Pregnancy

• During pregnancy blood flows through remodelled spiral arteries into placenta and pools in intervillus space where gas exchange takes place
• Until 8 weeks the corpus luteum secretes progesterone. After the luteal-placental shift the placenta is the predominant secretor of progesterone.
• Progesterone decreases uterine contractions and motility to prevent labour and rejection of foetus
• Oestriol is produced by foetal adrenal glands and the trophoblasts covert it to oestrogen to promote organ development
• Relaxin is produced by the placenta to relax the uterus for embryo implantation and increase blood supply to maternal heart and kidneys.
• Relaxin in partuition ruptures membranes and relaxes pelvic ligaments
• At labour initiation- myometrial cells awaken and increase expression of CAPS to increase contractility of uterus
• Oestrogen in labour promotes uterine contraction and cervical dilation through CAP genes
• At the end of pregnancy- uterus becomes desensitised to progesterone and disinhibits oestrogen actions so it is prepared for labour
• Prostaglandins increase towards the end of term
• Prostaglandin F2A and E2 are produced by uterine decimal cells and increase contractions via positive feedback
• Oxytocin sustains labour- uterus becomes sensitised at 20 weeks and oestrogen increased oxytocin receptor quantities
• Oxytocin acts on myometrial cells to increase intracellular Ca to promote muscle contraction. Facilitated through PGF2A
• Oxytocin also acts on decimal cells to increase expression of COX enzymes to increase prostaglandin production and clamp spiral arteries after delivery
• Ferguson reflex = oxytocin released from posterior pituitary is stimulated by cervical distension
• Maternal blood volume increases by 1-2 L in pregnancy
• Oestrogen acts on hypothalamus and brainstem to increase renal sympathetic nerve activity and increase RAAS leading to increased thirst
• To compensate for increased blood vol, bone marrow increased erythrocyte production but this is not enough so there is a decrease in Hb and Red cell count
• Oestradiol increases NO production to decrease blood pressure. Mixed with resistance to AngII there is increase in orthostatic hypotension
• Cardiac output, HR and stroke volume increases due to increased left ventricular mass
• Increase in Factors VIII, IX and X and fibrinogen to cause an increase in clotting
• Increase in GFR causes increased urinary frequency and glucosuria
• Pregnancy causes a hypervolaemic hyponatraemic state due to increased water retention and tempered effects of aldosterone
• Increased metabolic rate In pregnancy increases oxygen demand. Means there is a slight alkalosis compensated by more urinary excretion of bicarbonate
• Total lung capacity decreases due to growing foetus but is compensated by increase in subcostal angle
• Progesterone causes smooth muscle relaxation so an increase in constipation, bloating and nausea is seen