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Home , Pregnancy (mammals)

Pregnancy and Human Development

1 and Human Development • Terminology

œ Pregnancy œ from time of conception until

œ Conceptusœ term used for the devolopingoffspring

œ œ time period of development (last menstrual cycle until birth)

œ PreembryonicDevelopment œ two weeks following fertilization

œ œ conceptusfrom 2 œ 8 weeks

œ œ week 9 - birth

2 Pregnancy and Human Development • From Egg to Embryo

œ Fertilization

• 200 million sperm enter vagina, 1% reach cervix, 200 reach secondary oocyte

• Typically occurs 12 œ 24 hours following ovulation

• Remain viable for 24 - 72 hrs. (secondary oocyteviable for 24 hours) œ 4 day window for fertilization to take place

• Capacitationœ takes about 7 hrs. chemicals from result in changes in the sperm make it capable of fertilization

• AcrosomalReaction and Sperm Penetration

• Blocks to Polyspermy

3 Pregnancy and Human Development

• First Week of Development œ four events

œ Fertilization

œ Cleavage of

œ Blastocystformation

œ Implantation

4 Pregnancy and Human Development

5 Pregnancy and Human Development

• PrembryonicDevelopment

œ Completion of Meiosis II and Fertilization

6 Pregnancy and Human Development

œ Cleavage and BlastocystFormation

7 Implantation

8 9 Placentation œ Placentation

• Extraembryonicmesoderm gives rise to the developing chorion

• Choriondevelops chorionicvilli, which develop blood vessels that connect with the developing embryo via the umbilical arteries and vein

• Erosion results in large lacunae forming in the stratum functionalis of the , chorionicvillilie close to these

10 Placentation

• Layer of endometrium between the chorionicvilliand stratum basalis becomes the decidua basalis; layer surrounding the embryo facing the lumen of the the decidua capsularis

• Chorionicvilliplus deciduabasalismakes up the

11 Placentation

12 Events of Embryonic Development

• Formation and Roles of Embryonic Membranes

œ Amnion

• Formed from cells of the embryonic disc, epiblast

• Becomes a fluid filled sac that surrounds the developing embryo

• Functions

œ Cushioning

œ Temperature regulation

œ Prevents adhering of developing structures

13 Events of Embryonic Development

œ Yolk Sac

• Formed from cells of the embryonic disc, hypoblast

• No real nutritive function

• Forms part of the gut tube

• Earliest site of erythropoiesis

• Primordial germ cells

œ Allantois

• Small outpocketingat caudal end of yolk sac

• Site for waste disposal

œ Chorion

• Helps form the placneta

• Surrounds the embryo and all of the other membranes

14 Events of Embryonic Development

• : Formation

œ Occurs at week 3

œ Three germ layers arise

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15 16 Events of Embryonic Development • Organogenesis: Differentiation of the Germ Layers

œ Specializations of Ectoderm - neuralation

17 Events of Embryonic Development

18 Events of Embryonic Development

œ Specializations of the Endoderm œ forms primitive gut

19 Events of Embryonic Development

œ Specialization of Mesoderm

• First seen as the notochord which persists as the pulposusof the intervertebraldiscs

• Aggregates appear on each side of the notochord, somites, each made of three parts

œ Sclerotome, gives rise to

» Vertebral column

» Ribs

œ Dermatome œ gives rise to the

œ Myotomeœ develop in skeletal muscles

20 Development of Fetal Circulation

21 Effects of Pregnancy on the Mother • Anatomical Changes

œ Reproductive organs become large and fill with blood (vagina develops a purplish hue, Chadwick‘s Sign)

• Enhances sexual sensations

œ Breasts

• Fill with blood • Glandular tissue develops • Areola darkens

œ Pigmentation in face œ —mask of pregnancy“

22 Effects of Pregnancy on the Mother

œ Uterus enlarges

• Relaxinœ adjusts center of gravity

23 Effects of Pregnancy on the Mother

• Metabolic Changes

œ Placenta begins to secrete

• Human placental latogen(hPL) or human chroionicsomatomammotropin (hCS)

