epididymis leads to a vas deference (a large thick walled tube lined with smooth muscle)
Which cells promote sperm cell development?
Sertoli cells
What forms the blood-testis barrier
tight junctions between sertoli cells separating sperm from immune system
Heat exchange of Pampiniform Plexus
- Spermatogenesis cannot take place at 37 degrees but needs to take place at a temperature that is lower (35)
- A special temperature regulation is done by heat exchange that happens by the pampiform plexus where venous blood carries away heat
Spermatogenesis
- Spermatogonia produce 2 kinds of daughter cells
- Type A remain outside blood-testis barrier and produce more daughter cells until death
- Type B differentiate into primary spermatocytes and these cells must pass through the blood-testis barrier to move inward toward lumen. Meiosis I produces 2 secondary spermatocytes and Meiosis II produce 4 spermatids.
What is spermiogenesis?
the transformation of spermatids into spermatozoa (where a tail is sprouted and cytoplasm is discarded)
Which two structures secrete most of the fluid in which ejaculated sperm is suspended?
- prostate gland
- seminal vesicles
Chemical substances secrete by main two secretory structures (male)
- The prostate and seminal vesicle secretions contain a large number of different chemical substances
- Buffers for protecting sperm against the acidic vaginal secretions and residual urine in the male urethra
- Chemicals (particularly from SV) increase sperm motility e.g. fructose to provide energy
- Prostaglandins - to stimulate female peristaltic contractions
What percentage of the expelled fluid is from which structure?
- 60% seminal vesicle fluid
- 30% prostatic
- 10% sperm and trace of bulbourethral fluid
Normal sperm count
50-120 million mL
How do bulbourethral glands contribute?
small volume of lubricating mucoid secretions
Summary of path of sperm to outside:
8
- Seminiferous tubules
- Rete testis
- Efferent ducts
- Epididymis
- Vas Deferens
- Ejaculatory ducts
- Urethra
- Penile urethra
Spermatic ducts
Efferent ductules
Epididymis
Ductus vas deferens
Ejaculatory duct
Efferent ductules
12 small ciliated ducts collecting sperm from the rete testes and transporting it to the epididymis
Epididymis
- 6 m long coiled duct adhering to the posterior of testis
- Site of sperm maturation and storage
- fertile for 40-60 days
Ductus vas deferens
muscular tube 45cm long passing up from scrotum through the inguinal canal to posterior surface of bladder
Ejaculatory duct
2cm duct formed from ductus deferens and seminal vesicle and passing through prostate to empty into urethra
2 main phases of menstrual cycle
Follicular phase: Day 1-13
Luteal phase: Day 14-28
Different types of follicles
Primordial Primary Preantral Early antral Mature
Primordial follicles
Consist of one primary oocyte surrounded by a single layer of granulosa cells which secrete oestrogen, small amounts of progesterone (just before ovulation) and inhibin.
Primary follicles
- The oocyte increases in size and become separated from the inner granulosa cells but the zona pellucida (secreted by the surrounding follicular cells).
- The zona pellucida contains glycoproteins that play an important role in the binding of a sperm cell to the surface of the egg after ovulation.
- The inner layer of granulosa cells stay in contact with the oocyte via cytoplasmic processes that transverse the zona pellucida and form gap junctions through which nutrients and chemical messengers are passed to it.
Preantral follicle
- Through the mitosis of the granulosa cells the follicle grows larger
- Connective-tissue cells surrounding the granulosa cells differentiate and from layers of cells known as the THECA which function together with the granulosa cells in the synthesis of oestrogen.
