MD210 Anatomy Lecture 4 – Implantation PDF

MD210 Anatomy Lecture 4 – Implanta on Embryology - Fer lisa on - Implanta on - Placenta on Fer lisa on - Begins with contact of sperm with secondary oocyte (cell formed in meiosis I) - ends forma on of Zygote (zygote = 1 cell embryo) - Semen deposited in vagina - 1990’s 182 million 300 million -1940’s (there’s a decline in the number of sperm men are producing) - Products of male accessory sex glands Human Semen - Creamy texture – grey to yellow - Average volume 2.5-3.5 ml a er 3 days abs nence (2-6ml) - Fer lity index o at least 20 million sperm/ml o 40% sperm show vigorous swimming o 60% normal shape (abnormal shape means they are immature?) o pH 7.35-7.5 - Epididymis o Water, nutrients o (70 days to grow sperm – majority of me in epididymis) - Seminal Vesicles (2/3) o Water, fructose ﬁbrinogen Vit C Prostaglandins - Prostate (1/3) o Water Buﬀers, ﬁbrinogenase (clo ng) Fibrinoly c enzyme (liquefac on) citric acid prostaglandins o (Semen coagulates to stay in female) - Bulbourethral (expels spent urine during erec on, route where many microorganisms that cause STDs enter into penis) o water buﬀers mucous Fer lisa on - ‘Vaginal’ Sperm - 1min - semen coagula on ﬁbrinogenase - 20min - semen liquefac on ﬁbrinoly c enzyme in seminal plasma - Vagina acidic inhibits mo lity basic content of semen makes pH 7.2 (rela on between bacteria and glycogen lowers pH to keep out microorganisms) - Pass through cervical canal - Thick mucus prevents entry (nature of cervical mucus changes – oestrogen dominant – thin & watery, progesterone dominant – thick & s cky – other things also aﬀect hydra on of bodily secre ons) - Preovulatory rise is oestrogen - Thin watery - Swim through 1.2-3mm/min (only have ~3mm to swim) (reverse peristal c mo on on endometrium that selec vely pulls sperm towards the ovary containing the egg) - Uterine cavity - Ampulla of Fallopian tube – site of fer lisa on - Life span around 3-6 days - Capacita on – con nues in female tract - Secondary oocyte (1st polar body) surrounded by granulosa cells, zona pellucida - Acrosome reac on - Hyaluronidase - loss of corona - Acrosin and neuaminidase facilitate passage through zona pellucida - On contact with plasmallema of oocyte Zona reac on prevents polyspermy-release of cor cal granules (as soon as sperm head touches membrane of secondary oocyte, cor cal granules released – barrier against polyspermy) - Contact induces secondary oocyte to divide to become oo d (ovum) and second polar bodynucleus known as the female pronucleus - Tail of sperm degenerates - Head and centriole enter - Head forms male pronucleus - Pronuclei fuse - to form Zygote (Mitochondria from father tagged for destruc on so all mitochondria from mother) Results of fer lisa on - restora on of diploid number (46) - determina on of chromosomal sex of embryo - varia on of human species new combina on of chromosomes - ini a on of cleavage - mito c division of zygote into blastomeres (cell division – cleavage – each cell smaller than 1 before – ﬁlled & hatched – enzyma c breakdown of egg cell) The ﬁrst week of human life - As zygote passes along fallopian tube undergoes cleavage daughter cells-blastomeres (fer lisa on in ampulla of fallopian tube) - new cells smaller a er each division - 16 cell embryo - Morula - blastocyst with blastocyst cavity - 4days - Outer ﬂa ened cells -Trophoblast - Inner cells inside -Inner cell mass - Trophoblast - embryonic part of the placenta - Inner cell mass - primordium of the embryo - Zona pellucida disappears ~ 5-6 days a er fer lisa on - Process of implanta on begins - Part that touches uterus has inner cells Hatches & forms blastocyst – ﬂa ened outside cells (trophoblast) – give rise to embryonic por on of placenta Inside inner cell mass – give rise to ssues of body – contain primordial stem cells Implanta on - Trophoblast diﬀeren ates into outer syncy otrophoblast, inner cytotrophoblast - Uterine stroma decidual (shedding) response - Co-ordinated sequence of complex interac ons between gene cally diﬀerent cell types of embryonic and maternal ssues. - Success requires trophoblast penetra on of several ssue components to reach maternal blood supply. o Epithelial lining of the uterus, o the basal lamina - o underlying stroma. This sequence of events resembles invasion of malignant