The Endocrine System and its changes in pregnancy

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Fertilisation and Embedding

• Corpus Luteum does not regress but continues to produce high amounts of progesterone (P4), and estradiol (E2) during the first trimester of pregnancy. This causes: 

• Development of the mammary glands (breasts) 

• Inhibition of ovulation (negative feedback at hypothalamus and pituitary) 

• P4 increases fat deposition (increasing appetite and diverting energy stores from sugar to fat) 

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Functions of hCG (Human chorionic gonadotropin)

Rescue and maintenance of function of the corpus luteum (continued progesterone production) 

• progesterone producing life span of the corpus luteum of menstruation could be prolonged for 2 weeks by hCG administration 

• about the 8th day after ovulation or 1 day after implantation- hCG takes over for the corpus luteum 

• Continued survival of the corpus luteum is totally dependent on hCG 

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Endocrine function of the placenta

• At about 5 weeks of pregnancy, the placentastarts secreting estrogens (estradiol, estrone but mostly estriol) and later progesterone 

 • When the placenta is fully established (3rd or 4th month of pregnancy), the Corpus Luteum has regressed and hCG levels drop dramatically

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Human Placental Lactogen

Also called human chorionic somatomammotropin or chorionic growth hormone 

– potent lactogenic and growth hormone-like bioactivity 

– immunochemical resemblance to human growth hormone 

• Concentrated in the syncytiotrophoblast like hCG 

• Detected in the trophoblast as early as the second or third week after fertilization of the ovum 

 • Before 6 weeks- hPL is also identified in cytotrophoblasts 

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Human Placental Lactogen

Also called human chorionic somatomammotropin or chorionic growth hormone 

– potent lactogenic and growth hormone-like bioactivity 

– immunochemical resemblance to human growth hormone 

• Concentrated in the syncytiotrophoblast like hCG 

• Detected in the trophoblast as early as the second or third week after fertilization of the ovum 

 • Before 6 weeks- hPL is also identified in cytotrophoblasts 

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Actions of HPL(Human Placental Lactogen)

1. Maternal lipolysis and increase in the levels of circulating free fatty acids - providing a source of energy for maternal metabolism and fetal nutrition 

2. Anti-insulin or "diabetogenic" action - increase in maternal insulin - favoring protein synthesis and provision of mobilisable amino acids for transport to the fetus 

3. Potent angiogenic hormone - may play an important role in the formation of fetal vasculature 

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Relaxin

• Found in: corpus luteum, decidua, and placenta 

• Relaxin along with rising progesterone levels acts on myometrial smooth muscle to promote uterine relaxation in early pregnancy 

• Also acts on smooth muscle layer of blood vessels and cartilidge in pregnancy 

• Relaxin and relaxin-like factors in the placenta and fetal membranes may play a role in regulation of extracellular matrix degradation in the puerperium 

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Progesterone

• After 6 to 7 weeks of gestation ovarian progesterone production is minimal 

• After about 8 weeks – placenta replaces the ovary as the source of progesterone & continues to increase production throughout pregnancy 

• End of pregnancy - maternal levels of progesterone are 10 to 5000 times those in nonpregnant women, depending on the stage of the ovarian cycle Prepares and maintains the endometrium to allow implantation 

• Has a role in suppressing the maternal immunologic response to fetal antigens thereby preventing preventing maternal rejection of the trophoblast 

• Has a role in parturition 

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The endocrine glands

Endocrine glands 

• Pineal gland 

• Adrenal. 

• Thyroid. 

• Also: 

• Pancreas 

• Ovaries 

• Testes 

• and placenta 

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Hypothalamus

  • Portion of the brain largely connected with the renal and endocrine systems via the pituitary gland

• Together the pituitary and hypothalamus regulate the activity of most of the other endocrine glands. 

• The hypothalamus constitutes the major intergrating link between the nervous and endocrine systems & can be called a neuroendocrine organ – producing, releasing and inhibiting hormones by the anterior pituitary (APG) gland. 

• So, controls the release of hormones from the pituitary gland.

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The pituitary gland

• “Master endocrine gland”. 

• Anterior pituitary releases hormones. 

• Posterior pituitary gland – storage unit. 

• Weight increases 30% in first pregnancies and 50% in subsequent pregnancies (almost entirely in anterior pit) 

• Increase in number of lactotrophs (prolactin secreting cells), 

• Pituitary vulnerable to a reduced blood supply – Sheenan’s syndrome – necrosis – severe/prolonged shock. 

• Fall in Growth Hormone producing cells 

• Hormones produced influenced by feto-placental unit 

• FSH and LH inhibited (due to hCG) 

• Posterior pituitary: oxytocin released in labour 

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Thyroid Gland

• Produces Thyroxine (T4) – major hormone 

• and Triiodothyronine (T3) which maintain normal metabolic function 

• Thyroid function remains normal in pgy. 

• Significant changes in plasma concentration of thyroid hormones- influenced by hCG and oestrogen. 

• TSH reduced in 1st trimester & then returns to normal level for remainder of pregnancy. 

• Some of these changes affect the metabolism of carbohydrate, protein and lipids 

• Basal metabolic rate increases by approx 25% 

• The changes have been linked to nausea and vomiting in early pregnancy

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Adrenal Glands

• Adrenocorticotropic hormone (ACTH) is released by the anterior pituitary gland, which in turn causes the release of cortisol. 

• ACTH levels rise 

• Plasma cortisol levels rise – double plasma cortisol levels 

• Has been linked to straie gravidarum, carbohydrate intolerance and PIH 

• Cortisol production increased during labour 

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Aldosterone

• It regulates sodium balance by targeting distal tubules in kidneys & stimulates reabsorption of sodium ions from the urine & returns them to the bloodstream 

• Excretion of sodium and chloride increased due to progesterone 

• Increased aldosterone enhances reabsorption of sodium to maintain balance 

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Pineal glands

 Neural connections between the retina & pineal gland also light-regulated secretion of the hormone melatonin. 

• Melatonin controls reproduction. 

• In humans melatonin causes the hypothalamus to inhibit release of gonadotrophin-releasing hormone. 

• Causes daily variations in temp, sleep & appetite

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