œ Works synergistically with estrogen and progesterone to prepare the breasts

œ Promotes growth of the fetus

œ Promotes glucose sparing in mother (can result in gestational diabetes)

• Human chorionicthyrotropin(hCT) œ similar to thyroid stimulating hormone

œ Increases maternal metabolic rate

œ Increased plasma calcium levels

24 Effects of Pregnancy on the Mother • Physiological

œ Gastrointestinal

• Morning sickness

• Heartburn

• Constipation œ intestinal motility declines

œ Urinary

• Compressed bladder

• Increased glomerularfiltration

25 Effects of Pregnancy on the Mother

œ Respiratory

• Tidal Volume > 30 œ 40%

• Expiratory reserve < 40%

• Functional residual capacity < 25%

• Minute ventilation rate > 30 œ 40%

• Oxygen consumption > 10 œ 20%5555

• Dyspnea

26 Effects of Pregnancy on the Mother

œ Cardiovascular

• Stroke volume > 30%

• CO > 20 œ 30 %

• Rate > 10 œ 15%

• Blood Volume > 30 œ 50%

• When lying down weight of fetus can compress on aorta and vena cava (leg edema)

• Compression of renal arteries (renal hypertension)

27 Parturition (Birth) • Initiation of Labor

œ Rising levels of fetal cortisolstimulates the uterus to secrete large amounts of estrogen, in response

• Myometrialcells produce oxytocinreceptors

• Removes inhibiting effects of progesterone on uterine smooth muscle

• Weak, irregular contractions begin, Braxton Hicks Contractions (false labor)

œ Fetal cells release oxytocinwhich causes placenta to release prostaglandins œ both initiate stronger uterine contractions (positive feedback mechanism begins)

œ Fetal fibronectinbecomes a lubricant

28 Parturition (Birth)

29 Parturition (Birth) • Stages of Labor

œ Stage 1: Dilation Stage

• Time from beginning of labor until cervix reaches 10 cm

• Contractions 15 œ 30 min. apart; last for 10 œ 30 sec.

• Cervix softens, effaces, and dilates

• Amnion ruptures

• Can last for 6 œ 12 hrs.

• Baby rotates for birth position

30 Parturition (Birth)

œ Stage 2: Expulsion Stage

• Time from full dilation until birth

• Strong contractions every 2 œ 3 min., last about 1 min.

• Can last up to 2 hours, typically less than an hour

• Crowning œ when largest portion of baby‘s head appears (episiotomy may be done)

œ Stage 3: Placental Stage

• Usually about 30 min. after birth

31 Adjustments of the Infant to ExtrauterineLife

• Neonatal Period œ first 4 weeks of life

• ApgarScore œ performed 1 œ 5 minutes after birth, scored from 0 œ 2 for each parameter (score of 8 œ 10 indicates a healthy baby)

œ Heart rate

œ Respiration

œ Color

œ Muscle tone

œ Reflexes

32 Adjustments of the Infant to ExtrauterineLife • Taking the First Breath

œ Loss of link with placenta result in respiratory acidosis (Effect?)

œ Requires a great deal of effort (Why?)

œ Rate fast for first several weeks, 45/min

33 Lactation

• Towards end of pregnancy hypothalamus releases prolactinreleasing hormone

• Colostrum œ first secretion produced by the breasts

œ Yellowish fluid

œ No fat

œ Less lactose than true milk; more

• Protein

• Vit. A

• Minerals

œ Rich in IgA(what type of immunity?)

34 Lactation

• True Milk Production œ in the absence of suckling prolactin production decreases; suckling results in bursts of prolactinbeing release œ same stimulus results in milk let-down reflex

35 Lactation • Advantages of Breast Feeding

œ Nutrients more easily absorbed

œ Immune system bolstered, antibodies, complement, lysozyme, etc.

œ Laxative œ cleanses bowl

• Helps remove bilirubin

• Provides environment for development of natural bacterial flora

36