physiology of pregnancy for undergraduates
DESCRIPTION
Physiology of pregnancy for medical undergrads.TRANSCRIPT
Prepared by:Fadziyah zaira bte md fadzil,
4th year, MBBS,Gef international medical school,
Bangalore,India
Physiology of Pregnancy
Introduction
During pregnancy there is progressive anatomical and physiological changes not only confined to the genital organs but also all systems of the body.
Principally, this a phenomenon of maternal adaptation to the increasing demands of the growing fetus.
Genital organ changes
Vulva Edematous and hyperaemic Superficial varicosities may appear especially
multipara. Labia minora- pigmented, and hypertrophied.
Vagina Hypertrophied Edematous and more vascular. Bluish discoloration of the mucosa (Jacquemier’s
sign) Due to increased blood supply of the venous plexus.
Length of anterior vaginal wall increased.
Contd.
Vaginal secretion Copious, thin and curdy white
Due to marked exfoliated cells and bacteria. pH becomes acidic (3.5—6)
Due to more conversion of glycogen into lactic acid by Lactobacillus acidophilic consequent on high estrogen level.
Prevents pathogenic infection
Vaginal cytology Preponderance of navicular cells (small intermediate
cells with elongated nuclei) in cluster.
Uterus
At term 900-1000gm at weight 35cm in length
Changes occur at all parts of uterus Body Isthmus Cervix
Uterus-cont
Body of uterus There is increase in growth and enlargement of the
body of the uterus.
Enlargement Factor affecting the enlargement of the uterus.
1. Change in the muscles1. Hypertrophy and hyperplasia-first half of pregnancy2. Stretching of muscle fibre beyond 20 wks of
pregnancy.
Uterus-cont
2. Arrangement of the muscle fibres1. Outer longitudinal-hoodlike arrangement2. Intermediate-thickest and strongest, criss-cross
arrangement3. Inner circular-scanty, sphincter-like arrangement.
3. Simultaneous increase in number and size of supporting fibrous and elastic tissue.
4. Increased vascularity1. Ovarian artery carries more blood during pregnancy2. Markes spiraling of the arteries-maximum at 20 wks
and then straigthen up and becomes dilated.
Arrangement of muscle fibres during pregnancy
Uterus-cont
Shape of the uterus Pyriform Globular – at 12 wks Pyriform – by 28 wks Spherical – beyond 36 wks
Position Normal anteverted upto 8 weeks. Erect afterwards
Lateral obliquity Uterus enlarged and rotates to the right (dextrorotation)
Uterus-cont
Uterine peritoneum Maintains relation proportionately with the growing
uterus.
*Braxton-Hicks contraction spontaneous uterine contraction in pregnancy that occur
from early weeks of pregnancy. Irregular, infrequent, spasmodic and painless without any
effect on dilatation of the cervix.
Uterine endometrium Changes from non-pregnant uterus into decidua of
pregnancy.
Uterus-cont
Isthmus 1st trimester, isthmus hypertrophies and elongates to
about 3 times its original length. >12 weeks, it progressively unfolds from above
downwards. Circularly arranged muscle fibres in this region acts
as sphincter that helps in retaining the fetus within the uterus.
Uterus-cont
Cervix Stroma:
Hypertrophy and hyperplasia Fluid accumulation Increased vascularity-bluish colouration(Chadwick’s
Sign) Softening of the cervix (Goodell’s sign)
Epithelium Marked proliferation of the endocervical mucosa with
downward extension beyond squamocolumnar junction.
Uterus-cont
Secretion Copious and tenacious (leucorrhea of pregnancy) Due to effect of progesterone Mucus forms thick plug to seal cervical canal.
Cervical length Unaltered but cervix becomes bulkier.
Advantage of having mucus plug formed during pregnancy
Other organs
Fallopian tube Held vertical by side of the uterus Total length is increased Tube becomes congested Epithelium is flattened Patches of decidual reaction observed
Ovary Persistent growth of the corpus luteum until 8th wks
and then regresses following decline of HCG secretion from the placenta.
It becomes colloid degeneration at 12 wks and later becomes calcified at term.
Breasts
Changes are best evident in primigravidae.Size
increased due to marked hypertrophy and proliferation of the ducts and the alveoli
Nipples and areola Larger, erect, deeply pigmented Montgomery tubercles-hypertrophied sebaceous
glands that is visible in the areola during pregnancy. Secondary areola- outer zone of less marked and
irregular pigmented area that appear at 2nd trimester.
Breast changes
Pigmented, erect nipple
Montgomery tubercles
Secondary areola
Secretion Can be squeezed out at 12th wks which is sticky at
first. 16th wks-it becomes thick and yellowish. Later-colostrum may be expressed from the nipples.
