Anatomy

1
Anatomy PhysiologyBio 2402 Lecture

• Instructor Daryl Beatty
• Reproduction
• Pregnancy Childbirth
• Version 28.3

2
Hormones of Pregnancy
p. 1120
3
Fertilization Implantation
p. 1118
4
From Egg to Embryo

• Pregnancy events that occur from fertilization
  until the infant is born
• Conceptus the developing offspring
• Gestation period from the last menstrual period
  until birth

5
From Egg to Embryo

• Preembryo conceptus from fertilization until it
  is two weeks old
• Embryo conceptus during the third through the
  eighth week
• Fetus conceptus (baby) from the ninth week
  through birth

6
Relative Size of Human Conceptus
Figure 28.1
7
Accomplishing Fertilization

• The oocyte is viable for 12 to 24 hours
• Sperm is viable 24 to 72 hours
• For fertilization to occur, coitus must occur no
  more than
• Three days before ovulation
• 24 hours after ovulation
• Fertilization when a sperm fuses with an egg to
  form a zygote
• So, the total time period when fertilization may
  occur is how long?

8
Ovarian Cycle

• Count beginning with the first day of the
  menstrual period
• Follicular Phase typically day 1-14
  development of the oocyte in the ovary
• About day 14 Surge of LH leads to ovulation
• Luteal Phase - is the time from when the egg is
  released (ovulation) until the first day of
  menstruation.

9
Uterine Cycle

• Proliferative Phase - is the time after
  menstruation and up to ovulation.
• Secretory phase is the time after ovulation until
  the beginning of menstruation. Glands within the
  endometrium secrete proteins in preparation for a
  fertilized egg to implant. If implantation
  doesnt occur, the endometrium begins to break
  down and the glands stop secreting. The result is
  shedding of the lining

10
Acrosomal Reaction and Sperm Penetration

• An ovulated oocyte is encapsulated by
• The corona radiata and zona pellucida
• Extracellular matrix
• Sperm binds to the zona pellucida and undergoes
  the acrosomal reaction
• Enzymes are released near the oocyte
• Hundreds of acrosomes release their enzymes to
  digest the zona pellucida

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Figure 28.2a
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Blocks to Polyspermy

• Only one sperm is allowed to penetrate the oocyte
• Two mechanisms ensure monospermy
• Fast block to polyspermy membrane
  depolarization prevents sperm from fusing with
  the oocyte membrane
• Slow block to polyspermy zonal inhibiting
  proteins (ZIPs)
• Destroy sperm receptors
• Cause sperm already bound to receptors to detach

13
Completion of Meiosis II and Fertilization

• Upon entry of sperm, the secondary oocyte
• The ovum nucleus swells, and the two nuclei
  approach each other
• When fully swollen, the two nuclei are called
  pronuclei
• Fertilization when the pronuclei come together

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Events Immediately Following Sperm Penetration
Figure 28.3
15
Preembryonic Development

• The first cleavage produces two daughter cells
  called blastomeres
• Morula the 16 or more cell stage (72 hours old)
• By the fourth or fifth day the preembryo consists
  of 100 or so cells (blastocyst)

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Pre-Embryonic Development

• The unfertilized oocyte
• The four cell blastomere phase

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Pre-Embryonic Development

• Early divisions are synchronous this is the 8
  cell stage
• In the morula stage, this is perhaps 20 30 cells

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Germ Layers

• The blastocyst develops into a gastrula with
  three primary germ layers ectoderm, endoderm,
  and mesoderm
• Before becoming three-layered, the inner cell
  mass subdivides into the upper epiblast and lower
  hypoblast
• These layers form two of the four embryonic
  membranes

19
Primary Germ Layers

• Serve as primitive tissues from which all body
  organs will derive
• Ectoderm forms structures of the nervous system
  and skin epidermis
• Endoderm forms epithelial linings of the
  digestive, respiratory, and urogenital systems
• Mesoderm forms all other tissues
• Endoderm and ectoderm are securely joined and are
  considered epithelia

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Preembryonic Development

• Blastocyst a fluid-filled hollow sphere
• inside of which is a small cluster of cells
  called the inner cell mass Trophoblasts take part
  in placenta formation.

