Weirong Gu

Obsterics & Gynecology Hospital of Fudan university

Physiology of Pregnancy

pregnancy

The condition of being with child or gravid, is the process of embryo and fetus growing and developing in the uterus

From the fertilization to the expelling of the fetus with placenta and membranes

contents

fertilization, development, transport and implantation of fertilized ovum

formation and function of fetal attachment maternal changes during pregnancy

concepts

sperm capacitation fertilization acrosome reaction zona reaction

sperm capacitation

Spermatozoons contact with endometrium

the α-/β- amylase remove the decapacitation factor on spermatozoons’ acrosomal enzyme

the spermatozoons with the ability of fertilization(capacitation)in uterus and fallopian tubes

acrosome reaction

Acrosome rupture, acrosomal enzyme released and lysis the radiate corona and zone pellucida

The spermatozoons penetrate and fuse with oocyte

zona reaction

the cortical particle of cytoplasm release lysosomal enzyme

zona structure changed and sperm receptor degenerated to prevent other sperm into the zona

fertilization

The course of combination of the oocyte and sperm Time : 12h after ovulation Place : usually in ampulla of the oviduct (fallopian

tube)

development and transport of the zygote

implantation Late blastosphere implanted in endometrium

Apposition Adhesion penetration

The necessary condition of implantation Disapearing of the zona pellucid Formation of syncytiotrophoblast Synchronizing development of blastocyst and

endometrium Adequate progesterone

Changes of endomertium after implantation The endometrium changes into dicedua

Basal decidua Capsular decidua Ture decidua

Embryo and fetal development

Embryo: the first 8 weeks from pregancy Fetus: after 9 weeks from pregnancy ,human shape

12 Gestational Weeks The uterus usually is just palpable

above the symphysis pubis, and the fetal crown-rump length is 6 to 7 cm.

Centers of ossification have appeared in most of the fetal bones, and the fingers and toes have become differentiated.

Skin and nails have developed and scattered rudiments of hair appear.

The external genitalia are beginning to show definitive signs of male or female gender.

The fetus begins to make spontaneous movements.

16 Gestational Weeks fetal crown-rump length: 12 cm weight : 110 g Gender can be determined by 14 weeks

20 Gestational Weeks Weight: more than 300 g, and increase in a linear manner Movement: about every minute and is active 10 to 30

percent of the time skin : less transparent, a downy lanugo covers entire body,

some scalp hair has developed.

24 Gestational Weeks The fetus now weighs about 630 g. The skin is characteristically wrinkled, and fat deposition begins. The head is still comparatively large, and eyebrows and eyelashes

are usually recognizable. The canalicular period of lung development, during which the

bronchi and bronchioles enlarge and alveolar ducts develop, is nearly completed.

A fetus born at this time will attempt to breathe, but many will die because the terminal sacs, required for gas exchange, have not yet formed.

28 Gestational Weeks The crown-rump length is approximately 25 cm, and the

fetus weighs about 1100 g. The thin skin is red and covered with vernix caseosa. The pupillary membrane has just disappeared from the

eyes. The otherwise normal neonate born at this age has a 90-

percent chance of survival without physical or neurological impairment.

32 Gestational Weeks The fetus has attained a crown-rump length of about 28 cm

and a weight of approximately 1800 g. The skin surface is still red and wrinkled.

36 Gestational Weeks The average crown-rump length of the fetus is about 32

cm, and the weight is approximately 2500 g. Because of the deposition of subcutaneous fat, the body

has become more rotund, and the previous wrinkled appearance of the face has been lost.

40 Gestational Weeks This is considered term from the onset of the last menstrual

period. The fetus is now fully developed. The average crown-rump length is about 36 cm, and the

weight is approximately 3400 g.

