Pregnancy, Placenta, Lactation and Labor

Lecture Objectives Define Fertilization and implentation Enumerate the placental hormones Mention the hormones affecting mammary gland Identify the role of prolactin in lactation Mention the causes of Gynaecomastia Describe the mechanism of labor

Fertilization Normal site of fertilization is the ampulla of oviduct at the upper one third of oviduct. Must occur within 24 hours after ovulation Viability of ovum is 24 hrs. Sperms usually survive about 48 hours but can survive up to 5 days in female reproductive tract Sperm deposited in vagina travel through cervical canal, uterus, and to upper one third of oviduct

Fertilization

Fertilization & Implantation Fertilized ovum (zygote) having 46 chromosomes divides mitotically. Within a week, zygote grows and differentiates into blastocyst capable of implantation. The blastocyst implants in the posterior wall of uterus on 6-7 th day after fertilization. The blastocyst has inner cell mass that becomes the embryo and outer cellular layer, Trophoblast (= fetal portion of placenta). At site of implantation, Endometrium transforms into Decidual layer (= maternal portion of placenta).

Early Stages of Development from Fertilization to Implantation

FUNCTIONS OF PLACENTA Placenta performs the functions of Digestive system, Respiratory system and Kidney for the fetus. Nutrition and O2 move to fetus from maternal blood across the placental barrier. Acts as transient, complex endocrine organ that secretes essential pregnancy hormones 1. Human chorionic gonadotropin (HCG) 2. Estrogen 3. Progesterone 4. Human Chorionic Somatomammotropin

Placental hormones

Placental hormones 1- Estrogens: Placenta secretes hormones for maintaining pregnancy and preparing mother for Labor & Lactation: 1- Estrogens: secreted from Corpus Luteum at 1st trimester, After that Placenta secretes Estriol. Stimulates growth of myometrium increasing uterine strength for parturition. Promotes development of ducts in mammary gland preparing for lactation . Cause enlargement of female external genitalia for labor. Relax sacroiliac joint and symphysis pubis ligaments for labor.

Placental hormones 2- Progesterone: secreted from Corpus Luteum at 1st Trimester, after that from Placenta. Inhibits uterine contractions “Hormone of pregnancy” and prevents spontaneous abortion. Stimulates alveolar development in Mammary gland preparing for lactation . Promotes formation of mucus plug in cervical canal preventing uterine contamination. Increases decidual reaction development.

Placental hormones 3- Human Chorionic Gonadotropin (HCG): LH-like glycoprotein. It stimulates growth of corpus Luteum to be corpus Luteum of pregnancy to increase its secretion of estrogen and progesterone. It stimulates Leydig cells in testes of fetus to secrete testosterone  descent of testes into scrotum and development of male sex organs. It can be detected in maternal blood, 7 days after fertilization and in urine within 2 weeks (basis of pregnancy test).

Placental hormones 4- Placental Lactogen (Somatomammotropin): Secreted about 5th week of pregnancy. It stimulates corpus luteum to secrete estrogen & progesterone (luteotrophic). It stimulates breast development (mammotrophic). It stimulates cellular growth and it inhibits glucose transport (inhibits insulin effect) i.e. similar to growth hormone. 5- Relaxin: It is secreted from Placenta and Corpus Luteum. It relaxes Pelvic ligaments to help in process of delivery.

Secretion Rates of Placental Hormones

LABOUR (=PARTURITION) Def.: The process by which fetus is delivered from uterus after full term of gestation. About 280 days (40 weeks) after last menstruation preceding conception). Suggested mechanisms: 1- Role of hormones: a-  Ratio of estrogens to progesterone: - As Estrogen   uterine contraction. - Progesterone  uterine contraction. - ↑ Estrogen to Progesterone ratio at late pregnancy   oxytocin receptors  initiation of uterine contraction by oxytocin at time of labour.

LABOUR b- Oxytocin   uterine contraction: - ↑ Uterine muscle response to oxytocin at time of labour. - ↓Oxytocin in hypophysectomized animals  prolonged labour. c- Fetal hormones: By contractions of uterine muscle, pressure is exerted on head of fetus as a stress that stimulates fetal hypothalamus to release CRF  release of ACTH from fetal anterior pituitary  Glucocorticoids secreted from adrenal cortex  1- ↓ Placental Progesterone  ↑ uterine contractility. 2- ↑ Prostaglandins  ↑ uterine contractility.

LABOUR 2- Mechanical factors: Stretch of uterus  uterine contraction. Stretch of cervix  contraction of uterus  downward descent of baby’s head  more stretch of cervix more contraction (+ve feed back mechanisms). 3- Role of abdominal muscles: - During labor, abdominal muscles contract to aid delivery by ↑ intra-abdominal pressure (voluntary or reflexely by impulses from birth canal).

HORMONAL CONTROL OF LACTATION Initiation of milk production (lactogenesis) is under control of anterior pituitary prolactin (LTH). True milk production is established about two days after delivery; continued lactation is dependent on suckling which initiates milk ejection reflex and maintains prolactin secretion. With continued suckling, lactation can go on for years, and during this time, the raised prolactin levels, to some extent, depress ovulation and fertility.

HORMONAL CONTROL OF LACTATION 1- Estrogen: Stimulates Proliferation of duct system and nipples. It increases Blood flow to breast. It is responsible for Pigmentation of areolas. 2- Progesterone: Stimulates formation of mammary gland acini.

HORMONAL CONTROL OF LACTATION 3- Prolactin: Secreted by anterior pituitary and placenta. It stimulates formation and secretion of milk by acini. 4- Placental Lactogen: Stimulates breast development.

HORMONAL CONTROL OF LACTATION 5- Oxytocin: It squeezes milk from acini (=milk ejection). 6- Adrenal corticoids, insulin & Thyroxin: Needed for metabolic activities of the gland, no specific role in milk production. 7- Growth hormone: Necessary for mammary gland development in response to other hormones.

GYNAECOMASTIA Feminine enlargement of breast in male. At Puberty (physiological): boys develop a tender subareolar plaque (1-2 cm) which shrinks slowly and never persists for more than few years (Unknown cause). Adult (pathological): Primary testicular failure. -Liver failure. Bronchogenic carcinoma. Endocrine diseases.

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