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Physio Exam 3 > L29 Maternal And Fetal Circulation > Flashcards

L29 Maternal And Fetal Circulation Flashcards

1
Q

Placenta originates from

A

Fetal zygote tissue during development and forms a chorionic plate of branching vessels

Becomes fully functional at end of 1st trimester

Fetal circulatory system differentiates from mesoderm of embryo

Fetal blood travels via umbilical cord which made of two umbilical arteries and a single umbilical vein

Fetal heart begins to beat in 4th week of gestation

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2
Q

Fetal circulation has two special circuits

A

Do not mix! Communicate through capillaries

Utero-placental circulation ( not fully established until end of 1st trimester)

Placental-umbilical circulation

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3
Q

Development of fetal zygote

A

Fertilized ovum divides mitotically, within a week grows and differentiates into a blastocyst capable of implantation

Blastocyst implants in endometrial lining by means of enzymes that digest endometrial tissue

Only after implantation is completed, human chorionic gonadotrophin (hCG) is detectable in maternal serum

Placental hCG signals the ovary to continue production of estrogen and progesterone

Most pregnancy tests detect placental hCG

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4
Q

Development of placenta

A

Shortly after blastocyst has implanted (6-7 days after fertilization), the syncytiotrophoblast invades the storms of uterus (decidua) forming fluid-filled holds called lacunae

Fetal circulatory system differentiates from mesoderm of embryo. Cytotrophoblasts proliferate and form chorionic villi and fetal blood vessels form within them

Lacunae become in contact with lateral blood vessels and eventually merge with one another to create intervillous space

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5
Q

Anatomy of placenta

A

Fetal side and maternal side

Fetal side develops from same blastocyst that forms the fetus and contains chorionic plate of branching vessels from umbilical cord

Lateral side develops from maternal uterine tissues and it can release substances into maternal or fetal circulations

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6
Q

Umbilical cord

A

Is lifeline that attaches fetal side of placenta to the fetus forming a chorionic plate of branching vessels

Unlike systemic arteries after birth, umbilical arteries carry deoxygenated blood. As they approach placenta they branch repeatedly forming chorionic villi that form a capillary network

Blood that has obtained sig higher O2/nutrient return to fetus from placenta through a single umbilical vein

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7
Q

Utero-placental circulation

A

Oxygenated maternal blood enters intervillous space via spiral arteries

Blood flow spreads over fetal chorionic villa toward chorionic plate then reversed direction, aided by arterial BP, intra-uterine P, and contractions of myometrium

Blood leaves through venous orifices via maternal vein

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8
Q

Placental-umbilical circulation

A

Forest of fetal chorionic villi from capillary network

Fetal blood entered through paired umbilical arteries in deoxygenated state

Oxygenated blood leaves through a single umbilical vein

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9
Q

Functions of placenta

A

Temporary organ of pregnancy with special functions

Two special circulations that don’t mix

Acts as lung to allow gas exchange

Acts as kidney to remove waste from fetal blood

Acts as GI tract to absorb nutrients from mother

Act as a barrier to protect fetus from mothers immune system

Acts as endocrine organ- source of steroids and growth factors

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10
Q

Cardiovascular changes during pregnancy that facilitates fetal perfusion

A

Maternal blood volume increases

Peripheral a vascular resistance decreases

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11
Q

Cardiovascular changes during pregnancy that decreases heart work

A

Blood viscosity decreases

Mean arterial Pressure (MAP) decreases

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12
Q

Changes in blood volume and viscosity

A

Total blood volume : 40% increase
Protects against impaired venous return when going from supine to erect position
Ameliorates parturition-associated blood loss

Blood plasma: 40-50% increase
RBC: ~30% increase
% hematocrit: decreases 2-3% (physiological anemia to minimize work of heart)

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13
Q

Changes in heart function during pregnancy

A

CO increases 30-50%
SV increases ~30% (from increase V)
HR increases ~20%

EF increases 3-5%

Ventricular volumes increases promoting frank-starling mechanisms for increased cardiac performance

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14
Q

Highly targeted effects in body

A

Renal flow increases 40% CO
Uterine flow increases 15% CO
Perfusion of heart, skin, and breasts increase

Perfusion of brain, gut, and skeleton not changed

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15
Q

Changes in BP and R during pregnancy

A

Systemic vascular resistance decreases up to 50%
Addition of parallel low R pal central circuit
Increased blood levels of estrogen and other factors (PGEs)

MAP decreases until mid pregnancy, then returns to original level
Decrease due to drop in total vascular R

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16
Q

Effect of adding a placenta on systemic vascular R

A

Adding another parallel vascular bed reduces resistance

17
Q

Chemical signaling from placenta

A

Placental and maternal steroids increase: estrogens and progesterone

Prostaglandins gradually increase

Increased angiotensin II and aldosterone (placental RAS pathway)
Decreased sensitivity to angiotensin II in mom

Decreased norepinephrine

Endothelin-I in placental arteries and veins is a potent vasodilator

Eiconsanoids: thrombaxne present, potent vasoconstrictor and prostacyclin is a strong vasodilator

