Reproduction, Early Development, Pregnancy

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Reproduction, Early Development, Pregnancy

• 1. From 2 cells
• a 3-layer embryo
• a yolk sac, amniotic cavity, chorionic cavity
• a placenta
• 2. Pregnancy and Childbirth
• Changes to female anatomy
• Labor and birth

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Ovulation

• 1o oocytes arrested in Meiosis I in female fetus
• After puberty, 1 primary oocyte/month completes
  Meiosis I as follicle matures
• Follicle ruptures--ATTENTION--CELL LOOSE IN CELOM
• Oocyte enters Fallopian tube
• If fertilization occurs, Meiosis II occurs and
  oocyte becomes ovum

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Ovulation and Meiosis
Fig. 24.15
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Spermatogenesis

• Sperms form in walls of seminiferous tubules
• Spermatogenic cells within sustentacular cells
• Meiosos proceeds as spermatocytes move towards
  lumen (4 sperm from each spermatocyte)
• Seminiferous tubule?rete testis ?head/body/tail
  epididymis ?vas deferens (through spermatic cord
  around bladder) ?urethra

Fig. 24.3
Seminiferous tubule?rete testis ?head/body/tail
epididymis ? vas deferens (through spermatic cord
around bladder) ?urethra
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Sustentacular cells

• Form thick epithelial lining of seminiferous
  tubules
• Tight junctiones between keep sperm proteins from
  entering bood
• Produce testicular fluid which helps move sperm
• Concentrate testosterone to stimulate sperm
  production
• Produce inhibin which slows sperm production

Fig. 24.4
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First week of development
From oocyte to blastocyst
Fig. 3. 3

• Oocyte?(fertilization)?zygote?4-cell stage (2
  days)? morula (ball)?blastocyste?inner cell mass
  (embryo)

Trophoblast (extraembronic membranes)
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Implantation

• Endometium ready for implantation
• Blastocyst implants with ICM against uterine wal
• Ectopic pregnancy--implantation outside built-up
  endometrium (potential for bleeding since embryo
  stimulates vascularization)

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Endometrium

• Two layers
• Stratum basalis
• Stratum functionalis
• Stratum functionalis builds up each month in
  response to ovarian hormones
• Uterine glands secrete glycoproteins--nutrients
  for potential zygote--into uterine cavity
• At menstruation, functional layer self-digests,
  spiral arteries kink and constrict so cells die.
• Just before menstrual flow starts, spiral aa.
  Open wide, capillaries burst and functional layer
  sloughs off.

Fig. 24.18
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Endometrium and menstrual cycle
Fig. 24.19
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Endometrium and menstrual cycle

• Menstrual Phase (Days 1-5) Sloughed Functional
  layer of endometrium expelled through vagina as
  menstrua flow
• Proliferative phase (Days 6-14) In response to
  estrogen from growing ovarian follicle, new
  functional layer elaborates
• Ovulation (about Day 14)
• Secretory phase (Days 15-28)
• Spiral aa. Elongate and coil
• Uterine glands secret glycoproteins
• More estrogen (and progesterone) from corpus
  luteum
• If pregnancy, secretory phase continues due to
  embryonic estrogen production
• If no pregnancy, corpus luteum degenerates,
  estrogen drops leading to menstruation

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Meanwhileback in the embryo

• Implantation with ICM towards uterine wall
• Trophoblast
• Cytotrophoblast (cells around ICM)
• Synctiotrophoblast (synctium of cells that
  becomes placenta)

Fig. 24.25
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Placenta formation
Fig. 24.25

• Lacunae form within synctiotrophoblast--maternal
  blood fills these spaces
• Vili form with embryonic capillaries down middle

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Placenta formation

• Villi bathed in maternal blood in
  lacunae--exchange of nutrients, O2, CO2
• After 13 weeks, full placenta--pancake-shaped
  organ.

Fig. 24.25
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Other extraembryonic tissues

• Cellular trophoblast forms amnion, yolk sac
• Fetal cells shed into amniotic cavity which fills
  with fluid from fetal kidneys extreted through
  ureter, bladder, urethra
• Amniocentesis--sample of amniotic fluid taken
  with hypodermic needle
• Part of yolk sac sucked into embryo to form
  endermic bladder

Fig. 3.4
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Embryo proper

• ICM forms hypoblast (yellow--becomes endoderm)
  and epitblast (blue--becomes ectoderm)
• See handout for all adult derivatives of
  embryonic tissues--HOW FAR WEVE COME!!

Fig. 3. 4
Animated movie of fetal deveopment http//www.cvil
lepregnancy.org/fetal.html
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Pregnancy--changes in female anatomy

• Shift in organs
• Bladder, rectum pushed superiorly,
  squeezed--change in urination, defecation
  patterns
• Stomach compressed--eat more often, less at each
  meal
• Immune response may change appetite to avoid
  possible poisons for fetus
• Postural changes to compensate for anterior
  weight
• Breasts enlarge--first milk production

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Birth

• Stage 1. Dilation Stage
• Ligaments loosen
• Cervix dilates
• Stage 2. Expulsion
• Baby moves through pelvic girdle--head is rotated
  90 degrees
• Floor of pelvis
• Kegel exercises
• Perineal support
• Avoid ripping or episiotomy
• Baby skull--sutures not fused, bones can be slide
  on top of each other giving pointed look
• Stage 3. Placenta.
• Detaches and is expulsed within one hour.

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Fig. 24.27