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How to make a baby, or year 1 HLC in an hour

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How to make a baby, or year 1 HLC in an hour Mark Chamberlain 21/5/09 – PowerPoint PPT presentation

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Title: How to make a baby, or year 1 HLC in an hour


1
How to make a baby, or year 1 HLC in an hour
  • Mark Chamberlain
  • 21/5/09

2
how and why have sex?
  • The key reason for sex is for the human species
    to procreate
  • This requires
  • Intercourse or IVF
  • Fertilisation
  • Reproductive system

MALE FEMALE
GONADS Testes Ovaries
INTERNAL DUCTS Efferent ducts Epididymis Vas Seminal vesicles Urethra Fallopian tubes Uterus Vagina
EXTERNAL GENITALIA Penis Scrotum Vulva
3
testis
  • housed in the scrotum
  • spermatic cord leads to back of bladder, where it
    joins with seminal vesicles and leads into the
    ejaculatory duct, which opens into the prostatic
    urethra
  • Consists of
  • seminiferous tubules - sperm production
  • Sertoli cells - maturation process
  • Leydig cells - production of testosterone

4
ovaries
  • cortex - contains follicles with oocytes
  • medulla - vascular area
  • no duct system
  • Contains developing follicles at varied stages
  • At ovulation secondary oocyte (Graafian or
    vesicular follicle) (stopped in metaphase II)
    ruptures through ovarian wall, ovulated into
    pelvic cavity and is picked up by fimbrae of
    fallopian tubes and transported to uterus

5
penile stimulation and erection
  • Tactile stimulation ? afferent fibres of pudendal
    nerve ? spinal cord
  • Thoughts from limbic system ? efferent fibres ?
    penis
  • parasympathetic via pelvic promotes
  • somatic via pudendal promotes
  • somatic via hypogastric suppresses
  • Involves change from flaccidity ? tumescence ?
    erection
  • Caused by ? parasympathetic activity to smooth
    muscle of pudendal artery, causing release of NO,
    stimulating ? cGMP to induce dilatation, leading
    to ? blood flow into the corpus cavernosum
  • This counteracts the sympathetic-maintained
    myogenic tone
  • Outflow of blood ? by compression of dorsal vein
    following ? in pressure
  • Urethra protected from increased pressure by
    surrounding corpus spongiosum

6
menstrual cycle
  • Endometrium consists of 3 layers
  • stratum compactum
  • stratum spongiosum
  • stratum basale (basal layer)
  • Cyclical events (28 days) of menstruation and
    ovulation throughout a womans reproductive life
  • UNLESS fertilization of a released ovum by a
    mature spermatozoon occurs
  • USUALLY, this occurs following copulation
    (coitus) between man and woman
  • BUT in vitro fertilization a reality

7
ovulation
  • GnRH acts on anterior pituitary to cause release
    of
  • FSH stimulates maturation of follicle
  • LH stimulates ovulation at day 14 (leading to
    oocyte completing Meiosis I, stopping in Meiosis
    II at metaphase)
  • Male germ cell spermatozoa
  • Female germ cell 2o oocyte
  • Meiosis - haploid chromosome
  • Fertilisation - diploid chromosome
  • Maternal and paternal chromosomes are the
    blueprint for new individual

8
fertilisation
  • Takes place in fallopian tubes at the distal end
    of the ampulla
  • Sperm capacitation needed before
  • Sperm binds to the ZP3 receptor
  • Sperm penetrates the several egg coats using the
    acrosome reaction
  • Cortical reaction prevents multiple sperm entry
  • Fertilisation causes oocyte to complete
  • Meiosis II restores diploid number of
  • chromosomes determines sex

9
post fertilisation
  • Takes 9 months (40wks) for a human baby to
    develop
  • 1st Trimester - most important as this is when
    body forms
  • Weeks 1-2 Blastocyst stage
  • Weeks 3-8 Embryonic stage (Organogenetic period)
  • Weeks 9-onwards Fetal stage
  • 2nd Trimester - rapid growth of fetus
  • 3rd Trimester - fat production
  • - zygote travels down fallopian tube
  • - first division at approximately 30h
  • - sheds zona pellucida and implants
  • - hCG production initially from corpus luteum

