Physiology of Pregnancy Flashcards
Length of trimester
12 weeks- measured from the first day of the menstrual cycle. Conception typically occurs in week 3 coinciding with ovulation.
What is decidualisation?
Changes to endometrium stromal cells of the uterus to prepare for embryo implantation. It involves change from fibroblast cells -> metabolically active decidual cells which forms the base of the placenta called the decidua. This is driven by progesterone.
What changes occur in decidualisation?
Endometrium of uterus undergoes changes to support the growth of the embryo in the early stages via histotrophic support
->Secretion of prolactin to provide uterine milk to the embryo
->Increase in vascularisation where arteries become more spiral and
->Cells become filled with glycogen and fat
Endometrial glands have the greatest secretion following blastocyst implantation once it hatches from the zona pellucida.
How does the embryo receive blood supply?
Intervillous space, located between the chorionic villi
What is the glycocalcyx in the embryo?
Epithelium progenitor which is important in cell-adhesion and signalling.
How does the synctiotrophoblast form?
Fusion of the cytotrophoblast. It is a single celled multineucleated unit which is highly invasive into the endometrium for remodelling of endometrial spiral arteries by altering their structure to enter spaces called lacunae in order to provide blood supply to the embryo.
Where it terminates in the lacunae is the foetal lobule that is the foundation of maternal nutrient supply.
What happens in the implantation stage?
Blastocyt hatches from the zona pellucida and glycocaclyx and causes alterations in the glycoprotein mucins of the endometrium, using fibronectin and integrin to bind to the uterus. Villi of the trophectoderm of the embryo interdigitate with villi epithelia for interaction with uterus. Portion of the trophoblast called the synctiotrophoblast fuses and invades into the endometrium for spiral artery remodelling.
What is required in initial implantation?
Blastocyt must use protease to alter mucin glycoproteins on the uterus which are anti-adhesive.
Which hormones are important in embryo implantation?
Oestrogen, leukemia inhibitory growth factor and epithelial growth factor.
What is the role of oestrogen?
Regulates implantation window and inhibits FSH and LH release.
Produced by the corpus luteum which improves vascularisation of the uterus. It stimulates the growth of the foetal adrenal gland. Responsible for foetal development of the organs and organ development.
What is the role of progesterone?
Progesterone causes systemic vasodilation of blood vessels and venous distensibility resulting in hypotension.
How is oestrogen synthesised in the foetus?
Foetal adrenal glands synthesise androgens which are converted to oestrogen via reductase enzyme.
What promotes attachment of the embryo to the uterus?
Leukemia inhibitory factor-cytokine which is induced by high levels of progesterone
What regulates the implantation window?
Oestrogen and progesterone.
When is the embryonic stage of pregnancy?
Week 3 to Week 8 of pregnancy- after fertilisation, the blastocyt becomes an embryo and begins to develop the body organs
When is the foetal stage of pregnancy?
Week 9 of pregnancy until birth
What happens in the first trimester in the embryo?
Fertilisation, implantation, initial development of bones, muscles and all body organs.
What happens in the first trimester in the mother?
Weight gain and nausea, nocturia
What happens in the 2nd trimester in the foetus?
Spine straightens, proportions of foetus changes, hair development, nervous system develops for Pain sensation.
What happens in the second trimester in the mother?
->Placental growth to accommodate growing foetus
-> Uterus rises to reduce bladder pressure
-> Hypervolemia occurs due to higher oestrogen and progesterone levels which increase RAAS system activity
What are the physical changes in trimester 2?
Uterus fundus rises to create bump
Fluid retention- Hypervolemia
Placenta overtakes endocrine role as corpus luteum regresses and cause drop in hCG
Foetus triples in size and eventually becomes larger than placenta
Quickening
What is quickening?
Sensation of movement of foetus in womb.
What happens in the third trimester in the foetus?
Growth in weight and development of body, brain, lungs and blood cells.
What happens in the third trimester in the mother?