Early antral follicle
- The primary oocyte reaches full size
- The ANTRUM (fluid filled space) begins to form in the midst of the granulosa cells as a result of the fluid they secrete)
Mature follicle
- At the beginning of each menstrual cycle around 10-25 of these preantral and early antral follicles being to develop into larger antral follicles
- Around 1 week into the cycle, a further selection process occurs whereby only one of the larger antral follicles - the dominant follicle - continues to develop
- The non-dominant follicles undergo atresia (a degenerative process)
- The dominant follicle enlarges as a result of the increase in fluid
- As the time for ovulation approaches the primary oocyte emerges from its meiotic arrest due to the surge in LH and completes its first meiotic division to become a secondary oocyte
- The mature follicle (graafian follicle) becomes so large that it balloons out on the surface of the ovary
When does ovulation occur?
When the thin walls of the follicle and ovary rupture at the site where they are joined because of enzymatic digestion the secondary oocyte is carried out of the ovary and onto the ovarian surface by the antral fluid - this occurs on DAY 14
Luteal phase - Day 14-28
- After the mature/graafian follicle discharges its antral fluid and egg, it collapses and undergoes rapid transformation
- The granulosa cells enlarge greatly and a gland-like structure called the CORPUS LUTEUM is formed, and secretes oestrogen, progesterone and inhibin
- If the discharged egg in the fallopian tube does not get fertilised by fusing with a sperm cell, the corpus luteum reaches its maximum development with in 10 days and then rapidly degenerates via apoptosis which triggers MENSTRUATION and the beginning of a new cycle.
Site of synthesis of ovarian hormones
Oestrogen
- Oestrogen is synthesised and released into the blood during the follicular phase mainly by GRANULOSA cells - After ovulation, oestrogen is synthesised and released by the CORPUS LUTEUM
Progesterone
- Progesterone is synthesised and released in very small amounts by the GRANULOSA and THECA cells just before ovulation
Major hormones in menstrual cycle
GnRH FSH LH Oestrogen Progesterone
Sequence of menstrual cycle depends on the levels of
GnRH
When does FSH increase, and then decrease?
Increases in the early part of the follicular phase and then steadily decreases throughout the remainder of the cycle except for a small mid-cycle peak.
Why does FSH secretion increase as one cycle ends and another begins?
This is due to decreased progesterone, oestrogen and inhibin and thus no negative feedback on the hypothalamus and anterior pituitary.
Elevated FSH secretion means that the enlargement of preantral and early antral follicles is stimulated.
FSH acts on – cells in the first week to …
FSH acts on the granulosa cells in the first week (because they have FSH receptors but no LH receptors at this point in the cycle) to stimulate their multiplication, and production of oestrogen. Oestrogen works with FSH (and growth factors) to stimulate the proliferation of granulosa cells
FSH is involved with the degradation of …
FSH is also involved with the degradation of non-dominant follicles; since there is not enough FSH to prevent size decrease and thus atresia
FSH induces – receptors on …
FSH induces LH receptors on dominant maturing follicles
When the dominant follicle starts to secrete more oestrogen, what is the effect on FSH?
When the dominant follicle starts to secrete more oestrogen it causes levels of FSH to decrease because oestrogen exerts a negative feedback mechanism on the secretion of gonadotrophins from AP + hypothalamus.
Levels of LH during menstrual cycle
Constant for most of the follicular phase but then shows a very large mid cycle increase (LH surge) peaking around 18 hours before ovulation, which is followed by a rapid decrease and then a further slow decline during the luteal phase
LH acts on – cells in the first week. Why?
LH acts on theca cells in the first week since at this point in the cycle, the theca cells have LH receptors but NO FSH receptors
LH stimulate – cells to …
stimulate theca cells to proliferate and synthesis androgens which then diffuse into the granulosa cells and are converted to oestrogen
Which enzyme converts androgens to oestrogen
aromatase
Oestrogen action (5 steps)
- Oestrogen remains fairly low and stable for the first week
- Increases rapidly during the second week as the dominant ovarian follicle grows and secretes more oestrogen
- It then begins decreasing shortly before LH has peaked
- This is then followed by a SECOND increase due to secretion by the CORPUS LUTEUM
- Ends with a rapid decrease during the last days of the cycle
– amounts of progesterone are released by the – during the – phase until just before –
Very small amounts of progesterone are released by the ovaries during the follicular phase until just before ovulation
Soon after –, the developing – – begins to produce – amounts of progesterone
Soon after ovulation, the developing corpus luteum begins to release LARGE amounts of progesterone
When do progesterone levels rapidly decrease?
the last days of the cycle
When does inhibin increase, stabilise and decrease?
