pregnancy

What is the role of the placenta?

• interface between maternal and fetal plasma

• protects fetus from attack by the maternal immune system

What hormones are produced by the placenta?

human chorionic gonadotrophin (hCG)

human placental lactogen (hPL)

placental growth hormone (pGH)

progesterone estrogens (steroid)

hCG production

• produced by placenta

  • GnRH produced by cytotrophoblast

  • stimulates hCG production by syncytiotrophobast

which hormone is hCG structurally similar to and effect

LH

• can bind to its receptor on the corpus luteum

• prevents luteolysis and maintains high levels of progesterone

if levels of hCG are low during pregnancy

could be non viable pregnancy or implanted somewhere else

if levels of hCG are high during pregnancy

• could be twins, triplets etc

what hormone prevents the degeneration of the corpus luteum

hCG

what 2 cells primarily make up the human placenta

• cytotrophoblast

• syncytiotrophoblast

luteal placental shift

week 9, placenta can produce predignelone then sex steroids

what is progesterone produced by in placenta

• syncytiotrophoblast

what is progesterone production in placenta dependent on

dependent on maternal cholesterol because the placenta lacks enzymes to produce cholesterol from acetate

• regulated by hCG

function of progesterone

• maintains decidual lining

• dec prostaglandin function - relaxes myometrium

• suppresses t lymphocyte mediated tissue rejection

if the progesterone levels are low

progesterone levels low → quite likely the pregnancy will fail

what does the production of oestrogen in the placenta depend on

• mothers adrenal gland

• foetus adrenal gland

• placenta expresses aromatase in abundance for conversion of androgens to oestrogens

can estriol be produced by placenta without a feotus

• no

• so can dictate foetal wellbeing

Purpose of oestrogens in pregnancy

• vasodilatory - effective in promoting uteroplacental blood flow

• regulate placental progesterone production (3rd trimester)

• fetal adrenal gland function

• mammary gland development

oestrogen and progesterone regulation of respiration

• mums respiratory rate does not alter

• increase in tidal volume and minute ventilation to supply more oxygen

• oestrogen receptor is expressed in relevant regions in brain but likely action is indirect but likely regulating progesterone receptor

  • progesterone increases respiratory activity

oestrogen and progesterone regulation of cardiovascular system

• heart rate increases

• cardiac output increases

  • oestrogen can increase heart rate via SA node

  • less certain about role in the CNS

• progesterone causes vasodilation of vascular smooth muscle

  • may have affect in CNS

progesterone and oestrogen thermoregulation

• initial increase in core body temp then a steady decline over the course of pregnancy

• fever response is altered, decline

  • by oestrogen

  • oestrogen receptors in brain regions crucial by pyrogenic response

  • pregnant individuals with covid less likely to present with temperature

• progesterone inc body temperature during menstrual cycle

  • progesterone may be responsible for early inc in body temp?

which placenta hormone is not pulsatile or regulated by GnRH

pGH

pGH function

• regulation of foetal growth but not necessary

• IGF-1 production

• gluconeogenesis and lipolysis

hPL function

• lactogenic activity in animals but maybe not humans

• metabolic hormone regulating glucose in mother via IGF-I

• stimulates onset of maternal behaviour after birth

what is quiescence state maintained by

• inhibitors

• progesterone decreases prostaglandins

• hPL inhibits smooth muscle contraction

activators of parturition

• oestrogen - inc contraction associated proteins with gap junctions needed for electrical coupling

• prostaglandins

• oxytocin

what phase happens after parturition?

involution

the contractility decreases after parturition

potential triggers for parturition

• change in oestrogen progesterone ratio

• functional progesterone withdrawal

• increased oestrogen synthesis

ducts development for lactation

• when the baby is born there are few atrophic ducts

• duct grow and divide, more alveoli form

  • under the influence of oestrogen, GH and adrenal steroids

• as the individual grows older

  • lobulo alveolar growth

  • stimulated by progesterone and prolactin

what hormones stimulate milk secretion

oestrogen, progesterone, prolactin and possibly hPL

Where is prolactin produced?

anterior pituitary

What suppresses prolactin levels?

high steroid and hPL levels

What does milk ejection into ducts require?

• oxytocin from posterior pituitary

• stimulated by suckling reflex, also inhibits GnRH

What does suckling inhibit?

GnRH

foetal thyroid hormones

• T4 levels increase

• T3 levels decrease

why are T3 levels low in a foetus

• low type 1 deiodinase

• placenta is high in type 3 deiodinase

  • gives rise to reverse T3 - inactive

what happens to thyroid hormones after birth

• TSH, T3 and T4 rise rapidly

• adult levels achieved within a few weeks

why are the glands large in a foetus?

• due to foetal zone of cortex

• produces DHEAs - essential for estrio

what is the growth controlled by for a foetus?

• genetic factors

• placental function - nutrient uptake and hormone production

• insulin like growth factors

what happens in neonate for growth?

• GH receptors increase

• IGF responsive to pituitary GH

what inc the adhesivity of the epithelium of the uterine endometrium

• pinopodes and adhesive proteins

• by progesterone action

how does the sperm change to become capable of fertilising the egg

1. An altered membrane fluidity due to the removal of cholesterol from the sperm membrane

2. The removal of proteins and carbohydrates from the membrane that may otherwise block sites that bind to the egg

3. A change in membrane potential that may permit Ca 2+ to enter the sperm and thereby facilitate the acrosome reaction

4. Phosphorylation of numerous proteins

functions of hormones produced by the syncytiotrophoblasts

• Maintaining the pregnant state of the uterus

• Stimulating lobuloalveolar growth and function of maternal breasts

• Adapting aspects of maternal metabolism and physiology to support a growing fetus

• Regulating aspects of fetal development

• Regulating the timing and progression of parturition

what does egg activation depend on ?

• intracellular release of calcium conc in the egg

  • stimulated by production of IP3 in response to PLC

what is the production of DHEAS dependent on?

fetal ACTH by the end of the 1st trimester

hormonal abortion

• achieved up to 49 days after gestation by administration of mifepristone

  • progesterone receptor antagonist, induces the collapse of the pregnant endometrium

  • followed by ingestion or vaginal insertion of synthetic prostaglandin E

  • this will induce myometrial contractions