8. Pregnancy Flashcards
Describe the different roles of the different cell types in the blastocyst
Cytotrophoblast: implantation role & stem cells
Syncytiotrophoblast: multinucleated cellular sheet, good for transport
Produces enzymes to aid invasion of endometrium
Was is meant by implantation being interstitial
Uterine epithelium breached & conceptus implants within stroma
What is meant by the placenta being haemomonochroial
1 layer of trophoblast separates maternal blood from feral capillary wall
What are the aims of implantation
Establish basic unit of exchange Anchor placenta (establish outermost cytotrophoblast shell) Establish maternal blood flow within placenta
(Establishment of placenta takes priority in early embryonic dev: support for pregnancy)
Describe the development of the basic unit of exchange
Primary villi: early, finger-like projections of trophoblast
Secondary villi: invasion of mesenchyme into core of villi
Tertiary villi: invasion of mesenchyme core by fetal vessels
= functional chorionic villus
How is the endometrium prepared for implantation
Decidualisation
Remodelling of spiral arteries
Describe decidualisaton in preparation for implantation
Pre-decidual cells:
Cells that fall away (endometrium)
Decidual reaction:
Provides balancing force for invading trophoblast
Interaction between pre-Decidual cells & trophoblast
Stimulated by progesterone
Describe re modelling of spiral arteries in preparation for implantation
Creates low resistance vascular bed
Maintains high flow required to meet fetal demand, especially in late gestation
Describe the main implantation defects
Simple inappropriate site: Ectopic pregnancy (implantation @ site other than uterine body) Placenta Praevia (implantation in lower uterine segment)
Incomplete invasion:
Placental insufficiency (affects fetus e.g. Poor dev)
Pre-eclampsia (fetal affects & maternal signs/symptoms)
Describe the 2 components of the placenta after 4th month
Fetal portion:
Formed by chorion frondsum
Bordered by chorionic plate
Maternal portion:
Formed by Decidua basalis
Decidual plate most intimately in incorporated into placenta
Btw chorionic & decidual plates = intervillous spaces, filled with maternal blood
During 4th & 5th months, decidua form no of decidual septa:
Divide placenta into no of compartments: cotyledons
Project into intervillous spaces but don’t reach chorionic plate
Describe the 1st trimester placenta
Placenta established
Barrier to diffusion still relatively thick
Complete cytotrophoblast later beneath syncytiotrophoblast
Describe the term placenta
Surface area for exchange dramatically increased
Placental barrier now thin
Cytotrophoblast layer beneath syncytiotrophoblast lost
Describe the arrangement of umbilical arteries & veins
Project into tertiary villi, bathed in oxygenated maternal blood
2 umbilical arteries:
Deoxygenated blood from fetus to placenta
1 umbilical vein:
Oxygenated blood from placenta to fetus
What are cotyledons
Group of chorionic villi bathed in maternal blood
A buffer for fetal support, especially at end of pregnancy
How do cotyledons receive blood
Receive blood thru spiral arteries that pierce decidual plate
Pressure in arteries forces oxygenated blood into intervillous spaces & bathes small villi in oxygenated blood
As pressure decreases, blood flows back from chorionic plate towards decidua & enters endometrial veins
What factors influence passive diffusion of substances across the placenta
Concentration gradient
Barrier to diffusion (placental membrane)
Diffusion distance (haemomonochroial)
What methods of trans epithelial transport occur across the placenta
What substances are transported
Simple diffusion:
Water, electrolytes, urea & Uric acid, gases (O2, CO2)
Facilitated diffusion:
Glucose
Active transport:
Specific transporters expressed by syncytiotrophoblast - amino acids, iron, vitamins
What harmful substances can be transported across the placenta
Teratogens:
Thalidomide, alcohol, therapeutic drugs e.g. Anticonvulsants, drugs of abuse, maternal smoking
Some pathogens:
Varicella zoster, cytomegalovirus, treponema Pallidum, toxoplasma gondii, rubella
The placenta plays a role as an endocrine organ in supporting pregnancy
What hormones does it secrete
Protein hormones: Human Chorionic Gonagotrophin (hCG) Human Chorionic Somatotrophin Human Chorionic Thyrotrohin Human Chorionic Corticotrophin