- Increases during the late follicular phase
- Remains high during the luteal phase
- Decreases as the corpus luteum degenerates
How does oestrogen cause an LH surge to induce ovulation?
- Increasing oestrogen secretion for 1-2 days during the oestrogen peak of the late follicular phase results in the secretion of large amounts of oestrogen, which acts on the anterior pituitary gland and hypothalamus in a different way to what low conc. did.
Large concentrations act to INCREASE SENSITIVITY of LH-RELEASING CELLS to GnRH = a positive feedback mechanism - Net result = rapidly rising oestrogen leads to LH surge and the high plasma [LH] acts upon the granulosa cells which induces ovulation
When does the LH surge decline?
Just as ovulation is occurring due to the small increase in progesterone from corpus luteum which induces a negative feedback on the AP + H.
What does the LH surge do other than induce ovulation?
Stimulate the reactions that transform the remaining granulosa and theca cells of that follicle into a corpus luteum
In order for pregnancy to occur, the introduction of sperm must occur between — days before and — day after ovulation - why?
- 5 days before - 1 day after
- This is due to the fact that sperm, following ejaculation into the vagina, remain capable of fertilising an egg for up to 4-6 days and the ovulated egg remains viable for only 24-48 hours
Egg transport (4 steps)
- At ovulation, the egg is extruded onto the surface of the ovary
- The smooth muscles of the fimbrae (located on the end of the fallopian tube) cause the fimbrae to pass over the ovary while the cilia of the fimbriae beat in waves towards the interior of the fallopian tube
- These ciliary motions sweep the egg into the fallopian tube
- Once inside the fallopian tube, the eggs move by the fallopian tube cilia, the cilia are slow and it takes around 4 days for the egg to be beaten into the uterus
What is passage of the sperm through the cervical mucus dependent on?
The release of oestrogen causing the mucus to be water to enable to sperm to easily travel through it
Why is sperm mortality high during the trip to the vagina?
The vaginal environment is acidic to provide protection against yeast and bacterial infections
Capacitation of sperm; what is it?
CAPACITATION = the final maturation stage of spermatozoa that takes place in the female genital tract before the spermatozoa gain the ability to fertilise the oocyte
Capacitation of sperm; why does it happen?
Once the sperm have reached the fallopian tube they are unable to fertilise the egg since they are not mature enough so must reside in the female tract for several hours and then be acted upon by secretions of the tract
What does capacitation cause?
- The previous wavelike beats of the sperms tail to be replaced by more whip like action that will propel the sperm forward in stronger surges
- The sperms plasma membrane to become altered to that it will be capable of fusing with the surface membrane of the egg
Pre-implantation stages
Days 1 to ~6
Fertilisation Cleavage Compaction Cavitation and differentiation Expansion Hatching
Fertilisation (7)
Day 1
- Begins with the fusion of egg and sperm within a few hours of ovulation (occurs at the AMPULLA of the fallopian tube)
- Many sperm bind to the glycoprotein receptors on the zona pellucida
- Acrosomal enzymes digest a path through the zona pellucida
- The first sperm to penetrate the entire zona pellucida fuses with the egg
- The head of the sperm passes into the cytosol of the egg and the egg is now known as the ZYGOTE
- 4-7 hours after gamete fusion the zygote completes meiosis 2; the 2 sets of haploid chromosomes (23 egg 23 sperm) are known as PRONUCLEI, and the pronuclei migrate to the centre of the cell where DNA replication occurs in preparation for the first mitotic division.