Physiology of fetus

circulation Fetus---placenta---mother 1 umbilical vein (full of oxygen) 2 umbilical arteries (lack of oxygen) Mixed blood ( vein and artery)

Ductus arteriosus Foramen ovale Ductus venosus

hematology

erythropoiesis From yolk sac: 3 weeks From liver: 10 weeks From bone marrow and spleen: term (90%)

EPO production: 32nd week Fetal blood volume:125ml/kg of the fetus at term

Fetal hemoglobin Fetal hemoglobin: early pregnancy Adult hemoglobin: 32nd week Term : fetal type Hb 25%

White cells Leukocytes: 8 week Lymphocytes (antibody production): 12 week thymus and

spleen

Fetal respiratory system The timetable of lung maturation and identification of

biochemical indices of functional fetal lung maturity are important to the obstetrician

A sufficient amount of surface-active materials in the amniotic fluid is evidence of fetal lung maturity

Surfactant: produced by type cells of the lung alveoli; Ⅱactive component is a specific lecithin or dipalmitoylphosphatidylcholine

Gastrointestinal tract Swallowing begins at 10-12 weeks, 16weeks,

gastrointestinal function is established Liver

Hepatic enzyme is lack during fetal period, a very limite capacity for converting free bilirubin to conjugating bilirubin

Urinary system The fetal kidneys start producing urine at 12 weeks’

gestation. 7-14ml/d by 18 weeks, 27ml/hr or 650ml/d at term

Genital system Genital organ is developed from 9 weeks of

pregnancy(male), 11-12 weeks(female)

Attachment of the fetal

Placenta Fetal membranes Umbilical cord Amniotic fluid

placenta

An exchange organ between maternal and fetal Organization

Amniotic membrane Chorion frondosum Basal decidua

Chorion frondosum

13-21 days after ovulation, villi fomulating gradually Primary viilus

Syncytiotrophoblast cytotrophoblast

Secondary villus Third class villus Fetal capillary enter the stroma

Structure of placenta

Round Weight: 450-650g Diameter: 16-20cm Thickness: 1-3cm thick in center and thin in margin

Function of placenta

One important function of placenta is substance exchange between maternal and fetal

Transfer oxygen and nutrients from the mother to the fetus and conversely the transfer of carbon dioxide and other metabolic wastes from fetus to mother

The position exchange is VSM(vasculosyncytial membrane) VSM is comprised of

Syntrophoblastocyte Basal membrane of syntrophoblastocyte Stroma of villi Basal membrane of capillary Endothelium of capillary

The way of substance exchange

Simple diffusion Facilitated diffusion Active transportion phagocytosis

The function of placenta

Gas exchange Suply of nutrition Depletion of fetal product of metabolism Defence function Hormone synthesis

Human chorionic gonadotropin (HCG) Human placental lactogen (HPL) Pregnancy specific ß-glycoprotein (PS ß1G) Human chorionic thyrotropin(HCT) Estrogen, P, Oxytocinase, heat stable alkaline phosphatase(HSAP)

Fetal membrane

Chorion Amnion

A double-layered translucent membrane Become distended with fluid

Umbilical cord

Extends from the fetal umbilicus to the fetal surface of the placenta

Length: 30-70cm average : 50cm Diameter: 0.8-2.0cm Consist of 2 artery and 1 vein, Wharton jelly amnion, yolk sac

Amniotic fluid Source:

early from serum dialysis Mid-pregnancy from fetal urine Late from fetal lung

Absorse: fetal membrane Umbilical cord Fetal skin Fetal fetal swallowing (500ml/day)

Amniotic exchange: between maternal and fetal 400ml/h Volume: 50ml at 12 weeks, 400ml at midpregancy, 1000ml at term

Volume of amniotic fluid

8 weeks: 5-10ml 10 weeks: 30ml 20 weeks: 400ml 38 weeks: 1000ml

feature of amniotic fluid

pH: 7.20 Density: 1.007-1.025 Contained: water(98-99%) inorganic substance organic substance(1-2%)Early transparentLate slighty turbid

The function of amniotic fluid

Protect maternal and fetus Move freely Warm

Protect mother Prevent infection

Maternal changes during pregancy The maternal system may produce a series of changes

in order to adapt to the needing of fetal growth and development influenced by placenta hormone and neuro-endorine

Changes of reproductive system

Uterus Capacity : 5ml - 5000ml Weight: 50g – 1000g Hypertrophy of muscle cells

fundus-inferior portion-cervix Endometrium –decidua

Blood supply increases 4-6times (500-700ml/min) Most transported to the placenta(80-85%)

