Physiology of Pregnancy

Daniel HodycDepartment of Physiology

Pregnancy

1. Fertilization2. Placenta development, nutrition3. Hormonal changes during pregnancy4. Other physiological changes5. Metabolism

Fertilization

Fertilization

Fertilization in the ampulle of the FT.

• Prostaglandins• Oxytocin

Ectopic (extrauterine) gravidity

Fertilization

Transport into the uterus - 3-5 days

• Contraction of the FT isthmus• Relaxation - progesteron

Fertilization

Implantation 5-7 days after fertilization

• Proteolytic enzymes of the trophoblast cells

Placenta

Placenta development

• Early nutrition of the embryo - invasion of trophoblastic cells into the decidua• Progesteron produced by CL - stimulates decidual cells to concentrate glycogen, proteins and lipids

Placenta works as a physiological A-V shunt

Placenta - oxygen transport•Similarities betwen placenta and lungs•Oxygen transport - simple difusion

Lungs• pO2 in alveoli…………………………..100mmHg• pO2 in the venous blood……………40mmHg• dO2 in (pressure gradient)…………60mmHg

Placenta:• pO2 in placental sinuses…………50mmHg• pO2 in fetal umbilical vein………30mmHg• dO2 in (pressure gradient)………20mmHg

How is a sufficient oxygenation of the fetus possible?

Placenta - oxygen transport

1. Fetal hemoglobin

2. Higher Hb concentration in the fetal blood (50% more than in adults)

3. Double Bohr effect - Hb can carry more oxygen in low pCO2 than in high pCO2

Placenta - CO2, nutritients, waste products transport

• CO2 gradient - 2-3 mmHg, but extreme solubility (diffuses 20times faster than oxygen)

• facilitated diffusion for glucose (high glucose need in 3dr trimester)

• free diffusion of fatty acids• diffusion of waste products based on concentration gradient

• drugs crossing placental barier - teratogens:• Talidomide, Carbamazepine, Coumarins, Tetracycline…• Alcohol, nicotine, heroin, cocaine, caffeine• drugs (excluding alcohol) - 3% of all congenital malformations

Hormonal Changes During Pregnancy

Hormonal changes

HCG

HCS

Human Chorionic Gonadotropin• prevent involution of CL (pregesterone, estrogen)•effect on the testes of male fetus - development of sex organs

Human Chorionic Somatomammotropin• effect on latation (HPL) ?•growth hormone effects•decreases insulin sensitivity - more glucose for the fetus• low levels - placental insuf.

Hormonal changesProgesterone

Estrogens

• development of decidual cells• decreases uterus contractility• preparation for the lactation

• enlargement of uterus• breasts development• relaxation of ligments

• estriol level - indicator of vitality of the fetus

Progesterone and Cortisol metabolism

Placenta

Hormonal changes

Placenta Mother

CRH ACTH aldosteronecortisol

edemainsulin resistance

HCGHC thyrotropin

hyperthyroidism

hypertension

gestational diabetes

HyperparathyroidismCalcium demands

Other Physiological Changes

Cardiovascular changes

Cardiac output (CO)• 30 -50% above normal

• placental circulation• increased metabolism• skin - thermoregulation• renal circulation

• decreases in last 8 weeks (uterus compresses vena cava)• incr. 30% more during labor

• Heart rate (HR) increases up to 90/min• Blood pressure (BP) drops, periferal resistance decreases

• with twins CO increases more, BP drops more

• ECG changes• functional murmurs• heart sounds

Hematologic changes

• plasma volume increases (50%)• erythropoesis (RBC) increases (25%)• decreased Hb, hematocrite

• Iron requirements increases significantly• Iron suplements needed

Respiratory changes

• oxygen consumption increases• 20% above normal

• Progesterone increases sensitivity for CO2 in respiratory centre

• Growing uterus

• Frequency increases• Minute ventilation increases (50%)

• pCO2 decreases slightly

Urinary system

• Glomerulat filtration rate and renal plasma flow increases (up to 30 - 50 %)

• Increased reabsorption of ions and water - placental steroids - aldosterone

• Slight increase of urine formation

• Postural changes affect renal functions - upright position- supine position- lateral position during sleep

Preeclampsia, Eclampsia

• Preeclampsia - pregnancy induced hypertension + proteinuria• Incresing BP since 20th week - hypertension• Salt and water retention - edema formation• RBF and GFR decreases

• extensive secretion of placental hormones ?• insufficient blood supply to placenta - ischemia

- increased resistance - TNF alfa, cytokines ?

•Eclampsia - vascular spasms, chronic seizures, coma

Nutrition and Metabolism

Maternal weight gain

Fetus 5 kg

Mother 6 kg

Maternal-Fetal Metabolism

• 250 - 300 extra kcal/day should be ingested - 85% fetal metabolism, 15% stored in maternal fat

• Extra protein intake - 30g/day• End of pregnancy - fetal glucose need 5mg/kg/min

(mother 2,5mg/kg/min)• 2 phases of pregnancy:

1st - 20th week - mother´s anabolic phase:- anabolic metabolism of the mother- quite small nutrition demands of the conceptus

21 - 40 week (esp. last trimester):- high metabolic demands of the fetus- accelerated starvation of the mother

Maternal-Fetal Metabolism

Mother´s anabolic phase:- normal or increased sensitivity to insulin- lower plasmatic glucose level- lipogeneses, glycogen stores increases- growth of breasts, uterus,weight gain

Catabolic phase (accelerated starvation):- maternal insuln resistance - increased transport of nutritients trough placental membrane- lipolysis

• Insulin resistance caused by HCS, cortisol and growth hormone

Special nutrition need in pregnancy

• High protein diet, higher energy uptake• Iron supplements - 300mg ferrous sulfate• B - vitamins - erythropoesis • Folic acid (folate) - reduces risk of neural tube defects• Vitamin D3 + Ca supplements• Before parturition - K vitamin (prevention of intracranial bleeding during the labor)

Thank you forattention