- 46 chromosomes organise at the spindle equator.
Mechanism to block polyspermy
- egg membrane potential changes
- cortical reaction initiated resulting in exocytosis of secretory vesicles into the space between the ZP and egg plasma membrane → enzymes which inactivate sperm binding receptors
Cleavage
Day 2-3
- The zygote remains in the fallopian tube for 3-4 days because oestrogen maintains the contraction of the smooth muscle near where the fallopian tube enters
- Around 24 hours after fertilisation occurs, a number of mitotic cell divisions occur (CLEAVAGE).
- There is no cell growth but successive cleavages result in an increase in cell numbers - essential to provide sufficient cells for differentiation
- Each cell is TOTIPOTENT stem cell
Compaction
Day 4
The cells flatten and maximise intracellular contacts resulting in the formation of tight junctions and the polarisation of outer cells - ESSENTIAL to be able to differentiate QUICKLY
Cavitation and differentiation
Day 5
- Fluid filled cavity expands to form BLASTOCYST consisting of an outer layer of cells known as the trophoblast, an inner cell mass & a central fluid filled cavity
- BLASTOCYST is defined as having greater than 80 cells - these cells have lost their totipotentiality and have begun to differentiate
Expansion
Day 6
Cavity expands further and the diameter of the blastocyst increases and the zona pellucida THINS
Hatching
Day 6+
Blastocyst expansion and enzymes result in the hatching of the embryo from the zona pellucida; this is necessary for implantation
Implantation stages after the embryo reaches the uterus at day 5/6
Apposition Attachment Differentiation of trophoblast Invasion Decidual reaction Maternal recognition
Apposition - Day X after fertilisation
9
The hatched blastocyst orientates via embryonic pole and synchronises with the receptive endometrium on day 19-22 of menstrual cycle
Attachment
Endometrial epithelial cells and trophoblastic cells express integrins which connect with one another
Differentiation of trophoblast
The trophoblast differentiates into
- Cytotrophoblast
- Syncitiotrophoblast (erodes endometrial blood vessels - using proteolytic enzymes)
Invasion
Enzymatic degradation of the basal lamina
Decidual reaction
Differentiation of the stromal cells adjacent to the blastocyst
Maternal recognition
Secretion of interleukin-2 prevents antigenic rejection of embryo
When does the placenta begin to develop?
begins to develop at blastocyst implantation
What is the placenta?
A combination of interlocking foetal and maternal tissues which serves as an organ of exchange
Development of the placenta (4 stages)
- 8 cell morula arrives at the uterus and develops into blastocyst
- The outer cell layer from the primary trophoblastic cell mass (TCM) then invades the endometrium which degenerates and the trophoblast contacts stroma
- Implantation is complete by the 11th day post ovulation
- Implantation is the first stage of placental development
What is the embryonic portion of the placenta supplied by?
- the outermost layers of trophoblast cells, the CHORION
- Chorionic villi extend from the chorion into the endometrium which is altered by enzymes secreting from villi so that each villus becomes completely surrounded by a pool or placental sinus of maternal blood
How does maternal blood enter the placenta? (entry + which artery)
- placental sinuses
- umbilical artery
What simultaneously takes place in terms of blood flow?
Blood flows from the foetus into the capillaries of the chorionic villi via the umbilical arteries and out of the capillaries back to the foetus via the umbilical vein
What is the maternal portion of the placenta supplied by?
- decidua
- uterine lining forming the maternal part of the placenta
- underlying chorion
main functions of the placenta:
- metabolism
- transport
- endocrine
- provides nutrition, gas exchange, waste removal and endocrine + immune support
Placental metabolism; what does it synthesise?
- glycogen
- cholesterol
- fatty acids
Placental transport; what does it transport? (11)
- gases and nutrition (O2 + CO2)
- Water
- Glucose (faciltiated diffusion via hexose transporters)
- Vitamins
- Amino acids (active transport)
- Hormones, mainly steroid NOT protein
- Electrolytes
- Maternal antibodies IgG and NOT IgM
- Waster products (urea, uric acid, bilirubin)
- Drugs and their metabolites - can result in foetal drug addiction
- Infectious agents
What are placental barriers to transport from maternal to foetus?