Tiredness
Lactation of colostrum milk which is nutrient dense
Back pain
Restricted breathing: increased oxygen demands
Braxton-Hicks
Relaxin production
Why does shortness of breath occur in pregnancy?
Diaphragm rises which reduces lung capacity and increases lung resistance. High progesterone levels increase the sensitivity of the respiratory centre to carbon dioxide. Higher oestrogen levels increases the sensitivity of progesterone receptors in the brain.
What is Braxton-Hicks?
Contraction and relaxation of the womb during the second and third trimester typically in preparation of true labour.
How does oestrogen cause physiological changes in the mother?
Increases levels of nitric oxide for vasodilation, that results in increased blood volume. It also increases blood flow.
Increases hepatic angiotensin II for the RAAS system.
How does progesterone cause changes in pregnancy?
Causes vasodilation and increases aldosterone levels that leads to greater thirst and fluid retention. Combined with high oestrogen, it leads to swolle ankles/pitting oedema.
It relaxes the intestinal muscles and lower oesophageal sphincter which can cause constipation and gastric reflux. The gall bladder is also relaxed and increases risk of cholestasis due to reduced contraction.
What are the cardiac changes in pregnancy?
Heart function increases by 30-50% with Higher cardiac output, blood volume and faster heart rate and stroke volume due to oestrogen .There is an Increase in heart size and atrial size.
->Dilation of the blood vessels prevents hypertension due to effects of progesterone
Cardiac output will peak in 3rd trimester.
How much does heart size increase in pregnancy?
Heart increases in size by 12%.
What are the respiratory changes in pregnancy?
Lung function increases by 40% which causes 16-20% more oxygen to be consumed.
Diaphragm elevates to accommodate for foetus which reduces the functional residual capacity so the Rib cage is displaced upwards.
Thoracic breathing which means quicker, shallower breathing and higher tidal volume due to progesterone increasing the responsiveness to CO2, resulting in a mild state of respiratory alkalosis. The sensitivity of chemoreceptors is lowered
How do the kidneys change in pregnancy?
Kidneys produce more EPO which increase the levels of RBC and reticulocytes in order to compensate for increasing oxygen demands from the foetus.
Kidney size increases because of increased excretion.
Increased blood flow due to progesterone causing afferent arteriolar vasodilation which increases GFR and kidney size
How does the urinary system change in pregnancy?
Ureters are displaced which decreased bladder tone (contraction) This increases capacity for storage, leading to stasis and higher UTI risk
How does hameatocrit change in pregnancy?
Low Haematocrit/relative anaemia
Increase in RBC due to higher EPO production, however there is greater salt and water retention that causes increased plasma volume
More pro-coagulation factors are produced and platelet aggregation is more likely to occur, increasing the risk for hypercoagubility.
How does MCV change in pregnancy?
Mean size of RBC does not change
When does implantation occur in pregnancy?
Day 6
Source of progesterone production in non-pregnant women?
Granulosa cells within the Corpus luteum
Source of progesterone production in pregnant women?
First 10 weeks: corpus luteum
Following 10 weeks: Placenta
How does the embryo gain access to maternal blood supply in implantation?
Fragments of spiral arteries are engulf by the synctiotrophoblast which contain pores called lacunae which fill with maternal blood and act as precursors for intervillous lacunae.
How does the endometrial blood supply change in implantation?
There is a switch from histotrophic support to haematotrophic support. Synctiotrophoblasts expand and anastomose with spiral arteries and remodel to reduce looping and blood pressure of the arteries, before it enters pores called the lacunae to supply the embryo with low pressure, low resistance blood flow.
What is the synctium?
Barrier between the embryo and developing placenta formed by trophoblast cells. It provides protection from the foetus against infection from the mother.
What happens post-implantation?
Day 9/Week 3 Lacunae form in synctiotrophoblast which invade spiral arteries.
Cytotrophoblast forms pirmary, secondary, tertiary, stem and floating villi
Embryo receives nutrition from uterine gland secretion and destruction of uterine stroma during implantation via histotrophic support