tumours. The invasive cells must a ach to ECM proteins; secrete proteases capable of degrading these proteins; and migrate through the degraded ECM. During implanta on and subsequent placenta on in the human, popula ons of trophoblast cells invade the endometrium and maternal vasculature within the uterus. Once reaching spiral arteries within the myometrium, trophoblast invasiveness ceases. (stops growing) Unlike tumour cells, which typically exhibit uncontrolled invasion, trophoblast invasion is ghtly regulated. Sub-op mal trophoblast invasion has been shown to occur in the pregnancy disease states of pre-eclampsia and intrauterine growth retarda on. (preeclampsia common in 1st pregnancy – not enough nutri on for foetus – low birth weight) Non-pregnant cycle Pregnant cycle Menstrual cycle is changes in lining of uterus, ovarian cycle is changes in ovary Message produced by embryo - Human chorionic gonadotropin (HCG) – “rescues” corpus luteum Corpus luteum – larger than ovary – ﬁrst trimester produc on of progesterone from corpus luteum maintains lining of uterus – not enough progesterone = spontaneous abor on Day 7.5 (amnio c cavity – within inner cell mass – where baby will grow) - Trophoblast : cytotrophoblast, syncy otrophoblast End of second week - uteroplacental circula on Inner cell mass - bilaminar disc - amnio c cavity Chorionic cavity Day 9 (spaces begin to appear within synch otrophoblast) (organism starts to grow very quickly – 8 weeks from single cell to a basic plan with discernible organs) (trophoblas c villi – ﬁnger-like projec ons gaining nutrients) The only one of these sites that’s compa ble with life is the internal os of uterus but it s ll has complica ons Zona pallucida – barrier to polyspermy but also only to hatch in uterus – not perineal cavity – ectopic pregnancy The Haemochorial Placenta - The chorionic villi cons tute the major fetal component of the placenta. - They consist of a mesenchymal core containing matrix, cells and foetal blood vessels. - During the ﬁrst trimester the villi are covered by the two-layered epithelium of Trophoblast - The cellular, non-invasive, villous cytotrophoblast and an outer layer of mul nucleated syncy otrophoblast which is bathed in maternal blood. - As gesta on con nues the cytotrophoblast becomes discon nuous and syncy otrophoblast thinner. - Nutrients from maternal blood transported across compartments to reach the foetal vessels. - Some chorionic villi - free others a ached to decidua at site of invasion- anchoring villi. - At these sites villous cytotrophoblast cells proliferate and break through the syncy otrophoblast to form cytotrophoblast columns and invade the decidua basalis. - Some extravillous cytotrophoblast cells also invade uterine spiral arteries becoming endovascular trophoblast. - These cells seem to augment vessel walls. - The maternal components of the placenta o Intervillous blood o Decidua basalis :decidualised endometrial cells and several kinds of immune cells including macrophages and Large Granular Lymphocytes. Evolu on of trophoblas c villi (mesoderm – primi ve connec ve ssue) (1 cell thick – very eﬃcient barrier) Foetal side Maternal side Embryology Basic Embryology Carnegie stages are named after the famous Institute which began collecting and classifying embryos in the early 1900's. Stages are based on the external and/or internal morphological development of the embryo, and are not directly dependent on either age or size. The human embryonic period proper is divided into 23 Carnegie stages. Criteria beyond morphological features include age in days, number of somites present, and embryonic length Normal plate by the anatomist Wilhelm His. For this ‘normal plate’ from the founding work of modern human embryology, His had his artist draw embryos from about the end of the second week to the end of the second month. The plate almost creates the impression of a single embryo at a succession of stages, but in fact brought together specimens from diverse medical encounters. Many would be considered abnormal today. Embryology - The study of the origin and development of an organism - Prenatal period: before birth 38 weeks from conception to birth (average) “fetal” age Gynecologic timing has been from LMP therefore refers to 40 weeks “gestational” age LMP (last menstrual