fetal growth and parturition. fetal growth rate of growth in humans –relatively slow during first...
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Fetal growth and parturition
Fetal growth
• Rate of growth in humans– Relatively slow during first 20 weeks– Rapidly increased during week 30-36– Slows down until birth– Different from domestic species
• Majority of growth takes place during the last trimester
• Accumulation of proteins– Muscle development– Precedes fat
deposition• Eventually exceeds
protein deposition• Energy storage
• Decreased placenta to fetus ratio
• Rate of growth– Fetal genome– Maternal factors
• Nutrients– Postnatal health– Postnatal development
• Placental lactogen– Stimulation of growth
Fetal metabolism
• Nutrients– Maternal source
• Glucose– Major energy source (50 % of total energy for fetal
growth)
• Amino acids• Fatty acids• Vitamins• Minerals
• Placenta– Physical barrier
• Diffusion of very small molecules and lipid-soluble molecules
• Large molecules and polar molecules – Transport system– Breach in the placenta
– Movement of molecules between maternal and fetal circulation
• Layers of cells between two circulations
Importance of fetal adrenal gland
Parturition
• Three stages– First stage
• Initiation of myometrium contraction• Initiated by the fetus
– Second stage• Expulsion of the fetus
– Third stage• Expulsion of fetal membrane
Parturition
• First stage– Initiated by fetus– Distress
• Maximum size that can be maintained– Lack of nutrients– Hypoxia
• Activation of fetal hypothalamus-pituitary-adrenal axis
– Release of ACTH by the fetal pituitary gland
• Fetal ACTH– Release of cortisol from
fetal adrenal gland• Fetal cortisol
– Removal of “progesterone block”
• Contraction of myometrium
• Conversion of progesterone to estradiol
– 17-hydroxylase– 17-20 lyase– Aromatase
• Fetal cortisol– Increase production of PGF2 by the
endometrium• Further removal of progesterone block
– Cause luteolysis
• Stimulates contraction of myometrium– Synergism with estradiol
• Contraction of myometrium– Pushes the fetus toward cervix
• Activation of the CNS– Secretion of oxytocin from the posterior pituitary gland
• Oxytocin– Increased contraction of the uterine smooth muscle
– Positive feedback• More contraction (pushing of fetus), increased oxytocin
secretion• Entering of the fetus in the cervical canal
– End of the first stage
Expulsion of fetus
• Relaxation of the cervix and pelvic ligaments– Relaxin
• Secretion stimulated by PGF2
• Role of estradiol on parturition– Increased overall secretory activity
• Mucus production by cervix and vagina– Removal of cervical plug– Lubrication
• Rupture of fetal membrane– Loss of amniotic and allantonic fluid
• Further lubrication
• Fetus becomes hypoxic– Movement of the fetus
• Stimulates further contraction of the myometrium– Increased strength of contraction
Expulsion of the fetal membrane
• Shortly after expulsion of the fetus– Dislodging of fetal membrane from the uterus– Vasoconstriction
Mammary gland development
• Cyclic changes in ovarian steroid hormones– Essential for mammary
development• Estradiol
– Development of mammary alveoli (secretory unit)
• Progesterone– Development of
mammary ducts
• Final stage of mammary gland development– Pregnancy
• Ovarian/placental steroid hormones
– Periparturient period• GH and prolactin
– Placental lactogen?
• Glucocorticoids
Lactation
• Parturition– Metabolic shift
• Fetal growth to synthesis and secretion of milk
– Mobilization of nutrients
• Storage within the body– Fats
• Triggered by changes in hormones
Lactation and re-initiation of reproductive cycle
• Lactating women– High prolactin– Low LH and estradiol
• No ovulation– Lactation-induced anovulation/amenorrhea (infertility)
– Women remain anovulatory as long as they breast-feed their babies
• Increased survivability of the infants
• Lactational anestrus in the domestic species– Divert nutrients for lactation
• Ensure the survival of offspring
– Lactation stimuli/physical contact between mother and offspring
– Animals remain in anestrus (absence of estrus) until nutrient intake exceeds nutrient demand