pregnancy Flashcards
(23 cards)
pregnancy
Full-term pregnancy is 40 weeks of gestation
Based on a 28 day menstrual cycle, this is actually 38 weeks since fertilisation
Pregnancy can be split into pre-embryonic, embryonic and fetal periods, OR first, second and third trimester
establishment of pregnancy
Fertilisation of ovum by sperm
Multiple cell divisions leading to implantation of blastocyst into uterine endometrium (decidua) around days 5-7
The trophoblast cells invade then into the decidua to start to establish the placenta
hCG
Produced by syncytiotrophoblasts (following implantation of the blastocyst)
Maintains integrity of corpus luteum (mimics LH) to promote continued progesterone and oestrogen secretion and prevent menstruation
Once the placenta is established, it takes over this function (producing progesterone), the level of hCG declines
embryonic period
During the embryonic period gastrulation and organogenesis occurs and the placenta becomes established
fetal development
Fetal period (from 9 weeks to birth) represents rapid growth and physiological maturation of organ systems
Placenta must be functionally able to cope with this demand
lung maturation
lungs went involved in respiratory gas exchange- instead filled with fluid made by the lungs
fetes makes breathing moments in utero- expulsion of fluid into the amniotic sac via trachea
secretion of pulmonary surfactant by type II pneumocytes from 24 weeks gestation- facilitate lung expansion at birth and reduces surface tension
renal system maturation
New nephrons formed until 36 weeks of gestation
Kidneys produce dilute urine but otherwise minimal function (placenta fulfils role)
Fetus swallows ~7 ml amniotic fluid per hour and produces 300ml/kg of urine per day
digestive tract maturation
Not fully functional in fetus due to placenta but maturation of enzymes for digestion and absorption occurs
Crypts and villi develop during weeks 8-24 of gestation then elongate with gestational age
Meconium production -
greenish mixture of shed intestinal cells, lanugo, mucus, amniotic fluid
fetal circulation maturation
Haemopoiesis in the fetal liver becomes dominant from the second trimester
Most erythrocytes contain fetal haemoglobin (HbF) which has greater affinity for oxygen than adult haemoglobin
fetal circulation- ducts arteriousus and foramen ovale
During fetal life, the ductus arteriosus connects the pulmonary artery to the aortic arch but closes minutes after birth
The foramen ovale is a hole between the left and right atrium and takes several months to close after birth
These allowing most of the blood to bypass the fetal lungs where it is not needed (placenta fulfils gaseous transport)
endocrine function
Endocrine glands produce small amounts of hormones from second trimester
- contribute to fetal development and labour
Before birth, fetus has a very large adrenal cortex
- Adrenal gland produces steroid precursor for oestrogen biosynthesis by the placenta
Fetal posterior pituitary gland secretes oxytocin from second trimester and levels rise during labour
- To initiate contractions
maternal adaptations to pregnancy
Maternal respiratory rate & tidal volume increases–
To deliver excess oxygen and remove excess carbon dioxide
Maternal blood volume increases by ~50%
— Placenta removes blood from systemic circulation, erythropoietin/renin production induced to increase blood volume
Nutrient requirements increase——To supply nutrients to fetus via placenta
Glomerular filtration rate increases by ~50%
—– Due to increased blood volume. Accelerates excretion of fetal metabolic waste
progesterone
Essential for the continuation of pregnancy
Also has a role in breast development
Corpus luteum (early pregnancy)
Placenta (once developed)
oestrogen
At end of third trimester oestrogen helps with stimulating labour/birth.
Human fetus and placenta cooperate to produce oestrogens – fetal adrenal gland secretes androgens > converted to oestrogens by placenta
Fetal adrenal gland and placenta
hPL (human placental lactogen)
Polypeptide hormone.
Promotes growth and differentiation of mammary gland tissue for lactation
Stimulatory function on maternal tissues (like growth hormone (GH)) – ensures glucose and protein available to fetus
secreted from Placenta
relaxin
Peptide hormone. Increases pubic symphysis flexibility and cervix dilation
Suppresses release of oxytocin by hypothalamus and delays onset of labour contractions
secreted from Placenta
placental growth hormone
Suppresses/replaces maternal GH
Enhances nutrient availability to fetus by stimulating lipolysis and gluconeogenesis (glucose production)
secreted from Placenta
hormones stimulate breast maturation
Trimester 1 - Oestrogen promotes growth and branching of the ductal system
Trimester 2 -Progesterone promotes development of lobules and alveolar cells to proliferate, enlarge and become secretory
Trimester 3 - Lobules continue to grow into areas of fat and connective tissue
No lactation as progesterone inhibits the pituitary hormones needed
parturition (childbirth)- hormones
Parturition occurs through series of strong, rhythmic uterine contractions (labour)
Requires fetal and maternal endocrine coordination
—> Progesterone levels reduce towards term
—-> Fetal pituitary secretes oxytocin which enters the maternal blood stream via placenta
—–> Maternal pituitary also secretes oxytocin
—–> Prostaglandin production by fetal membranes on top of oestrogen and maternal oxytocin
parturition- feedback dependent
Contractions begin at superior portion of uterus towards cervix and increase in force and frequency
Stretching of cervix further stimulates oxytocin release
stage 1 of childbirth- dilation
- cervical ripening and dilation
- freqeuncy of myometrial contractions increase steadily
- amniochorionic membrane ruptures ‘water break’
- by end of stage 1, cervix fully dilated
- longest phase- hours to days
stage 2 of childbirth
Stage 2 - Expulsion stage
Contractions strong and frequent
Mother feels urge to push baby out
May need episiotomy
cut in perineum to prevent perineal tear
Minutes to 3 hours
Neonatal health assessed by Apgar score
stage 3 of childbirth - placental stage
Stage 3 - Placental stage
Active or physiological management (see NICE guidelines: Delivering the placenta)
Active management = oxytocin injection and removal by midwife. Lower risk of haemorrhage.
Physiological management = delivery up to 1 hour postpartum via contractions