period) is on average two weeks before ovulation Traditional (artificial) division: - Embryonic period: first 8 weeks after conception o All major organs formed (but embryo wouldn't survive outside of mother) - Fetal period: remaining 30 weeks o Organs grow larger and become more complex Fertilisation to Implantation Ectopic pregnancy- vascular supplying it can rupture – blood loss & potential death for mother - Ovulation: egg released into the peritoneal cavity Travels down fallopian tube in which fertilization occurs At conception in fallopian tube, maternal and paternal genetic material join to form a new human life (zygote) Cell division occurs with travel down the tube and into the uterus Week 1 post conception - Zygote divides repeatedly moving down tube toward uterus (cleavage) The daughter cells are called blastomeres - Morula: the solid cluster of 12-16 blastomeres at about 72 hours - Day 4: late 60 cell morula enters uterus, taking up fluid becoming blastocyst Blastocyst - Two distinct types of cells o Inner cell mass: forms the embryo o Trophoblast: layer of cells surrounding the cavity which helps form the placenta - Floats for about 3 days - Implantation on about day 6 post conception o Trophoblast erodes uterine wall o Takes 1 week to complete - If inner cell mass of a single blastocyst divides: monozygotic (identical) twins Week 2 - Inner cell mass divides into epiblast and hypoblast - 2 fluid filled sacs o Amniotic sac from epiblast o Yolk sac from hypoblast - Bilaminar embryonic disc: area of contact (gives rise to the whole body) Week 3 - Bilaminar to trilaminar disc - Three primary “germ” layers: all body tissues develop from these o Ectoderm o Endoderm o Mesoderm Formation of the 3 “germ” layer - Primitive streak (groove) on dorsal surface of epiblast - Grastrulation: invagination of epiblast cells - Days 14-15: they replace hypoblast becoming endoderm - Day 16: mesoderm (a new third layer) formed in between - Epiblast cells remaining on surface: ectoderm The three “germ” tissues - Early specialization of cells - ectoderm and endoderm are epithelial tissue (form sheets of tissue) - Mesoderm is a mesenchyme tissue o Mesenchyme cells are star shaped and do not attach to one another, therefore migrate freely Notochord (organised bundle of cells growing towards the front of embryo – long axis of embryo – signals change in other cells) - Days 16-18 - Primitive node epiblast cells invaginate and migrate anteriorly with some endoderm cells - Rod defining the body axis is formed - Future site of the vertebral column Neurulation - Notochord signals overlying ectoderm - Formation begins of spinal cord and brain (neurulation) - Neural plate to neural groove to neural tube: pinched off into body - Closure of neural tube: begins at end of week 3; complete by end of week 4 (folic acid important for this step) Extends cranially (eventually brain) and caudally (spinal cord) - Neural crest, lateral ectodermal cells, pulled along and form sensory nerve cells and other structures - Mesoderm begins to differentiate o Lateral to notochord, week 3 o Extends cranially and caudally (from head to tail or crown to rump) Division of mesoderm into three regions o Somites: 40 pairs of body segments (repeating units, like building blocks) by end week 4 o Intermediate mesoderm: just lateral to somites o Lateral plate: splits to form coelom (“cavity”) (Gastrulation – formation of 3 layered embryo from 2 layered embryo) - Divisions of the mesodermal lateral plate - Somatic mesoderm: apposed to the ectoderm - Splanchnic mesoderm: apposed to the endoderm - Coelom in between will become the serous cavities of the ventral body cavity: – Peritoneal – Pericardial – Pleural Folding begins at week 4 (main difference between the 3 week embryo and the adult body is that the embryo is still a flat disc) Lateral folding + degree of longitudinal folding Major derivatives of the embryonic germ layers 29 day embryo (this is when the heart starts pumping, about 4 weeks or 1 month, ½ cm size) By 8 weeks, about 2 months, all major organs are in place in at least a rudimentary form; this is why drugs early in pregnancy are so important to avoid – many cause birth defects; baby is a little over 2.5cm long There are many different ways that developmental abnormalities can occur the 2 major types are 