Chapter 82

Pregnancy & Lactation

Figure 82-2 A, Ovulation, fertilization of the ovum in the fallopian tube, and implantation of the blastocyst in the uterus. B, Action of trophoblast cells in implantation of the blastocyst in the uterine endometrium.

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Overview of fertilization & implantation

Increased estrogen in late follicular phase promotes sperm transport to ovum

• ↑ growth/activity of oviduct cilia• ↑ oviduct smooth muscle contraction• ↑ isthmus smooth muscle contration• ↑ myometrium contraction• ↑ glycogen (for lactic acid ferm., which ↓ pH in vagina)• ↓ viscosity of cervical mucos

The rise in progesterone after ovulationpromotes the arrival & implantation of the blastocyst

• ↑ progesterone receptor expression on oviduct & uterine smooth muscle • ↑ differentiation & secretion of uterine milk by endometrium• ↓ myometrium contraction• ↑ viscosity of cervical mucos

progesterone: pregnancy hormone

Figure 82-1 Fertilization of the ovum. A, The mature ovum surrounded by the corona radiata. B, Dispersal of the corona radiata. C, Entry of the sperm. D, Formation of the male and female pronuclei. E, Reorganization of a full complement of chromosomes and beginning division of the ovum. (Modified from Arey LB: Developmental

Anatomy: A Textbook and Laboratory Manual of Embryology, 7th ed. Philadelphia: WB Saunders, 1974.)

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Prostaglandins and oxytocin assist w/sperm transport to fallopian tubes

• prostaglandins & oxytocin stimulate smooth muscle contraction of the myometrium

• isthmus circular smooth muscle contraction stimulated by α-adrenergic receptors

• Fertilization disperses remaining granulosa cells

• fertilization requires interaction of autonomic nervous system, estrogen,

& progesterone

Figure 82-1 Fertilization of the ovum. A, The mature ovum surrounded by the corona radiata. B, Dispersal of the corona radiata. C, Entry of the sperm. D, Formation of the male and female pronuclei. E, Reorganization of a full complement of chromosomes and beginning division of the ovum. (Modified from Arey LB: Developmental

Anatomy: A Textbook and Laboratory Manual of Embryology, 7th ed. Philadelphia: WB Saunders, 1974.)

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Fertilization triggers completion of meiosis II & extrusion of 2nd polar body

• fertilization window narrow (6-24 hrs) after ovulation

• embryo in fallopian tube 3-5 days• blastocyst (about 100 cells)

reaches uterus & implants• nourishment comes from fluid in

oviducts and endometrium, until placenta forms

Online ISSN 1460-2369 - Print ISSN 1355-4786Copyright © 2012 European Society of Human Reproduction and Embryology

Implantation: proliferation & differentiation ofthe trophoblast into syncytial & cytotrophoblasts

Effects of human chorionic gonadotropin

hCG

progesterone

progesteroneestrogeninhibin

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Figure 82-3 Implantation of the early human embryo, showing trophoblastic digestion and invasion of the endometrium. (Courtesy Dr. Arthur Hertig.)Downloaded from: StudentConsult (on 5 February 2012 11:30 PM)

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Digestion of the decidua & endometriumleads to formation of placenta

• decidualization• IGF-1• IL-1• progesterone

• killed decidual cells phagocytized by trophoblasts

• hyperemia & ↑ vasc. perm. • blood pools in small sinuses• syncytial & cytotrophoblasts

digest endometrium• blood drains into endomedtrial

venous sinuses• syncytial & cytotrophoblasts

differentiate into placental villi

Figure 82-5 Above, Organization of the mature placenta. Below, Relation of the fetal blood in the villus capillaries to the mother's blood in the intervillous spaces. (Modified from Gray H, Goss CM: Anatomy of the Human Body, 25th ed. Philadelphia: Lea & Febiger, 1948; and from Arey LB: Developmental Anatomy: A Textbook and

Laboratory Manual of Embryology, 7th ed. Philadelphia: WB Saunders, 1974.)

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Placental maturation leads to trophoblastthinning

• syncytial trophoblast becomes hormone producer & main transport tissue

Figure 82-6 Oxygen-hemoglobin dissociation curves for maternal and fetal blood, showing that fetal blood can carry a greater quantity of oxygen than can maternal blood for a given blood Po2. (Data from Metcalfe J, Moll W, Bartels H: Gas exchange across the placenta. Fed Proc 23:775, 1964.)

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Oxygen-hemoglobin dissociation curves

3 reasons fetal blood sogood at O2 delivery1.fetal hemoglobin2.high Hb concentration3.Bohr effect

Figure 82-7 Rates of secretion of estrogens and progesterone, and concentration of human chorionic gonadotropin at different stages of pregnancy.

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Rates of hormone secretion during pregnancy

Figure 82-8 Effect of pregnancy to increase the mother's blood volume.

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Pregnancy increases blood volume

Other increased parameters1.secretion of adrenalcorti- cal & T4 hormones2.cardiac output3.BMR4.maternal respiration5.renal Na+ & H2O reab-6. sorption7.PTH secretion8.TRH, CRH secretion

ACTH

cortisolDHEA

placenta

estrogens

uterus

CRH

fetal adrenals

fetal pituitary

fetal lungs, guts

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redrawn from Basic Medical Endocrinology copyright 2003

Placental CRH secretion in late pregnancycreates positive feedback loop with cortisol

Positive feedback loops initiate parturition

ACTHCRH prostaglandins

uterinecontract.cervicalripening

estrogens

progesterone

Figure 82-9 Theory for the onset of intensely strong contractions during labor.Downloaded from: StudentConsult (on 5 February 2012 11:30 PM)

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Parturition involves hormones & mechanoreception

• progesterone opposes production of prostaglandins & uterine contractions during pregnancy

• increased estrogen:progesterone ratio

• increased secretion of oxytocin

Figure 82-10 The breast and its secretory lobules, alveoli, and lactiferous ducts (milk ducts) that constitute its mammary gland (A). The enlargements show a lobule (B) and milk-secreting cells of an alveolus (C).

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Growth & development of mammary glands

Key hormones:1.oxytocin2.prolactin

Figure 82-11 Changes in rates of secretion of estrogens, progesterone, and prolactin for 8 weeks before parturition and 36 weeks thereafter. Note especially the decrease of prolactin secretion back to basal levels within a few weeks after parturition, but also the intermittent periods of marked prolactin secretion (for about 1 hour at a time)

during and after periods of nursing.

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Changes in hormone levels prior to &after birth