Cutaneous changes
Face Chloasma gravidarum/pregnancy mask
Abdomen Linea nigra - brownish black pigmented area in the
midline from xiphisternum to symphysis pubis. Striae gravidarum – slightly depressed linear marks
with varing length and breadth. Striae albicans- glistening white scar tissue after
delivery
Chloasma gravidarum
Linea Nigra
Striae gravidarum
Weight gain
Early wks pt may lose weight because of vomiting.
Subsequent months, the weight gain is progressive until last one or two wks where weights becomes static.
Total weight gain during course of single pregnancy for healthy woman is 11 kg.
1kg rise during first trimester, 5kg each during subsequent trimesters.
Weight gain-cont
Retention of electrolytes- sodium, potassium and chlorides.
Retention of Na+ causes water retention.At term, nearly 6.5liters water is retained.
Importance of weight checking Rapid gain in weight of more than 0.5kg a week/>2kg
a month is maybe an early manifestation of pre-eclampsia and need for careful supervision.
Stationary / falling weight- IUGR/intrauterine death of fetus.
Body water metabolism
Pregnancy is a state of hypervolemia.Causes of sodium retention and volume overload are
Changes in osmoregulation Increased estrogen and progesterone Increased renin angiotensin activity Increased aldosterone Atrial natriuretic peptide.
Resetting of osmotic threshold for thirst and ADH secretion.
Increased water intake due to lowered osmotic threshold for thirst causes polyuria in early pregnancy.
Hematological changes
Blood volume Markedly raised Increased from 6th wks, expands rapidly tp maximum
40-50% above nonpregnant level at 30-32 wks.
Plasma volume Increases to 1.25liters
RBC and Hb RBC volume increased 20-30% Total volume increase: 350ml
Hematological changes
Hemodilution occur during pregnancy and fall in Hb concentration.
Advantage of hemodilution during pregnancy Diminished blood viscosity thus optimum gaseous
exchange between mama and baby Protection from the mother against the adverse
effects of blood loss during pregnancy.
Hematological changes
Leucocytes Neutrophilic leucocytosis Due to increased estrogen and cortisol
Total protein Increases from normal 180gm to 230gm at term A:G ratio is diminished to 1:1
Blood coagulation factor Pregnancy is hypercoagulable state. Fibrinogen level is raised by 50% 4-fold rise in ESR
Heart and circulation
Anatomical changes Heart is pushed upwards and outwards
CO Increased from 5th wks of pregnancy reaches peak 40-
50% at 30-34wks. Caused by
Increased blood volume To meet additional O2 required due to high metabolic
activity during pregnancy
BP Decreased due to decreased vascular resistance
Heart and circulation
Venous pressure Femoral venous pressure is markedly increased due to
pressure exerted by gravid uterus on the common iliac veins.
Central hemodynamics No significant change in CVP, MAP, and PCWP.
Postural hypotension Compression of gravid uterus to IVC and failed
collateral circulation (parasternal and azygos veins)
Heart and circulation
Regional distribution of blood flow Uterine blood flow increased to 750ml/min near term. Pulmonary BF increased by 2500ml/min Renal BF increased by 400ml/min
Explains flushing, sweating or stuffy nose in pregnancy.
Metabolic changes
General metabolism increased due to needs of growing fetus BMR increased to extent of 30% higher
Protein metabolism Positive nitrogenous balance throughout pregnancy Anabolism!
Carbohydrate metabolism Insulin secretion increased Sensitivity of insulin receptor reduced To ensure continous supply of glucose to fetus
Metabolic changes
Fat metabolism 3-4kg fat stored at abdoment,breast, hips and thighs.
Lipid metabolism HDL level increased by 15% LDL utilised for placental steroid synthesis.
Iron metabolism Pregnancy is an iron deficiency state Absorption from gut is increased but lost along the
routes, to placenta and during delivery. Serum iron and ferritin will fall if supplementation is
not given.
Systemic changes
Respiratory system Breathing becomes diaphragmatic Transverse diameter of chest expends by 2 cm Chest circumference increased by 5-7cm Mucosa of URT shows congestion Hyperventilation occur due to increased tidal volume
and progesterone acting at the respiratory center.Acid base balance
PCO2 fall, PO2 rises- facilitate transfer of gases between mam and baby
pH rises- respiratory alkalosis due to high maternal O2 consumption and fetal demand.
Systemic changes
Urinary system Dilatation of ureter and renal pelvis Kidney enlarges by 1cm Renal plasma flow increased by 50-75%
Alimentary system Muscle tone and motility of entire GI tract are
diminished due to increased progesterone level Cardiac sphincter relaxes chemical esophagitis and
heart burn Diminished gastric secretion
Systemic changes
Liver and gallbladder Functions are depressed except LFT serum levels.
Nervous system Psychological changes-nausea, sleeplessness Postpartum blues, depression or psychosis
Summary
There is various changes happening in a pregnant mother, not only at specific organs, but also systemically.
It is important to know these changes so we as doctors should assure them that the changes are normal whenever they have doubt about what’s happening to their own body.