1. Congenital (inherited or genetic) and 2. Maternal/environmental derived abnormalities. Congenital abnormalities These developmental abnormalities usually involve only small DNA mutations affecting individual or a few genes, two exceptions are the major chromosomal abnormalities usually trisomy; trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome) (also trisomy 9, 13, 15). Note that the occurance of chromosomal abnormalities also increases with increasing maternal age Maternal derived abnormalities: Relate to lifestyle, environment and nutrition. Some examples of this form of abnormality are the impact of excess alcohol on neural development (Fetal alcohol syndrome), viral infection (rubella) at a critical stage of development, inadequate dietry folate intake (neural tube defects), effects of prescription drugs (Thalidomide- limb development) and even maternal endocrine function (thyroid development). In addition to these obvious maternally-derived abnormalities, there is growing evidence that the interuterine environment has a strong influence on later postnatal health. This theory is based on the early statistical analysis of disease/longevity in babies with low birth weights in England by Barker, and has been called the "Barker Hypothesis". Teratogen - any agent that causes a structural abnormality following fetal exposure during pregnancy. The overall effect depends on dosage and time of exposure. Absolute risk - the rate of occurrence of an abnormal phenotype among individuals exposed to the agent. (e.g. fetal alcohol syndrome) Relative risk - the ratio of the rate of the condition among the exposed and the nonexposed. (e.g. smokers risk of having a low birth weight baby compared to non-smokers) A high relative risk may indicate a low absolute risk if the condition is rare. Assisted reproductive technologies Assisted Conception Objective - To bring sperm and oocyte close to each other to promote chances of fertilization and, ultimately, achieve a pregnancy Assisted Conception - IUI: intrauterine insemination* - IVF: in vitro fertilization * - ICSI: intracytoplasmic sperm injection * - GIFT: gamete intrafallopian transfer - ZIFT: zygote intrafallopian transfer - PESA: percutaneous epididymal sperm aspiration - ET: embryo transfer - TESE: testicular sperm extraction - SUZI: subzonal sperm injection - PGD: preimplantation genetic diagnosis *main types - - - Required procedures • Superovulation (Hormonal manipulation to enhance ovulation and release multiple oocytes during ovulatory cycle) (increases chances but uncontrolled overstimulation is risky – twins, triplets, etc.) • Sperm preparation • Assisted fertilization Human menopausal gonadotropin • Taken from urine of postmenopausal women • Follicle stimulating hormone (FSH) and luteinizing hormone (LH) activity Recombinant FSH Recombinant LH Sperm Preparation - Select PMNS (progressively motile normal sperm) - Remove seminal plasma, WBC, and bacteria - Sperm capacitation (ability of sperm to fertilise egg) • Coating of sperm with seminal plasma proteins • Allow sperm to become fertile • In vivo or in test tube Intrauterine insemination - Sperm sample deposited in uterus just before release of an oocyte (s) in a natural or stimulated cycle - Soft catheter - Give hCG at injection or up to 24 hrs later - Sperm volume: 0.2-0.3 ml - Pregnancy rates • Around 15% per cycle Gamete intrafallopian transfer - Laparoscopic technique in which oocyte and sperm placed in fallopian tube, allowing in vivo fertilization - Procedure • Superovulation • US guided transvaginal oocyte retrieval - 0.1-0.2 mil sperm with 2-3 oocytes In vitro fertilisation – IVF - Taking oocytes from woman - Fertilizing them in lab with her partner's sperm - Transferring resulting embryos back to her uterus 3 or 5 days later - Procedure • Superovulation • Insemination • Embryo transfer • Luteal support (giving HCG to maintain corpus luteum) IVF – Superovulation - Gonadotropin stimulation - Monitoring follicular development - US guided transvaginal oocyte retrieval - Oocyte fertilization with sperm IVF – Insemination - Containers used • Test tubes, Petri dishes, multi-well dishes - Each oocyte inseminated with 0.5-1.0 mil PMNS - Fertilization detected 12-20 hrs later by presence of • 2 pronuclei in oocyte cytoplasm • 2 polar bodies in perivitelline