10
Days 1-6
11
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12
twins
13
ectopic pregnancy
14
developmental abnormalities
  • Can arise at different levels
  • Chromosone
  • Genetic
  • (Environment)
  • Chromosomal and genetic effects account for
    majority of losses of pregnancies or
    abnormalities in first few weeks which often go
    unrecognised
  • May be numerical or structural. 50 of
    conceptions end in abortion - 50 of these due to
    chromosomal abnormality.T hus, 25 of conceptuses
    have a chromosomal defect.
  • Chromosomal abnormalities account for 7 of major
    birth defects.
  • Downs syndrome(trisomy 21)
  • Turner syndrome (45, X0)
  • Patau Syndrome (trisomy 13)
  • cri-du-chat (chr 5 partial loss)

15
developmental abnormalities
  • Genetic accounts for 8 of major birth defects
  • vascular formation (lethal),
  • holoprosencephaly (lethal)
  • cleft lip
  • Polydactyly
  • Environmental influences have a major
    impact/influence on patterning and growth events
    in later development, less so on very early
    development
  • lack of Folic acid in diet
  • alcohol abuse
  • drug use
  • Radiation
  • viruses eg Rubella

16
teratogens
17
implantation
  • Contact between maternal and fetal systems is
    dynamic
  • Invasion of syncytiotrophoblast then
    cytotrophoblast causes vascular remodelling and
    the fetomaternal interface
  • Point of contact is the placental villi and the
    placental spiral arteries

18
Day 9 - invasion
19
Day 13 lacunae formation
20
bilaminar disc _at_ day 9
21
gastrulation
  • First stage of folding starts with gastrulation
  • Primitive streak forms, setting up
    antero-posterior axis

22
germ layer formation
23
germ layers
Germ layer organs
ectoderm Skin, nervous system
Mesoderm Skeleton, muscle, kidney, heart, blood
endoderm Gut, liver, lungs
24
notochord formation
  • The notochord forms at the primitive node from
    invaginating epiblast cells, from around day 17,
    and extends cranially - forms the basis of the
    axial skeleton.
  • -The notochord is involved in inducing the neural
    tube and somite formation

25
neurolation
  • Ectoderm is induced via notochord/mesoderm to
    become neuroectoderm
  • Neuroectoderm gives rise to neural plate, neural
    groove and folds and ultimately to the neural
    tube
  • Failure of this process leads to spina bifida
  • Neurulation begins around day 19, and ends by day
    27 with closure of posterior neuropore.

26
body cavities
  • Cavities form in the preoral and lateral plate
    mesoderm
  • these join to form a horseshoe-shaped space
    called the (intraembryonic) coelom.
  • The coelom will develop into
  • Pericardial cavity (cranially)
  • Pleural cavities (intermediate)
  • Peritoneal cavity (caudally)
  • The caudal ends open into the chorionic cavity
    (extraembryonic coelom)

27
neural crest
  • arise from crest of the neural folds
  • migrates from neuroectoderm into underlying
    mesoderm
  • give rise to a whole host of tissues including
  • connective tissue and bones of face skull
  • melanocytes
  • glial cells and schwann cells
  • cranial nerves
  • odontoblasts

28
somatogenesis
  • form on either side of neural tube from paraxial
    mesoderm
  • made up of 3 parts
  • sclerotome - cartilage/tendon/vertebral column
  • myotome - muscle precursors
  • dermatome - skin precursors
  • first somite appears day 20
  • form anterior to posterior as the axis of embryo
    elongates
  • by day 30 there will be 35 somites

29
mesoderm
  • Intraembryonic
  • Paraxial mesoderm somites
  • Intermediate mesoderm urogenital
  • Lateral plate mesoderm - line body cavities and
    surround the organs
  • Extraembyonic
  • Body stalk - umbilical cord
  • Amnion, yolk sac, chorion

30
Lateral folding
  • Axis elongates
  • Lateral plate mesoderm develops a cavity
    (intraembryonic coelom)
  • splits into two mesoderm layers
  • parietal (adjacent to ectoderm) lines body
    cavities and forms body wall
  • Visceral (adjacent to endoderm) forms gut wall
  • Turns the embryos body into a cylinder instead
    of a sheet
  • Rolls up the gut tube and nips it off from the
    yolk sac
  • Cuts the intraembryonic coelom off from the
    chorionic cavity
  • Means that the amniotic cavity surrounds the
    embryo except at the body stalk

