Pregnancy and Lactation

Maturation and Fertilization of the Ovum

When ovulation occurs, the ovum, along with corona radiata, is expelled directly into the peritoneal cavity and then enter one of the fallopian tubes (fimbria) to reach the cavity of the uterus.

The inner surfaces of the fimbriated tentacles are lined with ciliated epithelium, and the cilia are activated by estrogen from the ovaries.

This activation causes the cilia to beat toward the opening, or ostium, of the involved fallopian tube.

So, the ovum enters one of the fallopian tubes.

Fertilization of the Ovum

After the male ejaculates semen into the

vagina, a few sperm are transported within

5 to 10 minutes upward from the vagina

and through the uterus and fallopian tubes

to the ampullae of the fallopian tubes.

This transport of the sperm is aided by

contractions of the uterus and fallopian

tubes stimulated by prostaglandins in the

male seminal fluid and also by oxytocin (in

female).

.

Fertilization of the ovum normally takes place in the ampulla

of one of the fallopian tubes after both the sperm and the

ovum enter the ampulla.

Before a sperm can enter the ovum, it must first penetrate

the multiple layers of granulosa cells attached to the corona

radiata and then bind to and penetrate the zona pellucida

After sperm binding zona pellicuda,

sperm binds plasma membrane,

then nucleus of sperm enters the

ovum.

So; in the ovum, intracellular Ca

levels increase, proliferation of zona

pellicuda stops, Meiosis II completes

(membrane potential changes).

The zona pellicuda becomes rigid for

protection of entering the another

sperm.

After fertilization has occurred, an additional 3 to 5 days is normally required for transport of the fertilized ovum (the fallopian tube into the cavity of the uterus).

This transport is effected mainly by a feeble fluid current in the tube resulting from epithelial secretion.

the isthmus of the fallopian tube remains spastically contracted for about the first 3 days after ovulation.

The fallopian tube secretory cells produce large quantities of secretions used for the nutrition and the swim of the developing blastocyst.

After this time, the rapidly increasing progesterone secreted by the CL first promotes increasing progesterone receptors on the fallopian tube SMC;

then the progesterone activates the receptors of isthmus SMC that allows entry of the ovum into the uterus.

This delayed transport of the fertilized ovum allows several stages of cell division to occur before the dividing ovum (blastocyst) enters the uterus.

Implantation of the Blastocyst in the Uterus

After reaching the uterus, the developing blastocyst usually remains in the uterine cavity an additional 1 to 3 days before implantation.

So, implantation occurs on about the fifth to seventh day after ovulation. Before implantation, the blastocyst obtains its nutrition from the uterine

endometrial secretions, called “uterine milk.”

Implantation results from the action of trophoblast cells.

They develop over the surface of the blastocyst.

These cells secrete proteolytic enzymes that digest and liquefy the adjacent cells of the uterine endometrium.

Once implantation occurs, the trophoblast cells and other adjacent cells (from the blastocyst and the uterine endometrium) proliferate, forming the placenta and the various membranes of pregnancy.

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Development of embryo and fetus

Definition

1. embryo: ≤ 8 weeks

2. Fetus: ≥ 9 weeks, human shape

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Normal Pregnancy

Pregnancy

The course that the embryo and the fetus grow in the maternal body

Stages of pregnancy

1. Early pregnancy: ≤12 weeks

2. Mid pregnancy: ≥13 weeks,≤27 weeks

3. Late pregnancy:≥28 weeks

4. Term pregnancy:≥37 weeks,<42 weeks

Early Nutrition of the Embryo

The progesterone (secreted by CL) effects endometrium. (Secretory phase of uterine cycle)

Then, when implantation occurs, the continued secretion of progesterone causes the endometrial cells to swell further and to store even more nutrients.

These cells are now called decidual cells, and the total mass of cells is called the decidua.

As the trophoblast cells invade the decidua, digesting and imbibing it, the stored nutrients in the decidua are used by the embryo for growth and development.

The embryo continues to obtain at least some of its nutrition in this way for up to 8 weeks, although the placenta also begins to provide nutrition after about the 16th day beyond fertilization.