space - Syngamy (combination of maternal and paternal pronuclei 24 hrs after insemination Further cleavages occur at 24 hr intervals IVF - Embryo transfer - Embryos transferred to uterus on 2nd or 3rd day after in vitro insemination - 4-8 cells embryos - 2-3 embryos transferred in 20 µl of culture fluid - Transabdominal US to see fluid placed in uterus - Cryopreserve excess embryos IVF - Luteal support - Progesterone (P4) necessary for pregnancy maintenance - Premature luteolysis in some superovulatory regimens - P4 supplementation until menses occur or woman has positive pregnancy test Intracytoplasmic sperm injection – ICSI - Injection of single sperm into single oocyte in order to get fertilization - Procedure • Superovulation • US guided transvaginal oocyte retrieval • IVF ▪ Oocytes injected with sperm using special microscopes, needles and micromanipulation equipment ICSI – Indications - Low sperm concentration, motility, abnormal morphology - Antisperm antibodies - Fertilization failure after conventional IVF - Ejaculatory disorders - absence of vas deferens or obstruction of ejaculatory ducts Assisted Hatching - Indications • Couples having IVF with ▪ Female partner's age over 37 ▪ Poor quality embryos • Excessive fragmentation • Slow rates of cell division (Hatching of zona pallucida –tricky – not as successful as other procedures) Assisted Hatching – Procedure - Embryo held with a specialized holding pipette - A needle used to expel an acidic solution against ZP - A small hole made in ZP - Embryo washed and put back in culture in incubator - ET shortly after hatching procedure • Hope for the best Further Advances And Uses Of Assisted Conception Technology - Cryopreservation of • Sperm • Embryo • Oocyte • Ovarian tissue - Growth of human follicles and oocytes in vitro - In vitro maturation and transplantation of human spermatozoa Assisted Reproductive Technology (ART) - - - - Infertility • Inability to conceive after 1 year of unprotected and regular sexual intercourse Primary infertility • Couples have never had children Secondary infertility • Couples initiated conception in the past and then had difficulty Infertility • Female partner: 35% • Male partner: 35% • Both partners: 20% • Unknown cause: 10% Infertility more common with increasing age USA women infertility rate • Ages 20-24: 4.1% • Ages 25-29: 5.5% • Ages 30-34: 9.4% • Ages 35-39: 19.7% 80% of infertility cases can be diagnosed 85% of cases can be successfully treated - Female infertility • Disorders of ovulation: 27% • Fallopian tube disorders: 22% • Pelvic adhesions: 12% • Endometriosis: 5% to 15% • Hyperprolactinemia: 7% (Patches of tissues that behave like endometrial tissue – clumps of tissues – patches not inside uterus – bleeding – outside ovary, mesentery, broad ligament – bleeding in “wrong” place – more discomfort/pain in menstrual cycle, can still get pregnant) - Male infertility • Abnormal semen parameters ▪ Count, motility, morphology Infertility treatment • Correcting underlying abnormality • ART - - Main techniques • IUI • IVF - embryo transfer • ICSI • Assisted hatching Preimplantation Genetic Diagnosis (PGD) - Identify genetic conditions in embryo before ET - Hemophilia - Cystic fibrosis - Aneuploidy - Performed with IVF 8-cell stage (3 days old) embryo biopsy Obtain 1-2 blastomeres for genetic PGD - Genetic analysis - Multicolor fluorescence in situ hybridization (FISH) - Polymerase chain reaction (PCR) MD210 Anatomy Lecture 7 - Anatomy of Pregnancy The uterus Muscle and Connective Tissue - The myometrium, grows very markedly during pregnancy. - Muscle fibres hypertrophy and increase in number. - Muscle - three layers; outer longitudinal, middle interlacing and inner circular - The connective tissue becomes more vascular. The uterus - The peritoneum intimately attached to the upper uterine segment - Loose and mobile over the lower segment. - The uterine supports hypertrophy. (has to grow to accommodate foetus – tissue would tear otherwise) - The broad ligaments show hypertrophy of all their content. - Levatores anii muscles hypertrophy and become softer. - As a result the pelvic floor becomes progressively more distensible, thereby facilitating passage of the fetus. (process of maturation and softening of tissues to prepare for labour) Uterus - The uterine bloody supply