31
Head and tail
  • developing heart and pericardial sac (cranial
    coelom) tuck in ventrally
  • gut tube pinches off from the yolk sac and
    narrows the body stalk
  • Completion of the head-fold
  • Forebrain now cranial to heart
  • Gut tube connected to yolk sac by a narrow stalk
  • Heart ventral to gut tube
  • Originally cranial part of coelom now ventral to
    intermediate parts (pericardial sac ventral to
    pleural sacs)

32
Genetic regulation of development
  • All of the processes discussed are controlled by
    signals from genes. Complex gene interactions
    occur throughout development to form a normal
    fetus.
  • Example Hox genes
  • establish A-P axis,
  • differences in the vertebrae,
  • CNS divisions,
  • pattern the limbs.
  • One of the signals that control the activation of
    Hox genes is Retinoic acid, a derivative of
    Vitamin A.

33
Developmental milestones
  • 1st Trimester
  • Wks1-2 Blastocyst stage cell division/implantati
    on
  • Wks 3-8 Embryonic stage patterning and
    formation of organs/tissues
  • Wks 9- Fetal stage - growth
  • 2nd Trimester
  • Massive growth and development of fetus and
    maturation of internal organs.
  • Placental growth.
  • 3rd Trimester
  • Fat deposition
  • Movements
  • all patterning, organogenesis etc complete by 3
    months then just growth of fetus

34
Fetus in utero
  • Higher vertebrates produce amniote eggs
  • Complex system of cavities servicing the
    developing embryo
  • Well wrapped up in membranes
  • Floating in its own pond of amniotic fluid
  • Extraembryonic coelom develops from spaces in the
    trophoblast
  • Yolk sac rudimentary apart from role in gut
    development
  • Chorion gives rise to placenta
  • Chorionic cavity obliterated early
  • Amniotic cavity embryo floats in it, later
    tests its urinary and respiratory systems into it
  • Allantois gives rise to part of urinary bladder
  • Allantoic mesoderm gives rise to placental
    blood vessels
  • Chorion and amnion eventually fuse, creating a
    chorio-amnion and obliterating the chorionic
    cavity
  • Amniocentesis may be used to test for fetal
    plasma protein (a-fetoprotein) in amniotic fluid

35
placenta
  • A disc of fetal tissue
  • Interface between maternal and fetal vascular
    systems
  • Transporter
  • Anchor
  • Biosynthetic factory
  • Immunological conundrum

36
exchange
  • Products in
  • Glucose, amino acids, lipids, oxygen
  • Peptides and proteins
  • Products (waste) out
  • Carbon dioxide
  • Metabolites
  • Diffusion
  • Concentration gradient
  • Facilitated diffusion
  • Active transport
  • Receptor-mediated
  • Aqueous or lipid-specific

37
immunoregulation
  • Normally exposure of tissue to foreign antigens
    activates the immune response, leading to
    rejection within a few days or weeks.
  • In pregnancy there is intimate contact between
    maternal and fetal tissues, with no evidence of
    any rejection

38
separation
  • Maternal blood and fetal blood never mix
  • Pregnancy MAY be independent of the uterus - e.g.
    ectopic pregnancy

39
biosynthesis
  • Hormones (pregnancy specific or general)
  • Growth factors for placental development
  • Cytokines to regulate feto-maternal interface

40
Intermediate mesoderm
  • Gives rise to most of the upper urinary and
    genital systems
  • Gives rise to Urogenital Ridge
  • Within which develops the nephrogenic cord
  • Source of most of UG system (except Primordial
    Germ Cells, lower urinary tract and perineum)

41
Kidney differentiation
  • sweeps cranio-caudally
  • Cervical part (pronephros) never completes
    differentiation and regresses by wk 4
  • Thoraco-lumbar mesonephros differentiates but has
    mainly gone by wk 8
  • Mesonephric duct persists in male
  • Sacral metanephros appears in wk 5 and becomes
    definitive kidney
  • Ureter grows out from mesonephric duct

42
Urinary bladder
  • The allantois is a hindgut outgrowth into the
    body stalk gives rise to most of the bladder
  • The duct extending to the umbilicus normally
    closes but may persist and cause problems
  • The cloaca becomes partitioned into the
    urogenital sinus and the rectal sinus
  • Sometimes this is incomplete and a congenital
    fistula connects the urogenital and the
    alimentary tubes

