The Endocrine System and its changes in pregnancy

• 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) 

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 

• 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

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 

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 

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 

• 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 

• 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 

Endocrine glands 

• Pineal gland 

• Adrenal. 

• Thyroid. 

• Also: 

• Pancreas 

• Ovaries 

• Testes 

• and placenta 

• 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.

• “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 

• 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

• 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 

• 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 

 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