The fetus’s blood flows through two umbilical arteries, then into the capillaries of the villi, and finally back through a single umbilical vein into the fetus.

At the same time, the mother’s blood flows from her uterine arteries into large maternal sinuses that surround the villi and then back into the uterine veins of the mother.

Placenta

Structure

1. Primary villus

syncytiotrophoblast cytotrophoblast

2. Secondary villus

3. third class vilus

fetal capillary enter the stroma

Function of the Placenta

The total surface area of all the villi of the mature placenta is only a few square meters.

The nutrients and other substances pass through this placental membrane mainly by diffusion, but also faciliated diffusion, active transport, phagocytosis

Placental Permeability and Membrane Diffusion Conductance The major function of the placenta is to provide for: diffusion of foodstuffs and oxygen from the mother’s blood

into the fetus’s blood and, diffusion of excretory products from the fetus back into the

mother.

In the early months of pregnancy, the placental membrane is still thick, its permeability is low.

in later pregnancy, the permeability increases because of thinning of the membrane diffusion layers and, the surface area expands many times over.

So, placental diffusion increases.

Diffusion of Oxygen Through the Placental Membrane

The dissolved oxygen in

the blood of the large

maternal sinuses passes

into the fetal blood by

simple diffusion, driven by

an oxygen pressure

gradient from the mother’s

blood to the fetus’s blood.

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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?

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These factors facilitate diffusion of O2 from

placenta:

1- Fetal hemoglobin, (the fetal hemoglobin

can carry 20 to 50 per cent more oxygen

than adult Hb)

2- Higher Hb concentration: the Hb

concentration of fetal blood is about 50 per

cent greater than that of the mother;

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

Diffusion of Carbon Dioxide Through the Placental Membrane

Carbon dioxide is continually formed in the tissues of the fetus.

The PCO2 of the fetal blood is 2 to 3 mm Hg higher than that of the maternal blood.

This small pressure gradient CO2 across the membrane is more than sufficient to allow adequate diffusion of C02.

the extreme solubility of CO2 in the placental membrane allows CO2 to diffuse about 20 times as rapidly as oxygen.

CO2 is excreted through the placenta.

Diffusion of Foodstuffs Through the Placental Membrane

For instance, in the late stages of pregnancy, the fetus

often uses as much glucose as the entire body of the

mother uses.

To provide this much glucose, the trophoblast cells lining

the placental villi provide for facilitated diffusion of

glucose through the placental membrane.

fatty acids, ketone bodies, potassium, sodium, and

chloride ions diffuse from the maternal blood into the

fetal blood.

Excretion of Waste Products Through the Placental Membrane. In the same manner that CO2 diffuses from the fetal blood into the

maternal blood, other excretory products (urea, uric acid, and

creatinine) formed in the fetus also diffuse through the placental

membrane into the maternal blood and are then excreted along with

the excretory products of the mother.

• 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

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Development of embryo and fetus

Physiology of fetus

1. Circulation

1) fetus ←→placenta←→ mater

2) 1 umbilical vein (full of oxygen), 2 umbilical artery (lack of oxygen)

3) Mixed blood (vein and artery)

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Development of embryo and fetus

2. Hematology

1) Erythropoiesis

From yolk sac: 3 weeks

From liver: 10 weeks

From bone marrow and spleen: term (90%)

EPO production: 32nd week

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Development of embryo and fetus

2) Fetal hemoglobin

Fetal hemoglobin: early pregnancy

Adult hemoglobin: 32nd week

Term: fetal type Hb 25%

3) White cells

Leukocytes: 8 week

Lymphocytes (antibody production): 12 week, thymus and spleen

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Development of embryo and fetus

3. Gastrointestinal tract

1) drink amniotic fluid: 4th month

2) no proteolytic activity

3) enzymatic deficiencies in liver:

bilirubin is not easy to be clear.