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Cleavage From Zygote to Blastocyst
Figure 28.4
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Human Fetal Development

• Fertilization 8.5 million possibilities per
  parent
• 7.2 Trillion possibilities from 2 parents
• A unique combination

23
Human Fetal Development Implantation

• About 6 days after fertilization, implantation in
  the richly vascular tissue of the endometrium of
  the uterus occurs. The cells are multiplying
  rapidly.

24
Implantation

• Begins six to seven days after ovulation when the
  trophoblasts adhere to a properly prepared
  endometrium

25
Implantation

• The implanted blastocyst is covered over by
  endometrial cells
• Implantation is completed by the fourteenth day
  after ovulation

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Implantation of the Blastocyst
Figure 28.5a
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Implantation of the Blastocyst
Figure 28.5b
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Implantation

• Viability of the corpus luteum is maintained by
  human chorionic gonadotropin (hCG) secreted by
  the trophoblasts
• hCG prompts the corpus luteum to continue to
  secrete progesterone and estrogen
• Chorion developed from trophoblasts after
  implantation, continues this hormonal stimulus
• Between the second and third month, the placenta
  
• Assumes the role of progesterone and estrogen
  production
• Is providing nutrients and removing wastes

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Human Fetal Development 3 Weeks

• At 3 weeks, the heart and circulatory system
  continue to develop, even as they are functioning.

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Development of Fetal Circulation

• By the end of the 3rd week
• The embryo has a system of paired vessels
• The vessels forming the heart have fused

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Placentation

• Formation of the placenta from
• Embryonic trophoblastic tissues
• Maternal endometrial tissues

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Placentation

• The placenta is fully formed and functional by
  the end of the third month

33
Placentation

• Embryonic placental barriers include
• The chorionic villi
• The endothelium of embryonic capillaries
• The placenta also secretes other hormones human
  placental lactogen, human chorionic thyrotropin,
  and relaxin

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Placentation
Figure 28.7ac
35
Placentation
Figure 28.7d
36
Placentation
Figure 28.7f
37
Ectopic Pregnancies
p. 1118
38
Maternal Serum Screen Amniocentesis
MSS a.k.a Barts test, Triple Screen,
Maternal Serum Test
39
Endodermal Differentiation
Figure 28.11
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Human Fetal Development 6 Weeks

• At 6 weeks, neural activity is detectable, and
  there is reflexive response to touch or
  stimulation.

41
Embryonic Membranes

• Amnion epiblast cells form a transparent
  membrane filled with amniotic fluid
• Provides a buoyant environment that protects the
  embryo
• Helps maintain a constant homeostatic temperature
• Amniotic fluid comes from maternal blood, and
  later, fetal urine

42
Embryonic Membranes

• Yolk sac hypoblast cells that form a sac on the
  ventral surface of the embryo
• Forms part of the digestive tube
• Produces earliest blood cells and vessels
• Is the source of primordial germ cells

43
Embryonic Membranes

• Allantois a small outpocketing at the caudal
  end of the yolk sac
• Structural base for the umbilical cord
• Becomes part of the urinary bladder
• Chorion helps form the placenta
• Encloses the embryonic body and all other
  membranes

44
Human Fetal Development 8 Weeks

• At 8 weeks, major organ systems are developing.

45
Excellent Developmental Video

• http//www.babycenter.com/2_inside-pregnancy-weeks
  -1-to-9_10302602.bc
• (Cue up after short ad)

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Human Fetal Development 10 Weeks

• At 10 weeks details of the hands and feet are
  clear.

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Human Fetal Development 16 Weeks

• At 16 weeks, we are now in the second trimester
  of pregnancy. More details are clear.

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Human Fetal Development 18 Weeks

• At 18 weeks, reflexes and behaviors are observed.
  