- Maternal endothelial cells
- Maternal connective tissue
- Endometrial epithelial cells
- Chorionic epithelial cells
- Fetal connective tissue
- Fetal endothelial cells
When does the placenta become well-established?
5 weeks after implantation (the foetal heart has begun to pump blood, the entire mechanism for nutrient of the embryo is in operation)
What forms between the inner cell mass and the chorion while the placenta develops? What is the name for the epithelial layer lining this?
- amniotic cavity
- amnion or amniotic sac
Throughout pregnancy, plasma concentrations of which hormones continuously increase?
oestrogen
progesterone
Why does oestrogen plasma conc continuously increase during pregnancy?
- stimulates growth of uterine muscle mass
- regulates progesterone levels
- prepares breasts for feeding
- induces the synthesis of receptors for the posterior pituitary hormone OXYTOCIN
Why does progesterone plasma conc. continuously increase during pregnancy?
- Inhibits uterine contractility so that the foetus is not expelled prematurely
- Increases thickness of uterine lining to prevent miscarriage
What is the full name of hCG?
human chorionic gonadotrophin
What is hCG produced by? When?
trophoblast cells around the time they begin their endometrial invasion at day 7-8 (onset of implantation)
What does hCG do?
prevents degradation of the corpus luteum, strongly stimulates CL secretion of oestrogen and progesterone
When does hCG peak and then decrease?
60-80 days after last menstruation, then rapidly decreases so by the end of the 3rd month it has reached a low conc. that remains constant until the end of pregnancy
What happens as hCG levels decrease?
placenta begins to secrete large quantities of O + P
What are the precursors of oestrogen? What is supplied by these via which structures? What happens to them there?
- androgens
- The placenta is supplied with androgens by maternal ovaries, maternal adrenal medulla and foetal adrenal medulla
- The placenta then converts the androgens into oestrogen by expressing the enzyme called AROTOMASE
Prolactin function
has roles in milk production and the prevention of ovulation
What is prolactin produced by?
antetior pituitary gland
When do prolactin levels increase and decrease?
increase @ end of pregnancy when O and P decrease
After birth, O and P levels drop drastically which allows prolactin to stimulate production of milk
What controls prolactin release?
suckling
What is the function of relaxin?
limit uterine activity
soften the cervix
involved in cervical ripening
What is relaxin produced by?
ovary
placenta
When are relaxin levels high?
early pregnancy
What does oxytocin stimulate?
uterine contractions during pregnancy and labour
triggers caring reproductive behaviours
Where is oxytocin produced?
posterior pituitary gland
When does oxytocin secretion increase?
secreted throughout pregnancy but increases at the end
What is oxytocin function during labour?
drug used to induce labour
What is the main prostaglandin?
PGF2a
What is the most powerful prostaglandin?
PGE2
What is the function of the main and most powerful prostaglandin?
initiate labour
What are the prostaglandins produced by?
uterine tissues
Cardiovascular changes during pregnancy
- Increased Cardiac Output
- Reduced Systemic Blood Pressure
- Reduced Total Peripheral Resistance
- Increased Uterine Blood Flow
- Increased Blood Volume
- Increased Plasma & Blood cell mass
Respiratory changes during pregnancy
Increased alveolar ventilation
GI changes during pregnancy
Increased acid reflux and gastroparesis (Delayed emptying)
Skin changes during pregnancy
- Linea nigra - dark central line on abdomen
- Striae gravidarum - stretch marks in lumbar/lower
abdominal regions - Darkened areolar of breasts
Biochemical changes during pregnancy
Weight gain - maternal & fetoplacental:
• Obese women do not put on much weight during pregnancy since they
have fat stores which can be mobilised to supply the energy for
pregnancy
• Skinny women do not have these fat stores so must put on weight thus
they put on more extra weight during pregnancy
- Increased protein and lipid synthesis
- Insulin RESISTANCE
How long does a normal pregnancy last?