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Development of embryo and fetus

4. Kidney

Its function begins at 11-14th week

5) Endocrinology

6) Fetal thyroid: the first endocrine gland (6th week), synthesize

thyroxine at 12th week

7) Fetal adrenal cortex: widen (20th week), a fetal zone.

synthesize steroid hormones

Hormonal Factors in Pregnancy

In pregnancy, the placenta produces large quantities of

human chorionic gonadotropin, estrogens, progesterone, and human chorionic somatomammotropin

The First Trimester (0-12 Weeks)

The Second Trimester (13-28 Weeks)

The Third Trimester (29-40 Weeks)

Human Chorionic Gonadotropin (hCG)and Its Effect

The hormone human chorionic gonadotropin is secreted by the syncytial trophoblast cells into the fluids of the mother.

The secretion of hCG can first be measured in the blood 8 to 9 days after ovulation, shortly after the blastocyst implants in the endometrium.

Then the rate of secretion rises rapidly to reach a maximum at about 10 to 12 weeks of pregnancy and,

decreases back to a lower value by 16 to 20 weeks.

hCG continues at this level for the remainder of

pregnancy.

Its most important function is to prevent involution of the

corpus luteum.

Instead, it causes the CL to secrete larger quantities of

progesterone and estrogens for the next few months.

These hormones prevent menstruation and cause the

endometrium to continue to grow and store large

amounts of nutrients.

estrogens and progesterone maintains the decidual nature (greatly swollen

and nutritious) of the uterine endometrium, which is necessary for the early

development of the fetus.

After, the placenta secretes sufficient quantities of progesterone and

estrogens to maintain pregnancy for the remainder of the gestation period.

The corpus luteum involutes slowly after the 13th to 17th week of

gestation.

HCG also exerts an interstitial cell–stimulating effect on the

testes of the male fetus, resulting in the production of

testosteron in male fetuses until the time of birth.

This small secretion of testosterone during gestation is what

causes the fetus to grow male sex organs instead of female

organs.

Secretion of Estrogens by the Placenta

The placenta, like the corpus luteum, secretes both estrogens and progesterone (by the syncytial trophoblast cells.)

toward the end of pregnancy, the daily production of placental estrogens increases to about 30 times the mother’s normal level of production.

the estrogens secreted by the placenta are not synthesized de novo in the placenta.

Instead, they are formed almost entirely from dehydroepiandrosterone and 16- hydroxydehydroepiandrosterone, which are formed both in the mother’s adrenal glands and in the adrenal glands of the fetus.

These weak androgens are transported by the blood to the placenta and converted by the trophoblast cells into estradiol, estrone, and estriol.

Function of Estrogen in Pregnancy

enlargement of the mother’s uterus, enlargement of the mother’s breasts and growth of

the breast ductal structure, enlargement of the mother’s female external

genitalia Uterin contraction (during parturition) Relaxation of the pelvic ligaments of the mother, so

that the sacroiliac joints become relatively limber and the symphysis pubis becomes elastic.

Secretion of Progesterone by the Placenta Progesterone is also essential for a successful pregnancy. The special effects of progesterone are essential for the normal

progression of pregnancy: 1. Progesterone causes decidual cells to develop in the uterine

endometrium, and these cells play an important role in the nutrition of the early embryo.

2. Progesterone decreases the contractility of the pregnant uterus, thus preventing spontaneous abortion.

3. Before implantation, Progesterone increases the secretions of the mother’s fallopian tubes and uterus.

4. The progesterone secreted during pregnancy helps the estrogen prepare the mother’s breasts for lactation.

Human Chorionic Somatomammotropin (Human Placental Lactogen)

Development of breasts

Human placental lactogen

Promotion of growth

Similar to growth hormone

hCS (or hPL) causes decreased insulin sensitivity and utilization of glucose in the mother

Making larger quantities of glucose available to the fetus (Because glucose is the major substrate used by the fetus to

energize its growth)

Hormonal Changes During Pregnancy

Other Hormonal Factors in Pregnancy

Pituitary Secretion: The anterior pituitary gland of the mother enlarges

at least 50 percent during pregnancy: of corticotropin, thyrotropin, and prolactin increase FSH and LH suppress.

Corticosteroid Secretion: The rate of adrenocortical secretion of the

glucocorticoids is moderately increased throughout pregnancy.