43
  • The shared sections of the ureters and the
    mesonephric ducts (in the male) are absorbed into
    the back of the bladder
  • The ureters now open into the bladder, the
    mesonephric ducts into the urethra
  • Differential growth shifts the metanephric
    kidneys from their sacral site of origin to the
    posterior wall of the upper abdomen

44
urinary maldevelopment
  • Quite often a ureter may be completely or
    partially duplicated
  • Less commonly a second ureter may be ectopic
    opening into the vagina, urethra or other organs
    instead of the bladder
  • One kidney may fail to reposition properly and so
    retains a sacro-pelvic position pelvic kidney
  • If the kidneys are joined together, their ascent
    is prevented because they are trapped below the
    inferior mesenteric artery a horseshoe kidney

45
  • The urogenital sinus and rectal sinus become
    separated by the uro-rectal septum
  • At this stage the cloacal membrane still persists
    so that the urogenital and anal openings are
    closed.
  • These subsequently open but may cause serious
    problems for the newborn child if this fails to
    happen

46
  • The gonads develop medially to the mesonephric
    kidneys
  • Most of each mesonephros atrophies but the parts
    between the gonads and the mesonephric ducts
    persist
  • These persistent mesonephric tubules will become
    the efferent ducts that connect the testis to the
    ductus deferens

47
paramesonephric ducts
  • The paramesonephric (formerly called Mullerian)
    ducts develop in the most lateral part of the
    intermediate mesoderm in both sexes
  • In males they play no important part in
    development
  • In females they become the uterine tubes, uterus
    and upper vagina

48
primordial germ cells
  • PGCs are the cells that give rise to the eggs and
    sperms - the germ line is an expression
    describing this continuity of germ cells from
    generation to generation
  • They arise from the yolk sac and in week 6
    migrate via the hindgut and its mesentery to the
    genital ridges medial to the mesonephros

49
  • PGCs colonise the gonads
  • They are the only cells that can become eggs or
    sperms
  • They are the only cells that can undergo meiotic
    ( reduction) division to form haploid cells
  • Unlike the somatic cells, a few of them survive
    to form the somatic tissues and PGCs of the next
    generation

50
gonadal development
  • In both sexes, the gonads are derived from
  • Somatic mesenchymal tissues forming matrix
  • Primitive germ cells forming gametes
  • Gonads indifferent up to 6th week in utero
  • Y chromosome then actively initiates formation of
    testes
  • Otherwise undifferentiated gonads develop into
    ovaries

51
the SRY gene
  • Located on Y chromosome
  • expressed in male Sertoli cells
  • sry gene initiates formation of Sertoli cells
  • sry gene expression
  • synthesis of a transcription protein - the SRY
    protein
  • transcription factor regulating other gene
    activities
  • other genes clearly involved in early gonadal
    development and sex determination

52
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53
  • The gonads develop medially to the mesonephric
    kidneys
  • Most of each mesonephros atrophies but the parts
    between the gonads and the mesonephric ducts
    persist
  • These persistent mesonephric tubules will become
    the efferent ducts that connect the testis to the
    ductus deferens

54
  • Developing testes link up with the mesonephric
    duct though some persistent mesonephric tubules
  • Mesonephric duct develops into the ductus
    deferens that will carry sperm to the male
    urethra
  • Paramesonephric duct undergoes no further
    development

55
  • During the 4th month the testes descend through
    the inguinal canal towards their final site in
    the scrotum
  • Remember that the male genital duct system
    develops from the mesonephric duct and persisting
    mesonephric tubules

56
  • The accessory male genital glands (seminal
    vesicles and prostate) develop from buds from the
    lower end of the ductus deferens and from the
    urethra respectively

57
  • Between week 8 and the 4th month the
    paramesonephric ducts link with each other and
    with the urogenital sinus to assemble the
    definitive female system
  • The ovaries descend from their original upper
    lumbar location to the pelvis

58
development of the external genitalia
  • Between the 3rd and 6th weeks the external
    genitalia develop in the same indifferent form in
    embryos of both sexes

59
  • In the absence of androgens the indifferent form
    progressively develops into the definitive female
    pattern
  • The urethral folds and genital swelling form the
    labia minor and majora
  • The urethra opens into the vestibule posterior to
    the clitoris

60
  • Androgen stimulation in the male stimulates
  • Expansion of the phallus
  • Fusion of the urethral folds to enclose the
    penile urethra incomplete in hypospadias
  • Expansion and fusion of the genital swellings to
    form the scrotum

61
any questions?
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