increases - uterine and ovarian arteries become larger and very tortuous. Protective function. - The lymphatics, like the blood vessels, increase in size and number, - Large lymph spaces beneath the decidua and a well-developed plexus under the enveloping peritoneum. - From the 2nd month onwards, hypertrophy of blood vessels and lymphatics produces progressive softening of whole of the body. By 9th month: - The whole of uterus and outer pelvic viscera are so engorged with the blood and lymph that the outlines of the various organs become vague and difficult to define. Size and Position - The non-pregnant uterus measured approximately 2.5x5x7.5cm - At full term the corresponding measurements are 23x25x30cm - The uterus lies in the true pelvis at first but by week 12 the fundus is level with the top of the symphysis pubis. - By week 16 it lies mid-way between the symphysis pubis and the umbilicus - 20 weeks below umbilicus - 24 weeks it is just above it. - Thereafter the fundus rises two fingerbreadths every 4 weeks until 36 weeks when it lies at the xiphisternum. Between 36 and 40 weeks it drops by 1 fingerbreadth per week and at week 40 it lies at the same level that it had reached at week 32. The drop which occurs during the last month( lightening), is due to the descent of the foetal head into the cavity of the true pelvis. Although the woman may feel more comfortable and may breathe more easily after lightening has occurred, she may notice frequency of micturition (urination) due to lack of space in the pelvis. Cervix - Unlike the body, which adapts to the accommodation and expulsion of the foetus, the cervix plays a relatively passive role. - Cervical blood vessels and lymphatics hypertrophy, thereby causing progressive softening which may be detected very early in pregnancy. - The connective and muscular tissues, although they both become more vascular and softer, do not undergo hyperplasia. - The cervical mucosa hypertrophies markedly until it constitutes nearly half the cervix at full term. Eventually, the complex of glands resembles a honeycomb full of sticky tenacious mucus. When this protective mucus plug is expelled at the onset of labour, it carries most of the honeycombed mucosa with it. The external os comes to have anterior and posterior lips, especially in multiparae (has had more than one pregnancy). Isthmus and lower uterine segment - Approximately upper 1/3 of cervix constitutes the isthmus. - Unaffected in 1st month of pregnancy, - Dilates and is taken up into the body of the uterus, to form the lower uterine segment. - The fetal membranes are less firmly blended with the mucosa in the isthmus than elsewhere. - The endometrium lining the lower segment does not undergo a full decidual change. Extra-uterine structures Vagina - Changes are similar to those which occur in uterus. - The blood supply increases enormously (deep violet colour is typical of pregnancy). - Hypertrophy of wall increase both length and width of vaginal canal. Vulva - The vulva undergoes similar changes increased blood and lymphatic supply - causes progressive softening. Breasts - During the first six months of pregnancy the duct system proliferates. - During the last three months of pregnancy the alveoli proliferate. Accompanying these changes in the alveoli, there is hypertrophy of the blood vessels and lymphatics which supply them. - About week 8, Montgomery’s tubercles (raised bumps around aerola that produce a waxy secretion which protects the skin during breatfeeding), which are the mouths of enlarged sebaceous glands, become prominent in the areola. - By week 12, darkening of the primary areola occurs. - From week 16 a paler, secondary areola forms, which is most noticeable in dark-haired women. Abdominal Viscera - The stomach is displaced upwards during the second half of pregnancy. - Diaphragmatic herniation is a fairly common complication of pregnancy. Pelvis - The symphyseal, sacroilac and sacrococcygeal joint capsules soften and relax. - This reaches a maximum about week 28 and may cause sacroiliac backache, - May be accompanied by pain and tenderness in the symphysis. Skin - Skin Pigmentation. Deposition of melanin occurs in certain areas in the body, particularly in dark haired women. - In the face, staining occurs on the forehead and cheeks which is known as the