Steroid hormones:
Progesterone
Oestrogen
What role do protein hormones (secreted from placenta) play in supporting pregnancy
hCG:
Supports secretory function of corpus luteum
Increases glucose availability to fetus
Produced by syncytiotrophoblast during 1st 2m of pregnancy
Excreted in maternal urine: clinically useful
hCS:
Influences maternal metabolism; increases availability of glucose to fetus
What role do steroid hormones play in supporting pregnancy
Maintain pregnant state
By end of T1, plants produces adequate steroid to support
Progesterone: influences maternal metabolism - increases appetite
What else does the placenta synthesise
Glycogen
Cholesterol
Fatty acids
Largely to support own function
How does the function of the placenta provide passive maternal immunity to the neonate
Receptor mediated endocytosis
Immunological competence begins in T3; fetus then making all components of complement
Fetal immunoglobulin consist almost entirely of maternal immunoglobulin (IgG) (transported from approx 14 weeks)
Fetus gains passive immunity against many infectious diseases
Describe the mechanism of Rhesus blood group incompatibility between mother & fetus
Mother previously sensitised to Rhesus antigen (e.g. In a previous pregnancy)
IgG against Rhesus crosses placenta & attack so fetal rbc’s
Now uncommon because prophylactic treatment
Describe the maternal physiological adaptations to pregnancy
CVS:
increased HR, SV, CO, blood vol
Urinary:
Increased renal plasma flow, glomerular filtration rate
Filtration capacity intact
Respiratory:
Diaphragm displaced
AP & transverse diameters of thorax increase
Physiological hyperventilation driven by progesterone
Increased O2 consumption, tidal vol, resp minute vol, alveolar ventilation
Decreased functional residual capacity
Unchanged vital capacity, resp rate
GI:
alterations on position of viscera (e.g. Appendix moves to RUQ)
Smooth musc relaxation by progesterone (delayed GI emptying, biliary tract stasis, increased risk pancreatitis)
Immune system:
Transfer of antobodies
Non-specific suppression of local immune response @ maternal-fetal interface
Haematology:
Mother pro-thrombotic: high fibrin deposition @ site of implantation, stasis, venodilation
Anaemia (plasma vol increases & rbc’s mass can’t keep up, iron/folate deficiency)
Describe the metabolic changes that occur in pregnancy
Carbohydrate:
Glucose & aa metab altered to favour nutrition to fetus
Fat laid down in 1st 1/2 pregnancy helps meet demands of fetus later
Oestrogen stimulates prolactin release (contributes to maternal insulin resistance)
Progesterone stimulates appetite
Later on, maternal energy met by metabolising peripheral FAs
Lipid:
Increased lipolysis from T2
Increased plasma conf of free FAs on fasting
Increased utilisation FAs increases risk ketoacidosis
Thyroid hormones:
Increased TBG, T3, T4 (stimulated by hCG)
Free T4 in normal range because More TBG
Describe How insulin levels are normally controlled in pregnancy
Rate of insulin secretion (basal & stimulated) normally increases as pregnancy proceeds
Ability of pancreatic beta cells to meet increased demand for insulin achieved by:
Increased rate of insulin synthesis in beta cells
Beta cell hyperplasia & hypertrophy
Describe what goes wrong with insulin levels in gestational diabetes
Endocrine pancreas unable to respond to metabolic demand of pregnancy
Pancreas fails to release increased insulin
Loss of control of metabolism: blood glucose increases
Describe the physiological changes that occur in Pre-Eclampsia
Vasoconstricted Plasma-contracted BP raised proteinuria Pitting oedema
Poor uteroplacental circulation
Widespread endothelial dysfunction
Reduced tendon reflexes
Describe what is normally included in antenatal screening
History & examination (risk factors)
Blood test:
Blood group
Haemoglobin
Infection
Urinalysis:
Protein
Describe the process of implantation
4-5 days post fertilisation: blastocyst enters uterine cavity
after a day or so in uterine cavity, implants in endometrium
Implantation involves interaction between trophoblast cells & epithelium of uterus:
Further embedding of blastocyst into endometrium dependent on invasive property of trophoblasts
10 days post fertilisation: blastocyst fully embedded in endometrium