49
Human Fetal Development 20 Weeks

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Hormonal Changes During Pregnancy
Figure 28.6
51
Circulation in Fetus and Newborn
Figure 28.13
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Effects of Pregnancy Anatomical Changes

• Chadwicks sign the vagina develops a purplish
  hue
• Breasts enlarge and their areolae darken
• The uterus expands, occupying most of the
  abdominal cavity

53
Effects of Pregnancy Anatomical Changes

• Lordosis is common due to the change of the
  bodys center of gravity
• Relaxin causes pelvic ligaments and the pubic
  symphysis to relax
• Typical weight gain is about 29 pounds

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Relative Uterus Size During Pregnancy
Figure 28.15
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Effects of Pregnancy Physiological Changes

• GI tract morning sickness occurs due to
  elevated levels of estrogen and progesterone
• Urinary system urine production increases to
  handle the additional fetal wastes
• Respiratory system edematous and nasal
  congestion may occur
• Dyspnea (difficult breathing) may develop late in
  pregnancy

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Effects of Pregnancy Physiological Changes

• Cardiovascular system blood volume increases
  25-40
• Venous pressure from lower limbs is impaired,
  resulting in varicose veins

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Parturition Initiation of Labor

• Estrogen reaches a peak during the last weeks of
  pregnancy causing myometrial weakness and
  irritability
• Weak Braxton Hicks contractions may take place
• As birth nears, oxytocin and prostaglandins cause
  uterine contractions
• Emotional and physical stress
• Activates the hypothalamus
• Sets up a positive feedback mechanism, releasing
  more oxytocin

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Parturition Initiation of Labor
Figure 28.16
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Stages of Labor Dilation Stage

• From the onset of labor until the cervix is fully
  dilated (10 cm)
• Initial contractions are 1530 minutes apart and
  1030 seconds in duration
• The cervix effaces and dilates
• The amnion ruptures, releasing amniotic fluid
  (breaking of the water)
• Engagement occurs as the infants head enters the
  true pelvis

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Stages of Labor Dilation Stage
Figure 28.17a, b
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Stages of Labor Expulsion Stage

• From full dilation to delivery of the infant
• Strong contractions occur every 23 minutes and
  last about 1 minute
• The urge to push increases in labor without local
  anesthesia
• Crowning occurs when the largest dimension of the
  head is distending the vulva

63
Stages of Labor Expulsion Stage
Figure 28.17c
64
Parturition
p. 1135
65
Stages of Labor Expulsion Stage

• The delivery of the placenta is accomplished
  within 30 minutes of birth
• Afterbirth the placenta and its attached fetal
  membranes
• All placenta fragments must be removed to prevent
  postpartum bleeding

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Stages of Labor Expulsion Stage
Figure 28.17d
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Extrauterine Life

• At 1-5 minutes after birth, the infants physical
  status is assessed based on five signs heart
  rate, respiration, color, muscle tone, and
  reflexes
• Each observation is given a score of 0 to 2
• Apgar score the total score of the above
  assessments
• 8-10 indicates a healthy baby
• Lower scores reveal problems

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First Breath

• Once carbon dioxide is no longer removed by the
  placenta, central acidosis occurs
• This excites the respiratory centers to trigger
  the first inspiration
• This requires tremendous effort airways are
  tiny and the lungs are collapsed
• Once the lungs inflate, surfactant in alveolar
  fluid helps reduce surface tension

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Transitional Period

• Unstable period lasting 6-8 hours after birth
• The first 30 minutes the baby is alert and active
• Heart rate increases (120-160 beats/min.)
• Respiration is rapid and irregular
• Temperature falls

70
Lactation

• The production of milk by the mammary glands
• Estrogens, progesterone, and lactogen stimulate
  the hypothalamus to release prolactin-releasing
  hormone (PRH)
• The anterior pituitary responds by releasing
  prolactin

71
Lactation

• Colostrum
• Solution rich in vitamin A, protein, minerals,
  and IgA antibodies
• Is released the first 23 days
• Is followed by true milk production

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Lactation and Milk Let-down Reflex

• After birth, milk production is stimulated by the
  sucking infant

Figure 28.18
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Breast Milk

• Advantages of breast milk for the infant
• Fats and iron are better absorbed
• Its amino acids are metabolized more efficiently
  than those of cows milk
• Beneficial chemicals are present IgA, other
  immunoglobulins, complement, lysozyme,
  interferon, and lactoperoxidase
• Interleukins and prostaglandins are present,
  which prevent overzealous inflammatory responses
• Its natural laxatives help cleanse the bowels of
  meconium