chloasma uterinum. - Increased pigmentation also occurs in the midline of the abdominal wall to form the linea nigra. The Obstetric Pelvis - Dimensions and shape of the maternal pelvis must facilitate passage of the fetal head without injury to it. - The fetal cranium is relatively deformable: the bones of the calvaria are thin and elastic and can alter their shape to some extent. - In addition, they are attached to one another by relatively loose fibrous sutures. - Accordingly, they can override one another somewhat in response to compression forces as the head is squeezed down through the pelvis. - This is known as moulding. - There is, of course, a limit to the amount of moulding which can take place without damage, most significantly to the brain. Moulding is thus something of a fine adjustment. There must be sufficient prior congruity to permit first engagement and then passage of the fetus through the pelvic cavity. Pelvic Measurements The pelvic inlet - The inlet is heart-shaped and is bounded posteriorly by the sacral promontory, laterally by the iliopectineal line and anteriorly by the symphysis pubis. - The plane of the pelvic inlet makes an angle of about 60 degrees with that of the floor. Diameters - The true conjugate. This is measured from the top of the symphysis pubis to the sacral promontory and averages about 4.5 in. - The oblique diameter. This is measured from the sacroiliac joint to the obturator foramen of the opposite side and averages 4.75in. - The transverse diameter. This is the widest measurement from side to side and averages 5.25in. The Pelvic Cavity - This is bounded anteriorly by the symphysis pubis and posteriorly by the sacrum and coccyx. - Its diameters are usually taken at the level of the junction of the second and third sacral vertebrae posteriorly and the middle of the symphysis anteriorly. - Here the anteroposterior, oblique and transverse diameters all measure ca 12cm The Pelvic Outlet - The outlet is bounded by the pubic arch anteriorly, by the ischial tuberosities and sacroiliac ligaments laterally and by the tip of the coccyx posteriorly. Diameters - Anteroposterior. This is measured from the lower border of the symphysis pubis to the sacroiliac joint, and averages 5.25 in. - Transverse (bituberous) diameter. This is taken between the lower borders of the ischial tuberosities and averages 4.25 in. - The subpubic angle. This is bounded buy the pubic rami and symphysis and averages 86 degrees. Method of Pelvic Analysis The Inlet is divided into the forepelvis and the hindpelvis by the widest transverse diameter. - The walls of the hindpelvis include that portion of the ilium overlying the sacroiliac notch. - This is one of the most variable sections in the pelvis and this region is most affected most by sexual and evolutionary differences. The Outlet is divided into anterior and posterior segments by the intertuberous diameter. Three factors influence the capacity of the anterior segment: - (a) The subpubic arch. The arch may be wide, moderate or narrow. - Its shape depends the curve of the inferior pubic rami and is usually well curved in the female pelvis and straight-edged in male pelvis. - (b) The side walls which may incline toward or away from one another, or may be parallel, as they pass downward. - (c) The depth of the pelvis, which is taken from the iliopectineal line along the back of the obturator foramen to the ischial tuberosity. - The posterior segment is mainly influenced by the following factors: The width of the greater sciatic notch; The sacral curve and inclination. The greater the upward and backward tilt of the lower end of the sacrum, the more room there is in the lower pelvis for passage of the fetal head; The degree to which the ischial spines project inward. Anatomical changes during normal labour - In a primigravida (first pregnancy) the head normally becomes engaged in the pelvic inlet by week 37 or 38 of pregnancy. - In a multipara, engagement may not occur until the membranes rupture at the end of the first stage of labour. - Although labour is continuous, for descriptive convenience it is divided into three stages. (First labour usually longer than subsequent deliveries) Stage 1 - During labour, rhythmic uterine contractions increase markedly in strength, frequency and duration. - These are