Uterine contraction Braxton hicks contraction-contraction without pain Rare, irregular,and asymmetric Intrauterine pressure: 5-25mmHg, duration <30s

Isthmus softer and longer (1,7-10cm) lower segment

Cervix Colored Cerical mucus plugs

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Maternal Physiology

Changes of ovary

Enlarged Ovulation and new follicle is stopped. Luteum produces E and P from 7 weeks of pregnancy,

but start to atrophy after 10 weeks of pregnancy, the fuction is replaced by placenta

Fallopian tubes: is prolonged but not hypertrophy Vagina: dilated and soft , violet coloration,

desquamation of epithelium with more glycogen acidity pH (anti- bacteria)

Vulva: pigmentation Ligaments: relaxed

breasts

An increase in size and a nodular sensation due to the hypertrophy of the mammary alveoli, the nipples soon become larger, more deeply pigmented and more erectile. Scattered around the areola are some roundish nodules called Montgomery tubercles which result from the hypertrophy of the sebaceous glands

Changes of the circulation

Heart border: become enlargement, move upward, hypertrophy of cardiac muscle

Heart rate: increased 10-15 beat per min at the late pregnancy Heart volume: increased 10% at the late pregancy The growing uterus pushes the diaphragm upward, with the

result that the heart is displaced to the left, upward and somewhat in the direction of the anterior chest wall. A certain degree of rotation is believed to take place. The capacity increases by 10%, the heart rate increases by 10-15bpm

Cardiac output

Very important for fetal growth and development Increase by 30%, from 10weeks and up to the peak at

32 weeks 80ml/bp and keeps the level to the term pregnancy

Blood pressure changes due to pregancy No obvious change in systolic pressure Mild decreased in diastolic pressure Vein pressure

No significantly changes in upper limb vein pressure Lower limb vein pressure increased demonstrable in later

months of pregnancy because of the disturbance of vein reflux Supine hypotension syndrom: supine position for a long

time---inferior vene cava compressed---back volume ---output ---Bp ---cm. of hypotension

Changes of blood system

Volume: increased (30-45%) from 6-8 weeks , peak at 32-34weeks, about 1500ml (including plasma 1000ml and 500ml erythrocytes---hemodilution)

Changes of blood component

Red cell Hb decreasd 110g/L Hct : 38%--31%

WBC: Slightly increase neutrophilic granulocyte increased

Coagulating power of blood: Albumin: 35g/L

Urinary system

Kidney Renal plasma flow (RFP): 35% Glomerular filtration rate (GFR):

Ureter: dilated ( P ) Bladder

Frequent micturation

Respiratory system

R rate : slightly Vital capacity: no change Tidal volume: 40% Functional residual capacity: O2 consumption: 20%

Gastrointestinal system

Gastric emptying time is prolonged nausea The motility of large bowel is diminished

constipation Liver function: unchanged

skin

The pigmentation of the areola, linea alba, vulva, occasionally irregularly shaped, brownish patches of varying size appear on the face and neck, the cloasma or the mask of pregnancy, which fortunately usually disappears after delivery

During late months of pregnancy, reddish, slightly depressed streaks often develop in the skin of abdomen, and sometimes also in the skin covering the breasts and the thighs.these striae gravidarum occur in about ½ of all pregnancies

Endocrine changes

Pituitary ( hypertrophy) LH/FSH PRL TSH and ACTH

Thyroid Enlarged (TSH and HCG ) Thyroxine and TBG free T3 T4 unchanged

Metabolic changes

BMR: mildly rising Weight: from 13w increases by 350g per week, about

12.5kg during the entire pregnancy Metabolism of carbohydrate

Fasting-sugar lower due to higher insulin-secretion Insulin-resistant factors

Fat metabolism: deposit of fat increasing chareterized by a hyperlipemia and a tendency to ketosis

Protein metabolism: positive nitrogen balance Water metabolism: water-retention of about 7L Mineral metabolism: in the late months of gestation Calcium and iron supplying---to avoid deficiency of

calcium and iron

Bone, joint, and ligament

Bone: no changes normally Joint and ligament: relaxin---loosening of joint and

ligaments---the birth canal widened

THANKS!