Pregnant women usually have about a twofold increase in the secretion of aldosterone, reaching a peak at the end of gestation.

This, along with the actions of estrogens, causes a tendency for from her renal tubules and,

therefore, to retain fluid, occasionally leading to pregnancy-induced hypertension.

Secretion by the Thyroid Gland: The thyroxine production increases. the placenta secretes HCG and small quantities of a

specific TSH. Secretion by the Parathyroid Glands: The mother’s parathyroid glands usually enlarge during

pregnancy. Enlargement of these glands causes calcium absorption

from the mother’s bones, thereby maintaining normal calcium ion concentration in the mother’s extracellular fluid even while the fetus removes calcium to ossify its own bones.

Secretion of “Relaxin” by the Ovaries and Placenta:

Relaxin is secreted by the corpus luteum and by placental tissues.

Its secretion is increased by a stimulating effect of HCG at the same time that the corpus luteum and the placenta secrete large quantities of estrogens and progesterone.

It causes relaxation of the pelvic ligaments. It causes relaxation of the cervix. It decreases contraction of myometrium.

Endocrine changes in pregnant woman

1. Pituitary (hypertrophy)1) LH/FSH: ↓2) PRL:↑3) TSH and ACTH:↑2. Thyroid1) enlarged (TSH and HCG↑)

2) thyroxine↑ and TBG↑ → free T3 T4 unchanged

Response of the Mother’s Body to Pregnancy

Weight Gain in the Pregnant Woman: The average weight gain during pregnancy is about 11

kg, with most of this gain occurring during the last two trimesters.

3.2 kg is fetus 1.8 kg is amniotic fluid, placenta, and fetal membranes 1 kg is uterus 1 kg is breasts 3 kg is extra fluid in the blood and extracellular fluid 1.5 kg is generally fat accumulation

Metabolism During Pregnancy BMR increases in the pregnant woman (As a

consequence of the increased secretion of many hormones during pregnancy, including thyroxine, adrenocortical hormones, and the sex hormones)

Cardiovascular system1. Heart: move upward, hypertrophy of cardiac

muscle2. Cardiac Output increase by 30%, reach to peak at 32nd

–34th week3. Blood pressure early or mild pregnancy Bp↓ late pregnancy Bp↑.

Hematology1. Blood volume1) Increase by 30%-45% at 32nd –34th (peak)2) Relatively diluted2. Composition1) Red cells Hb:130→110g/L, HCT:38%→ 31%.2) White cells: slightly increase3) Coagulating power of blood: ↑ 4) Albumin: ↓,35 g/L

Physiological coagulation Changes in Pregnancy

A fine physiological hemostatic balance between coagulation and fibrinolysis is shifted in favor of pro- coagulation.

Thus pregnancy is a hyper coagulation state. venous thrombosis disease becomes a potential risk in

pregnancy as Virchow’s triad of coagulation , vessel wall damage and blood flow rate are affected.

Bleeding disorders may develop from (a) coagulation defect (b) deficiency coagulopathy (c) reduction or functional Defect in platelets—

Thrombocytopenia .

Changes in clotting factors in Pregnancy 1- Predominantly pro – hemostatic changes ( shortened Clotting Time )

Increased Fibrinogen concentration. Increased factor II , V, VII, VIII , IX, X and XII other coagulation

factor. 2. reduced platelet count due to low grade intravascular

coagulation. 3. Increased Plasminogen activator inhibitor concentration

(reduced systemic fibrinolytic capacity ) 4. reduced Protein S concentration . 5. Increased protein C concentration.

Blood Volume in Pregnancy

The Respiratory system

1. R rate: slightly ↑

2. vital capacity: no change

3. Tidal volume: ↑ 40%

4. Functional residual capacity:↓

5. O2 consumption: ↑ 20%

• 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

The urinary system1. Kidney1) Renal plasma flow (RFP):↑35%2) Glomerular filtration rate (GFR):↑ 50%2. Ureter Dilated 3. Bladder Frequent micturition• Increased reabsorption of ions and water - placental steroids - aldosterone

Gastrointestinal system

1) Gastric emptying time is prolonged→ nausea.