Increased NO production via eNOS expression in placental vessel endothelium

18
Q

Cardiac remodeling

A

Increases: left ventricular wall thickness
Left ventricular mass
Valve orifice areas

19
Q

Spiral artery remodeling creates a

A

High flow, low resistance vascular bed with steep drops in resistance from uterine arteries to the intervillous space

Uterine artery: 80-100mmHg

Spiral artery: 70mmHg

Intervillous space: 10mmHg

20
Q

Preeclampsia

A

Elevated maternal BP

Develops in two stages:
1. Altered perfusion in circulation causes placental ischemia: placental or vascular abnormalities , deficiencies in spiral artery remodeling failing to produced conditions of high flow, low resistance (more narrow cone shaped) or placental abruption(detachment)

  1. Ischemic placenta releases factors that cause maternal endothelial dysfunction, vasoconstriction and hypertension (AT-1, thromboxane)
21
Q

Fetal circulation: four unique shunt

A

Fetal heart pumps large quantities blood through placenta and smaller amount of blood through other organs

Fetal pulmonary circuit is low flow, high resistance

Enhances delivery of O2 to fetal brain

Works in parallel not series

Shunts bypass postnatal route:
Placenta 
Ductus venosus 
Foramen ovale 
Ductus arteriosus
22
Q

Placental shunt

A

Low resistance, high volume

Receives 50% of CCO from fetus

Shunts blood away from lower trunk and abdominal visceral (kidneys)

Umbilical veins carriers higher O2 saturated blood to fetus

Umbilical arteries carrier O2 mixed blood to placenta

23
Q

Ductus venosus

A

Shunts blood from umbilical vein to IVC, bypassing fetal liver

Transports blood to IVC, blood from portal vein 19% CCO combined with umbilical blood (50% CCO)

IVC carries 69% CCO

24
Q

Foramen ovale

A

Oval hole in septum diving the atria

Represents right to left shunt of well-oxygenated blood from IVC

No blood from SVC or coronaries enter foramen ovale

Of IVC blood, 27% shunts to left atrium and combined w 7% poorly-oxygenated blood from lungs

This blood enters left ventricle, 24% enters brain, upper body, coronary sinus and ~10% stays in descending aorta

25
Q

Ductus arteriosus

A

Shunts blood 58% CO from left pulmonary artery to aorta

Represents right to left shunt

42% of IVC blood mixes w poorly oxygenated blood from SVC and enters right ventricle

Of IVC blood, 69% CCO, 27% shunts to left atrium and remaining 42% combines w 24% poorly oxygenated blood from SVC

This blood entered the right ventricle (66% CCO) where 59% is shunted to aorta and ~7% to fetal lungs

26
Q

Fetal heart has higher P

A

On right side than left side

That’s why blood is pushed from right to left , pressure differential

27
Q

Fetal heart works in parallel

A

Outputs of right and left hearts both deliver O2 containing blood to body

28
Q

Adjustments to circulation at birth

A

Newborns paced with hypoxia, hypoglycemia, and hypothermia
Placenta lost, doubling total peripheral resistance
Umbilical vasoconstriction
Closure of placental circulation

Increased SA of lungs and increased return from lungs

Aortic and left atrial pressure increases

Closure of foramen ovale (reversed pressure gradient), ductus venosus (sphincter constricts~3hrs after birth) and ductus arteriosus (increased systemic resistance reverses flow via ductus arteriosus )

29
Q

First breath: expansion of lungs

A

Pulmonary circulation opens, decreasing pulmonary vascular resistance

Pulmonary blood flow increase

Pulmonary arterial pressure (right side) decreases
RV pressure falls

30
Q

Closure of foramen ovale

A

Decreased pulmonary P

Increased systemic resistance and increased pulmonary return leads to increase LV pressure

31
Q

Closure of ductus arteriosus

A

Maintained open by prostaglandins during fetal life; lost after birth

At birth blood flow reverses

W/in a few hrs after birth closes functionally due to vasoconstriction in response to:
Loss of prostaglandins
Elevated PO2

Shifts from pumping in parallel to series
CO is now same btw right and left heart

32
Q

Closure of ductus venosus after birth

A

~3hrs-18days after birth by vasoconstriction of sphincter

Closure forces blood into portal vein and into liver

Remnant of ductus venosus and umbilical vein forms ligament that divides left part of liver into medial and lateral sections = ligamentum teres hepatis

33
Q

Atrial septal defect

A

Forman ovale didn’t close
Left to right shunt

Oxygenated blood to right atria

More blood to lungs

Leads to dilation of RA, pulmonary vessels and pulmonary hypertension

34
Q

Ventricular septal defect

A

Hole in heart
Left to right ventricular shunt

Severity depends on size of defect

Sends oxygenated blood to RV and more blood to lungs

Overload pulmonary side, resulting in pulmonary hypertension

Increased pulmonary return to left atria

Leads to left heart remodeling

35
Q

Patent ductus arteriosis

A

Ductus arteriosus remains open

Left to right shunt

Increase in pulmonary and right ventricle P

left heat becomes overloaded from increased volume bc increased pulmonary return

Systemic blood oxygenated normally

Physio Exam 3 (9 decks)

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