40 weeks
What is parturition?
birth process (intra- to extra-uterine life)
What changes are there to smooth muscle cells of myometrium in the last few weeks of pregnancy?
Throughout most of pregnancy the smooth muscle cells of the myometrium are relatively disconnected from each other:
- This feature is maintained mainly by progesterone
- During the last few weeks of pregnancy, as a result of the increasing
concentrations of oestrogen, the smooth muscle cells synthesis CONNEXINS - proteins that form gap junctions between the cells, which allow the
myometrium to undergo coordinated contractions
What is cervical ripening?
growth and remodelling of the cervix prior to labour
During pregnancy, the uterus is …
This feature is maintained mainly by what hormone?
- sealed at its outlet by the firm, inflexible collagen fibres that constitute the cervix;
- progesterone
What changes to the cervix in the last few weeks of pregnancy?
becomes soft and flexible due to an enzymatically mediated breakdown of its collagen fibres
What mediates the synthesis of the enzymes which change the cervix in the last few weeks of pregnancy ?
- oestrogen
- placental prostaglandins - PGE
- Relaxin
- softens cartilaginous joins in the pelvis in preparation for labour
Summary of the events of prelabour (7)
- Enhanced prostaglandin production
- Initiation of labour
- Maternal signal: oxytocin
- Foetal signal: oxytocin, vasopressin and cytokines
- PGF2a enhances the action of oxytocin
- Increased pressure on the cervix stimulates the release of prostaglandins
- Contraction of the actomyosin in the myometrium
Action of the two hormones involved in initiating and promoting labour
Labour is initiated by increased PGFa which in turn enhances the action of oxytocin which results in myometrial contraction which in turn exerts pressure on the cervix and promotes further contraction
What happens during onset of labour and initial contractions?
- At the onset of labour, the amniotic sac RUPTURES and the amniotic fluid flows through the vagina
- When labour begins in earnest the uterine contractions become stronger and occur at 10-15 minute intervals - the contractions begin in the upper portion of the uterus and sweep downward
- Cervix gradually forced open (dilation) to max. diameter of 10cm
Phases of labour
Latent phase
Active phase
Post-partum phase
Latent phase
little cervical dilation: 8 hours
Active phase
- Stronger higher freq contractions
- Full dilation resulting in foetal expulsion (birth)
- Placental expulsion
What are oral contraceptives based on?
the fact that oestrogen and progesterone can inhibit anterior pituitary gland gonadatrophin release thereby preventing ovulation
Mechanism of menopause (8)
- Depletion of primordial follicles - occurs around 40 years
- Decrease in follicular oestrogen production
- Gradual increase in FSH and LH due to lack of negative feedback
- Decline of inhibin → further increase in FSH and LH
- Increase in FSH results in the rapid increase in oestrogen secretion from existing follicles
- Short menstrual cycle
- As fewer follicles remain, increase in FSH no longer stimulates the increase in oestrogen (6-12 months pre-menopause)
- Decrease in oestrogen and lack of ova = menopause
Signs of menopause - short term
- Hot flushes, sweats, palpitation, headaches
- Irritability, lethargy, panic attack & depression
- Shorter menstrual cycle
- Altered blood loss
- Skin dryness
Signs of menopause - long term
- Vaginal dryness - resulting in painful intercourse
- Decrease in libido
- Hair loss/thinning
- Diminished urethral seal and loss in compliance
- General aches and pains
Osteoporosis
Women are more at risk of developing osteoporosis than men because of the hormone changes that occur in menopause directly affect bone density – oestrogen is essential for healthy bones, after menopause, oestrogen levels drop resulting in a rapid decrease in bone density