2) The motility of large bowel is diminished → constipation

3) Liver function: unchanged

Pre-Eclampsia

Definition-

“a disorder associated with pregnancy consisting of

hypertension, proteinuria and new-onset dependent

oedema, most commonly after 20 weeks of

gestation”

Pre-eclampsia

Also known as Toxemia Cause is unknown, but occurs only in pregnant women

could be related to the placenta failing to implant properly in the lining of the uterus; preventing arteries from dilating as they should, restricting blood flow and leading to a host of other problems

No known cure (other than having the baby) High risk for first pregnancies, multiple gestations, women under

age 20, pre-existing hypertension, or diabetes Occurs after 20 weeks gestation Usually detected early with adequate prenatal care

Signs & Symptoms

Principle Signs: Proteinuria (protein in urine) Hypertension due to vasoconstriction

Other signs & symptoms include: edema rapid weight gain HELLP syndrome (20% of women with severe

pre-eclampsia) Hemolysis (breakdown of RBC) Elevated Liver

enzymes, and Low Platelets

Rapid progression of Pre-eclampsia may not show such symptoms.

Lactation

Prolactin release:

Pituitary secretion

Hypothalamic control

Role of dopamin as inhibitory factor

Prolactin Inhibiting Hormone (PUH)

Changes in Breasts

• Breast tissue is mostly fat and glandular

• The glandular portions have ducts that converge at the nipple

• During pregnancy, particularly during the third trimester, hormones cause the glandular tissue to become active – produce milk

• These tissues are surrounded by smooth muscle, as are the ducts to the nipple

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Lactation: Producing and Releasing Milk Estrogen: growth of ductile system Progesterone: development of lobule-

alveolar system Both E and P inhibit milk production Prolactin stimulate milk production

(other roles in fertility) Sucking stimulus Oxytocin

"Milk let-down" reflex

• Lactation response

• Sound of a child crying

• Baby sucking on the nipple

• Activates hypothalamus to release oxytocin which activates smooth muscle contraction

• Decreases the production of prolactin inhibitor;

• prolactin allows the milk glands to secrete their product

• Initial breast milk contains colostrum containing several antibodies

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•Milk production continues as long as a mother continues to nurse her child

•Nursing is superior in terms

of baby’s digestion and

nervous tissue development;

it lowers risk of tooth decay;

and reduces mother’s risk of

ovarian cancer; some links

to higher scores on

intelligence tests

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The Milk Let-Down Reflex

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BreastfeedingInfant Health Benefits

COLOSTRUM Small amount for the immature digestive

system ‘paints’ the digestive tractLow fat for easy digestionContains mothers antibodies which boost

infants’ immune systemActs as a laxative to ease passage of meconium

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BreastfeedingInfant Health Benefits

The milk comes in Transitional milk for up to 2 weeks

May still have yellow appearanceAmounts increase quickly as infant hungers and

digestive system matures Mother's" milk making” changes from endocrine to

autocrine system Mature milk

Supply/demand system engorgement decreasesProperties of fore milk and hind milk present

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BreastfeedingInfant Health Benefits

Lower risk of Diarrhea Constipation Infections

Ear, respiratory, meningitis, urinary tract

SIDS Allergic diseases Chronic digestive diseases Juvenile onset diabetes Acute leukemia Adult obesity

Provides immunologic protection while the infant’s immune system is maturing Antimicrobial agents Anti-inflammatory agents Immunomodulating agents,

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BreastfeedingInfant Health Benefits

Preterm Infants Decreased necrotizing enterocolitis Decreased ROP Decreased infection rates Better able to tolerate feedings Increased IQ rates

Contains long chain polyunsaturated fatty acids that help the infant’s brain develop – these are normally provided by the mother in late pregnancy, therefore preterm infants miss this

Benefits of Breastfeeding

babies moms

balance of nutrients with high bioavail.

good hormones cognitive development less infections less diseases less food allergies

contracts the uterus delays menstruation conserves iron stores may protect against breast

cancer convenient bonding time with baby

Composition of Milk