typically experience as pain, beginning in the sacral region and passing round to the front of the abdomen, rising to a climax and then fading away. - Associated with the successive contraction and retraction of the upper uterine segment, the lower uterine segment becomes progressively thinner and the cervix dilates. - This leads to detachment of the mucosa lining the lower uterine segment, with rupture of the small blood vessels attaching it to the uterine wall. In this manner the forewaters are formed. - The blood that has been shed mixes with the mucous of the cervical plug, which separates at the same time, to form the blood-stained mucous discharge known as the show. - Cervical dilation is termed effacement. The internal os of the cervix and the cervical canal are gradually “taken up”: they merge with the cavity of the lower uterine segment. - This process is completed by the dilation of the external os. - There are two pacemakers, one on each side, at the uterine end of each uterine tube, which drive uterine contractions. - Uterine contractions have the following sequence: increasing strength, a maximum, a quick decline and a period of rest. Some of the shortening of a muscular contraction is permanently maintained. - - - This progressive process is known as retraction. Retraction occurs throughout the upper uterine segment but manly at the fundus. With each contraction, traction is applied to the relatively passive lower segments and through it to the cervix. At the same time the forewaters and the presenting part are forced downwards. Retraction causes the upper segment to progressively thicken and the lower segment to stretch. The junction of the two parts is known as Bandl’s ring. The stretching and expansion of the lower segment, combined with effacement and dilation of the cervix, ultimately converts the cavities of the uterus, cervix and vagina into a single unit – the birth canal. This is a low resistance pathway down which the foetus may be driven by the upper uterine segment. Its formation is completed by the end of the first stage. Towards the end of pregnancy the membranes begin to degenerate. This, together with increased pressure exerted by retraction of the upper segment, and removal of support from below as a result of cervical dilatation, contribute to membrane rupture. 2nd Stage - The second stage is concerned with the expulsion of the foetus and last from full dilatation of the cervix until the child has been delivered. - As in the fist stage, force is provided by the contraction and retraction of the upper uterine segment. After the membranes rupture, uterine contractions become stronger, more frequent and more sustained. - In addition, as the liquor drains away, the force of the uterine contractions is applied directly to the foetal breech. - From the breech the force is transmitted to the foetal spinal column and from there to the foetal head. (Width of shoulders – overstretching – damage to brachial plexus) - - - At the same time the uterus rears forward straightening out the curve of the foetal spine, which results in elongation of the foetus which is an additional aid to its descent. Expulsion is aided by contraction of abdominal wall muscles and diaphragm. The foetus is gradually forced, head first, down through the birth canal. Anterior pelvic structures, such as the urethra, bladder and ant anterior vaginal all, are drawn upward out of the path of the descending fetus by contraction and retraction of the upper uterine segment transmitted dot them by the elastic tissues of the lower segment and the intervening connective tissue. This movement is facilitated by the extensive softening of pelvic tissues late in pregnancy. By contrast, the relatively more fixed posterior pelvic structures, such as the posterior vaginal wall, rectum, anal canal and levator ani muscles are forced downward and backward. During descent, the fetal head rotates. Third Stage - The third stage of labour is concerned with the separation and expulsion of the placenta and membranes. (Can have a planned caesarean e.g., if woman’s diameters wont accommodate size of baby, but can also need emergency caesarean, e.g., in low implantation the placenta can block birth canal)

MD210 Anatomy Lecture 4 – Implantation PDF

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